Study Of Bolton Index Discrepancy For Skeletal Maloculusion

ObjectiveTo evaluate the sex differences in tooth size ratios and distributions of Bolton anterior and overall ratios among different skeletal malocclusions. To investigate the change of different premolar extraction models on overall ratio for skeletal ClassⅠ,Ⅱ,Ⅲmalocclusion patients with normal Bolton ratio and offer the guidelines for clinical diagnosis, analysis and treatment of malocclusion.MethodsPart one,180 subjects were involved in this study. All the subjects were divided into three groups, Group A (ANB 0～5°), Group B (ANB>5°), Group C (ANB<5°), according to different skeletal malocclusions. Each malocclusion group consisted of 60 subjects (30 males and 30 females). The mesio-distal width from left first molar to right first molar was measured, using electronic digital caliper which precision was 0.01mm. Bolton anterior and overall ratios were calculated. Student's t test, ANOVA, LSD andχ2 test were performed for statistical analysis with SPSS 17.0 software package.Part two,120 dental casts of skeletal malocclusion patients with normal Bolton ratio (anterior ratios 78.8%±1.72%, overall ratios 91.5%±1.51%) were selected randomly. According to different premolar extractions, the dental casts were divided into five groups. Group One, no tooth extraction; Group Two, four first-premolars were extracted; Group Three, the upper jaw extracted two first-premolars and the mandible extracted two second-premolars; Group Four, the upper jaw extracted two second-premolars and the mandible extracted two first-premolars; Group Five, four second-premolars were extracted. Overall ratios of the patients in each group were measured before and after hypothetical premolar extractions.Then the laws and changes of the overall ratios were explored with SPSS 17.0 software package.ResultsPart one,①The Bolton anterior and overall ratios had no sex difference among different skeletal malocclusions.②Among different skeletal malocclusions, the Bolton anterior ratio had no statistical difference. For Bolton overall ratio, the population means were unlikeness in each group(P<0.01). The skeletalⅢmalocclusion's Bolton overall ratio was greater than skeletalⅡmalocclusion's Bolton overall ratio(P<0.05) and evidently greater than skeletalⅠmalocclusion's Bolton overall ratio(P<0.01). There was no statistical difference between skeletalⅠmalocclusion's Bolton overall ratio and skeletalⅡmalocclusion's Bolton overall ratio.③Significant difference was found in the distribution of subjects with overall ratio discrepancies between skeletal ClassⅢand skeletal ClassⅠ. However, no statistical difference was found in the distribution of quantity for anterior ratio among different skeletal malocclusions.Part two,①The Bolton overall ratios in each group were smaller after premolar extractions than those before extractions.②In ClassⅠand ClassⅢskeletal malocclusion group, there were statistically significant difference of the overall ratios between every two groups except the second,third group or the fourth,fifth group.③In ClassⅡskeletal malocclusion group, the changes of the overall ratios in different premolar extraction models were obvious except the fourth and fifth group.Conclusions①The skeletal ClassⅢmalocclusion's Bolton overall ratio is greater than skeletal ClassⅡmalocclusion and skeletal ClassⅠmalocclusion's Bolton overall ratio.②To the Bolton's discrepancies, the skeletal ClassⅢmalocclusion has large Bolton overall ratio, but the skeletal ClassⅠmalocclusion has small overall ratio.③For the skeletal ClassⅠmalocclusion and skeletal ClassⅢmalocclusion patients with normal Bolton ratio, the Bolton overall ratio have no statistical difference, if they extract the same teeth in upper jaw.④For the skeletal ClassⅡmalocclusion patients with normal Bolton ratio, the Bolton overall ratio after premolar extractions is affected by the different premolar extraction.