Change in maxillary incisor inclination during surgical-orthodontic treatment of skeletal Class III malocclusion: comparison of extraction and nonextraction of the maxillary first premolars.Am J Orthod Dentofacial Orthop. 2013 Mar; 143(3):324-35.AJ
The purpose of this study was to investigate differences in preoperative decompensation and postoperative compensation of the maxillary incisors in patients with skeletal Class III malocclusion treated with 2-jaw surgery and extraction or nonextraction of the maxillary first premolars.
The subjects consisted of 50 skeletal Class III patients who had a normal maxillary position, prognathic mandible, and mild crowding in the maxillary arch (≤4 mm). All patients were treated with 2-jaw surgery. They were divided into 2 groups: group 1 (n = 25) had extraction of the maxillary first premolars, and group 2 (n = 25) had no extractions. Lateral cephalograms were analyzed before treatment (T0), 1 month before surgery (T1), 1 day after surgery (T2), and after debonding (T3). After measurement of the skeletodental variables, statistical analyses were performed.
At T0, group 1 exhibited more compensated maxillary incisors compared with group 2 (U1-SN, P <0.001). Considerable preoperative decompensation in group 1 and negligible preoperative decompensation in group 2 occurred at T1 (ΔU1-SN, -9.1° vs 1.1°). Although maxillary incisor inclination significantly decreased with surgical movement of the maxilla at T2, this increased to compensate for the postsurgical skeletal relapse in both groups at T3. Although 24% of group 1 had a normal range of maxillary incisor inclination (U1-SN) at T0, it increased to 68% at T1. A dominant pattern of the subjects within the normal range of U1-SN was maintained in groups 1 and 2 (80% and 96% at T2, and 72% and 80% at T3, respectively). According to the achievement ratio, the U1-SN value became close to the norm mainly by preoperative decompensation in group 1 (95.5%) and by surgery in group 2 (130.2%).
The results of this study might provide effective guidelines for predicting the amount and pattern of preoperative decompensation and postoperative compensation of the maxillary incisors in skeletal Class III patients treated with 2-jaw surgery.