Vertical changes in class II division 1 malocclusion after premolar extractions

The purpose of this study was to compare changes in the facial vertical dimension in patients with Class II division 1 malocclusion after the extraction of either mandibular first premolars or mandibular second premolars. The records of two groups of patients were used: one group was treated with extraction of mandibular first premolars (age: 13.2 +/- 1.5 years) and the other group with extraction of mandibular second premolars (age: 13.4 +/- 1.4 years). Each group consisted of 26 subjects (16 boys and 10 girls). Maxillary first premolars were extracted in both groups. The two groups were matched by sex, age (within six months), and facial divergence measured by maxillary-mandibular plane angle (MM angle) and ratio of posterior facial height to the total anterior facial height. Student's t-test was used to compare the two groups. Significance was predetermined at P <.05. Second premolar extraction was associated with more forward movement of the mandibular molars, but there was no significant difference in vertical facial growth between the two groups. In both groups, there was no significant change in the mandibular plane angle and the MM angle. The results of this study do not support the hypothesis that mandibular premolar extraction is associated with mandibular overclosure or reduction in the vertical dimension, or both, in subjects with Class II division 1 malocclusion.