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 twojaw 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, criteria524u; SN-GoMe, criteria 5 35u) at the T0 stage, the samples were allocated into group 1 (severe anteroposterior discrepancy/hypodivergent vertical type, N 5 17), group 2 (moderate anteroposterior discrepancy/hypodivergent vertical type, N 5 17), group 3 (severe anteroposterior discrepancy/hyperdivergent vertical type, N 5 17), or group 4 (moderate anteroposterior discrepancy/hyperdivergent vertical type, N 5 17). After measurement of variables, one-way analysis of variance with Duncans 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. (Angle Orthod. 2011;81:64–74.)