目的 利用三维有限元方法比较下颌外斜线区微种植钉远移下牙列时，使用不同长度牵引钩放置不同位点时下颌牙齿的应力分布情况。方法 根据患者锥形束计算机断层扫描（cone beam computed tomography，CBCT）影像数据，在侧切牙和尖牙托槽之间、尖牙和第1前磨牙托槽之间分别固定高度为2、7 mm牵引钩，依次构建出4种微种植钉远移全牙列的有限元模型。在牵引钩与微种植钉间加载 3 N牵引力，观察4种工况中下颌牙齿及牙列等效应力、初始位移变化情况。结果 除高度7 mm牵引钩置于侧切牙与尖牙间时，下中切牙发生冠唇向根舌向的顺时针旋转外，其他3种工况下中切牙均发生冠根均舌向的逆时针旋转趋势；除高度7 mm牵引钩置于尖牙与第1前磨牙间时，下尖牙发生冠向近中移动，其他3种工况下尖牙冠根均向远中移动趋势；4种工况中，下磨牙均发生冠根向远中的逆时针方向旋转趋势。结论 通过三维有限元分析阐明了下牙列整体远移时，不同牵引钩对下颌牙齿移动影响的生物力学机制。在充分理解生物力学机制的情况下，恰当选择牵引钩长度及放置位置可以更有效实现下颌牙列的整体远移。
Objective To study stress distributions of lower dentition distally moved with miniscrews in external oblique line area when the traction hooks with different lengths were placed at different positions by the three-dimensional (3D) finite element method. Methods Based on cone beam computed tomography (CBCT) data from a patient, traction hooks with the heights of 2 mm and 7 mm were constructed and fixed between the lateral incisors and the canine brackets, as well as between the canines and the first premolar brackets. Four kinds of 3D finite element models of full dentition distally moved with miniscrews were constructed. The 3 N traction force was loaded between the traction hook and the miniscrews. The maximum von Mises stress and initial displacement of the mandibular teeth and dentition under four working conditions were analyzed. ResultsWhen the traction hook with 7 mm-height was placed between the lateral incisor and the canine, the lower central incisor rotated clockwisely, with the crown moving labially and the root moving lingually. But under the other three working conditions, the central incisor rotated counterclockwisely, and the crown and root moved lingually. When the traction hook with 7 mm-height was placed between the canine and the first premolar, the lower canine crown moved proximally. But under the other three working conditions, both the crown and root moved distally. Under four working conditions, the mandibular molars all rotated counterclockwisely,with the crown and root moving distally. Conclusions Through 3D finite element analysis, biomechanical mechanism of the effect of different traction hooks on mandibular tooth movement during distalization of the lower dentition was elucidated.With full understanding of the biomechanical mechanism, proper selection for length and placement of the traction hook can achieve distal movement of the entire mandibular dentition more efficiently.