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目的建立颅颌面三维有限元模型，分析前牵引角度顺时针增大时其反作用力在颞下颌关节（TMJ）和颌骨的应力及位移变化，为正畸临床更好地治疗骨性Ⅲ类错铪，避免对TMJ和颌骨的损伤提供实验依据。方法本研究于2010---2012年在山东大学机械工程学院机械制造及其自动化实验室完成。选择1名健康青年男性志愿者作为研究对象，建立完整的包含TMJ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顺时改变施力的方向，测定TMJ和颌骨应力及位移的变化情况。结果（1）应力方面：从不同角度加载节点力之后产生最大应力点出现在加栽部位颏部，关节窝、髁突头颈部等部位应力也比较集中；从不同角度施加相同载荷时，上下颌骨均产生接触应力，40°时最小。（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栽部位；下颌发生了顺时针旋转。结论（1）前牵引矫治器在牵引上颌向前的同时，确实对TMJ及颌骨产生反作用力，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；（2）传统加力方式中的角度（37°）似乎并不是最佳的选择，从作用力与反作用力两方面考虑40°要优于37°。

A three-dimensional(3-D)finite element study on the influence of reaction force when protraction direction magnifies clockwise

Objective To offer a scientific basis for treating Class III malocclusion more well, and avoid injuring TMJ, a three-dimensional finite element model （FEM） of craniomaxillofacial complex was used to analyse the influence of the reactive force on TMJ when protraction direction magnified clockwise. Methods A healthy young male volunteer was selected;establish a complete three-dimensional （3-D） finite element model, which included TMJ;imitate the force pat- tern of maxillary protraction; exert a given force on chin ; change the direction clockwise ; the stress distribution and dis- placement on jaw and TMJ were analysed. Results Stress distribution： the biggest stress points appeared in the loading position chin after loading nodal force from different angle. The stess in the contact region, such as the glenoid fossa, con- dylar head and neck, was also relatively concentrated. Under the action of different angle, the maxilla and mandible both produced contact stress. Displacement： in a certain angle on the nodal force, the model produced tiny displacement change, the largest position displacement in loading part. Conclusion （ 1 ） Protraction appliance does produce reactive force on mandible and TMJ when making maxilla forward, so we need to consider both the two aspects; （2）The traditional way of boosting does not seem to be the best choice, and from the two aspects of action and reac- tion, 40° is superior to 37°.