Objectives: To investigate differences in the anterior hard and soft tissue changes observed during treatment between class I and class II patients treated with and without four bicuspid extraction. Method: This exploratory study sought to identify cephalometric variables whose change during treatment differed as a function of four bicuspid extraction. A new random sample was collected retrospectively in the practice of a single experienced orthodontist. The sample included 48 growing subjects equally balanced (i.e., 24/24) for extraction/non-extraction, Class I/Class II and Male/Female. All subjects had been treated using the full bonded Edgewise appliance. Treatment-associated changes in twenty-four hard and soft tissue linear and angular measures were computed from triple determined landmark coordinates. Results: Only four of the twenty-four measures had mean differences in change during treatment in excess of one degree or one millimeter. These were Interincisal Angle (D 3.03° ), Lower 1 to NB Angle (D 2.35° ), Naso-Labial Angle (D 1.5° ), and Lower 1 to NB Distance ( D 1.41mm). Only the differences in change for Lower 1 to NB Distance were statistically significant (t = 2.44, p<0.02). For the other three measures, inter-individual variability was too great to be sure the observed differences in mean were beyond the probability of chance. It was noted that among the extraction cases (n=24), the retraction of the lower incisor was statistically significantly but mildly associated with greater retraction of the lower lip (r = 0.45, p<0.04). This association was not observed among the non-extraction cases (r = 0.07, p< 0.76).
Conclusions: In general, differences in change during treatment between extraction and non-extraction patients did not appear to be sufficiently large to have substantially different effects on the pretreatment profile.