Commercially available archwire forms compared with normal dental arch forms in a japanese...

ORIGINAL ARTICLE

Commercially available archwire formscompared with normal dental arch forms ina Japanese population

Souichiro Oda,a Kazuhito Arai,b and Rizako Nakaharac

Tokyo, Japan

Introduction: The objective of this research was to evaluate commercially available preformed archwireforms compared with normal dental arch forms. Methods: Thirty mandibular dental casts were made oforthodontically untreated subjects with the most ideal occlusions, selected from among approximately3500 students at Nippon Dental University. Canine and first-molar widths were measured on the dental castswith a 3-dimensional laser scanning system. Twenty preformed mandibular archwires were scanned by usinga flatbed scanner. The archwire widths were measured at the level of the mean canine and first-molar depths,and then compared with the natural dental arch widths, considering bracket thickness, measured witha modified caliper. The results were statistically analyzed with the Mann-Whitney test. Results: The preformedarchwires that most closely matched the normal dental arch forms were the Orthos (Ormco, Glendora, Calif)and Vari-Simplex large (Ormco) types. The preformed archwires were significantly narrower than the normaldental arches at both the canine (P\0.05) and molar (P\0.01) levels. Conclusions: The variations in currentpreformed archwires do not correspond entirely with various arch forms in a group with ideal occlusion. Themost commonly used archwires are similar and can be considered imitations of the Roth arch form, which wasdesigned primarily for extraction patients in the 1970s. Therefore, preformed archwires that are approximately1 to 3 mm wider at the canine level and 2 to 5 mm wider at the first-molar level might be required for today’sorthodontic needs. (Am J Orthod Dentofacial Orthop 2010;137:520-7)

The invention of the edgewise appliance1 in thelate 1920s brought about the consideration ofthe relationship between the dental arch form

of a normal occlusion as a goal of orthodontic treat-ment on the one hand and the archwire form of ortho-dontic appliances on the other.2 In 1934, Chuck3

stated, ‘‘With edgewise arch appliance, arch formbecomes the basis of our treatment planning, becausein the use of the appliance we predetermine the archform and create an ideal archwire to which we movethe teeth.’’ The classic Bonwill-Hawley type of pre-formed stainless steel archwire blanks4 were intro-duced to improve the efficacy of orthodontic

From the Department of Orthodontics, Nippon Dental University School of

Life Dentistry, Tokyo, Japan.aAssistant professor.bProfessor and chair.cFormer professor and chair [deceased].

Partly supported by a grant-aid for Scientific Research from the Ministry of

Education, Culture, Sports, Science and Technology-Japan, No. 07407061

and 11470457.

The authors report no commercial, proprietary, or financial interest in the

products or companies described in this article.

Reprint requests to: Kazuhito Arai, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-

8159, Japan; e-mail, [email protected].

Submitted, December 2007; revised and accepted, April 2008.

0889-5406/$36.00

Copyright � 2010 by the American Association of Orthodontists.

doi:10.1016/j.ajodo.2008.04.025

520

treatment.5 When the preadjusted edgewise appliancewas introduced in the 1970s,6 preformed archwireblanks for this new system also became available.7

This new preformed archwire, designed by Andrewsbased on his extensive research on nonorthodontic nor-mal occlusion and the clinical experience of Roth,8

met with great success. With the spread of this appli-ance, a variety of archwire forms have been developedfor various reasons.9-12

To date, little research has been conducted on the ra-tionale behind the prefabricated archwire form. Moststudies in this area sought stable orthodontic results,and their findings have not varied.13,14 For example,Felton et al13 compared 10 kinds of archwires with thedental arch forms of 30 subjects with untreated normalocclusions selected from the 120-patient sample of An-drews.6 They successfully classified all 30 dental archforms into 10 archwire shapes and reported that 27%of the subjects fit the Vari-Simplex form from Ormco,and 20% were close to the Tru-Arch form fromOrmco/‘‘A’’ Company. On the other hand, Braunet al14 analyzed 16 popular nickel-titanium (NiTi) arch-wires and compared them with the mean shape of thedental arch. They reported that all sampled strong-sell-ing, preformed archwires were wider than the normaldental arch form.

mailto:[email protected]

Table I. The 8 kinds of brackets selected for this study

Bracket Manufacturer

MiniTwin Ormco/‘‘A’’ Company, Orange, Calif

Mini Diamond Ormco, Glendora, Calif

Mini Master American Orthodontics, Sheboygan, Wis

Elite Opti-MIM Ortho Organizers, San Marcos, Calif

MicroArch GAC International, Bohemia, NY

American Journal of Orthodontics and Dentofacial Orthopedics Oda, Arai, and Nakahara 521Volume 137, Number 4

Therefore, it is necessary to study preformed arch-wire forms to increase the efficacy of tooth movementand to achieve stability of orthodontic treatment. Thepurpose of this study was to evaluate whether the vari-ous commercially available orthodontic archwire formsare comparable with the diversity of natural normal den-tal arch forms.

Victory 3M Unitek, Monrovia, Calif

Metal Bracket Dentsply, Sankin, Japan

NU Edge-LN TP Orthodontics, LaPorte, Ind

Table II. The 20 preformed archwires selected for thisstudy

Archwire form Manufacturer

Accu Form GAC International, Bohemia, NY

Broad Arch (large) Ormco, Glendora, Calif

Broad Arch (small) Ormco, Glendora, Calif

Natural Arch Form I American Orthodontics, Sheboygan, Wis

Natural Arch Form II American Orthodontics, Sheboygan, Wis

Natural Arch Form III American Orthodontics, Sheboygan, Wis

Ortho Form I 3M Unitek, Monrovia, Calif

Ortho Form II 3M Unitek, Monrovia, Calif

Ortho Form III 3M Unitek, Monrovia, Calif

Orthos (large) Ormco, Glendora, Calif

Orthos (small) Ormco, Glendora, Calif

Pro Form Ortho Organizers, San Marcos, Calif

Smooth Arch Form Oral Care, Tokyo, Japan

Standard Form GAC International, Bohemia, NY

Tru-Arch (medium) Ormco/‘‘A’’ Company, Orange, Calif

Tru-Arch II (medium) Ormco/‘‘A’’ Company, Orange, Calif

Tynilloy (large) Dentsply-Sankin, Tokyo, Japan

Tynilloy (small) Dentsply-Sankin, Tokyo, Japan

Vari-Simplex (large) Ormco, Glendora, Calif

Vari-Simplex (small) Ormco, Glendora, Calif

MATERIAL AND METHODS

From a total population of approximately 3500 stu-dents at Nippon Dental University, 30 orthodonticallyuntreated subjects (15 men, 15 women; mean age, 23years 2 months) were clinically examined accordingto the following inclusion criteria: no history of ortho-dontic treatment; Angle Class I molar relationshipwith arch form symmetry and minimal arch-length dis-crepancy; complete dentition, excluding third molars;ideal overjet and overbite; no prosthetic crowns andminimal restorations; minimal signs of occlusal attri-tion; and balanced facial esthetics (no significant dis-crepancies noted). About 100 sets of dental casts werethen made, and the most ideal Class I occlusions wereselected for analysis.15 The mandibular arch was ana-lyzed for this study, because therapeutic possibilitiesin the mandible are more limited than in the maxilla,the maxillary arch form is strongly associated with themandible, and also maintaining mandibular caninewidth is an essential element in achieving stable ortho-dontic treatment results.10,13,16,17

Eight kinds of brackets for the central incisor, ca-nine, and first molar with 0.022-in slots from 7 manu-facturers were selected to obtain the mean bracketbase thickness (Table I).

Twenty kinds of preformed NiTi archwires from 8manufacturers were selected for analysis (Table II). Al-though we evaluated NiTi archwires, each manufactureralso produces preformed stainless steel archwires iden-tical in design to the NiTi archwires.

Mean bracket thicknesses were used for the distancebetween the facial axis point (FA point) and the bracketslot point (BS point). A ceramic sphere (diameter, 4.75mm) was attached to 1 tip of a digital caliper (Digimaticcaliper, NTD12-15C, Mitutoyo, Kawasaki, Japan) to fitthe curvature of the bracket base. Brackets were thentied with elastic ligatures to a 0.0215 3 0.028-in stain-less steel wire. The distances between the center of thebracket mesh base and the base of the bracket slots forthe central incisor, canine, and molar were measuredby the modified caliper in 0.01 mm resolution (Fig 1).

The means and standard deviations of bracket thick-nesses at the mandibular central incisor, canine, and first

molar were 1.34 6 0.16, 0.75 6 0.11, and 0.73 6 0.08mm, respectively.

Thirty mandibular dental casts were scanned and an-alyzed by using a noncontact 3-dimensional orthodonticcast measuring system (Surflacer VMS-250R, UNISN,Osaka, Japan).18 The FA point for 14 teeth (from bothsides of the central incisors to the second molars)were plotted on the surface of a cloud data set froma 3-dimensionally digitized mandibular dental cast ac-cording to the original anatomic definition of thepoints.6 In addition, the 30 sets of 14 x- and y-coordi-nates of the FA points for each dental arch were ana-lyzed by using Excel 2000 (Microsoft, Redmond,Wash).

The BS point represents the position of the base ofthe bracket slot in relation to the tooth. The positions ofthe BS points on the labial and buccal sides of the teethwere defined by first connecting a line between the FA

Fig 1. Method for measuring bracket thickness.

Fig 2. Definition of the bracket slot (BS) points, and thecanine and first-molar width and depth of the normaldental arch.

Fig 3. Calculations of archwire width at the canine andfirst-molar levels.

522 Oda, Arai, and Nakahara American Journal of Orthodontics and Dentofacial Orthopedics

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points on the 2 adjacent teeth on both sides of the toothof interest. A line perpendicular to this axis was thenextended so that it passed through the FA point onthe tooth of interest. The BS points were then estab-lished at the outward distance of the mean bracketthickness from the corresponding FA point (Fig 2).An axis was extended between the BS points on thecentral incisors, and a reference point was establishedon the axis halfway between the BS points. This mid-point served as the point of reference from which thedepths of the canine and the first molar could be mea-sured (Fig 2). The means and standard deviations ofthe canine and the first-molar depths of the 30 normalsubjects were 5.09 6 0.70 and 26.95 6 1.56 mm,respectively.

The 20 kinds of archwires were scanned with milli-meter gauges by using a flatbed scanner (ES-2000,Epson, Suwa, Japan) at a resolution of 600 dpi (23.6dots per mm) (Fig 3) by using image-editing software

(version 7.0, Photoshop, Adobe, San Jose, Calif). Theimages were then analyzed by using image processingand analysis software (Scion Image, National Institutesof Health, Bethesda, Md). The points on the lingual sur-face at which the archwire and the line parallel to theline connecting the distal ends of the wire intersectedwith the level of the mean canine and first-molar depthswere digitized. The distance between the bilateral inter-section points at the canine and first-molar levels wascalculated as the width of the archwire. The meansand standard deviations of the archwire widths at the ca-nine and first-molar levels of 20 preformed archwireswere calculated and statistically analyzed.

The absolute error of the FA point identification ondental casts with the 3D scanning system we used wasless than 0.08 mm.15

All sample archwires were measured twice inrandomized order more than 2 months later. The mea-surement error was evaluated according to Dahlberg’sformula.19 The errors of the method of measurement onthe scanned images of archwires were 0.04 mm for caninewidth and 0.02 mm for molar width. The means of the 2repeated measurements were used for the analysis.

Statistical analysis

Means and standard deviations; median, lower(first) quartile, 25th percentile (Q1), and upper (third)quartile,75th percentile (Q3); and the differences inthe median values of the arch widths were calculated.The nonparametric Mann-Whitney test was used to an-alyze the average differences in canine and first-molarwidths at the 5% and 1% levels. A nonparametric testwas used for this study because the distributions of

Table III. Comparison of the arch widths at the canines and first molars between the normal dental arch and preformedarchwire, with the results of nonparametric statistical analyses (mm)

Normal dentalarch (mm) Preformed archwire (mm)

Mean (SD) Median Q1 Q3 Mean (SD) Median Q1 Q3 Difference between medians

Canine width 30.13 (1.32) 30.13 29.43 30.93 29.05 (1.56) 29.79 28.38 30.02 0.34*

First-molar width 55.28 (2.66) 54.90 53.24 57.06 51.96 (2.00) 52.27 51.00 52.88 2.62†

*P \0.05; †P \0.01.

Fig 4. Distribution of the canine widths for each archwire compared with the means and standarddeviations of the normal dental arch, including mean bracket thickness.


archwire widths among the 20 commercial products didnot fit normal distribution. Additionally, the distribu-tions of preformed archwire widths at the canine andfirst-molar levels were graphically compared withmeans and standard deviations of normal dental archwidths, because the distribution of natural dental archwidths is usually considered normal distribution.

RESULTS

Table III shows the means and standard deviations,medians, maximums, and Q1 and Q3 values of the ca-nine and first-molar widths of the 30 normal subjectsand the 20 preformed archwires. Statistically significantdifferences between the subjects and the archwires wereobserved for the widths of both canine and first molar(canine width: U 5 188.5, P 5 0.0272; molar width:U 5 92.0, P \0.0001 [U is the calculation of a statisticin a non-parametric Mann-Whitney test, given by theformula: U 5 R-n(n11)/2, where n is the total number

of observations, and R is the sum of the ranks in thesample]).

Figure 4 shows the distribution of widths at the ca-nine level of the 20 archwires compared with the meansand standard deviations of the normal dental arch width,and Figure 5 shows the distribution of the widths at thefirst-molar level. Fourteen of the 20 archwires hadwidths at the canine level within 1 SD of the mean forthe normal sample. In contrast, only 7 archwires werewithin 1 SD of the mean for normal first-molar width.

DISCUSSION

Previous studies showed that dental arch widthchanges with age. Arch width rapidly increases espe-cially during the mixed dentition.20 However, most cur-rent orthodontic treatments include the second molars.Reported results of average arch-width changes afterthe eruption of the second molars were varied, eg, archwidth was constant,20 increased for male subjects and

Fig 5. Distribution of the first-molar widths of the archwires compared with the means and standarddeviations of the normal dental arch, including mean bracket thickness.


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decreased for female subjects,21 decreased for all sub-jects,22 and did not change or decreased slightly.23 Ad-ditionally, these changes in arch width duringadolescence were smaller than 1 mm. Therefore, theadult dental arches used in this study were adequately se-lected.

It is necessary to consider the variation of bracketthicknesses to analyze the horizontal relationship be-tween tooth surfaces and archwires.14,24 Our resultsshowed that the maximum difference in the bracketthicknesses between brands was 0.80 mm for the man-dibular incisors. Anteroposterior position of the arch-wire at the incisors moves because of the variation inbracket thicknesses, and consequently archwire widthsat the canine and first-molar levels changed. Therefore,in this study, the mean values of bracket thicknesses ofpopular products were used to evaluate the general rela-tionship between variation of archwire forms and natu-ral diversity of normal occlusion. This method can beused to analyze the influence of bracket thickness forarchwire width evaluation without damaging the fragiledental casts by replacement of many bracket sets.

Today, a wide variety of preformed archwires areavailable for orthodontics. An orthodontist theoreticallyselects the size and shape of preformed archwires tomatch the patient’s original dental arch forms as closelyas possible to achieve a stable treatment result. Usingpreformed archwires that fit the most commonly ob-served natural dental arch forms minimizes the needfor adjustments to the archwires’ curvatures and reduces

the patient’s chair time. Therefore, our primary objec-tive was to determine which commercially available or-thodontic archwire form most accurately fits the mostcommon natural dental arch forms. Figures 4 and 5show the distribution of the canine and first-molarwidths of the 20 archwires compared with the normaldental arch forms. The width of most of the sampledarchwires was narrower than the mean of normal dentalarch widths. At the canine level, only 2 of the 20 arch-wires were wider than the mean of the normal dentalarch width, whereas, at the first-molar level, only 1 arch-wire was wider than the mean of the normal dental archwidth. Archwires with overall width measurementsclosest to the mean of the normal dental arch widthswere the Orthos large and small (Ormco, Glendora, Ca-lif), and Vari-Simplex large (Ormco). Although the de-tails are still unclear, the Orthos archwire forms appearto have been designed solely according to the results ofresearch conducted on 100 orthodontic patients in theUnited States and might not have included adjustmentsbased on clinical findings.25 This result supports previ-ously published findings, and, therefore, these archforms are considered suitable for orthodontic patientsin both Japan and the United States.13,25 In contrast, itis obvious that orthodontists who need expanded arch-wires for some reason, or patients who have widerarches than the average might require wider preformedarchwires than the current selection in the market.

The average widths of the 20 archwires at the canineand first-molar levels were narrower than normal dental

Fig 6. Main products for each brand. Note the close re-semblance between the 4 archwires. The archwirewidths of these products are all within a narrow rangeand were close to the dimensions of the traditionalRoth arch form.


arch widths measured in this study. The differences inmedian values between the dental and archwire widthsat the canines and first molars were 0.34 and 2.62mm, respectively, and were statistically significant(P\0.05 and P\0.01). In contrast to our results, Braunet al14 reported that all sampled preformed archwireswere wider than the normal dental arch form. Sixteenpopular NiTi archwires were indirectly compared withthe mean shape of the dental arch as represented bya mathematical curve with a beta function. The reportedmean differences between the dental and archwirewidths at the mandibular canine and first molar were5.95 and 0.84 mm, respectively, wider than human den-tal arch.14 Beta function is defined by the width anddepth of a dental arch at the molar area. But as Norooziet al26,27 stated, we can have 3 dental arches of ortho-dontic patients with different canine widths, but theirmolar depths and widths are the same. So we willhave the same beta function model for the 3 arches, al-though they have completely different shapes. There-fore, it might be possible that a beta function is notflexible enough to evaluate the natural dental archform, especially in the canine area.26-28

One genetic factor contributing to the dental archform is the patient’s ethnic background, which is oftenconsidered when selecting preformed archwire blanks.29

Therefore, ethnic differences should also be consideredwhen evaluating the results of this study. We compared

the widths of commercially available orthodontic arch-wires with normal dental arch forms in Japanese dentalstudents. However, the original form for the straight-wire appliance was determined based on the mean dentalarch form of an orthodontically untreated normal occlu-sion sample in the United States.6 Furthermore, most or-thodontic archwires were designed in the United Statesand have been distributed all over the world withoutmuch research. Recently, it was reported that, in compar-ison with age- and sex-matched white subjects, the meandental arch widths of Japanese Class I subjects with mal-occlusions were approximately 0.9 and 1.5 mm wider atthe canine and molar levels, respectively.30 It is impossi-ble to directly compare the results of these studies be-cause of differences in sample selection, differentdefinitions of reference points, and the considerationof bracket base thickness. Thus, when ethnic differencesbetween subjects from the United States and Japan areconsidered, the average width of the preformed archwireforms seems to still be 1.5 to 2 mm narrower than the nat-ural dental arch form at the first molars. Future studiesshould evaluate additional ethnic groups by using thisnew method of analysis.

While conducting this research, we collected sam-ple wires and asked Japanese corporate distributors ofthe 4 brands of 3 major orthodontic manufacturers abouttrends in the sale of preformed archwires. Figure 6shows the archwires and widths of the most popularNiTi archwires. The differences in width between themain archwire products from the major companieswere all within about 1 mm at the canine level and 2mm at the first-molar level. These wires are so similarbecause the Roth prescription remains the most com-mon,30 and these wires can be all imitations of the orig-inal Roth arch form. In 1934, Chuck3 wrote that his goalin orthodontic treatment was to use the edgewise appli-ance to align the teeth according to the shape of thearchwire. Because he had treated few premolar extrac-tion patients, he did not need to consider the space clo-sures of premolar extractions. In contrast, Roth’streatment goal was not directly equal to his archwireform. It is widely accepted that, when the originalTru-Arch form was designed about 1970, the frequencyof extractions was much higher than in the 1930s or to-day.16,31,32 In general, during extraction-space closure,the posterior teeth tend to rotate into the extractionsite. Therefore, the Roth arch form includes overcorrec-tion on the brackets and a narrower posterior arch widthto counter the archwire’s tendency to curve outward atthe molar level in extraction patients.8 It remains to beseen whether the archwire form developed in the1970s, when extraction orthodontic treatment wasmost popular, can be used successfully in the future,


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when nonextraction treatment might be more common.To be successful, the form must maintain the same levelof efficiency of treatment by minimizing the treatmentduration, the patient’s chair time, and the stable occlu-sion. Therefore, more research is needed to elucidatethis matter.

This study confirmed that the range of selection incurrent commercially available preformed orthodonticarchwire forms does not appropriately cover the re-quired natural human diversity. For example, a majororthodontic technique recommends the 3 shape varia-tions of tapered, square, and ovoid, shown in Figures4 and 5 as Ortho Forms I, II, and III (3 M Unitek,Monrovia, Calif), respectively.33 However, even forthe widest shape, the canine width of the square arch-wire was narrower than the average of the normal var-iation. Additionally, these 3 archwire shapes were allnarrower than the mean: 1 SD at the molar level. Al-though we compared preformed archwires with normalsamples as a reference group, the diversity in malocclu-sions is apparently greater.34-36 Hence, the variation inprescribed categories of archwire templates mightrequire not only shape selection but also a wider sizevariation for clinical applications. Also, further studycomparing the prefabricated archwire form with thepretreatment dental arch forms of orthodontic patientscould be required.

These facts suggest that, even if an ethnicallymatched preformed archwire is selected for a patientfrom the currently available variations, archwire ad-justments are often necessary. Therefore, even withthe latest orthodontic appliances, education in the bi-ologic diversity of our patients and reasonable tech-nical training for archwire fabrication andadjustment are still essential in advanced orthodonticprograms.

CONCLUSIONS

1. The average width of preformed archwires is nar-rower than the average width of the normal dentalarch form.

2. The variation in available preformed archwiresdoes not entirely correspond with the range of di-versity of natural arch form widths.

3. The preformed archwires with measurements thatmost closely matched the dental arch form of thesampled normal subjects were the Orthos andVari-Simplex large types.

4. Although there are many commercially availablearchwires with varying arch widths, the mostcommonly used archwires are similar and canbe considered imitations of the Roth arch form,

which was designed with clinical modificationsprimarily for extraction patients in the 1970s,when extraction orthodontic treatment was ata peak.

5. Therefore, preformed archwires that are approxi-mately 1 to 3 mm wider at the canine level and 2to 5 mm wider at the first-molar level might berequired for today’s orthodontic needs.

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