Mesial rotation of upper first molars in Class II division 1 malocclusion in the mixed dentition: a controlled blind study

OBJECTIVE:To compare the amount of upper molar rotation in subjects with Class II Division 1 malocclusion and subjects with normal occlusion in the intermediate and late mixed dentition phases. MATERIALS AND METHODS:Dental cast measurements were performed in a sample of 120 Class II Division 1 subjects (CL2 group, 67 females and 53 males, mean age 9.4±1.1 years), and in a sample of 58 Class I subjects (CL1 group, 34 females and 24 males, mean age 9.7±1.2 years). Independent sample t tests were used for statistical comparisons (P<.05). RESULTS:The amount of upper molar rotation was significantly greater in CL2 group when compared with CL1 group as assessed by both the mesial and buccal molar cusp angles. No differences were found with regard to upper or lower arch depths, or upper intercanine width. CL2 group showed a significant deficiency in upper intermolar width along with a significant posterior transverse interarch discrepancy when compared with CL1 group. CONCLUSIONS:Subjects with Class II malocclusion in the mixed dentition present with mesial upper molar rotation in about 84% of the cases. The correction of molar rotation may provide between 1 and 2mm of gain in arch perimeter and of improvement in molar relationships per side in 5 out 6 Class II patients.