|Year : 2017 | Volume
| Issue : 4 | Page : 225-232
Applicability of bolton's analysis to a South Telangana population
T Saritha, C Sunitha, P Kiran Kumar, R Naveen
Department of Orthodontics, Mamata Dental College, Khammam, Telangana, India
|Date of Web Publication||1-Dec-2017|
Department of Orthodontics, Mamata Dental College, Giriprasad Nagar, Khammam, Telangana
Source of Support: None, Conflict of Interest: None
Aim: The aim of the study was to assess the anterior and overall tooth size discrepancies in different malocclusions and evaluate its effect on gender in a sample of South Telangana (Khammam) population and to compare it with Bolton standards. Materials and Methods: The study sample consisted of 311 pretreatment study casts, which were selected from records of orthodontic patients, who were residents of Khammam, South Telangana. The sample was divided into three groups based on Angle Class I, II, and III malocclusions and further subdivided into male and female groups. The mesiodistal diameters of the teeth were measured using digital calipers, and the Bolton's analysis was carried out. Statistical Analysis Used: Intraclass correlation coefficient was assessed using Dahlberg's formula. ANOVA and post hoc least significant difference test were used. Results: The mean anterior and overall ratios were 79.17 ± 2.91 and 92.3 ± 1.88, respectively. A total of 64% and 45% of the study population had tooth size discrepancies in the anterior and overall ratios when assessed for >±1 standard deviation (SD). When the sample was assessed for discrepancies >±2 SD, it was observed that a total of 33.8% and 5.5% patients had anterior and overall tooth size discrepancies. Conclusions: With significant differences being observed between Bolton's and the present study values, the need for population standards gains importance for better results at the end of orthodontic treatment.
Keywords: Bolton ratio, South Telangana (Khammam) population, tooth size discrepancy
|How to cite this article:|
Saritha T, Sunitha C, Kumar P K, Naveen R. Applicability of bolton's analysis to a South Telangana population. Indian J Dent Sci 2017;9:225-32
|How to cite this URL:|
Saritha T, Sunitha C, Kumar P K, Naveen R. Applicability of bolton's analysis to a South Telangana population. Indian J Dent Sci [serial online] 2017 [cited 2018 Mar 19];9:225-32. Available from: http://www.ijds.in/text.asp?2017/9/4/225/219637
| Introduction|| |
Comprehensive orthodontic treatment aims at achieving optimal occlusion with ideal overjet and overbite. An intermaxillary tooth size discrepancy is one of the many factors that jeopardize an excellent orthodontic treatment result. A tooth size discrepancy is a disproportion between the sizes of individual teeth. Of the different phases of orthodontic treatment, “finishing phase” is considered to be very difficult because of tooth size imbalances that could have been detected and considered during initial diagnosis and treatment planning. The clinician should be familiar with such discrepancies in tooth size at the initial diagnosis and treatment planning stages if excellence in orthodontic finishing is to be achieved.
Several investigators have deemphasized the role of genetics in the determination of tooth size and have concluded that the influence on variations in tooth size is multifactorial, with the environment playing an important role. Significant gender and ethnic differences in tooth size between males and females have also been reported in many studies. In 1949, Neff  found that the ratio of anterior teeth size is mathematically related to overbite and proposed the “anterior coefficient.” Lundstrom  in 1955 gave “the anterior index” after studying the ratio between maxillary and mandibular anterior teeth. Gilpatric  in 1923 found that when the sum of the mesiodistal widths of all maxillary teeth exceeds that of the mandibular teeth by 8–12 mm, and the greater this value, greater was the overbite. Bolton , compared the sums of maxillary and mandibular mesiodistal tooth size and determined the ideal anterior and overall tooth size ratio. During diagnosis and planning, a quick analysis of Bolton's ratios will give the clinician a clue to determine the need for addition or reduction of tooth material.
Neff, Lundstrom, Ballard, and others have given several methods to determine interarch tooth size discrepancy. Of all these methods, Bolton's , analysis has found wide usage and acceptance because of its simplicity and clinical reliability. Bolton developed his anterior and overall ratios after evaluating 55 cases with “excellent” occlusion. After considering tooth sizes from one first molar to the other first molar and from one canine to the other canine in the maxillary and mandibular arches, he established a value of 77.2% and 91.3% for the anterior and overall ratios, respectively. He concluded that it would be very difficult to obtain an excellent occlusion in the finishing phase of treatment without a correct mesiodistal tooth size ratio, and McLaughlin and Bennett  added the absence of interarch tooth size discrepancies as the “seventh key” to the Andrews six keys of normal occlusion because of its importance.
Interarch tooth size relationships differ between populations because differences in tooth sizes are not systematic. Population and gender differences in maxillary tooth size may not be the same as the differences in mandibular tooth size; hence, different interarch relations might be expected. Sharma R, Lavelle et al., Smith et al., Santoro et al., Bernabé et al., Paredes et al., and several others from their studies reported that tooth size discrepancies vary with different populations. Till recently, no study has been carried out on Khammam (South Telangana) population to measure the interarch tooth material discrepancies between different malocclusion groups and its relationship to gender. Hence, the aim of this study is to assess the overall and anterior tooth size discrepancies in different malocclusions and evaluate its effect on gender in a sample of Khammam (South Telangana) population reporting for orthodontic treatment and to compare it with Bolton standards.
| Materials and Methods|| |
The pretreatment casts were selected from records of the patients attending the Department of Orthodontics, Mamata Dental College, Khammam District, Telangana state. A total of 311 patients were randomly chosen after analyzing the pretreatment study models of 510 patients who reported to the department during 2013–2015. The mean age group of the selected sample was 14–30 years which was chosen to avoid age-related changes such as attrition and abrasion. The diagnosis was based on bilateral molar relationship and an ANB angle between 0° and 4° for Class I; ANB angle > 4° for Class II, and <0° for Class III. The sample was thus divided into three groups, namely, Class I, Class II, and Class III and the whole sample was further subdivided into male and female groups.
The patients were included based on the following inclusion criteria:
- Presence of all permanent teeth from the first molar to the first molar in both arches in both arches
- Ancestors from at least one previous generation residing in Khammam district
- Absence of caries and restorations which will alter tooth size measurement
- Good quality study models
- Fully erupted permanent dentition
- Absence of individual tooth anomalies which could alter the shape of the teeth.
Patients were excluded from the study when the following conditions were present:
- Presence of dental anomalies such as supernumerary teeth and mesiodens
- Previous history of orthodontic treatment
- Presence of dental prosthesis, crowns, and composite restorations
- Presence of attrition and abrasion
- Presence of congenitally missing or impacted teeth.
After scrutinizing the samples based on inclusion and exclusion criteria, the final sample consisted of 311 models with 167 patients having a Class I, 102 with Class II, and 42 with Class III malocclusion. Ethnicity of the patient was based on their response. Measurement of the maxillary and mandibular teeth in all the study models was done using an electronic digital caliper which was calibrated to an accuracy of 0.01 mm. The width of every tooth was measured from its mesial contact point to its distal contact point at its greatest mesiodistal dimension. The caliper was held parallel to the occlusal plane and perpendicular to the long axis of the tooth to make the measurement more accurate. In the posterior teeth, measurement was done from the occlusal view, and in the anterior, facial view was used to maximize mesiodistal width of each tooth [Figure 1]. Everyday 5–10 models were assessed to avoid effect of visual exhaustion. All the measurements were done by a single examiner after the teeth sizes were recorded, the anterior and overall ratios were calculated for each sample using the following formula as proposed by Bolton.
To test intraoperator reliability, ten models from each group were randomly assessed by the same examiner after 1 month. The first and the second measurements were compared statistically to evaluate intraoperator reliability using Dahlberg's formula and intraclass correlation coefficient which showed good intraobserver reliability [Table 1].
| Results|| |
The mean anterior ratio for all the malocclusion groups is shown in [Table 2]. The anterior ratio was found to be 79.17 ± 2.91 and was found to be statistically significant when compared to the Bolton's norm of 77.2 ± 1.65 (P < 0.001) [Graph 1]. [Table 3] reveals that when the anterior ratio was compared between genders, no significant differences were found (P = 0.964).
|Table 2: Comparison of mean anterior ratio between study population and standard Bolton's ratio|
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Mean anterior ratio for the individual malocclusion groups is tabulated in [Table 4]. The mean anterior ratio for Class I malocclusion group was found to be 79.368; for Class II, it was 78.642, and for Class III, it was 79.72. When the ratios were compared between the different malocclusion groups, statistically significant differences were found when Class I was compared with Class II (P = 0.046) and Class II with Class III (P = 0.046). The mean anterior ratio was highest in the Class III group. Comparison between gender and the different malocclusion groups for the anterior ratio revealed no statistically significant differences [Table 5].
|Table 4: Comparison of mean anterior ratio between different malocclusion groups|
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|Table 5: Comparison of mean anterior ratio between malocclusion groups and genders|
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The mean overall ratio for the study population is shown in [Table 6]. The value was found to be 92.3 ± 1.88. Comparison of this mean value with the Bolton's standard of 91.3 ± 1.91 revealed statistically significant differences (P < 0.001) [Graph 1]. However, comparison between genders for the overall ratio revealed no significant differences [Table 7] (P = 0.949). Overall ratio for the individual malocclusion groups is presented in [Table 8]. The mean overall ratio for Class I malocclusion was 92.38 ± 1.86; 92.30 ± 1.99 in Class II, and 92.97 ± 1.55 in Class III malocclusion. Comparison between the three malocclusion groups and between genders revealed no statistically significant differences [Table 9].
|Table 6: Comparison of mean overall ratio between study population and standard Bolton's ratio|
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|Table 8: Comparison of mean overall ratio between different malocclusion groups|
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|Table 9: Comparison of mean overall ratio between malocclusion groups and genders|
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The distribution of patients with a significant discrepancy in anterior and overall ratio exceeding 1 standard deviation (SD) is tabulated in [Table 10]. A total of 64% of patients in the study population had discrepancies in the anterior ratio and 45.30% in the overall ratio exceeding 1 SD [Graph 2] and [Graph 3]. The highest discrepancy for anterior and overall ratio exceeding 1 SD was found in Class III males. When the study population was assessed for discrepancy exceeding 2 SD [Table 11], a total of 33.8% of the patients had a discrepancy in the anterior ratio and 5.5% in the overall ratio [Graph 2] and [Graph 3]. The greatest discrepancy for the anterior and overall ratio exceeding 2 SD was found in Class I males.
|Table 10: Frequency and distribution of tooth size discrepancies exceeding 1 standard deviation|
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|Table 11: Frequency and distribution of tooth size discrepancies exceeding 2 standard deviation|
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| Discussion|| |
Ideal tooth proportions play an important role in achieving good occlusion at the end of orthodontic treatment. Ideal tooth proportion was studied and reported by Bolton in 1958 who assessed the relationship of maxillary and mandibular dentition and proposed two indices: the anterior ratio and the overall ratio based on a study conducted on 55 American patients with excellent occlusion. Bolton's analysis, however, provides no information with regard to gender, ethnicity, and malocclusion type. Lavelle et al., Smith et al., Santoro et al., Bernabé et al., Paredes et al., Endo et al., Ta et al., and several others from their studies reported that tooth size discrepancies vary with different populations and hence population-specific standards are important to achieve optimal orthodontic results.
In the present study, an analysis of tooth size discrepancies was carried out to assess the extent of discrepancy from the original Bolton's norms, its relationship to gender, and to different malocclusion groups in a sample of South Telangana, India. A total of 311 patients were included in the study who presented with different malocclusion types. The mean anterior ratio was found to be 79.17 which was significantly different from that proposed by Bolton. This value was found to be in close range with ratios from other Indian studies such as those carried out by Jhala et al., Jindal and Bunger, Saini and Moirangthem, Kumar et al., Murmu et al., and several other researchers [Table 12]. Studies carried out by investigators on other ethnic populations have also reported values in a close range and these include studies by Smith et al., Fattahi et al.,,,,,,,,,, Baidas and Hashim, Alkofide and Hashim, and Nourallah et al. [Table 13].
The mean overall ratio was found to be 92.43 which was also significantly different from the ratio proposed by Bolton. Jindal and Bunger, Reddy et al., Subbarao et al., Anil and Monika, and several others [Table 12] have reported similar findings in their studies on Indian populations. Studies on other ethnic populations conducted by Smith et al., Baidas and Hashim, Alkofide and Hashim, Nourallah et al., Al-Omari et al., [Table 13] have reported values close to the values of the present study. The present mean overall ratio of 92.43 was similar to the finding in a Himachali ethnic population  with the overall ratio 92.02.
When tooth size was related to gender, both the anterior and the overall ratio revealed no significant differences suggesting that no sexual dimorphism existed in the present study population. Similar findings were reported by Araujo and Souki,,,,,,,, Akyalçin et al., Sameshima, Nie and Lin, Johe et al., and several other investigators. Between the different groups, Class III males were found to have the highest mean values for both the anterior and the overall ratio even though these values were not statistically significant. These findings correlate with the findings of Wedrychowska-Szulc, Nie and Lin, and Lavelle et al., who also reported that Class III males have the highest discrepancy for both the ratios.
Evaluation of the relation between tooth size and different malocclusions revealed that the mean anterior ratio was highest in Class III malocclusion patients followed by Class I and least in Class II malocclusion group. Nie and Lin  reported the following finding between different malocclusion groups: class III > Class I > Class II which were similar to our findings. Lavelle, in his study, stated that Class III patients had smaller maxillary teeth and larger mandibular teeth in comparison to Class I and Class II individuals. Nie and Lin, Sperry et al., and several other authors mirrored the findings of Lavelle et al. which could possibly explain the finding of Class III individuals having greater Bolton values in comparison to other malocclusions. Several studies reported that the maxillary lateral incisor in Class III individuals are smaller in size and may contribute to the discrepancy in Bolton ratio in these patients. However, individual tooth size abnormalities were not assessed in the present study, and hence direct effect of a small maxillary lateral on Bolton's ratio could not be assessed. It is, however, important to consider such individual variations in tooth anatomy during treatment planning to ensure good anterior tooth inclination and interdigitation. The mean overall ratio, however, was not significantly different between the different malocclusion groups.
Several authors have suggested that it is important to measure individual tooth sizes before initiating orthodontic treatment (Othman and Harradine, 2006).,, Bolton, in his study, suggested that discrepancies >1 SD can cause problems in clinical situations. However, in Bolton's study, casts of patients with ideal occlusion were used, and hence it might be difficult to determine the level of discrepancies which can have clinical implications. Santoro et al., Araujo and Souki, Freeman et al., Othman and Harradine, Crosby and Alexander, and several other investigators have stated that a tooth size discrepancy of >2 SD or 1.5 mm of the Bolton norm can cause difficulties in tooth alignment and final occlusion. Proffit et al. stated that a discrepancy >1.5 mm can create problems and should be considered during the treatment planning process.
The frequency and distribution of tooth size discrepancies were found to be very high in this study population, which further emphasizes the importance of taking into consideration tooth proportions during the treatment planning process. Bolton, in his study, reported that 29% of the population had anterior tooth size discrepancies >±1 SD. Of the 311 patients included in this study, a total of 199 (64%) patients were found to have anterior tooth size discrepancies >±1 SD A total of 141 (45%) patients were found to have overall tooth size discrepancies >±1 SD Richardson and Malhotra  reported that 33.7% of patients had tooth size discrepancies >1 SD in their study.
When the sample was assessed for discrepancies >±2 SD, it was observed that a total of 105 (33.8%) patients had anterior tooth size discrepancies and 17 (5.5%) patients had overall tooth size discrepancies >±2 SD. Crosby and Alexander  found that 22.9% of the patients had tooth size discrepancies >2 SD. Santoro et al. found that 28% of their study population had anterior discrepancies and 11% had overall tooth size discrepancies >2 SD. Freeman et al. reported a 30% anterior tooth size discrepancy in their study. Bernabé et al. and Oathman and Harradine  reported that 5.4% of their study samples had overall tooth size discrepancies >2 SD.
The findings of the present study indicate that the mean anterior and overall ratios were significantly higher for the population studied when compared with the Bolton's norms which are being currently used to assess the prevalence of tooth size discrepancies. Hence, it is important to take into consideration the present values specific for this population during diagnosis and treatment planning of orthodontic patients as treating them to the already existing values might not provide the ideal occlusion sought at the end of treatment.
| Conclusions|| |
Bolton's analysis was carried out in a total of 311 patients with Class I, Class II, and Class III malocclusions. The mean anterior ratio and mean overall ratios were compared between the study population and the original Bolton's ratio and the following conclusions were drawn:
- The mean anterior ratio and mean overall ratio was significantly higher at 79.17 ± 2.91 and 92.3 ± 1.88, respectively
- No sexual dimorphism was seen when tooth size was assessed as a function of gender
- When the anterior ratio was assessed as a function of malocclusion, patients with Class III malocclusion had the highest ratio in comparison to Class I and Class II. However, no differences existed for the overall ratio
- 33.8% of the population had anterior tooth size discrepancy, and 5.5% of the population has overall tooth size discrepancy >2 SD. Significant differences with the original Bolton's ratio and the increased prevalence of tooth size discrepancies within the population suggest the need for population-specific standards for better clinical assessment, treatment planning, and occlusion.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13]