Abstract
Background:
To compare Overall and Anterior Bolton ratio in different malocclusion groups in Indian population with Bolton standards.
Material and Methods:
Sample comprised of 300 pre-treatment casts taken from the Department of Dentistry, Government Doon Medical College, Dehradun which included Angle’s Class I, Class II, and Class III malocclusion. Anterior and Overall Bolton’s ratio was measured in different malocclusion groups, and the results were compared with the standard Bolton values. Ratios were also calculated on gender basis and were compared with standard values.
Results:
The mean overall Bolton’s ratio was non-significant in the three groups. The mean anterior Bolton’s ratio in the Class I malocclusion group and Class III malocclusion group when compared with the standard Bolton’s ratio was found to be increased but the difference was found to be non-significant. In the Class II malocclusion group, a significant increase was found in the mean anterior Bolton’s ratio as compared to the standard Bolton’s ratio. On comparison of the mean overall Bolton’s ratio among males in the Class II malocclusion group with the standard Bolton’s ratio, the difference was found to be statistically significant while it was non-significant for Class I and Class III patients.
Conclusion:
The findings of the present study confirm the reliability of Bolton’s ratio in the Indian population. There were statistical non-significant differences among various groups for Overall ratio and for Anterior ratio except in Class II male patients, which was found to be significant.
KEYWORDS: Bolton ratios, tooth size discrepancy, tooth size
INTRODUCTION
Orthodontic diagnosis and treatment planning present numerous challenges in achieving predictable, esthetic, and functional outcomes. One crucial aspect is the assessment of intermaxillary tooth size discrepancies, which can impact occlusion and treatment results. Bolton’s analysis, introduced in 1958, remains a widely accepted method for identifying such discrepancies by evaluating the proportional relationships between maxillary and mandibular teeth dimensions using two indices—anterior and overall ratios.[1]
The anterior Bolton index is derived by dividing the mesiodistal width of the six lower anterior teeth by that of the six upper anterior teeth, while the overall index involves the same calculation using twelve teeth from first molar to first molar.[2] Although Bolton’s standards were established using patients with ideal Class I occlusion, multiple studies have shown that tooth size ratios can vary significantly among different malocclusion groups and ethnic populations.[3,4] These variations highlight the need for population-specific assessments in orthodontic planning.
This study aimed to evaluate the anterior and overall Bolton’s ratios among Indian subjects with Class I, II, and III malocclusions and compare the values with Bolton’s standards. Additionally, gender-based comparisons were made to assess whether sex-based differences influence these ratios. Previous research has consistently reinforced the clinical relevance of Bolton’s analysis, considering it a fundamental diagnostic tool and the seventh key to occlusion in modern orthodontics.[5]
MATERIALS AND METHODS
This study was conducted on dental casts derived from 300 orthodontic patients aged 18–28 years, attending the Department of Dentistry at Government Doon Medical College, Dehradun. The sample included 107 male and 193 female subjects. Based on Angle’s classification and Simon’s canine classification, the participants were divided into three malocclusion groups: Class I (150 subjects), Class II (142 subjects), and Class III (8 subjects). Diagnostic records such as OPGs, lateral cephalograms, study casts, and IOPA radiographs were used to ensure accurate classification.
Strict inclusion and exclusion criteria were applied to maintain the accuracy of the measurements. Subjects with complete permanent dentition up to the first molar, good quality dental casts, and without any dental anomalies or significant restorations were included. Impressions were made using metal perforated trays and Algitex alginate material, followed by cast preparation with Dental Stone and Plaster of Paris. A digital vernier caliper was used to measure the mesiodistal width of teeth to the nearest 0.01 mm, and Bolton’s anterior and overall tooth size ratios were calculated accordingly.
Statistical analysis was performed using SPSS version 17.
RESULTS
On comparing the mean overall Bolton’s ratio with the standard value (91.30 ± 1.91), all three malocclusion groups (Class I, II, III) showed no statistically significant difference (P > 0.05). However, when stratified by gender, the Class II male subgroup showed a statistically significantly higher mean overall Bolton’s ratio (92.23 ± 2.49, P = 0.029), while all other groups—male and female—showed non-significant differences [Table 1].
Table 1.
Comparison of overall Bolton’s ratio with standard ratio across groups and gender
| Group | Subgroup | n | Mean±SD | Standard Mean±SD | t | P | Significance | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Class I | Overall | 150 | 91.84±2.94 | 91.30±1.91 | 1.531 | 0.127 | NS | |||||||
| Males | 48 | 92.12±3.07 | 91.30±1.91 | 1.6 | 0.11 | NS | ||||||||
| Females | 102 | 91.71±2.89 | 91.30±1.91 | 1.062 | 0.289 | NS | ||||||||
| Class II | Overall | 142 | 91.96±2.89 | 91.30±1.91 | 1.866 | 0.063 | NS | |||||||
| Males | 56 | 92.23±2.49 | 91.30±1.91 | 2.210 | 0.029 | S | ||||||||
| Females | 86 | 91.79±3.12 | 91.30±1.91 | 1.156 | 0.249 | NS | ||||||||
| Class III | Overall | 8 | 91.77±2.52 | 91.30±1.91 | 0.5067 | 0.614 | NS | |||||||
| Males | 3 | 92.39±2.32 | 91.30±1.91 | 0.799 | 0.427 | NS | ||||||||
| Females | 5 | 91.40±2.82 | 91.30±1.91 | 0.0777 | 0.938 | NS |
Similarly, for the anterior Bolton’s ratio, Class II malocclusion group overall demonstrated a statistically significant increase (78.13 ± 3.29 vs. 77.20 ± 1.65, P = 0.009). Further gender-wise analysis revealed that this difference remained significant only in Class II males (P = 0.028), while all female subgroups and male Class I and III groups showed non-significant variations from the standard [Table 2].
Table 2.
Comparison of anterior Bolton’s ratio with standard ratio across groups and gender
| Group | Subgroup | n | Mean±SD | Standard Mean±SD | t | P | Significance | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Class I | Overall | 150 | 77.80±3.68 | 77.20±1.65 | 1.602 | 0.11 | NS | |||||||
| Males | 48 | 77.81±4.32 | 77.20±1.65 | 0.9214 | 0.359 | NS | ||||||||
| Females | 102 | 77.80±3.35 | 77.20±1.65 | 1.497 | 0.136 | NS | ||||||||
| Class II | Overall | 142 | 78.13±3.29 | 77.20±1.65 | 2.623 | 0.009 | S | |||||||
| Males | 56 | 78.38±3.60 | 77.20±1.65 | 2.226 | 0.028 | S | ||||||||
| Females | 86 | 77.98±3.08 | 77.20±1.65 | 1.951 | 0.053 | NS | ||||||||
| Class III | Overall | 8 | 77.30±2.82 | 77.20±1.65 | 1.021 | 0.311 | NS | |||||||
| Males | 3 | 77.31±1.07 | 77.20±1.65 | 0.1675 | 0.867 | NS | ||||||||
| Females | 5 | 77.30±3.65 | 77.20±1.65 | 0.0607 | 0.951 | NS |
S=Significant; NS=Not Significant
DISCUSSION
Bolton’s analysis remains the most widely accepted method for evaluating interarch tooth size discrepancies, providing anterior and overall ratios by comparing mesiodistal tooth widths of maxillary and mandibular arches.[3] While the original study was conducted on subjects with ideal occlusion, later investigations have revealed that these ratios may vary across malocclusion types and ethnic groups.[4] In the present study, the mean overall (91.85%) and anterior (77.7%) Bolton’s ratios closely resembled the original values proposed by Bolton (91.3% and 77.2%, respectively), though with broader variability. Notably, only the Class II malocclusion group showed a statistically significant increase in anterior Bolton’s ratio (P = 0.009), whereas other groups showed non-significant differences.[5]
A significant proportion of previous studies have reported that 13–30% of patients present with clinically relevant tooth size discrepancies exceeding two standard deviations from Bolton’s mean, particularly in the anterior segment.[6] For instance, Crosby and Alexander observed 22.9% of their orthodontic sample had such discrepancies, while Johe et al. and Othman and Harradine reported values of 17% and 17.4%, respectively.[6,7] These studies reinforce the importance of pre-treatment Bolton analysis for better treatment planning. Additionally, most findings, including the present study, suggest that males generally have larger tooth sizes, although the prevalence of tooth size discrepancies between genders remains statistically insignificant.[8]
The results of this study align with prior findings indicating no significant difference in Bolton’s ratios across malocclusion groups or between sexes. Johe et al.’s extensive study involving 306 subjects of diverse backgrounds also concluded similarly, supporting the universal applicability of Bolton’s analysis.[9]
CONCLUSION
The present study confirms that Bolton’s ratios are generally applicable to the Indian population, with minimal statistical differences observed across malocclusion groups and genders. A significant anterior ratio discrepancy was noted only in Class II males, suggesting the need for individualized assessment.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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