Comparison of Second Molar Development Amongst Differing Skeletal Patterns

Class II-2 is a difficult malocclusion to treat. Early treatment is recommended. This entails distal movement of the maxillary 1^st molars which can result in impaction of the 2^nd molars. This could be avoided if the developmental stage of the maxillary 2^nd molar were known. Objective: To compare the ages at which the maxillary 2^nd molars reach specific developmental stages for subjects with Class I, Class II-1, Class II-2, and Class III skeletal growth patterns. Method: Records from the Michigan growth study, which contains longitudinal data for over 300 Caucasian subjects of Northern European descent, were investigated. All available records for Class II-2 and Class III subjects were included in the study as those were rare. An attempt was made to match the Class II–1 and Class I subjects to the Class II-2 and Class III subjects. Subjects were selected and classified based on their last available plaster casts and cephalometric radiographs, as Class I, Class II-1, Class II-2, or Class III. ANB of ≥ 5° was regarded as Class II while that ≤ 0° was considered Class III. The age at which each of the upper 2^nd molars of each subject reached the development stages described by Demirjian (1973) were established using serial lateral oblique radiographs. The GLM procedure in SAS was used to compare among and within the skeletal patterns. Result: The GLM procedure did not reveal any significant differences among the skeletal patterns (P=0.09719). As such, there was no need to stratify the data by the skeletal pattern. The developmental stages were reached at significantly different ages (p<0.001). Conclusion: There was no statistically significant difference in the stage of development of the 2^nd molars among Class I, Class II-1, Class II-2 and Class III subjects. However, the developmental stages (A to H) did differ significantly.