目的·应用三维有限元分析法比较骨支抗式和牙支持式快速扩弓联合前方牵引对颅颌面骨缝、骨骼点、骨骼及上颌牙列的作用效果，以指导临床上选择合适的牵引方式及位置。方法·选取一名替牙列期骨性Ⅲ类错伴上颌发育不足的青少年的锥形束计算机断层扫描（cone beam computed tomography，CBCT）影像，建立上颌复合体的三维有限元模型（包括颅颌面骨缝、骨骼点、骨骼及上颌牙列），并在此基础上分别建立骨支抗式、牙支持式快速扩弓联合前方牵引三维有限元模型，而后将前述模型组装成为上颌复合体和骨支抗式快速扩弓联合前方牵引三维有限元模型（模型1）、上颌复合体和牙支持式快速扩弓联合前方牵引三维有限元模型（模型2）。依次根据扩弓方式、牵引位置的不同，在模型1、2中分别建立以下工况：① 根据扩弓方式，将模型1设置为A组，模型2设置为B组。② 根据牵引位置，将上述2组继续分为试验组Ⅰ组（牵引钩位于双侧尖牙颊侧）、Ⅱ组（牵引钩位于双侧第一前磨牙颊侧）和Ⅲ组（牵引钩位于双侧第二前磨牙颊侧）。同时，分别将A、B组中不联合前方牵引设置为对照组（即为A0组、B0组）。采用图表分析的方法对A、B组在不同牵引位置时的颅颌面骨缝应力分布特征，以及颅颌面骨骼点、颅颌面骨骼及上颌牙列的位移趋势进行分析。结果·在颅颌面骨缝应力分布特征方面，A、B组中翼突上颌缝的等效应变最大，且随着牵引位置的后移其等效应变均逐渐增加；AⅠ组各骨缝的最大主应变大于BⅠ组。在颅颌面骨骼位移趋势方面，随着牵引位置的后移，在水平向上A、B试验组的鼻骨和上颌骨均向右移动且位移趋势逐渐减小，在矢状向上该2组的鼻骨均向后移动且位移趋势均减小、上颌骨均向前移动且位移趋势均增大，在垂直向上该2组的鼻骨均向下移动且位移趋势逐渐减小、上颌骨均向上移动且位移趋势逐渐减小。在颅颌面骨骼点（ANS、PNS）位移趋势方面，A组中上颌平面（ANS-PNS平面）发生顺时针旋转，且随着牵引位置的后移该平面顺时针旋转趋势减小；而B组中ANS-PNS平面发生逆时针旋转，且随着牵引位置的后移该平面逆时针旋转趋势更加明显。在上颌牙列位移趋势方面，A、B试验组的中切牙在水平向、矢状向、垂直向上的位移均为负值，即存在远中、唇向、伸长的位移趋势，第一磨牙在水平向上的位移均为负值，即存在颊向位移趋势；且随着牵引位置的后移，中切牙牙冠的唇向移动趋势增大，第一磨牙牙冠从远中移动变为近中移动。结论·临床上前方牵引位置放于后侧有利于上颌骨前移；骨性Ⅲ类错青少年患者可选择不同的扩弓方式联合前方牵引，在实现上颌骨前移的同时实现上颌平面的有利旋转。

Objective ·To compare the effects of bone-anchored rapid expansion and tooth-borne rapid expansion combined with protraction on craniofacial sutures, skeletal points, bones and maxillary dentition using three-dimensional finite element analysis, and provide guidance for the clinical selection of appropriate traction methods and sites. Methods ·A cone beam computed tomography (CBCT) image of one adolescent with skeletal class Ⅲ malocclusion and maxillary hypoplasia during the mixed dentition period was selected to establish a three-dimensional finite element model of the maxillary complex (including craniofacial sutures, skeletal points, bones and maxillary dentition). Based on this, the three-dimensional finite element models of bone-anchored and tooth-borne rapid expansion combined with protraction were respectively established. Then, the aforementioned models were assembled into a three-dimensional finite element model of maxillary complex with bone-anchored rapid expansion combined with protraction (Model 1), and a three-dimensional finite element model of maxillary complex with tooth-borne rapid expansion combined with protraction (Model 2). According to the different expansion methods and protraction sites, the following conditions were set up: ① Based on the expansion methods, Model 1 was set as Group A, and Model 2 was set as Group B. ② Based on the protraction sites, Group A and B were further divided into experimental group Ⅰ(protraction hooks were placed buccally on both sides of the maxillary canines), experimental group Ⅱ(protraction hooks were placed buccally on both sides of the maxillary first premolars) and experimental group Ⅲ (protraction hooks were placed buccally on both sides of the maxillary second premolars), respectively. Additionally, as a control, Group A0 used bone-anchored rapid expansion alone without protraction, while Group B0 used tooth-borne rapid expansion without protraction. The stress distribution characteristics of craniofacial sutures in groups A and B at different protraction sites, as well as the displacement trends of craniofacial skeletal points, craniofacial bones and maxillary dentition were analyzed by using charts and tables. Results ·In terms of stress distribution characteristics of craniofacial sutures, pterygomaxillary suture′s equivalent strain was maximal in both groups A and B, and it increased when protraction hooks were placed backwards. The maximum principal strain value of each suture in Group AⅠ was larger than that in Group BⅠ. In terms of the displacement trend of craniofacial bones, as the protraction sites shifted posteriorly, both the nasal bones and maxilla in the horizontal direction moved rightward with decreasing displacement trends in both groups A and B. In the sagittal direction, the nasal bones moved posteriorly with decreasing displacement trends, while the maxilla moved anteriorly with increasing displacement trends in groups A and B. In the vertical direction, the nasal bones moved downward with decreasing displacement trends, and the maxilla moved upward with decreasing displacement trends in groups A and B. In terms of displacement trends of craniofacial skeletal points (ANS, PNS), the maxillary plane (ANS-PNS plane) in Group A underwent clockwise rotation, with the clockwise rotation trend decreasing as the protraction sites shifted posteriorly, while the maxillary plane (ANS-PNS plane) in Group B underwent counterclockwise rotation, with the counterclockwise rotation trend becoming more apparent as the protraction sites shifted posteriorly. In terms of the displacement trend of the maxillary dentition, the displacement of the central incisors in the horizontal, sagittal and vertical directions in the experimental groups A and B was all negative, presenting a tendency to move distally, labially and extrusively. The displacement of the first molar in the horizontal direction was also negative, indicating a trend of buccal displacement. Additionally, as the protraction site shifted posteriorly, the labial movement trend of the central incisors′ crown increased, and the crowns of the first molars changed from mesial to distal movement. Conclusion ·Clinically, placing protraction sites posteriorly is beneficial for the anterior movement of the maxilla. Adolescent with skeletal class Ⅲ malocclusion can choose different rapid expansion with protraction to achieve maxillary anterior displacement while realizing favorable rotation of maxillary plane.