无托槽隐形矫治器治疗下颌不同形态扭转牙的三维有限元分析

Clear aligner orthodontic therapy of rotated mandibular teeth with different shapes:a three-dimensional finite element analysis

背景:旋转移动是无托槽隐形矫治中最难以预测的牙齿移动方式之一,牙体形态可影响牙齿去扭转的矫治效果,目前尚无相关的生物力学研究。目的:探讨无托槽隐形矫治器纠正下颌不同形态扭转牙时每步旋转量设计对牙齿生物力学的影响。方法:选择1例伴下颌中切牙及第二前磨牙扭转的成人患者,获取其锥形束计算机断层扫描数据及口内光学扫描数据,建立具有高仿真牙冠形态的下颌牙列、牙周膜、牙槽骨及无托槽隐形矫治器三维有限元模型,分析矫治器在3种不同旋转量设计(1.0°,1.5°,2.0°)下纠正扭转左下颌中切牙(A组)、第二前磨牙(B组)时,目标牙与邻牙的初始位移、牙移动趋势及牙周膜von Mises应力分布。结果与结论:①在不同旋转量加载下,A组目标牙的位移量及牙周膜应力值均明显高于B组,增加无托槽隐形矫治器的每步旋转量可在一定程度上提高目标牙的矫治效率,但相应牙周组织损伤风险亦增加,建议下切牙每步旋转量不超过1.5°,前磨牙不超过2.0°;②A组近中邻牙的最大位移量可达目标牙的65%-105%,对于切牙区的扭转,需特别警惕对邻牙的不利影响;③目标牙在旋转移动过程中伴随近中倾斜及轻微压低移动趋势,邻牙出现倾斜移动趋势,需额外措施加强矫治器对牙齿的三维移动控制。

BACKGROUND:The rotation is unpredictable tooth movement in clear aligner treatment.Tooth shape can affect the efficiency of tooth de-rotation,but there is no relevant biomechanical study.OBJECTIVE:To investigate aligner activation influencing on biomechanics of clear aligner orthodontic therapy of rotated mandibular teeth with different shapes.METHODS:A three-dimensional finite element model of mandibular dentition-periodontium-alveolar bone-appliance with highly simulated crown shape was established based on cone-beam computed tomography and intraoral optical scanning data of an adult who had rotated lower central incisor and second premolar.The initial displacement,movement trend and von Mises stress distribution of periodontium of target teeth and adjacent teeth were analyzed when the loading of three different aligner activation of 1.0°,1.5°and 2.0°was applied to rotated the left lower central incisor(group A)and second premolar(group B).RESULTS AND CONCLUSION:(1)The displacement and periodontium stress of target teeth were significantly higher in the group A than those in the group B under different rotation loads.Increasing the aligner activation could improve the efficiency of tooth de-rotation to a certain degree,but the risk of periodontal tissue injury was also increased.It was suggested that aligner activation should not exceed 1.5°for the lower incisor and 2.0°for the lower premolars.(2)In group A,the displacement of meso-adjacent tooth was 65%-105%as much as target tooth.For incisor de-rotation,we should pay attention to the adverse effect on adjacent teeth.(3)During the rotation movement,mesial tipping and slightly intrusive movement of target teeth were observed,and adjacent teeth showed the trend of tipping movement,which required additional measures to strengthen the grip on three-dimensional movement of teeth.