Jakub Mateusz Gryko

Fifth year, OF group 15

Analysis of biomechanics of glass fiber posts and ferrule, using

finite elements method as analytical tool. Systemic review.

Master’s Thesis

Supervisor

Lecturer Rimantas Ožiūnas

Kaunas, year (12 pt)

2

LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

MEDICAL ACADEMY

FACULTY OF PROSTHODONTICS

Analysis of biomechanics of glass fiber posts and ferrule, using finite elements method as

analytical tool. Systemic review. Stiklo pluošto kaiščių ir "movos" efekto biomechanikos analizė baigtinių elementų metodu.

Sisteminė litaratūros apžvalga.

Master’s Thesis

The thesis was done

by student ................................................ Supervisor ............................................... (signature) (signature)

..................................................... ............................................................................. (name surname, year, group) (degree, name surname)

.............................. 20…. .............................. 20…. (day/month) (day/month)

Kaunas, year (12 pt)

3

EVALUATION TABLE OF THE MASTER’S THESIS OF THE TYPE OF SYSTEMIC

REVIEW OF SCIENTIFIC LITERATURE

Evaluation: .....................................................................................................................................

Reviewer: ................................................................................................................................... (scientific degree. name

and surname)

Reviewing date: ...........................................

No.

MT parts

MT evaluation aspects

Compliance with MT

requirements and

evaluation Yes Partially No

1

Summary

(0.5 point)

Is summary informative and in compliance withthe thesis content and requirements?

0.3 0.1 0

2 Are keywords in compliance with the thesis essence?

0.2 0.1 0

3 Introduc-

tion, aim

and tasks

(1 point)

Are the novelty, relevance and significance of the work justified in the introduction of the thesis?

0.4 0.2 0

4 Are the problem, hypothesis, aim and tasks formed clearly and properly?

0.4 0.2 0

5 Are the aim and tasks interrelated? 0.2 0.1 0 6

Selection

criteria of

the studies,

search

methods and

strategy

(3.4 points)

Is the protocol of systemic review present? 0.6 0.3 0

7 Were the eligibility criteria of articles for the

selected protocol determined (e.g., year, language,

publication condition, etc.)

0.4

0.2

0

8

Are all the information sources (databases with

dates of coverage, contact with study authors to

identify additional studies) described and is the last

search day indicated?

0.2

0.1

0

9

Is the electronic search strategy described in such a

way that it could be repeated (year of search, the

lastsearchday;keywordsandtheircombinations;

number of found and selected articles according to

the combinations of keywords)?

0.4

0.1

0

10

Is the selection process of studies (screening,

eligibility, included in systemic review or, if

applicable, included in the meta-analysis)

described?

0.4

0.2

0

11 Is the data extraction method from the articles

(types of investigations, participants, interventions,

analysed factors, indexes) described?

0.4

0.2

0

12 Are all the variables (for which data were sought

and any assumptions and simplifications made)

listed and defined?

0.4

0.2

0

13 Are the methods, which were used to evaluate the risk of bias of individual studies and how this

0.2 0.1 0

4

information is to be used in data synthesis, described?

14 Were the principal summary measures (risk ratio, difference in means) stated?

0.4 0.2 0

15

Systemiza-

tion and

analysis of

data

(2.2 points)

Is the number of studies screened: included upon assessment for eligibility and excluded upon giving

the reasons in each stage of exclusion presented?

0.6

0.3

0

16

Are the characteristics of studies presented in the included articles, according to which the data were

extracted (e.g., study size, follow-up period, type of

respondents) presented?

0.6

0.3

0

17

Are the evaluations of beneficial or harmful outcomes for each study presented? (a) simple

summary data for each intervention group; b) effect

estimates and confidence intervals)

0.4

0.2

0

18 Are the extracted and systemized data from studies presented in the tables according to individual

tasks?

0.6

0.3

0

19

Discussion

(1.4 points)

Are the main findings summarized and is their relevance indicated?

0.4 0.2 0

20 Are the limitations of the performed systemic review discussed?

0.4 0.2 0

21 Does author present the interpretation of the results?

0.4 0.2 0

22

Conclusions

(0.5 points)

Do the conclusions reflect the topic, aim and tasks of the Master’s thesis?

0.2 0.1 0

23 Are the conclusions based on the analysed material? 0.2 0.1 0 24 Are the conclusions clear and laconic? 0.1 0.1 0

25

References

(1 point)

Is the references list formed according to the requirements?

0.4 0.2 0

26 Are the links of the references to the text correct? Are the literature sources cited correctly and

precisely?

0.2

0.1

0

27 Is the scientific level of references suitable for Master’s thesis?

0.2 0.1 0

28 Do the cited sources not older than 10 years old

form at least 70% of sources, and the not older than

5 years – at least 40%?

0.2

0.1

0

Additional sections, which may increase the collected number of points

29 Annexes Do the presented annexes help to understand the analysed topic?

+0.2 +0.1 0

30 Practical

recommen-

dations

Are the practical recommendations suggested and

are they related to the received results?

+0.4

+0.2

0

31 Were additional methods of data analysis and their

results used and described (sensitivity analyses,

meta-regression)?

+1

+0.5

0

5

*Remark: the amount of collected points may exceed 10 points.

Reviewer’scomments:

32 Was meta-analysis applied? Are the selected

statistical methods indicated? Are the results of

each meta-analysispresented?

+2

+1

0

General requirements, non-compliance with which reduce the number of points

33

General

require-

ments

Is the thesis volume sufficient (excluding annexes)?

15-20 pages (-2 points)

<15 pages (-5 points)

34 Is the thesis volume increased artificially?

-2 points -1 point

35 Does the thesis structure satisfy the requirements of Master’s thesis?

-1 point -2 points

36 Is the thesis written in correct language, scientifically, logically and laconically?

-0.5 point -1 points

37 Are there any grammatical, style or computer literacy-related mistakes?

-2 points -1 points

38 Is text consistent, integral, and are the volumes of its structural parts balanced?

-0.2 point -0.5 points

39 Amount of plagiarism in the thesis. >20%

(not evaluated)

40

Is the content (names of sections and sub-

sections and enumeration of pages) in

compliance with the thesis structure and

aims?

-0.2 point

-0.5 points

41

Are the names of the thesis parts in

compliance with the text? Are the titles of

sections and sub-sections distinguished

logically and correctly?

-0.2 point

-0.5 points

42 Are there explanations of the key terms and abbreviations (if needed)?

-0.2 point -0.5 points

43 Is the quality of the thesis typography

(quality of printing, visual aids, binding)

good?

-0.2 point

-0.5 points

*In total (maximum 10 points):

6

TABLE OF CONTENTS

SUMMARY ........................................................................................................................................ 7

INRODUCTION ................................................................................................................................. 8

Aim and Tasks ............................................................................................................................... 10

SELECTION CRITERIA OF THE STUDIES. SEARCH METHODS AND STRATEGY ............ 10

2. Methods ..................................................................................................................................... 11

2.1. Inclusion/Exclusion Criteria ................................................................................................... 12

2.2. Online search of databases ..................................................................................................... 12

SYSTEMIZATION AND ANALYSIS OF DATA .......................................................................... 13

3. Results .......................................................................................................................................13

DISCUSSION ................................................................................................................................... 19

CONCLUSION ................................................................................................................................. 23

CLINICAL IMPLICATIONS...................................................................................................... .............24

REFERENCES .................................................................................................................................. 25

7

Summary

Objectives: The aim of this study is to present a review of the contemporary literature regarding the

finite element method used in dentistry, the positive effect of ferrule and glass fiber restoration and

type of software that was used to create 3D models.

Material and Methods: Three different databases were investigated during literature search. A total

amount of 407 articles from PubMed (2009-2018), ScienceDirect (2009-2018) and Google Scholar

(2014-2018) were investigated by title and abstract as shown in study flow below. (Fig. 1) In

addition to the electronic search, a hand search of reference lists, of full articles was made.

Results: This study compared glass fibre posts with other types of posts, usually metal and the

positive effect of ferrule preparation over the restored tooth. The final results show that GFP and

ferrule effect have positive influence on stress distribution. The only exception were mandibular

lateral incisors which show worse fracture resistance properties when additional preparation of the

endodontically treated tooth was performed.

Conclusions: Ferrule effect seem to have very good prognosis for teeth restored with glass fibre

posts. Endodontically treated teeth with higher and uniform ferrule show lower stresses at adhesive

interfaces, that may lead to decrease the chance of clinical failure. The most important is first mm of

ferrule because the stresses are mainly ditributed in this region. Restorations with glass fiber posts

without ferrule effect had much higher Maximum principal stress values (Mpa) compared to teeth

restored with ferrule effect. Teeth restored without ferrule were more prone to increased stresses and

risk of fracture. The absence of a ferrule was directly related with increased strain values on buccal

and proximal surfaces for cast post and core. Post length did not have influence for stress

distribution in the dental tissues. So far we can terminate that there are several correct ways to

perform the FEA if the results obtained are reliable. It can be suggested to create a protocol to

follow when analysing tissues with FEA, this would provide more transparent and understandable

records.

Keywords: "finite elements method", "post and core", "glass", "fiber", "ferrule effect" and

additionally, to precise the search in Google Scholar "dentistry" as keyword was added.

8

INTRODUCTION

Dentistry since many years is struggling not only with oral diseases, but also with limitations

to the mechanical properties of materials used during restorations. The clinicians are looking for

new methods to investigate the abilities of adaptation of materials used in daily dentist's routine and

now as finite element (FE) analysis is widely used in dental biomechanical studies we should

consider if the method is beneficial.

The finite element method (FEM) is a numerical method for solving problems of engineering

and mathematical physics. It is also called as finite element analysis (FEA). The method is possible

to use in structural analysis of heat transfer, fluid flow, mass transport, and electromagnetic

potential. When the problem is formulated by the finite element method the results are presented in a

system of algebraic equations. To solve the problem, the programme subdivides a large problem into

smaller, simpler parts that are called finite elements. Finite element method then uses different

options from the calculus of variations to approximate a solution by minimizing an associated error

function. With this method, in computer mechanics (CAE - computer aided engineering) the

structural strength of the structure is tested, it simulates strains, stresses, displacements, heat flow

and liquid flow. Dynamics, kinematics and statics of machines as well as electrostatic, magnetostatic

and electromagnetic interactions are also investigated in different branches of medicine, like cardio

surgeries, maxillofacial surgeries or even planning surgical excisions of tumors.

FEM calculations can be carried out in two-dimensional space (2D), where discretization

comes to dividing the area into triangles. This solution allows you to calculate the values appearing

in the cross-section of a given system. There are, however, some limitations related to the specificity

of the problem being solved.

Due to the progress of computer technology in recent years, the majority of simulation

packages are equipped with the ability to solve issues in three-dimensional space (3D).

Discretization usually involves the division of the area into tetrahedrons. Such modeling is devoid of

the fundamental limitations of 2D technology, but is much more demanding in terms of memory and

computing power of the computer. [1]

9

Prosthetic dentists are using this technique more, and more often to understand stresses and

strains apearing in the tooth after endodontic restoration. Endodontically treated teeth are considered

more prone to fracture than vital teeth [2, 3]. Loss of dental tissue structure during instrumentation

of the canal or the crown is causing the change in the biomechanical behavior of the tooth [2]. The

presence of the ferrule, protection of healthy, intact, radicular and coronal tooth structures have huge

influence in strengthening weakened teeth [4,5]. By ferrule it is meant - parallel walls of dentin

extending above the step of the preparation [6]. When the crown is casted with designed ferrule it

provides a protective collar around the tooth which is reducing stresses within a tooth, such action is

called the ferrule effect [5].

It is suggested to use glass fiber post when a prefabricated post is about to be applied [7]. The

posts are showing homogeneous stress distribution to the dentins external surface alike dental tissues

and reduce the stresses in the tooth. It's because of low elastic modulus materials which are used in

GFP [8]. It has been claimed that, ferrule incorporation improves the fracture resistance by

distributing forces to the saved structures when it comes to restoring an endodontically treated tooth

with a post and core, and crown [9].

To be able to understand the behaviour of the particles 2D or 3D models are being created

using different methods of scanning and proper software eg. PRO Engineer software

(Parametric Technology Corporation, USA) for modeling [7], Algor Fempro software (ALGOR,

Inc. Pittsburgh, USA) for stress analysis [10], for numerical simulations ABAQUS/CAE

(SIMULIA, Version 6.10, Providence, RI, USA) [11], for tissue identification Mimics 16.0

(Materialise, Leuven,Belgium) [10, 12]. Von Mises stresses are then being analyzed which allows

the researchers to know the limitations of the materials (such as glass-fiber posts) which later got

under tension of miscellaneous forces depending on the study. Von Mises proposed values used to

determine if a given material will yield or fracture. It is mostly used for flexible materials, such as

metals, glass-fiber, carbon fiber but also bone and other anatomical structures. The von Mises yield

criterion states that if the von Mises stress of a material under load is equal or greater than the yield

limit of the same material under simple tension then the material will yield [13]. Authors to better

determine the properties of the object are also using Young's modulus, to understand the relationship

between stress (force per unit area) and strain (proportional deformation) in a material [14]. The role

10

of elastic properties in the post and core restorations have been extensively studied over the years.

Literature includes numerous researches with different outcomes regarding the elastic modulus.

Aim:

The aim of this study is to present a review of the contemporary literature regarding the finite

element method used in analyzing biomechanics of ferrule effect and glass fiber posts as well as

metal posts and type of software that was used to create 3D models.

Tasks:

1. To analyze the importance of uniformity and height of ferrule using FEA.

2. To investigate biomechanical behavior of glass fiber post and core complex in case of absent

ferrule, using FEA.

3. To see if the ferrule effect is important for cast post and core complex, using FEA.

4. To verify influence of posts length on biomechanics of the complex, using FEA.

5. To see what kind of software was most likely used for investigation of biomechanics of post and

core complex.

SELECTION CRITERIA OF THE STUDIES. SEARCH METHODS AND STRATEGY

METHODS

This systematic review was conducted in accordance with the Preferred Reporting Items for

Systematic reviews and Meta-Analyses (PRISMA) guidelines [15].

Three different databases were investigated during literature search. A total amount of 407

articles from PubMed (2009-2018), ScienceDirect (2009-2018) and Google Scholar (2014-2018)

were investigated by title and abstract as shown in study flow below. (Fig. 1) In addition to the

electronic search, a hand search of reference lists, of full articles was made.

11

Figure 1, Study flow.

12

The Population, Intervention, Comparison, Outcome, Study (PICOS) framework was used to

form the following search strategy as seen in the table. (Fig. 2)

Figure 2. PICOS Table

The inclusion criteria were:

1. Clinical studies.

2. Studies related to restorative treatment of endodontically treated teeth.

3. Studies using finite elements method to investigate the problem.

4. Full-text.

5. Not older than 10 years and human filters were applied.

Keywords used in the search were: "finite elements method", "post and core", "glass",

"fiber", "ferrule effect" and additionally, to precise the search in Google Scholar "dentistry" as

keyword was added.

Articles were analyzed by title and abstract, and excluded according to the following criteria:

1. Language different than english,

2. Older than 10 years,

3. Title not matching 'fiber glass' and 'ferrule',

4. Animal study.

5. Nine studies were also removed because of the duplication.

13

Filters application can be seen in Fig. 3.

Figure 3. Filters application

Database and date of search Filters and results

Keywords order: No filter Human 10

years

5

years

English

languag

e

PubMed 02.23.2018

Keywords order: ((((((finite elements method)

AND post) AND core) AND glass) AND fiber)

AND ferrule)

10 6 6 3 N/A

GoogleScholar 02.23.2018

Keywords order: finitie, elements, method, post,

core, glass, fiber, ferrule effect, dentistry

925 N/A N/A 366 334

ScienceDirect 02.23.2018

Keywords order: finite elements method, post and

core, glass fiber, ferrule

72 N/A 36 N/A N/A

If the title and abstract had not enough information according the inclusion criteria, the full

article was read. The full text reading of related publications and the data extraction were carried

out.

SYSTEMIZATION AND ANALYSIS OF DATA

RESULTS

The initial electronic search resulted in 407 publications, of which 399 were excluded after

title and/or abstract assessment and foreign language. Based on the inclusion criteria, 8 papers were

selected for full-text reading. Of these, all were accepted for the review. (Fig. 1). Total of 8 in-vitro

studies were analyzed.

14

Authors Scanning

method

Programs

used

2D

or

3D

Type of

posts

Load

and

angle

Ferrule height

and uniformity

Results

Zhang et al Laser-

based 3D

digitizing

system

Finite

element (FE)

models with

different

ferrule

configuratio

n

were

obtained

using

ScanIP1

module

All

numerical

simulations

were

performed

using

ABAQUS

3D Quartz

fiber

post

350N ,

45

angle

degree

with

respect

to the

long

axis of

the

tooth

6 models

Group 1: no

ferrule

Group 2: 1 mm

labial ferrule

and 0 mm

palatal ferrule.

Group 3: 2 mm

labial ferrule

and 0 mm

palatal ferrule.

Group 4: 0 mm

labial ferrule

and 1 mm

palatal ferrule.

Group 5: 0 mm

labial ferrule

and 2 mm

palatal ferrule.

Group 6:

uniform 2mm

ferrule

Group 6 presented the highest fracture

resistance, whereas, the lowest

fracture resistance appeared in the

Group 1.

The study showed that there were no

significant differences among Group

1, 2 or 3, in which the teeth have no

palatal ferrule.

With the increase of palatal ferrule

height in Groups 4 and 5 the ultimate

loads increased.

A clear stress concentrations noticed

around the palatal margin of cement

layer in groups 1, 2 and 3.

The bigger the palatal ferrule the more

anti-fracture ability of adhesive

cement. The labial ferrule had less

influence in this case.

In all of the FE models the loads

which caused the initial damage in the

glass ionomer cement were similar.

Rodrigues et

al

CBCT

Identifying

software

Mimics 16.0

STL design

and meshing

software

3Matic 8.0,

remeshed-

REMESH

3D Smooth

conical

fiber

post

155N Right maxillary

incisor -

uniform

Left maxillary

incisor - not

uniform

Stresses in the root dentin and fiber

post of the left maxillary central

incisor were higher than the right

maxillary central incisor.

Highest stress concentration - on the

distal region of the left maxillary

central incisor, where the ferrule was

smaller.

15

Jelena

Juloski,

Davide

Apicella,

Marco

Ferrari

Laser-

based 3D

digitizing

scan of a

plaster cast

The scanned

profiles were

assembled in

a 3D wire

frame

structure

using a 3D

CAD, Auto-

cad 12 and

parametric

solid

modeler

Pro-

Engineering

4 solid

models were

imported to

the FEA

software

ANSYS

3D Glass

fiber

posts

200N

load, 45

degrees

1 model

simulated a

premolar

restored with a

crown in

absence of

dentin ferrule.

3 models

simulated teeth

with different

uniform ferrule

heights.

Comparing to the model without

ferrule it was presented that tensile

stress observed in the composite

abutment is significantly higher than

those observed in models with ferrule.

FE-models with different height

shared similar stress values and

distribution patterns in the 1st mm of

the ferrule area.

Considering this finding, it may be

stated that ferrule height does not

influence the stress state neither in the

ferrule structure nor the root. Still the

presence of ferrule effect is crucial for

good prognosis for restored tooth.

Tensile stress state in the ferrule

structure of 3 FE-models with

designed ferrule does not reach the

dentin tensile failure limit ranging

from 105 to 135 MPa.

Beata

Dejak,

Andrzej

Młotkowski

Dental 3D

Scanner

D250, a

CT of the

tooth

was made

with a

GXCB-

500/i-CAT

system.

3Shape

Dental

Designer

CAD

software

used to

process

obtained the

scans.

FEA

software –

ANSYS 14.

3D GFP

and

NiCr

alloy

100N,

130

degrees

to the

long axis

of the

tooth

3 models with

ferrule effect,

glass fiber post.

2 models

without ferrule

effect glass

fiber post.

3 models with

ferrule effect,

cast NiCr posts

2 models

without ferrule

effect, cast

NiCr posts

In models with ferrule stresses in

dentin were reduced to 11 MPa, while

without ferrule stresses in dentin

increased to 17.6 MPa. Ferrule effect

in teeth reduces mvM stresses in

dentin by 42–60% and in posts by 20–33%, depending of of posts materials.

The mvM stresses in post and core

were concentrated around the core-

post junction, in the tooth cervix.

In GFP posts in teeth with ferrule

according Tsai-Wu ratio presented no

risk of fracture.

The highests stresses were observed in

metal post and core without ferrule

99.7 MPa.

No matter if the posts are made of

metal or FRC, are not prone to

fractures under physiological loads, if

they are ideally cemented in anterior

teeth.

Post length did not have an influence

on stresses in crowns and dentin.

16

Savychuk et

al

CT scans 3D

computer-

aided design

FEA -

Algor.

3D Gold

cast

post

and

core

Fiber

post

140N

oblique

loading,

angled at

135

degrees

from the

vertical

tooth

axis

A total of 10

models were

created.

5 models of

lateral incisors:

1 vital

1 CP with

uniform ferrule

1 CP without

ferrule

1FP with

uniform ferrule

1 FP without

ferrule

5 models of

canine:

1 vital

1 CP with

uniform ferrule

1 CP without

ferrule

1FP with

uniform ferrule

1 FP without

ferrule

Glass fiber posts showed a not clear

ferrule effect on the MnPS parameters

in different teeth, lowering the stress

values in the canine (33%) but

increasing them in the mandibular

lateral incisor (42%), if compared with

the models without ferrule - no impact

on the MxPS parameters was noticed.

The ferrule preparation infuenced the

stress generated in the dentin of the

mandibular lateral incisor and

mandibular canine.

The ferrule effect in lateral incisor

increased MPa in the dentin when in

the canine the dentin stresses were

decreased.

Ferrule effect in teeth restored with

GFP for lateral incisor and canine

reducied MPa in the core.

Lateral incisor without ferrule

experienced reduced maximum

principal stress (MPa) for gold cast

post and core (70.6 MPa) when for the

model with ferrule it was higher (73.4

MPa).

Roscoe et al The 3D

numerical

models of

an intact

maxillary

canine

were

possessed

from

DT3D.

The 3D

models were

created with

computer-

aided design

software

Rhinoceros

3D

FEA

software

NeiNASTR

N

3D Cast

post

and

core

Glass

fiber

post

Load

from 0 to

100N

4 models with

uniform ferrule

were used;

1 GFP with

uniform ferrule

1 GFP without

ferrule effect

1 cast post and

core with

uniform ferrule

effect

1 cast post and

core without

ferrule effect

The study showed significant

difference between teeth restored with

cast post and core, restored with glass

fiber post and teeth restored

with/without ferrule.

Restorations with glass fiber posts

with ferrule effect had much lower

Maximum principal stress values

(Mpa) compared to teeth restored

without ferrule and the traditional

casted NiCr with or without ferrule

effect.

The absence of a ferrule was directly

related with increased strain values on

buccal and proximal surfaces for all

groups.

17

Rajambigai

et al

CT The

modeling

was done

using

software

called PRO

Engineer,

Stress

analysis -

ANSYS

3D Parallel

sided

prefabri

cated

titaniu

m post

parallel

sided

prefabri

cated

glass

fiber

post

Load of

100N

was

applied

with an

angle of

45

degrees

to the

long axis

of the

tooth

4 models were

created:

-Titanium post

with uniform

ferrule

-Titanium post

without ferrule

-Glass fiber

post with

uniform ferrule

-Glass fiber

post without

ferrule

Glass fiber post with a ferrule of

coronal dentin had the lowest stress

value.

The highest stress value was obtained

for Titanium post without a ferrule of

coronal dentin.

Santos et al A contact

scanner

was used

for

acquisition

of the

external

morpholog

y data

(MDX-40;

Roland

Co, Osaka,

Japan) by

scanning

an

extracted

sound

maxillary

central

incisor.

The external

geometry

was obtained

by 3D

Bundle

STL files

imported to

computer-

aided design

(CAD) soft

ware

Rhinoceros

3D

Meshing -

Femap

3D Glass

fiber

post

Casted

post

and

core

100N

oblique

loading

8 models

2 models of

CPC with

uniform ferrule

and different

post length

2 models of

CPC without

ferrule and with

different post

length

2 models of

GFP with

uniform ferrule

and different

post length

2 models of

GFP without

ferrule and with

different post

length

Relined GFP models showed

homogeneous stress distribution to the

dentin external surface and related

structures which was similar to the

behavior found for a healthy tooth.

CPC models elevated stress in the root

canal regardless of ferrule presence.

Increased tensile stress inside the root

canal for CPC models.

The presence of ferrule was important

for both post systems used in this

study for the rehabilitation.

The worst condition for stress

distribution was observed for the CPC

with ferrule.

The stress distribution of relined GFP

models were not influenced by the

post length, no matter if the ferrule

was presented.

Although the researchers used different types of loadings they came up with similar results.

Most of them noticed that usage of glass fiber posts and ferrule effect had positive outcome for

stress distribution over dentine and restorative materials that were used.

Surprising data were presented by Savychuk et al. [10] they analyzed a total of 10 3D models

under 140N oblique loading, angled at 135 degrees from the vertical tooth axis. During their

investigation of canine and lateral incisor in mandible, they spotted an interesting outcome. Minimal

18

principal stresses in mandibular lateral incisors were bigger in model with designed ferrule, than in

models without ferrule or canines with or without ferrule. The MPa increased in lateral incisor by

42% when in canine it decreased by 33%.

Santos et al. [8], by creation of 8 3D models they claimed that the stress distribution of

relined glass fiber posts models were not influenced by the post length, no matter if the ferrule was

present or not (similar results were presented by Dejak and Młotkowski [16]). On the other hand, the

post length was more important for the cast post and core models in which stresses were

concentrated in a smaller area. Better stress distribution in GFP is probably achieved because of the

materials elastic modulus which is similar to dentine.

Zhang et al. [11] and Rodrigues et al. [12], noticed that the most important part of the

ferrule design is in palatal region. The bigger the palatal ferrule the more effective was increase of

anti-fracture ability of adhesive cement. On the other hand, the labial ferrule had less influence in

this case.

Roscoe et al. [9] showed significant difference between teeth restored with cast post and core, glass

fiber post and teeth restored with/without ferrule. Restorations with glass fiber posts with ferrule effect had

much lower Maximum principal stress values (Mpa) compared to teeth restored without ferrule. The

traditional casted NiCr with or without ferrule effect had bigger Mpa than GFP. The absence of a ferrule was

directly related with increased strain values on buccal and proximal surfaces for all groups.

As well as Roscoe et al., Juloski et al. [17] state that the presence of ferrule effect is crucial for good

prognosis for restored tooth. Comparing to the model without ferrule it was presented that tensile stress

observed in the composite abutment was significantly higher than those observed in models with ferrule. FE-

models with different height shared similar stress values and distribution patterns in the 1st mm of the ferrule

area. Considering this finding, it may be stated that ferrule height does not influence the stress state neither in

the ferrule structure nor the root. However, stress state in the ferrule structure of 3 FE-models with designed

ferrule does not reach the dentin tensile failure limit ranging from 105 to 135 MPa.

Computer analyzes performed by the authors are presented in the annexes.

19

DISCUSSION

Endodontically treated teeth with severe loss of coronal tissues are most favorably restored

by using cast posts, prefabricated glass fiber and metal posts supported with composite cores.

Prefabricated posts made of titanium are becoming more and more popular among metal posts

because of their favorable physical properties and resistance to corrosion [18]. When it comes to

non-metal posts, glass fiber reinforced composite posts are increasing in popularity due to their

translucency and flexibility [7].

Uncontrolled preparation or caries-caused loss of tooth structure decreases the retention of

future restorations, making them more problematic to apply. It is well known that after root canal

treatment, dentin faces changes not only in its physiologic characteristics but also in its physical

properties, leading to decrease of immature collagen levels. This can proceed to reduced hardness

and resistance to shearing [19]. Dehydration of dentine tubules because of the use of etching, air

drying and drilling, also occurs. It is causing a decrease in the value of Young’s modulus, in

accordance a tooth is more prone to fractures [20]. The problem primarily appears as a result of

tensile and shear stresses [16]. The development of computers and increase of their calculating

abilities, allow that the finite element analysis can be used for prognosis of fracture (or even fracture

pattern). It is possible by analyzing the models of the tissue scans achieved by processing them in

3D software. The experiments lead under experimental loading provide crucial data about tensile

and shear strength values of a material, tissue or an interface between them. This allows practitians

to choose the materials for restorations more accurate.

When restored with elastic posts, the tooth, cement and post will all deform during

mastication. Most favorably, the failure appears at the post-cement-dentin interface as this is an

adhesive connection and the weakest point at the same time. The more the coronal structure of the

tooth is destroyed the bigger will be the stress on the adhesive joint [21]. When the endodontic

treatment of a tooth is completed, the whole structure must be protected due to risk of fracture

during functional loading. As other studies showed, FE analysis has been often used to analyze

stress and strain distributions in teeth restored with different types of post and core, adhesive

techniques or ferrule designs [22-24]. A ferrule is defined as a 360 degrees metal band of the crown

which is surrounding matching preparation of dentin walls [4]. The current study evaluated stress

distribution in teeth restored with glass fiber or metal posts, with or without ferrule and different

20

height and uniformity of it taking into consideration load application on the crown surfaces. Inside

failures of endodontically treated teeth may be due to the fracture of a component or debonding at

the adhesive connections between the parts [11].

Dejak and Młotkowski [16] in their study, using finite element method, stated that the

presence of ferrule in a tooth treated with a post and core restoration reduces stresses in dentin, post

and luting cement applied around the post. As proved in their analysis the usage of posts and cores

in teeth with ferrule effect makes teeth more resistant, but increases stresses in dentin in teeth if the

supragingival structure is missing. High stresses in the cement were mainly spotted around short

fiber glass reinforced posts without ferrule. Not preparing a ferrule leads to significant tensile

contact stresses around posts and the area around the root may predispose to micro-leakage in the

borders of restoration and debonding of the post. The calculations performed by Dejak and

Młotkowski [16] allowed to determine that the higher the Young’s modulus of the post materials, the

smaller modified von Mises failure criterion (mvM) stresses applied on dentin and cement around

posts. Simillar results of FE analysis of ferrule effect and post and core restorations were achieved

by other researchers [22, 25-28] As specified by Pereira [29], ferrule causes a statistically

significant increase in tooth resistance to fracture. An interesting study was as well presented by

Lima et al. [30] The research tested the maximum loading that can be sustained by teeth restored

with and without ferrule. It showed that teeth with ferrule effect The maximum load for tooth with

ferrule at which it failed was 573.3 N, when without ferrule the force that the tooth was capable to

resist was 275,3 N [31]. According to a study performed by Zhang et al. [11], the best for support

and retention, if the amount of tissues allow for it, is a 2mm uniform ferrule. Group 6 containing a

model with 2mm uniform ferrule presented in the reasearch had the highest fracture resistance.

However, the lowest fracture resistance appeared in the Group 1which had 0mm ferrule.

Rodrigues et al. [12] came up with more precise statement. When the load is applied to a

structure, deformation and stresses are initiated. To simulate the masticatory forces, this study used

contact forces applied through the opposing incisal teeth. After analyzing the anatomic finite

element model, which they received by transferring cone-beam computed tomography image into

the software, they found that ferrule uniformity is more important than ferrule height unlike claimed

by Zhang et al[11]. The stress investigation verified that the ferrule design is an important factor in

the distribution of stresses in glass fiber posts and root dentin. They also agreed that ferrule

uniformity might be the key, even though it would have smaller height. As presented in this study

21

the right maxillary central incisor had more uniform ferrule and was approximately 1.6 +/- 0.2mm

high. In second model the ferrule of the left maxillary central incisor was higher medially - 3.5 mm

and left with no ferrule distally - 0.3 mm. Stresses in the root dentin and fiber post of the left

maxillary central incisor were higher than the right maxillary central incisor. Authors observed

highest stress concentration on the distal region of the left maxillary central incisor in root dentin

and also in the root canal, where the ferrule was smaller and less uniform. Authors proved that

ferrule had positive effect on distribution of tensile contact stresses around posts in teeth without

supragingival structure.

In choosing a post system not only ferrule and physical/physiological changes have

important meaning. One of the most determining factors is related to the post length. A couple of

studies have reported positive results in the rehabilitation of endodontically treated teeth when the

post length was the same or higher than the crown length [30, 31], when for a shorter posts, a high

rate of root fractures was found [33]. Santos-Filho et al. [28, 34] has stated that the length of

metallic posts is directly related to the fracture resistance abilities of endodontically treated teeth. In

presented study of Santos et al., [8] finite element analysis showed that the stress distribution of cast

posts and cores was negatively affected by the reduction of post length. The stiffness of the material

is transmitting higher stress concentration in the thin dentin wall for the weakened tooth. When

finally the whole restored complex fails because of the fatigue, the stresses are transferred to dentin,

causing even vertical root fractures [11]. In the absence of palatal ferrule, the root canal associated

with the use of a glass fiber post showed a stress concentration at the connection between the resin

composite and the post. This situation may cause that this adhesive interface will lead to post

debonding and resin core fractures, resulting in bacterial colonization and periapical lesions [11].

On the other hand Dejak and Młotkowski [16] claimed in their study that post length had an

insignificant effect on mvM stresses in roots, no matter of post material [ANNEX 2]. Widely

spreading finite element analysis allows other authors to perform their tests more homogenously.

Some of them also stated that they found no significant differences between post length, distribution

of their stresses and the values obtained in the study [35]. Also Rodriguez-Cervantes et al. observed

there was no connection between length of posts (4-14 mm) and fracture force [36]. Similar to

Zhang et al. [11], Nissan et al. validated that post length does not affect tooth strength where there is

22

a 2 mm ferrule [37]. So, when choosing a correct post for restoration the post length should be

considered and the post:crown ration should be lower than 1:1.

Rajambigai et al. [7] comparing the titanium post with, the glass fiber post agreed that post-

cement-dentin interface is the area where failure is more likely to initiate, so the stresses were

measured in this region. Glass fiber post with a ferrule of coronal dentin had the lowest stress value,

when the highest stress value was obtained for titanium post without a ferrule of coronal dentin.

What is more, Santos et al. [38] reported that the risk of fracture occurs in the composite core and/or

it is higher in the post than in the root, which makes teeth restored with a glass fiber post less likely

to fail.

What's surprising, not every tooth is acting similar to its neighbor. Data collected by

Savychuk et al. [10] provided very interesting outcome. Namely, the mechanical properties of

mandibular incisors are different than those of bigger mandibular teeth. They admitted that no

matter if the ferrule was present or what type of post and core material was used, models of lateral

incisors showed higher tensile and compressive stress values than mandibular canines. This was not

the only study revealing such behavior. Gluskin et al. [339] wrote that the characteristics of

mandibular lateral incisors separate them from teeth with bigger and uniform roots. This finding

was also proved by Deutsch et al. [40], who found that the smaller was the root diameter the more

prone to fractures it was, no matter what was the type of post used. In this case all potst had

standardized 1.5 mm diameter. There is a close relationship between the fracture resistance of a

tooth and thickness of the dentin covering the post as verified in another studies [41-42]. The same

studies also found that preparation of ferrule had a role in stress distribution in dentin and also

depended on a a type of tooth. Savychuk et al. [10] concluded that the preparation of ferrule

increased tensile stress in dentin, almost to the critical level of dentin withstanding limit [43], when

for mandibular canine the reaction to stresses was opposite. As proposed by the above autor, this

phenomenon might be described by the anatomy of mandibular lateral incisors. Narrow

buccolingual and mesiodistal root dimensions of these teeth, allowing to prepare smaller chamfer

width and ferrule thickness which will lead to expansion of high stress fields. It is necessary to keep

this results in mind when designing a prosthetic restoration of mandibular incisors.

The software and methods of scanning used by the researchers were the most varied part in

this study. For example Zhang et al. [11], used two different programs to receive six accurate

23

models with different ferrule designs when Juloski et al. [17], decided to apply three programs, to

obtain four models with different ferrule heights and Roscoe et al. [9] used only two. There is no

agreement on one diagnosing method which could be helpful in simplifying the results. Also, the

situation may be dictated by the years when the studies were performed or/and hardware capabilities.

Finite element analysis is a handful tool in calculating stress distribution in complex

structures. The results are provided without variation. The accuracy of the study depends on how the

model approaches reality. The huge advantage is that, it provides detailed information concerning

stress in a non-homogenous structure such as tooth. There is no need for human material, the

measurements can be corrected easily and simulation can be performed without risk of failing and

starting from the begining [17].

CONCLUSIONS

Based on the results of the present systematic review it can be concluded that glass fibre post

are the best choice for most of the clinical cases. However, the preparation in mandibular incisors

must be as least traumatic as possible to provide safe restoration without risk of fracture.

1. Endodontically treated teeth with higher and uniform ferrule show lower stresses at adhesive

interfaces, that may lead to decrease the chance of clinical failure. The most important is first mm of

ferrule because the stresses are mainly ditributed in this region.

2. Restorations with glass fiber posts without ferrule effect had much higher Maximum principal

stress values (Mpa) compared to teeth restored with ferrule effect. Teeth restored without ferrule

were more prone to increased stresses and risk of fracture.

3. The absence of a ferrule was directly related with increased strain values on buccal and proximal

surfaces for cast post and core. On the other hand CPC models presented elevated stress in the root

canal regardless of ferrule presence.

4. Post length did not have influence for stress distribution in the dental tissues when minimal 1:1

(root:crown) ratio was preserved.

24

5. The researchers used different types of software, provided by companies from all around the

world, to obtain their results. 2D or 3D models were being created using different methods of

scanning and proper software eg. PRO Engineer software (Parametric Technology Corporation,

USA) for modeling [7], Algor Fempro software (ALGOR, Inc. Pittsburgh, USA) for stress analysis

[10], for numerical simulations ABAQUS/CAE (SIMULIA, Version 6.10, Providence, RI, USA)

[11], for tissue identification Mimics 16.0 (Materialise, Leuven,Belgium) [10, 12] So far we can

terminate that there is several correct ways to perform the FEA if the results obtained are reliable. It

can be suggested to create a protocol to follow when analysing tissues with FEA, this would provide

more transparent and understandable records.

Clinical Implications

A ferrule has a positive impact on the mechanical stress values of restorative elements,

especially teeth restored with glass fiber posts. It is important to keep proper length of the post, ratio

at least 1:1 (root:crown), not for stress distribution but for proper retention of the complex. Glass

fiber posts should be a considered as main choice during restoring of endodontically treated teeth.

However, it is important to keep in mind that additional preparation for ferrule in mandibular incisors

leads to a considerable rise in stress in the dentin.

25

References

1. Daryl L. Logan. A first course in the finite element method. Cengage Learning. (2011)

2. Dietschi D, Duc O, Krejci I, Sadan A. Biomechanical considerations for the restoration of

endodontically treated teeth: a systematic review of the literature – Part 1. Composition and micro-

and macrostructure alterations. Quintessence Int 2007;38:733–43.

3. Tang W, Wu Y, Smales RJ. Identifying and reducing risks for potential fractures in

endodontically treated teeth. J Endod 2010;36:609–17.

4. Juloski J, Radovic I, Goracci C, Vulicevic ZR, Ferrari M. Ferrule effect: a literature review. J

Endod 2012;38:11–9.

5. Stankiewicz N, Wilson P. The ferrule effect. Dent Update 2008;35:222–8.

6. Sorensen JA, Engelman MJ. Ferrule design and fracture resistance of endodontically treated teeth.

J Prosthet Dent 1990;63:529–36.

7. Rajambigai A. “Comparison of Stress Distribution in a Maxillary Central Incisor Restored with

Two Prefabricated Post Systems with and without Ferrule Using Finite Element Method.” Journal Of

Clinical And Diagnostic Research, 2016,

8. Santos-Filho, PC Freitas, et al. “Influence of Ferrule, Post System, and Length on Stress

Distribution of Weakened Root-Filled Teeth.” Journal of Endodontics 2014;40:1874-1878.

9. Roscoe, M G, et al. “Influence of Alveolar Bone Loss, Post Type, and Ferrule Presence on the

Biomechanical Behavior of Endodontically Treated Maxillary Canines: Strain Measurement and

Stress Distribution.” The Journal of Prosthetic Dentistry 2013;110(2):116-126

10. Savychuk A et al. “Stress Generation in Mandibular Anterior Teeth Restored with Different

Types of Post-and-Core at Various Levels of Ferrule.” The Journal of Prosthetic Dentistry, 2017.

11. Zhang, Y.y., et al. “The Effects of Ferrule Configuration on the Anti-Fracture Ability of Fiber Post-

Restored Teeth.” Journal of Dentistry, 2015;43(1):117-125

12. Rodrigues, M De Paula, et al. “Patient-Specific Finite Element Analysis of Fiber Post and Ferrule

Design.” Journal of Endodontics, 2017;43(9):1539-1544

13. "Von Mises Criterion (Maximum Distortion Energy Criterion)". Engineer's edge. Retrieved 8

February 2018 (www.engineersedge.com)

14. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online

corrected version: (2006–) "modulus of elasticity (Young's modulus), E".

15. Liberati A, Altman DG, Tetzlaff J, Mulrow C, Gøtzsche PC, Ioannidis JP, et al. The PRISMA

statement for reporting systematic reviews and meta-analyses of studies that evaluate health care

26

interventions: explanation and elaboration. J Clin Epidemiol 2009;62:1-34

16. Dejak B and A Młotkowski. “The Influence of Ferrule Effect and Length of Cast and FRC Posts

on the Stresses in Anterior Teeth.” Dental Materials, 2013;29(9)

17. Juloski J, et al. “The Effect of Ferrule Height on Stress Distribution within a Tooth Restored

with Fibre Posts and Ceramic Crown: A Finite Element Analysis.” Dental Materials,

2014;30(12):1304-1315

18. Vaconecellos WA, Cimini CA, Albuquerque RC. Effect of the post geometry and material on the

stress distribution of restored upper central incisors using 3D finite element stress distributiom on

incisors with posts. JIPS. 2006;6:139-44.

19. Fernanda GP, Cecilia DF, Jceue M, Luiz FMS. Hypercementosis: a challenge for endodontic

therapy. RSBO. 2011;8(3):321-28.

20. Pierrisnard L, Bohin F, Renault P, Barquins M. Corono-radicular reconstruction of pulpless

teeth: A mechanical study using finite element analysis. J Prosthet Dent. 2002;88:442-48.

21. Torbjomer A, Lic O, Fransson B. A literature review on the prosthetic treatment of structurally

compromised teeth. Int J Prosthodont. 2004;17:369-75.

22. Sorensen JA, Engelman MJ. Ferrule design and fracture resistance of endodontically treated

teeth. J Prosthet Dent 1990;63:529–36.

23. da Silva NR, Raposo LH, Versluis A, Fernandes-Neto AJ, Soares CJ. The effect of post, core,

crown type, and ferrule presence on the biomechanical behavior of endodontically treated bovine

anterior teeth. J Prosthet Dent 2010;104:306–17.

24. Tan PL, Aquilino SA, Gratton DG, Stanford CM, Tan SC, Johnson WT, et al. In vitro fracture

resistance of endodontically treated central incisors with varying ferrule heights and configurations.

J Prosthet Dent 2005;93: 331–6.

25. Schmitter M, Rammelsberg P, Lenz J, Scheuber S, Schweizerhof K, Rues S. Teeth restored

using fiber-reinforced posts: in vitro fracture tests and finite element analysis. Acta Biomaterialia

2010;6:3747–754.

26. Eraslan O, Aykent F, Yucel MT, Akman S. The finite element analysis of the effect of ferrule

height on stress distribution at post-and-core-restored all-ceramic anterior crowns. Clinical Oral

Investigations 2009;13:223–227.

27. Pierrisnard L, Bohin F, Renault P, Barquins M. Corono-radicular reconstruction of pulpless

teeth: a mechanical study using finite element analysis. Journal of Prosthetic Dentistry 2002;88:442–448.

28. Santos-Filho PC, Castro CG, Silva GR, Campos RE, Soares CJ. Effects of post system and

length on the strain and fracture resistance of root filled bovine teeth. Int Endod J 2008;41:493-501.

27

29. Pereira JR, de Ornelas F, Conti PC, do Valle AL. Effect of a crown ferrule on the fracture

resistance of endodontically treated teeth restored with prefabricated posts. Journal of Prosthetic

Dentistry 2006;95:50–4.

30. Lima AF, Spazzin AO, Galafassi D, Correr-Sobrinho L, Carlini-Junior B. Influence of ferrule

preparation with or without glass fiber post on fracture resistance of endodontically treated teeth.

Journal of Applied Oral Science 2010;18:360–363.

31. Sokol DJ. Effective use of current core and post concepts. J Prosthet Dent 1984;52: 231–234.

32. Standlee JP, Caputo AA, Holcomb J, Trabert KC. The retentive and stress-distributing properties

of a threaded endodontic dowel. J Prosthet Dent 1980;44:398–404.

33. Holmes DC, Diaz-Arnold AM, Leary JM. Influence of post dimension on stress distribution in

dentin. J Prosthet Dent 1996;75:140–147.

34. Santos-Filho PC, Verissimo C, Soares PV, et al. Influence of ferrule, post system, and length on

biomechanical behavior of endodontically treated anterior teeth. J Endod 2014;40:119–123.

35. Ferrari M, Sorrentino R, Zarone F, Apicella D, Aversa R, Apicella A. Non-linear viscoelastic

finite element analysis of the effect of the length of glass fiber posts on the biomechanical behavior

of directly restored incisors and surrounding alveolar bone. Dental Materials Journal 2008;27:485–98.

36. Rodriguez-Cervantes PJ, Sancho-Bru JL, Barjau-Escribano A, Forner-Navarro L, Perez-

Gonzales A, Sanchez-Marin FT. Influence of prefabricated post dimensions on restored maxillary

central incisors. Journal of Oral Rehabilitation 2007;34:141–52.

37. Nissan J, Barnea E, Carmon D, Gross M, Assif D. Effect of reduced post length on the resistance

to fracture of crowned, endodontically treated teeth. Quintessence International 2008;39:179–82.

38. Santos AF, Meira JB, Tanaka CB, et al. Can fiber posts increase root stresses and reduce

fracture? J Dent Res 2010;89:587–591.

39. Gluskin AH, Radke RA, Frost SL, Watanabe LG. The mandibular incisor: rethinking guidelines

for post and core design. J Endod 1995;21:33-7.

40. Deutsch AS, Musikant BL, Cavallari J, Silverstein L, Lepley J, Ohlen K, et al. Root fracture

during insertion of prefabricated posts related to root size. J Prosthet Dent 1985;53:786-9.

41. Chen A, Feng X, Zhang Y, Liu R, Shao L. Finite element analysis of stress distribution in four

different endodontic post systems in a model canine. Biomed Mater Eng 2015;26:629-35.

42. Toman M, Toksavul S, Sarikanat M, Nergiz I, Schmage P. Fracture resistance of endodontically

treated teeth: effect of tooth coloured post material and surface conditioning. Eur J Prosthodont

Restor Dent 2010;18:23-30.

28

43. Shillingburg HT. Fundamentals of fixed prosthodontics. 3rd ed. Chicago: Quintessence; 2007. p.

119-54.

ANNEX 1 Rodriguez et al. (Modified von Mises stress results).

29

ANNEX 2 Dejak and Młotkowski (Maximal mvM stresses in materials in the models of teeth

restored with different posts and cores).

30

ANNEX 3 Dejak and Młotkowski (Distribution of stresses in different materials of the tooth

restored with FRC, F +).

31

ANNEX 4 Dejak and Młotkowski (Distribution of stresses in different materials of the tooth

restored with NiCr post 13mm length, F +)

32

33

ANNEX 5 Juloski et al. (Distribution of tensile and compressive stress with the interfaces).

34

ANNEX 6 Juloski et al. (Distribution of tensile and compressive stress within the restored tooth components).

35

ANNEX 7 Roscoe et al. (Stress distribution within dentine and bone structure).

36

ANNEX 8 Rajambigai et al. (Distribution of von Mises stress in model restored with glass fiber post, F -)

ANNEX 9 Rajambigai et al. (Distribution of von Mises stress in model restored with titanium post, F - and F +.

Distribution of von Mises stress in model restored with glass fiber post, F +).

37

ANNEX 10 Santos et al. (Stress distribution in teeth).

38

ANNEX 11 Savychuk et al. (Von Mises stress distribution patterns or mandibular incisors F + and F -),

ANNEX 12 Zhang et al. (The maximum principal stress ditribution in cement layer).