[Construction and assessment of a three-dimensional finite element model of mandibualr second molar mesialization using customized lingual appliance and mini-implant].

Objective: To construct a three-dimensional (3D) finite element model and analyze the biomechanical characteristics during mandibular second molar mesialization using customized lingual appliances and mini-implant. Methods: One adult student volunteer from The First Affiliated Hospital of Zhengzhou University with lower left first molar extraction was selected. After CT scanning, Mimics, Geomagic, ANSYS were employed to develop a 3D finite element model including customized lingual brackets, stainless steel lingual arch wire, buccal buckles, lower dentition, periodontal ligaments and alveolar bone. Four different loading methods (1. the force of 1.470 N loaded at the lingual side only; 2, 3, 4. the forces of 0.490, 0.735 and 0.980 N loaded at both buccal and lingual sides, respectively.) were included. The initial displacements of the lower second molar and stress distribution in the periodontal ligaments were analyzed. Results: More uniform stress distributions in the periodontal membrane of mandibular left second molar were found when the mesial force were loaded at both buccal and lingual sides than the force loaded at lingual side only. More inclination of the second molar was observed when force loaded at both sides than at lingual side only. With the values of the force increased, the mesial inclination potential of the second molar, the initial movement of the second molar and the stress distribution in the periodontal membrane increased. Under the force of 0.735 N at both buccal and lingual sides, mesially inclined initial displacements of the mandibuar second molar were observed and the stress values of von Mises was in the suitable area. Conclusions: Less second molar rotation was found when the force loaded at both buccal and lingual sides than loaded at lingual side only. However, force loaded at both sides would increase the measial inclination potential of the second molar.目的： 通过三维有限元法分析个性化舌侧矫治近中移动下颌第二磨牙的移动规律及牙周膜应力分布特征，为正畸临床提供参考。 方法： 选取来源于郑州大学第一附属医院的下颌左侧第一磨牙缺失的男性成年学生志愿者1名，通过多排螺旋CT扫描及三维重建，建立包括个性化舌侧托槽和弓丝、下牙列、牙周膜、下颌骨的舌侧矫治三维有限元模型，设置4种工况近中牵引下颌左侧第二磨牙：工况一为单纯舌侧加载1.470 N力；工况二、三、四为颊舌侧同时加载，设置下颌左侧第二前磨牙牙根远中为颊侧种植体支抗植入位置，分别在颊舌侧同时各加载0.490、0.735、0.980 N力。分析第二磨牙的初始位移趋势和牙周膜应力分布。 结果： 近中牵引下颌第二磨牙时，相比工况一，工况二、三、四的牙齿扭转和整体前移的趋势减少，但颊舌侧同时前移的趋势更均匀，牙周膜应力分布更加均匀。工况二、三、四下，随着载荷的增加，磨牙初始位移趋势和牙周膜应力均增加，工况三牙周膜的应力范围为（1.43~3.58）×10(－2) MPa，较适宜磨牙的近中移动。 结论： 相较单纯舌侧加力，颊侧种植体辅助下颊舌侧同时加力可控制舌侧矫治下颌第二磨牙前移时牙齿冠状向扭转，但可增加近中倾斜的趋势，临床应用时还需配合额外的控制磨牙近中倾斜的措施。.