三类错颌前牵引角度及其反作用力的探究

A Study on the Influence of Reactive Force of Protraction Direction

摘要: 目的：建立并使用颅颌面三维有限元模型，分析前牵引37˚牵引方向反作用力在颌骨和颞下颌关节的应力及位移分布情况，为正畸临床更好地治疗骨性111类错牙合，避免对颞下颌关节的损伤提供实验依据。方法：建立完整的颅颌面三维有限元模型，模拟前牵引矫治器反作用力，直接在颏部施以一定大小的力并施力，测定颌骨和颞下颌关节应力及位移变化。结果：1、应力方面：模型产生较明显应力部位有加载部位、上颌顶固定部位以及接触部位。下颌最大应力出现在节点力加载部位颏部，上颌最大应力出现在刚性固定面，上下颌接触部位如关节窝，髁突头、颈部应力集中也较为明显。2、位移方面：以一定力值不同角度施加节点力后，该模型产生微小的位移变化，位移最大部位产生在加载部位，下颌骨位移由颏部到升支部逐渐减小。结论：1、颅颌面三维有限元模型成功建立；2、前牵引矫治器在牵引上颌向前的同时，确实对颌骨及颞下颌关节区产生反作用力，如下颌的后下旋转，颏部的应力变形等，因此临床上在保证上颌牵引效果的同时，要考虑将其不利的反作用力降到最低；3、前牵引矫治作用于颏部的反作用力角度37˚时应力值和位移值相对较小，更利于关节组织的健康，为临床前牵引角度的选择提供一定的参考依据。

Abstract: OBJECTIVE: To offer a scientific basis on treating Class 111 malocclusion more well and avoiding injuring TMJ by establishing and using three-dimensional finite element model (FEM) of Craniomaxillofacial Complex, analyze the influence on Temporomandibular joint (TMJ) of reactive force of different protraction direction. METHODS: Establish a complete three-dimensional (3-D) finite element model which includes TMJ, imitate the force pattern of maxillary protraction, exert a given force on chin and change the protraction direction. The displacement and stress distribution in the TMJ were analyzed. RESULTS: 1. Stress distribution: the biggest stress points appeared in the loading position after loading nodal force from different points of view. 2. Displacement: In a certain angle on the nodal force, the model produces tiny displacement change. The largest position displacement produced in loading part, mandible displacement decrease from front to rear gradually. When the nodal force and angle change, the nodal displacement increases with the nodal force increases, decreases with the increase of the angle. CONCLUSIONS: 1) The mandible rotates clockwise in the process of protraction; 2) 37˚ is the right angle, not only making the maxillary translation but also protecting the TMJ.