Study Of Bolton Index Discrepancy In Skeletal And Dental Class Ⅱ Division 2 Malocclusion

Objective: The study was undertaken to compare the overall and anterior ratios of tooth size discrepancies in skeletal and dental class Ⅱ division 2malocclusion and to observe the characteristics of arch.Methods: The study samples consists of 450 initial study casts of patients with class Ⅱ division 2 malocclusion selected from four hospitals who applied for orthodontic treatment in 2014-2016.The subjects were divided into four groups according to the type of malocclusion:skeletal males(98casts);skeletal females(152casts);dental males(70casts)and dental females(130casts).The measurement of the greatest mesiodistal width of the teeth was performed using a vernier caliper directly on the models,from the distal surface of the left first molar to the distal surface of the right first molar.The overall and anterior ratios between the maxillary and mandibular teeth were evaluated using Bolton’s method.314 cases over 16 years old selected from the total sample were used to fulfill the criteria for the study sample.The subjects were divided into four groups according to the type of malocclusion: skeletal males(56casts);skeletal females(130casts);dental males(44casts)and dental females(84casts).The total length of arch,width of anterior,middle,posterior segment of the upper and lower dental arch,alveolar arch width and length was measured,then the difference between skeletal and dental groups was analyzed.The following statistical tests were applied independent t-test.Results: 1 The results showed no differences in the overall and anterior ratios of tooth size discrepancies among males and females with class Ⅱdivision 2 malocclusion(P>0.05).2 There were no significant differences observed when comparing the overall and anterior ratios among skeletal anddental groups(P>0.05).3 A mean total Bolton ratio of 90.34%±1.71% and a mean anterior Bolton ratio of 77.93%±2.32% were found for skeletal malocclusion and a mean total Bolton ratio of 89.94%±1.69%,anterior Bolton ratio of 77.74%±2.23% for dental groups.The results were significantly smaller than standard value(P<0.01).4 A significant gender difference was found for some measurements in characteristics of arch.There were significant differences observed in the total length of arch in skeletal malocclusion(P<0.01),although males with dental malocclusion were larger than females,but the difference was not statistically significant(P>0.05).The results also showed that males had statistically significant wider dental arch width values on the upper middle and posterior dentition than females counterparts in skeletal groups.While in dental groups,anterior dentition also showed statistically significant difference between males and females(P<0.05).In addition,on the lower posterior dentition,males were significantly larger than females in skeletal and dental groups(P<0.05).5 The dates showed males in maxillary alveolar arch width and length in skeletal groups were significantly higher than that of females,and there were significant differences showed in mandibular alveolar arch length.While in dental groups there were significant differences showed in upper and lower alveolar arch width.6 It can be noticed that the dates showed no statistically significant difference in arch width and length between skeletal and dental groups(P<0.05),but the total length of mandibular arch,skeletal groups were significantly larger than dental groups in males(P<0.01).Conclusions:1 There were no statistically significant differences observed when comparing the overall and anterior ratios among skeletal and dental class Ⅱdivision 2 malocclusion.Therefor,it can be concluded that Bolton index was affected by the type of malocclusion.2 There were no significant differences between skeletal and dental classⅡ division 2 malocclusion in the characteristics of dental arch.3 The results showed significant differences between genders in the characteristics of dental arch for skeletal and dental class Ⅱ division 2malocclusion.