关键词: 无托槽隐形矫治器, 微种植钉, 磨牙远移, 三维有限元模型

Abstract: Objective    To investigate the effect of different micro-implant anchorage（MIA） positions on the molar displacement trend and stress distribution of anterior teeth when applying invisible orthodontics appliance combined with MIA by using three-dimensional finite element model. Methods    One female patient requiring non-decreasing orthodontic treatment of distally displaced molars with invisible orthodontics appliance who visited the Department of Orthodontics of Dalian Stomatological Hospital on 2021-02-16 was selected as the modeling subject. A three-dimensional finite element model was constructed to simulate 8 working conditions with MIA located between the second premolar and the first molar，between the first molar and the second molar，and at 4，6，8，and 10 mm away from the top of the alveolar ridge，respectively，and 1.47 N orthodontic force was loaded between the MIA and the lingual clasps on the labial surfaces of the cuspids. The displacement of the maxillary anterior teeth and the distribution of the periodontal stress in the cuspids in the 8 working conditions after 1 s of loading were analyzed. Results    In all eight conditions，the maxillary mesial incisors showed a trend of displacement in the labial direction of the crowns and palatal direction of the roots；the labial displacement of the crowns of the maxillary mesial incisors decreased with the increase in the height of the micro-implant anchorage，and the displacement was smaller when the anchorages were located in the relatively proximal mesial area（between the maxillary second premolar and the first molar）. The maxillary cuspids showed a trend of displacement in the labial direction of the crowns and palatal direction of the roots，and the crowns showed a trend of labial inclination. The absolute values of the minimum principal stresses in the periodontium of the maxillary cuspids increased with the increase in the height of the micro-implant anchorages，and the minimum principal stresses were greater when the micro-implant anchorages were located in the relatively proximal center. Conclusion    When the invisible orthodontic appliance is used with MIA for distal displacement of maxillary molars，the higher MIA position in the relatively proximal mesial region is good for the torque control of incisors，and the lower MIA position in the relatively distal mesial region is good for the maintenance of periodontal tissues in the cuspal region in the eight conditions of the present experiment.

Key words: invisible orthodontic appliance, micro-implant anchorage, molar distraction, three-dimensional finite element model