[Three-dimensional finite element study on the effects of maxillary anterior two-step retraction and en-masse retraction with clear aligners].

Objective: To investigate the effects of two-step retraction and en-masse retraction on tooth movement pattern of anterior teeth and posterior anchorage with clear aligners using three-dimensional finite element analysis. Methods: A finite element model of maxillary first premolar extraction case undergoing clear aligner treatment was established based on maxillofacial cone-beam CT data of a 24-year-old adult male with individual normal occlusion, who visited Department of Oral Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine for impacted mandibular third molar in June, 2022. The initial tooth displacement of five anterior retraction protocols (two-step with canine retraction, two-step with incisor bodily retraction, two-step with incisor retraction-overtreatment, en-masse bodily retraction, and en-masse retraction-overtreatment) were evaluated. Results: Two step with canine retraction caused distal tipping of the canine and labial tipping of the incisors (0.18° for central incisor and 0.13° for lateral incisor). Two step with incisor retraction caused mesial tipping of the canine. In two step with bodily retraction protocol, uncontrolled lingual tipping was found in central incisor (0.29°) and lateral incisor (0.32°). In two-step with incisor retraction-overtreatment protocol, the movement pattern of the incisors didn't change, but the inclinations reduced to 0.21° and 0.18°. En-masse retraction caused distal tipping of the canine. In en-masse bodily retraction protocol, uncontrolled lingual tipping was also found in central incisor (0.19°) and lateral incisor (0.27°). In en-masse retraction-overtreatment protocol, the central incisor showed controlled lingual tipping (0.02°) and the lateral incisor showed palatal root movement (0.03° labial inclination). Posterior teeth exhibited mesial tipping in all five protocols. Conclusion: En-masse retraction with incisor overtreatment was beneficial to incisor torque control in clear aligner treatment.目的： 通过三维有限元分析探讨无托槽隐形矫治上颌前牙分步内收和整体内收对切牙移动方式和后牙支抗的影响，以期为临床提供参考。 方法： 选取1例2022年6月因下颌第三磨牙阻生就诊于上海交通大学医学院附属第九人民医院口腔外科的患者（24岁，男性，个别正常（牙合）），使用其口腔颌面部锥形束CT构建无托槽隐形矫治三维有限元模型，设计减数上颌第一前磨牙，建立5组工况：分步内收-尖牙平移组、分步内收-切牙平移组、分步内收-切牙过矫治组、整体内收-切牙平移组和整体内收-切牙过矫治组。分析各组前牙和支抗后牙的初始位移。 结果： 分步内收-尖牙平移组尖牙发生远中倾斜移动，中切牙和侧切牙分别唇向倾斜0.18°和0.13°。分步内收-切牙平移组和分步内收-切牙过矫治组尖牙均表现为近中倾斜移动；其中，切牙平移组中切牙和侧切牙出现不可控舌倾，分别倾斜0.29°和0.32°；切牙过矫治组中切牙和侧切牙的舌倾角减少至0.21°和0.18°。整体内收-切牙平移组和整体内收-切牙过矫治组尖牙均表现为远中倾斜移动；其中，切牙平移组中切牙和侧切牙仍出现不可控舌倾，分别倾斜0.19°和0.27°；切牙过矫治组中切牙发生可控的倾斜移动，舌倾角降至0.02°，侧切牙呈控根移动，表现为0.03°唇倾。5组后牙均发生近中倾斜移动。 结论： 无托槽隐形矫治内收上前牙时，设计整体内收和切牙过矫治有利于切牙的转矩控制。.