滑动法关闭下颌拔牙间隙的力学行为有限元分析

Mechanical characteristics during closing mandibular extraction space through sliding mechanics with finite element analysis

目的模拟临床加载力系统,研究滑动法内收下前牙过程中,不同方向载荷作用下,牙及弓丝力学行为的变化。方法建立含有托槽、弓丝、前后牙牵引钩的下牙列及下颌骨有限元模型。连接前后牵引钩上的点来确定矫治力的方向。并通过改变牵引钩高度来改变矫治力的作用点和方向。分析计算每一组加载力对牙的三维瞬间移动趋势、牙周膜的单元应力、弓丝的节点最大位移。结果前后牵引钩高度的变化与各牙角位移及牙周膜应力间均有相关性(P<0.01),各牙在不同后牙牵引钩高度,均随着前牙牵引钩高度变化而产生不同的移动。①随着前牙牵引钩高度的增加,中切牙、侧切牙的移动趋势逐渐由近中舌侧倾斜变为近中唇侧倾斜;而尖牙则向远中舌侧倾斜;第二前磨牙由近中颊侧倾斜变为近中舌侧倾斜;第一磨牙则由近中舌侧倾斜变为远中舌侧倾斜,且近中根比远中根舌向倾斜角度要大。②全牙弓牙周膜的最大应力始终出现在侧切牙的唇侧根尖1/3处;而尖牙、第一磨牙的牙周膜最大应力分别集中在牙槽嵴顶、根分叉处。结论在临床治疗中,可通过改变牵引钩的高度来实现前后牙的不同移动趋势,在弓丝上弯制不同的序列以更好地控制支抗牙。

Objective To analyze the mechanical characteristic changes of teeth and arch in different loading directions during closing mandibular extraction space through sliding mechanics to simulate clinical loading system. Methods Three-dimensional finite element model,comprising brackets,archwire,crampable hooks ,mandibular dention and mandible,was reconstructed. The force direction was determined by connecting the points in the anterior and posterior crampable hook,and the force point and force direction were changed with the adjustment of the heights of crampable hook. Then three-dimensional movement trend of teeth,stress distribution in periodontal membrane and the largest displacement of archwire nodes in each group were calculated and analyzed. Results It was found that the heights of crampable hook were correlated with the movement of teeth and stress distribution in periodontal membrane （P〈0.01）. Under different height of the posterior crampable hook,the movement trend of teeth was changed according to the height of anterior crampable hook. ①With the height increase of the anterior crampable hook,the movement trend of the central and lateral incisors varied from mesial lingual tipping to mesial labial tipping. However,canines tipped distally and lingually. The movement of the second premolars changed from mesial buccal tipping to mesial lingual tipping. The movement of the first molar changed from mesial lingual tipping to distal lingual tipping,and the angle of tipping was higher in the mesial root than that in the distal root. ②The largest stress distribution in the whole arch was always located in the labial apicaesiall one-third area of the lateral incisors,while those of canines and the first molars were located in the alveolar ridges and root bifurcations. Conclusion The different movement trends of the anterior and postior teeth can be achieved through the adjustment of the height of crampable hook,and the bending of different orders in the arch can control the anchorage teeth effectively.