隐形矫治磨牙远移的三维有限元分析

目的　构建隐形矫治器上颌磨牙远移的生物力学研究模型，分析矫治体系的初始位移及应力分布特点，为该技术的临床应用提供指导。方法 建立隐形矫治上颌磨牙远移的三维有限元模型，在ANSYS软件中采用非线性有限元法通过数值仿真分析求得受力瞬间牙齿在牙周膜及周围牙槽骨等约束下的移动方式、牙套形变、牙周膜应力分布，并探索适宜的Ⅱ类牵引增强前牙支抗的必要性及适宜力值。结果 第二磨牙远移的同时伴有其牙冠远中倾斜、伸长及舌侧倾斜；其余牙表现为唇/颊倾、压低且位移量与距支抗牙距离成反比。牙周膜等效应力越靠近颈缘越大，距离第二磨牙越远越小，均小于牙周组织可承受最大应力。矫治器在第二磨牙处出现应力集中现象，位移峰值小于材料的弹性极限和拉伸极限强度。100 g Ⅱ类牵引可以有效抵抗前牙唇倾，300 g牵引力作用于牙列后超过牙周膜最大承受力值。结论 使用无托槽矫治技术远移磨牙不能实现单纯的整体移动且支抗牙有一定的支抗丧失，需要进行必要的支抗控制。100 g Ⅱ类牵引即可有效抵抗推磨牙带来的前牙支抗丧失，300 g牵引力作用下牙周膜受力过大，尽量避免使用。

Three dimensional-finite element analysis of molar distalization with clear aligners

Objective　 To establish a three-dimensional (3D) model of maxillary molar distalization with clear aligners, analyze the initial displacement and stress distribution of the orthodontic system and find the optimal force for anterior anchorage. Methods A 3D Finite Element (FE) model of maxillary molars distalization including the teeth, periodontal ligament (PDL), alveolar bone and clear aligners were conducted to analyze the effects of molar distalization and different forces on Class II elastics. Results The distal movement of the second molar was accompanied by distal inclination, distal rotation, extrusion and lingual inclination. The anterior teeth showed labial inclination and depression, and the displacement was inversely proportional to the distance from the abutment teeth. All the anterior teeth moved backward in every group of Class II elastic. Except for applying a force of 300g on the aligner, all stress didn’t exceed the maximum magnitude for the periodontal tissue. In addition, the stress concentration in the second molar and the displacement peak was less than the elastic and tensile limit of the aligner material. Conclusion Molar distalization with clear aligners can’t completely induce bodily movement, and the anterior teeth require additional anchorage control. A Class II elastic of 100g is sufficient to enhance anterior anchorage, while applying a force of 300g on the aligner should be avoided for the health of periodontal tissues.