THE DIFFUSION OF INNOVATION IN DENTISTRY:

FACTORS ASSOCIATED WITH THE ADOPTION OF

ROTARY NICKEL-TITANIUM ENDODONTIC

INSTRUMENTS

Peter Parashos

BDSc (Melb), LDS (Vic), MDSc (Melb), FRACDS, FACD

A thesis submitted in total fulfilment of the requirements for the

degree of Doctor of Philosophy.

January 2004

School of Dental Science

The University of Melbourne

ABSTRACT

The aim of this research was to investigate possible reasons for the

adoption or non-adoption of new technology in dentistry, using rotary nickel-

titanium (NiTi) technology as a model.

This thesis first investigated the proportions of Australian dentists and

endodontists who were using rotary NiTi instruments and their experiences with

them. A questionnaire survey was conducted that explored general and specific

issues concerning rotary NiTi instruments and techniques. An assessment of

response rate and non-response bias was made by analysing responses to a

question requiring a simple yes/no answer. Secondly, intraoperative defects,

specifically fracture, of rotary NiTi instruments were assessed by collecting and

examining over 7,000 rotary NiTi instruments used in patients by 14 endodontists

from four countries and subsequently discarded. Thirdly, an assessment was made

of whether rotary NiTi instruments can be predictably cleaned in the busy private

practice setting.

Analysis of the response rate and non-response bias in the questionnaire

survey indicated the existence of differences between early and late responders

despite no apparent demographic differences. Respondents to the questionnaire

indicated many different reasons for adoption or non-adoption of the new

technology, which could be interpreted as demonstrating behavioural differences

i

between adopters and non-adopters. Analysis of the discarded instruments

indicated that the differences in technical ability between the endodontists was a

more important clinical consideration in defect and fracture rates of rotary NiTi

instruments than the perceived fragility of the instruments themselves. Also, a

simple and effective protocol was developed for the predictable cleaning of rotary

NiTi instruments. Therefore, overall, the results of the three parts of this thesis –

the questionnaire survey, the instrument defects and the instrument cleaning –

indicated the existence of personality and behavioural factors, which could

potentially influence the adoption of new technology. The perceived technical

concerns preventing adoption of the new technology were not necessarily valid,

and there were other issues affecting these decisions.

This thesis has shown that the diffusion of innovation in dentistry involves a

complex interplay of factors. Those factors included perceived benefits and

advantages, and psychosocial and behavioural factors in decision-making. This

work has also highlighted the usefulness of questionnaire survey research in

elucidating reasons for adoption and non-adoption of new technology. The finding

of significant differences in clinical experiences between individual dentists

brings into question the role of the factors of clinical competency and error in the

diffusion of innovation. The importance of continuing education in dentistry has

been highlighted but also that such courses must be authoritative.

ii

DECLARATION

This is to certify that:

(i) the thesis comprises only my original work except where indicated in the

Preface,

(ii) due acknowledgment has been made in the text to all other material used,

(iii) the thesis is less than 100,000 words in length, exclusive of tables,

bibliographies and appendices.

PETER PARASHOS

January 2004

iii

PREFACE

This thesis represents a part of ongoing research at the University of

Melbourne into different aspects of rotary nickel-titanium technology. In one

respect this thesis acts to unite the findings of the many individual projects, not in

a way that attempts to answer specific metallurgical or physical questions, but

rather in a way that seeks to address a more fundamental, somewhat esoteric, yet

often-ignored property of any new technology. That subliminal aspect involves

the reasons behind the adoption of the technology and its subsequent diffusion or

rejection. Although this thesis does not always directly refer to each of the

projects, it indirectly utilises their findings. Some of the nickel-titanium studies

form an integral part of this thesis, whilst others lend weight to the argument of

this work and retrospectively can be seen to have contributed to the diffusion of

nickel-titanium technology. Those studies include the following:

Sattapan B., Palamara J.E.A., Messer H.H. Torque during canal instrumentation

using rotary nickel-titanium files. Journal of Endodontics 2000;26:156-

160.

Sattapan B., Nervo G.J., Palamara J.E.A., Messer H.H. Defects in rotary nickel-

titanium files after clinical use. Journal of Endodontics 2000;26:161-165.

Chen J.L., Messer H.H. A comparison of stainless steel hand and rotary nickel-

titanium instrumentation using a silicone impression technique. Australian

Dental Journal 2002;47:12-20.

iv

Tan B.T., Messer H.H. The effect of instrument type and preflaring on apical file

size determination. International Endodontic Journal 2002;35:752-758.

Tan B.T., Messer H.H. The quality of apical canal preparation using hand and

rotary instruments with specific criteria for enlargement based on initial

apical file size. Journal of Endodontics 2002;28:658-664.

O’Hoy P.Y.Z., Messer H.H., Palamara J.E.A. The effect of cleaning procedures

on fracture properties and corrosion of NiTi files. International Endodontic

Journal 2003;36:724-732

During the course of this research other collaborative work related to the

thesis theme was completed. The following articles resulted from those

collaborations:

Ward J.R., Parashos P., Messer H.H. Evaluation of an ultrasonic technique to

remove fractured rotary nickel-titanium endodontic instruments from root

canals. An experimental study. Journal of Endodontics 2003;29:756-763.

Ward J.R., Parashos P., Messer H.H. Evaluation of an ultrasonic technique to

remove fractured rotary nickel-titanium endodontic instruments from root

canals. Clinical cases. Journal of Endodontics 2003;29:764-767.

Parashos P., Linsuwanont P., Messer H.H. Effective cleaning protocols for rotary

nickel-titanium files. Australian Endodontic Journal 2003;29:23-24.

Messer H.H., Parashos P., Moule A. Should endodontic files be single-use only?

A position paper from the Australian and New Zealand Academy of

Endodontists. Australian Endodontic Journal 2003;29:143-145.

v

Linsuwanont P., Parashos P., Messer H.H. Cleaning of rotary nickel-titanium

endodontic files. International Endodontic Journal 2004;37:19-28.

Weis M.V., Parashos P., Messer H.H. Effect of obturation technique on sealer

cement thickness and dentinal tubule penetration. International Endodontic

Journal (Submitted).

Studies currently in progress include the investigation of frequency of

fracture in clinical practice and its influence on healing, and effects on prepared

canal shape and susceptibility to fracture.

Several chapters of this thesis have already been submitted or accepted for

publication as indicated in the thesis. Thus, the thesis is structured such that

Chapters 1-4 cover theoretical issues and results of the questionnaire survey,

Chapters 5-8 are the articles. Chapter 9 links the different parts of the thesis in an

extended general discussion. The raw data were deemed to not be necessary to the

understanding of the thesis, and because of the very large quantity are not

included in this thesis but are available from the author. Spelling and referencing

formats differ in Chapters 5-8 according to the requirements of each particular

journal. References are included at the end of each chapter because of the

structure of the thesis. Throughout the thesis, superscripted upper case letters refer

to the statistical analyses presented in Appendix G.

vi

ACKNOWLEDGMENTS

This thesis would not have been possible if it were not for the assistance and

support of the following:

• Professor Harold H. Messer for his constant encouragement, guidance and

supervision of a difficult project and an overcommitted student. His research

experience and insight were, and are, truly inspirational.

• Associate Professor Mike Morgan for his valuable input and assistance with

the questionnaire survey, and for his patience.

• Associate Professor Ian Gordon for his assistance with the statistical

interpretation of the hundreds of pages of data.

• The National Health and Medical Research Council of Australia for a Medical

Postgraduate Research Scholarship.

• The School of Dental Science, the Australian Society of Endodontology

Incorporated, The Australian Dental Association Incorporated, Dentsply

Australia (Pty Ltd), Halas Dental Limited, and the J. Morita Corporation for

generously providing funding and materials.

Most importantly, I thank my wife Mary and son Ethan not only for making

sacrifices that allowed me to indulge in my dream but also for constantly

supporting me and ensuring I was able to have sufficient quiet time to work.

Ethan’s birth on Christmas Day of 1999 changed my whole outlook on life and

motivated me to pursue my PhD. Mary’s love and encouragement allowed me to

make the commitment and see it through to completion.

vii

TABLE OF CONTENTS

Abstract i

Declaration iii

Preface iv

Acknowledgements vii

List of Tables and Figures xi

PART I: GENERAL INTRODUCTION 1

Chapter 1. Introduction 2

References 8

PART II: QUESTIONNAIRE SURVEY OF ROTARY NICKEL-

TITANIUM INSTRUMENTATION 11

Chapter 2. Introduction 12

Basics of questionnaire survey research 12

Questionnaire survey rationale and design 25

References 34

Chapter 3. Questionnaire Results 39

Response details 39

Raw data 45

Part A. Demographics 45

Part B. Patterns of rotary NiTi usage 53

Part C. Issues associated with rotary NiTi usage 62

viii

Part D. NiTi Education 70

Chapter 4. Discussion Of Questionnaire Results 76

Questionnaire design 76

Part A. Demographics 80

Part B. Patterns of rotary NiTi usage 81

Part C. Issues associated with NiTi usage 84

Part D. NiTi education 85

References 86

Chapter 5. Response Rate And Non-Response Bias In A

Questionnaire Survey Of Dentists – Manuscript 87

Chapter 6. Questionnaire Survey On The Use Of Rotary Nickel-

Titanium Endodontic Instruments By Australian Dentists –

Manuscript 116

PART III: INSTRUMENT DEFECTS 160

Chapter 7. Factors Influencing Defects Of Rotary Nickel-Titanium

Instruments Following Clinical Usage – Manuscript 161

PART IV: INSTRUMENT CLEANING 177

Chapter 8. A Cleaning Protocol For Rotary Nickel-Titanium

Endodontic Instruments – Manuscript 178

ix

PART V: GENERAL DISCUSSION AND CONCLUSIONS 210

Chapter 9. New Technology In Dentistry: Diffusion Of An Innovation 211

Technology, diffusion and innovation: theoretical considerations 211

Diffusion of innovation in dentistry 214

Rotary NiTi technology 217

Rotary NiTi: diffusion of an innovation 219

Conclusions 238

References 239

PART VI: APPENDICES 255

Appendix A. Survey of rotary NiTi instrumentation 256

Appendix B. Table of Australian postcodes and zones 263

Appendix C. First letter 264

Appendix D. Second letter 265

Appendix E. Third letter 266

Appendix F. Telephone contact 267

Appendix G. Statistical analyses 268

x

LIST OF TABLES AND FIGURES

TABLES

2.1 ADA general dentists according to state 28

2.2 Stratification according to postal zone 30

2.3 Endodontists according to state and postal zone 31

3.1 Details of number of endodontists responding to each contact 44

3.2 Details of number of general dentists responding to each contact 44

3.3 Response details according to location – general dentists 48

3.4 Response details according to location – endodontists 49

3.5 Responses according to Australian or foreign degree 51

3.6 Responses according to origin of degree within Australia 51

3.7 Responses according to region of the world from which degree

was obtained 52

5.1 Response element details from the questionnaire 109

5.2 Details of the response elements after each contact in the

questionnaire survey of NiTi use 110

5.3 Response details relative to year of graduation in the

questionnaire survey of NiTi use 111

5.4 Response details relative to location of practice in the

questionnaire survey of NiTi use 112

xi

5.5 Comparison between affirmative (“Yes”) and negative (“No”)

to the main question in the NiTi survey at each contact from

the 731 usable replies 113

5.6 Comparison of affirmative (“Yes”) and negative (“No”) to

the main question in the NiTi survey between early and late

responders from the 731 usable replies 114

5.7 Comparison of affirmative (“Yes”) and negative (“No”) to

the main question in the NiTi survey between “threshold

responders” and late responders from the 731 usable replies 115

6-1 Use of rotary NiTi according to type of practice 149

6-2 Response details for year of graduation 150

6-3 Details of non-users of NiTi according to location 151

6-4a Reasons for non-use of rotary NiTi in descending order,

for all dentists 152

6-4b Statistically significant reasons for non-use of rotary NiTi

for the two differing graduation year ranges 153

6-5 Length of time of use of rotary NiTi 154

6-6 Weekly frequency of use of rotary NiTi with experience

(number of respondents) 155

6-7 Number (n) of endodontists (E) and general dentists (GD)

encountering each procedural problem 156

6-8 Number (n) of endodontists (E) and general dentists (GD)

indicating positive experiences with rotary NiTi compared

with manual instrumentation with stainless steel instruments 157

xii

6-9 Incidence of file fracture for endodontists (E) and

general dentists (GD) 158

6-10 Reported reasons for file fracture by endodontists (E) and

general dentists (GD) 159

7-1 Summary of instrument defects from 14 endodontists worldwide 175

7-2 Summary of instrument defects from 14 endodontists

according to file cross-section 176

8-1 Order, processes and results of cleaning experiments

performed on debris laden files 201

8-2 Summary of results of cleaning experiments with emphasis on

the four main components of the cleaning procedure 202

8-3 Summary of results of cleaning for complex files with

emphasis on the four main components of the cleaning procedure 203

8-4 Results of all cleaning experiments according to file type 204

8-5 Effect on file cleanliness by progressive incorporation of

best factors 205

8-6 Recommended protocol for cleaning of endodontic files 206

FIGURES

3-1 Frequency histogram for year of graduation 46

5-1 Response elements after each contact in the questionnaire

survey of NiTi use 108

xiii

8-1 Small plastic container with chlorhexidine-soaked scouring

sponge used chairside to clean files and keep them moist 207

8-2 Small metal mesh basket used to support the files during

pre-soaking and ultrasonication 208

8-3 Mesh basket supported in a 600ml glass beaker during

pre-soaking and ultrasonication 209

9-1 Cumulative percentage of adopters of rotary NiTi 222

9-2 Comparison of adoption curves for four studies 223

xiv

PART I

GENERAL INTRODUCTION

1

CHAPTER 1

INTRODUCTION

“It is high time that rotary root canal instrumentation be included in the core

endodontic curriculum in dental schools and be required in the standards for

accreditation” (Spångberg 2001).

This quotation from Professor Larz Spångberg, when viewed from a new

technology perspective, is quite profound. It demonstrates that the dental

profession has reached a point where it acknowledges that an initially disruptive

innovation (Chambers 2001) has reached a sufficient level of acceptance to be

recommended for teaching at an undergraduate level. This recommendation

implies that a new technology is recognised as superior to existing practice and

therefore merits adoption as standard procedure. However, in a broader context,

the statement alludes to a potential dilemma concerning the diffusion of

innovation in dentistry. The problem posed is: Why have some dentists decided to

implement a new technology whereas others have not or may actually be

vehemently opposed to it?

The daily practice of dentistry is difficult and rarely problem-free. Dentists

(and their staff) must constantly update their professional skills commensurate

with changing standards in dental practice and their own individualised practice

requirements, together with trying to keep a small business viable (Weintraub

2

1996, Best 1999). Keeping current with advances in dentistry and being able to

manage patients with often complex needs and demands is a challenge for

practising dentists (Sutherland 2001). Dental manufacturers are constantly

introducing new instruments, materials and techniques to stimulate dentists to

make changes in their practices (Morris et al. 1989, Sutherland 2001), and dentists

need the skills to be able to evaluate the merits of new products or procedures. In

other words, there is a need for dentists, as professionals, to be life-long learners

(Nash 1994). There comes a time when routine clinical techniques must be

changed based on new technology, clinical research, new materials and/or

advances in techniques and procedures (Simonsen 1993).

The word “technology” represents things, actions, processes, methods and

systems, but also involves philosophical factors. To understand these various

usages of “technology”, an understanding is required of patterns of human

behaviour (Kline 2003). Philosophically, this refers to an expansion of

“technology” to acknowledge the critical role that people have in technology and

diffusion of innovation. This leads to the concept of “sociotechnical” systems

where technology is part of a complete working system including people,

machinery, resources, processes, and legal, economic, and political factors in the

extension of human capacities (Kline 2003). In the last 50 years, technological

innovation in medicine and health care has accelerated at an unprecedented rate

(Perry & Thamer 1999). Failure to respond to the opportunities created by

technological change means that much actual or potential technology is not used

at all or is not used to its full potential (Mesthene 2003). In the specific realm of

3

dentistry there is little literature available exploring the reasons associated with

dentists adopting new technologies.

A new technology recently introduced into dentistry is endodontic

instruments manufactured from a nickel-titanium (NiTi) alloy. Before this

innovation, endodontic instruments were made first of carbon steel and later of

stainless steel. The lack of flexibility of stainless steel endodontic instruments,

especially in the larger sizes, meant that apical sizes necessarily remained small,

risking inadequate microbial control in the apical portion of the root canal. Whilst

the skill of the clinician is an important factor influencing the quality of root canal

treatment (Sjögren et al. 1990, Eriksen 1991, Friedman 1998), the limitations of

stainless steel root canal instruments (Serene et al. 1995) must be seriously

considered as another major factor.

NiTi alloys are one of several shape memory alloys, but they have the most

important practical applications due to their biocompatibility and corrosion

resistance (Serene et al. 1995, Otsuka & Wayman 1998). NiTi alloy was

discovered by Buehler et al. (1963) and named Nitinol (nickel, titanium, Naval

Ordinance Laboratory). The first dental application of NiTi suggested was as an

orthodontic wire (Andreasen & Hilleman 1971). The alloy was then suggested to

be used in manufacture of endodontic instruments (Civjan et al. 1974), and Walia

et al. (1988) found NiTi files to show promise for instrumenting curved root

canals. Their super-elasticity, shape memory effect and corrosion resistance have

led to the alloy having many dental, medical and commercial applications (Otsuka

4

& Wayman 1998). The properties of the alloy occur as a result of the austenite to

martensite transition, which in turn is due to the alloy having an inherent ability to

alter its type of atomic bonding (Otsuka & Wayman 1998, Thompson 2000).

The adoption of rotary NiTi technology provides a good model of how

dentists may approach the incorporation of new procedures into daily clinical

practice. Whilst there is a considerable amount of information available

concerning the adoption of new technologies, the vast majority relates to the

diffusion of innovations in industry (Rogers 1995, Scharff & Dusek 2003). Dental

examples of diffusion of innovation, however, are rare. To date, only one study

has investigated the incorporation of rotary NiTi into general dental practice but it

did not specifically look for reasons of adoption or non-adoption (Barbakow &

Lutz 1997). Implementation of scientific innovations is most important in

advances both in dental science and the dental-care system (Nakata 1990).

The reluctance amongst dental clinicians, including experts, to adopt this

particular new technology, even in the face of positive research, represents a

potential hindrance to the advancement of the quality of clinical endodontics. This

is particularly so at a general practice level. The question of why this new

technology meets undue resistance amongst practitioners is critically important,

because it directly affects the quality of endodontic treatment, which ultimately

affects the retention of natural teeth. These have both financial and health

implications for the community. Logically, if dentists can perform better

endodontic treatment with reference to the eradication of root canal infection, then

5

more natural teeth are likely to be retained. This will result in reduction in the

need for prosthetic replacement of teeth whose efficiency cannot compare with the

natural dentition. Frequently, the cost of such prosthodontic options, particularly

fixed bridgework and implants, is far greater than the cost of endodontic

treatment. Often the costs can be prohibitive for many patients who have no

option but to go without a replacement resulting in reduced masticatory

efficiency, aesthetic concerns and, in some instances, psychological effects.

Furthermore, technically good endodontic treatment at a general practice level

will reduce the incidence of endodontic retreatment in specialist endodontic

practice in both private and public sectors. A possible sequel to this is reduced

waiting lists in public institutions and in private specialist endodontic practices.

The cost savings to the community would follow on. “To fail to move forward as

a result of laziness or to resist moving forward, based on habit or tradition, or

simply out of fear of change, is contrary to the profession’s responsibility to the

public” (Simonsen 1993).

Therefore, the aim of this research was to investigate possible reasons for

the adoption or non-adoption of new technology in dentistry, using rotary NiTi

technology as a model.

To achieve this aim, this thesis first investigated the proportion of

Australian dentists and endodontists who were using rotary NiTi instruments and

their experiences with them. Part II of this thesis reports on a questionnaire survey

that explored general and specific issues concerning rotary NiTi instruments and

6

techniques. This section of the thesis looks at the basics of questionnaire survey

research, and reports and discusses the specific findings of the questionnaire. An

important issue arising from the survey concerned response rates and non-

response bias, which will be shown to imply personality and behavioural factors,

which in turn potentially influence adoption of new technology. Other more

practical issues were also identified and these were investigated in Parts III and IV

of the thesis to ascertain whether they were valid concerns.

Part III of the thesis considers the issue of intraoperative defects,

specifically fracture, of rotary NiTi instruments. Because this concern has been

present since the introduction of rotary NiTi instrumentation, and was confirmed

as such in Part II, Part III investigates actual defect rates of the instruments.

Part IV of the thesis reports on an issue, which, during the course of this

research, proved to be an important factor that may influence adoption. This

section involves an assessment of whether these instruments can be predictably

cleaned in the busy private practice setting. This aspect of the overall thesis was

motivated by recent Australian recommendations for single use of rotary NiTi

instruments, based on cross-infection concerns. This recommendation has major

financial implications for private practice, particularly general practice, but more

so from an educational point of view in a public institution setting for

undergraduate and postgraduate endodontic training.

7

Part V of the thesis is the general discussion relating the findings of the

survey, the instrument defect rate and the cleaning of instruments back to the

adoption of rotary NiTi. It considers some of the philosophical issues related to

new technology and theories related to adoption of new technology, using rotary

NiTi as an example. This part also briefly reviews the development and current

status of rotary NiTi and shows that the perceived technical concerns preventing

adoption of the new technology are not necessarily valid, and that there are other

issues affecting these decisions. From this arises a hypothesis for the adoption or

non-adoption of new technology in endodontics in particular, and in dentistry in

general.

REFERENCES

Andreasen G.F., Hilleman T.B. An evaluation of 55 cobalt substituted Nitinol

wire for use in orthodontics. Journal of the American Dental Association.

1971;82:1373-1375.

Barbakow F., Lutz F. The Lightspeed preparation technique evaluated by Swiss

clinicians after attending continuing education courses. International

Endodontic Journal 1997;30:46-50.

Best H. Quality and Dentistry [PhD Thesis]. Melbourne: University of

Melbourne; 1999.

Buehler W.J., Gilfrich J.V., Wiley R.C. Effect of low-temperature phase changes

on the mechanical properties of alloys near composition TiNi. Journal of

Applied Physics 1963;34:1475-1477.

8

Chambers D.W. Technology innovation. Journal of the American College of

Dentists 2001;68:41-46.

Civjan S., Huget E.F., DeSimon L.B. Potential applications of certain nickel-

titanium (Nitinol) alloys. Journal of Dental Research 1974;54:89-96.

Eriksen H.M. Endodontology - epidemiologic considerations. Endodontics &

Dental Traumatology 1991;7:189-195.

Friedman S. Treatment outcome and prognosis of endodontic therapy. In Essential

Endodontology. eds. D. Ørstavik & T. R. Pitt Ford, pp. 367-401. Oxford:

Blackwell Science Ltd. 1998.

Kline S.J. What is Technology. In: Scharff R.C., Dusek V., editors. Philosophy

of Technology. The Technological Condition: An Anthology. Oxford, UK:

Blackwell Publishing Ltd.; 2003. pp. 210-212.

Mesthene E.G. The Social Impact of Technological Change. In: Scharff R.C.,

Dusek V., editors. Philosophy of Technology. The Technological Condition:

An Anthology. Oxford, UK: Blackwell Publishing Ltd.; 2003. pp. 617-637.

Morris A., Vito A., Bomba M., Bentley J. The impact of a quality assessment

program on the practice behavior of general practitioners: a follow-up study.

Journal of the American Dental Association 1989;119:705-709.

Nakata M. Transfer of innovations for advancement in dentistry. Journal of

Dental Research 1990;69:1543.

Nash D.A. The life-long learning imperative … ends and means. Journal of

Dental Education 1994;58:785-790.

Otsuka K., Wayman C.M. Shape Memory Alloys. Cambridge: Cambridge

University Press. 1998.

9

Perry S., Thamer M. Medical innovation and the critical role of health

technology assessment. Journal of the American Medical Association

1999;282:1869-1972.

Rogers E.M. Diffusion of Innovations. 4th ed. New York, NY: The Free Press, A

Division of Simon & Schuster Inc; 1995.

Scharff R.C, Dusek V., editors. Philosophy of Technology. The Technological

Condition: An Anthology. Oxford, UK: Blackwell Publishing Ltd.; 2003.

Serene T.P., Adams J.D., Saxena A. Nickel-titanium instruments. Applications in

endodontics. St. Louis, Missouri: Ishiyaku EuroAmerica, Inc. 1995.

Simonsen R.J. Why not sealants? Journal of Public Health Dentistry

1993;53:211.

Sjögren U., Hägeland B., Sundqvist G., Wing K. Factors affecting the long-term

results of endodontic treatment. Journal of Endodontics 1990;16:498-504.

Spångberg L. The wonderful world of rotary root canal preparation. Oral Surgery

Oral Medicine Oral Pathology Oral Radiology Endodontics 2001;92:479.

Sutherland S.E. Evidence-based dentistry: Part 1. Getting started. Journal of the

Canadian Dental Association 2001;67:204-206.

Thompson S.A. An overview of nickel-titanium alloys used in dentistry.

International Endodontic Journal 2000;33:297-310.

Walia H.M., Brantley W.A., Gerstein H. An initial investigation of the bending

and torsional properties of Nitinol root canal files. Journal of Endodontics

1988;14:346-351.

Weintraub A. Continuous quality improvement and dental practice: a marriage of

necessity. Journal of the American Dental Association 1996;127:1099-1106.

10

PART II

QUESTIONNAIRE SURVEY OF ROTARY NICKEL-

TITANIUM INSTRUMENTATION

11

CHAPTER 2

INTRODUCTION

BASICS OF QUESTIONNAIRE SURVEY RESEARCH

Overview

A questionnaire survey is a method used for collecting information to

describe, compare, or explain knowledge, attitudes, preferences, beliefs, opinions,

experiences, behavioural experiences, practices and demographics (Fink 1995a;

Weisberg et al. 1996). The data obtained and their analysis allow the researcher to

describe, compare, predict, or estimate population characteristics and relationships

among variables (Jolliffe 1986; Fink 1995b). Questionnaire survey research is

carried out with the use of a survey instrument, which is commonly a mailed, self-

administered, questionnaire, but can also be by telephone, face-to-face

interviewing and by electronic means (Dillman 2000). It is well established that

such research should involve not only a carefully planned and prepared set of

questions, but also multiple attempts to improve response rates (Dillman 2000).

There are several sources of error, which can compromise the validity of

questionnaire survey research, namely, errors in sampling, coverage, measurement

and non-response (Dillman 2000). Consequently, researchers should consider the

sample results as approximations rather than as absolutes (Weisberg et al. 1996).

If the response rate of a questionnaire survey is low, the interpretation of the data

is open to the criticism that they do not represent the entire population sampled

12

(Tambor et al. 1993). Such errors can lead to data that are unreliable and invalid

(Litwin 1995), where reliability is defined as a statistical measure of the

reproducibility or stability of the questionnaire data, and validity is an assessment

of how well a questionnaire measures what it is intended to measure (Litwin

1995). There is very little written in the dental literature on how to conduct

questionnaire survey research on dental topics, and it appears that the

questionnaire survey literature originates mainly from the social sciences (Jolliffe

1986; Weisberg et al. 1996). The reason for this may be that, historically, the

origins of surveys date back to at least biblical times when surveys were in the

form of censuses, which later formed the basis for Roman taxation (Weisberg et

al. 1996). In the 19th century, social surveys in England and the United States

studied social conditions and poverty, while in the 20th century surveys in the

form of polls were conducted to predict the outcomes of political elections

(Weisberg et al. 1996). Therefore, questionnaire research originates from a need

to obtain information concerning communities and society in general.

There are many reasons to preclude collecting data from a whole

population, including cost, time, and manpower issues (Sapsford 1999). This

generally applies to large target populations, although there will be times when the

sampled population will be the same as the target population (Lohr 1999).

Consequently, a technique of sampling is employed to obtain data from a subset

of a population, that is, selecting a sample of the population from which

predictions about the whole population can be made.

13

A good sample is one that has ideally the same, but realistically as close

as possible, distribution of characteristics as the target population (Fink 1995b;

Lohr 1999; Sapsford 1999). Such a sample is termed as being “representative” of

the population and relies on using an unbiased method to choose survey

participants, on obtaining adequate numbers of participants, and on collecting

high-quality data with valid and reliable survey instruments (Fink 1995b).

Therefore, two essential requirements for a good survey are to select a

good representative sample, and then to ensure as high a response rate as possible.

Designing a representative sample will depend on the data being sought and the

method of obtaining a sample of adequate size free from selection bias, which

occurs when some part of the target population is not in the sampled population

(Lohr 1999). A recognised method of producing a representative sample is to use

probability sampling, which includes simple random sampling, stratified random

sampling and cluster sampling (Lohr 1999; Dillman 2000). These methods all

involve random selection of units included in the sample. If this requirement is

fulfilled, it is possible to use a relatively small sample to make inferences about an

arbitrarily large population (Lohr 1999). A variation is systematic sampling,

which is used as a simple random sampling method where the list is in roughly

random order, and is really a special case of cluster sampling (Lohr 1999).

Definitions

Survey research is not itself an academic discipline, with a common

language, a common set of principles for evaluating new ideas, or a well-

14

organised professional reference group (Groves 1989). Lacking such an

organization the field has evolved through the somewhat independent and

uncoordinated contributions of researchers trained as statisticians, psychologists,

political scientists and sociologists (Groves 1989). This explains the finding that

definitions relating to survey research are inconsistent amongst authors.

Therefore, the following definitions represent a simplification and summary of the

various definitions presented in the literature (Groves 1989; Fink 1995d;

Weisberg et al. 1996; Lohr 1999) and which will be referred to in this thesis:

• Target population – the finite set of people to be studied.

• Sampling frame – the list of units from which the sample will be drawn. This

will, once implemented, comprise respondents, non-respondents, and

ineligible units.

• Sampled population – the respondents providing usable data.

• Respondents – those who provide completed or partially completed

questionnaires (i.e., usable).

• Non-respondents – comprise non-participants and non-returners.

• Non-participants – returned a blank questionnaire.

• Non-returners – did not return a questionnaire.

• Ineligible units – those who do not meet the criteria for inclusion in the study,

as set by the researcher.

Sample size

Selecting the sample size is neither simple nor straightforward. There is

no specific formula to obtain the perfect sample size (Lohr 1999). A fundamental

15

factor to consider is whether statistical analysis is to be carried out on the data. If

so, then there are certain criteria that can be applied to estimate a sample. If not,

then two issues that need to be considered are that the larger the sample, the more

accurately the data will reflect the population, and that the more questions asked,

the larger the sample needs to be to provide sufficient data for analysis (Bouma

1993). Also, the size of the sample may be determined partly by the expected

variability in the data to be collected and partly by the size of error acceptable to

the researcher in estimates computed from the sample (Jolliffe 1986). Surveys

generally require a sample size greater than 100 because the error rate at this level

would be too great, but at some point, added precision is not worth the added cost

(Fink 1995a; Weisberg et al. 1996). From another perspective, a large change in

population size does not produce a large change in needed sample size, because

the sampling fraction (percentage of the population being sampled) has little effect

on the margin of error (Weisberg et al. 1996).

In evidence-based practice there is a requirement for the collection of

evidence, mostly in the form of numerical data, and its evaluation and

interpretation by statistical methods (Bland 2000). Because a population sample is

the basis for estimating characteristics of the population, probability theory in the

form of inferential statistical methods makes estimates and inferences about the

population from the sample (Rowntree 1981). Hence, statistical calculations are

used to determine the appropriate sample size.

16

Fink (1995c) presented checklists of factors to consider and questions to

ask when determining sample size, which are based on statistical concepts. She

showed that as the sample size increases, the standard error decreases, with the

size of the change in standard error reducing with increase in the sample size.

Various authors have presented mathematical formulae to calculate the sample

size required in order for an effect of a given size to be statistically significant

(Fink 1995c; Lohr 1999; Sapsford 1999; Dillman 2000). A simple version is

presented by Dillman (2000) as follows:

( )( )( )

( ) ( )( )ppCBNp

ppNpNs−+⎟

⎠⎞

⎜⎝⎛−

−=

11

12

where: Ns is the sample size required,

Np is the number of people in the survey population,

p is the proportion of the population expected to choose one of two

response categories (the most conservative value is 0.5),

B is an acceptable amount of sampling error; commonly +3% (.03) of the

true population value,

C is the Z statistic associated with the confidence level; 1.96 corresponds

to the 95% level (the most common level set).

17

Conversely, the margin of error for an established sample size can be

determined from the following formula (Weisberg et al. 1996):

( )( )( ) ( )1

98.01

1−

=−−

×NsNs

ppC

where, as in the previous formula, C=1.96 and ( )( ) ( )( )5.05.01 =− pp . This

formula can also be re-arranged to calculate Ns but does not incorporate a finite

population correction recommended for samples over 5% of the population size

(Levine et al. 1999), as does the previous formula.

Although formulae provide guidance in sample size selection, it is true

that the larger the sample, the smaller the sampling error, but also that non-

sampling errors may be greater with a larger sample (Lohr 1999). Hence, several

factors must be considered when selecting a sample size, not the least of which are

convenience and cost factors. Applied sampling involves compromises between

probability theory and practical considerations (Weisberg et al. 1996).

Survey error

All sample surveys are subject to various types of errors. There are four

main sources of error (Groves 1989; Dillman 2000):

• Sampling error – the error resulting from taking one sample instead of

examining the whole population.

18

• Coverage error – where the list from which the sample is drawn does not

include all elements of the population.

• Non-response error – failing to collect data from all persons in the sample and

where the respondents differ from the non-respondents in a way relevant to the

study.

• Measurement error – this results from inaccuracies in responses recorded on

the survey instrument. Such error may result from factors such as (Groves

1989; Lohr 1999):

the effect of the interviewer(s):

qualifications, motivation, training, work load, data collection methods

error due to the respondents:

availability, burden, motivation, proxy, ability, psychological factors

questionnaire factors:

design (eg., wording, layout), type (telephone, mail, anonymous,

follow-up, incentives), timing (time, date).

Response rate and non-response bias

Non-response to a questionnaire survey is always a problem, although it

is hoped that non-responders do not differ from responders other than being less

co-operative (Weisberg et al. 1996). Problems with questionnaire design and with

the wording of questions can promote non-response bias by creating confusion

and uncertainty in the mind of the potential respondent. If the non-respondents

differ from the respondents then the introduced biases can invalidate the

questionnaire survey results (Lohr 1999). However, if the non-response is not due

19

to questionnaire design and not due to any variable measured for the sample (for

example, gender, age, location), then the non-respondents are said to be “missing

at random”, and hence they can be ignored and the respondents can be used as a

representative sample of the population (Lohr 1999). Dillman (2000) commented

that very low response rate expectations suggest that respondents are quite likely

to be different from non-respondents on such things as interest in the issue and

simply being more likely to read such mail. The higher the non-response rate, the

more important it is to ascertain whether the refusals are concentrated amongst a

certain group (Weisberg et al. 1996).

In questionnaire surveys non-response consists of two components – non-

contacts and refusals (Locker 2000). High response rates for questionnaire surveys

are important and unless response rates are high, it is prudent to investigate non-

response bias (McCarthy & MacDonald 1997). One group of authors stated that it

is impossible to generalise an adequate return rate for all populations (Hovland et

al. 1980) because it depends on the difference between the responders and non-

responders. It is essential to the validity of questionnaire survey data that response

rates are high (Gough & Hall 1977). Small random samples with high response

rates are more valuable than large non-random samples or those with low

response rates (Evans 1991; Ward & Wain 1994). A high response rate will

strengthen a study when the absolute number of potential respondents is small

(Ward & Wain 1994). Other authors go so far as to classify achieved response

rates into categories such as good, acceptable, suspect and unacceptable (Locker

20

2000), or very good, good and adequate, which can lead to dangerous

complacency about non-response (Lohr 1999).

Non-response bias may result not only from some of those people in the

sample not participating, but also to some questions not being answered, a

phenomenon known as item non-response (Fink 1995c). The main reasons for

item non-response are refusal to answer the particular question, which may be

related to sensitive issues such as income and education, or respondents not

knowing the answers (Fink 1995d; Lohr 1999). However, it could also be due to

poor or confusing wording of the question.

Little attention has been given to the problem of non-response bias, and

the majority of researchers do not report attempts to detect such bias (McCarthy &

MacDonald 1997). Various authors recommend different response rates with a

range of 70-80% to minimise the risk of bias (Gough & Hall 1977; Evans 1991;

Christie et al. 1997; Brennan et al. 2000). Gough and Hall (1977) based their

figure of 75% or more on a review of previous questionnaire surveys and made no

mention of whether those papers they reviewed considered non-responder bias. In

their own questionnaire survey, with a response rate of 80.7%, they studied the

demographic, scholastic and psychological test data for 1,119 doctors and

concluded that there were only very slight differences between responders and

non-responders. Furthermore, when they attempted to combine variables in order

to classify responders and non-responders, the differences were trivial.

21

One study found no significant differences when the responses from the

initial questionnaire survey group were compared to those of the follow-up group

(Epstein et al. 1995b). However, only a sample of 100 non-responders were sent

the second questionnaire survey out of 1,519 who did not respond to the first

questionnaire, indicating the likelihood of bias. An early study on medical health

care professionals looked at the data from questionnaire surveys from 1961 to

1977 (Cartwright 1978) and found response rates varying from 56% to 99% with a

mean of 81% of a total of 11,345 people surveyed. A conclusion from this study

was that a comparison between responding and non-responding professionals did

not indicate any large bias. Hovland et al. (1980) claimed that non-response bias

does not affect the results of dental surveys on a typical dentist response rate of

50-70% and that a response rate as low as 43% may still have minimal non-

response bias.

Non-response bias can be assessed by comparing responses of

respondents who return questionnaires after an initial request, with those who

respond after follow-up requests (McCarthy et al. 1997). Investigations of late-

response bias as an indicator of non-response bias are based on the assumption

that the characteristics and responses of late-responders are more representative of

non-responders than those of early responders (McCarthy et al. 1997; McCarthy

& MacDonald 1997). An explanation for this assumption is lacking. An indication

of the magnitude of non-response bias can be obtained using linear extrapolation:

the cumulative percent of respondents reporting a given item is regressed against

the cumulative percent of questionnaires returned after different time intervals

22

(McCarthy et al. 1997). If there is a linear trend, the population prevalence value

for a given item assuming a 100% response rate can be estimated.

Some authors have concluded that questionnaire studies are biased due to

non-response and incorrect answers and that other ways of obtaining required

information should be sought (Sjöström et al. 1999). This view was based on a

questionnaire survey concerning oral health of a general Swedish population.

However, those authors conceded that scientific questionnaires must describe the

procedure carefully. The consensus is that despite difficulties with design,

execution and analysis of questionnaire surveys, valuable information can still be

obtained (Fink 1995a; Dillman 2000).

Improving response rates

Although there are differing views on the significance of non-response

bias in questionnaire survey research, there can be no doubt that a high response

rate is essential. The next step, then, is to implement measures to achieve these

high response rates. Although some authors believe that a 100% response rate is

impossible (Evans 1991; Sjöström et al. 1999), it is likely that it will depend on

such issues as the target population, sample size and survey techniques. Methods

to compensate for low mail returns and aimed at improving response to self-

administered questionnaire surveys include: follow-up mailings, telephone

contacts, monetary incentives, material (gift) incentives, respondent-friendly

questionnaires, a real stamp on the return envelope, personalisation of

correspondence, and many smaller details (Sadowsky & Kunzel 1986; Maheux et

23

al. 1989; Tambor et al. 1993; Weisberg et al. 1996; Ward et al. 1998; Young &

Ward 1999; Dillman 2000). A minimum recommendation is for a three-stage

questionnaire survey consisting of an initial mailing and two follow-ups (Locker

& Grushka 1988). Dillman (2000) commented that the inevitably high non-

response to any mailing is probably due less to conscious refusals than to either

unrealised good intentions or the lack of any reaction at all. A questionnaire may

be put aside with the intention of attending to it later, but the longer it remains

uncompleted, the less the chance that it will be completed and returned (Dillman

2000).

The use of material incentives is believed by some authors to be

obtaining responses from people who would otherwise not have participated and

so their responses may not be reliable (Bourque & Fielder 1995). On the other

hand, it is a way of showing the respondents that their time is considered valuable

by the researcher (Bourque & Fielder 1995). In any case, there do not appear to be

any deleterious effects of incentives on the quality of survey responses (Singer et

al. 1999). One review of response rates to questionnaires revealed that response

rates can be improved by first supplying a reply-paid return envelope, and then

actively following-up non-responders (Tan & Burke 1997). In another review,

written reminders with a copy of the questionnaire and telephone reminders were

considered beneficial, whereas promising anonymity and offering financial

incentives were not (Asch et al. 1977). Some authors recommend the inclusion of

telephone prompts and telephone reminders in questionnaire survey protocols

(Ward & Wain 1994; Osborn et al. 1996; Rikard-Bell & Ward 2000).

24

Furthermore, an experienced non-medical research assistant is as effective as a

medical practitioner in administering telephone prompts to enhance questionnaire

survey response rates (Gupta et al. 1997). Rikard-Bell and Ward (2000) found that

a telephone prompt produced a higher initial response rate than a postal prompt.

With these differing views on the validity of non-response bias, it follows

that a high response rate is desirable. The response rate of a questionnaire survey

is defined as the number of completed and partially completed

questionnaires/surveys/interviews divided by the number of eligible sample units

(Kviz 1977; Groves 1989; Locker 2000).

QUESTIONNAIRE SURVEY RATIONALE AND DESIGN

Purpose

This questionnaire survey was conducted to investigate aspects of the use

of rotary nickel-titanium (NiTi) instruments and techniques in general dental

practice and in specialist endodontic practice within Australia. In particular, the

following aspects were to be investigated: demographics, patterns of NiTi usage,

issues (problems and experiences) with NiTi usage, and training in the use of

NiTi.

25

Methods

Pilot study

The survey was a mailed self-administered questionnaire because the

sample size was large and geographically wide-spread. This, together with the

non-complex nature of the information sought did not warrant an interview type

survey. Some of the questions asked by Barbakow & Lutz (1997) were used as a

starting point and expanded upon to create an initial series of questions covering

issues related to the use of rotary nickel-titanium instruments and techniques. That

pilot questionnaire was tested on ten volunteer postgraduate students in

endodontics at the University of Melbourne. From their responses and comments

the questionnaire was modified by three reviewers (the authors of Chapter 5) to

arrive at the final version.

Questionnaire survey instrument

The mailed questionnaire survey comprised a total of 43 questions

(Appendix A), many of which had multiple parts, over six single-sided A4 pages.

The format included both closed and open-format questions. The questionnaire

was structured as follows:

• Part A. Demographics – 3 questions.

• Part B. Patterns of rotary NiTi usage – 18 questions.

• Part C. Issues associated with NiTi usage – 11 questions.

• Part D. NiTi education – 11 questions.

26

Questionnaire survey implementation

The required sample size was calculated using the formula above

(Dillman 2000). From the target population, Np = 5,742. The values substituted

for p, B and C were 0.5, 0.03 and 1.96 respectively as recommended above. The

conservative value for p (i.e., 0.5) was selected because that would yield the

highest Ns with the other variables held constant. Applying the formula gave the

result that Ns = 900. By comparison, values of p on either side of 0.5 resulted in

much lower values of Ns. When p = 0.4 (or 0.6), 0.3 (or 0.7), 0.2 (or 0.8), or 0.1

(or 0.9), Ns = 869, 775, 610, or 360.

The sample size of 900 comprised 64 endodontists and 836 general

dentists. The sample consisted of all practising Australian endodontists who were

members of the Australian and New Zealand Academy of Endodontists

(ANZAE), and a stratified systematic sample of Australian dentists who were

members of the Australian Dental Association Incorporated (ADA). More than

90% of Australian dentists are members of the ADA (Clarkson et al. 2003). In

April 2001, a list of all ADA members was received from the ADA by e-mail in

alphabetical order and in Microsoft® Excel format. There were 5,755 dentists on

this list and from this list were removed all endodontists (67) and all dentists with

an overseas address (10). This left a population of 5,678 general dentists and

dentists in specialties other than endodontics. This list was then sorted into

postcode order. To ensure that each region (six states and one territory) of

Australia was equally represented, the number of dentists in each region was

27

calculated as a percentage of all dentists on the adjusted list. These percentages

were then applied to the selected sample size of 836 (Table 2-1).

Table 2-1: ADA general dentists according to state.

State* № of Dentists Sample Size % of Total†

Northern Territory 32 5 0.6

Tasmania 77 11 1.3

South Australia 473 70 8.4

Western Australia 604 89 10.6

Queensland 971 143 17.1

Victoria 1,451 214 25.6

New South Wales 2,070 304 36.4

Totals 5,678 836 100

* For simplicity, the Northern Territory is referred to as a state.

† Percentage applies to both Number of Dentists and Sample Size for each state.

28

Stratification was also carried out to differentiate metropolitan from rural

areas in each state. To achieve this, Australia Post was consulted, and from them a

booklet was obtained containing postal charges according to zones (AusPost

zones) within each State (Australia Post 2000). The zones are determined by

Australia Post according to distance from the General Post Office within each

state capital city of Australia (Appendix B). From these zones, as determined by

postcode, another table was drawn up such that the percentages of metropolitan

and rural dentists overall was applied to the sample size (Table 2-2). Metropolitan

areas were those with a zone 1 rating, that is, N1, V1, Q1, S1, NT1, W1 and T1.

All other zones were considered to be rural areas.

To allow a better weighting within the rural zones for Queensland and

Western Australia, these samples were further stratified according to the

additional Australia Post zones within these two states (Table 2-2). Thus, the final

sample size is made up of a systematic sample from each zone, and is proportional

to both the numbers in each state and to the numbers in metropolitan and rural

areas.

From each stratum every seventh dentist was selected, with the starting

point being the first name appearing on the list for each stratum. The number

seven is approximately the number of dentists on the adjusted list (5,678) divided

by the sample size (836).

29

Table 2-2: Stratification according to postal zone.

State № Dentists AusPost Zone №* %† Sample‡ Totals

NT 32 Metro (NT1) 32 100 5 5

TAS 77 Metro (T1) 77 100 11 11

Metro (S1) 419 88.6 62 SA 473

Rural (S2) 54 11.4 8

70

Metro (W1) 505 83.6 74

Mid (W2) 90 14.9 13

WA 604

North (W3) 9 1.5 2

89

Metro (Q1) 640 65.9 94

Near (Q2) 176 18.1 26

Mid (Q3) 58 6.0 9

QLD 971

North (Q4) 97 10.0 14

143

Metro (V1) 1251 86.2 184 VIC 1451

Rural (V2) 200 13.8 30

214

Metro (N1) 1542 74.5 227 NSW 2070

Rural (N2) 528 25.5 77

304

5,678 5,678 100 836 836

* This refers to the number of dentists in each zone according to Appendix B.

† Proportions in metropolitan and rural areas for each state.

‡ Sample size for each zone according to the State percentages indicated.

30

The list of endodontists was the most current one available from the

ANZAE as at April 2001 and included 77 members. From this were removed

those practising in New Zealand (n = 10) and those who were known to have

retired (n = 3). This left an endodontist population of 64 (Table 2-3). Thus, the

total sample frame of all endodontists and general dentists was 5,742.

Table 2-3: Endodontists according to state and postal zone.

State* № Endodontists† Zone Sample

Metro (N1) 21 NSW 24 (37%)

Rural (N2) 3

VIC 17 (27%) Metro (V1) 17

QLD 12 (19%) Metro (Q1) 12

SA 7 (11%) Metro (S1) 7

WA 4 (6%) Metro (W1) 4

Total 64 64

* Tasmania and the Northern Territory did not have resident endodontists.

† Percentage of total in brackets.

31

Mailing procedure

The questionnaire was accompanied by a letter (Appendix C) on

University of Melbourne letterhead explaining the survey and requesting

participation. The letter also indicated that the survey itself was to be confidential

and the results would be reported in an anonymous manner. A reply paid envelope

was included, and the three items were mailed together in an envelope with the

University of Melbourne emblem. The reply paid envelopes for all mail contacts

were individually and consecutively numbered on the front to enable follow up

mailing to non-respondents. Non-respondents were sent a further questionnaire

with a differently-worded letter (Appendix D) and another reply-paid envelope.

This time the letter specified a return date. The third mail-out included yet another

copy of the questionnaire and another letter (Appendix E) with different wording

and this time dated, individually addressed, and personally signed by the principal

investigator. The first two letters carried a photocopied signature. Finally, the

remaining non-respondents were telephoned by secretarial staff already in the

employ of the author in his private practice. These secretaries were provided with

a set script (Appendix F) to use in order to request either completion and return of

the questionnaire, a reason for non-participation or, in cases where the sample unit

did not use NiTi, answers to the four questions on the first page.

After the first two mailings, eight letters were returned unopened and

post-marked that the person was no longer at that address. In these cases

alternative units were selected from the population by selecting someone else

32

from the same postcode, either the name above or below the returned and

unopened questionnaire. This resulted in a total mailing of 908.

The timing of the mail-outs was not pre-defined, rather it was decided to

wait to see whether a pattern developed with time. Based on this, the timing and

number of further mail-outs would be decided as the project progressed. The data

collection period extended from June 2001 to November 2001.

Data analysis

The raw data were collected and manually entered into a Microsoft®

Excel spreadsheet. Each possible response to each question was allocated its own

column and any non-numerical data were numerically coded for ease of data

manipulation. The spreadsheet was imported into Minitab™ and SPSS™

Statistical Software and analysis was carried out using the Chi-Square test, Chi-

Square test for trend using logistic regression, Fisher’s Exact test, and the Linear-

by-Linear Association test. Fisher’s Exact test was used when the Chi-Square

value was low and the test produced at least one expected cell count less than five

and may have been unreliable; the higher P-value is reported. These analyses

tested for differences both between and within the endodontist and general dentist

groups. The differences with increasing experience with the technology were also

tested. The significance level was set at P < 0.05. Because of the small number of

endodontists relative to the number of general dentists, most data from both

groups are combined unless there were interesting or significant differences

between the two, or within either group.

33

The results are presented and discussed in Chapters 3 and 4, and also in

Chapters 5 and 6 as part of papers submitted for publication.

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37

Tambor E.S., Chase G.A., Faden R.R., Geller G., Hofman K.J., Holtzman N.A.

Improving response rates through incentive and follow-up: the effect on a

survey of physicians' knowledge of genetics. American Journal of Public

Health 1993;83:1599-1603.

Tan R.T., Burke F.J.T. Response rates to questionnaires mailed to dentists. A

review of 77 publications. International Dental Journal 1997;47:349-354.

Ward J., Bruce T., Holt P., D'Este K., Sladden M. Labour-saving strategies to

maintain survey response rates: a randomised trial. Australian and New

Zealand Journal of Public Health 1998;22:394-396.

Ward J., Wain G. Increasing response rates of gynaecologists to a survey: a

randomised trial of telephone prompts. Australian Journal of Public Health

1994;18:332-334.

Weisberg H.F., Krosnick J.A., Bowen B.D. An Introduction to Survey Research,

Polling, and Data Analysis. Thousand Oaks, California: Sage Publications.

1996.

Young J.M., Ward J.E. Improving survey response rates: a meta-analysis of the

effectiveness of an advance telephone prompt from a medical peer.

Medical Journal of Australia 1999;170:339.

38

CHAPTER 3

QUESTIONNAIRE RESULTS

RESPONSE DETAILS

The responses to all 43 questions in the questionnaire are summarised in this

chapter. Data presented generally include only material not submitted for

publication unless otherwise specified and/or necessary to the understanding of

the remaining data. Chapters 5 and 6 address specific topics in more detail, and

are in the form of manuscripts prepared for publication, in which are documented

data not presented in the current chapter. Therefore, when required, reference will

be made to the appropriate sections of Chapters 5 and 6. Discussion of the results

occurs mainly in Chapters 5 and 6, and Chapter 4 discusses the remainder of the

findings. Superscripted upper case letters refer to the statistical analyses presented

in Appendix G. Because of the multiple answers to most questions, the

percentages often add up to more than 100%.

Sampling experiences

According to the definitions presented in Chapter 2, the target population

was all practising dentists and endodontists within Australia. The sampling frame

did not include dentists who were not ADA members. Ineligible units consisted

initially of specialists in disciplines other than endodontics or had an overseas

address. Non-responders and further ineligible units were identified as the survey

progressed.

39

From the complete membership list provided by the ADA, the

endodontists were easily identified by the ANZAE list, and subsequently

removed. The ADA also supplied mailing labels from which were removed those

for the endodontists and overseas dentists. From the format of the ADA list there

was no way of differentiating between general dentists and specialists other than

endodontists, except for those personally known to the author. When drawing the

sample, it was simplest to eliminate non-eligible non-endodontist specialists when

and as their names appeared, if recognised. In that event, the next dentist below or

above that name was selected, the determining factor being the same postcode.

However, in order not to disrupt the sequence of every seventh dentist, the

counting continued from the original (excluded) name, not the new name. This

was not frequent and occurred only with some non-endodontist specialists with

whom the author was acquainted. The process of obtaining the sample was

straightforward because the list was received in Microsoft® Excel format and

could be easily sorted first into postcode order and then stratified into

metropolitan and rural areas.

The timing of the follow-up mail-outs was not defined until the first mail-

out had been completed, when it was found that there was an initial rush of replies

followed by a gradually declining trickle of responses. It was decided to wait until

a working week had elapsed with no further replies before sending the next

reminder to non-responders. Although the first two mail-outs produced good

returns it was decided to conduct a third mailing to be followed up by a telephone

40

contact in order to ascertain the effects of the extra contacts on response rate.

Following this procedure, the contacts occurred on the following dates:

• First mail-out on June 14, 2001.

• Second mail-out on September 6, 2001 (12 weeks after first mail-out).

• Third mail out was on October 10, 2001 (5 weeks after second mail-out).

• The telephone contact was between November 7-14, 2001 (5 weeks after third

mail-out).

As questionnaires were received, the envelopes were separated from the

questionnaire unless there were demographic details missing. Those missing

details were obtained by cross-referencing to the sample list, and then the survey

and envelope were separated. This was in keeping with the project being

confidential but not anonymous. This process was completed by a person

unrelated to the project and acting as an Administrative Officer. The data were

then entered into Microsoft® Excel producing an extensive spreadsheet.

For the telephone contact of the 139 non-respondents to the three mailings,

the author enlisted the services of three dental secretaries who used the supplied

script (Appendix F) either to remind dentists to return their questionnaires or to

obtain usable responses, or both. Because the prime question was whether the

dentists currently used rotary NiTi instruments or not, the telephone contact was

designed to establish this fact first. If they did not use NiTi, then they were asked

to fax the completed first page, or alternatively the secretaries asked those

questions over the telephone. The questions covered the three demographic details

41

and also the question of whether or not they had tried rotary NiTi instruments, and

related reasons (Question 5 of the survey). If they did use the instruments, the

dentists were requested to complete the questionnaire if they still had it or a new

one would be mailed if required. One respondent requested the survey be faxed to

him and he would complete it immediately, which he did and returned by fax. The

telephone contact proved to be quite time consuming and difficult because it

required considerable time first to be able to track down respondents and then to

ask the questions. Two attempts were made to contact each person on the list.

Response details

As described in Chapter 2, the response elements to the survey resulted in

four main categories:

• Responders – completed or partially completed questionnaires (i.e., usable).

• Non-participants – returned a blank questionnaire.

• Non-returners – did not return a questionnaire.

• Ineligible units – those who had moved, retired were on vacation or ill in the

long-term, did not perform any endodontics, or were in a specialty other than

endodontics.

Non-participants and non-returners together represented the non-responders.

Summaries of the response details for each contact are presented in Chapter 5 in

the form of a manuscript prepared for publication. The following provides detail

not presented in Chapter 5. Table 3-1 indicates the numbers of resulting response

elements after each contact for the endodontists. The data relating to general

42

dentists is presented in Table 3-2. Overall, 58 (91%) of the endodontists provided

usable responses, whilst of the remaining six (9%), four did not respond to any

contact (non-returners) and two returned a blank questionnaire (non-participants).

There were no ineligible units amongst the endodontists.

Of the 776 eligible general dentists, 673 (87%) provided usable responses,

whilst of the remaining 103 (13%), there were 50 non-returners and 53 non-

participants. There were 68 ineligible units amongst the general dentists. The

combined data are presented in Table 5-1 in Chapter 5. There was no significant

difference in proportions of usable responders and non-responders between the

endodontists and general dentists. From Tables 3-1 and 3-2, when grouping the

usable respondents according to early (contact 1) or late (contacts 2-4) response,

significantly more endodontists (50/58) than general dentists (389/673) responded

early (χ2 = 17.961, 1DF, P < 0.001)A.

43

Table 3-1: Details of number of endodontists responding to each contact.

Contact Usable responses Non-participant* Totals†

1 50 2 52 (81%)

2 5 0 5 (8%)

3 3 0 3 (5%)

4 0 0 0

Totals† 58 (91%) 2 (3%) 60 (94%)‡

Table 3-2: Details of number of general dentists responding to each contact.

Contact Usable responses

Non-participant§

Ineligible Totals**

1 389 26 11 426 (50%)

2 185 11 6 202 (24%)

3 72 6 3 81 (10%)

4 27 10 48 85 (10%)

Totals** 673 (80%) 53 (6%) 68 (8%) 794 (94%)††

* Non-responders who returned a blank questionnaire. † Proportion of the total endodontists sample of 64. ‡ Four non-responders did not return a questionnaire. § Non-responders who returned a blank questionnaire. ** Proportion of total general dentists sample of 844. †† Fifty non-responders did not return a questionnaire.

44

RAW DATA

When entering the raw data into the Microsoft® Excel spreadsheet it

proved easier to produce two main spreadsheets – one for those respondents who

did use rotary NiTi (“Yes”), and one for those who did not (“No”). The analysis of

these data is presented under the same headings as used in the questionnaire

(Appendix A).

PART A. DEMOGRAPHICS

Question 1. Year of graduation

The range of years spanned 1948 to 2000 (Table 6-2). The only years not

represented were 1952 and 1959. When questionnaires were returned without the

year of graduation completed, the 2001 ADA Directory was consulted to ascertain

the year. However, this may not have actually been the graduation year but rather

the first year of registration as a dentist. This was necessary in only 15 instances

out of the 805 returns. Of these, four were in the non-respondent category.

The distribution for the eligible sample (includes respondents and non-

respondents is depicted in Figure 3-1. The mode year for the eligible sample

population was 1982 with 45 units followed by 1978 with 40. Most usable

responses were from dentists who graduated between 1971 and 1980 (Table 6-2).

As described in Chapter 6, there was no significant difference in proportions

between responders and non-responders according to year of graduation. The

45

influence of year of graduation on use or non-use of rotary NiTi is discussed in

Chapter 6.

1950 1960 1970 1980 1990 2000

0

10

20

30

40

50

Year

Freq

uenc

y

Figure 3-1: Frequency Histogram for Year of Graduation.

Question 2. Main practice postcode

As with the year of graduation, some postcodes were omitted from

returned questionnaires but in most instances it was possible to trace it back

through the Directory. Tables 3-3 and 3-4 present the response details for general

dentists and endodontists in each state according to location of metropolitan or

rural. Some of the figures for the totals for each zone do not match those of the

original sample size (Table 2-2). This may possibly be due to the original

postcode of the mail-out not actually being the main practice address rather it may

have been the home postcode. This will depend on which address a particular

46

member gives as the mailing address. Alternatively, it is possible that a dentist

could live in the metropolitan area but work in a rural region, and vice versa.

Furthermore, where a dentist works at multiple locations it is possible that there is

a combination of metropolitan and rural locations. Another possibility is that

members may have recently moved to another state with their mail having been

forwarded to their new address.

When comparing the proportions of sample units (Table 2-2) with the

proportions of usable respondents (Tables 3-3 & 3-4) there were no significant

differences.

47

Table 3-3: Response details according to location – general dentists*

State Zone Response Type Totals

Use Don’t use No response

NT Metro (NT1) 2 (50%) 2 (50%) 0 4 (0.5%)

TAS Metro (T1) 4 (36%) 5 (45%) 2 (18%) 11 (1%)

Metro (S1) 3 (5%) 42 (74%) 12 (21%) 57 (7%) SA

Rural (S2) 2 (15%) 10 (77%) 1 (8%) 13 (2%)

Metro (W1) 11 (16%) 49 (73%) 7 (10%) 67 (9%) WA

Rural (W2, W3) 3 (18%) 11 (65%) 3 (18%) 17 (2%)

Metro (Q1) 16 (19%) 59 (70%) 9 (11%) 84 (11%) QLD

Rural (Q2-Q4) 9 (19%) 31 (66%) 7 (15%) 47 (6%)

Metro (V1) 36 (21%) 112 (64%) 26 (15%) 174 (23%) VIC

Rural (V2) 7 (23%) 22 (73%) 1 (3%) 30 (4%)

Metro (N1) 41 (21%) 129 (64%) 30 (15%) 200 (26%) NSW

Rural (N2) 16 (24%) 47 (69%) 5 (7%) 68 (9%)

150 519 103 772†

* Percentages in the Response Type columns refer to the total for the particular location. The percentages in the last column refer to the total of 772 in the last row. † Does not include the four respondents who did not provide a postcode.

48

Table 3-4: Response details according to location – endodontists*

State Zone Response Type Totals

Use Don’t use No response

WA Metro (W1) 4 (100%) 0 0 4 (6%)

SA Metro (S1) 3 (43%) 4 (57%) 0 7 (11%)

QLD Metro (Q1) 10 (77%) 1 (7%) 2 (15%) 13 (20%)

VIC Metro (V1) 10 (63%) 4 (25%) 2 (12%) 16 (25%)

Metro (N1) 8 (40%) 10 (50%) 2 (10%) 20 (31%) NSW

Rural (N2) 2 (50%) 2 (50%) 0 4 (6%)

37 21 6 64

* Percentages in the Response Type columns refer to the total for the particular location. The percentages in the last column refer to the total of 64 in the last row.

49

For general dentists and endodontists there were no significant differences

between proportions of usable responses and non-respondents according to state

or according to location (metropolitan or rural). For metropolitan general dentists,

for rural general dentists, and for endodontists there were no significant

differences in proportions who used or did not use rotary NiTi. Hence, there was

no measurable demographic non-response bias.

Question 3. Origin of dental degree

Tables 3-5 indicates that some 85% of usable responses were from

graduates of Australian universities. Table 3-6 details the origin of degree within

Australia. There were no significant differences in proportions of dentists using or

not using rotary NiTi when comparing Australia with Foreign or when comparing

the states of Australia. When arranging the data into regions of the World (Table

3-7), of some 10% of overseas-trained dentists most were from Europe (which

included the UK, Sweden, Bosnia, Poland, Romania, Denmark, France, Greece

and Russia). Of the 48 dentists from Europe, 35 were from the United Kingdom.

Almost all dentists from Africa were from South Africa and only one from Egypt.

Asia included India, Indonesia, the Philippines, and Singapore. Interestingly, only

one dentist was American trained. Significantly more dentists whose degree

originated in Africa used rotary NiTi (Fisher’s Exact test: P = 0.002)B than

dentists whose degree was obtained in other regions of the world.

50

Table 3-5: Responses according to Australian or foreign degree*.

Origin Totals Use Don’t use

Australia 622 (85%) 155 (25%) 467 (75%)

Foreign 89 (12%) 29 (33%) 60 (67%)

Unknown 20 (3%) 4 16

Totals 731 188 (26%) 543 (74%)

Table 3-6: Responses according to origin of degree within Australia†.

Origin Totals Use Don’t use

NSW 209 (34%) 53 (25%) 156 (75%)

VIC 134 (21%) 34 (25%) 100 (75%)

QLD 130 (21%) 36 (28%) 94 (72%)

SA 87 (14%) 17 (20%) 70 (80%)

WA 62 (10%) 15 (24%) 47 (76%)

Total 622 155 (25%) 467 (75%)

* Percentages in the “Use” and “Don’t use” columns relate to the origin total. Percentages in the Totals column relate to the overall total of 731. † Percentages in the “Use” and “Don’t use” columns relate to the origin total. Percentages in the Totals column relate to the overall total of 622.

51

Table 3-7: Responses according to region of the world from which degree was obtained*.

Region Total Use Don’t use

Australia/New Zealand 641 (88%) 162 (25%) 479 (75%)

Europe 48 (7%) 12 (25%) 36 (75%)

Africa 16 (2%) 10 (63%)† 6 (37%)

Asia 5 (1%) 0 5 (100%)

Americas 1 (0%) 0 1 (100%)

Unknown 20 (3%) 4 (20%) 16 (80%)

World 731 188 (26%) 543 (74%)

* Percentages in the “Use” and “Don’t use” columns relate to the region total. Percentages in the “Total” column relate to the overall total of 731. † Significantly greater proportion than all other regions combined but ignoring “unknown” (Fisher’s Exact Test; P = 0.002)B.

52

PART B. PATTERNS OF ROTARY NITI USAGE

In response to Question 4, 188 dentists (26%) indicated that they currently

used rotary NiTi instruments and 543 indicated that they did not. The reasons for

non-use are given in Table 6-4a and discussed in Chapter 6.

This part of the questionnaire asked questions aimed at determining the

patterns of use of rotary NiTi. The questions and data obtained are presented

together in the format of the actual questionnaire, and the number of respondents

for each question is also provided to give an indication of item non-response bias.

Some of the analysis of the remainder of the questionnaire is in Chapter 6 and will

be so indicated where applicable.

The number after each option represents the total number of responses.

The percentage relates to the number of respondents for the particular question.

The number in square brackets represents the number of endodontists. Some

questions relating to specific instruments and techniques may no longer be

relevant because of recent advances; in these cases detailed analysis was not

indicated.

6. Over what period of time have you been using rotary NiTi instruments?

Less than 1 month 8 (4%) [0]

1-12 months 46 (25%) [8]

13-24 months 50 (27%) [7]

25-36 months 38 (20%) [9]

53

Longer than 36 months 45 (24%) [13]

Total responses – 187/188 (99%).

An overall Chi-Square test indicated no significant differences between

proportions of dentists and endodontists over all the various time periods. Fisher’s

Exact test indicated no significant differences between individual time periods.

See Chapter 6 – “Frequency of use” and Table 6-5.

7. On average, how often do you use rotary NiTi files for root canal cleaning and

shaping?

Less than once weekly 26 (14%) [1]

Once weekly 20 (11%) [0]

Twice weekly 26 (14%) [1]

Three times weekly 26 (14%) [0]

Four times weekly 23 (12%) [2]

Five or more times weekly 66 (35%) [33]

Total responses – 187/188 (99%)

Overall the numbers in each choice were similar except for the last option, which

is clearly influenced by the number of endodontists. These data do not necessarily

reflect the amount of endodontic treatment carried out by general dentists.

Similarly, the data pertaining to endodontists do not reflect how often rotary

instruments are used compared with hand instruments.

See Chapter 6 – “Frequency of use” and Table 6-6.

54

8. In which particular teeth do you use them? (If applicable, please tick more than

one)

Anterior teeth 114 (61%) [21]

Premolar teeth 163 (87%) [32]

Molar teeth 174 (93%) [37]

Total responses – 187/188 (99%).

The number of people who used NiTi on only one tooth type was 24 (13%), and

of these 22 (92%) used them only for molars, and the rest (8%) for anteriors. None

used rotary NiTi in premolar teeth only. Of the 33% who used the instruments on

two tooth types, most used them for premolars and molars (82%). The rest (18%)

used them for both anterior and premolar teeth. No respondents used them for the

combination of anterior and molar teeth. Overall, 54% used rotary NiTi for all

three tooth types.

There was no significant difference in type of teeth treated with rotary NiTi with

increasing experience, and no difference between endodontists and general

dentists.

9. For which particular situation do you use them? (If applicable, please tick both)

Straight root canals 152 (82%) [27]

Curved root canals 172 (93%) [36]

Total responses – 185/188 (98%).

Only 25% of respondents used rotary NiTi for only one type of canal, with most

of these (72%) using them only in curved canals. The remaining 75% of

respondents used the instruments for both curved and straight canals.

55

There was no significant difference in type of canals treated with rotary NiTi with

increasing experience, and no difference between endodontists and general

dentists.

10. Do you use them for: (If applicable, please tick both)

The coronal part of the root canal? 167 (90%) [35]

The apical part of the root canal? 168 (90%) [32]

Total responses – 186/188 (99%).

Most respondents used the instruments for both parts of the canal (80%), but of

the 37 (20%) who used them in only one part of the canal, the numbers were

similar for coronal (n=18; 49%) and for apical (n=19; 51%).

There was no significant difference in part of the canal instrumented with

increasing experience, and no difference between endodontists and general

dentists.

11. Which system do you mostly use?

Quantec LX 40 (22%)

Quantec SC 36 (19%)

ProFile 111 (60%)

Other 27 (15%)

Total responses – 185/188 (98%).

The majority of respondents (n=158; 86%) used only one system of rotary NiTi

instruments. Of these, 93 (58%) used the ProFile system, 53 (33%) used either the

LX or SC Quantec, and the remaining 13 (8%) used some other system. Twenty-

56

two respondents (12%) used two systems and 4 (2%) used three. At the time of

this survey the two main rotary systems on the Australian market were the

Quantec and ProFile systems, but a number of other rotary NiTi instruments had

been or were being released. Of the 15% of respondents who used such “other”

systems the types specified included the Greater Taper series, the Orifice Shaper

series, ProTaper, HERO, Lightspeed, the Flare series and Endomagic. One

respondent answered “unsure” whilst another answered “TRZX”, both of which

indicate uncertainty.

12. Have you used any other systems? Please indicate:

Have not used other systems 94 (57%)

Quantec LX 32 (19%)

Quantec SC 36 (22%)

ProFile 21 (13%)

Other 15 (9%)

Total responses – 166/188 (88%).

Most respondents here had not used another system, but of those who had, the

Quantec safe-cutting series was slightly more common. Of the “other” files, the

brands included those named in Question 11 but also included the K3 instruments.

13. Which instrumentation technique do you use? (Please tick as many as apply)

Crown-down 115 (61%) [21]

Step-back 27 (14%) [3]

Modified crown-down 72 (39%) [22]

57

Other 3 (2%) [2]

Total responses – 187/188 (99%).

The crown-down technique was by far the most common technique. Of the 187

respondents, 162 (87%) used only one instrumentation technique (59% crown-

down; 9% step-back), 8% used two, 3% used three and 2% used four. In the

“other” category, the balanced force and Endomagic techniques were recorded

and the third respondent commented that the instrumentation technique varied

with the case.

A significantly larger proportion of endodontists than general dentists indicated

that they used a modified crown-down technique (χ2 = 8.556, 1DF, P = 0.003)C.

There was no significant difference in instrumentation technique with increasing

experience.

14. Which sequence of instruments do you use? (Please tick as many as apply)

NiTi coronally and apically 110 (59%) [21]

NiTi coronally and stainless-steel hand instruments apically 90 (48%) [20]

NiTi coronally and NiTi hand instruments apically 35 (19%) [9]

Gates-Glidden burs coronally and rotary NiTi apically 56 (30%) [11]

Other 16 (9%) [4]

Total responses – 187/188 (99%).

A total of 97 (52%) respondents used only one sequence, the most common being

the use of rotary NiTi for the whole canal length. The remaining respondents used

two (35%), three (11%), four (2%) or five (1%) instrument sequences. In the

“other” category, most specified exact sizes aimed for and the exact sequence.

58

Five of these respondents ticked only the “other” box and each specified that they

used hand stainless-steel instruments apically first, to various sizes, followed by

rotary NiTi instruments.

There was no significant difference in instrument sequence with increasing

experience, and no difference between endodontists and general dentists.

15. How many times do you feel it is appropriate to use each file?

Once only 22 (12%) [8]

2-5 times 131 (70%) [28]

6-10 times 35 (19%) [3]

Until it distorts 10 (5%) [3]

Total responses – 188/188 (100%).

Of the respondents, 179 (95%) ticked only one answer. Of the remainder, 4%

ticked two answers (mostly once and 2-5 times) and 1 person ticked the first three

choices. Of these multiple responses some made comments indicating that they

used the instruments once in very curved and very narrow canals, but used them

2-5 times in larger canals.

The only significant difference was that endodontists were more likely than

general dentists to use the instruments once only (Fisher’s Exact test, P = 0.047)D.

There was no significant difference in number of uses of instruments with

increasing experience.

16. How do you decide when to dispose of a file? (Please tick as many as apply)

After the number of uses as indicated in the last question 156 (84%) [34]

59

When the file unwinds or distorts 93 (21%) [25]

After use in very curved canals 77 (41%) [27]

After use in very narrow canals 53 (28%) [18]

When it no longer feels to be cutting 48 (26%) [9]

When it can no longer be cleaned 21 (11%) [3]

Total responses – 186/188 (99%).

Seventy-one (38%) respondents indicated only one choice, the most popular being

the first option (82%). The remaining respondents chose either two (15%), three

(27%), four (11%), five (4%), or six (4%) criteria used when deciding to dispose

of rotary instruments.

See Chapter 6 – “Instrument re-use”.

17. Which motor do you use to drive the instruments?

Tri Auto ZX by Morita 91 (50%) [10]

Dentsply motor 59 (32%) [16]

Other 42 (23%) [21]

Total responses – 183/188 (97%).

Only 5% of respondents used two brands or types of motor, whilst the remainder

used only one. The “other” category included a wide range of different brands and

types of motor of which 23 (55%) were air-driven reduction handpieces. The

“other” electric motors (45%) included motors used to place osseo-integrated

implants.

A significantly greater proportion of endodontists than general dentists used the

TRZX handpiece (χ2 = 8.637, 1DF, P = 0.003)E.

60

There was no significant difference in type of motor used with increase in

experience.

18. If you use the Dentsply motor, please specify the model, torque setting and

RPM.

Of the 59 people who used a Dentsply motor, 31 provided the type, which

included the Nouvag TCM Endo Motor (n=25) and the ATR Tecnika Motor

(n=6). It appeared that some respondents were confused concerning the torque

setting because 12 of 32 provided the reduction ratio instead. The 20 who

provided a torque setting gave a figure in the range 1-5 Ncm (n=13) or indicated

that it varied (n=7). The rpm was provided by 49 respondents. The rpm range was

120-400, with a mode of 250 and a mean of 257. Of these, one person just wrote

“very, very slow”.

19. If you use the Tri Auto ZX, do you;

Use it in automatic mode only? 26 (29%) [1]

Use it in manual mode only? 34 (38%) [6]

Use both modes? 34 (38%) [2]

Use the apex locator function? 49 (55%) [2]

Total responses – 89/91 (98%).

Of these, 40 (45%) ticked one choice only, namely, manual (n=23, 58%),

automatic (n=10, 25%), both modes (n=6, 15%), and apex locator (n=1, 2%). The

remainder (55%) ticked two (n=45) or three (n=4) choices indicating that they

used a greater range of the features of the handpiece.

61

For all respondents, significantly more dentists used the TRZX in manual mode

than in automatic mode (Fisher’s Exact test, P = 0.02)F. When assessing the data

for general dentists and endodontists separately, only the endodontists showed a

similar trend (Fisher’s Exact test, P = 0.05)G.

There were no other significant differences in proportions between endodontists

and general dentists in the mode of use of the handpiece.

20. Do you undertake endodontic re-treatments?

Yes 131 (70%) [35]

No 56 (30%) [2]

Total responses – 187/188 (99%).

See Chapter 6 – “Retreatment” for analysis.

21. If “Yes”, do you use rotary NiTi for removal of gutta-percha in re-treatments?

Always 18 (15%) [8]

Sometimes 49 (39%) [15]

Never 58 (46%) [10]

Total responses – 125/131 (95%).

See Chapter 6 – “Retreatment” for analysis.

PART C. ISSUES ASSOCIATED WITH ROTARY NITI USAGE

In this section the questions related to difficulties that respondents may have

encountered when using rotary NiTi instruments. If exact numbers were not

known the respondents were asked to estimate. Again, the questions and data

62

obtained are presented together in the format of the actual questionnaire, and the

number of respondents for each question is also provided to give an indication of

possible item non-response bias.

22. Have you encountered any of the following procedural problems with the use

of rotary NiTi instruments? (Please tick as many as apply)

Ledging of the canal 85 (60%) [26]

Transportation of the apical terminus of the canal 42 (30%) [13]

Strip perforation of a curved canal 16 (11%) [2]

Perforation of a canal other than strip perforation 18 (13%) [5]

Straightening of curved canals 35 (25%) [11]

Excessive dentine removal 15 (11%) [3]

Binding of the file in the canal 100 (70%) [21]

Total responses – 142/188 (76%).

Of the respondents to this question, one procedural problem had been encountered

by 40%, two by 31%, three by 15%, four by 9%, five by 4%, six by 1%, and 7 by

1%. Of the 46 (24%) non-respondents to this question, 13 wrote “none” and 33

made no comment. This question may suffer from non-response bias because of

the ambiguous wording. A category of “No problems encountered” should have

been included which would have clarified the intention of the 33 people who

made no comments.

See Chapter 6 – “Procedural experiences in general” for analysis.

23. Have any of your rotary NiTi files fractured in root canals?

63

Yes, but only in the first six months of using them 55 (29%) [4]

Yes, periodically since starting with rotary NiTi 85 (45%) [27]

No 48 (26%) [6]

Total responses – 188/188 (100%).

Overall there was no significant difference in fracture experience between

endodontists and general dentists (Chapter 6). However, a significantly higher

proportion of endodontists reported fracturing files periodically since adopting

rotary NiTi, compared with having fractured instruments only in the first six

months of use (χ2 = 11.619, 1DF, P = 0.001)H.

In order to ascertain if other factors may influence the fracture incidence, the

proportions of respondents who had and who had not experienced file fracture

were compared according to other survey questions. There were no significant

findings.

See Chapter 6 – “File fracture” for further analysis.

The remaining nine questions in this section pertained to those 140 respondents

who had answered “yes” to the previous question.

24. How many in total, and over what period of time?

1-5 99 (72%) [12], over a mean of 20 months

6-10 25 (18%) [12], over a mean of 26 months

11-15 6 (4%) [2], over a mean of 40 months

more than 15 8 (6%) [5], over a mean of 45 months

Total responses – 138/140 (99%).

64

See Chapter 6 – “File fracture” for further analysis.

25. Which file type fractured? (Please tick as many as apply)

Quantec series 60 (43%)

Flare series (Quantec) 7 (5%)

ProFile series 77 (55%)

Greater Taper (ProFile) 11 (8%)

Other 13 (9%)

Total responses – 139/140 (99%).

Of these respondents, 113 (81%) fractured only one type of file, and the rest had

fractured two or more types.

26. Which tip size(s) fractured? (Please tick as many as apply)

15 47 (35%) 35 25 (18%) 55 1 (1%)

20 67 (49%) 40 9 (7%) 60 2 (1%)

25 66 (49%) 45 4 (3%) 90 1 (1%)

30 41 (30%) 50 3 (2%)

Total responses – 136/140 (97%).

Of these, many respondents (45%) had fractured only one file size. The remainder

had fractured two (29%), three (19%), four (5%), or five (1%) file sizes. Only one

person had fractured all file sizes. These data must be interpreted cautiously

because of the possibility that some respondents may not have been certain of the

fractured file size. This may have been due to relying on memory and also that the

65

colour coding of rotary NiTi instruments can be potentially confusing as it is not

always consistent with traditional ISO colours.

27. Which taper fractured? (Please tick as many as apply)

.02 38 (30%) .05 11 (9%) .10 6 (5%)

.03 19 (15%) .06 29 (23%) .12 4 (3%)

.04 81 (65%) .08 11 (9%)

Total responses – 125/140 (89%).

Of these, many respondents (60%) had fractured only one file taper. The

remainder had fractured two (27%), three (10%), or four (2%) file tapers. Only

one person had fractured all file tapers. The same caution applies concerning this

data as for the data in Question 27.

28. Which part of the file fractured? (Please tick as many as apply)

Apical part 123 (88%) [28]

Middle part 28 (20%) [3]

Coronal part 10 (7%) [3]

Total responses – 139/140 (99%).

Most respondents (86%) had fractured only one part of the file, two parts by 12%,

and three parts by 2%. The data appear to correspond to clinical experience in that

the “apical” part of the instruments fractured more often than the more “coronal”

ends. Therefore, respondents seemed to understand the terminology used.

However, it may have been appropriate to use “tip” and “shank end” for apical

66

and coronal to avoid confusion in the terminology. Furthermore, the boundaries

between the different regions of the file are not distinct.

See Chapter 6 – “File fracture” for further analysis.

29. In which region of the canal did the file fracture? (Please tick as many as

apply)

Apical 113 (82%) [26]

Mid portion 51 (37%) [15]

Coronal 18 (13%) [7]

Total responses – 138/140 (99%).

Of these, 72% fractured files in only one region of the canal, 25% in two regions,

and 2% in all three regions. As for the last question, the boundaries between the

three regions of a canal are not distinct and could be open to interpretation.

See Chapter 6 – “File fracture” for further analysis.

30. What was, or may have been, the reason for the file(s) fracturing? (Please tick

as many as apply)

Excessive pressure on the file 85 (62%) [21]

Incorrect insertion angle of the file 26 (19%) [5]

Complex root canal anatomy 50 (36%) [16]

Non-constant speed of rotation of the file 6 (4%) [0]

RPM too high 15 (11%) [2]

Over-usage 59 (43%) [7]

No irrigant in the canal 19 (14%) [0]

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Incorrect file sequence 10 (7%) [1]

Patient biting on handpiece 12 (9%) [3]

Unknown 43 (31%) [12]

Total responses – 137/140 (98%).

Of these, one reason was given by 28%, two reasons by 33%, three reasons by

22%, four reasons by 12%, five reasons by 2%, and six, seven or eight reasons by

1% each. Of the respondents who ticked “unknown”, one commented that he/she

believed the instrument was too small and another attributed the fracture to not

concentrating. Whilst it can be argued that respondents with varying experience

with rotary NiTi instruments may not have been able to provide perfectly accurate

answers, the wording of the question allows the interpretation to be broad.

Nevertheless, the options are distinct and likely to be satisfactorily understood.

See Chapter 6 – “File fracture” for further analysis.

31. How have you usually managed the fractured portion? (Please tick those that

apply)

Referred the patient to an endodontist 33 (25%) [0]

Successfully retrieved fractured portion 40 (30%) [13]

Portion not retrievable despite attempt 106 (79%) [27]

Total responses – 134/140 (96%).

Most of these respondents (72%) ticked only one option, 23% ticked two, and 5%

ticked all three.

See Chapter 6 – “File fracture” for further analysis.

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32. If the fractured portion was not retrievable, what would you usually do?

(Please tick those that apply)

Refer patient to an endodontist? 30 (25%) [0]

Extract the tooth? 5 (4%) [1]

Obturate the tooth with file in situ and review? 114 (96%) [28]

Other 25 (21%) [10]

Total responses – 119/140 (85%).

Many respondents (61%) ticked only one option for this question, while 31%

ticked two and 8% ticked three. Of the five people (four general dentists and one

endodontist) who indicated that they would extract the tooth, all would first

obturate and then review. Of the 25 respondents who indicated “other”

management, the most common alternatives were to attempt to bypass the

fractured instrument (n=9, 36%), and to consider surgery (n=6, 24%). Informing

the patient of the fractured instrument was specified by 5(20%). The remainder of

the “other” forms of management included long-term calcium hydroxide by one

general dentist and one endodontist (8%), seeking specialist advice (4%) and one

general dentist (4%) would prescribe a combination of antibiotics and anti-

inflammatory drugs. Three of this “other” group indicated that the management

would be more radical for country patients because of the lack of availability

locally of endodontists.

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PART D. NITI EDUCATION

These questions related to what instruction respondents may have had in the

use of rotary NiTi instruments and techniques. See Chapter 6 – “Part D. NiTi

Education” for further analysis.

33. Have you attended any postgraduate rotary NiTi courses?

Yes 136 (73%) [30]

No 50 (27%) [6]

Total responses – 186/188 (99%).

There was no significant difference between proportions of endodontists and

general dentists attending courses.

The following seven questions were asked of those who had indicated that they

had attended a postgraduate NiTi course.

34. Was the course:

Theory only? 37 (28%)

Practical (hands-on) only? 15 (12%)

Both theory and practical? 90 (69%)

Total responses – 130/136 (96%).

Most of these respondents (n=122) ticked only one choice, but eight respondents

(6%) ticked more than one because they had attended more than one course.

35. Who provided the course?

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University 40 (30%)

Dental supply company 86 (64%)

Other 44 (33%)

Total responses – 134/136 (99%).

Of the 37 respondents who provided the name of the particular university, 33

(89%) had attended a course provided by an Australian university comprising 16

(48%) at Sydney, 10 (30%) at Melbourne, and 2 (6%) each at Adelaide and

Western Australia. The remaining 4 (11%) attended courses in the United States

(3) and Hong Kong (1).

Some of the respondents who ticked “dental supply company” provided the

names of more than one company indicating co-sponsorship of courses by the

companies or that the respondent had attended courses run by different

companies. Fifteen people did not specify the supply company. Thus, of a total of

74 separate responses (from 71 respondents), Dentsply was indicated by 40

(54%), Halas by 26 (35%), Erskine Dental by 6 (8%), Regional by 1 (1%), and

Formby (HERO) by 1 (1%).

Of the respondents who indicated “other”, 35 specified the organisation that

provided the course. These included the Australian Society of Endodontology

(51%), The Australian and New Zealand Academy of Endodontists (17%), the

Australian Dental Association (11%), and 20% indicated they had attended

privately run courses in the United States.

71

Of the 134 respondents 100 ticked only one box, 33 ticked two, and one

person ticked all three options. Of those who ticked only one box, an overall Chi-

Square test indicate a significant relationship (χ2 = 29.737, 1DF, P < 0.001)I.

Paired comparisons indicated that a significantly greater proportion of respondents

attended a dental company-run course than either a university (χ2 = 25.774, 1DF,

P < 0.001)J or “other” (χ2 = 13.776, 1DF, P < 0.001)K courses, but there was no

difference when combining university and “other”, and no difference between

university and “other”.

36. When did the course take place?

Of the 118/136 (87%) respondents, 115 provided either a single year

(n=105) or multiple years (n=10) and three stated that they could not remember

the year. The range of years was 1996 to 2001, the mode (and mean) year was

1999.

37. How long was the course?

Of the 128/136 (94%) respondents, the most common length of the course

was one day (61%). Next was the half-day (27%), two days (8%), three days (2%)

and four days (2%). It was stated by some respondents that the multiple day

courses were on endodontics in general.

38. Did you use rotary NiTi before the course?

Yes 71 (53%) [17]

No 62 (47%) [13]

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Total responses – 133/136 (98%).

There were no significant differences in proportions of dentists who had or had

not used rotary NiTi before the course, or between endodontists and general

dentists.

Those who did use rotary NiTi before the course were then asked questions 39

and 40.

39. Did you benefit from the course?

Yes 64 (90%) [15]

No 5 (10%) [2]

Total responses – 69/71 (97%).

40. Please identify the strengths and weaknesses of the course.

Of the 69 people who answered question 39, only 39 (57%) provided

answers to this open-ended question. Of these 39 respondents, 35 people felt they

had benefited from the course and 4 felt they had not. The strengths identified

covered a wide range of issues but could be summarised into two basic areas,

namely hands-on and theory. The hands-on component allowed participants to try

various systems under close supervision by experienced clinicians. The theoretical

aspects allowed a better appreciation of why the instruments fracture and how

preparation philosophies are different with the use of rotary NiTi. The weaknesses

identified by respondents also covered a range of issues. Most common was that

the particular course was too limited in the amount of hands-on and theory

73

presented. This resulted in participants feeling that the problems associated with

the instruments were not explained or stressed adequately. Some respondents felt

that the course was too commercialised and was perceived as being aimed at

selling a product. Furthermore, many respondents commented on the unsuitability

of plastic blocks for the hands-on component.

41. Which of the following steps did you complete during your learning of NiTi?

(Please tick as many as apply).

Practice in plastic blocks 133 (76%) [32]

Practice in extracted teeth 116 (67%) [29]

Anterior teeth in patients 62 (36%) [8]

Premolar teeth in patients 67 (39%) [11]

Molar teeth in patients 64 (37%) [12]

Other 6 (3%) [2]

Total responses – 174/188 (93%).

For the number of blocks used to practise, the range was 1-50, with a mode of 2

and a mean of 5. For the number of extracted teeth, the range was 1-50, with a

mode of 2 and a mean of 6. Only 38 (22%) respondents completed only one step

during the learning phase of the use of rotary NiTi instruments. Thus, of the

majority of respondents, two steps were completed by 38%, three by 13%, four by

16%, and five by 11%. Of all the respondents to this question, 20 (11%) used only

plastic blocks to practise, compared with 6 (3%) who only used extracted teeth.

Twenty-two (13%) people did not practise on either plastic blocks or extracted

teeth, but instead learned the technique in patients. Fifty-one respondents (29%)

74

practised on both plastic blocks and extracted teeth. The six comments in the

“other” category included: video tapes (n=2), either stainless steel or NiTi hand

files first (n=2), 99% on patients (n=1), or still learning (n=1).

42. Which of the following have you found to occur in your experience with

rotary NiTi compared to your manual instrumentation technique with stainless-

steel instruments? (Please tick those that apply)

Canal curvatures are maintained 128 (73%) [33]

Canal preparation is much faster 141 (80%) [23]

Working lengths are maintained 116 (66%) [22]

Final canal obturation is easier 127 (72%) [22]

Total responses – 176/188 (94%).

Of these respondents only one choice was selected by 18 (10%), two by 50 (28%),

three by 38 (22%), and four by 70 (40 %).

See Chapter 6 – “Procedural experiences in general”.

43. Please provide any other comments concerning rotary NiTi instruments you

believe may be relevant.

Only 87/188 (49%) responded to this question, but an extensive range of

comments were provided. It was possible to categorise the comments as follows:

Better 42 (48%), Not for everything 24 (28%), Fracture 9 (10%), Still learning 8

(9%), Expensive 2 (2%), Not as advertised 1 (1%), Slow 1 (1%).

These results are discussed in Chapter 4.

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CHAPTER 4

DISCUSSION OF QUESTIONNAIRE RESULTS

A large portion of the results of the questionnaire are discussed in the next

two chapters and will not be repeated here. The following discussion gives

consideration to aspects presented in the results (Chapter 3) but not covered in

Chapters 5 and 6. It should be noted that where percentages add up to more than

100% it is due to multiple answers.

QUESTIONNAIRE DESIGN

One purpose of the questionnaire survey was to gain some general insight

into the experiences and beliefs of dentists and endodontists in Australia

concerning the new endodontic technology of rotary NiTi instrumentation. The

questions were designed to ascertain the problems, patterns of use and educational

history related to the use of the instruments. Another purpose was to identify areas

of perceived or potential concern related to the new technology, which were to be

addressed in the subsequent studies of the overall project. Furthermore, it was

intended that the information so obtained would allow a better understanding of

the needs within the Australian dental community of NiTi teaching requirements

and facilities. Although a large number of questions were asked, they covered the

three broad areas of patterns of usage, issues (problems), and education. Hence,

the number of questions in each section (greater than 10) placed each section in a

moderate length category and the overall questionnaire length can be considered

76

complicated (Tan & Burke 1997). Therefore, from the outset, the questionnaire

was not designed to obtain strictly accurate data that would have had profound

influence or implications for endodontology. Although specific survey techniques

to test for reliability and validity were not implemented, an assessment of these

factors follows.

Reliability is a measure of how reproducible the questionnaire’s data are,

and will be influenced by random error and measurement error (Litwin 1995). To

overcome random error in this survey, a large representative sample was selected.

The very high overall response and item-response rates based on a large

probability-based sample support the data as being representative. Measurement

error relates to the reliability characteristics of the questionnaire and commonly

includes three forms: test-retest, alternate form, and internal consistency (Litwin

1995). Because the subject of this survey represented new technology, its adoption

should follow a normal, bell-shaped curve when plotted over time on a frequency

basis (Rogers 1995). Some 26% of respondents had adopted the new technology,

which corresponds to the steep ascending portion of the curve representing the

third (early majority) adopter category. Once a critical mass of between 10% and

20% of a group has adopted a new technology, the speed and extent of the

adoption can be reasonably predicted (Chambers 2001). Therefore, to attempt an

analysis of test-retest reliability would be pointless because of the relatively rapid

changes occurring in the questionnaire attributes.

The alternate form method, which essentially asks the same question but in

a different way, was not employed because to do so would require a greater

77

number of questions. Similarly, measuring internal consistency would have

required a larger number of questions to measure different aspects of the same

concept. The alternative approach used in this survey was to assess the individual

questions. Where questions were likely to produce unreliable data, analysis was

either not carried out or not given any practical significance. An example was in

the identification of rotary file types, tapers and sizes. Experience from teaching

of rotary techniques to endodontists, general dentists and postgraduate endodontic

students, clearly demonstrates that the range of rotary nickel-titanium instruments

and techniques available is confusing to the neophyte. Another example was the

reporting of torque and rpm. The two seemed to be confused by some

respondents.

Validity is a test of how well the survey measures what it sets out to

measure (Litwin 1995). Whilst there are several different types of validity criteria,

there are both theoretical and empirical considerations, which may be more

relevant in psychological measurements (Groves 1989). In this survey, validity

was based on the design of the questionnaire (Sapsford 1999) because of the

nature of the questions asked. The question writing process and questionnaire

construction are quite complex with many criteria and principles available to

assist in the process (Dillman 2000), but guidelines in the scientific literature are

lacking. This survey was mailed to a population with similar attributes related to

education and socio-economic standing. The design was intentionally one of

mainly closed-format questions (n=36) offering as many categorical alternatives

as could be identified in advance, in order to limit uncertainty for the respondent.

78

However, closed-format questions will always be a balance between too

few alternatives leading to vagueness and too many alternatives leading to

excessive specificity (Dillman 2000). A response which is a product of human

judgement is liable to variation (Sapsford 1999) and so open-format questions

were utilised mainly to allow respondents to add extra information if they wished.

The open-format questions had lower response rates than the closed-format

questions. The fundamental problem with questions of this nature is that the

answer depends upon the extent to which respondents are willing to think hard

about the question and write a complete answer (Dillman 2000). Whilst the pilot

study identified potential areas of confusion, the participants of that study were

endodontic postgraduate students whose understanding of the questions asked and

information required were probably better than some of the general dentists who

responded to the survey. It is impossible to know exactly what proportion of the

general dentist sample did not quite understand particular questions. Therefore,

face and content validity based on the assessment by the three reviewers and the

pilot study participants of the questionnaire were judged as good. The other forms

of validity testing (criterion and construct) require comparison with established

questionnaires and long-term theoretical measurements, which were beyond the

scope of this questionnaire.

Whilst incorrect answers from respondents are largely unintentional, it is

recognised that some inaccurate or untruthful reporting is intentional (Wentland &

Smith 1993). According to Wentland & Smith (1993) some possible motives for

such behaviour include a desire to answer questions according to perceived social

expectations; unwillingness to provide information that may be incriminating or

79

lead to sanctions; desire for personal status or ego enhancement; and the perceived

need to present oneself as possessing particular characteristics, or as having

behaved in certain ways, perhaps due to reference group identification. The

questions asked in this survey were considered non-threatening and even when

asking about the perceived sensitive issue of instrument fracture, the high

numbers of respondents admitting to that clinical occurrence implies truthfulness

and a valid response. Therefore, given the purposes of the survey, the nature of the

questions, the target audience and the response rate, the data obtained can be

considered reliable and valid at that point in time of the innovation adoption

curve.

PART A. DEMOGRAPHICS

Overall, the lack of statistically significant differences between non-

responders and responders according to year of graduation, main practice

postcode and origin of dental degree indicate no measurable demographic non-

response bias. Furthermore, the very similar proportions of usable responses

compared with the samples from each state and each metropolitan and rural

location indicates that the sampled population can be considered representative.

The clinical significance of the finding of greater use of rotary NiTi by dentists

originally trained in Africa is uncertain. The result was still significant (P = 0.001)

after eliminating the endodontist data (Appendix G; B) and possible explanations

could include a different attitude toward new technology instilled at

undergraduate level, different cultural attitudes, or simply a random event. To

80

elucidate a reason may need to entail assessing the adoption or use of other

technologies.

PART B. PATTERNS OF ROTARY NITI USAGE

Of 731 usable respondents to the survey, 188 (26%) used rotary NiTi,

whereas 543 (74%) did not. Then, of the 543 non-users (non-adopters of the new

technology), 91 (17%) had tried but abandoned the instruments, 377 (69%) had

not tried them and the remaining 14% did not answer the question. A large

proportion of the 543 respondents (39%) gave more than one reason for non-

adoption of rotary NiTi instruments. Looking at the numbers who gave only one

reason, the same three reasons predominated – no perceived advantage (n=79), too

expensive (n=20) and too fragile (n=16). The reasons elucidated by that question

point to the importance of educators addressing such concerns. The implications

of the reasons for non-use of rotary NiTi are discussed in more detail in Chapter 6.

The influence of behavioural factors involved in the adoption of new technology

must be considered, not from the point of view of making excuses for non-

adoption but rather to attempt to incorporate an understanding of such traits into

continuing education courses. From this survey’s data it would seem that there are

three different personality types represented – those who tried the new technology

and continued with its use, those who tried but abandoned the technology, and

those who did not even try the new instruments. The Swiss psychiatrist, Carl Jung,

developed the idea of psychological type as one means of explaining human

behaviour (Barger & Kirby 1995). Being able to understand the differences in

81

these “types” could lead to better educational methods. This concept will be

developed and discussed in Chapter 9.

The data on clinical situations (Questions 8-10) indicated that respondents

were aware of the advantages of rotary NiTi use in molars, in curved root canals

and for both regions of the canal. Thus, the full potential of the new technology

was understood and had been embraced. It was interesting that there were no

differences in the proportions with increasing experience or between endodontists

and general dentists. This indicated that from the outset general dentists had the

confidence to use the new technology as designed and in as advanced a way as

endodontists. This was further confirmed in Questions 13 and 14, which

investigated the techniques and instrument sequences used and also illustrated that

the concept of crown-down had been accepted. The finding of a significantly

greater proportion of endodontists using a modified crown-down technique may

be related to endodontists being more likely to vary their canal preparation

protocol. Conversely, the finding could be artefact related to a lack of

understanding on the part of general dentists as to what a modified crown-down

technique actually is. Hence, the validity of this comparison is uncertain and, in

any case, it is probably of little clinical significance. The main clinical

significance here is that the traditional stainless steel technique of step-back

instrumentation was not practised widely, indicating an understanding of

properties of the new technology.

Questions 11 and 12 are no longer of any clinical relevance because of the

introduction of several new rotary NiTi systems onto the market since the survey

82

was conducted. Furthermore, the distinction between the two types of Quantec

instruments can be confusing so no valid conclusions can be drawn concerning the

preference of clinicians for an active cutting tip. Nevertheless, these data showed

that rapid changes were occurring in the new technology as evident from the 11%

using “other” systems in Question 11. Furthermore, Question 12 indicated that

some 57% of respondents had not tried a different system. If these respondents are

excluded from these data, then 94% of the remaining respondents had used one or

other of the Quantec instruments whilst only 29% had used ProFile and 21% had

used a different system. This may mean that respondents who had used Quantec

instruments previously, had changed over to a different system for some reason.

A greater proportion of endodontists used the TRZX handpiece to drive the

rotary instruments, but this finding is of uncertain clinical significance. When

analysing the data from Question 19, and considering those respondents who

indicated only one choice, significantly more dentists used the TRZX handpiece

in manual mode. This may be due to the fact that the handpiece is clinically easier

to use in manual mode. This finding is unlikely to be due to a dislike of electronic

apex locators because of the large number of respondents who indicated they used

the apex locator function (55%).

The instrument re-use data are not surprising. That most dentists use the

instruments 2-5 times (70%) was expected but a relatively large proportion of

dentists (12%) indicated that single use was appropriate. When analysing the

answers to the other survey questions for those who indicated single use compared

with the other respondents, there were no significant differences between the two

83

groups. Hence, there is no indication from the survey data as to why these

respondents preferred single use. The statistically just-significant finding that

endodontists were more likely than general dentists to use the instruments only

once probably carries no clinical significance.

PART C. ISSUES ASSOCIATED WITH NITI USAGE

The answers to the questions pertaining to procedural problems (Questions

22-32) must be interpreted carefully, taking into account the possibility that

general dentists may not have had enough experience to identify accurately the

various problems and entities. Ledging and transportation, for example, may not

have been accurately reported, but this is not necessarily so for binding or strip

perforation. Similarly, reasons for file fracture may be speculative but less likely

so than for differentiating between the various procedural problems. On the other

hand, the finding of very few statistically significant differences between

endodontists and general dentists may indicate that the general dentists were

actually able to identify the various entities. It is impossible to be certain of this in

a self-administered mailed questionnaire survey such as this. Confusion between

the various files both within and between brands indicates that the information

concerning which files fractured must also be interpreted with this in mind. The

deficiencies identified in the wording of the questions have been noted earlier in

Chapter 3. The forms of management of fractured files can generally be

considered appropriate. There were very few dubious answers, which can be

interpreted to imply a satisfactory standard of care.

84

PART D. NITI EDUCATION

The results of this part are discussed in detail in Chapter 6. An obvious

deficiency in these data is the somewhat incomplete wording of Question 42. The

question would have been better if “yes” or “no” options were provided for each

of the various alternatives. Question 43 demonstrated a very poor response rate,

which may be due to the open format and the fact that it was the last question of a

very long questionnaire. By this stage it may be assumed that most respondents

would have had enough. Most of the comments had been made in earlier

questions but an important view given by ten respondents was that they felt much

less fatigue when using rotary NiTi, particularly to the fingers and hands.

Generally, the questionnaire survey indicated a sensible approach to the

incorporation of the new technology into general dental practice and specialist

endodontic practice. Many of the comments made and views held by respondents,

particularly the non-adopters, can be interpreted as being related to behavioural

factors. An important factor regarding the adoption rate of an innovation is its

compatibility with the values, beliefs, and past experiences of individuals in the

social system (Rogers 1995). Therefore, the diffusion of innovations is as much a

social process as it is a technical one (Rogers 1995) and these processes will be

discussed in greater detail in Chapter 9.

85

REFERENCES

Barger N.J., Kirby L.K. The Challenge of Change in Organizations: Helping

Employees Thrive in the New Frontier. Palo Alto, California: Davies-

Black Publishing. 1995.

Chambers D.W. Technology innovation. Journal of the American College of

Dentists 2001;68:41-46.

Dillman D.A. Elements of the tailored design method. In Mail and Internet

Surveys. The Tailored Design Method. 2nd edition, pp. 3-213. New York:

John Wiley & Sons Inc. 2000.

Groves R.M. Survey errors and survey costs. New York: John Wiley & Sons Inc.

1989.

Litwin M.S. How To Measure Survey Reliability And Validity. (vol. 7). Thousand

Oaks, California: SAGE Publications Inc. 1995.

Rogers E.M. Diffusion of Innovations. 4th edition. New York, NY: The Free

Press, A Division of Simon & Schuster Inc. 1995.

Sapsford R. Survey Research. London: SAGE Publications Ltd. 1999.

Tan R.T., Burke F.J.T. Response rates to questionnaires mailed to dentists. A

review of 77 publications. International Dental Journal 1997;47:349-354.

Wentland E.J., Smith K.W. Survey Responses. An Evaluation of their Validity.

San Diego, California: Academic Press Inc. 1993.

86

87

CHAPTER 5

RESPONSE RATE AND NON-RESPONSE BIAS IN A

QUESTIONNAIRE SURVEY OF DENTISTS

A manuscript submitted to Community Dentistry and Oral Epidemiology.

88

RESPONSE RATE AND NON-RESPONSE BIAS IN A

QUESTIONNAIRE SURVEY OF DENTISTS

Dr Peter Parashos MDSc

Associate Professor Michael V. Morgan BDS, MDSc, PhD

Professor Harold H. Messer MDSc, PhD

The authors are all affiliated with The School of Dental Science, University of

Melbourne, Australia.

Running title: Response rates and non-response bias.

Corresponding author: Dr Peter Parashos

School of Dental Science,

University of Melbourne,

711 Elizabeth Street,

Melbourne, Victoria, 3000,

Australia.

E-mail: parashos@iprimus.com.au

89

Parashos P, Morgan MV, Messer HH: Response rate and non-response bias in a

questionnaire survey of dentists. Community Dent Oral Epidemiol.

Abstract – Objectives: 1) to report on response rate and non-response bias

of a questionnaire survey of dentists. 2) to make recommendations for future

questionnaire survey research in dentistry. Methods: a questionnaire survey was

mailed to a stratified systematic sample of 908 Australian dentists. The strategy

included three mailings, a final telephone contact, university stationery, reply paid

envelopes and personalized correspondence. Non-response bias was assessed by

comparing responses to a simple yes/no question from each contact (late

responders), and by comparing demographic information (non-responders).

Results: The response rate achieved was 87% and there was no evidence of non-

response bias based on practice location or year of graduation. The cumulative

proportions of yes/no responses essentially remained constant after each contact,

but significantly more late responders answered in the negative to the test question

than did early responders. The telephone contact aided in identification of non-

participants and ineligible units. Conclusions: The current survey indicates that

differences in data between early and non-responders can occur despite there

being no demographic differences. Therefore, assessment of non-response bias

based on demographic data alone would seem to be insufficient. Questionnaire

survey research must first be based on sound sampling techniques, then on

achieving as high a response rate as possible using the many incentive techniques

available.

Key words: Data collection, questionnaires, dentists, bias (epidemiology).

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INTRODUCTION

The response rate of a questionnaire survey is defined as the number of

completed and partially completed questionnaires/surveys/interviews divided by

the number of eligible sample units (1-3). A high response rate from a

representative sample is essential in order for the data to represent the entire

population sampled (4, 5). The literature recommends that unless response rates

are high, it is prudent to investigate non-response bias (6, 7), at least in socio-

demographic terms (8). If the non-respondents differ from the respondents then

the introduced biases can invalidate the questionnaire survey results (9). If the

non-response is not due to questionnaire design and not due to any particular

variable measured within the sample (for example, gender, age, location), then the

non-respondents are said to be “missing at random”. Hence they can be ignored

and the respondents can be used as a representative sample of the population (9).

Importantly, cognitive and social processes have been recognized as influencing

respondent behaviour (10), but these characteristics are likely to be unknown to

the questionnaire survey researcher. Consequently, relying on assessment of non-

response bias to justify a low response rate may be inherently flawed.

Opinions differ as to an optimal response rate high enough to eliminate

non-response bias, but the range reported is 70-80% (8, 11-13). It may well be

impossible to generalize an adequate return rate for all populations because it will

depend on the differences between the responders and non-responders (14) and on

such issues as the target population, sample size and survey techniques.

Furthermore, when describing response rates of questionnaire surveys, different

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researchers use different methods for calculating and reporting response rates (2),

“if indeed they are reported at all” (3). Confusion between completion rate and

response rate will continue until a standard definition is adopted (1).

Methods to compensate for low mail returns and aimed at improving

response to self-administered questionnaire surveys include: follow-up mailings,

telephone contacts, monetary incentives, material (gift) incentives, respondent-

friendly questionnaires, a real stamp on the return envelope, personalization of

correspondence, and many smaller details (4, 6, 15-19). There do not appear to be

any deleterious effects of incentives on the quality of survey responses (20).

The aims of this paper were to report on the response rate and non-

response bias of a questionnaire survey conducted by the authors, and to make

recommendations for future questionnaire survey research in dentistry.

METHODS

This questionnaire survey was conducted to investigate aspects of the use

of rotary nickel-titanium (NiTi) instruments and techniques in general dental

practice and in specialist endodontic practice within Australia. The main points of

interest from the questionnaire survey for this current paper are the response rates,

both overall and after each contact, and an indication of non-response bias. The

project received approval from the Health Sciences Human Ethics Subcommittee

of the University of Melbourne.

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Questionnaire survey instrument

The questionnaire survey comprised a total of 43 questions, many of

which had multiple parts, over six single-sided A4 pages. The format included

mainly closed (n=36) but also open-format (n=7) questions. Only the question

regarding the use or non-use of NiTi is considered in the current analysis. This

question was: “Do you currently use rotary NiTi instrumentation to prepare root

canals?” Respondents were able to answer “Yes” or “No”.

Questionnaire survey implementation

The sample size was calculated using an equation as presented by Dillman

(19). It consisted of all endodontists practising in Australia who were members of

the Australian and New Zealand Academy of Endodontists (ANZAE), and a

stratified systematic sample of dentists practising in Australia who were members

of the Australian Dental Association Incorporated (ADA). The original calculated

sample size was 900 (64 endodontists and 836 general dentists). Stratification was

according to Australian State and whether metropolitan or rural, which was based

on postcode zones as determined by Australia Post according to distance from the

capital city within each state. Based on the sample size and total population, every

seventh dentist on the postcode-order list was selected. In order to ensure equal

representation from each stratum, the stratum sample size proportions were

exactly the same as the proportion of all dentists in each stratum relative to the

overall number of ADA dentists in Australia. The total number of dentists in the

questionnaire survey population was 5,742 (5,678 general dentists + 64

endodontists).

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• Ineligible – cases not meeting certain set criteria that render an individual

appropriate for inclusion in the particular survey, e.g., age, gender, address,

A letter explaining the questionnaire survey and requesting participation

accompanied the questionnaire and a reply paid envelope was included. There

were no identifying marks on the questionnaire or envelope. The letter made clear

that the results would be reported in such a way as to keep the identity of the

participants anonymous. Non-respondents were sent a second copy of the

questionnaire with a differently-worded letter and another reply paid envelope.

The third mail-out included yet another questionnaire and a further letter with

different wording. As a final contact, secretarial staff telephoned the remaining

non-respondents. After the first two mailings, eight letters were returned with

indications that the address was no longer valid. In these eight cases, another

person was selected with the same postcode. This increased the total mailing to

908.

Data analysis

The response element definitions used in this study were those previously

published (2, 3), and included the following:

• Usable responses – completed (CC) and partially completed cases (PC)

• Non-participants – eligible cases who refused to participate and returned a

blank questionnaire (R)

• Non-returns – cases not interviewed and did not return a questionnaire (NI)

• Non-respondents – the non-participants and non-returns (R + NI)

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knowledge, experience (NE). In the current survey, ineligible units were those

who had moved, retired, were on vacation or ill in the long-term, did not

perform any endodontics, or were in a specialty other than endodontics.

Response elements for each contact were assessed by noting the numbers

of usable responses (response rate), non-participants and ineligible units. Non-

response bias was assessed in two ways. First, by noting and comparing the

proportions of respondents who answered affirmatively (“Yes”) or negatively

(“No”) to the main survey question after each contact. Second, by comparing

demographic details of usable respondents and non-respondents, and those after

each contact. The year of graduation and practice location (metropolitan or rural)

were determined for respondents and non-respondents. Also, endodontists were

compared with general dentists for differences in response rates for each contact.

Statistical analysis involved the Chi-Square, logistic regression and Fisher’s Exact

tests.

RESULTS

Response element details from the questionnaire are given in Table 5-1,

and the following ratios were calculated:

• Overall response rate = NIRPCCC

PCCC+++

+ = 840731 = 87%

• General dentist response rate = 776673 = 87%

• Endodontist response rate = 6458 = 91%

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There were no statistically significant differences between endodontists

and general dentists for any of the analyses and so data from both groups are

combined. Table 5-2 details the numbers of resulting response elements after each

contact. For each contact, each questionnaire survey sample unit (except for non-

returns), is accounted for and allocated to one of three categories:

• those responding with a usable questionnaire survey (Usable responses),

• those returning a blank questionnaire (Non-participant),

• those deemed to be ineligible to participate (Ineligible) as described above.

Table 5-2 shows that after the second contact in this survey a minimum

acceptable response rate of 71% was reached. The telephone contact (contact 4),

produced significantly fewer usable responses than the first three contacts (χ2 =

221.887, 1DF, P < 0.001)L. This is illustrated in Figure 5-1 where the exponential

“usable response” curve is relatively unaffected by the fourth contact, but the

“non-respondents” and “ineligible” units curves are clearly affected by contact 4.

Tables 5-3 and 5-4 show response details relative to year of graduation and

location of practice. There were no statistically significant differences between

proportions of respondents and non-respondents according to year of graduation

or location of practice. Furthermore, there were no significant differences in

proportions of usable responses after each contact according to either year of

graduation or location of practice. Similarly there were no significant differences

between proportions when usable responses were grouped to compare early

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(contact 1) with late (contacts 2-4) or according to minimum response rate

(contacts 1+2 versus contacts 3+4).

Table 5-5 demonstrates the change in number and proportions of negative

(“No”) and affirmative (“Yes”) responses to the question on the use of rotary NiTi

with each contact. After the second contact there were 629 usable responses,

which represented a response rate of 71%. After one contact, with a usable

response rate of only 49% (Table 5-2), the percentage ratio of cumulative negative

to cumulative positive was 71:29. After four contacts, the usable response rate had

increased to 87%, and the cumulative percentage ratio was now 74:26, which

represents only a 3% change. Chi-Square analysis revealed a significant change in

response with increasing contacts (χ2=8.106; 3df; P=0.04)M. The Chi-Square test

for trend using logistic regression confirmed that the proportion of “No” responses

increased and the proportion of “Yes” responses decreased with increasing

numbers of contacts (χ2=8.45; 1df; P=0.004)N.

Table 5-6 groups the numbers of “No” and “Yes” responses according to

“early” (contact 1) and “late” responders (contacts 2-4). The difference in

proportions was statistically significant (P = 0.01, Fisher’s Exact Test)O. Table 5-7

groups responses after having reached a minimum threshold response rate (gained

after contact 2) and compares the proportion with late responders (contacts 3 & 4).

The difference in proportions was statistically significant (P = 0.03, Fisher’s Exact

Test)P. Tables 5-5 and 5-6 indicate that the main difference in the proportions of

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“No” and “Yes” results occurred between contact 1 and contact 2. Thereafter, the

differences were smaller.

DISCUSSION

Very little has been written on how to conduct questionnaire survey

research in dentistry. The questionnaire survey literature originates mainly from

the social sciences (6, 21). Only two papers have analysed the literature on

questionnaire surveys of dentists exploring the matter of response rates (22, 23).

Asch et al. (22) analysed 25 questionnaire surveys of dentists and found a mean

response rate of 65%, while Tan and Burke (23) reviewed 77 questionnaire

surveys of dentists and found a mean response rate of 69%.

In the current survey on rotary NiTi, the response rate for endodontists was

slightly higher than for general dentists but not significantly so. The overall

response rate of 87% compares very favourably with the highest recommended

response rate in the literature of 80% (8, 13). At this level non-response bias can

be expected to be minimal providing the sample size is adequate and a form of

probability sampling is utilized, both of which ensure a representative sample. In

the current study, two contacts were adequate to exceed an empirical minimum

response rate of 70% (11).

One reported method of investigating non-response bias is to determine

the late-response bias by comparing responses of respondents who return

questionnaires after an initial request, with those who respond after follow-up

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requests (24). Locker (25) reported that estimates based on the first response to

mail questionnaire surveys differed only marginally from those obtained from

respondents to three or more mailings. The current questionnaire survey is in

agreement with these findings in that there were only slight differences in

percentages of cumulative negative and affirmative responses between the four

contacts and the overall results (Table 5-5). It could be argued, from the data in

this survey, that one contact was probably enough, practically, for this outcome.

However, when analysing the data for trends, and when the late responders

(contacts 2-4) were grouped, the differences became statistically significant.

Grouping contacts 1 and 2 also produced a significant difference compared with

contacts 3 and 4. The practical significance of this finding supports the accepted

view that multiple attempts at increasing the response rate are recommended. The

indication from the current questionnaire survey was that non-responders were

more likely not to be users of rotary NiTi instruments. Investigations of late-

response bias as an indicator of non-response bias are based on the assumption

that the characteristics and responses of late-responders are more representative of

non-responders than those of early responders (7, 24). An explanation for this

assumption is lacking, but the current survey supports that view based on a

comparison between the results after the first contact and those after the

subsequent contacts.

Other methods of assessing non-response bias include assessing socio-

demographic factors of responders and non-responders (26, 27), and extrapolation

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of trends (7). Socio-demographic information describes survey respondents, and

facilitates assessment of the generalisability of questionnaire results (28). The

current survey confirmed no significant differences in demographic details

between responders and non-responders (Tables 5-3 & 5-4). Extrapolating the

exponential-like trend of the data in the current survey, as recommended by

McCarthy and MacDonald (7), indicates there would be very little difference in

the results if the remaining non-responders did cooperate (Fig. 5-1).

Importantly, Locker (3) emphasises that all methods for assessing the

magnitude of non-response are based on assumptions about the non-responders.

Bias may exist in items such as knowledge and attitudinal variables rather than

socio-demographic variables (7). The current study exemplifies that view. Early

responders may be more interested in the questionnaire survey topic (7), which is

supported by the findings of the current survey. Responders to surveys may

include the more active and concerned segments of the dental community (29).

Hence, there is probable involvement of cognitive and social processes

influencing respondent behaviour, such as self reflection (10), the controlled use

of perception and judgment in decision making (30), and individual value systems

(31). The influence of behavioural factors is alluded to in the reported reasons for

non-participation by non-responders mentioned above. To be confident about

absence of non-response bias based only on socio-demographic factors makes the

assumption of no behavioural differences both between and within respondent and

non-respondent groups. Clearly, differences must exist, which leads back to the

critical importance of high response rates in questionnaire survey research.

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Multiple mailings appear to be an essential requirement for high response

rates (19, 32). Several authors have recommended the inclusion of telephone

prompts and telephone reminders in questionnaire survey protocols (33-36).

However, in the current survey the telephone contact increased the response rate

by only 3% on an already high response rate. Furthermore, the three mailings

produced a very high response rate using only the incentives of a reply paid

envelope, an explanatory letter, university letterhead and personalised contacts.

The telephone contact was significantly more important in identifying non-

participants and those ineligible rather than producing a large increase in usable

responses.

When considering the question of the use of incentives to improve

response rate it is unlikely that any one method or any one series of methods will

always be productive. A single survey design attribute will have different

“leverages” on the cooperation decision for different people (37). Hence,

changing the nature of successive appeals in mail questionnaire surveys (19) may

contribute to high response rates. This technique was adopted in this survey and

may have contributed to the high response rate. Importantly, there is likely a need

to tailor the questionnaire survey technique to the target population and the

required information (19). Asch et al. (22) found that higher response rates were

achieved with telephone reminders and with written reminders together with

another questionnaire. They also found that anonymous questionnaire surveys had

lower response rates. Anonymous surveys do not allow for follow-up, as do de-

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identified surveys such as the current one. Tan and Burke (23) found that the more

incentives used, the higher the response rate. A reply paid envelope would seem to

be indispensable (19, 23, 38, 39). Locker and Grushka (40) recommend a

minimum of a three-stage questionnaire survey consisting of an initial mailing and

two follow-ups. The current questionnaire survey successfully followed these

recommendations.

Tan and Burke (23) concluded that response rates were improved by

interesting or topical questionnaire subjects, use of incentives, and fewer

questions. On the other hand, Asch et al. (22) found that length of the

questionnaire did not seem to influence the response rate. Despite the current

questionnaire containing 43 questions and being considered complicated (23), the

87% response rate indicates that other factors have influenced the response. Long

questionnaires on interesting topics may be more likely to be answered than short

questionnaires on topics perceived as dull. The current survey explored new

technology in the form of nickel-titanium instrumentation, a very topical subject.

It is not unreasonable to expect that a prime prerequisite for a high response rate

of a questionnaire survey is for the topic to generate interest. The questionnaire

characteristics and techniques are no less important but may be reliant on first

gaining the prospective respondent’s attention.

The definition of response rate includes partially completed

questionnaires. Therefore, a low response rate even with no non-response bias

runs the risk that particular questions may suffer from a lower response rate due to

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item non-response (3). Item non-response may be associated with problems with

questionnaire design, with the wording of questions, or with respondent

behavioural factors. Consequently, the methods of determining non-response bias

assume importance in being able to justify a low response rate and obtaining

benefit from the data. Interestingly, Asch et al. (22) found that most (71%) of the

questionnaire surveys they studied did not attempt to determine non-responder

bias. They concluded that the actual response rate is not as important as the

question of the presence and influence of bias. Similarly, Tan and Burke (23)

found no available information on non-respondents in any of the 77 questionnaire

surveys in their review. Reported reasons for not participating include lack of

time, lack of interest, working part-time and being on holiday (41, 42). Some non-

responders simply choose not to participate with no particular reasons given (29).

The current survey found similar attitudes, and also that some people simply do

not wish to complete surveys.

CONCLUSIONS

Despite asking many questions, the current questionnaire survey achieved

a very high response rate of 87%. This may have been due to the survey technique

and an interesting subject that represented new endodontic technology. The

significant differences found between early and late responders in responses to the

survey question analysed, despite the absence of differences in the demographic

data, implies the possibility of behavioural differences between responders and

non-responders. Regardless of high response rates and no apparent non-response

bias in well-designed and conducted questionnaire surveys, the role of cognitive

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and social processes in respondent behaviour is difficult to assess but it must at

least be acknowledged. Such processes can and likely do affect respondent and

non-respondent behaviour. Survey research may need to routinely include

consideration of such behavioural factors in design and interpretation of

questionnaires, particularly in the case of low response rates. Striving for very

high response rates will reduce the effects of non-response bias due to socio-

demographic and behavioural differences between responders and non-

responders. Avoiding the complexities of non-response bias is best managed by

incorporating measures to achieve a high response rate.

ACKNOWLEDGEMENTS

The assistance and support of the following are gratefully acknowledged – the

School of Dental Science, University of Melbourne; the Australian Dental

Association Incorporated; the Australian Society of Endodontology Incorporated;

Associate Professor Ian Gordon of the Statistical Consulting Centre, University of

Melbourne; Dentsply Australia (Pty Ltd); Halas Dental Limited; the J. Morita

Corporation; and the National Health and Medical Research Council of Australia.

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Figure 5-1: Response elements after each contact in the questionnaire survey of NiTi use.

0

50

100

150

200

250

300

350

400

450

500

1 2 3 4

Contact number

Num

ber o

f sam

ple

units

Usable responses Non-respondents Ineligible units

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Table 5-1: Response element details from the questionnaire

survey of NiTi use.

Category Number % of Mail-out*

Usable responses (CC + PC) 731 81

Non-participants (R) 55 6

Non-returns (NI) 54 6

Non-respondents (R + NI) 109 12

Ineligible cases (NE) 68 7

* The total mail-out is defined by (CC + PC) + (R + NI) + NE = 908

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Table 5-2: Details of the response elements after each contact in the questionnaire survey of NiTi use.

Contact Total response elements*

Cumulative response

rate†

Usable responses (CC+PC)‡

Non-participants

(R)‡

Ineligible (NE)‡

1 (mail) 478 49% 439 28 11

2 (mail) 207 71% 190 11 6

3 (mail) 84 79% 75 6 3

4 (phone) 85 87% 27§ 10 48

Totals** 854 (94%) 731 (81%) 55 (6%) 68 (7%)

* Sum of CC + PC + R + NE for each contact. † Cumulative response rate = cumulative usable responses ÷ (908-total ineligible). ‡ CC = completed cases; PC=partially completed cases, R=refused to participate, NE=not eligible. § Significantly lower proportion of usable responses than for the first three contacts combined (χ2 = 221.887, 1df, P< 0.001)L. ** Percentages relate to the overall total sample size of 908. The remaining 6% (n=54) comprises the non-returns (NI) group.

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Table 5-3: Response details relative to year of graduation in the questionnaire survey of NiTi use.

Usable responses for each contact

Years Total

Usable* 1 2 3 4 Non-

responders†

1946-50 4 (0.5%) 3 0 1 0 1

1951-60 19 (2.5%) 9 6 4 0 4

1961-70 95 (13%) 64 21 7 3 18

1971-80 240 (33%) 138 67 24 11 34

1981-90 234 (32%) 144 58 22 10 31

1991-00 139 (19%) 81 38 17 3 20

Totals 731 439 190 75 27 108‡

* Percentages relate to the total of 731. There were no statistically significant differences. † Includes non-participants and non-returns. ‡ One non-responder’s graduation year was unknown.

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Table 5-4: Response details relative to location of practice in the questionnaire survey of NiTi use.

Usable responses for each contact

Years Total

Usable* 1 2 3 4 Non-

responders†

Metro 565 (78%) 334 151 56 24 92

Rural 162 (22%) 101 39 19 3 17

Totals 727 435 190 75 27 109

* Percentages relate to the total of 727; four respondents did not provide a postcode. † Includes non-participants and non-returns. There were no statistically significant differences.

112

Table 5-5: Comparison between affirmative (“Yes”) and negative (“No”) to the main question in the NiTi survey at each contact from the 731 usable replies.

Contact Total usable

responses

Negative* Cumulative negative

Affirmative* Cumulative affirmative

1 (mail) 439 311 (71%) 311 (71%) 128 (29%) 128 (29%)

2 (mail) 190 147 (77%) 458 (73%) 43 (23%) 171 (27%)

3 (mail) 75 62 (83%) 520 (74%) 13 (17%) 184 (26%)

4 (phone) 27 23 (85%) 543 (74%) 4 (15%) 188 (26%)

Totals 731 543 (74%) 188 (26%)

* Figures in brackets refer to the percentage of total for each contact. The overall Chi-Square test on proportions of negative and affirmative responses was significant (χ2=8.106; 3df; P=0.04)M. There was also a statistically significant trend for increase in negative responses and decrease in positive responses with increasing contacts (χ2=8.45; 1df; P=0.004)N.

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Table 5-6: Comparison of affirmative (“Yes”) and negative (“No”) to the main question in the NiTi survey between early and late responders from the 731 usable replies.

Contact Total usable

responses

Negative* Cumulative negative

Affirmative Cumulative affirmative

Early (1) 439† 311 (71%) 311 (71%) 128 (29%) 128 (29%)

Late (2-4) 292 232 (79%)‡ 543 (74%) 60 (21%) 188 (26%)

Totals 731 543 (74%) 188 (26%)

* Figures in brackets refer to the percentage of total for each contact. † Represents a response rate of 49% [439÷(908-11); where 11 were ineligible]; refer Table 5-2. ‡ Significantly greater proportion than for early responders (P = 0.01, Fisher’s Exact Test)O.

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Table 5-7: Comparison of affirmative (“Yes”) and negative (“No”) to the main question in the NiTi survey between “threshold responders”* and late responders from the 731 usable replies.

Contact Total usable

responses

Negative† Cumulative negative

Affirmative Cumulative affirmative

Threshold response (1+2)

629‡ 458 (73%) 458 (73%) 171 (27%) 171 (27%)

Late (3+4) 102 85 (83%)§ 543 (74%) 17 (17%) 188 (26%)

Totals 731 543 (74%) 188 (26%)

* Threshold responders refers to the number of usable responders, resulting from a minimum number of contacts, that reached an empirical minimum threshold response rate of 70%. † Figures in brackets refer to the percentage of total for each contact. ‡ Represents a response rate of 71% [629÷(908-17); where 17 were ineligible]; refer Table 5-2. § Significantly greater proportion than for response rate responders (P = 0.03, Fisher’s Exact Test)P.

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CHAPTER 6

QUESTIONNAIRE SURVEY ON THE USE OF

ROTARY NICKEL-TITANIUM ENDODONTIC

INSTRUMENTS BY AUSTRALIAN DENTISTS

A manuscript accepted for publication in the International Endodontic Journal.

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Questionnaire survey on the use of rotary nickel-titanium

endodontic instruments by Australian dentists

P. Parashos, H.H. Messer.

School of Dental Science, University of Melbourne, Melbourne, Victoria,

Australia.

Running title: Survey of rotary nickel-titanium instrumentation.

Key words: questionnaire survey, rotary NiTi.

Address for correspondence: Dr Peter Parashos

School of Dental Science

University of Melbourne

711 Elizabeth Street,

Melbourne, Victoria, 3000

Tel.No.: +61-3-9349 7600

Fax No.: +61-3-9349 7602

E-mail: parashos@iprimus.com.au

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Abstract

Aim To ascertain the extent of the adoption and use of rotary nickel-

titanium (NiTi) instruments and techniques in general dental practice and

specialist endodontic practice in Australia in 2001.

Methodology A questionnaire survey comprising 43 questions was

developed by first creating questions, then pilot testing with 10 postgraduate

students in endodontics, followed by a final revision. The final series of questions

covered demographics, patterns of rotary NiTi usage, issues associated with NiTi

usage, and training in NiTi use. The sampling frame was 908, comprising 64

endodontists and 844 general dentists.

Results The overall response rate was 87%. Rotary NiTi instruments were

used by 22% of general dentists and 64% of endodontists. The two main reasons

for not using rotary NiTi were “no perceived advantage” and “too fragile”.

Instrument fracture had been experienced by 74% of respondents, and 72% of

these had fractured one to five files for the two main perceived reasons of

“excessive pressure on the file”, and “over-usage”. The next two most common

problems encountered were “binding” (53%) and “ledging” (45%). Very high

proportions of positive experiences were noted. Most respondents (73%) had

attended one or more continuing education courses, most of which were provided

by dental supply companies (64%).

Conclusions The results indicate a sensible and responsible approach to

the incorporation of rotary NiTi instruments and techniques into root canal

treatment. Dentists were aware of the limitations of the new technology, but were

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taking steps to become familiar with the properties and behaviour of the

instruments. Instrument fracture was common, but it was of low frequency and it

did not deter dentists from using the technology.

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INTRODUCTION

The cleaning and shaping of root canal systems by various techniques of

debridement has been, and still is, a complex procedure that can be daunting for

both the patient and clinician. Nevertheless, endodontics is of major interest in

general dental practice. In Australia, for example, this is evident by the fact that

more than 10% of dentist members of the Australian Dental Association

Incorporated (ADA Inc.) are also members of the Australian Society of

Endodontology Incorporated (Moloney 2002).

Traditionally, the hand instruments used in root canal shaping have been

made of stainless steel, but these instruments lack flexibility, particularly in the

larger sizes, and can sometimes lead to procedural errors (Serene et al. 1995)

resulting in a decreased success rate for endodontic treatment (Sigurdsson 2002).

These errors may be partly due to the nature and limitations of stainless steel

instruments. Furthermore, little improvement has occurred over the years in the

designs of these stainless steel instruments. Briseño & Sonnabend (1991)

commented that no hand stainless steel instrument produced ideal results although

their in vitro results led them to conclude that the nine instruments compared

produced clinically acceptable canal shapes.

Soon after the introduction of Nickel-Titanium (NiTi) instruments (Walia

et al.1988), NiTi rotary instrumentation began to increase in popularity. The

super-elastic property of NiTi, coupled with advanced instrument design,

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promised to allow safe and effective instrumentation of curved and narrow root

canals using handpiece-driven instruments operated at low speeds (Serene et

al.1995).

However, very little is known about the adoption of this particular new

technology into clinical dental practice, with specific reference to familiarity and

philosophies. Only Barbakow & Lutz (1997) have attempted to study dentists’

attitudes toward, and experiences with, rotary NiTi instruments and techniques.

Using a questionnaire survey of general dentists in Switzerland they found that of

305 participants who attended a continuing education course in the use of a

specific rotary NiTi technique, only 58% responded but of those, 80% had

integrated the new technology into their practice. Generally, little information is

available regarding the attitude of general dental practitioners toward new

endodontic concepts, techniques and instruments, and on how far these have been

incorporated into daily practice (Slaus & Bottenberg 2002).

Consequently, the current questionnaire survey was conducted to add to

our knowledge concerning the use of rotary NiTi instruments and techniques in

general dental practice and in specialist endodontic practice. In particular, the

following aspects were investigated: demographics, patterns of NiTi usage, issues

(problems and experiences) with NiTi usage, and education and training in NiTi

use.

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METHODS

Survey instrument and questionnaire implementation.

The survey was a mailed self-administered questionnaire because the

sample size was large and geographically widespread. This, together with the

noncomplex nature of the information sought did not warrant an interview-type

survey. Some of the questions asked by Barbakow & Lutz (1997) were used as a

starting point and expanded upon to create an initial series of questions covering

issues related to the use of rotary NiTi instruments and techniques. A pilot

questionnaire was tested on 10 volunteer postgraduate students in endodontics at

the University of Melbourne, Australia. From their responses and comments the

questionnaire was modified to arrive at the final version. The questionnaire survey

(available from the authors) comprised a total of 43 questions, many of which had

multiple parts, over six single-sided A4 pages. The questions included both

closed- and open-format questions. The closed-format questions offered from 2 to

12 categorical choices but with an average of four. The questionnaire was

structured as follows:

-Part A. Demographics – 3 questions (1 closed; 2 open).

-Part B. Patterns of rotary NiTi usage – 18 questions (17 closed; 1 open).

-Part C. Issues associated with NiTi usage – 11 questions (11 closed).

-Part D. Training in NiTi use – 11 questions (7 closed; 4 open).

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The sampling frame population was 908 and comprised 64 endodontists

and 844 general dentists. This sample size was based on a formula for calculating

sample size (Dillman 2000), which takes the following factors into consideration:

1. The number of people in the questionnaire survey population,

2. The proportion of the population expected to choose one of two response

categories,

3. An acceptable amount of sampling error,

4. The statistical confidence level.

The sample consisted of all practising Australian endodontists who were

members of the Australian and New Zealand Academy of Endodontists

(ANZAE), and a stratified systematic sample of Australian dentists who were

members of the ADA Inc. Stratification was according to state of Australia and

whether metropolitan or rural, which was based on postcode zones as determined

by Australia Post according to distance from the capital city within each state. The

total number in the target population was 5742, and the sampling frame

represented approximately 16% of all practising Australian dentists. In order to

ensure equal representation from each stratum, the stratum sample size

proportions were exactly the same as the proportion of all dentists in each stratum

relative to the overall number of dentists in Australia. That is, if a stratum

contained x% of all Australian dentists then the sample size from that stratum was

x% of the total sample size.

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The questionnaire was accompanied by a letter explaining the objectives

of the survey and requesting participation. The letter explained that the survey was

confidential and de-identified. A numbered reply paid envelope was included but

there were no identifying marks on the questionnaire itself. The letter stated that

when the questionnaire was returned, a third person unrelated to the study would

remove the questionnaire from the envelope and separate them. That person had

no access to the coded mailing list, and only recorded the number codes from the

envelopes as they were received. The letter further made clear that the code

numbers would be cross-checked against the list of participants to enable follow-

up, and that the results would be reported in such a way as to keep the identity of

the participants anonymous. Nonrespondents received another two mail-outs

comprising a reminder letter and another copy of the questionnaire. As a final

contact, the remaining nonrespondents received a telephone call from another

person unrelated to the study. Ethics approval was granted by the Health Sciences

Human Ethics Subcommittee of the University of Melbourne.

The data collection period extended from June 2001 to November 2001.

The raw data were collected and manually entered into a Microsoft® Excel

spreadsheet (Microsoft Corporation, WA, USA). Each possible response to each

question was allocated its own column and any non-numerical data were

numerically coded for ease of data manipulation. The spreadsheet was imported

into Minitab™ (Minitab Inc., State College, PA, USA) and SPSS™ (SPSS Inc.,

Chicago, IL, USA) Statistical Software and analysis was carried out using the

Chi-squared test, Fisher’s exact test, and the Linear-by-Linear Association test.

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Fisher’s exact test was used when the Chi-squared value was low and the test

produced at least one expected cell count less than five and may have been

unreliable; the higher P-value is reported. These analyses tested for differences

both between and within the endodontist and general dentist groups. The

differences with increasing experience with the technology were also tested. The

significance level was set at P < 0.05. Because of the small number of

endodontists relative to the number of general dentists, most data from both

groups are combined unless there were interesting or significant differences

between the two, or within either group.

RESULTS

The response rate details are based on the numerator consisting of

completed or partially completed questionnaires and the denominator consisting

of all eligible sample units (Locker 2000). The following ratios were achieved:

-Overall response rate = 840731 = 87%

-General dentist response rate = 776673 = 87%

-Endodontist response rate = 6458 = 91%

The completion rate of the survey was 80.5% (731 of 908 questionnaires

mailed). Of the original sample size of 908, 68 proved to be ineligible due to

having changed address, having retired or specialising in another discipline. Of

the remaining 840, 776 were general dentists of whom 103 chose not to

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participate in the survey. Most of these (78) did not give reasons for not

participating. Of the remainder, 16 said they would return their questionnaire but

did not, five stated that they did not want to complete the questionnaire because

they were not interested in doing so, and four stated that they did not have a

questionnaire and agreed to be sent another, but still did not return it. Of the six

endodontists who did not participate, none gave a reason.

Overall, of the 731 usable responses, 26% of dentists used rotary NiTi at

the time of the survey, with 22% of general dentists and 64% of endodontists

using the new technology (Table 6-1). Endodontists were significantly more likely

to use rotary NiTi than general dentists (χ2 = 47.806, 1DF, P < 0.001)Q.

Part A. Demographics

Year of graduation

The overall range of graduation years spanned 1946 to 2000 (Table 6-2).

For statistical analysis, the 1946-50 and 1951-60 groups were combined. The

overall Chi-squared test was not significant. In comparison to 1991-2000

graduates, 1981-1990 graduates had a significantly higher usage of rotary NiTi (χ2

= 8.319, 1DF, P = 0.004)R; all the other categories (1946-60, 1961-70 and 1971-

1980) did not differ significantly from the 1991-2000 group. Furthermore,

comparison between various combinations of the ranges of graduation year

indicated no significant differences.

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Main practice location and origin of dental degree

Of the 727 dentists who provided their main practice postcode, 565 (78%)

practised in a metropolitan location and the remainder practised in a rural location.

Of 711 dentists who provided the origin of their dental degree, 622 (87%) were

graduates of Australian universities and the remainder were trained overseas. No

statistically significant differences were noted between the proportions of those

who used or did not use rotary NiTi when considering practice location

(metropolitan or rural) and origin of degree (Australia or overseas).

Part B. Patterns of rotary NiTi usage

The first question of this part of the survey asked whether or not the

respondent currently used rotary NiTi. If they answered “No”, these respondents

were then asked only whether or not they had tried rotary NiTi and were asked for

reasons. Those who did use the instruments were asked to complete the remainder

of the questionnaire.

Negative (“No”) response to the use of rotary NiTi

Of the 543 dentists who did not use rotary NiTi instruments at the time of

the survey, 75 did not indicate whether or not they had tried the technology (Table

6-3). Of the 468 dentists who did answer the question, 81% had never tried rotary

NiTi, while 19% had tried the instruments but were not currently using them.

General dentists practising in rural locations were more likely to have tried but

abandoned rotary NiTi than metropolitan dentists (χ2 = 6.174, 1DF, P = 0.01)S, but

there was no significant difference for endodontists.

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Respondents were asked to indicate reasons for not having tried NiTi or

for having abandoned their use, by choosing as many as applied from a list of nine

reasons. An “other” category was provided as well, and it was found that these

answers could be sorted into four more groups – “lack of NiTi education and/or

training”, “perform little or no endodontics”, “fear of perforating or extruding

debris”, and “no reason”. Some of the “other” reasons could actually be

interpreted to belong to one of the original nine reasons. The authors together

decided and agreed on the category into which the “other” reasons were placed.

This decision was based firstly on matching key words common to the main list

and to the respondents’ comments. Then, the authors sought key words from the

remaining “other” comments and sorted them into the four new groups. After this

sorting process, Table 6-4a was produced, which lists in descending order, the

reasons (key words) and the respondent details. The 543 nonuser respondents

gave varying numbers of reasons – one (61%), two (20%), three (8%), four (9%),

five (1%), six (1%). None gave more than six reasons.

Although fragility (i.e. risk of fracture) and the expense of the instruments

were a concern, overall, the main reason given for not using rotary NiTi was that

they were perceived to provide no advantage over traditional techniques (Table 6-

4a). Comparisons were carried out for each reason between those who had never

tried rotary NiTi and those who had but had abandoned them. Significant findings

were that general dentists who had tried but abandoned the instruments were more

likely to state that the instruments were “too fragile” (χ2 = 14.029, 1DF, P <

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0.001)T, “too difficult to use” (χ2 = 5.896, 1DF, P = 0.02)U, and “too difficult to

learn” (χ2 = 12.408, 1DF, P < 0.001)V. There were no significant differences

between endodontists who had tried rotary NiTi and endodontists who had not.

These data were then analysed for the two graduation year ranges that

differed significantly in their use of rotary NiTi, that is 1981-1990 and 1991-2000

(Tables 6-2 and 6-4b). Only the statistically significant data are presented in Table

6-4b. A significantly higher proportion of the 1981-1990 graduates who did not

use rotary NiTi gave the reason that the technique took too much time to learn (χ2

= 5.296, 1DF, P = 0.02)W. The finding of a greater proportion of the 1991-2000

graduates indicating nonavailability of the technology was highly significant (χ2 =

17.343, 1DF, P < 0.001)X.

Affirmative (“Yes”) response to the use of rotary NiTi

One hundred and eighty eight dentists (26%) indicated that they currently

used rotary NiTi instruments (Table 6-1). Comparing rural and metropolitan

dentists revealed no significant differences in proportions of dentists using or not

using rotary NiTi. These 188 respondents were asked to complete the remainder

of the questionnaire. For the remaining 38 questions, the overall mean item

response rate was 94%, with a range of 46-100%, mode of 99% and median of

98%. These questions comprised 33 closed- and five open-format questions with

mean response rates of 97% and 73%, medians of 99% and 83%, and ranges of

85-100% and 46-94% respectively. For the questions of Part B alone, the mean

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item response rate was 97%, with a range of 83-100%, mode of 99% and median

of 99%.

Frequency of use: Respondents had been using the instruments for various periods

of time with similar numbers of users in each time period (Table 6-5). This table

formed the basis for subsequent comparisons in order to determine how responses

changed with increasing experience. Table 6-6 demonstrates the changes in the

number of times per week that respondents used rotary NiTi. In this table the

“Linear by Linear Association test” was carried out to evaluate the tendency for

greater frequency of use to be associated with longer clinical experience. The

result was highly significant (χ2 = 14.18, 1DF, P < 0.001)Y.

Clinical situation: Respondents used rotary NiTi for molar teeth (93%) and

premolar teeth (87%), but a smaller number used them in anterior teeth (61%).

More respondents used the instruments in curved canals (93%) than in straight

canals (82%), but equal numbers used them in the coronal (90%) and in the apical

part (90%) of the canal. These proportions did not change significantly either in

those with greater experience, or between general dentists and endodontists.

Technique: Two questions asked were which instrumentation technique, and

which sequence of instruments respondents used. Multiple responses were

possible as was the opportunity to specify “other”. The majority of respondents

used a crown-down (61%) or a modified crown-down technique (39%). A number

of respondents (13%) used a combination of techniques depending on the case.

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However, 14% indicated that they used a step-back technique. Hand instruments,

either stainless steel or NiTi, were sometimes used by 67% of respondents to

prepare the apical part of the canal, while 30% used stainless steel Gates Glidden

burs in the coronal part of the canal. Many of the respondents (48%) indicated that

they used variable instrument sequences, depending on the clinical situation. It

should be noted here that any apparent discrepancies in percentages between

technique and clinical situation are due to respondents using multiple techniques

according to the demands of the particular case before them. No significant

differences were found between endodontists and general dentists in

instrumentation technique or sequence of instruments.

A wide range of different motors was used to drive the instruments. The

Tri Auto ZX (J.Morita Corporation, Kyoto, Japan) was used by 50% of

respondents, 32% used one of the Dentsply (Dentsply Maillefer, Ballaigues,

Switzerland) range of motors, while 23% used an “other” variety of high and low

torque motors. These figures include the 5% of respondents who indicated that

they used or had used two types of motor. Of the “other” group, 55% were air-

driven reduction handpieces.

Instrument re-use: Of the 188 respondents, most (70%) indicated that they thought

two to five uses per instrument was appropriate, while six to ten uses were

indicated by 19%. Only 12% indicated single use (8 endodontists and 14 general

dentists) and 5% used the instruments until distortion occurred. Ten respondents

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ticked more than one box and some of these people indicated that the answer

depended on the file size and canal shape.

When asked what criteria were used when deciding to dispose of an

instrument, 87% of 186 respondents indicated that they based it on their

assessment of the instrument’s serviceability, up to a predetermined maximum

number of uses. Reasons for discarding instruments sooner included factors such

as distortion, unwinding, decreased cutting efficiency and inability to be cleaned.

A large number (84%) also based this decision on the predetermined number of

uses as reported immediately above. Anatomical reasons, specifically curved

and/or narrow canals, were indicated by 70% of respondents. Again, it should be

noted here that any apparent discrepancy in percentages is due to respondents

using multiple criteria when deciding when to dispose of instruments. Greater

experience with rotary NiTi did not result in significant changes in the criteria for

the number of uses. Endodontists were significantly more likely to include the

criteria of curved canals (χ2 = 19.526, 1DF, P < 0.001)Z, narrow canals (χ2 =

9.523, 1DF, P = 0.002)AA, and unwound or distorted files (χ2 = 6.037, 1DF, P =

0.01)AB in deciding when to dispose of the instruments.

Retreatment: A total of 70% of respondents undertook endodontic retreatment

and of these 54% used rotary NiTi instruments to remove gutta-percha either

always (15%) or sometimes (39%). Significantly greater proportions of

endodontists than general dentists undertook retreatments (χ2 = 13.242, 1DF, P <

0.001)AC and used rotary NiTi instruments to remove gutta-percha (χ2 = 4.671,

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1DF, P = 0.03)AD. The range of file sizes used was 15-45, with a mode and mean

size of 30.The taper range was 0.02-0.12, with a mode of 0.04. The range of rpm

used was 10-1250, with a mode of 250 and a mean of 364. A Linear by Linear

Association test showed that there was a significantly greater likelihood of using

rotary NiTi for removal of gutta-percha in retreatments with greater experience in

the use of the instruments for both endodontists (χ2 = 9.46, 1DF, P = 0.002)AE and

general dentists (χ2 = 13.60, 1DF, P < 0.001)AF.

Part C. Issues associated with NiTi usage

For the questions of Part C alone, the mean item response rate was 97%,

with a range of 83-100%, mode of 99% and median of 99%.

Procedural experiences in general

In this section, the questions related to difficulties that respondents may

have encountered when using rotary NiTi instruments, and also the benefits they

had noted. Before investigating the experiences of respondents with file fracture

in particular, respondents were first asked a broad question on a range of

procedural problems they may have encountered. Of the sample, 142 (76%)

respondents indicated that they had experienced one or more of the listed

procedural problems (Table 6-7). The remainder (24%) did not indicate having

experienced any of these problems. One procedural problem had been

encountered by 40%, two by 31%, three by 15%, four by 9%, five by 4%, six by

1%, and seven by 1% of respondents. The only statistically significant difference

was that more endodontists than general dentists noted having experienced (or at

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least having recognised) canal ledging (χ2 = 11.677, 1DF, P = 0.001)AG. When

compared with manual instrumentation techniques with stainless steel

instruments, high proportions of positive experiences with rotary NiTi were noted

(Table 6-8). Of the 176 respondents to this question, 90% indicated more than one

of these particular benefits. A significantly higher proportion of general dentists

found canal preparation to be faster (χ2 = 5.686, 1DF, P = 0.02)AH, whereas a

significantly greater proportion of endodontists found that canal curvatures were

maintained (χ2 = 10.237, 1DF, P = 0.001)AI.

Instrument fracture

The question on instrument fracture (Table 6-9) revealed that 74% of

respondents had experienced fracture of an instrument. Of these 138, 72% had

fractured 1-5 instruments and 28% had fractured 6 or more. No significant

difference was found between endodontists and general dentists in fracture

experience. However, significantly more endodontists had fractured six or more

instruments (χ2 = 21.514, 1DF, P < 0.001)AJ. All sizes of instruments had been

fractured but most seemed to be the smaller sizes – 15 (35%), 20 (49%), 25

(49%), 30 (30%), 35 (18%), 40 (7%) and 45-90 (8%). Similarly, all instrument

tapers had been fractured with the 0.04 taper instruments showing the most (65%).

The majority of these 138 respondents had experienced fracture of the tip

of instruments (88%), while 20% reported fracturing the middle portion and only

7% the top part of instrument blades. Similarly, most respondents indicated that

instruments fractured in the apical part of canals (82%), but 36% fractured in the

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middle and 13% in the coronal parts of canals. No significant differences were

found with greater experience or between endodontists and general dentists.

Reasons for instrument fracture were many and varied (Table 6-10), and

most respondents (72%) gave two or more possible reasons. The choices given in

Table 6-10 were based on a similar question by Barbakow & Lutz (1997). The

only differences between general dentists and endodontists were that significantly

more general dentists believed that instrument fracture was due to their over-usage

(χ2 = 6.249, 1DF, P = 0.01)AK or to the lack of root canal irrigant during

instrumentation (χ2 = 6.252, 1DF, P = 0.01)AL. When asked about the management

of the fractured portion, 32% of 103 general dentists responding to the question

had referred the patient to an endodontist. Overall, the 134 dentists responding to

this question, reported 146 instances of attempting to remove fractured

instruments. Of these instances, 27% of fractured files were retrieved, whereas

73% were not. No significant differences were found in retrieval and non-retrieval

rates between dentists and endodontists.

When the fragment was not retrievable, 97% of 119 respondents indicated

that they would obturate the root canal with the fragment in situ and review. Some

(8%) of the respondents indicated that they would attempt to bypass the

instrument and 5% would resort to surgery if symptoms were present. Again,

there were no significant differences between dentists and endodontists.

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Part D. NiTi Education

For the questions of Part D alone, the mean item response rate was 87%,

with a range of 46-99% and median of 99%.

These questions related to what instruction respondents may have had in

the use of rotary NiTi instruments and techniques. A high proportion (73%) of

respondents had attended one or more courses in the use of rotary NiTi. Of these

136 respondents, 64% attended courses run by dental supply companies, while

only 30% had attended courses run by universities. A proportion of the

respondents (33%) had attended courses run either privately or by various dental

associations and societies. The numbers of people who had (53%) or had not

(47%) used rotary NiTi instruments before the course were similar. When asked

whether they had benefited from the course(s), 90% of 93 respondents indicated

that they had. This was attributed to the hands-on component primarily but also

because of the theory component. The 10% of respondents who did not benefit

from the course indicated that they felt the course was too product oriented

presenting the instruments as a panacea. Four of these referred to courses run by

the dental trade and one run by a university.

Of 174 respondents, 76% had practised on plastic blocks, and 67% used

extracted teeth. Thirty-six dentists (21%), but no endodontists, did not practise on

either plastic blocks or extracted teeth, but instead learned the technique in

patients. Endodontists were significantly more likely than general dentists to have

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practised in plastic blocks (χ2 = 5.467, 1DF, P = 0.02)AM and extracted teeth (χ2 =

5.168, 1DF, P = 0.02)AN.

DISCUSSION

The interpretation of the results of questionnaire survey research rests

firmly on the response rate and a representative sample size. Low response rates

may invalidate the data (Tambor et al. 1993). Although a crude assessment of

nonresponse bias may seem to validate low response rates, high response rates

allow precise estimates and more detailed examination of the data (Locker 2000).

The correct sample size and sample selection are equally important (Dillman

2000). The literature indicates that the minimum valid response rate is in the range

of 75-80% (Gough & Hall 1977, Evans 1991). Hence, the overall response rate of

87% in this paper can be considered representative of all dentists practising in

Australia, not only because it is so high but also because of the systematic

stratified probability sampling method used and the calculated sample size. In

addition, the very high item response rates for the questions further validate the

data. Nevertheless it is acknowledged that interpretation of any survey data must

consider the possibility of incorrect answers due to factors related to questionnaire

design, question wording and respondent factors.

Generally, the overall results of this questionnaire survey indicate a

sensible approach to the incorporation of rotary NiTi instruments and techniques

into endodontic practice. The multiple answers provided to many questions

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indicate that dentists appreciate that clinical circumstances can direct the course

and sequence of the instrumentation phase. Dentists were using the instruments

more frequently with increasing experience, and 35% used the instruments five or

more times weekly. This is considerably more than the 11% in the study by

Barbakow & Lutz (1997) on Lightspeed instruments but may be because of the

totally different instruments and technique. The instruments used by respondents

in the present study did not include Lightspeed. The crown-down and modified

crown-down techniques were most commonly employed but dentists often

adapted the instrument sequence to suit the particular clinical situation. Many

dentists (54%) used rotary NiTi for all tooth types, and this was comparable to the

60% of Barbakow & Lutz (1997). Most dentists used the instruments two to five

times and based the number of uses on an assessment of the instrument’s

serviceability and also its size and the canal shape. General dentists were using the

instruments in retreatments but less than endodontists were, presumably because

more endodontists undertook retreatments. An interesting finding was the variety

of motors used by respondents which supports the research of Yared (2002) that

air, very low torque, low torque and high torque motors were safe if used

correctly.

More endodontists than general dentists were using rotary NiTi

instruments, and the open-question data indicated that many dentists planned to

use the instruments once matters of availability of the instruments and of training

in their use were addressed. Overall, 22% of Australian general dentists were

using rotary NiTi instruments at the time of this survey. Barbakow & Lutz (1997)

138

found that 80% of 177 Swiss dentists had integrated rotary NiTi into their

practices. Slaus & Bottenberg (2002) reported that despite a variety of new

instruments and techniques, most Flemish general dentists still used conventional

preparation and obturation techniques. Additionally, Hommez et al. (2003)

reported that some 28% of 309 Flemish dentists were using rotary NiTi

instruments although 26% combined the technique with hand instruments. Jenkins

et al. (2001) believed that the use of hand instruments could be both physically

taxing and time consuming, which they believed explained their finding that

dentists who performed many root fillings tended to use handpiece-energised files.

The finding in the present study that the numbers of respondents in each period of

time of use of rotary NiTi were similar indicates a relatively constant number of

dentists incorporating the new technology into their practices. Hence, the data

indicate a steady rate of adoption of the new technology.

The significantly fewer respondents in the graduation range 1991-2000

using rotary NiTi instruments compared with 1981-1990 is difficult to explain. A

possible factor may be nonavailability of the technology to younger dentists

working as assistant dentists to more senior colleagues. Another possibility is that

younger dentists may be focussed on perfecting their hand instrumentation

technique before contemplating changing to new technology with its own inherent

learning curve. Furthermore, a greater proportion of the 1981-1990 graduates

considered that the technique took too much time to learn. Perhaps these dentists

had progressed to a stage of being comfortable with their hand instrumentation

technique and not keen to devote time to a very different concept and technique.

139

These speculations indicate a need for further work in the area of adoption of new

technology in endodontics and dentistry in general.

Of concern is the finding that dentists were giving negative factors as

reasons for not having tried the new technology. The majority (81%) of dentists

who were not using the technology had never tried the instruments, and their main

reason was that they felt there was no perceived advantage to using the new

technology. This, together with the beliefs that the instruments were too fragile

and too difficult to use and learn, indicates that dentists may be accepting the

opinions and experiences of other dentists. The negative influences may come

from colleagues who have had bad experiences or perhaps from people in

authority (educators and endodontists) who had themselves not yet embraced the

technology. However, Table 6-4a indicates that 16% of those who had never tried

rotary NiTi had no access to the instruments. Furthermore, an overall 12% of

dentists not using rotary NiTi at the time of the survey indicated a lack of training

and education as a reason, but they were otherwise positive toward the new

technology. Many of these dentists would very likely adopt the new technology

with suitable training as implied by the 80% of dentists in the study of Barbakow

& Lutz (1997) who had integrated the new technology into their practices.

Furthermore, the need for “suitable” training is supported by the finding that 10%

of dentists who had abandoned the use of NiTi did so because of a lack of

education. From the comments provided by respondents it appears that dentists

want hands-on courses that adequately cover the theory and are run by clinicians

140

experienced in the technology. Another very important consideration for

respondents was the cost of the instruments as indicated in Table 6-4a.

This questionnaire survey clearly demonstrates that dentists are well aware

of the limitations of the new technology. While dentists have discovered the

benefits of rotary NiTi instrumentation, they acknowledge that there can be

procedural problems as well. As indicated in the list of reasons for nonuse of

rotary NiTi instrumentation, fragility of the instruments was a concern to

respondents. However, when considering the list of procedural problems other

than instrument fracture, it is encouraging that the main problem encountered was

binding of the instrument within the canal. An unexpected finding was the

significantly higher proportion of endodontists reporting ledging as a problem. A

possible explanation is that general dentists may not have recognised the

occurrence of ledging, although this is not supported by the lack of other

significant differences and that a relatively high proportion of dentists reported the

problem. It is more likely that there are other unidentified factors involved in the

differences in clinical technique between endodontists and general dentists. A

discussion of factors affecting the performance of dentists and endodontists in

clinical situations is beyond the scope of this paper. Overall, the numbers of

respondents experiencing each procedural problem (Table 6-7) can be considered

low. In comparison, the numbers of respondents reporting positive experiences

(Table 6-8) were relatively much higher. That 70% of the respondents believed

that it was appropriate to use the instruments two to five times indicates a

141

responsible approach particularly when 84% of respondents based instrument

disposal on that number of uses.

Respondents who had abandoned the use of the instruments because of

fragility (47%) presumably had experienced fractures. Of the dentists who were

currently using the technology most had experienced fractures (74%) and the list

of possible reasons (Table 6-10) indicates that these dentists were trying to

understand the mechanisms behind this. This list was based on the one presented

by Barbakow & Lutz (1997) whose top three reasons were excessive pressure

(25%), incorrect insertion angle (17%) and complex anatomy (15%). In

comparison, the present survey found that incorrect insertion angle was the fifth

most common reason for fracture and over-usage was second (43%). Over-usage

in the Swiss study was reported by only 6% of their respondents (Barbakow &

Lutz 1997). Again, the two instrumentation techniques are quite different, which

makes direct comparison difficult. In 97% of instances in the present study,

dentists would obturate and review the case if fragment retrieval was not possible,

which demonstrates a conservative attitude presumably due to a perception that

prognosis is favourable despite an instrument fracture. The questionnaire did not

seek information about time of instrument fracture relative to the stage of root

canal treatment, which may influence subsequent treatment decisions.

Based on these findings it is reasonable to suggest that the majority of

dentists who experience instrument fracture seek to understand why it happens

and continue to use rotary NiTi instruments because they perceive that the

142

advantages outweigh the disadvantages. This supports the finding by Barbakow &

Lutz (1997) that 90% of the dentists in their survey would recommend the rotary

NiTi technique to colleagues despite 76% having experienced fractures. The most

commonly experienced benefit in the present survey (80%) was the faster

preparation of root canals, while in the Swiss study 54% indicated that their canal

preparations were quicker. It should be noted here that some of the percentages

presented in that study (Barbakow & Lutz 1997) were erroneously based on all the

returned questionnaires (177) rather than the 141 who were actually using the

technology. This was a simple but unnoticed editorial process error (Dr Fred

Barbakow, personal communication) that has been taken into account in the

present paper. Also, in the Swiss study 76% found the technique easier and 82%

found it safer which compares favourably with the present study (Table 6-8).

These data assume considerable importance in light of the recent finding that

patients treated by endodontists were significantly more satisfied than those

treated by general dentists mainly because of the shorter treatment time in the

former case (Dugas et al. 2002). Hence, both the present study and that by

Barbakow & Lutz (1997) indicate that the new technology will be of major benefit

once general dentists have become proficient in rotary NiTi techniques.

Despite the limitations of the instruments, dentists were taking steps to

become familiar with the properties and behaviour of the instruments. The finding

that 73% of respondents currently using rotary NiTi had attended at least one

continuing education course in the use of the instruments supports this. Such

courses enable dentists to update their theory and learn new techniques (Barbakow

143

& Lutz 1997). Also, most dentists demonstrated due care and diligence by first

practising in plastic blocks and/or extracted human teeth. That 64% of

respondents had attended training courses run by the dental trade has both positive

and negative implications. The positive side is that it highlights again that dentists

are actively seeking out knowledge and instruction. Furthermore, the dental trade

is being responsible in recognising the need for instruction in the use of the new

technology.

A negative aspect, as indicated by several respondents, is that some

commercially run courses were perceived to be biased and aimed purely at selling

their product. This is a somewhat harsh indictment when considering that the

companies, by definition, are in the business of selling their product, and also

considering that they are taking the trouble to provide courses. From a different

perspective, this finding may be indicative of a degree of caution surrounding a

technology that has, as yet, not been widely adopted. However, it should be of

great concern to universities that only 30% of respondents attended a university-

run programme. At best, this finding implies that the universities are slow to

acknowledge the need within the dental profession of training courses in the new

technology. At worst, the universities may not be in tune with the needs of the

dentist in private practice possibly because of relying on the opinions of experts

who themselves have not been adequately informed. This survey shows clearly

that there is a demand for NiTi education, which must be broad, unbiased and

presented by clinicians with experience with the new technology as indicated

earlier when examining the reasons for nonuse of rotary NiTi.

144

CONCLUSIONS

The very high overall response rate of 87% in this paper, together with the

very high item response rates for the majority of questions can be considered

representative of all dentists practising in Australia. Generally, the results of this

questionnaire survey indicate a sensible approach to the incorporation of rotary

NiTi instruments and techniques into endodontic practice. This study clearly

demonstrates that dentists are well aware of the limitations of the new technology,

but were taking steps to become familiar with the properties and behaviour of

rotary NiTi instruments. Although instrument fracture was a common experience

amongst respondents, it was generally of low frequency and it did not deter

dentists from using the instruments. These findings indicate a responsible attitude

by an increasing number of dentists adopting a new technology that has clear

benefits over traditional techniques. The responses indicate that further NiTi

education and training is sought by dentists and addressing the negative

perceptions based on opinion should be an objective of that education.

ACKNOWLEDGEMENTS

The assistance and financial support of the following are gratefully acknowledged

– the Australian Dental Association Inc.; Australian Society of Endodontology

Inc.; Associate Professor Ian Gordon of the Statistical Consulting Centre,

145

University of Melbourne; Dentsply Australia (Pty Ltd); Halas Dental Limited; the

J. Morita Corporation; and the National Health and Medical Research Council of

Australia.

REFERENCES

Barbakow F, Lutz F (1997) The Lightspeed preparation technique evaluated by

Swiss clinicians after attending continuing education courses. International

Endodontic Journal 30, 46-50.

Briseño BM, Sonnabend E (1991) The influence of different root canal

instruments on root canal preparation: an in vitro study. International Endodontic

Journal 24, 15-23.

Dillman DA (2000) Elements of the tailored design method. Mail and Internet

Surveys. The Tailored Design Method, 2nd edn; pp. 203-213. New York: John

Wiley & Sons Inc.

Dugas NN, Lawrence HP, Teplitsky P, Friedman S (2002) Quality of life and

satisfaction outcomes of endodontic treatment. Journal of Endodontics 28, 819-

27.

Evans SJW (1991) Good surveys guide. British Medical Journal 302, 302-3.

146

Gough HG, Hall WB (1977) A comparison of physicians who did and did not

respond to a postal questionnaire. Journal of Applied Psychology 62, 777-80.

Hommez GMG, Braem M, De Moor RJG (2003) Root canal treatment performed

by Flemish dentists. Part 1. Cleaning and shaping. International Endodontic

Journal 36, 166-73.

Jenkins SM, Hayes SJ, Dummer PMH (2001) A study of endodontic treatment

carried out in dental practice within the UK. International Endodontic Journal 34,

16-22.

Locker D (2000) Response and nonresponse bias in oral health surveys. Journal of

Public Health Dentistry 60, 72-81.

Moloney L (2002) Secretary/Treasurer's Report; Australian Society of

Endodontology Inc. Australian Endodontic Journal 28, 131.

Serene TP, Adams JD, Saxena A (1995) Nickel-Titanium Instruments:

Applications in Endodontics. St. Louis, MO, USA: Ishiyaku EuroAmerica.

Sigurdsson A (2002) Evaluation of success and failure. In RE Walton, M

Torabinejad eds. Principles and Practice of Endodontics.; pp. 331-44.

Philadelphia: W.B. Saunders Company.

147

Slaus G, Bottenberg P (2002) A survey of endodontic practice amongst Flemish

dentists. International Endodontic Journal 35, 759-67.

Tambor ES, Chase GA, Faden RR, Geller G, Hofman KJ, Holtzman NA (1993)

Improving response rates through incentive and follow-up: the effect on a survey

of physicians' knowledge of genetics. American Journal of Public Health 83,

1599-603.

Walia H, Brantley WA, Gerstein H (1988) An initial investigation of the bending

and torsional properties of nitinol root canal files. Journal of Endodontics 14, 346-

51.

Yared GM (2002) Behaviour of Hero NiTi instruments by an experienced

operator under access limitations. Australian Endodontic Journal 28, 64-7.

148

Table 6-1: Use of rotary NiTi according to type of practice.

Practice type Number Use Don’t use

General dentist 673 151 (22%) 522 (78%)

Endodontist 58 37 (64%)* 21 (36%)

Total 731 188 (26%) 543 (74%)

* Significantly more than general dentists (χ2 = 47.81, 1DF, P < 0.001)Q.

149

Table 6-2: Response details for year of graduation*.

Range Number Use NiTi Don't use NiTi

1946-1950 4 1 (25%) 3 (75%)

1951-1960 19 4 (21%) 15 (79%)

1961-1970 95 25 (26%) 70 (74%)

1971-1980 240 62 (26%) 178 (74%)

1981-1990 234 72 (31%)† 162 (69%)

1991-2000 139 24 (17%) 115 (83%)

Total 731 188 (26%) 543 (74%)

* Percentages refer to each range of years. † Significantly more than graduates in the range 1991-2000 (χ2 = 8.319, 1DF, P = 0.004)R.

150

Table 6-3: Details of non-users of NiTi according to location.

Location n Never tried Tried but abandoned

Unknown

Metropolitan dentists 417 [16]* 300 [11] 62 [5] 55

Rural dentists 123 [2] 75 [1] 29† [1] 19

Unknown 3 2 0 1

Total number of nonusers 543 377 (81%) 91 (19%) 75

* Number of endodontists in square brackets. † Significantly higher proportion of rural general dentists than metropolitan general dentists (χ2 = 6.174, 1DF, P = 0.01)S.

151

Table 6-4a: Reasons for non-use of rotary NiTi in descending order, for all dentists.

Reason n* Never tried Tried but abandoned

No perceived advantage

197 (36%) [10]†

135 (36%) [3] 36 (40%) [7]

Too fragile 130 (24%) [18] 77 (20%) [4] 43 (47%) [12]

Too expensive 106 (20%) [5] 72 (19%) [3] 21 (23%) [2]

Not available 68 (13%) [1] 61 (16%) [0] 2 (2%) [0]

Lack of education 64 (12%) [2] 45 (12%) [1] 9 (10%) [1]

No/little endo 40 (7%) [0] 29 (8%) [0] 5 (5%) [0]

Takes too much time to learn

36 (7%) [4] 25 (7%) [1] 7 (8%) [3]

Too difficult to use 22 (4%) [3] 11 (3%) [0] 10 (11%) [3]

Too flexible 16 (3%) [2] 11 (3%) [2] 5 (5%) [0]

No reason 15 (3%) [0] 14 (4%) [0] 0 [0]

Too difficult to learn 14 (3%) [0] 6 (2%) [0] 7 (8%) [0]

Too slow 12 (2%) [4] 6 (2%) [2] 5 (5%) [2]

Complications‡ 5 (1%) [1] 4 (1%) [0] 1 (1%) [1]

Number of respondents

543 [21] 377 [6] 91 [12]

* Includes 75 respondents who provided reasons but did not specify whether they had tried rotary NiTi or not. Many respondents provided multiple reasons. † Number of endodontists in square brackets. ‡ Included fear of perforation and fear of extruding debris.

152

Table 6-4b: Statistically significant reasons for non-use of rotary NiTi for the two differing graduation year ranges.

Reason 1981-1990 1991-2000

Takes too much time to learn 17* 4

Not available 14 33†

Number of respondents 153 115

* Significantly higher proportion than 1991-2000 (χ2 = 5.296, 1DF, P = 0.02)W. † Significantly higher proportion than 1981-1990 (χ2 = 17.343, 1DF, P < 0.001)X.

153

Table 6-5: Length of time of use of rotary NiTi.

Period Number of respondents

0-12 months 54 (29%)

13-24 months 50 (27%)

25-36 months 38 (20%)

Longer than 36 months 45 (24%)

Total 187*

* One respondent did not indicate the period of use of rotary NiTi.

154

Table 6-6: Weekly frequency of use of rotary NiTi with experience (number of respondents).

Frequency (per week)

Up to 12 months

13-24 months

25-36 months

Over 36 months

Totals

< 1 7 9 4 6 26

1 11 7 1 1 20

2 13 5 5 3 26

3 9 6 5 6 26

4 4 8 5 6 23

5 or more 10 15 18 23* 66

Totals 54 50 38 45 187

* Significant increase in frequency of use with longer clinical experience (χ2 = 14.18, 1DF, P < 0.001)Y.

155

Table 6-7: Number (n) of endodontists (E) and general dentists (GD) encountering each procedural problem.

Problem n E GD

Binding of the file in the canal 100 (53%) 21 79

Ledging of the canal 85 (45%) 26* 59

Transportation of the canal terminus 42 (22%) 13 29

Straightening of curved canals 35 (19%) 11 24

Canal perforation, other than stripping 18 (10%) 5 13

Strip perforation of a curved canal 16 (9%) 2 14

Excessive dentine removal 15 (8%) 3 12

Number of respondents 188 37 151

* Significantly higher proportion than general dentists (χ2 = 11.677, 1DF, P = 0.001)AG.

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Table 6-8: Number (n) of endodontists (E) and general dentists (GD) indicating positive experiences with rotary NiTi compared with manual instrumentation with stainless steel instruments.

Benefit n E GD

Canal preparation is much faster 141 (80%) 23 118*

Canal curvatures are maintained 128 (73%) 33† 95

Final canal obturation is easier 127 (72%) 22 105

Working lengths are maintained 116 (66%) 22 94

Number of respondents 176 35 141

* Significantly higher proportion than endodontists (χ2 = 5.686, 1DF, P = 0.02)AH. † Significantly higher proportion than general dentists (χ2 = 10.237, 1DF, P = 0.001)AI.

157

Table 6-9: Incidence of file fracture for endodontists (E) and general dentists (GD).

Number of files fractured n E GD*

1-5 99 (53%) 12 87

6 or more 39 (21%) 19† 20

None 48 (26%) 6 42

Number of respondents 186 37 149

* Two general dentists who had fractured instruments did not indicate how many. † Significantly higher proportion than general dentists (χ2 = 21.514, 1DF, P < 0.001)AJ.

158

Table 6-10: Reported reasons for file fracture by endodontists (E) and general dentists (GD).

Reason n E GD

Excessive pressure on file 85 (62%) 21 64

Over-usage 59 (43%) 7 52*

Complex root canal anatomy 50 (36%) 16 34

Unknown 43 (31%) 12 31

Incorrect insertion angle of file 26 (19%) 5 21

No irrigant in canal 19 (14%) 0 19†

RPM too high 15 (11%) 2 13

Patient biting on handpiece 12 (9%) 3 9

Incorrect file sequence 10 (7%) 1 9

Nonconstant speed of rotation of file

6 (4%) 0 6

Number of respondents 140 31 109

* Significantly higher proportion than endodontists (χ2 = 6.249, 1DF, P = 0.01)AK. † Significantly higher proportion than endodontists (χ2 = 6.252, 1DF, P = 0.01)AL.

159

PART III

INSTRUMENT DEFECTS

160

CHAPTER 7

FACTORS INFLUENCING DEFECTS OF ROTARY

NICKEL-TITANIUM INSTRUMENTS FOLLOWING

CLINICAL USAGE

A manuscript submitted to the Journal of Endodontics.

161

Factors Influencing Defects of Rotary Nickel-Titanium

Instruments Following Clinical Usage

Peter Parashos MDSc

Ian Gordon PhD

Harold H. Messer PhD

Dr Parashos and Professor Messer are affiliated with the School of Dental

Science, University of Melbourne, 711 Elizabeth Street, Melbourne, Victoria,

3000, Australia. Associate Professor Gordon is affiliated with the Statistical

Consulting Centre, University of Melbourne, Victoria, 3010, Australia.

Running title: Defects of Rotary Instruments.

Address for correspondence: Dr Peter Parashos

School of Dental Science

University of Melbourne

711 Elizabeth Street,

Melbourne, Victoria, 3000

Tel. No.: +61-3-9349 7600

Fax No.: +61-3-9349 7602

E-mail: parashos@iprimus.com.au

162

ABSTRACT

This study examined used, discarded rotary NiTi instruments obtained

from 14 endodontists from four countries to identify factors that may influence

defects produced during clinical use. A total of 7,159 instruments were examined

for the presence of defects. Unwinding occurred in 12% of instruments and

fractures in 5% (1.5% torsional, 3.5% flexural). Defect rates varied significantly

among endodontists. Instrument design factors also influenced defect rate, but to a

lesser extent. The mean number of uses of instruments with and without defects

was 3.3 ± 1.8 (range: 1-10), and 4.5 ± 2.0 (range: 1-16) respectively. The most

important influence on defect rates was the operator, which may be related to

clinical skill or a conscious decision to use instruments a specified number of

times or until defects were evident.

163

INTRODUCTION

An important perceived disadvantage of rotary nickel-titanium (NiTi)

instruments is their propensity to develop intraoperative defects, particularly

fracture. Furthermore, there is a perception amongst clinicians and researchers

that the number of uses of an instrument may be an important factor in the defect

rate. However, there is no consensus concerning a recommended number of uses

of rotary NiTi instruments, which varies from one to 27 canals, with a mean of

some 11 canals (1-9).

Previously published data on instruments used in patients variously suffer

from low numbers of instruments (n = 20 to 786), from few operators, and non-

detailed analysis of the instruments (1, 2, 7, 10, 11). The objective of this study

was to examine a large number of used, discarded rotary NiTi instruments to

identify factors that may influence defects produced during clinical use.

MATERIALS AND METHODS

Fourteen endodontists from four countries (Australia, England,

Switzerland, USA) were asked to save all discarded rotary NiTi instruments

following routine clinical use up to a total of at least 150. The instruments were

collected between October 2000 and April 2003 and were first examined with the

naked eye for the presence of any defects. The instruments were then placed

against a transparent plastic microscope ruler with 0.1mm gradations and

164

examined under a stereo microscope at 10-45x magnification (American Optical

Corporation, Buffalo, NY, USA). The instruments were all examined by one

investigator (PP).

The data collected were entered into a Microsoft® Excel spreadsheet,

recording endodontist and each instrument brand, length, size, taper and, where

available, the number of uses. Each instrument was rated in one of the following

categories – no defect, unwinding, torsional fracture or flexural fracture.

Instruments in the torsional fracture category were associated with unwinding

defects, while flexural fracture instruments were not (10). Instruments in the

unwinding category did not include any fracture. Torsionally fractured

instruments were assessed according to the location of the fracture relative to the

tip, and the length and degree of unwinding of the remaining instruments.

Flexurally fractured instruments were assessed for distance from the tip. Data

were summarised into tables and statistically analysed using logistic regression,

the Chi-Square test and Fisher’s Exact test.

RESULTS i. General findings

A total of 7,159 instruments included eight different brands used –

FlexMaster (VDW GmbH, Munich); GT, Orifice Shapers, ProFiles, ProTaper

(Dentsply Maillefer, Ballaigues, Switzerland); Quantec, Quantec Flare (Analytic

Endodontics, CA, USA); HERO (Micro-Mega, Besaçon, France). For the

purposes of comparison these instruments were categorized according to their

165

cross-sectional shape as S-shaped (Quantec, Quantec Flare), triple-U (GT, Orifice

Shapers, ProFile), triangular fixed-taper (HERO, FlexMaster), and triangular

variable-taper (ProTaper). All sizes and tapers of instruments were represented,

predominantly smaller instruments (≤ ISO size 35) and moderate taper (0.04 –

0.06). Most endodontists used only one brand of instrument (either exclusively or

predominantly), and only three used two brands in substantial numbers (>100

discarded instruments).

Tables 7-1 and 7-2 present the details of the different instrument defects

received from the different endodontists. Very large differences in the defect rate

were found among endodontists, varying between 1% and 91% (χ2 = 1792, 13df,

P < 0.001)AO. There were also highly significant differences among endodontists

when comparing fracture rates (0.3 – 39%; χ2 = 771, 13df, P < 0.001)AP and

unwinding rates (3 – 89%; χ2 = 1740, 13df, P < 0.001)AQ. Eight endodontists used

the instruments for a specified number of times (3 – 5 cases), four used them only

once, and two used them until either a defect was apparent or the instruments were

no longer perceived to cut efficiently. All the endodontists discarded instruments

immediately when a defect was apparent.

The type and frequency of defects among different instrument designs also

differed. Table 7-2 shows the numbers of different instrument defects when

compared with instrument cross-section and, for example, shows that the overall

defect rate was greatest for S-shaped instruments (28%), compared with 8-16%

for the other three types. S-shaped instruments also showed the highest frequency

166

of unwinding (14%) and fracture (14%). However, the results of the comparisons

between files were affected after accounting for endodontist in a logistic

regression. Due to this very strong confounding between variables, it was

necessary to allow for the effects of instrument characteristics to assess the

strength of this association more appropriately. There was such a strong

association between endodontist and file type that a model in which both variables

were included was very limited in scope; it was restricted to only three

endodontists.

For each instrument type separately, logistic regression analyses were

carried out with “any defect (unwound or fracture)” as the binary outcome, and

endodontist, size, taper, and length as the explanatory variables. Due to variations

in the types of files used by endodontists, this resulted in data from varying

numbers of endodontists for each file type: S-shaped – 6, triangular variable-taper

– 4, triangular fixed-taper – 6, and triple-U – 10. For each of the four file types,

the association between endodontist and defect rate, adjusted for size, taper, and

length, was highly statistically significant. Specifically, the results for the

endodontist / defect rate association wereAO:

S-shaped files: χ2 = 177, 5df, P < 0.001;

Triangular variable-taper: χ2 = 10.1, 3df, P = 0.017;

Triangular fixed-taper: χ2 = 19.0, 5df, P = 0.002;

Triple-U: χ2 = 554, 9df, P < 0.001.

167

Defect rates were then compared between instruments with different cross-

sectional shapes for endodontists who used more than one type (endodontists 3, 4,

5, 8, 10, 11 and 14). The numbers of instruments used by endodontists 3, 5, 8 and

10 were too small for comparison. There was no significant difference in defect

rate between TRV and TU instruments for endodontist 4, but for endodontist 11

the defect rate was higher for TU than for TRV instruments (Fisher’s Exact test,

P = 0.04)AR. For endodontist 14 the only significant difference was a higher defect

rate for S-shaped instruments compared with the other instruments combined (χ2 =

9.4, 1df, P = 0.002)AS.

ii. Instrument fracture

The proportions of fractured instruments within various sizes were 15

(13%), 20 (4%), 25 (9%), 30 (2%), 35 (1%), and 40 (4%). The proportions of

fractured instruments within various tapers were 0.02 (15%), 0.04 (2%), 0.06

(7%), and variable (6%). The mean length of instrument fractured was 2.8 ±

2.2mm (range: 0.2 to 15.9mm) for flexural, and 1.3 ± 0.9mm (range: 0.2 to

5.2mm) for torsional fractures. Approximately 25% of flexural fractures and 75%

of torsional fractures occurred 1.5mm or less from the instrument tip.

iii. Instrument unwinding

The beginning point of unwinding of instruments occurred mostly at, or

very close to, the tip of the instrument (1.0 ± 1.4mm) with a range of 0 to 7.5mm.

The degree of unwinding of the 879 unwound instruments varied as follows:

Unwound – 45%, Straight – 31%, Reversed – 17% and Twisted – 6%.

168

iv. Number of uses

Three endodontists recorded the number of uses for 930 instruments (six

brands) by notching the shanks. The overall mean number of uses of instruments

with and without defects was 3.3 ± 1.8 (range: 1-10) and 4.5 ± 2.0 (range: 1-16)

respectively. Only small differences were found among the different types of

defect: Unwinding – 3.1 ± 1.6 (range: 1-10) uses, Torsional fracture – 3.6 ± 1.9

(range: 1-8) uses, Flexural fracture – 3.8 ± 2.0 (range: 1-10) uses. The mean

number of uses for all fractures was 3.7 ± 2.0 (range: 1-10). Of the 69 fractured

instruments for which the number of uses was known, 10% fractured during first

use, 23% during second use, 14% during third use, 26% during fourth use, 7%

during fifth use, and the remaining 20% during sixth use or more.

DISCUSSION

The overall defect rate in the current study was 17% consisting of 12%

unwinding and 5% fracture, which resulted in instruments being discarded on

average after the third or fourth use (mean 3.3). In contrast, instruments not

showing any defects were typically discarded after the fourth or fifth use (mean

4.5). The defect rates were influenced by a complex interplay of instrument

factors including brand, size, taper, and cross-sectional shape. The most important

factor was the influence of the operator, which confirms the importance of

operator proficiency (12-14). Instrument design also influenced the defect rate.

Discarding almost 20% of instruments prematurely because of a defect indicates

169

that there is still considerable scope for improvement in metallurgical properties

and flute design to make the instruments more robust. In the meantime, the careful

clinician will be heedful of the multivariate cause of instrument fracture.

Instrument fracture is a greater clinical concern than unwinding. The

fracture rate of rotary NiTi instruments must be considered in the context of the

length of instrument fractured, the location of the fragment within the root canal

system, the fragment retrieval rate and the fragment by-pass rate. In the current

study, because many (approximately 25% flexural and 75% torsional) of the

fractured instrument fragments were 1.5mm or less in length, we postulate that

many of these fragments are small enough that the clinician may well not even be

aware of their fracture and/or be able to by-pass the fragments. This is supported

by the findings that magnification is often required to recognise instrument

fracture (15), and that fractured rotary NiTi instruments can be bypassed, thus

regaining access to the apical part of the root canal (11). In very recent

unpublished work in this laboratory, it has also been observed that some very

short length (0.5-1.5mm) fractures of rotary NiTi instruments were not noticed

during the preparation and filling of mesial canals of extracted molars. These

instrument fragments were noticed only after cross-sectioning the apical portions

of the roots. Clearly, these fragments were unknowingly either bypassed or forced

into isthmuses or canal fins. Furthermore, whilst there is a general perception that

fracturing an instrument in a root canal may compromise the prognosis of

endodontic treatment, there is no evidence that this is so with rotary NiTi

170

instruments. Also, recent work has found that the majority of fractured

instruments can be successfully removed utilising modern technology (16, 17).

There is no agreement concerning a recommended number of uses of

rotary NiTi instruments. The finding of fractured instruments having been used

fewer times (3.7 ± 2.0 teeth) than instruments with no defects (4.5 ± 2.0 teeth)

probably reflects the fact that the variables of operator and root canal anatomy are

more influential than the instruments per se on fracture rate. This is especially so

if operators use an instrument until it fails. Furthermore, these data support the

literature that multiple uses of rotary NiTi instruments are clinically acceptable (1-

4, 6, 8, 19), and do not support the routine single use of rotary NiTi instruments to

prevent fracture based on the finding of a very low incidence of fracture during

first use (10%). Instances of substantial and severe use will influence the single-

use decision. Clearly, to recommend single use for prudence (7) ignores the fact

that instruments can still fracture during first use (18).

ACKNOWLEDGEMENTS The cooperation of the endodontists who contributed the rotary NiTi instruments

examined in this study is gratefully acknowledged. Funding was provided by the

School of Dental Science, University of Melbourne and the National Health and

Medical Research Council of Australia.

171

REFERENCES

1. Yared G.M., Bou Dagher F.E., Machtou P. Cyclic fatigue of ProFile

rotary instruments after clinical use. Int Endod J 2000; 33: 204-7.

2. Gambarini G. Cyclic fatigue of ProFile rotary instruments after

prolonged clinical use. Int Endod J 2001; 34: 386-9.

3. Kuhn G., Jordan L. Fatigue and mechanical properties of nickel-

titanium endodontic instruments. J Endodon 2002; 28: 716-20.

4. Peters O.A., Barbakow F. Dynamic torque and apical forces of ProFile

.04 rotary instruments during preparation of curved canals. Int Endod J 2002; 35:

379-89.

5. Zelada G., Varela P., Martin B., Bahillo J.G., Magan F., Ahn S. The

effect of rotational speed and the curvature of root canals on the breakage of

rotary endodontic instruments. J Endodon 2002; 28: 540-2.

6. Alapati S.B., Brantley W.A., Svec T.A., Powers J.M., Mitchell J.C.

Scanning electron microscope observations of new and used nickel-titanium

rotary files. J Endodon 2003; 29: 667-9.

7. Arens F.C., Hoen M.M., Steiman H.R., Dietz D.B. Evaluation of single-

use rotary nickel-titanium instruments. J Endodon 2003; 29: 664-6.

172

8. Martín B., Zelada G., Varela P., Bahillo J., Magán F., Ahn S.,

Rodríguez C. Factors influencing the fracture of nickel-titanium rotary

instruments. Int Endod J 2003; 36: 262-6.

9. Peters O.A., Peters C.I., Schönenberger K., Barbakow F. ProTaper

rotary root canal preparation: assessment of torque and force in relation to canal

anatomy. Int Endod J 2003; 36: 93-9.

10. Sattapan B., Nervo G.J., Palamara J.E.A., Messer H.H. Defects in

rotary nickel-titanium files after clinical use. J Endodon 2000; 26: 161-5.

11. Al-Fouzan K.S. Incidence of rotary ProFile instrument fracture and the

potential for bypassing in vivo. Int Endod J 2003; 36: 864-7.

12. Regan J.D., Sherriff M., Meredith N., Gulabivala K. A survey of

interfacial forces used during filing of root canals. Endod Dent Traumatol 2000;

16: 101-6.

13. Yared G.M., Bou Dagher F.E., Machtou P., Kulkarni G.K. Influence of

rotational speed, torque and operator proficiency on failure of Greater Taper files.

Int Endod J 2002; 35: 7-12.

173

14. Sonntag D., Delschen S., Stachniss V. Root-canal shaping with manual

and rotary Ni-Ti files performed by students. Int Endod J 2003; 36: 715-23.

15. Gabel W.P., Hoen M.M., Steiman H.R., Pink F.E., Dietz R. Effect of

rotational speed on nickel-titanium file distortion. J Endodon 1999; 25: 752-4.

16. Ward J.R., Parashos P., Messer H.H. Evaluation of an ultrasonic

technique to remove fractured rotary nickel-titanium endodontic instrumentsfrom

root canals: an experimental study. J Endodon 2003; 29: 756-63.

17. Ward J.R., Parashos P., Messer H.H. Evaluation of an ultrasonic

technique to remove fractured rotary nickel-titanium endodontic instruments from

root canals: clinical cases. J Endodon 2003; 29: 764-7.

18. Roland D.D., Andelin W.E., Browning D.F., Hsu G.-H.R., Torabinejad

M. The effect of preflaring on the rates of separation for 0.04 taper nickel titanium

rotary instruments. J Endodon 2002; 28: 543-5.

19. Svec T.A., Powers J.M. The deterioration of rotary nickel-titanium

files under controlled conditions. J Endodon 2002; 28: 105-7.

174

Table 7-1: Summary of instrument defects from 14 endodontists worldwide.

Endodontist* Cross-section† Total No defect Unwinding Fracture

1 S 234 215 (92%) 16 (7%) 3 (1%) 2 TU 249 22 (9%) 222 (89%) 5 (2%)

S 3 2 1 0 TRF 7 7 0 0 TRV 2 2 0 0

3

TU 834 798 (96%) 26 (3%) 10 (1%) TRV 860 788 (92%) 40 (5%) 32 (4%) 4 TU 360 320 (89%) 16 (4%) 24 (7%) TRF 5 1 1 3 5 TU 587 554 (94%) 31 (5%) 2 (0.3%)

6 TU 891 857 (96%) 29 (3%) 5 (1%) 7 TU 551 465 (84%) 86 (16%) 0

S 172 161 (94%) 10 (6%) 1 (0.6%) 8 TU 1 0 0 1

9 S 280 232 (83%) 33 (12%) 15 (5%) TRF 127 111 (87%) 16 (13%) 0 10 TU 3 3 0 0 TRF 2 0 2 0 TRV 166 128 (77%) 16 (10%) 22 (13%)

11

TU 422 284 (67%) 121 (29%) 17 (4%) 12 S 526 267 (51%) 111 (21%) 148

(28%) 13 TRF 145 144 (99%) 0 1 (1%)

S 28 15 (54%) 2 (7%) 11 (39%)TRF 2 2 0 0 TRV 172 125 (73%) 35 (20%) 12 (7%)

14

TU 530 424 (80%) 65 (12%) 41 (8%) Totals 7159 5927 (83%) 879 (12%) 353 (5%)

* The differences in overall defect rates between endodontists were statistically highly significant (χ2 = 1792, 13df, P < 0.001)AO. There were also significant differences when comparing fracture rates (χ2 = 771, 13df, P < 0.001)AP and unwinding rates (χ2 = 1740, 13df, P < 0.001)AQ among endodontists. † S = S-shaped. TU = triple-U, TRF = triangular fixed-taper, TRV = triangular variable-taper.

175

Table 7-2: Summary of instrument defects from 14 endodontists according to file cross-section.

Cross-section*

n No defect Unwinding Torsional Fracture

Flexural Fracture

TRF 288 265 (92%) 19 (6.6%) 1 (0.3%) 3 (1%)TRV 1200 1043 (87%) 91 (7%) 33 (3%) 33 (3%)TU 4428 3727 (84%) 596 (13%) 27 (1%) 78 (2%)S 1243 892 (72%) 173 (14%) 42 (3%) 136 (11%)Totals 7159 5927 (83%) 879 (12%) 103 (1.5%) 250 (3.5%)

* S = S-shaped. TU = triple-U, TRF = triangular fixed-taper, TRV = triangular variable-taper.

176

PART IV

INSTRUMENT CLEANING

177

CHAPTER 8

A CLEANING PROTOCOL FOR ROTARY NICKEL-TITANIUM ENDODONTIC INSTRUMENTS

A manuscript accepted for publication in the Australian Dental Journal.

178

ABSTRACT

Background: The cleaning of endodontic and all dental instruments prior to

sterilisation is a prerequisite for their processing for re-use. This study aimed to

develop a clinically practical cleaning protocol for rotary nickel-titanium (NiTi)

endodontic files prior to sterilisation.

Methods: Cleaning experiments were conducted on six different types of files that

had been used in human teeth. The experiments involved three components of

mechanical and chemical removal of root canal debris from the files: the use of

sponges soaked with chlorhexidine to remove gross debris, pre-soaking, and

ultrasonication. After cleaning, the files were immersed in Van Gieson’s solution

and examined under magnification for stained debris. New unused files were also

examined.

Results: Macroscopically, there were no instances of visible debris and all files

appeared clean after all cleaning sequences. Microscopically, new files showed

both stained and unstained debris, and several experimental cleaning regimens

produced files that were free of stained debris. Combining elements of the most

effective cleaning sequences resulted in a cleaning protocol that predictably

produced clean files.

Conclusions: The results do not support the recommendation for the single use of

endodontic files based on inability to clean files between uses. Under

experimental conditions the cleaning protocol developed rendered rotary NiTi

files 100% free of stained debris. The protocol comprises ten vigorous strokes in a

scouring sponge soaked in 0.2% chlorhexidine solution, a 30 minute pre-soak in

an enzymatic cleaning solution, 15 minutes ultrasonication in the same solution,

179

and a 20 second rinse in running tap water. The protocol can be applied to all

endodontic files.

INTRODUCTION

Infection control guidelines indicate that cleaning of instruments to

remove organic residue is a required step in order to achieve sterility of

instruments.1-4 Endodontic instruments must be cleaned and sterilised before their

first use.5 However, currently there is no one method recognised to test the

cleanliness (ie, lack of soil and bioburden) of an item.6 The Australian/New

Zealand Standard AS/NZS 4187:20032 stipulates that instruments should be

“clean to the naked eye (macroscopic) and free from any protein residues”. It does

not stipulate how protein residues are to be assessed. Recommendations

concerning cleaning and sterilisation processes should be based on scientifically

obtained and clinically relevant data,7 and be justifiable, achievable, and

consistent with known risks.2 Unfortunately, there is little research information

available on which to base infection control procedures.8 Cleaning and

sterilisation recommendations made by various groups may in fact be too stringent

and not reflect clinical practice.7

Most endodontic instruments as supplied from the manufacturer are not

sterile and have been found to have metallic spurs and debris on their surfaces.9-13

In some cases even epithelial cells have been found on new unused files.9, 11

Furthermore, the manufacturing process produces milling marks and metal

debris,14 and dentine fragments appear to adhere to deposits of carbon and sulphur

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resulting from the decomposition and oxidation of the lubricating oil used during

machining.5

Although there is considerable evidence that endodontic files can be

predictably sterilised even in the presence of biologic debris,12, 15-18 the cleaning of

instruments to remove microorganisms and biological debris (bioburden)

effectively eliminates the majority of microorganisms.7, 19, 20 Very little

information is available in the literature with reference to efficient cleaning

protocols for dental instruments in general and endodontic instruments in

particular. Similarly, the medical literature relating to the cleaning of instruments

is sparse but the findings of the few available papers can be extrapolated to the

dental scenario with reference to general dental instruments. Principally, it is

difficult to clean instruments where their design does not allow access to all

surfaces with complex designs21 but most other instruments are not a challenge to

clean and sterilise.7, 19

As endodontic files have no internal surfaces that cannot be reached, it

would be expected that a cleaning protocol could be developed that results in files

free of bioburden. One such cleaning protocol for rotary nickel-titanium (NiTi)

endodontic files has recently been developed, which involved a sequential

combined mechanical and chemical cleaning procedure.13 That laboratory

protocol depended on carefully controlled conditions, and in the private practice

setting all files were rendered macroscopically clean but only 87% of files were

rendered microscopically clean. The procedure involved brushing used files in an

endodontic stand, followed by 10 minute immersion in 1% sodium hypochlorite

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(NaOCl) and then ultrasonication in the same solution for five minutes. The

purpose of the present study was to test alternative combinations of mechanical

and chemical cleaning methods to derive a simple, more effective protocol for the

cleaning of rotary NiTi files.

MATERIALS AND METHODS

Overview

Cleaning experiments were conducted on six different types of rotary NiTi

files, which differed in their cross-sectional shape and design. The files examined

were ProTaper, ProFile and GT (Dentsply/Maillefer, Ballaigues, Switzerland);

Flexmaster (VDW GmbH, Munich); Quantec (Analytic Endodontics, CA, USA)

and K3 (SybronEndo, Sybron Dental Specialties, CA, USA). For the purposes of

comparison the instruments were categorised according to their cross-sectional

shape as triple U (ProFile, GT), triangular (ProTaper, Flexmaster), and complex

(Quantec, K3).

Assessment of new files.

Thirty-six new, straight-from-the-packet files to be used in the

experiments on the extracted teeth were first stained with Van Gieson’s solution, a

histological stain, to assist in identification of debris of biological origin. The

instruments were completely submerged into a glass beaker containing Van

Gieson’s solution for three minutes, rinsed in running tap water for 30 seconds,

and allowed to air dry in a covered file stand. Files were then first examined with

the naked eye and subsequently at 15-45x magnification using a dissecting

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microscope (American Optical Corporation, Buffalo, NY, USA). For this process

the files were placed into a hollow rectangular metal block, square in cross-section

with an insert of rubber impression material to accept the instrument handle.

Scoring of the files involved recording the presence of red or orange stained

material, of unstained material, or of totally clean files. The entire flute surface of

each file was scored. Any stained material anywhere on the file led to a rating of

“dirty”. Both totally-clean files and files with slight non-stained debris were

considered “clean”.

Experiments in extracted teeth.

After scoring, these new files were individually cleaned of any debris

under the microscope using a moist sponge. The files were then used to

instrument the root canals of extracted human molars and premolars until debris

was easily visible on the files with the naked eye. The debris-laden files were used

in experiments to determine feasible cleaning protocols as assessed using the

staining and scoring procedure described above. Because the objective of this

project was to develop a protocol with the end result of a biologically clean

endodontic file, the analysis was purely a comparison of the final results of the

various protocols. The protocols involved different methods of mechanical and

chemical removal of the root canal debris. Based on previous experience in this

laboratory,13 a sequence of storage in a moist sponge, mechanical removal of

gross debris followed by chemical dissolution and ultrasonication served as the

basis for effective cleaning protocols.

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Experiments on files used clinically.

Once certain favourable methods of cleaning the files were identified, their

clinical practicality was assessed by applying these cleaning techniques to

instruments previously used in patients. Rotary NiTi files used in a private

endodontic practice were subjected to the cleaning techniques by the dental

assistants after instructions were provided by the principal author. No distinction

was made between new or previously used instruments. The various protocols

consisted of a chairside manual process followed then in the sterilisation room by

a chemical process and a final ultrasonication.

Details of experiments.

The various elements of the three processes of the experiments involved the

following materials and procedures (Table 8-1):

Chairside manual processes.

Different types of sponges for chairside wet storage of instruments and

initial cleaning were tested. These included scouring pads, scourer sponges, dense

(that is, relatively non-porous) sponges and porous sponges. All sponges were the

most inexpensive generic brands available at any supermarket. The sponges were

cut to fit small plastic containers (Fig 8-1). The sponges were saturated in either

0.2% chlorhexidine gluconate aqueous solution (Colgate Oral Care, Sydney) or

1% NaOCl solution (Milton solution, Procter & Gamble, Parramatta). The

different methods of use of the sponges tested included wiping the files with dry

scouring pads, using 5 or 10 “in-and-out” strokes with the file in a saturated

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sponge and “screwing in” the file in the saturated scourer sponges followed by 5

or 10 strokes.

Chemical processes.

Different solutions were tested for pre-soaking instruments after the

chairside cleaning. These included 1% NaOCl, 4% NaOCl (Endosure, Dentalife

P/L, Croydon); 15% EDTA (EndoPrep, PDS, Bayswater); EmPower enzyme

solution (Metrex Research Corporation, Romulus, Michigan). The solutions were

tested for 5, 15, or 30 minutes of pre-soaking.

Ultrasonication.

After the pre-soaking stage the files were placed into an ultrasonic bath

(Biosonic UC100, Coltène, Whaledent, New Jersey) to test different solutions.

These solutions were 1% NaOCl, 15% EDTA, EmPower enzyme solution. Each

solution was tested for 5, 10, 15, 30 or 45 minutes. The different containers used

to hold the files during the ultrasonication included a glass beaker, a fine metal

mesh basket (Premier Housewares, China) (Figs 8-2 & 8-3), or a plastic file stand

(Dentsply/Maillefer, Ballaigues, Switzerland).

For each protocol, new sponges and new enzyme solution were used each

time. After each of the protocols, instruments were rinsed in running tap water for

20 seconds and placed into autoclave pouches to await the staining and scoring

phase as detailed earlier.

185

The resulting data were entered into a Microsoft® Excel spreadsheet from

which tables were drawn and Chi-square statistical analysis performed and

reported where significance was reached (P < 0.05).

RESULTS

After the various protocols, and for new and unused instruments, there

were no instances of visible debris and all files appeared “clean” when files were

first examined with the naked eye. Microscopic examination found that all 36

rotary NiTi instruments examined straight from their packets showed evidence of

non-stained debris and six had slight stained debris. This included one brand of

files that is pre-sterilised, individually packaged, and ready-to-use. All

instruments showed evidence of the manufacturing process including machining

grooves on the blades and metal debris from grinding. The instrument surfaces

were usually scratched by the scourer pad and scouring sponge but these scratches

were always clearly much shallower than the manufacturing milling marks and

ran in the flutes along the long axis of the files.

The potential number of combinations of the materials and procedures

tested is in the thousands, so that systematic evaluation of all procedures was

impractical. The experiments were conducted in the order listed in Table 8-1,

which represents the progressive development of the final protocol and indicates

that the numbers of files examined in each protocol (for a particular file type)

varied. The lower end of this range represents initial trials of particular

combinations and the higher end resulted from increasing the number of files

186

tested where the initial trials pointed to promising sequences. In this way, only

relatively successful procedures and materials were tested, and problems or

ineffective methods were identified and progressively modified or replaced. This

included methods within each protocol that proved to be clinically impractical,

risky, unrealistic, detrimental, or tedious.

The four remaining clinically acceptable variables were the type of sponge

(other than porous), the number of cleaning strokes in the sponge, the length of

pre-soaking time in the enzyme solution (EmPower) and the ultrasonication time.

Table 8-2 illustrates the effect of each of these on the cleanliness of all file types.

The result for each individual variable was not exclusive of the influence of the

other three, nor of file type. Nevertheless, it was apparent that the number of

strokes and the pre-soaking time were important relative to the sponge type and

ultrasonication time.

This finding was confirmed in Table 8-3 where only complex cross-

sectional design files are considered. Tables 8-2 and 8-3 both indicate that

ultrasonication for 15 minutes was beneficial, and there was a trend for a scouring

sponge to work better than a dense sponge in the case of complex file designs.

When using the sponge with the coarse (scourer) top layer (Fig 8-1), small

delicate files often needed to be “screwed” into the sponge before initiating the in-

and-out strokes to avoid bending the file. Ten in-and-out strokes produced

significantly better results than five strokes. More than ten strokes proved to be

tedious, particularly chairside. Overall, the results did not statistically confirm that

187

complex designs were more difficult to clean although there was a small trend in

that direction (Table 8-4).

Pre-soaking in NaOCl for short periods achieved better results than pre-

soaking in other solutions, and a 1% solution was as effective as a 4% solution. A

15-minute pre-soak was more effective than five minutes. However, to prevent

corrosion the files had to be placed upright in a very small beaker such that the

shanks, which are not NiTi, were not immersed in the solution. This proved to be

clinically tedious and there was a risk of spillage. In some instances where NaOCl

was used to saturate the sponges, evidence of corrosion resulted on some file

blades. The use of EDTA as a pre-soak solution proved to be ineffective and was

abandoned. Commonly, corrosion of the files occurred when they were

ultrasonicated for more than ten minutes in a beaker of either 1% or 4% NaOCl.

The instrument shanks were particularly affected, but the NiTi portion appeared to

be affected when it came into contact with the handle of another instrument. The

areas of corrosion of the instruments were sometimes stained by the Van Gieson’s

solution. These defects appeared as irregular eroded cavities of various

dimensions, often producing a honeycomb effect.

As an ultrasonic bath solution, the enzyme solution (EmPower) was as

effective as NaOCl but was considered safer than the NaOCl because it lacked the

potential for corrosion. EDTA in the ultrasonic bath was ineffective. Files were

cleaned better during ultrasonication if they were placed into a supported basket

(Figs 8-2 & 8-3) rather than left in a beaker. There seemed to be no difference in

188

cleanliness between using the basket or using the file stand during ultrasonication.

The EmPower solution did not cause damage to the fine metal mesh basket as

determined by no macroscopic evidence of deterioration after conducting the

many experiments.

The results illustrate that no one single procedure by itself predictably

resulted in “clean” endodontic files. However, sequentially adding the various

factors resulted in a protocol that achieved 100% cleanliness of files (Table 8-5).

Thus, the combination of favourable factors acted synergistically to produce a

predictable result. Therefore, a simple effective protocol based on the above

findings is presented in Table 8-6.

DISCUSSION

Whilst there are no reported cases of accidental cross infection subsequent

to dental treatment, the current concern over the risk of iatrogenic transmission of

prion diseases has contributed to the view that consideration should be given to

treating endodontic instruments as single use.22 However, it is extremely

important to consider that the consensus of expert opinion seems to be that highly

specific cross-infection control measures in dentistry are required only for patients

with, or at notable risk of, prion diseases.23, 24 Hence, there seems to be no

scientific justification for the single use of endodontic instruments on the basis

that prion diseases may be transmitted via contaminated files. Nevertheless,

concerns have been raised regarding the safety of multiple use files because of an

inability to clean them.22

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The present paper assessed the ability of different protocols to produce

endodontic files that were microscopically free of biological (stained) debris, and

did not assess sterility. To this end this study has developed a simple protocol that

reliably produces rotary NiTi files that are 100% free of stained debris at a

microscopic level. Importantly, the protocol was equally effective for simple file

designs and for complex designs incorporating deep and narrow flutes. Therefore,

the protocol described in this study can be applied effectively to other endodontic

files as well as to new unused files prior to their first use.

In the progressive development of the final protocol, certain procedures

proved to be unsuitable and were abandoned. These included: the dry-wipe with a

scouring pad because of the potential for needle-stick injury; the use of porous

sponges because they seemed to dry rapidly; the use of NaOCl at any stage in the

procedure because of the risk of file corrosion; the use of EDTA at any stage

because of its ineffectiveness; and ultrasonication for 30 minutes or more, which

slowed the process too much to be clinically suitable.

Some authors have reported that endodontic instrument cleaning was

extremely difficult and time consuming because of the inability of a gauze wipe or

ultrasonics to remove some of the plastic manufacturing debris within the flutes.9

However, details of the cleaning procedures were not provided in that report, and

plastic does not pose a cross-infection risk. Murgel et al25 reported that files could

not be totally cleaned with sponge, gauze or ultrasonics. These authors, however,

190

used only two thrusts into the sponge and the ultrasonic time was for just five

minutes. The present study clearly indicates that both the mechanical and

chemical aspects of the cleaning protocol must be applied for a sufficient time in

order for proper cleaning to occur. It has been previously established that debris

and microorganisms can be reduced by a cleaning protocol that includes a

mechanical action,11, 25, 26 and ultrasonic agitation of the instruments in a solvent

solution.10, 27-29 The present study has confirmed these previous findings as well as

confirming that new files straight from the packet, whether pre-sterilised or not,

have considerable amounts of unstained debris and, in some instances, stained

debris on their flutes.

The use of nylon bristle brushes and metal bur brushes to clean endodontic

instruments is a common and long-used method. However, Linsuwanont13 found

that brushing was not a very successful procedure. This may be due to the

brushing of instruments, while they are in a stand, restricting the access of the

bristles to all surfaces of the file blade. In the case of very small files, the bristles

of the brush are larger than the width of the instrument flutes. Furthermore, the

brushing action in this case is perpendicular to the long axis of the instrument and

not in line with the instrument flutes. Metal bur brushes are commonly used to

clean down the long axis of individual instruments whilst being held between the

dental assistant’s fingers. With this action, the bristles of the metal brush are not

moving along the instrument flutes but rather over them, and it will be

unpredictable as to whether the entire circumference of the file is being contacted.

Furthermore, this procedure is usually performed dry and there is a risk of needle-

191

stick injury. The literature supports this view of the inadequacy of hand scrubbing

of instruments.27, 29

The use of a sponge implies that all sides of the instrument are likely to be

contacted by the sponge simultaneously. The use of the sponge is also safer from a

needle-stick-injury point of view compared with wiping with gauze or brushing.30

The findings of the present study indicate that a dense, relatively non-porous

sponge is firm enough to exert a force against the instrument during the in-and-out

strokes enabling the sponge material to expand, at least partially, into the

instrument flutes. A more porous sponge has less sponge material per unit volume

and so there is less material available to physically remove debris from the

instrument flutes. The coarse top layer of scouring sponges consists of very fine,

relatively stiff fibres that enter the file flutes, thus explaining the efficacy of these

sponges particularly for complex design files. Another advantage seen in the

present study was that the dense sponges and scouring sponges retained the

chlorhexidine solution better than the porous sponge. The latter allowed the

solution to drain downward leaving the top layer almost dry. The purpose of the

sponge is not only the physical cleaning action but also to keep the files and

remaining debris moist, which is an important aspect of instrument cleaning.30

The significantly better cleaning results with the greater number of strokes

indicates the importance of this mechanical component of the protocol.

Pre-soaking before ultrasonication has been shown to be an important step

in the cleaning process28, 30 and should begin as close to the point of use as

192

possible to prevent the drying of debris and fluid on the instrument.6 Drying of

debris on the instruments results in it being more difficult to remove.6, 13, 30 The

question posed during this investigation was which solution to use for pre-

soaking? NaOCl effectively dissolves pulp tissue,31, 32 but the possibility of

corrosion damage to the instruments is a concern. The present investigations

confirmed that NiTi was resistant to corrosion, as has been shown by others,33, 34

but the metal shanks of the instruments often became heavily corroded after

ultrasonication for 30 minutes in 1% and 4% sodium hypochlorite.

Enzymatic detergents such as the one used in this study are currently

widely recommended for the cleaning of medical devices because they help to

remove proteins, lipids and carbohydrates from the instrument surface.35 There are

many enzymatic detergents available, all of which require a minimum contact

time (2min-10min) and a minimum temperature (35o-45oC) for optimal effect.35

The temperature should not exceed 55oC during ultrasonication because this may

prevent cavitation by producing large vapour-filled pockets instead of minute

bubbles.36 Pre-soaking in the enzyme solution EmPower produced favourable

results and eliminated the problem of corrosion. This study indicated that the pre-

soaking time in the enzyme solution was more important than the ultrasonication

time. A pre-soaking time of 30 minutes produced significantly better results than

15 minutes but was also clinically feasible. Longer times tended to interrupt the

natural flow of tasks in the private practice setting. Although this study did not

assess the relative effectiveness of different enzyme solutions, a previous study

has indicated that their cleaning abilities are comparable.35 It is important to

193

remember that manufacturers make recommendations on such factors as times for

pre-soaking and ultrasonication, but there is no information available upon which

to base these recommendations.

The present study showed that ultrasonic use is an important step in

instrument cleaning, and this is consistent with other studies.27, 29, 30 Ultrasonics

may even have an antimicrobial effect.37 The literature recommends 6-10 minutes

in special solutions,21, 27, 29, 30 whilst the EmPower manufacturer’s instructions

recommend a minimum of two minutes ultrasonication time. In the present study

better results were obtained with a long pre-soaking time (30 minutes) and a

shorter ultrasonication time (15 minutes), which may be due to debris being re-

deposited with extended ultrasonication time as suggested by Gardner and Peel.36

The 15 minutes of ultrasonication was suitable from a practice flow perspective.

Shorter times tended to result in dental assistants not getting back to the ultrasonic

unit in time, which left the files sitting in the still solution conceivably long

enough for debris to be re-deposited. Furthermore, thorough rinsing after

ultrasonication is important in the removal of residual contaminated solution.29, 30

In the world of busy private practice if too much of the cleaning procedure

relied on human effort the chances of producing acceptable cleaning results would

likely diminish due to hurried manual attempts at instrument cleaning.29 Human

error likely plays a major role in instrument processing failures where there are

many factors that can interfere with instrument sterilisation.29 The protocol

presented in this paper relies more on chemicals and equipment than human effort

194

for a satisfactory cleaning result of endodontic instruments. The initial cleaning

with a scourer sponge is important and it is simple and quick to perform for the

clinician and the assistant. The subsequent pre-soaking and ultrasonication are

very important stages. Because the protocol presented in this paper is simple, it

can be easily learned and implemented in any private practice or institutional

setting. Dental personnel need to be taught the rationale for each step in the

protocol including the underlying scientific principle, in order to eliminate

processing errors.38 Importantly, the protocol has been developed using a private

practice setting to ensure not only its efficacy but also its practicality. This is in

line with the recommendation that studies of this nature should be consistent with

actual clinical practices.39 Furthermore, the cleaning protocol recommended in

this paper costs approximately 90c-$1.00 for each batch of instruments, which is

only approximately 10% the cost of one NiTi endodontic file.

CONCLUSIONS.

This present work has shown that it is possible to process instruments

easily to be “clean to the naked eye” as required by AS/NZS 4187:2003. This

paper has shown that even microscopic cleanliness can be achieved, thus

exceeding the requirements.

New unused endodontic files are contaminated with both manufacturing

debris and biologic debris. Root canal instrumentation creates biologic debris on

files. A protocol has been developed using inexpensive, easily obtained materials

to simply, quickly and predictably clean endodontic files to a standard that

195

exceeds recommended levels of cleanliness in preparation for sterilisation. Under

the experimental conditions of this study rotary NiTi files were 100% free of

biologic (stained) debris. The protocol comprises ten vigorous strokes in a

scouring sponge soaked in 0.2% chlorhexidine solution, a 30 minute pre-soaking

in an enzymatic cleaning solution, 15 minutes ultrasonication in the same solution,

and a 20 second rinse in running tap water. The authors surmise that this protocol

could be used for other endodontic files.

ACKNOWLEDGMENTS

Many of the instruments used in this study were generously donated by Dentsply

(Australia) Pty Ltd, Gunz Dental and Halas Dental Ltd. The EmPower solution

was donated by Halas Dental Ltd.

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1. Association of Operating Room Nurses. Recommended practices for the

care and cleaning of surgical instruments and powered equipment. AORN

J 1997;65:124-130.

2. Australian/New Zealand Standard 4187. Cleaning, disinfecting and

sterilizing reusable medical and surgical instruments and equipment, and

maintenance of associated environments in health care facilities.:

Standards Australia International Ltd/Standards New Zealand, 2003.

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guidelines for the prevention of transmission of infectious diseases in the

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health care setting. Canberra: Communicable Diseases Network of

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2003.

5. Martins R, Bahia M, Buono V. Surface analysis of ProFile instruments by

scanning electron microscopy and X-ray energy-dispersive spectroscopy: a

preliminary study. Int Endod J 2002;35:848-853.

6. Dunn D. Reprocessing single-use devices - the equipment connection.

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7. Rutala W, Gergen M, Jones J, Weber D. Levels of microbial

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9. Segall RD, Del Rio CE, Brady JM, Ayer WA. Evaluation of endodontic

instruments as received from the manufacturer: the demand for quality

control. Oral Surg 1977;44:463-467.

10. Zmener O, Spielberg C. Cleaning of endodontic instruments before use.

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11. Marsicovetere ES, Clement DJ, Del Rio CE. Morphometric video analysis

of the engine-driven nickel-titanium Lightspeed instrument system. J

Endodon 1996;22:231-235.

12. Johnson M, Primack P, Loushine R, Craft D. Cleaning of endodontic files,

part 1: the effect of bioburden on the sterilization of endodontic files. J

Endodon 1997;23:32-34.

13. Linsuwanont P. Cleaning of rotary nickel-titanium endodontic files.

School of Dental Science. Melbourne: University of Melbourne,

2002:MDSc thesis.

14. Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int

Endod J 2000;33:297-310.

15. Miller C, Sheldrake M. Sterilization beneath rings on dental instruments.

Am J Dent 1991;4:291-294.

16. Boyd K, Sonntag K, Crawford J. Efficacy of sterilization of endodontic

files after autoclaving in a synthetic sponge. Int Endod J 1994;27:330-333.

17. Muscarella LF. Are all sterilization processes alike? AORN J

1998;67:966-976.

18. Vélez AE, Thomas DD, Del Rio CE. An evaluation of sterilization of

endodontic instruments in artificial sponges. J Endodon 1998;24:51-53.

19. Chu N, Chan-Myers H, Ghazanfari N, Antonoplos P. Levels of naturally

occurring microorganisms on surgical instruments after clinical use and

after washing. Am J Infect Control 1999;27:315-319.

20. Alvarado C. Sterilization vs disinfection vs clean. Nurs Clin N Amer

1999;34:483-491.

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21. Heeg P, Roth K, Reichl R, Cogdill P, Bond WW. Decontaminated single-

use devices: An oxymoron that may be placing patients at risk for cross-

contamination. Infect Control Hosp Epidemiol 2001;22:542-549.

22. Smith A, Dickson M, Aitken J, Bagg J. Contaminated dental instruments. J

Hosp Infect 2002;51:233-235.

23. Porter S, Scully C, Ridgeway G, Bell J. The human transmissible

spongiform encephalopathies (TSEs): implications for dental practitioners.

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24. Porter SR. Prions and dentistry. J Roy Soc Med 2002;95:178-181.

25. Murgel CAF, Walton RE, Rittman B, Pecora JD. A comparison of

techniques for cleaning endodontic files after usage: A quantitative

scanning electron microscopic study. J Endodon 1990;16:214-217.

26. Hubbard TM, Smyth RN, Pelleu GB, Tenca JI. Chairside decontamination

of endodontic files. Oral Surg Oral Med Oral Pathol 1975;40:148-152.

27. Cafruny W, Brunick A, Nelson DM, Nelson RF. Effectiveness of

ultrasonic cleaning of dental instruments. Am J Dent 1995;8:152-156.

28. Sanchez E, Macdonald G. Decontaminating dental instruments. J Am Dent

Assoc 1995;126:359-368.

29. Burkhart NW, Crawford J. Critical steps in instrument cleaning: Removing

debris after sonication. J Am Dent Assoc 1997;128:456-463.

30. Miller C. Tips on preparing instruments for sterilization. Am J Dent

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31. Hand RE, Smith RE, Harrison JW. Analysis of the effect of dilution on the

necrotic tissue dissolution property of sodium hypochlorite. J Endodon

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32. Koshinen KP, Stenvall H, Uitto VJ. Dissolution of bovine pulp tissue by

endodontic solution. Scand J Dent Res 1980;88:406-411.

33. Busslinger A, Sener B, Barbakow F. Effects of sodium hypochlorite on

nickel-titanium Lightspeed instruments. Int Endod J 1998;31:290-294.

34. Haikel Y, Serfaty R, Wilson P, Speisser JM, Alleman C. Cutting

efficiency of nickel-titanium endodontic instruments and the effect of

sodium hypochlorite treatment. J Endodon 1998;24:736-739.

35. Alfa MJ, Jackson M. A new hydrogen peroxide-based medical-device

detergent with germicidal properties: comparison with enzymatic cleaners.

Am J Infect Control 2001;29:168-177.

36. Gardner J, Peel M. Sterilization, Disinfection and Infection Control.

Marrickville.: Churchill Livingstone, 1988.

37. Bettner M, Beiswanger M, Miller C, Palenik C. Effect of ultrasonic

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38. Reichert M. Reuse of single-use devices. Nurs Clin N Amer 1993;28:697-

709.

39. Belkin N. Testing for Creutzfeld-Jakob disease. Am J Infect Control

2002;30:197-198.

200

Table 8-1: Order, processes and results of cleaning experiments performed on debris laden files.

Group* Chairside manual process† Chemical process‡ Ultrasonication§ Cleaning success**

A Scouring sponge, chlorhexidine, 5 strokes

1% NaOCl, 5 1% NaOCl, beaker, 5 15/20 (75%)

B Dense sponge, chlorhexidine, 5 strokes

1% NaOCl, 5 1% NaOCl, beaker, 5 7/8 (88%)

C Scouring sponge, chlorhexidine, 5 strokes

EmPower, 15 1% NaOCl, beaker, 10 11/14 (79%)

D Scouring sponge, chlorhexidine, 5 strokes

EmPower, 15 1% NaOCl, beaker, 5 9/12 (75%)

E Scouring pad-dry wipe; dense sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, basket, 30 6/6 (100%)

F Dense sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, basket, 30 4/6 (67%)

G Scouring sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, basket, 45 5/6 (83%)

H Dense sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, basket, 45 6/6 (100%)

I Scouring sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, stand, 45 2/6 (33%)

J Dense sponge, chlorhexidine, 5 strokes

EmPower, 15 EmPower, stand, 45 5/6 (83%)

K Scouring pad-dry wipe; dense sponge, chlorhexidine, 5 strokes

4% NaOCl, 15, not handle EmPower, basket, 30 7/8 (88%)

L Scouring sponge, chlorhexidine, 10 strokes

4% NaOCl, 15, not handle EmPower, basket, 30 6/6 (100%)

M Scouring pad-dry wipe; dense sponge, chlorhexidine, 5 strokes

4% NaOCl, 15, not handle EmPower, basket, 15 8/9 (89%)

N Scouring sponge, chlorhexidine, 5 strokes

1% NaOCl, 15, not handle EmPower, basket, 30 19/20 (95%)

O Dense sponge, chlorhexidine, 5 strokes

1% NaOCl, 15, not handle EmPower, basket, 30 18/20 (90%)

P Dense sponge, 1% NaOCl (15 mins), 10 strokes

Nil EmPower, basket, 30 11/13 (85%)

Q Scouring sponge, 1% NaOCl (15 mins), 10 strokes

Nil EmPower, basket, 30 14/16 (88%)

R Dense sponge, chlorhexidine, 10 strokes

1% NaOCl, 15 EmPower, basket, 30 9/12 (75%)

S Scouring sponge, chlorhexidine, 10 strokes

1% NaOCl, 15 EmPower, basket, 30 16/18 (89%)

T Scouring sponge, chlorhexidine, 10 strokes

EmPower 30, basket EmPower, basket, 10 30/32 (94%)

U Scouring sponge, chlorhexidine, 10 strokes

EmPower 30, basket EmPower, stand, 10 16/18 (89%)

V Dense sponge, chlorhexidine, 10 strokes

EmPower 30, basket EmPower, basket, 10 29/32 (91%)

W Scouring sponge, chlorhexidine, 10 strokes

EmPower 30, basket EmPower, basket, 15 30/30 (100%)

* Each group represents a separate experiment performed sequentially from A to W. Each experiment comprised, in order, the chairside, the chemical and the ultrasonication processes. † Details include type of sponge, solution used to soak the sponge and number of strokes of the file in the sponge. ‡ Details include the pre-soaking solution and the pre-soaking time (min). Files were placed into a glass beaker containing the solution. “Not handle” indicates only the NiTi portion of the file was treated. “Basket” indicates that the files were supported in the mesh basket whilst in the glass beaker. § Details include the solution used, the means of holding the files and the time period of ultrasonication. ** The fraction represents the number of clean files over the number of files tested, and is also expressed as a percentage.

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Table 8-2: Summary of results of cleaning experiments with emphasis on the four main components of the cleaning procedure.

Procedure* Totals Dirty Clean

Scouring sponge 198 25 173 (87%)

Dense sponge 106 14 92 (87%)

5 strokes in either sponge 131 25 106 (81%)

10 strokes in either sponge 193 16 177 (92%)†

EmPower pre-soak – 15 min 62 14 48 (77%)

– 30 min 112 7 105 (94%)‡

EmPower ultrasonic – 10 min 82 7 75 (91%)

– 15 min 39 1 38 (97%)§

– 30 min 125 15 110 (88%)

– 45 min 24 6 18 (75%)

* Each procedure includes all files exposed to that particular variable irrespective of the other variables to which it was also exposed. † Significantly more with 10 strokes (χ2=8.225; DF=1; P=0.004)AT. ‡ Significantly more after 30 mins (χ2=10.029; DF=1; P=0.002)AU. § Significantly more than after 45 mins (Fisher’s Exact test, P=0.01)AV.

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Table 8-3: Summary of results of cleaning for complex files with emphasis on the four main components of the cleaning procedure.

Procedure* Totals Dirty Clean

Scouring sponge 50 7 43 (86%)

Dense sponge 9 3 6 (67%)

5 strokes in sponge 25 8 17 (68%)

10 strokes in sponge 41 2 39 (95%)†

EmPower pre-soak – 15 min 21 8 13 (62%)

– 30 min 40 2 38 (95%)‡

EmPower ultrasonic – 10 min 10 2 8 (80%)

– 15 min 32 0 32 (100%)§

– 30 min 9 2 7 (78%)

– 45 min 12 5 7 (58%)

* Each procedure includes all files exposed to that particular variable irrespective of the other variables to which it was also exposed. † Significantly more with 10 strokes (Fisher’s Exact Test, P = 0.005)AW. ‡ Significantly more after 30 min (Fisher’s Exact Test, P = 0.002)AX. § Significantly more than after 30 min (Fisher’s Exact Test, P = 0.04)AY or 45 min (Fisher’s Exact Test, P = 0.001)AZ.

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Table 8-4: Results of all cleaning experiments according to file type.

File type* Totals Dirty Clean

Triangular 93 10 83 (89%)

Triple U 165 21 144 (87%)

Complex 66 10 56 (85%)

* Refers to cross sectional shape of the files. See text for details if file brands in each category.

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Table 8-5: Effect on file cleanliness by progressive incorporation of best factors.

Procedure Totals Dirty Clean

Scouring sponge 198 25 173 (87%)

+ 10 strokes 120 8 112 (93%)

+ 30 min EmPower pre-soak 80 4 76 (95%)

+ 15 min EmPower ultrasonication 30 0 30 (100%)

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Table 8-6: Recommended protocol for cleaning of endodontic files.

Step Method

1 10 vigorous strokes in a scouring sponge soaked in 0.2% chlorhexidine solution

2 30 minute pre-soaking in an enzymatic cleaning solution

3 15 minute ultrasonication in an enzymatic cleaning solution

4 20 second rinse in running tap water

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Figure 8-1: Small plastic container with chlorhexidine-soaked sponge used chairside to clean files and keep them moist.

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igure 8-2: Small metal mesh basket used to support the files during pre-soaking Fand ultrasonication.

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Figure 8-3: Mesh basket supported in a 600 ml glass beaker during pre-soaking and ultrasonication.

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PART V

GENERAL DISCUSSION AND CONCLUSIONS

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CHAPTER 9

NEW TECHNOLOGY IN DENTISTRY: DIFFUSION OF AN INNOVATION

TECHNOLOGY, DIFFUSION AND INNOVATION: THEORETICAL CONSIDERATIONS

The term “technology” is commonly used to denote 1) manufactured

articles, 2) manufacturing hardware, and 3) technique, methodology or “know-

how” (Kline 2003). Most technologies have two components – the hardware,

consisting of the tool that embodies the technology as a material or physical

object, and the software, consisting of the information base for the tool (Rogers

1995). The software is knowledge stored outside the human brain in, for example,

books and computers. Knowledge stored in the human brain has been termed

“wetware” and includes entities such as beliefs, skills, and talents resulting from

the natural endowments with which each person is born, but also from the

accumulation of experience and education (Conceição et al. 1998). Together with

the acquired features of reminiscences and intuitions, experience and education

represent cognitive resources (Ropohl 1997).

An “innovation” is an idea, practice, or object that is perceived as new, and

“diffusion” refers to the processes whereby an innovation spreads (Rogers 1995).

The innovation is disruptive when it redefines a procedure and sustaining when it

is a better way of doing something (Chambers 2001). The terms “innovation” and

211

“technology” seem to be used interchangeably in the literature but applying the

“wares” definitions to these terms means that innovation consists of wetware and

software, while technology also includes hardware. Worboys (1993) pointed out

three phases in innovation studies, namely invention, innovation and diffusion. He

explained that innovation is a process rather than distinct stages and that various

social groups and agencies shaped their form, use, adoption and impact.

In the fourth edition of his comprehensive work on the diffusion of

innovations, Rogers (1995) described the four main elements in diffusion as being

the innovation itself, communication channels, time and the social system. He

based his theory on ten main research fields and merged them into a single

integrated body of concepts and generalisations. Rogers (1995) classified

members of a social system on the basis of innovativeness into five “adopter

categories”: innovators (2.5%), early adopters (13.5%), early majority (34%), late

majority (34%) and laggards (16%). This is based on the relative time at which an

innovation is adopted. From an alternative perspective, Tann (1995)

recommended the integration of social science theory with the history of

technology, and presented a stage model of the diffusion of technology from one

social system to another. Stage 1 represented the initial dispersal of the technology

among early adopters, stage 2 represented diffusion within a society, and stage 3

represented assimilation of the technology by a society to the point where local

manufacture commences (Tann 1995). Another model of transferring of scientific

information to dentists included manufacturers, academic institutions, dental

associations and governmental administration (Nakata et al. 1989). Generally,

212

social change occurs when new ideas are created, diffused, and are adopted or

rejected (Rogers 1995), and innovations have different social meanings for

different social groups (Worboys 1993).

Diffusion of innovations theory has recently also been discussed in relation

to information system processes (Mustonen-Ollila & Lyytinen 2003) and

institutional change (Redmond 2003). However, Rogers (1995) noted that up to

1994 only some 7% of 3,890 diffusion studies were on public health and medical

sociology. That percentage included the classic study on the diffusion of a new

drug among physicians (Coleman et al. 1957). Since 1994, hundreds more

diffusion studies have appeared in the medical literature. Studies on the diffusion

of drug innovations seem to be common (Peay & Peay 1990; Armstrong et al.

1996; McGettigan et al. 2000; Robertson et al. 2001; Ruof et al. 2002). Other

areas investigated in medicine include factors involved in making clinical changes

(Allery et al. 1997; Stein 2000), hospital acquisition of technology (Friedman et

al. 2000), and adverse effects of new technology (Deyo 2002). The medical

literature also explores innovation from a creative philosophical perspective

(Blumberg 1999; Perry & Thamer 1999; David 2000; Wheeler 2000), and from a

social history perspective (Stanton 2002). Innovation as it pertains to knowledge

transfer in dentistry and medicine has also been discussed (O'Keefe 2000; LaPorte

et al. 2003), which in itself represents an innovation.

213

DIFFUSION OF INNOVATION IN DENTISTRY

A review of the dental literature reveals very little concerning reasons for

the adoption of new technology in dentistry and even less on the diffusion of

innovations. An early study on the levels of support of three innovations in the

organization and delivery of dental services, assumed that the greater the support

the quicker the diffusion (Tryon 1974). Diffusion of caries-preventive innovations

(fissure sealants and topical application of fluorides) has been studied and has

indicated that the process is complex and cannot necessarily be generalised

beyond the particular innovation studied (Goldhaber 1978; Coombs et al. 1980;

Hunt et al. 1984; Haugejordan 1988; Nakata et al. 1989). Sadowsky & Kunzel

(1986) studied the extent to which attitudes and orientations of dentists were

predictive of knowledge acquisition concerning an innovation. They found that

acceptability of an innovation (bacterial endocarditis guidelines) was not

necessarily compatible with the individual’s previously established practices.

Instead the situational context in relation to access to interpersonal

communication networks was more relevant. Reit et al. (1985) and Reit &

Gröndahl (1987) stressed the importance of value judgements in clinical decision-

making. Molander et al. (1996) speculated that the non-diffusion of

microbiological root canal sampling may have been due to individuals not seeing

any clinical advantage. Kvist et al. (1994) and Kvist & Reit (2002) found clinical

symptoms more influential on behaviour than radiographic signs and theorised

that cognitive and social processes influence respondent behaviour in terms of

decision-making. Selden (2002) noted the slow diffusion of the dental operating

214

microscope but offered no explanations. Recently the importance of

understanding the diffusion of innovations in health care in general has been

addressed (Berwick 2003). Furthermore, the connection between innovations and

entrepreneurship in dentistry has been related to research, education, and

credibility (Nakata et al. 1989; Rossomando 2002b, 2002a, 2003a, 2003b).

Dentists tend to be innovators in technology (Chambers 2001), and the

history of dentistry abounds with contributions to both the knowledge and

technical bases of our profession (Ring 1985; Curtis 2002; Gutmann 2002). Based

on enduring innovations such as rubber dam, local anaesthesia, disposable

needles, stainless steel instruments, the high-speed turbine handpiece, compressed

air, high speed suction and dental radiography, to name but a few, there can be no

doubt that the intentions of the innovators have been to improve the quality and

experience of dentistry for both patient and clinician. Dentistry as practised today

would be impossible without ongoing innovation in instruments and materials, but

none of the mechanical principles established in the past have been discarded

(Vinski 1979). On the other hand, the intentions and motives behind adoption or

non-adoption of innovation by the profession as a social system are somewhat less

certain. This is illustrated historically by the slow diffusion of some innovations.

Dr C. Edmund Kells, who is credited with having exposed the first intraoral

radiograph in a living patient in the US, was surprised and disappointed that

"skiagraphy" did not catch on immediately in the dental profession in 1896

(Kracher 2000). On the contrary, at that time, the use of x-rays was opposed and

215

openly condemned by some (Hubar 2000). However, the technology was slowly

accepted and much later led to new related innovations such as radiovisiography

(Shearer et al. 1991), which is also continually being improved (Lozano et al.

2002). When air-driven high-speed handpieces were first developed in the late

1950s, the innovators boasted benefits including increased patient comfort, better

control and less effort for the dentist, increased efficiency of dental burs, shorter

operating times, reduced vibration perception, and reduced fatigue for both patient

and dentist (Dyson & Darvell 1993). But most dentists did not acquire such high-

speed handpieces until the early 1960s (Glenner 2000). Sanford C. Barnum

introduced the use of rubber dam isolation into general dentistry in 1864

(Grossman 1946), but almost 140 years later a large proportion of dentists never

use it (Slaus & Bottenberg 2002).

The operating microscope has been used in medicine since around 1953

(Piontkowski 1998). It was introduced into dentistry in 1982, but it was not until

1997 that microscope training became mandatory for specialty endodontic

programmes in the US (Selden 2002). In 1997 an estimated 20% of all

endodontists used the dental operating microscope in their clinical practice

(Chinnock 1997). Soon after (1998), it was estimated that 52% of the endodontists

in the US used the dental operating microscope (Mines et al. 1999). To be sure,

the microscope is not easy to learn, but the advantages and opportunities far

outweigh the time and frustration that may be experienced initially (Cohen 1995).

Furthermore, general dentists have also begun to implement this innovation into

their practices because of the increased skill and comfort levels it allows

216

(Piontkowski 1998). On the other hand some innovations that have been

introduced in the past have not diffused for reasons of inadequacy. Some

examples include ultrasonic devices, sonic devices, reciprocating handpieces and

lasers, which have not been shown to be effective (Walton 1992; Ingle et al.

2002). Clearly, all of these examples demonstrate the existence of diffusion

factors (both supportive and resistant), which affect the adoption of an innovation,

despite obvious and established benefits of the innovation. The role of resistance

in the diffusion of innovation in medicine has been highlighted (Stanton 2002).

ROTARY NITI TECHNOLOGY

Historically, until about 1875, instruments used in root canal therapy were

not readily available from dental suppliers and were manufactured to the

individual dentist's specifications, or the dentist made his own instruments

(Grossman 1946). In 1901, the Kerr Manufacturing Company introduced K-files

and K-reamers (Miserendino 1994). Hedström files (H-type) were the third major

design for many years. All these instruments were originally made of carbon-steel

and standardization appeared in the 1950s (Ingle et al. 1985). Further

improvements took the form of the use of stainless-steel and of design

modifications to the cross-sectional shape, to the depth and angle of cutting flutes,

and to the tip design. These incremental changes were intended to address the

clinical problems encountered with these instruments such as ledging, perforation,

elbows, zips (Weine et al. 1975; ElDeeb & Boraas 1985; Lim & Webber 1985;

Miserendino 1994). Alternative techniques such as anticurvature filing and the

217

balanced force concept were developed to further attempt to counter these

procedural problems and to allow larger canal preparations apically (Abou-Rass et

al. 1980; Roane et al. 1985). Various automated techniques have also been

developed including sonic instruments, ultrasonic instruments and engine-driven

stainless-steel instruments, but their problems have generally outweighed their

advantages (Walton 1992).

Extensive favourable findings of NiTi endodontic instruments were

presented by Serene et al. (1995). Although the early work on NiTi files involved

hand instruments (Walia et al. 1988), the properties of NiTi alloy have made

mechanical (rotary handpiece) instrumentation rapid and predictable (Serene et al.

1995). Subsequently, many clinical and laboratory studies have supported these

findings. Overall, many studies have now been published which confirm the

ability of the instruments to maintain original canal curvatures, allow larger apical

preparation sizes, minimise dentine removal and shorten treatment time

(Bergmans et al. 2001; Hübscher et al. 2003; Hülsmann et al. 2003; Zuckerman et

al. 2003). These studies also confirm that the degree of canal cleanliness varies

with the instrument type and that elimination of debris and smear layer is still less

than ideal. Furthermore, the fracture of rotary NiTi instruments remains a major

concern, but importantly, recent studies indicate that frequency of instrument

fractures depends heavily on operator skill (Hülsmann et al. 2003). Therefore, the

advantages of the new technology outweigh the disadvantages.

218

ROTARY NITI: DIFFUSION OF AN INNOVATION

Rotary NiTi instruments are now well accepted and considered exceptional

in their ability to shape root canals (Spångberg 2001). In this respect the new

technology must be regarded as a major innovation. Again, very little is known

about the adoption of this particular new technology into clinical dental practice,

with specific reference to diffusion. Only Barbakow & Lutz (1997) and Slaus &

Bottenberg (2002) have studied attitudes and experiences with rotary NiTi

instruments and techniques, but not specifically the diffusion of the innovation.

Furthermore, it has been recommended that advances in medical technology

should be studied from different perspectives including as a body of knowledge, a

practice, a profession, a cultural and social phenomenon, and a political issue

(Löwy 1993). Dentistry as an entity in itself has been largely ignored. Although

social factors in relation to diffusion of innovation have been considered (Rogers

1995; Stanton 2002), and psychological factors (type) have been considered in

organisational change (Barger & Kirby 1995), there seems to be no published

work directly linking sociology, psychology and diffusion theory in medicine, and

certainly not in dentistry. Here the relevant psychological factors involve

behaviour and decision-making.

Behaviour has been explained in terms of the concept of personality. The

assessment of individual differences, which define personality and temperament,

has been undertaken from as early as 2200 B.C. (Piedmont 1998). Monte (1999)

219

reviewed 25 theories of personality, which seemed to be based on the very

personal reflections of the psychology of their creators. Personality models exist

for explaining both normal and abnormal personality functioning. Of the

thousands of personality scales that exist in the psychological literature, there is

no established framework for evaluating all these diverse scales or for linking

them together conceptually (Piedmont 1998). Human behaviour has also been

studied from biological perspectives including individual-specific properties of

the central nervous system (Strelau et al. 1999), genetic control and evolutionary

psychology (Pope 2000). Furthermore, change involves choices, which in turn

involves decision theory (Zimbardo 1969; Schick 1997; Lipshitz et al. 2001).

This thesis makes observations on the diffusion of an innovation in

dentistry, correlating it with sociological and psychological factors. The model

used considered the reasons for adoption or non-adoption of rotary NiTi

technology by Australian dentists, the factors that may have influenced the

decision-making process, and how psychological factors may tie in with diffusion

of innovation. The series of three studies analysed different clinical aspects of

rotary NiTi instruments and techniques. These studies represented a progression

from a questionnaire designed to gain some insight into attitudes and beliefs

concerning rotary NiTi to studies to clarify the actual role of elucidated perceived

negative attributes (resistances) to the new technology. The data from these

studies were analysed and interpreted from a somewhat uncommon approach in

dental research, namely to elucidate cognitive and behavioural reasons for the

adoption or non-adoption of the new technology. These reasons may help provide

220

a picture of the diffusion of this particular innovation, which can then be

extrapolated to derive a general hypothesis on the diffusion of innovation in

dentistry.

This research has shown that the numbers of general dentists and specialist

endodontists who had adopted the new technology at the time of the current

survey had passed the critical mass of adopters (10 – 20%) required to ensure that

the innovation’s further rate of adoption becomes self-sustaining (Rogers 1995).

In fact, the 64% of endodontists using the technology placed that social system in

the late majority category, and the 22% of general dentists were in the early

majority. This supports the view of differences in the rate of adoption for the same

innovation in different social systems (Rogers 1995; Stanton 2002). The diffusion

curves in this study are essentially linear (Fig. 9-1), which do not correspond to

the S-shape generally reported (Rogers 1995). Figure 9-2 allows a broad general

comparison of four studies, although it is important to keep in perspective the very

different time frames and measurements, which does not allow reliable

conclusions to be drawn. Furthermore, the figures from the current study were

based on respondents’ recollections rather than actual measurements at each time

interval. The S-shaped agricultural example of Rogers (1995) extended over 14

years with two-year adoption measurements (for simplicity, four-year data are

shown in Fig. 9-2), while Coleman et al. (1966) looked at the adoption of a

medical drug bi-monthly over 15 months, Molander et al. (1996) looked at

adoption of root canal sampling at five-year periods over 24 years, and the current

study looked at yearly figures over some four years.

221

Figure 9-1: Cumulative Percentage of Adopters of Rotary NiTi (actual numbers in brackets).

26 (187)

18 (132)

11 (82)

6 (45)

22 (150)

15 (103)

9 (60)

5 (32)

64 (37)

50 (29)

38 (22)

22 (13)

0

100

1 2 3 4

Year of Availability of NiTi

Perc

enta

ge o

f Ado

pter

s

All Dentists

General Dentists

Endodontists

222

Figure 9-2: Comparison of Adoption Curves for Four S

66

70

76

82

6

11

1821

53

(

15

32

51

26 (at 4 years)

26

30 (at 24 years)

16

12

8

3

8

6

4

1

80

0

100

Time

Cum

ulat

ive

perc

enta

ges

tudies.

86at 15 months)

86(at 14 years)

Coleman et al (1966)

Current study

Molander et al (1996)

Rogers (1995)

223

In the current questionnaire survey, the response rate for endodontists was

not significantly different from that for the general dentists, nor were there

differences in the demographic data between non-respondents and respondents or

between early and late respondents. However, the significant differences in

proportions between early and late responders of dentists who had adopted the

innovation indicated the existence of differences between the two groups. Non-

responders were more likely not to be users of rotary nickel-titanium instruments.

Rural dentists were more likely to have tried but abandoned the use of rotary NiTi

than metropolitan dentists, which supported the finding that rural clinicians have

more difficult access to interpersonal, extra-office communication networks

(Sadowsky & Kunzel 1986). Similarly, just as the characteristics and responses of

late-responders are assumed to be more representative of non-responders than

those of early responders (McCarthy & MacDonald 1997), the same relationship

may apply to late-adopters and non-adopters. Further, there may be similarities

between early responders and early adopters, and between late responders and late

adopters. In addition, whilst there were some differences between respondents

within the two main groups of users and non-users of rotary NiTi, the differences

were few in number.

It follows that there may be two broad types of differences present amongst

the respondents. First, a difference between the specialists and the general

practitioners, and, second, a difference between early and late responders. The

former may represent a difference between two social systems, whereas the latter

a difference between interrelated units in the same system. However, the

224

boundaries segregating different social systems are not clearly defined and the

existence of definite boundaries must be questioned. Rogers (1995) defines a

social system as “a set of interrelated units that are engaged in joint problem-

solving to accomplish a common goal”, but Nicholson (2002) refers to a “relevant

social group” influenced by interpretations of the technology. Furthermore,

because change is effected on a daily basis, it is not appropriate to explain

technological change solely based on social groups (Nicholson 2002). Such a

view is supported by the findings of the current survey, which demonstrated both

similarities and differences within the two social groups studied. An important

example is the similarity in reasons provided by general practitioners and

specialists for the non-use of rotary NiTi. Consequently, the social group itself

may be considered to be a dynamic entity influenced by constant change in

technological development.

Similarly, the innovation process can also be considered dynamic by virtue

of constant modification or evolution over time as influenced by many factors

including networks, interest groups, negotiations, beliefs, economic pressures, and

politics (Stanton 2002). This thesis illustrated the diverse range of views

expressed by respondents concerning the attributes of the new technology. The

most common reason given for not adopting the new technology was that there

was no perceived advantage. This perception could arise from the lack of clinical

symptoms from patients with current techniques and materials, without

consideration for radiographic evidence of disease status and technical adequacy.

This hypothesis is in accordance with previous work (Kvist et al. 1994; Molander

225

et al. 1996; Kvist & Reit 2002) and could explain the slow diffusion of other

innovations in dentistry (Selden 2002; Slaus & Bottenberg 2002).

Of particular interest were the negative perceptions of the innovation

expressed by respondents who had not even tried the technology. Such views,

from clinicians who had not tried the innovation, must have been acquired from

external sources. It is likely that these clinicians were influenced by their

colleagues by means of personal contacts in an informal communication network,

(Coleman et al. 1957; Baptista 2001). Coleman et al. (1957) found that scientific

evaluations were not sufficient to persuade the average doctor to adopt a new

drug; instead the subjective personal experiences of a doctor’s peers were more

important in convincing the typical doctor to adopt the new drug. Rogers (1995),

supporting that view, suggested that the diffusion process is one of modelling and

imitation by potential adopters of their network partners who have adopted

previously. The concept and process of the diffusion of innovations may need to

begin at dental school level where dental industry and teaching institutions can

collaborate in the development of, and education in, new technology (Simonsen

1993; Rossomando 2003a, 2003b), thus highlighting the interrelationship of

science and technology (Roman 2001).

Whilst a negative influence imparted on non-users by colleagues may

superficially be difficult to understand, as is the resistance it imparts on others in

the social system, this phenomenon must be considered in the context of the stage

of diffusion of the innovation. In the present example, at the time of the current

226

survey, rotary NiTi technology had been adopted by only 26% of dentists and

endodontists, which approximately relates to the beginning of the early majority

stage of diffusion (Rogers 1995). Furthermore, 64% of 136 respondents had

attended a training course run by a dental supply company. Many of those courses

at that time did not include a hands-on component and if they did it was in plastic

blocks rather than natural teeth. The finding that 12% of respondents in the

current survey did not use rotary NiTi because of a lack of training stresses the

need for continuing education courses. Increased training results in an increased

frequency of use of new technology (Mines et al. 1999), and purchasing new

technology does not necessarily lead to correct use and incorporation into practice

(Stanton 2002).

Change is inevitable, and, in evolutionary terms, essential to survival

(Darwin 1859). The psychiatrist Rollo May considers that human beings are

change not accomplishment (Monte 1999). In considering ways to modify practice

behaviour, it is important to realise that dentists must perceive a need to change if

change is to occur (Morris et al. 1989). This concept was well demonstrated in the

current survey by the high proportion of dentists perceiving no advantage in the

innovation. Inducing change in clinical behaviour is the first consideration in

diffusion of innovation, but another is to provide appropriate reinforcements to

ensure that the new behaviour is maintained (Coombs et al. 1980; Armstrong et

al. 1996). Whilst a lack of guidance acted negatively for some potential adopters

in the current survey, other individuals in the social system persisted with the

innovation despite clinical setbacks. This is well demonstrated by the 74% of

227

adopters who had experienced file fracture but were still using the instruments.

According to Rogers (1995), these individuals (earlier adopters) are better able to

cope with risk and change than later adopters, which goes part way toward

explaining their persistence with the innovation. Such individuals can be

considered to be contributing to the diffusion of the innovation by helping to

provide information on the technology, which when provided as feedback will

lead to improvements. Such persistence leads to habituation and improvement of

skills over time (Newcombe 2002). This is analogous to the concept of technology

and science exhibiting an interdependent relationship (Gardner 1997; Ihde 1997).

Such relationships and feedback result in gradual improvements, which represents

how science actually progresses (Boring 1964; Suplee 2000). Later adopters may

then be more receptive to the innovation because of their characteristic of being

less able to cope with uncertainty and risk (Rogers 1995). The greater the

proportion of people successfully using the new technology, the greater the

motivation for adopting the innovation (Nakata 1990). Thus, later users can

depend not only on the accumulated experience of others (Coleman et al. 1966),

but also on further improvements and understanding of the technology.

The practice behaviour of dentists is the result of many complex factors that

reflect past educational and professional experiences, work environment, and their

professional and personal aspirations (Morris et al. 1989). These factors possibly

impact on adoption of innovation by competing for priority in life’s ever-growing

list of responsibilities. Change will occur only when people are shown how to

change their old patterns and develop commitments to new ones. This will involve

228

changes in attitudes, values, and skills, not just changes in knowledge,

information, or intellectual rationales for action and practice (Chin & Benne

1984). Because technology creates changes in our available options, it has the

effect of facing us with contradictions in our own value system and calling for

deliberate attention to their resolution (Mesthene 2003). Such contradictions

create a psychological disequilibrium or cognitive dissonance, which requires a

behaviour change to resolve the dissonance (Seltzer & Bender 1965; Zimbardo

1969; Rogers 1995).

An extrapolation of this concept is the clinician’s insecurity concerning the

uncertainties inherent in new technology. If an innovation is perceived as

disruptive it may be rejected despite its advantages (Chambers 2001; Rossomando

2003a). This has implications for educators in the teaching of skills needed to

evaluate evidence and apply it to daily clinical practice. This is the primary aim

and the most valuable application of evidence-based dentistry (Sutherland 2001).

Hence, a more scientifically educated social system of dentists would be more

inclined to adopt innovations derived from an evidence-based approach for

applying new technology to clinical practice and education (DePaola et al. 2002).

However, evidence must first be collected from early users of new technology. It

follows that early users accept a lower level of evidence. This supports the view

that the personalities of early adopters include a more favourable attitude toward

science and change than later adopters, and that early adopters are better able to

cope with uncertainty and risk than later adopters (Rogers 1995).

229

General medical practitioners are influenced in their decision-making by

medical specialists (Robertson et al. 2001), who are seen as being innovative and

creative (Blumberg 1999; David 2000). Influential specialists have been described

in terms such as trusted, respected, having a good reputation, unbiased,

knowledgeable, fair and scientific (Hovland 1993; Armstrong et al. 1996). Such

people represent opinion leaders, defined as “individuals who are able to influence

other individuals’ attitudes or behaviour in a desired way with relative frequency”

(Rogers 1995). Opinion leaders can activate local networks to diffuse an

innovation by facilitating transfer of information (Young et al. 2003). Such a

position in a social system is earned and maintained by the individual’s technical

competence, social accessibility, and conformity to the system’s norms (Rogers

1995).

The same is likely true in dentistry. In the current survey, 14 of the 371

general dentists who had never tried the instruments commented that the feedback

from endodontists and other colleagues indicated potential problems with the new

technology. Therefore, social and cognitive factors are involved in individual

decision-making (Reit et al. 1985). Decision-makers seek the opinions of others,

assess the merit of each opinion, and then combine them to come up with their

own opinion, which acts as a basis for their decision (Yaniv & Kleinberger 2000).

Also, a decision may be influenced by anticipated regret when the decision-maker

has knowledge of the outcomes of the alternatives (Zeelenberg 1999). Both

positive and negative outcomes will therefore influence the decision. Decision

makers perceive risks and benefits, which consequently affect their judgements

230

(Finucane et al. 2000). Some respondents indicated non-adoption of the

technology because of the disagreement amongst the experts. This implies

difficulty in identifying colleagues who could be considered as opinion leaders

(Young et al. 2003) or difficulty in differentiating between good and bad opinions

of experts. Thus, members of a social system would seem to be exercising their

individuality and preferences in deciding for themselves by whom they will be

influenced. Furthermore, disagreement amongst experts indicates differences in

diffusion of innovation within that social system, probably due to behavioural

differences.

Importantly, any system may have both innovative opinion leaders and also

leaders who oppose change (Hovland 1993; Rogers 1995). For example, one

respondent in the current survey who had never tried rotary NiTi wrote the

following as the only reason for non-adoption: “[Endodontist] stated at a

discussion he didn’t want to experiment with his patients. I concur”. That

particular opinion leader had an unfavourable perception of the innovation and

communicated that perception to others in the network, though the others in that

network may not necessarily share or accept that perception. This is clearly an

example of being unduly influenced by an opinion leader or role model (Best

1999). An opinion leader has a responsibility not to be dismissive of new

technology but be fair in evaluation and thought (Hovland 1993). That 64% of

endodontists in Australia had adopted the new technology indicates that negativity

from non-adopter opinion leaders is unlikely due to fair and reasonable

assessment but rather due to behavioural factors.

231

From another perspective, opposition to change is not necessarily due to

recalcitrance or peer influence; it may simply be that the innovation is not as

appropriate for the non-adopters (Rogers 1995). This is exemplified in the current

survey by comments such as: “Too old to learn” and “Would try if I did more

endo”. Nevertheless, there are people who, despite extensive learning and

accomplishments, react to new ideas with arrogance, stupidity, and failure of

imagination (Berry 1996). A salient point is that those who adopt first are

generally least in need of the benefits of the innovation (Rogers 1995).

In response to the important issues of risk of adverse consequences (for

example, fragility of the instruments) and lack of perceived advantages of the new

technology, this thesis has shown that the performance of the instruments

depended primarily on the operator. The defect rates of the instruments varied

significantly among operators but were also influenced by a complex interplay of

instrument factors including brand, size, taper, and cross-section. This thesis thus

supports the view that many factors independently, and in combination, will

influence instrument fracture (Blum et al. 2003). Furthermore, as indicated earlier,

the endodontic literature is now replete with studies confirming the clinical

advantages of the new technology. Also, there is no evidence to show that fracture

of rotary NiTi instruments influences prognosis of endodontic treatment. Recent

work confirms that the majority of fractured instruments can be successfully

removed utilising modern techniques (Ward et al. 2003b, 2003a). A number of

instrument fragments can be bypassed (Al-Fouzan 2003). Successful clinical

232

outcomes will occur not only by the sophisticated advances in technology but also

from the fundamental understanding and acceptance of the simple biological and

clinical realities related to innovations (Rosenberg & Schilder 2000; Spångberg

2001).

Clearly then, in order for the correct message to diffuse through the social

system in relation to any innovation, there is a need for top-level educational

courses taught by experienced teachers (Nakata et al. 1989; Burns 1995).

Supervised and focussed continuing education improves clinical skills and

knowledge and helps delay declining clinical competence (Sackett et al. 1991;

Sadowsky & Kunzel 1992). Successful continuing education programmes will

include individualised feedback, face-to-face assistance, objective setting, the use

of opinion leaders as role models, appropriate data and educational underpinnings

(Brown et al. 1994; Barnett 2002). Failure by an educator to convey to the

practitioner the efficacy and benefits of an innovation is an impediment to the

diffusion of that innovation (Kennedy 1998). In the current work, most of the

innovators and early adopters of rotary NiTi had to accumulate their own

experience with the technology. Without correct guidance in the radically new

technology, this self-teaching may easily have led to procedural errors and a

negative impression of the instruments. Continuing professional education

provides a form of control over the diffusion of the innovation, which ultimately

may benefit the new technology by allowing supervised training culminating in

good results (Schlich 2002) and, hence, efficient diffusion of the innovation.

233

It must be remembered and stressed by educators that there will always be a

learning curve associated with new technology (Friedman et al. 1999). This

process will progress from a “reduced productivity phase” and “questioning

phase” before the target of the “maximum productivity phase” can be reached

(Friedman et al. 1999). Educators have a responsibility to be good role models

and be familiar with new technology (Simonsen 1994). They should be providing

information as a means of reducing uncertainty about an innovation, and

focussing on how to control and direct the innovation (Bennis et al. 1984).

Educators must recognise that different people have different aptitudes and

different skill levels (Newcombe 2002).

Even with experienced expert guidance, political issues may influence

science and rationality (Löwy 1993; Greenberg 2003). An example was the issue

of cleaning of endodontic instruments and its relationship to prion diseases. This

thesis demonstrated that endodontic instruments can be reliably and predictably

cleaned of biologic debris and that there is no evidence in the literature to

implicate endodontic instruments in the transmission of prion diseases, the classic

example being Creutzfeldt-Jakob disease (CJD). Importantly, recent information

recognises the low risk of transmission of infection from dental instruments

provided that optimal standards of infection control and decontamination are

maintained (Smith et al. 2003). Nevertheless, regulatory bodies responsible for

producing directives governing clinical standards may influence the decision to

adopt an innovation, despite such directives lacking a scientific basis. A salient

event in the current survey is the comment made by a respondent who wrote: “I

234

feel that with CJD it is not appropriate to re-use files, and so they are discarded

after a single use”. It is relevant to point out that that same respondent had never

tried rotary NiTi, giving only the reason that it takes too much time to learn, and

furthermore was a graduate of a university in the United Kingdom where prion

diseases have been well documented as a public health concern. Consequently,

that individual has been influenced by political opinion and could conceivably

negatively influence others in an informal communication network. From a

positive perspective, the influence of the expense of the new technology led to

efforts to develop effective cleaning protocols, which can be considered to have

had a positive input into infection control issues in general. Therefore,

introduction of an innovation can promote better health standards (Stein 2000).

Consideration should be given to what effects (positive or negative) an

innovation may have in other social systems and in society in general. In the

present example of rotary NiTi, and in the current state of the art of the

technology, consider the situation where a political decision results in the

instruments becoming single-use disposable items. Firstly, the survey indicated

that the cost of the rotary NiTi instruments was overall the third leading reason

(20%) for non-adoption of the new technology after no perceived advantage

(36%) and fragility (24%). Next, the survey found that 70% of the respondents

believed that it was appropriate to use the instruments more than once, and the

defects study confirmed that finding, thus conferring the instruments with a

suitable cost-effectiveness. To then declare the instruments single-use will

235

financially impact on their use in private dental practice, leading to either their

abandonment or an increase in the cost of endodontic treatment for the patient.

The result in the public health sector will likely be abandonment by many

dentists, but much worse will be the non-availability of the new technology to

undergraduate dental students. The best time for people to learn new techniques

seems to be at the undergraduate level. Students have been shown to experience

fewer problems with new technology than those with greater experience

(Christensen & Wittrock 1966; Baumann & Roth 1999; Sonntag et al. 2003a;

Sonntag et al. 2003b), which is likely due to the fact that the more we know about

how to do something, the harder it is to learn how to do it differently (Rogers

1995). Manufacturers may then be required to process and individually package

the instruments as single-use, thus likely leading to increased cost. Of greater

concern is that the standard of endodontic care will not be permitted to improve,

and failed endodontic treatment has its own financial implications.

The common theme elucidated by this discussion is that people differ both

between and within social systems. Rogers (1995) touched on personality

variables and communication behaviour as they apply to earlier and later adopters

but he also noted that such variables associated with innovativeness have not been

fully studied. He recommended that different approaches be used for different

adopter categories because of their different characteristics. Although many

models exist to “categorise” personality, one widely used and extremely popular

psychological instrument used to assess normal personalities by both

236

psychologists and non-psychologists is the Myers-Briggs Type Indicator (MBTI)®

based on the work of the psychiatrist Carl Jung (Barger & Kirby 1995; Scott

1999). Such approaches may address the question of what personality differences

may exist between early, late and non-adopters of an innovation and between

early, late and non-responders to a survey, and between the adopter and responder

groups. Carl Jung concluded that differences in behaviour result from people’s

inborn tendencies to use their minds in different ways. As people act on these

tendencies, they develop patterns of behaviour (Briggs Myers 1998).

Therefore, it is recommended that questions revealing personality

characteristics be incorporated into the design and interpretation of survey

research in order to correlate adopter and responder categories with psychological

factors. The input of psychologists is thus indicated. This may provide greater

understanding of findings such as in the current survey where differences between

early and late responders were demonstrated despite a lack of demographic

differences. Knowledge of personality types has implications for both

manufacturers and educators by virtue of approaches required for different

personality types. Just as manufacturers can and should adapt their

communication channels or messages for different adopter categories (Silversin et

al. 1977; Chin & Benne 1984; Rogers 1995), educators can do so to cater for

individual requirements of students. This supports similar recommendations in the

medical literature calling for research into factors influencing practice to include

studies on human behaviour (López Fernández et al. 2000).

237

Finally, currently, there is serious concern that scientific progress is not

applied efficiently in the dental profession (Shanley & Nattestad 2002). As a

profession, dentistry is rapidly evolving from being technique/procedure oriented

to recognising the importance of cognitive skills of the practitioner (Kennedy

1998). Consideration of behavioural sciences as well as biotechnological and

public health advances in dental research is critical to the advancement of

dentistry (Baum et al. 2002). This paper has provided some evidence to support

this view by noting the importance of psychosocial factors in the diffusion of

innovation in dentistry.

CONCLUSIONS

This thesis has shown that the diffusion of innovation in dentistry involves a

complex interplay of factors. Those factors included perceived benefits and

advantages, and psychosocial and behavioural factors. The adoption of rotary

NiTi instruments, techniques and philosophies as addressed in this thesis has

provided a basis for further study into diffusion of innovation in dentistry.

This work has highlighted the usefulness of questionnaire survey research in

elucidating reasons for adoption and non-adoption of new technology. The

findings from the survey clearly implicate behavioural factors in decision-making

and a recommendation is made to consider personality-type questions in

questionnaire survey research. The concept of assessment of non-response bias

based on demographic factors alone has been questioned. The complexity of

238

survey research is such that it is probably unrealistic to not seek input from

psychologists.

The finding of significant differences in clinical experiences between

individual dentists adds another dimension to the adoption of innovation. It brings

into question the role of the factors of clinical competency and error in diffusion

of innovation. The extreme importance of continuing education in dentistry has

been highlighted but also that such courses must be of a very high calibre.

Furthermore, the question of teaching the teachers arises.

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254

PART VI

APPENDICES

255

APPENDIX A

SURVEY OF ROTARY NITI INSTRUMENTATION PART A. DEMOGRAPHICS The first three questions relate to your background. 1. Year of BDSc/BDS graduation _______ 2. Main practice postcode _______ 3. Location of University where BDSc/BDS degree was obtained:

NSW QLD SA VIC WA Other. Please specify______________________________________

PART B. PATTERNS OF ROTARY NiTi USAGE In this part the questions pertain to the “how and why” of rotary NiTi usage. Please follow the guide arrows where indicated. 4. Do you currently use rotary NiTi instrumentation to prepare root canals? Yes No

5. If “No” is it because you –

Tried them but did not like them for one of the reasons below OR

Never tried them for one of the reasons below Reasons: (Please tick as many as apply)

Too expensive Too slow Too flexible Too fragile Too difficult to use Takes too much time to learn Too difficult to learn Not available No perceived advantage Other. Please specify ___________________

If you answered “No” to Question 4, this is the end of the Survey for you. Thank you for participating. If “Yes”, please continue with the Questionnaire commencing with Question 6 over the page.

256

If you answered “No” to Question 4, and answered Question 5, this is the end of the Survey for you. Thank you for participating.

If you currently use rotary NiTi instrumentation please continue with the Questionnaire commencing with Question 6 below.

6. Over what period of time have you been using rotary NiTi instruments?

Less than 1 month 1-12 months 13-24 months 25-36 months Longer than 36 months

7. On average, how often do you use rotary NiTi files for root canal cleaning and shaping? Less than once weekly

Once weekly Twice weekly Three times weekly Four times weekly Five or more times weekly

8. In which particular teeth do you use them? (If applicable, please tick more than one) Anterior teeth

Premolar teeth Molar teeth

9. For which particular situation do you use them? (If applicable, please tick both)

Straight root canals Curved root canals

10. Do you use them for: (If applicable, please tick both)

The coronal part of the root canal? The apical part of the root canal?

11. Which system do you mostly use?

Quantec LX Quantec SC ProFile Other. Please specify ______________________________________

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12. Have you used any other systems? Please indicate: Have not used other systems

Quantec LX Quantec SC ProFile Other. Please specify _____________________________________

13. Which instrumentation technique do you use? (Please tick as many as apply)

Crown-down Step-back Modified crown-down Other. Please specify _____________________________________

14. Which sequence of instruments do you use? (Please tick as many as apply)

NiTi coronally and apically NiTi coronally and stainless-steel hand instruments apically NiTi coronally and NiTi hand instruments apically Gates-Glidden burs coronally and rotary NiTi apically Other. Please specify _____________________________________

15. How many times do you feel it is appropriate to use each file?

Once only 2-5 times 6-10 times Until it distorts

16. How do you decide when to dispose of a file? (Please tick as many as apply)

After the number of uses as indicated in the last question When the file unwinds or distorts After use in very curved canals After use in very narrow canals When it no longer feels to be cutting When it can no longer be cleaned

17. Which motor do you use to drive the instruments?

Tri Auto ZX by Morita Dentsply motor Other. Please specify _______________________________

18. If you use the Dentsply motor, please specify the model, torque setting and RPM. ___________________________________________

19. If you use the Tri Auto ZX, do you;

Use it in automatic mode only? Use it in manual mode only? Use both modes? Use the apex locator function?

258

20. Do you undertake endodontic re-treatments?

Yes No If “No” please go to Part C.

21. If “Yes”, do you use rotary NiTi for removal of gutta-percha in re-treatments? Please specify the type of file and RPM used.

Always Sometimes File (size & taper): ________ RPM:_______ Never

PART C. ISSUES ASSOCIATED WITH NITI USAGE

In this section the questions relate to difficulties you may have

encountered when using NiTi rotary instruments. If exact numbers are not known, please estimate.

22. Have you encountered any of the following procedural problems with the use of rotary NiTi instruments? (Please tick as many as apply) Ledging of the canal

Transportation of the apical terminus of the canal Strip perforation of a curved canal Perforation of a canal other than strip perforation Straightening of curved canals Excessive dentine removal Binding of the file in the canal

23. Have any of your rotary NiTi files fractured in root canals?

Yes, but only in the first six months of my using them Yes, periodically since starting with rotary NiTi

No If “No” please continue with Part D on page 5.

If “Yes”: 24. How many in total, and over what period of time?

1-5, over __________months 6-10, over __________months 11-15, over __________months more than 15, over __________months

25. Which file type fractured? (Please tick as many as apply)

Quantec series Flare series (Quantec) ProFile series Greater Taper (ProFile) Other. Please specify _________________________

259

26. Which tip size(s) fractured? (Please tick as many as apply) 15 45 20 50 25 55 30 60 35 90 40

27. Which taper fractured? (Please tick as many as apply)

.02 .06 .03 .08 .04 .10 .05 .12

28. Which part of the file fractured? (Please tick as many as apply)

Apical part Middle part Coronal part

29. In which region of the canal did the file fracture? (Please tick as many as apply)

Apical Mid portion Coronal

30. What was, or may have been, the reason for the file(s) fracturing? (Please tick as many as apply)

Excessive pressure on the file Incorrect insertion angle of the file

Complex root canal anatomy Non-constant speed of rotation of the file RPM too high Over-usage No irrigant in the canal Incorrect file sequence Patient biting on handpiece Unknown

260

31. How have you usually managed the fractured portion? (Please tick those that apply)

Referred the patient to an endodontist Please go to Part D.

Successfully retrieved fractured portion Portion not retrievable despite attempt

32. If the fractured portion was not retrievable, what would you usually do? (Please tick those that apply)

Refer patient to an endodontist? Extract the tooth? Obturate the tooth with file in situ and

review? Other. Please specify _______________

PART D. NITI EDUCATION

These questions relate to what instruction you have had in the use of

rotary NiTi instruments and techniques.

33. Have you attended any postgraduate rotary NiTi courses? Yes No If “No”, please continue with Question 41.

If “Yes”: 34. Was the course:

Theory only? Practical (hands-on) only? Both theory and practical?

35. Who provided the course?

University. Please indicate which University and who the presenters were. ________________________________________

Dental supply company. Please indicate which company. _____ Other. Please specify __________________________________

36. When did the course take place? Month _________ Year __________

37. How long was the course? ______ Days

38. Did you use rotary NiTi before the course?

Yes No

If “Yes” 39. Did you benefit from the course?

Yes No

261

40. Please identify the strengths and weaknesses of the course. ______________________________________________________________________________________________________________________________________________________________________________________________________

41. Which of the following steps did you complete during your learning of NiTi? (Please tick as many as apply). Practice in plastic blocks. Number of blocks _________

Practice in extracted teeth. Number of teeth __________ Anterior teeth in patients Premolar teeth in patients Molar teeth in patients Other. Please specify ______________________________________

42. Which of the following have you found to occur in your experience with rotary NiTi compared to your manual instrumentation technique with Stainless-Steel instruments? (Please tick those that apply) Canal curvatures are maintained

Canal preparation is much faster Working lengths are maintained Final canal obturation is easier

43. Please provide any other comments concerning rotary NiTi instruments you believe may be relevant. ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

THANK YOU

262

APPENDIX B

Table of Australian Postcodes and Zones (adapted from post charges booklet, 1 July, 2000)

State/ Territory

Postcode ranges AusPost zone

Description

NT 0800 – 0999 NT1 Northern Territory

1000-2262, 2500-2530, 2555-2574, 2740-2786, 2890

N1 Sydney NSW

2264-2499, 2531-2554, 2575-2739, 2787-2889, 2891-2999

N2 Other NSW

3000-3220, 3335-3341, 3425-3443, 3750-3811, 3910-3920, 3926-3944, 3972-3978, 3980-3983

V1 Melbourne VIC

3221-3334, 3342-3424, 3444-3749, 3812-3909, 3921-3925, 3945-3971, 3979, 3984-3999

V2 Other VIC

4000-4299, 4500-4549 Q1 Brisbane 4300-4449, 4550-4699 Q2 Near QLD 4450-4499, 4700-4805 Q3 Mid QLD

QLD

4806-4899 Q4 North QLD 5000-5199, 5800-5999 S1 Adelaide SA 5200-5749 S2 Other SA 6000-6205, 6800-6999 W1 Perth 6206-6699 W2 Mid WA

WA

6700-6799 W3 North WA TAS 7000-7999 T1 Tasmania

263

APPENDIX C

First letter (University of Melbourne letterhead, photocopied signature)

Dear Colleague,

Re: USE OF ROTARY NiTi IN ENDODONTICS

This questionnaire is part of a study being carried out by myself, Dr Peter Parashos, a PhD student at the School of Dental Science, The University of Melbourne and Professor Harold Messer, Head of Restorative Dentistry. The purpose of this questionnaire is to determine how many dentists use rotary Nickel-Titanium (NiTi) and what their experiences have been with the available instruments and techniques. Even if you don’t use NiTi, we are still interested in your views. The questionnaire will take 10-15 minutes to complete and comprises four brief sections: A. Demographics B. Patterns of NiTi usage C. Issues associated with NiTi usage D. NiTi education The survey will be confidential and de-identified. This will be accomplished by having the returned forms separated from their envelopes by an administrative officer unrelated to the study and who will have no access to the mailing list or codes. The data will be stored in a computer for subsequent evaluation. The code number on the envelope will be cross-checked with the list of survey participants to enable me to follow-up those who have not returned a questionnaire. The results of this survey will be reported in such a way as to keep the identity of the participants anonymous. If you do not wish to participate in this study please return the unanswered questionnaire anyway, indicating your intention, so that I can send it to another dentist. I am very grateful for your time and effort in completing the questionnaire. Thank you very much for your participation. Sincerely, Peter Parashos

264

APPENDIX D

Second letter (University of Melbourne letterhead, photocopied

signature) Dear Colleague,

Re: USE OF ROTARY NiTi IN ENDODONTICS

Some time ago we mailed a questionnaire to you, which is part of a study being carried out by myself, Dr Peter Parashos, and also Professor Harold Messer. We have not received your survey and we would really appreciate your responses to the questionnaire. Even if you do not use rotary instruments or do not wish to complete the questionnaire, it would be helpful if you returned the form so that we have a record of your participation. Because the first questionnaire may have been misplaced or lost, I am sending you another including the original covering letter. Please complete and return the questionnaire by September 30. Thank you very much for your valued participation. Sincerely, Peter Parashos

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APPENDIX E

Third letter (University of Melbourne letterhead, addressee’s

name mail-merged beneath date, personally signed)

October 10, 2001 Re: USE OF ROTARY NiTi IN ENDODONTICS Thank you for your time concerning the important questionnaire we sent you recently. To the best of our knowledge we have not received yours yet. The responses to this national survey from dentists and endodontists who have already replied indicate some important views and experiences on the use of rotary NiTi instruments. We are writing again because of the importance that your questionnaire has for helping to get accurate results. We sent questionnaires to dentists and endodontists in country and metropolitan areas in each state and territory of Australia, and it is only by hearing from nearly everyone in the sample that we can be sure that the results are truly representative. Would you please help us by completing and returning the questionnaire today. If for any reason you prefer not to answer it please let us know by returning the blank questionnaire in the envelope provided. Thank you very much for your valued participation. Sincerely, Peter Parashos

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APPENDIX F

Telephone Contact (script used as a prompt by the secretarial

staff) Hello/Good morning/Good afternoon. My name is __________ and I'm calling for Melbourne University on behalf of Dr Peter Parashos and Professor Harold Messer. Can I speak with Dr ________ please? We recently sent you (him/her) a survey to complete and we would really value your (his/her) views on the subject. We have received a response rate of over 80% already but your contribution will provide greater significance to the overall results. Still have the survey? Could you please complete and return the survey in the next couple of days? Please use the reply paid envelope we included with the survey. Thank you very much. Don’t want to participate? That’s OK. Is there a particular reason that I can help you with? Lost the survey. That's OK - if you don't use Rotary Nickel-Titanium instruments, there are only a couple of very quick questions that we can complete right now. That's OK - if you do use Rotary Nickel-Titanium instruments, can we send you another survey and have you complete it and return it within the next week? Thank you very much for your time.

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APPENDIX G

STATISTICAL ANALYSES

CHAPTER 3

A: Chi-Square Test: Early contact compared with late for general dentists (G) and endodontists (E). Expected counts are printed below observed counts Early Late Total G 389 284 673 404.17 268.83 E 50 8 58 34.83 23.17 Total 439 292 731 Chi-Sq = 0.569 + 0.856 + 6.605 + 9.931 = 17.961 DF = 1, P-Value = 0.000

B: Chi-Square Test: Africa (A) compare with the rest of the world (R) for use or non-use of rotary NiTi. Expected counts are printed below observed counts Use Don’t Total R 174 521 695 179.86 515.14 A 10 6 16 4.14 11.86 Total 184 527 711 Chi-Sq = 0.191 + 0.067 + 8.291 + 2.895 = 11.444 DF = 1, P-Value = 0.001 1 cells with expected counts less than 5.0 Fisher’s Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 174,521,10,6

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Data Display P-values for Fisher's exact test - (Left) : 0.002 (Right) : 1.000 (2-tail): 0.002 C: Chi-Square Test: Q13. Endodontists (E) compared with general dentists (G) for the use of a modified crown down technique. Expected counts are printed below observed counts Mod CD No Total E 22 15 37 14.25 22.75 G 50 100 150 57.75 92.25 Total 72 115 187 Chi-Sq = 4.220 + 2.642 + 1.041 + 0.652 = 8.556 DF = 1, P-Value = 0.003 D: Chi-Square Test: Q15. Endodontists (E) compared with general dentists (G) for single use of rotary NiTi instruments. Expected counts are printed below observed counts Once No Total E 8 29 37 4.33 32.67 G 14 137 151 17.67 133.33 Total 22 166 188 Chi-Sq = 3.111 + 0.412 + 0.762 + 0.101 = 4.387 DF = 1, P-Value = 0.036 1 cells with expected counts less than 5.0 Fisher’s Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 8,29,14,137 Data Display P-values for Fisher's exact test - (Left) : 0.988 (Right) : 0.041 (2-tail): 0.047

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E: Chi-Square Test: Q17. Endodontists (E) compared with general dentists (G) for use of the TRZX handpiece. Expected counts are printed below observed counts TRZX No Total E 10 26 36 17.90 18.10 G 81 66 147 73.10 73.90 Total 91 92 183 Chi-Sq = 3.488 + 3.450 + 0.854 + 0.845 = 8.637 DF = 1, P-Value = 0.003 F: Chi-Square Test: Q19. Comparison between proportions of dentists using only the automatic mode or only the manual mode of the TRZX. Expected counts are printed below observed counts Auto Manual Total Y 10 23 33 16.50 16.50 N 79 66 145 72.50 72.50 Total 89 89 178 Chi-Sq = 2.561 + 2.561 + 0.583 + 0.583 = 6.287 DF = 1, P-Value = 0.012 Fisher’s Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 10,23,79,66 Data Display P-values for Fisher's exact test - (Left) : 0.010 (Right) : 0.997 (2-tail): 0.020 G: Chi-Square Test: Q19. Comparison between proportions of endodontists using only the automatic mode or only the manual mode of the TRZX. Expected counts are printed below observed counts Auto Manual Total 1 1 6 7 3.50 3.50 2 8 3 11 5.50 5.50

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Total 9 9 18 Chi-Sq = 1.786 + 1.786 + 1.136 + 1.136 = 5.844 DF = 1, P-Value = 0.016 2 cells with expected counts less than 5.0 MTB > %fisher Executing from file: C:\Program Files\MTBWIN\MACROS\fisher.MAC Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 1,6,8,3 Data Display P-values for Fisher's exact test - (Left) : 0.025 (Right) : 0.999 (2-tail): 0.050 H. Chi-Square Test: Q23. Endodontists compared with general dentists for periodicity of fracture. Expected counts are printed below observed counts 6mo Period Total E 4 27 31 12.18 18.82 G 51 58 109 42.82 66.18 Total 55 85 140 Chi-Sq = 5.492 + 3.554 + 1.562 + 1.011 = 11.619 DF = 1, P-Value = 0.001 I: Chi-Square Test: Q35. Comparison of proportions taking courses provided by university, dental supply company or “other”. Expected counts are printed below observed counts Uni Dent Other Total Yes 18 55 27 100 33.33 33.33 33.33 No 116 79 107 302 100.67 100.67 100.67 Total 134 134 134 402 Chi-Sq = 7.053 + 14.083 + 1.203 + 2.336 + 4.663 + 0.398 = 29.737 DF = 2, P-Value = 0.000

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J: Chi-Square Test: Q35. Comparison of proportions taking courses provided by university or dental supply company. Expected counts are printed below observed counts Uni Dent Total Yes 18 55 73 36.50 36.50 No 116 79 195 97.50 97.50 Total 134 134 268 Chi-Sq = 9.377 + 9.377 + 3.510 + 3.510 = 25.774 DF = 1, P-Value = 0.000 K: Chi-Square Test: Comparison of proportions taking courses provided by dental supply company or “other”. Expected counts are printed below observed counts Other Dent Total Yes 27 55 82 41.00 41.00 No 107 79 186 93.00 93.00 Total 134 134 268 Chi-Sq = 4.780 + 4.780 + 2.108 + 2.108 = 13.776 DF = 1, P-Value = 0.000

CHAPTER 5

L: Chi-Square Test: Usable responses, contact 4 vs 1-3 Expected counts are printed below observed counts Usable Non-usable Total 4 27 58 85 72.76 12.24 1-3 704 65 769 658.24 110.76 Total 731 123 854 Chi-Sq = 28.777 +171.025 + 3.181 + 18.904 = 221.887 DF = 1, P-Value = 0.000 M: Chi-Square Test: Negative vs Affirmative for each contact Expected counts are printed below observed counts Neg Aff Total 1 311 128 439 326.10 112.90

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2 147 43 190 141.14 48.86 3 62 13 75 55.71 19.29 4 23 4 27 20.06 6.94 Total 543 188 731 Chi-Sq = 0.699 + 2.019 + 0.244 + 0.704 + 0.710 + 2.050 + 0.432 + 1.248 = 8.106 DF = 3, P-Value = 0.044

N: Chi-Square Test for Trend using Logistic Regression supplied by Associate Professor Ian Gordon of Statistical Consulting Centre, University of Melbourne. O: Chi-Square Test: Negative vs Affirmative for Early and Late Expected counts are printed below observed counts Neg Aff Total E 311 128 439 326.10 112.90 L 232 60 292 216.90 75.10 Total 543 188 731 Chi-Sq = 0.699 + 2.019 + 1.051 + 3.035 = 6.804 DF = 1, P-Value = 0.009 MTB > %fisher Executing from file: C:\Program Files\MTBWIN\MACROS\fisher.MAC Fisher’s Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 311,128,232,60 Data Display P-values for Fisher's exact test - (Left) : 0.006 (Right) : 0.997 (2-tail): 0.010 P: Fisher’s Exact Test Enter the values for a, b, c and d for the 2x2 table

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Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 458,171,85,17 Data Display P-values for Fisher's exact test - (Left) : 0.014 (Right) : 0.993 (2-tail): 0.027

CHAPTER 6

Q: Chi-Square Test: Use and don't use, general dentists (G) vs endodontists (E). Expected counts are printed below observed counts T1-use T1-dont Total G 151 522 673 173.08 499.92 E 37 21 58 14.92 43.08 Total 188 543 731 Chi-Sq = 2.818 + 0.976 + 32.694 + 11.319 = 47.806 DF = 1, P-Value = 0.000

R: Chi-Square Test: Use, Don't; 1981-1990 (1) vs 1991-2000 (2). Expected counts are printed below observed counts Use Don't Total 1 72 162 234 60.23 173.77 2 24 115 139 35.77 103.23 Total 96 277 373 Chi-Sq = 2.302 + 0.798 + 3.876 + 1.343 = 8.319 DF = 1, P-Value = 0.004

S: Chi-Square Test: NT vs T for metro (M) and rural (R) Expected counts are printed below observed counts NT T Total M 289 57 346 280.35 65.65

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R 74 28 102 82.65 19.35 Total 363 85 448 Chi-Sq = 0.267 + 1.139 + 0.905 + 3.864 = 6.174 DF = 1, P-Value = 0.013 T: Chi-Square Test: Never tried, tried; general dentists; too fragile Expected counts are printed below observed counts NT T Total Y 73 31 104 85.74 18.26 N 298 48 346 285.26 60.74 Total 371 79 450 Chi-Sq = 1.894 + 8.893 + 0.569 + 2.673 = 14.029 DF = 1, P-Value = 0.000 U: Chi-Square Test: Never tried, tried; general dentists; diff to use Expected counts are printed below observed counts NT T Total 1 11 7 18 14.84 3.16 2 360 72 432 356.16 75.84 Total 371 79 450 Chi-Sq = 0.994 + 4.666 + 0.041 + 0.194 = 5.896 DF = 1, P-Value = 0.015 1 cells with expected counts less than 5.0 Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 11,7,360,72 Data Display P-values for Fisher's exact test - (Left) : 0.024 (Right) : 0.994 (2-tail): 0.024

V: Chi-Square Test: Never tried, tried; general dentists; diff to learn

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Expected counts are printed below observed counts NT T Total 1 6 7 13 10.74 2.26 2 365 71 436 360.26 75.74 Total 371 78 449 Chi-Sq = 2.093 + 9.956 + 0.062 + 0.297 = 12.408 DF = 1, P-Value = 0.000 1 cells with expected counts less than 5.0

W: Chi-Square Test: 1981-90 vs 1991-00; time to learn Expected counts are printed below observed counts 81-90 91-00 Total Y 17 4 21 11.99 9.01 N 136 111 247 141.01 105.99 Total 153 115 268 Chi-Sq = 2.095 + 2.787 + 0.178 + 0.237 = 5.296 DF = 1, P-Value = 0.021

X: Chi-Square Test: 1981-90 vs 1991-00; not available Expected counts are printed below observed counts 81-90 91-00 Total 1 14 33 47 26.83 20.17 2 139 82 221 126.17 94.83 Total 153 115 268 Chi-Sq = 6.137 + 8.165 + 1.305 + 1.736 = 17.343 DF = 1, P-Value = 0.000

Y: Linear by Linear Association test supplied by Associate Professor Ian Gordon of Statistical Consulting Centre, University of Melbourne.

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Z: Chi-Square Test: Curved canals, endodontists vs general dentists Expected counts are printed below observed counts E GD Total Yes 27 50 77 15.15 61.85 No 10 101 111 21.85 89.15 Total 37 151 188 Chi-Sq = 9.260 + 2.269 + 6.423 + 1.574 = 19.526 DF = 1, P-Value = 0.000 AA: Chi-Square Test: Narrow canals, endodontists vs general dentists Expected counts are printed below observed counts E GD Total Yes 18 35 53 10.43 42.57 No 19 116 135 26.57 108.43 Total 37 151 188 Chi-Sq = 5.493 + 1.346 + 2.156 + 0.528 = 9.523 DF = 1, P-Value = 0.002

AB: Chi-Square Test: Unwinding, endodontists vs general dentists Expected counts are printed below observed counts E GD Total Yes 25 68 93 18.30 74.70 No 12 83 95 18.70 76.30 Total 37 151 188 Chi-Sq = 2.450 + 0.600 + 2.399 + 0.588 = 6.037 DF = 1, P-Value = 0.014

AC: Chi-Square Test: Retreatments, general dentists vs endodontists Expected counts are printed below observed counts GD E Total Yes 96 35 131 105.08 25.92 No 54 2 56 44.92 11.08 Total 150 37 187

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Chi-Sq = 0.785 + 3.181 + 1.836 + 7.441 = 13.242 DF = 1, P-Value = 0.000

AD: Chi-Square Test: Gutta-percha, general dentists vs endodontists Expected counts are printed below observed counts GD E Total Yes 44 23 67 49.31 17.69 No 48 10 58 42.69 15.31 Total 92 33 125 Chi-Sq = 0.572 + 1.595 + 0.661 + 1.843 = 4.671 DF = 1, P-Value = 0.031

AE: Linear by Linear Association test supplied by Associate Professor Ian Gordon of Statistical Consulting Centre, University of Melbourne. AF: Linear by Linear Association test supplied by Associate Professor Ian Gordon of Statistical Consulting Centre, University of Melbourne. AG: Chi-Square Test: Ledging, endodontists vs general dentists Expected counts are printed below observed counts E GD Total Yes 26 59 85 16.73 68.27 No 11 92 103 20.27 82.73 Total 37 151 188 Chi-Sq = 5.138 + 1.259 + 4.240 + 1.039 = 11.677 DF = 1, P-Value = 0.001 AH: Chi-Square Test: Faster prep, endodontists vs general dentists Expected counts are printed below observed counts E G Total Yes 23 118 141 28.04 112.96 No 12 23 35 6.96 28.04 Total 35 141 176

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Chi-Sq = 0.906 + 0.225 + 3.649 + 0.906 = 5.686 DF = 1, P-Value = 0.017 AI: Chi-Square Test: Canal curvatures, endodontists vs general dentists Expected counts are printed below observed counts E G Total Yes 33 95 128 25.45 102.55 No 2 46 48 9.55 38.45 Total 35 141 176 Chi-Sq = 2.237 + 0.555 + 5.965 + 1.481 = 10.237 DF = 1, P-Value = 0.001 AJ: Chi-Square Test: Fractures, endodontists vs general dentists Expected counts are printed below observed counts E GD Total Yes 12 87 99 22.24 76.76 No 19 20 39 8.76 30.24 Total 31 107 138 Chi-Sq = 4.714 + 1.366 + 11.967 + 3.467 = 21.514 DF = 1, P-Value = 0.000 AK: Chi-Square Test: Overusage, endodontists vs general dentists Expected counts are printed below observed counts Table 10 Table10G Total 1 7 52 59 13.06 45.94 2 24 57 81 17.94 63.06 Total 31 109 140 Chi-Sq = 2.815 + 0.801 + 2.050 + 0.583 = 6.249 DF = 1, P-Value = 0.012

AL: Chi-Square Test: Irrigant, endodontists vs general dentists Expected counts are printed below observed counts Table 10 Table10G Total 1 0 19 19 4.21 14.79 2 31 90 121

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26.79 94.21 Total 31 109 140 Chi-Sq = 4.207 + 1.197 + 0.661 + 0.188 = 6.252 DF = 1, P-Value = 0.012 1 cells with expected counts less than 5.0 AM: Chi-Square Test: Plastic blocks, endodontists vs general dentists Expected counts are printed below observed counts q31e q31gd Total 1 32 101 133 26.75 106.25 2 3 38 41 8.25 32.75 Total 35 139 174 Chi-Sq = 1.029 + 0.259 + 3.338 + 0.841 = 5.467 DF = 1, P-Value = 0.019 AN: Chi-Square Test: Extracted teeth, endodontists vs general dentists Expected counts are printed below observed counts q31e q31gd Total 1 29 87 116 23.33 92.67 2 6 52 58 11.67 46.33 Total 35 139 174 Chi-Sq = 1.376 + 0.347 + 2.752 + 0.693 = 5.168 DF = 1, P-Value = 0.023

CHAPTER 7

AO: Analysis of File Defects

Associate Professor Ian Gordon,

Statistical Consulting Centre, 19 December 2003

Introduction This document examines a data set collected on file defects used in root canal operations by endodontists. Fourteen endodontists provided a total of 7159 used

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files, which were classified according to relevant characteristics, and examined for defects. The defects of special interest were unwinding and fracture; files that were recorded as “bent” have not been considered a defective file in this report. There were two types of fracture: flexural (type 1) and torsional (type 2). Data A file was provided with 2597 rows; the following is a description of the variables, some of which were derived from the original data sheet. The characteristics relevant to the file, which could potentially influence its failure, were:

• Endodontist: anonymised code for the endodontist who provided files; numbered 1 to 14.

• File type: a detailed and specific label for the exact file, e.g. Quantec No 2-15/.02.

• Brand: the brand of the file, e.g. Quantec. • File cross-section: S-shaped, triangular or Triple-U. • Size: the diameter of the file at the tip, in units of hundredths of a

millimetre; ranges from 15 to 90. Hence 15 means a diameter of 0.15mm at the tip of the file.

• X-taper: The triangular cross-section files had either a fixed taper or a variable taper. Therefore, the files were classified into four categories for this variable: S-shaped, triangular with fixed cross-section, triangular with variable cross-section, or Triple-U.

• Tapersize: The rate of increase in the diameter per millimetre from the tip; e.g. a taper of 0.06 means the diameter of the file increases by 0.06mm for each millimetre from the tip. Hence a file of size 25 with taper 0.06 is 0.25mm in diameter at the tip and 0.31mm in diameter 1 mm from the tip. For the purposes of analysing the effect of this variable, in the case of the variable taper files, after advice from Dr Parashos, the size was taken to be at the lower end of the range. Specifically, for the variable taper files, the following values were assigned for tapersize:

o 0.02 – 0.11: tapersize = 0.02 o 0.035 – 0.19: tapersize = 0.03 o 0.04 – 0.115: tapersize = 0.04 o 0.07 – 0.055: tapersize = 0.07 o 0.08 – 0.055: tapersize = 0.08 o 0.09 – 0.055: tapersize = 0.09

• Length (mm). • Number of uses of the file: only recorded by three endodontists at all

(Numbers 11, 13 and 14), for some files. The basic outcome was whether the file was unwound or fractured. The arrangement of the data file was such that if a number of files (n) with a given combination of characteristics had no defects, this was recorded as zero unwound, zero fractured and a “total” of n files with no defects.

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For every file with a defect, one row exactly was included in the data file, with the characteristics of the file, the nature of the defect, and a “total” of 1 file, e.g. zero unwound, one fractured and a total of one file. For the files which had unwound, there were a number of other variables recorded:

• Unwinding distance from the tip (mm) • Unwinding length (mm) • Unwinding visibility • Unwinding direction

There were two types of fracture distinguished: flexural (type 1) and torsional (type 2). For the flexural fractures the distance from the tip was recorded and for the torsional fractures the distance from the tip, length and direction of unwinding were recorded. All defects In this analysis a file was considered to have a defect if it had unwound or had fractured (either type) of fracture. There were 1232 such files:

Any defect (unwound or fractured)

Frequency Percent Valid Percent Cumulative Percent

No 5927 82.8 82.8 82.8 Yes 1232 17.2 17.2 100.0

Valid

Total 7159 100.0 100.0

Endodontists: a strong confounding variable

It is reasonable to assume that there is no real scientific interest in differences between endodontists in defect rates. It may be of interest practically to know how much variation there is, and obviously the differences could be important to potential patients, but in terms of comparisons of file features, the variable “endodontist” is a potential confounding variable: it may be associated with the file characteristics, and is itself, potentially, a variable that explains some of the differences in outcome. In these circumstances, we wish to adjust for endodontist differences. That is, in making inferences about the impact of file characteristics on defect rates, we need to take into account endodontist differences.

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It turns out that this is a particularly difficult challenge in these data, and for that reason this issue is explored in some depth here. There were very large differences in the defect rate by endodontist, varying between 0.7% (Number 13) to 91.2% (Number 2). All endodontists had a reasonable sample size, so these differences are real, and they are substantial by any measure, since they virtually span the total range of possibilities (from 0% to 100%).

Endodontist * Any defect (unwound or fractured) Crosstabulation

215 19 23491.9% 8.1% 100.0%

22 227 2498.8% 91.2% 100.0%

809 37 84695.6% 4.4% 100.0%

1108 112 122090.8% 9.2% 100.0%

555 37 59293.8% 6.3% 100.0%

857 34 89196.2% 3.8% 100.0%

465 86 55184.4% 15.6% 100.0%

161 12 17393.1% 6.9% 100.0%

232 48 28082.9% 17.1% 100.0%

114 16 13087.7% 12.3% 100.0%

412 178 59069.8% 30.2% 100.0%

267 259 52650.8% 49.2% 100.0%

144 1 14599.3% .7% 100.0%

566 166 73277.3% 22.7% 100.0%

5927 1232 715982.8% 17.2% 100.0%

Count% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within Endodontist

Number01

Number02

Number03

Number04

Number05

Number06

Number07

Number08

Number09

Number10

Number11

Number12

Number13

Number14

Endodontist

Total

no yes

Any defect (unwound orfractured)

Total

The characteristics of the files used by endodontists also differed markedly. In such a situation, interpreting the associations between file characteristics and the

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occurrence of defects needs particular care, since both conditions that define a confounding variable are present to a great extent. In extreme cases it may be impossible to separate the effects of two variables statistically. For example, consider the association between endodontist and brand:

Endodontist * BRAND Crosstabulation

Count

0 0 0 0 0 0 234 2340 2 0 0 247 0 0 2497 386 0 70 378 2 3 8460 0 0 164 196 860 0 12205 17 0 51 519 0 0 5920 0 0 0 891 0 0 8910 0 0 0 551 0 0 5510 0 0 0 1 0 172 1730 0 0 0 0 0 280 2800 3 127 0 0 0 0 1302 171 0 0 251 166 0 5900 0 0 0 0 0 526 526

144 0 1 0 0 0 0 1452 57 0 0 473 172 28 732

160 636 128 285 3507 1200 1243 7159

Number01Number02Number03Number04Number05Number06Number07Number08Number09Number10Number11Number12Number13Number14

Endodontist

Total

Flexma GT HERO OS ProFil ProTap QuantecBRAND

Total

The brand “HERO” was almost unique to Number 10, and was also almost the

only brand Number 10 used. A similarly strong association occurred between

“Flexma” and Number 13. This has the implication that univariate associations

between outcomes of interest and one of the variables (e.g. brand) are almost

impossible to interpret: it is necessary to fit a statistical model that takes into

account several variables simultaneously.

A simple example, considering the variable “X-taper” (cross-section and taper)

demonstrates the point. The basic table of the defect rate by this variable is as

follows:

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Cross-section and taper * Any defect (unwound or fractured) Crosstabulation

892 351 1243

71.8% 28.2% 100.0%

265 23 288

92.0% 8.0% 100.0%

1043 157 1200

86.9% 13.1% 100.0%

3727 701 4428

84.2% 15.8% 100.0%

5927 1232 7159

82.8% 17.2% 100.0%

Count% within Cross-sectionand taperCount% within Cross-sectionand taperCount% within Cross-sectionand taperCount% within Cross-sectionand taperCount% within Cross-sectionand taper

S-shaped

Tri fixe

Tri var

Triple-U

Cross-sectionand taper

Total

no yes

Any defect (unwound orfractured)

Total

This table shows that the defect rate was greater in the Triple-U files than the Tri-variable files, for example. However, the direction of this effect is reversed after accounting for endodontist in a logistic regression. This is due to the confounding between the two variables; one of the most glaring aspects affecting this comparison is that endodontist Number 2 had a very high defect rate and used Triple-U files exclusively. Before proceeding further, we consider the difference in the defect rate by endodontist in more detail, by a simple descriptive analysis. The files are split up into the four file types, and the defect rate is examined by size and endodontist. This allows direct comparisons of the defect rate for fixed values of the other two variables. These may not be the only variables that should be considered, but they seem important. The file type pertaining to the particular table is given at the foot of the table. In order, they are S-shaped, Tri fixed, Tri variable and Triple-U; note that the Triple-U table is spread over three pages.

285

Endodontist * Any defect (unwound or fractured) * SIZE Crosstabulationa

4 4100.0% 100.0%

19 5 2479.2% 20.8% 100.0%

56 48 10453.8% 46.2% 100.0%

1 1 250.0% 50.0% 100.0%

80 54 13459.7% 40.3% 100.0%

10 10100.0% 100.0%

23 12 3565.7% 34.3% 100.0%

38 59 9739.2% 60.8% 100.0%

2 2100.0% 100.0%

71 73 14449.3% 50.7% 100.0%

215 19 23491.9% 8.1% 100.0%

2 1 366.7% 33.3% 100.0%

132 11 14392.3% 7.7% 100.0%

141 26 16784.4% 15.6% 100.0%

82 122 20440.2% 59.8% 100.0%

6 8 1442.9% 57.1% 100.0%

578 187 76575.6% 24.4% 100.0%

7 7100.0% 100.0%

26 12 3868.4% 31.6% 100.0%

4 4100.0% 100.0%

37 12 4975.5% 24.5% 100.0%

4 4100.0% 100.0%

22 5 2781.5% 18.5% 100.0%

2 2100.0% 100.0%

28 5 3384.8% 15.2% 100.0%

2 2100.0% 100.0%

27 5 3284.4% 15.6% 100.0%

17 10 2763.0% 37.0% 100.0%

2 2100.0% 100.0%

46 17 6373.0% 27.0% 100.0%

1 1100.0% 100.0%

22 22100.0% 100.0%

15 1 1693.8% 6.3% 100.0%

38 1 3997.4% 2.6% 100.0%

1 1100.0% 100.0%

3 1 475.0% 25.0% 100.0%

1 1100.0% 100.0%

5 1 683.3% 16.7% 100.0%

3 1 475.0% 25.0% 100.0%

3 1 475.0% 25.0% 100.0%

5 5100.0% 100.0%

1 1100.0% 100.0%

6 6100.0% 100.0%

Count% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within Endodontist

Number08

Number09

Number12

Number14

Endodontist

Total

Number08

Number09

Number12

Number14

Endodontist

Total

Number01

Number03

Number08

Number09

Number12

Number14

Endodontist

Total

Number08

Number12

Number14

Endodontist

Total

Number08

Number12

Number14

Endodontist

Total

Number08

Number09

Number12

Number14

Endodontist

Total

Number08

Number09

Number12

Endodontist

Total

Number08

Number12

Number14

Endodontist

Total

Number12Endodontist

Total

Number12

Number14

Endodontist

Total

SIZE15

20

25

30

35

40

45

50

55

60

no yes

Any defect (unwound orfractured)

Total

Cross-section and taper = S-shapeda.

286

Endodontist * Any defect (unwound or fractured) * SIZE Crosstabulationa

3 3100.0% 100.0%

2 2100.0% 100.0%

26 13 3966.7% 33.3% 100.0%

2 2100.0% 100.0%

43 43100.0% 100.0%

1 1100.0% 100.0%

73 17 9081.1% 18.9% 100.0%

2 2100.0% 100.0%

1 1100.0% 100.0%

44 3 4793.6% 6.4% 100.0%

47 1 4897.9% 2.1% 100.0%

1 1100.0% 100.0%

94 5 9994.9% 5.1% 100.0%

2 2100.0% 100.0%

1 1100.0% 100.0%

40 40100.0% 100.0%

54 54100.0% 100.0%

96 1 9799.0% 1.0% 100.0%

1 1100.0% 100.0%

1 1100.0% 100.0%

1 1100.0% 100.0%

1 1100.0% 100.0%

Count% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within Endodontist

Number03

Number05

Number10

Number11

Number13

Number14

Endodontist

Total

Number03

Number05

Number10

Number13

Number14

Endodontist

Total

Number03

Number05

Number10

Number13

Endodontist

Total

Number05Endodontist

Total

Number10Endodontist

Total

SIZE20

25

30

35

45

no yes

Any defect (unwound orfractured)

Total

Cross-section and taper = Tri fixea.

287

Endodontist * Any defect (unwound or fractured) * SIZE Crosstabulationa

110 52 16267.9% 32.1% 100.0%

64 28 9269.6% 30.4% 100.0%

61 35 9663.5% 36.5% 100.0%

235 115 35067.1% 32.9% 100.0%

122 9 13193.1% 6.9% 100.0%

1 2 333.3% 66.7% 100.0%

123 11 13491.8% 8.2% 100.0%

1 1100.0% 100.0%

272 11 28396.1% 3.9% 100.0%

56 8 6487.5% 12.5% 100.0%

56 12 6882.4% 17.6% 100.0%

385 31 41692.5% 7.5% 100.0%

142 142100.0% 100.0%

1 1100.0% 100.0%

4 4100.0% 100.0%

147 147100.0% 100.0%

1 1100.0% 100.0%

142 142100.0% 100.0%

6 6100.0% 100.0%

4 4100.0% 100.0%

153 153100.0% 100.0%

Count% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within EndodontistCount% within Endodontist

Number04

Number11

Number14

Endodontist

Total

Number04

Number11

Endodontist

Total

Number03

Number04

Number11

Number14

Endodontist

Total

Number04

Number11

Number14

Endodontist

Total

Number03

Number04

Number11

Number14

Endodontist

Total

SIZE17

19

20

25

30

no yes

Any defect (unwound orfractured)

Total

Cross-section and taper = Tri vara.

288

Endodontist * Any defect (unwound or fractured) * SIZE Cross tabulation(a)

SIZE Any defect (unwound or fractured)

no yes Total

Endodontist Count 6 51 57 Number02 % within Endodontist 10.5% 89.5% 100.0%

Count 4 4 8 Number03 % within Endodontist 50.0% 50.0% 100.0%

Count 50 5 55 Number05 % within Endodontist 90.9% 9.1% 100.0%

Count 28 25 53 Number11 % within Endodontist 52.8% 47.2% 100.0%

Count 18 17 35

Number14 % within Endodontist 51.4% 48.6% 100.0%

15

Total Count 106 102 208 % within

Endodontist 51.0% 49.0% 100.0%

20 Endodontist Count 4 19 23 Number02 % within Endodontist 17.4% 82.6% 100.0%

Count 435 24 459 Number03 % within Endodontist 94.8% 5.2% 100.0%

Count 54 9 63 Number04 % within Endodontist 85.7% 14.3% 100.0%

Count 116 17 133 Number05 % within Endodontist 87.2% 12.8% 100.0%

Count 3 3 Number10 % within Endodontist 100.0% 100.0%

Count 118 95 213 Number11 % within Endodontist 55.4% 44.6% 100.0%

Count 54 24 78

Number14 % within Endodontist 69.2% 30.8% 100.0%

Total Count 784 188 972 % within

Endodontist 80.7% 19.3% 100.0%

289

(continued) 25 Endodontist Count 6 77 83 Number02

% within Endodontist 7.2% 92.8% 100.0%

Count 151 5 156 Number03 % within Endodontist 96.8% 3.2% 100.0%

Count 58 7 65 Number04 % within Endodontist 89.2% 10.8% 100.0%

Count 24 24 Number05 % within Endodontist 100.0% 100.0%

Count 1 1 Number08 % within Endodontist 100.0% 100.0%

Count 28 12 40 Number11 % within Endodontist 70.0% 30.0% 100.0%

Count 69 25 94

Number14 % within Endodontist 73.4% 26.6% 100.0%

Total Count 336 127 463 % within

Endodontist 72.6% 27.4% 100.0%

30 Endodontist Count 39 39 Number02 % within Endodontist 100.0% 100.0%

Count 73 3 76 Number03 % within Endodontist 96.1% 3.9% 100.0%

Count 103 20 123 Number04 % within Endodontist 83.7% 16.3% 100.0%

Count 66 6 72 Number05 % within Endodontist 91.7% 8.3% 100.0%

Count 459 33 492 Number06 % within Endodontist 93.3% 6.7% 100.0%

Count 229 74 303 Number07 % within Endodontist 75.6% 24.4% 100.0%

Count 44 6 50 Number11 % within Endodontist 88.0% 12.0% 100.0%

Count 122 25 147

Number14 % within Endodontist 83.0% 17.0% 100.0%

Total Count 1096 206 1302 % within

Endodontist 84.2% 15.8% 100.0%

290

(continued) 35 Endodontist Count 4 40 44 Number02

% within Endodontist 9.1% 90.9% 100.0%

Count 98 98 Number03 % within Endodontist 100.0% 100.0%

Count 73 3 76 Number05 % within Endodontist 96.1% 3.9% 100.0%

Count 398 1 399 Number06 % within Endodontist 99.7% .3% 100.0%

Count 236 12 248 Number07 % within Endodontist 95.2% 4.8% 100.0%

Count 31 31 Number11 % within Endodontist 100.0% 100.0%

Count 95 13 108

Number14 % within Endodontist 88.0% 12.0% 100.0%

Total Count 935 69 1004 % within

Endodontist 93.1% 6.9% 100.0%

40 Endodontist Count 21 21 Number03 % within Endodontist 100.0% 100.0%

Count 51 4 55 Number04 % within Endodontist 92.7% 7.3% 100.0%

Count 77 1 78 Number05 % within Endodontist 98.7% 1.3% 100.0%

Count 14 14 Number11 % within Endodontist 100.0% 100.0%

Count 35 2 37

Number14 % within Endodontist 94.6% 5.4% 100.0%

Total Count 198 7 205 % within

Endodontist 96.6% 3.4% 100.0%

291

(continued) 45 Endodontist Count 2 1 3 Number02

% within Endodontist 66.7% 33.3% 100.0%

Count 1 1 Number03 % within Endodontist 100.0% 100.0%

Count 46 46 Number05 % within Endodontist 100.0% 100.0%

Count 13 13 Number11 % within Endodontist 100.0% 100.0%

Count 12 12

Number14 % within Endodontist 100.0% 100.0%

Total Count 74 1 75 % within

Endodontist 98.7% 1.3% 100.0%

50 Endodontist Count 8 8 Number03 % within Endodontist 100.0% 100.0%

Count 54 54 Number04 % within Endodontist 100.0% 100.0%

Count 10 10

Number05 % within Endodontist 100.0% 100.0%

Total Count 72 72 % within

Endodontist 100.0% 100.0%

60 Endodontist Count 3 3 Number03 % within Endodontist 100.0% 100.0%

Count 51 1 52 Number05 % within Endodontist 98.1% 1.9% 100.0%

Count 3 3 Number11 % within Endodontist 100.0% 100.0%

Count 15 15

Number14 % within Endodontist 100.0% 100.0%

Total Count 72 1 73 % within

Endodontist 98.6% 1.4% 100.0%

70 Endodontist Count 2 2

Number03 % within Endodontist 100.0% 100.0%

Total Count 2 2 % within

Endodontist 100.0% 100.0%

80 Endodontist Count 8 8

Number05 % within Endodontist 100.0% 100.0%

Total Count 8 8

292

% within Endodontist 100.0% 100.0%

90 Endodontist Count 2 2 Number03 % within Endodontist 100.0% 100.0%

Count 33 33 Number05 % within Endodontist 100.0% 100.0%

Count 5 5 Number11 % within Endodontist 100.0% 100.0%

Count 4 4

Number14 % within Endodontist 100.0% 100.0%

Total Count 44 44 % within

Endodontist 100.0% 100.0%

a Cross-section and taper = Triple-U Perusal of the four tables above reveals that there is indeed a considerable difference between endodontists in their defect rates; for some of the particular combinations of file types and sizes, there are substantial numbers of files, and large variation between endodontists in the defect rates; hence, unequivocal evidence of real endodontist differences.

Analysis of effects of interest We now consider the effects of file size, taper size and number of uses on the overall defect rate. Consider the cross-tabulation of endodontist and cross-section and taper.

293

Endodontist * Cross-section and taper Crosstabulation

Count

234 0 0 0 2340 0 0 249 2493 7 2 834 8460 0 860 360 12200 5 0 587 5920 0 0 891 8910 0 0 551 551

172 0 0 1 173280 0 0 0 280

0 127 0 3 1300 2 166 422 590

526 0 0 0 5260 145 0 0 145

28 2 172 530 7321243 288 1200 4428 7159

Number01Number02Number03Number04Number05Number06Number07Number08Number09Number10Number11Number12Number13Number14

Endodontist

Total

S-shaped Tri fixe Tri var Triple-UCross-section and taper

Total

Note the following:

• The fixed taper triangular files were only used by two endodontists in any substantial numbers, and for these two endodontists they were virtually the only file type they used.

• Endodontist 14 is the only subject who used both S-shaped files and other types in non-negligible numbers.

• There are three endodontists who used variable taper triangular files and Triple-U files in substantial numbers.

If these observations are taken together with the (separate) observation that there are very large differences in the defect rates between endodontists, the conclusion is that the only sensible comparison is between Tri var and Triple-U, based on endodontists 4, 11 and 14. The following figure represents defect rates for this subset of data, considering also size.

294

0

20

40

60

Number04Tri var

20 40 60 80

Number11Tri var

Number14Tri var

20 40 60 80

Number04Triple-U

Number11Triple-U

20 40 60 80

0

20

40

60

Number14Triple-U

Size

defe

ctpe

rc

This graph shows some clear patterns: • If the size of the file is large, the defect rate is very small; there is almost a

threshold beyond which files do not fail. • For the Tri var types, the relationship between defect rate and size was

very similar across the three endodontists (the observation of 67% for Number 11 was based on 2 defects out of 3 files).

• The decline in defect rate with increasing size is rather more rapid for Tri var than for Triple-U.

A logistic regression was carried out using data from these three endodontists, restricted to files sizes < 45, and file types Tri var and Triple-U. The variables included in the model were endodontist, size, cross-section and taper, tapersize, length and number of uses.

The following table shows the results.

295

Categorical Variables Codings

423 1.000337 .000166 1.000594 .000

Triple-UTri var

Cross-sectionand taper

Number11Number14

Endodontist

Frequency (1)Paramete

Variables in the Equation

-.137 .260 .280 1 .597 .872-.080 .019 17.285 1 .000 .923.404 .276 2.140 1 .144 1.498

3.213 4.798 .448 1 .503 24.855-.128 .044 8.452 1 .004 .879-.211 .052 16.085 1 .000 .8104.154 1.118 13.794 1 .000 63.664

ENDODONT(1)SIZEXTAPER(1)TAPERSIZLENGTHNO._USESConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, XTAPER, TAPERSIZ, LENGTH, NO._USES.a.

By virtue of the inclusion of the variable number of uses, this analysis has excluded endodontist 4, who did not record this variable. The output from the logistic regression model is interpreted as follows.

1. Firstly, it is important to distinguish between categorical explanatory variables, such as endodontist and (cross-section and taper), and continuous explanatory variables, such as size. The categorical variables give estimates that reflect the difference of all but one of the categories compared to an arbitrary baseline category. Hence the table of categorical variables codings is important; in this case, ENDODONT(1) reflects the comparison of Number 11 with Number 14, and XTAPER(1) reflects the comparison of Triple-U with Tri var. The size of the estimate is interpreted as follows. If the estimate is positive, the index category had a higher proportion of the events of interest, relative to the baseline category, and if it is negative, the index category had a lower proportion of the events of interest. The continuous explanatory variables have a single parameter estimate. If this is positive, it means that the larger the variable, the greater the probability of the event of interest, in this case, any defect. If it is negative, it means that the larger the variable, the smaller the probability of the event of interest.

296

2. The column headed “Sig.” gives the P-value for the effects.

In this analysis, then, the effects of endodontist, cross-section and taper, and taper size were not statistically significant. Size, length and number of uses were all negatively associated with the defect rate; that is, the larger the size (or length or number of uses), the lower the probability of any defect. This analysis was repeated omitting number of uses, so as to include endodontist Number 4 in the analysis.

Categorical Variables Codings

338 1.000 .000256 .000 1.000671 .000 .000728 1.000537 .000

Number11Number04Number14

Endodontist

Triple-UTri var

Cross-sectionand taper

Frequency (1) (2)Parameter coding

Variables in the Equation

58.287 2 .000.058 .144 .161 1 .688 1.060

-1.222 .175 48.966 1 .000 .295-.136 .012 121.762 1 .000 .8731.165 .156 55.529 1 .000 3.207

-2.907 2.985 .949 1 .330 .055-.170 .033 26.847 1 .000 .8445.388 .826 42.583 1 .000 218.780

ENDODONTENDODONT(1)ENDODONT(2)SIZEXTAPER(1)TAPERSIZLENGTHConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, XTAPER, TAPERSIZ, LENGTH.a.

Using the S-shaped files only, an analysis of endodontist, size, taper size and length was carried out:

297

Variables in the Equation

176.866 5 .000-2.847 .482 34.826 1 .000 .058

.062 .408 .023 1 .879 1.064-1.596 1.305 1.495 1 .221 .203-2.947 .512 33.166 1 .000 .053-1.732 .437 15.708 1 .000 .177

-.050 .010 24.901 1 .000 .9515.705 3.550 2.582 1 .108 300.247-.091 .037 5.921 1 .015 .9133.143 1.046 9.022 1 .003 23.166

ENDODONTENDODONT(1)ENDODONT(2)ENDODONT(3)ENDODONT(4)ENDODONT(5)SIZETAPERSIZLENGTHConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, TAPERSIZ, LENGTH.a.

This shows that endodontist was highly significant statistically.

Using the Tri var files only, an analysis of endodontist, size, tapersize, length and number of uses was carried out:

Variables in the Equation

-.180 .264 .468 1 .494 .835-.140 .207 .459 1 .498 .869

-22.509 25.679 .768 1 .381 .000-.072 .066 1.186 1 .276 .930-.142 .075 3.540 1 .060 .8684.446 3.547 1.571 1 .210 85.248

ENDODONT(1)SIZETAPERSIZLENGTHNO._USESConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, TAPERSIZ, LENGTH, NO._USES.a.

Endodontist was not significant; for this analysis, there were only two endodontists.

If number of uses is removed from the model, the following results were obtained:

298

Variables in the Equation

10.143 3 .017-18.317 25385.595 .000 1 .999 .000

-.247 .269 .844 1 .358 .781-.817 .261 9.804 1 .002 .442-.279 .153 3.305 1 .069 .757

-40.345 18.165 4.933 1 .026 .000-.066 .053 1.501 1 .221 .9376.720 2.876 5.458 1 .019 828.819

ENDODONTENDODONT(1)ENDODONT(2)ENDODONT(3)SIZETAPERSIZLENGTHConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, TAPERSIZ, LENGTH.a.

For this data set endodontist was significant at the 2% level (P = 0.017). Using the Tri fixed files only, an analysis of endodontist, size, tapersize and length was carried out:

Variables in the Equation

18.983 5 .00219.215 27794.837 .000 1 .999 2.2E+08

-.289 30997.165 .000 1 1.000 .74925.177 27794.837 .000 1 .999 8.6E+1041.263 39752.867 .000 1 .999 8.3E+1715.549 27794.837 .000 1 1.000 5662485

-.398 .109 13.300 1 .000 .67231.730 20.080 2.497 1 .114 6.0E+13

-.077 .171 .205 1 .651 .925-11.437 27794.838 .000 1 1.000 .000

ENDODONTENDODONT(1)ENDODONT(2)ENDODONT(3)ENDODONT(4)ENDODONT(5)SIZETAPERSIZLENGTHConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, TAPERSIZ, LENGTH.a.

In this data set endodontist was highly significant statistically (P = 0.002). Using the Triple-U files only, an analysis of endodontist, size, tapersize and length was carried out:

299

Variables in the Equation

554.222 9 .000-21.973 23168.340 .000 1 .999 .000

.170 .170 1.000 1 .317 1.1853.887 .264 217.461 1 .000 48.783

-2.880 .237 147.201 1 .000 .056-1.240 .228 29.494 1 .000 .289-1.260 .223 31.986 1 .000 .284-1.086 .222 23.865 1 .000 .338

.609 .188 10.482 1 .001 1.83822.790 40192.970 .000 1 1.000 7.9E+09

-.103 .010 116.135 1 .000 .90316.162 3.077 27.591 1 .000 1.0E+07

-.190 .032 35.220 1 .000 .8275.070 .838 36.596 1 .000 159.102

ENDODONTENDODONT(1)ENDODONT(2)ENDODONT(3)ENDODONT(4)ENDODONT(5)ENDODONT(6)ENDODONT(7)ENDODONT(8)ENDODONT(9)SIZETAPERSIZLENGTHConstant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: ENDODONT, SIZE, TAPERSIZ, LENGTH.a.

Summarising the findings with respect to endodontist:

• There are very large differences in the defect rate by endodontist. The standard χ2 of association gives 1792 on 13 df (P < 0.001). Due to the very strong confounding between variables, it is necessary to allow for the effects of file characteristics to assess the strength of this association more appropriately.

• There is such a strong association between endodontist and file type (cross-section and taper) that a model in which both variables are included is very limited in its scope; it is restricted to three endodontists only.

• For each file type separately, logistic regression analyses were carried out with “any defect (unwound or fracture)” as the binary outcome, and endodontist, size, taper size and length as the explanatory variables. Due to variations in the types of files used by endodontists, this resulted in data from varying number of endontisists for each file type, specifically, S-shaped: 6, Tri var: 4, Tri fixed: 6 and Triple-U: 9. For each of the four file types, the association between endodontist and defect rate, adjusted for size, taper size and length, was highly statistically significant. Specifically, the results for the endodontist / defect rate association were: S-shaped files: χ2 = 177, df = 5, P < 0.001; Tri var: χ2 = 10.1, df = 3, P = 0.017; Tri fixed: χ2 = 19.0, df = 5, P = 0.002; Triple-U: χ2 = 554, df = 9, P < 0.001.

AP: Chi-Square Test: Fracture rates Expected counts are printed below observed counts T1-Fract T1-NO Total 1 3 231 234 11.54 222.46

300

2 5 244 249 12.28 236.72 3 10 836 846 41.72 804.28 4 56 1164 1220 60.16 1159.84 5 5 587 592 29.19 562.81 6 5 887 892 43.98 848.02 7 0 551 551 27.17 523.83 8 2 170 172 8.48 163.52 9 15 265 280 13.81 266.19 10 0 130 130 6.41 123.59 11 39 551 590 29.09 560.91 12 148 378 526 25.94 500.06 13 1 144 145 7.15 137.85 14 64 668 732 36.09 695.91 Total 353 6806 7159 Chi-Sq = 6.318 + 0.328 + 4.314 + 0.224 + 24.112 + 1.251 + 0.287 + 0.015 + 20.047 + 1.040 + 34.552 + 1.792 + 27.169 + 1.409 + 4.953 + 0.257 + 0.103 + 0.005 + 6.410 + 0.332 + 3.374 + 0.175 + 574.467 + 29.795 + 5.290 + 0.274 + 21.576 + 1.119 = 770.988 DF = 13, P-Value = 0.000 AQ: Chi-Square Test: Unwinding rates Expected counts are printed below observed counts T1-Unwin T1-NO Total 1 16 218 234 28.73 205.27

301

2 222 27 249 30.57 218.43 3 27 819 846 103.87 742.13 4 56 1164 1220 149.79 1070.21 5 32 560 592 72.69 519.31 6 29 863 892 109.52 782.48 7 86 465 551 67.65 483.35 8 10 162 172 21.12 150.88 9 33 247 280 34.38 245.62 10 16 114 130 15.96 114.04 11 139 451 590 72.44 517.56 12 111 415 526 64.58 461.42 13 0 145 145 17.80 127.20 14 102 630 732 89.88 642.12 Total 879 6280 7159 Chi-Sq = 5.641 + 0.790 + 1.2E+03 +167.765 + 56.892 + 7.963 + 58.730 + 8.220 + 22.775 + 3.188 + 59.201 + 8.286 + 4.975 + 0.696 + 5.854 + 0.819 + 0.055 + 0.008 + 0.000 + 0.000 + 61.153 + 8.559 + 33.360 + 4.669 + 17.803 + 2.492 + 1.635 + 0.229 = 1740.351 DF = 13, P-Value = 0.000 AR: Chi-Square Test: Endo 11, all defects Expected counts are printed below observed counts e11-all e11-no d Total TRV 40 128 168 50.68 117.32

302

TU 138 284 422 127.32 294.68 Total 178 412 590 Chi-Sq = 2.252 + 0.973 + 0.897 + 0.387 = 4.510 DF = 1, P-Value = 0.034 MTB > %fisher Executing from file: C:\Program Files\MTBWIN\MACROS\fisher.MAC Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 40,128,138,284 Data Display P-values for Fisher's exact test - (Left) : 0.020 (Right) : 0.988 (2-tail): 0.037

AS: Chi-Square Test: Endo 14, all defects, S-shaped vs rest Expected counts are printed below observed counts e14-all e14-no d Total S 13 15 28 6.35 21.65 Rest 153 551 704 159.65 544.35 Total 166 566 732 Chi-Sq = 6.965 + 2.043 + 0.277 + 0.081 = 9.366 DF = 1, P-Value = 0.002

CHAPTER 8

AT: Chi-Square Test: Strokes – 5 vs 10 Expected counts are printed below observed counts Dirty Clean Total 5 25 106 131 16.58 114.42 10 16 177 193 24.42 168.58 Total 41 283 324 Chi-Sq = 4.280 + 0.620 +

303

2.905 + 0.421 = 8.225 DF = 1, P-Value = 0.004 AU: Chi-Square Test: Presoak – 15 min vs 30 min Expected counts are printed below observed counts Dirty Clean Total 15 14 48 62 7.48 54.52 30 7 105 112 13.52 98.48 Total 21 153 174 Chi-Sq = 5.676 + 0.779 + 3.142 + 0.431 = 10.029 DF = 1, P-Value = 0.002 AV: Chi-Square Test: Ultrasonication – 15min vs 45 min Expected counts are printed below observed counts Dirty Clean Total 15 1 38 39 4.33 34.67 45 6 18 24 2.67 21.33 Total 7 56 63 Chi-Sq = 2.564 + 0.321 + 4.167 + 0.521 = 7.572 DF = 1, P-Value = 0.006 2 cells with expected counts less than 5.0 MTB > %fisher Executing from file: C:\PROGRAM FILES\MTBWIN\MACROS\fisher.MAC Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 1,38,6,18 Data Display P-values for Fisher's exact test - (Left) : 0.010 (Right) : 0.999 (2-tail): 0.010

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AW: Chi-Square Test: Strokes – 5 vs 10 Expected counts are printed below observed counts Dirty Clean Total 5 8 17 25 3.79 21.21 10 2 39 41 6.21 34.79 Total 10 56 66 Chi-Sq = 4.684 + 0.836 + 2.856 + 0.510 = 8.886 DF = 1, P-Value = 0.003 1 cells with expected counts less than 5.0 MTB > %fisher Executing from file: C:\PROGRAM FILES\MTBWIN\MACROS\fisher.MAC Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 8,17,2,39 Data Display P-values for Fisher's exact test - (Left) : 1.000 (Right) : 0.005 (2-tail): 0.005

AX: Chi-Square Test: Presoak – 15min vs 30min Expected counts are printed below observed counts Dirty Clean Total 15 8 13 21 3.44 17.56 30 2 38 40 6.56 33.44 Total 10 51 61 Chi-Sq = 6.033 + 1.183 + 3.167 + 0.621 = 11.004 DF = 1, P-Value = 0.001 1 cells with expected counts less than 5.0 Fisher's Exact Test Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+

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DATA> 8,13,2,38 Data Display P-values for Fisher's exact test - (Left) : 1.000 (Right) : 0.002 (2-tail): 0.002

AY: Fisher's Exact Test: Ultrasonic, 15 min vs 30 min. Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 0,32,2,7 Data Display P-values for Fisher's exact test - (Left) : 0.044 (Right) : 1.000 (2-tail): 0.044 AZ: Fisher's Exact Test: Ultrasonic, 15 min vs 45 min. Enter the values for a, b, c and d for the 2x2 table Column 1 2 +--------+ Row 1 | a b | 2 | c d | +--------+ DATA> 0,32,5,7 Data Display P-values for Fisher's exact test - (Left) : 0.001 (Right) : 1.000 (2-tail): 0.001

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Minerva Access is the Institutional Repository of The University of Melbourne

Author/s:Parashos, Dr Peter

Title:The diffusion of innovation in dentistry: factors associated with the adoption of rotary nickel-titanium endodontic instruments

Date:2004-01

Citation:Parashos, Dr Peter (2004) The diffusion of innovation in dentistry: factors associated withthe adoption of rotary nickel-titanium endodontic instruments, PhD thesis, School of DentalScience, The University of Melbourne.

Publication Status:Unpublished

Persistent Link:http://hdl.handle.net/11343/39037

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