Three-dimensional evaluation of skeletal and dental asymmetries in Class II subdivision malocclusions

The objective of this study was to determine if any significant differences existed with regard to dental and skeletal asymmetries between subjects wi th Angle Class II subdivision malocclusions and subjects with normal occlus ions. The sample consisted of 30 subjects in each of the 2 groups. Each pos sessed a full complement of permanent teeth, including first molars. The av erage age of subjects was 15.76 years in the Class II subdivision group and 22.42 years in the normal occlusion group. Measurements were obtained with the use of submentovertex, posteroanterior, and corrected oblique cephalom etric radiographs. In the submentovertex radiographs, symmetry was assessed by measuring the relative differences in the spatial positions of dental a nd skeletal landmarks between the right and the left sides in both anteropo sterior and transverse dimensions. Coordinate systems were used to represen t the mandible, cranial floor, and the maxilla. In the posteroanterior radi ographs, symmetry was assessed similarly by measuring the relative differen ces in the spatial positions of dental and skeletal landmarks between the r ight and the left sides. In the corrected oblique radiographs, symmetry was assessed by measuring the differences in size of dental and skeletal struc tures between the right and the left sides. Variables were analyzed with mu ltivariate logistic regression analysis. The results demonstrated that the primary contributor to the differences between the 2 groups was the distal positioning of the mandibular first molars on the Class ii side in patients whose mandibles showed no unusual skeletal or positional asymmetries. A se condary contributor was the mesial positioning of the maxillary first molar s on the Class II side. Furthermore, the posteroanterior radiographic analy sis showed that the more frequent distal positioning of the mandibular mola rs on the Class ii side, compared with the mesial positioning of the maxill ary molars on that side resulted in mandibular dental midline deviation to the Class II side more frequently than the maxillary dental midline to the opposite side.