Objectives: This study aimed to construct the finite element model of the mandibular first molar with the invisible appliance and explore the dentition movement characteristics of the mandibular first molar when using micro-implant anchorage and different initial positions of the first molar.
Methods: Models of the mandible, tooth, periodontal membrane, and invisible appliance were constructed using cone beam computed tomography (CBCT) data. The two groups were divided into the non-anchorage group and the micro-implant group (between the roots of the first molar and the second molar) based on whether the elastic traction of the micro-implant was assisted or not. The two groups were divided into the following conditions based on the starting position of the first molar: Working condition 1: the distance between the first molar and the second premolar was 0 mm; working condition 2: the distance between the first molar and the second premolar was 1 mm; working condition 3: the distance between the first molar and the second premolar was 2 mm; working condition 4: the distance between the first molar and the second premolar was 3 mm. The data characte-ristics of total displacement and displacement in each direction of dentition were analyzed.
Results: In the non-ancho-rage group, all the other teeth showed reverse movement except for the first molar which was moved distally. Meanwhile, in the micro-implant group, except for a small amount of mesial movement of the second molar in wor-king condition 1, the whole dentition in other working conditions presented distal movement and anterior teeth showed lingual movement, among which the distal displacement of the first molar in working condition 4 was the largest. With the change of the initial position of the first molar to the distal, the movement of the first molar to the distal, the premolar to the mesial, and the anterior to the lip increased, while the movement of the second molar to the mesial decreased.
Conclusions: The micro-implant can effectively protect the anterior anchorage, increase the expression rate of molar distancing, and avoid the round-trip movement of the second molar. The initial position of the first molar movement is related to the amount of distancing and the remaining tooth movement.
目的: 构建隐形矫治器远移下颌第一磨牙的有限元模型，探究是否使用微种植体支抗及不同第一磨牙起始位置进行远移时的牙列移动特点。方法: 使用锥形束CT（CBCT）数据构建下颌骨、牙齿、牙周膜及隐形矫治器模型，依据是否辅助微种植体弹性牵引分为无支抗组及微种植体组（第一磨牙与第二磨牙根间），在两组中以第一磨牙起始位置分为工况1：第一磨牙距第二前磨牙0 mm；工况2：第一磨牙距第二前磨牙1 mm，工况3：第一磨牙距第二前磨牙2 mm；工况4：第一磨牙距第二前磨牙3 mm。分析各工况牙列总体位移及各方向位移的数据特点。结果: 无支抗组：除第一磨牙向远中移动外，其余牙均表现为反向移动。微种植体组：除工况1中第二磨牙表现为少量近中移动，其余工况全牙列均表现为远中移动、前牙舌向移动，其中工况4第一磨牙远中位移值最大。随着第一磨牙起始位置向远中改变，第一磨牙向远中、前磨牙向近中及前牙向唇侧移动量增加，而第二磨牙向近中移动量减小。结论: 微种植体能够有效保护前牙支抗，增加磨牙远移的表达率，避免第二磨牙出现往返移动，且第一磨牙移动起始位置与其远移量及其余牙齿移动量有关。.
Keywords: clear aligner; finite element analysis; mandible; micro-implant anchorage; molar distalization.