Skeletal anteroposterior discrepancy and vertical type effects on lower incisor preoperative decompensation and postoperative compensation in skeletal Class III patients

Abstract

Objective: To determine the initial compensation, preoperative decompensation, and postoperative compensation of the lower incisors according to the skeletal anteroposterior discrepancy and vertical type in skeletal Class III patients. Materials and Methods: The samples consisted of 68 skeletal Class III patients treated with two-jaw surgery and orthodontic treatment. Lateral cephalograms were taken before preoperative orthodontic treatment (T0) and before surgery (T1) and after debonding (T2). According to skeletal anteroposterior discrepancy/vertical type (ANB, criteria = −4°; SN-GoMe, criteria = 35°) at the T0 stage, the samples were allocated into group 1 (severe anteroposterior discrepancy/hypodivergent vertical type, N = 17), group 2 (moderate anteroposterior discrepancy/hypodivergent vertical type, N = 17), group 3 (severe anteroposterior discrepancy/hyperdivergent vertical type, N = 17), or group 4 (moderate anteroposterior discrepancy/hyperdivergent vertical type, N = 17). After measurement of variables, one-way analysis of variance with Duncan's multiple comparison test, crosstab analysis, and Pearson correlation analysis were performed. Results: At T0, groups 3 and 2 exhibited the most and least compensated lower incisors. In group 2, good preoperative decompensation and considerable postoperative compensation resulted in different values for T0, T1, and T2 (IMPA, T0 < T2 < T1; P < .001). However, group 3 did not show significant changes in IMPA between stages. Therefore, groups 2 and 3 showed different decompensation achievement ratios (P < .05). Group 3 exhibited the worst ratios of decompensation and stability (24% and 6%, respectively, P < .001). Anteroposterior discrepancy/vertical type (ANB: P < .01 at T0 and T1, P < .001 at T2; SN-GoMe: P < .01, all stages) were strongly correlated with relative percentage ratio of IMPA to norm value. Conclusions: Skeletal anteroposterior discrepancy/vertical type results in differences in the amount and pattern of initial compensation, preoperative decompensation, and postoperative compensation of lower incisors in Class III patients.