Comparison of Tooth Size Ratios (Bolton Analysis) Among Different Malocclusion Groups

Introduction: For proper occlusal interdigitation or coordination of arches in the finishing stage of orthodontic treatment with proper overjet and overbite would have been a proper mesiodistal tooth size ratio (Bolton analysis) between maxillary and madibular teeth. The Bolton analysis should be taken into consideration when diagnosing, treatment planning and predicting prognosis in clinical orthodontics. In this study tooth size ratio was evaluated among different malocclusion groups. Materials and Method: This study was carried out on 200 pretreatment orthodontic casts, which were chosen through selective available sampling procedure according to selective criterias. They were classified by the Angle classification, coincided with skeletal categories.  Skeletal types were assessed by ANB angle from cephalometric analysis. All the subjects were divided into 4 groups: each group consisted of 25 males and 25 females. These groups were Cl I malocclusion, Cl II Div 1, Cl II Div 2 and Cl III. The greatest mesiodistal diameters of all the teeth on each cast were obtained except the second and third molars. The measurement was done by digital caliper with 0.01 mm accuracy. Then tooth size ratios were analyzed as Bolton described. Results: The main anterior ratio for male patients was larger than that of female patients in all groups (p<0.05), while there was no significant sexual dimorphism for overall and posterior ratios between the groups. The mean of the anterior ratio of Cl III patients was shown to be more than Cl II Div 1 amd Cl II Div 2. No statistical difference was found between Cl III and Cl I patients. Posterior and overall ratios of Cl III patients were larger than other groups. The mean overall ratio of Cl I patients was larger than Cl II Div 1, but it had no significant difference with Cl II Div 2 group. Conclusion: This study suggests that the tooth size discrepancy between the maxillary and mandibular teeth may be one of the important factors in the cause of malocclusions, especially in Cl III malocclusion. Key words: Bolton analysis, Anterior, Posterior and overall ratios, Malocclusion