Abstract: Objective    To investigate the effect of attachments on tooth movement pattern of maxillary anterior teeth en masse retraction upon clear aligner therapy by a three-dimensional finite element analysis. Methods    The maxillary cone-beam CT data of an adult was selected to construct a three-dimensional finite element model of first premolar extraction case treated with clear aligners. Four experimental groups were established according to the placement protocols of attachments on incisors：without attachments，attachments on centrals only，attachments on laterals only，and attachments on both centrals and laterals. The models were imported into Ansys Workbench software to simulate en mass incisor retraction with intrusion and lingual root torque. The initial displacement pattern of the dentition and the stress distribution on attachments were analyzed. Results    Models without attachments and with attachments on centrals only displayed lingual tipping movement on all incisors. Molars exhibited mesial tipping while the cuspids extruded and inclined mesially. The group with attachments on laterals only and group with attachments on both incisors displayed tooth movement pattern towards en masse retraction and intrusion. Compression stresses were noted concentrating on the gingival surface of the incisor attachments. Conclusion    During anterior retraction upon clear aligner therapy，placing attachments on lateral incisors is helpful to achieve en masse retraction，while central incisor attachments have less effect on the tooth movement pattern.

Key words: clear aligner, anterior retraction, tooth movement, attachment, finite element analysis

摘要： 目的    通过拔除上颌第一前磨牙后前牙内收的隐形矫治三维有限元模型，分析切牙上设置附件对牙齿移动方式的影响。方法    基于1例成年患者颌骨的锥形束CT影像数据，按照切牙上有无附件，构建4组拔除第一前磨牙的上颌隐形矫治模型，分别为切牙无附件组、侧切牙单附件组、中切牙单附件组和双附件组；导入Ansys Workbench三维有限元软件，设置4个上切牙控根压入内收的隐形矫治过程，分析牙列初始位移和附件的应力分布。结果    切牙无附件组及中切牙单附件组均发生4个切牙的舌向倾斜移动，后牙产生不同程度的近中倾斜移动，尖牙近中倾斜伴有伸长；侧切牙单附件组及双附件组切牙呈整体内收压入移动趋势，切牙附件的龈方可观测到压应力集中。结论    隐形矫治内收上前牙时，在侧切牙放置附件有助于切牙整体内收的表达，而中切牙附件对牙移动方式的影响较小。

关键词: 隐形矫治器, 前牙内收, 牙移动, 附件, 有限元分析