Evaluation of dental arch forms of Indo-Aryan and Mongoloid ethnicity using 3D models and its correlation with preformed archwires: A cross-sectional study

Atrayee Barman; Maninder Singh Sidhu; Seema Grover; Namrata Dogra; Ashish Dabas

doi:10.4103/jioh.jioh_203_20

ORIGINAL RESEARCH

Year : 2021 | Volume : 13 | Issue : 1 | Page : 29-37

Evaluation of dental arch forms of Indo-Aryan and Mongoloid ethnicity using 3D models and its correlation with preformed archwires: A cross-sectional study

Atrayee Barman, Maninder Singh Sidhu, Seema Grover, Namrata Dogra, Ashish Dabas
Department of Orthodontics, SGT University, Gurugram, Haryana, India

Date of Submission	09-Jun-2020
Date of Decision	14-Oct-2020
Date of Acceptance	23-Oct-2020
Date of Web Publication	28-Jan-2021

Correspondence Address:
Dr. Seema Grover
Department of Orthodontics, SGT University, Gurgaon-Badli Road Chandu, Budhera, Gurugram 122505, Haryana.
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jioh.jioh_203_20

Abstract

Aim: The aim of this study was to compare two ethnic groups in India: Indo-Aryan and Mongoloid for variation in arch dimensions, and to determine best-fitting preformed archwire for each group using three-dimensional (3D) models. Materials and Methods: An observational cross-sectional study was conducted on 40 subjects from two ethnic groups. Sample subjects were divided into Group I (n = 20) Indo-Aryan and Group II (n = 20) Mongoloid population. Their maxillary and mandibular plaster models were aligned and laser scanned to obtain 3D virtual models. Linear measurements included intercanine width, intermolar width, canine depth, and molar depth, whereas proportional measurements included canine width/depth ratio, and molar width/depth ratio. Statistical analysis was performed using SPSS statistical software (version 22; IBM, Armonk, New York). Shapiro–Wilk test was done to find if data for both groups were normally distributed (P < 0.05) and Mann–Whitney test for nonnormal distribution groups. Statistical significance was determined at the P < 0.05 level. Results: Intercanine width was similar in both groups, whereas Group II (Mongoloid) showed highly statistically significant increased IMW and IMW/D ratio (P ≤ 0.001) as compared to Group I (Indo-Aryan). Conclusion: Mongoloid arches were broader than that of Indo-Aryan group. For Indo-Aryan group, ovoid and tapered preformed archwire could be used in maxillary arch, whereas only tapered archwire was appropriate in mandibular arch. For Mongoloid group, both ovoid and tapered preformed archwire could be used in both maxillary and mandibular arch.

Keywords: 3D Models, Arch Form, Indo-Aryan Race, Intercanine Width, Mongoloid Race

How to cite this article:
Barman A, Sidhu MS, Grover S, Dogra N, Dabas A. Evaluation of dental arch forms of Indo-Aryan and Mongoloid ethnicity using 3D models and its correlation with preformed archwires: A cross-sectional study. J Int Oral Health 2021;13:29-37

How to cite this URL:
Barman A, Sidhu MS, Grover S, Dogra N, Dabas A. Evaluation of dental arch forms of Indo-Aryan and Mongoloid ethnicity using 3D models and its correlation with preformed archwires: A cross-sectional study. J Int Oral Health [serial online] 2021 [cited 2021 Mar 5];13:29-37. Available from: https://www.jioh.org/text.asp?2021/13/1/29/308352

Introduction

An accomplishment of a stable, functional, and aesthetic arch form has always been one of the key goals of orthodontics. Arch form may be defined as the position of teeth in all three dimensions which is maintained by counterbalancing force exerted by tongue and the tissues around the oral cavity. Orthodontic practice has evolved to witness the use of various arch form designs starting from Bonwill Hawley (1905), Cantenary curve (1949), Ellipse parabola (1949), Brader (1972), Pentamorphic, Computer prediction, Vari-Simplex design, Roth true arch, Straight wire, and M.B.T and Beggs.^[1] However, most studies have recognized three main arch form shapes: tapered, ovoid, and square. Overall ovoid arch form is most popularly used in orthodontic practice (45%), followed by tapered (40%) and rarely square arch form (15%).^[2]

Preservation of patient’s pretreatment arch form and size during the course of orthodontic mechanotherapy dictates the success of treatment.^[3] Little et al.,^[4] on the basis of 35 years of his research work, advocated the use of patient’s pretreatment arch form as a clinical yardstick for achieving an individual’s ideal arch shape after treatment. In recent times, with the introduction of pre-formed archwires; there have been tremendous changes in the culture of orthodontia and it has significantly reduced patient chairside time.^[5],[6] The probability of relapse increases with the inability to maintain arch form. Any undesirable contraction or expansion could give rise to instability, especially at canine and molar levels.^[7]

Arch size and arch form may also differ among dissimilar ethnic groups. There have been many studies in literature aimed at determining the arch forms specific to different ethnic groups and the preferred archwires with the best fit.^{[8],[9],[10],[11]} A study was done recently by Bhowmik et al.^[12] on the correlation of preformed rectangular NiTi archwires with the arch forms of male and female subjects in India, but it was done regardless of their ethnic specificity. With three-dimensional (3D) imaging technology expanding at a rapid pace, accuracy and reliability of 3D virtual models have been checked in several studies, especially of those obtained by laser scanning.^{[13],[14],[15]} Hence, this study was undertaken to compare two ethnic groups in India; Indo-Aryan and Mongoloid for variation in arch dimensions, and to determine best-fitting preformed archwire for each group using 3D models.

Materials and Methods

Study design

This cross-sectional analytical study was conducted on 40 subjects with 14–28 years of age from two ethnic groups: Indo-Aryan and Mongoloid race. Indo-Aryan population included students of university belonging to states of Haryana, Delhi, Uttar Pradesh, Uttarakhand, Punjab, Bihar, and Mongoloid population included subjects recruited through various orthodontic practices in Guwahati belonging to states of Assam, Meghalaya, Mizoram, Arunachal Pradesh, Manipur, and Nagaland. Once they were included in study, their informed consent, history regarding ethnicity/tribe, and native place were taken

Sample size calculation

Sample size was calculated using the findings of Lombardo et al.^[9] Keeping α = 0.05 and power of the study as 99%, sample size of 18 subjects in each group was required. This number was inflated to 20 subjects in each group making total sample of 40 subjects. Selected subjects were divided into two groups: Group I (n = 20) Indo-Aryan population and Group II (n = 20) Mongoloid population.

Sampling criteria

The inclusion criteria of the study were Angle’s Class I molar and canine relation, complete dentition except for third molars, second molars in occlusion, normal tooth size and shape, normal overbite and overjet. The exclusion criteria of the study included any previous orthodontic treatment, restoration extending up to contact areas, arch length discrepancy greater than 3 mm, any attrition/tooth fracture.

Study method

Dental plaster models of maxillary and mandibular dentition were made for all subjects which were aligned with the help of coordinating machine (CMM, COORD3, Italy) and scanned with laser scanner (V7 Laser scanner, Perceptron, USA) to obtain 3D virtual models of each patient’s dentition. After the virtual model was obtained, 3D analyzing software (Geomagic, ControlX, USA) was used to identify anatomical reference points using T 20 probe on that plane and to make appropriate measurements [Figure 1]. In Geomagic 3D analysis software, Cartesian system of axes (x, y, and z) was set [Figure 2].

Figure 1: Points taken on cast for orientation procedure using TP20 probe

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Figure 2: Complete 3D model

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3D virtual model reorientation method

Anteroposterior and transverse directions were established as X-axis and Y-axis, respectively, and a line perpendicular to these planes marked as Z-axis [Figure 3]. Z-axis values were nullified and x and y values were entered and tabulated on an Excel spreadsheet (Excel 2016, Microsoft, Redmond, Washington).

Figure 3: 3D orientation for measurement of arch parameters on maxillary arch and mandibular arch

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Observational parameters

Dental arch measurements were constructed and measured by Geomagic software. Linear measurements included Intercanine width (C), intermolar width (A), canine depth (D), and molar depth (B), whereas proportional measurements included canine width/ depth ratio and molar width/depth ratio on virtual 3D models of maxilla and mandible [Figure 4]. The definition presented by Paulino et al.^[16] expressed the maxillary and mandibular intercanine distance as a linear distance between the cusps of canines on either side or, in the case of attrition or wear, the distance between the centers of the worn surfaces.

Figure 4: 3D measurements on virtual model of maxillary arch and mandibular arch

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The curve-fitting program (MATLAB 7.5 [R2007b], Math Works, Natick, Massachusetts) was used to process the measured x and y coordinates of two archforms representing respective groups and graphically compare by superimposing at the origin of coordinate axes [Figure 5].

Figure 5: Polynomial function fed into MATLAB software using x and y coordinates of an arch and maxillary and mandibular archforms generated

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Correlation of evaluated archforms with preformed archwires

Arch measurements that were obtained from 20 subjects of each group were used for correlation with arch forms of nine preformed 0.019 × 0.025 inch rectangular nickel-titanium archwires. [Archwires were classified into three groups according to whether they were broad, ovoid, or tapered, as specified by their respective companies.

Selected preformed archwires in each group

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Statistical analysis

Statistical analysis was performed using SPSS statistical software (IBM SPSS statistics for Windows, version 21.0. Armonk, New York: IBM Corp. Released 2012.).The chi-square test was used to assess the association between sex and the two ethnic groups. Assessment of the data distribution type was performed by Shapiro–Wilk test. Independent Student’s t test was applied to find the differences between two groups for variables included within normal distribution and nonparametric Mann–Whitney test was applied for non-normal assumptions. A value of P = 0.05 was considered as the threshold to detect statistically significant differences at 95% Confidence level and a degree of freedom of 38. Ten 3D scans were randomly selected and measured again by the same operator 1 week after the initial measurement. Measurement error was calculated according to Dahlberg formula and was found to be 0.01 mm for linear values.

Results

Intragroup comparison of gender differences within maxillary and mandibular arches of Group I (Indo-Aryan) and Group II (Mongoloid), respectively, evaluated by Independent sample t tests showed statistically non-significant results (P > 0.05) [Table 1] and [Table 2]. Intergroup comparison of mean maxillary arch form parameters between Group I and Group II was done by using independent t tests. Mann–Whitney U test was applied to the ICW/D as the dependent variable was not normally distributed. On comparing mean mandibular arch form parameters between Group I and II by using independent t tests; highly significant differences were found in IMW and IMW/D ratio (P ≤ 0.001) [Table 3].

Table 1: Intragroup comparison of mean maxillary arch and mean mandibular arch form parameters between males and females in Group I (Indo-Aryan) using independent sample t tests

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Table 2: Intragroup comparison of Mean Maxillary Arch and Mean Mandibular Arch form parameters between males and females in Group II (Mongoloid subjects) using independent sample t tests

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Table 3: Intergroup comparison of mean maxillary arch form and mean mandibular arch form parameters between Group I (Indo-Aryan subjects) and Group II (Mongoloid subjects) by using Mann–Whitney U test and independent Student’s t test

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Correlation of mean intermolar width between three groups of pre-formed rectangular nickel-titanium archwires and Group 1 (Indo-Aryan subjects) and Group II (Mongoloid) in maxillary arch showed that broad preformed archwires showed very highly significant difference in intermolar width with both groups (P < 0.001). Group II (Indo-Aryan) had a significant difference with the tapered preformed archwires. Mean intercanine width correlation between preformed rectangular nickel-titanium archwires and Group 1 (Indo-Aryan subjects) and Group II (Mongoloid) in maxillary arch depicted highly significant difference in broad preformed archwires in both groups (P < 0.001) [Table 4].

Table 4: Correlation of mean intermolar width (IMW) and mean intercanine width (IMW) of maxillary arch in Group I (Indo-Aryan) and Group II (Mongoloid) with broad, ovoid, and tapered preformed archwires using independent t test

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In mandibular arch, correlation of mean intermolar width between three groups of pre-formed rectangular nickel-titanium archwires and Group 1 (Indo-Aryan) and Group II (Mongoloid) showed very highly significant difference in intermolar width in broad preformed archwires(P < 0.001).Ovoid and tapered preformed archwires showed significant differences in intermolar width of mandibular arches of both groups (P < 0.05). Mean intercanine width correlation between preformed rectangular archwires and Group 1 (Indo-Aryan) and Group II (Mongoloid) in mandibular arch reported very highly significant difference in broad preformed archwires in both groups (P < 0.001). Ovoid preformed archwires were found to have a significant difference with intercanine width of Group I (Indo-Aryan) [Table 5].

Table 5: Correlation of mean intermolar width (IMW) and mean intercanine width (IMW) of mandibular arch in Group I (Indo-Aryan) and Group II (Mongoloid) with broad, ovoid, and tapered preformed archwires using independent t test

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Discussion

The effect of ethnic background on arch form has been widely shown.^[9],[10] It is conceivable that a racial difference in head and facial form is closely related to variation in arch width and depth.^[17] In this study, measurements were done involving 3D scanning of precision impressions and digital software as shown by Bayome et al.^[18] Kusnoto and Evans^[19] tested the accuracy of laser scanner and found it to be accurate with an error range between 0.2 and 0.7 mm. Sousa et al.^[20] had previously evaluated the reliability of measurements made on 3D digital models obtained with a surface laser scanner and found no differences between the measurements made directly on the dental casts and on the digital models.

Al Barakati et al.^[21] had established in his study that using an archwire form with the best fit to the dental arch should produce minimal changes in the dental arch form when NiTi wires are used and require less customization when stainless-steel wires are used. In this study, the findings revealed no significant difference in intercanine width between Indo-Aryan and Mongoloid population. This is in similarity with findings of Lee et al.^[22] and Othman et al.,^[23] which reported no differences between their respective ethnic groups. However several other studies reported significant differences in intercanine width between different ethnic groups, which are in contrast with the finding of this study.^[18],[24] The obvious close resemblance in intercanine values of the Indo-Aryans and Mongoloid subjects imply that anterior dental dimension distribution between the two ethnic groups hints at similar smile characteristics and transverse smile relations. These results suggest that Indo-Aryans have narrower anterior archform as compared to Mongoloids but statistically insignificant for clinical relevance during archwire selection.

Maintenance of the intermolar distance also plays a major role in the shape of archform and is paramount to the stability of archform. In this study, highly significant differences were observed in Intermolar widths in both maxillary and mandibular arches, between Indo-Aryans and Mongoloids. Mongoloids had wider arches as compared to Indo-Aryan and such disparity in posterior transverse dimension between different races is well reported in the literature.^[18],[24] However, Celebi et al.^[10] and Othman et al.^[23] found no significant differences in transverse widths on comparing the respective ethnic groups in their studies, which are in contrast with our study results.

In this study, the intercanine and intermolar widths showed no significant gender dimorphism among the two ethnic subgroups. In a study done by Ahmed et al.^[25] on Pakistani subjects, in males, the archwires were found to be wider at canines and premolars, and significantly narrower at first and second molars as compared to the arch dimensions of the mandibular casts whereas in females, the archwires were significantly narrower at canines, and first and second molars. This inconsistency may be due to variation in sample size and different arch measurements techniques used in the other studies.

Transverse to sagittal ratio is applicable to purpose of finding the consistency of arch width and depth in relation to resulting overall shape. Higher is the ratio value, wider is the arch; at canine or molar level. When the canine width to molar width ratio increases; canine depth/molar depth ratio decreases and arch become squarer. Inversely, as canine depth to molar depth ratio increases and canine width to molar width ratio decreases, the arch gets more tapered. Mongoloids had comparatively broader posterior dimension than Indo-Aryan. Bayome et al.^[18] did a study on Egyptian and North American population and found similar results to ones in this study.

The intercanine and intermolar widths of preformed archwires were obtained^[12] and compared with that of the two ethnic groups to check best fit in this study. The tapered archform for the maxillary and mandibular intercanine widths showed no significant difference with the mean intercanine widths of the two subgroups. Therefore, use of tapered preformed archwire group is recommended in the maxillary and mandibular arches of both Indo-Aryan and Mongoloid population as there is no risk of expansion in intercanine width.

For Indo-Aryan population; three preformed archwires of tapered group, namely Orthoform I (3M Unitek), Natural archform 2 (American Orthodontics) and SIA standard (SIA orthodontics) and one from ovoid group, namely Orthoform III (3M Unitek) were closest to mean ranges for intercanine width in maxillary and mandibular arch. None of the preformed archwires came within normal range for intermolar width in maxillary and mandibular arches, the closest one being Orthoform I (3M Unitek).

For Mongoloid population; preformed archwires from broad group, Nitanium archwire (Ortho Organizers); ovoid group Orthoform III (3M Unitek); and three from tapered group, namely American Orthodontics (Natural Archform 2), SIA standard (SIA orthodontics) and orthoform I (3M Unitek) were best suited at canine level in maxillary arch. In mandibular arch; all preformed archwires fell within the mean range except Nuform (Orthotec) of ovoid group. For intermolar suitability, maxillary preformed archwires that best suited were Orthoform I (3M Unitek) closely followed by SIA standard (SIA orthodontics) and Orthoform III (3M Unitek). In mandibular arch, only Orthoform I (3M Unitek) was found to be closest to the mean range of intermolar width.

Using preformed archwires that fit the most commonly observed natural dental arch forms will minimize the need for adjustments to the archwires’ curvatures and reduce the patient’s chair time. Unsuitable or improperly shaped archwires create undesirable expansion or contraction and contribute to many post-treatment problems like instability; especially in the canine and molar regions.

Nevertheless, with fast-developing progress of computer-assisted analysis, new approach of custom designing arch forms may provide the necessary solution for precisely describing the ideal orthodontic arch form for individual patient. The influence of different bending techniques on the mechanical properties of nickel-titanium archwires has been investigated.^[26] Until archwires designed for the Indian population appear in the market, orthodontists would be wise to select the most appropriate NiTi archwires for individual patient particularly in the initial phases of treatment.

This study showed that Mongoloid arches were broader than that of Indo-Aryan group. For Indo-Aryan group, ovoid and tapered preformed archwire could be used in maxillary arch, whereas only tapered archwire was appropriate in mandibular arch. For Mongoloid group, both ovoid and tapered preformed archwire could be used in both maxillary and mandibular arch. The limitation of this study is that there may be some differences in digital measurements. It is suggested that in future the same study must be done in various ethnic groups comparing ovoid, tapered, and square arch forms with respective preformed arch forms

Conclusion

There was no difference in intercanine width between Group I (Indo-Aryan) and Group II (Mongoloid) in maxillary and mandibular arches were observed whereas intermolar width revealed broader arches in Mongoloids as compared to Indo-Aryans. For Group I (Indo-Aryan), preformed ovoid and tapered archwires are recommended in maxillary arch and in mandibular arch, only tapered archwires were suitable with utmost care for molar expansion. Orthoform I (3M unitek), Orthoform III (3M unitek), SIA standard (SIA orthodontics,) and Natural archform 2 (American Orthodontics) were most suitable for maxillary and mandibular arches.

For Group II (Mongoloid), ovoid and tapered group could be used in maxillary and mandibular arch. Nitanium (American Orthodontics), SIA standard (SIA orthodontics) and Orthoform I and III (3M unitek) were best suited for maxillary arch, whereas all preformed archwires except Nuform (Orthotec) were suitable for mandibular arch.

Future scope

Further studies may be encouraged to compare ovoid, tapered, and square arch forms in various populations with respective preformed arch forms. Although the accuracy of digital measurements using laser scanner have been well documented, there still exists a possibility of differences in scanning and magnification which may affect the results of this study.

Acknowledgement

We are highly indebted to patients who participated in the study and IT Department for their great support throughout study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Author’s contribution

Dr A Barman: Concepts, design of the study, investigation, and statistical analysis. Dr MS Sidhu: Definition of intellectual content and statistics. Dr S Grover: Manuscript writing and checking statistics. Dr N Dogra: Manuscript editing and review of literature. Dr A Dabas: Writing results. Finally, all authors had approved the manuscript for publication.

Ethical policy and institutional review board statement

Ethical approval for this study protocol was approved on November 28, 2017 by the ethical committee of institution of the Faculty of Dental Sciences, SGT University, Haryana, India with number SGTU/FDS/MDS/24/1/672. All the procedures have been performed as per the ethical guidelines laid down by Declaration of Helsinki (1964).

Patient declaration of consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Data availability statement

The data set used in this study is available in Department of Orthodontics, SGT University.

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