隐形矫治中不同附件及位置矫治扭转尖牙的三维有限元分析

Three-dimensional finite element analysis of torsional canines treated with different attachments and positions in clear aligner

目的 通过三维有限元法比较不同附件以及不同放置位置对隐形矫治器矫正左上颌尖牙扭转的影响。方法 通过扫描数据分别建立矫治器-附件-尖牙-牙周膜-松质骨-皮质骨(有附件组)与(无附件组)有限元模型。其中有附件组中的附件分为垂直矩形附件、垂直楔形附件、优化扭转附件,放置位置又分为颊侧中1/3、远中1/3以及颊-舌侧中1/3。将各组的矫治器以尖牙牙体长轴为旋转中心轴,将矫治器远中扭转2°,在MSC.Marc.Mentat软件中模拟运算,收集各应力、位移分布云图及最大应力、位移值。结果 (1)无论有无附件,尖牙位移及牙周膜应力分布趋势相似,但附件组的尖牙位移值及牙周膜各种应力值均大于无附件组;(2)选用相同附件情况下,放置于颊侧中1/3的应力值和最大初始位移最高,颊-舌侧放置的应力和位移表达更加高效,远中1/3放置效果相对较差。结论 (1)颊面中1/3与颊-舌侧放置应力值和最大初始位移量无明显差别,但是颊-舌侧放置矫治效果更加高效,消除了不必要的倾斜移动,对固位的要求也更低。(2)单牙模型中垂直矩形和垂直楔形附件矫治效果显著较优化扭转附件好,实际效果有待临床进一步验证。

Objective To compare the effect of different attachments and positions on the left maxillary canine tooth torsion in clear aligner by three-dimensional finite element analysis. Methods Finite element models of the clear aligner-attachment-maxillary canine-periodontal ligament-spongy bone-cortical bone(attachment groups and non-attachment group) were established according to the scanning data of in vitro maxillary canine. The models with attachments were divided into three groups based on different kinds of attachments, namely vertical rectangular attachment, vertical wedge-shaped attachment, optimized torsion attachment groups. The placement positions were divided into buccal middle 1/3, distal 1/3 and buccal-lingual middle 1/3. Two degrees clockwise rotation of the tooth long axis was applied to the clear aligner. Actions of the appliance and the canine were simulated and calculated by MSC.Marc.Mentat software. Then, nephograms of stress and displacement, and the maximum stress and displacement values were collected. Results(1) The distribution trend of the displacement of canine and the stress of periodontal ligament was similar with or without attachments, but the displacement value of canine and the stress value of periodontal ligament in the attachment group were higher than that in the non-attachment group.(2) When the same attachment was selected, the stress value and maximum initial displacement value were the highest in the buccal middle 1/3;the stress and displacement expression were more efficient in buccal-lingual middle 1/3, and the effect of the distal 1/3 was relatively bad. Conclusion(1) There is no significant difference in the stress value and the maximum initial displacement between the buccal middle 1/3 and the buccal-lingual middle 1/3, but the buccal-lingual middle 1/3 is more efficient, eliminating unnecessary tipping movement and requiring less retention.(2) The orthodontic effect of vertical rectangular and vertical wedge-shaped attachments in one tooth model is significantly better than that of optimized torsion attachments. The actual effect needs further clinical verification.