舌侧附件矫治扭转上颌前磨牙的有限元分析

目的　通过有限元分析颊侧和舌侧不同规格附件在矫治扭转上颌第一前磨牙时的矫治效率，以确定矫治率最优的附件位置及规格。方法　实验1：纳入1例正常 ]，建模分为空白对照组、颊侧水平矩形附件组、颊侧垂直矩形附件组、舌侧水平矩形附件组、舌侧垂直矩形附件组。除空白对照组外，其余4组每组内均含有3个亚组（以矩形附件长度3/4/5 mm分组）。以前磨牙牙体长轴为旋转中心，施加2° ]面观顺时针旋转矫治力后进行模拟运算，观察各组模型的应力分布、位移变化。实验2：对实验1的附件改良后分为4组，即对照组、舌侧b（2/3）矩形附件组、舌侧b（1/2）矩形附件组、舌侧b（1/3）矩形附件组，余方法同实验1。结果　实验1中牙周膜应力、牙冠最大位移量及施加位移后牙体旋转度均以舌侧垂直矩形附件组中3 mm附件最大，且随着各组内附件规格增加而减小，垂直矩形附件组较水平矩形附件组大，空白对照组最小。实验2中的舌侧b（2/3）垂直矩形附件组与舌侧3 mm垂直矩形附件组牙周膜应力、牙冠最大位移量最为接近，而旋转度以对照组最大，并随着附件规格减小而降低。结论　舌侧垂直3 mm矩形附件更利于上颌扭转前磨牙的矫治，舌侧b（2/3）垂直附件可作为优化附件的改良规格。

Finite element analysis of lingual attachment in the treatment of torsional maxillary premolars

Objective　To analyze the orthodontic efficiency of buccal and lingual attachments with different sizes by finite element method in order to determine the optimal position and size of the attachments. Methods　Experiment 1: a normal occlusion sample was selected to establish the model. Attachments were divided into five groups: the control group, the buccal horizontal rectangular attachment group, the buccal vertical rectangular attachment group, the lingual horizontal rectangular attachment group and the lingual vertical rectangular attachment group. Except for the control group, the other 4 groups contained 3 subgroups (grouped by rectangular attachment length 3/4/5 mm). The long axis of the maxillary first premolar was set as the rotation central axis, and a 2° clockwise rotation (occlusion view) displacement was applied to carry out simulation operation to observe the stress distribution and displacement changes. In experiment 2, the attachment was modified and divided into 4 groups: the control group, the lingual b (2/3) rectangular attachment group, the lingual b (1/2) rectangular attachment group and the lingual b (1/3) rectangular attachment group. The method was the same as experiment 1. Results　In experiment 1, the periodontal membrane stress, the maximum displacement of the crown and the torsion efficiency of orthodontic force showed the maximum stress with the 3 mm attachment size in the lingual vertical group, and it decreased with the increase of the attachment size units in each group. The vertical group was larger than the horizontal group, and the expression of the torsion degree efficiency was the smallest in the group without the attachment. In the experiment 2, the periodontal membrane stress and the maximum displacement of the crown of the b (2/3) lingual vertical group were the closest to that of the 3 mm lingual vertical group, while the highest expression of torsion efficiency was the 3 mm lingual vertical group, and decreased with the decrease of the size. Conclusion　The 3 mm lingual vertical group shows more beneficial to correct torsional premolars, and the b (2/3) lingual vertical attachment could be used as the improved specification.