Objectives: To investigate the compensation of upper first molar in adult skeletal class Ⅲ patients. Methods: The sample consisted of 48 skeletal class Ⅲ patients with orthodontic-surgical treatment from February 2011 to January 2015 in Peking University School and Hospital of Stomatology. They were allocated into 2 groups based on extraction, 28 patients in extraction group and 22 patients in non-extraction group. Dental casts were taken before and after treatment, and all the casts were scanned with a computer-assisted three-dimensional (3D) scanning system. Acquired 3D data were analyzed by Rapidform 2006. The tip and torque of the upper first molar were measured and analyzed. Results: The tip and torque of the upper first molar in the skeletal class Ⅲ patients after treatment had no difference between extraction group and non-extraction group (P=0.150, P=0.144). The torque of upper first molar in extraction group [-3.32° (-5.10°, 1.16°)] before treatment was bigger than that in non-extraction group [-6.94° (-13.06°, -0.42°)] (P=0.005), and the inclination of upper first molar in extraction group was more obvious. Conclusions: In skeletal class Ⅲ patients, the upper first molar inclined buccally to compensate the discrepancy and extraction was usually necessary for decompensation.
目的： 探讨正畸-正颌联合治疗骨性Ⅲ类错 畸形的上颌第一磨牙代偿特征，为临床医师制定矫治计划提供参考。 方法： 选取2011年2月至2015年1月于北京大学口腔医学院·口腔医院正畸科完成正畸-正颌联合治疗的骨性Ⅲ类错 畸形成年患者48例（男性22例，女性26例），根据上颌减数与否分为减数组（28例）和非减数组（20例）。采用激光扫描仪扫描矫治前后的牙颌模型。使用Rapidform 2006软件测量上颌第一磨牙的轴倾和转矩，获得并对比两组上颌第一磨牙的代偿特征数据。 结果： 骨性Ⅲ类错 畸形矫治后减数组与非减数组上颌第一磨牙的轴倾、转矩差异均无统计学意义（P=0.150，P=0.144 ）；矫治前减数组转矩的中位数（下四分位数，上四分位数）为-3.32°（-5.10°，1.16°），非减数组转矩为-6.94°（-13.06°，-0.42°），两组差异有统计学意义（P=0.005），即减数组颊倾代偿更明显。 结论： 骨性Ⅲ类错 畸形患者上颌第一磨牙颊向倾斜代偿，其颊倾代偿越明显，术前正畸去除上颌后牙代偿越需要间隙，正畸方案越有可能考虑减数。.
Keywords: Imaging, three-dimensional; Malocclusion, Angle class Ⅲ; Molar; Torque.