Abstract: PURPOSE: To analyse the stress distribution of temporomandibular joint(TMJ) and jaw and the displacement changes of each part from the reaction force generated from maxillary protraction appliance by establishing a craniomaxillofacial three-dimensional finite element model (3-D FEM). METHODS: A 3-D FEM of craniofacial structure including TMJ and jaw was established from a male healthy subject by using CT scan and Mimics, Magics, MSC and other data analysis softwares. It was based on the linear elastic materials which were continuous, homogeneous, and isotropic. Then the simulation model in craniofacial 3D structure model of maxillary protraction device was establish based on the reaction principle, and different forces from 3 N to 6 N with a 37° angle from the occlusal plane was loaded at the bottom of the lower jaw in order to measure and analyze changes of stress and displacement in TMJ and jaw with the finite element analysis software ANSYS10.0. RESULTS: At the same angle , the stress in articular fossa and the head and neck of condyle increased with the applied force. Maximum stress was located where the stress was loaded on the mandible and the rigid fixation of maxilla. Meanwhile, this model appeared slight variation of displacement which increased with loading force. The maxillary displacement from basis cranii and occlusal plane to the parietal decreased gradually. Moreover, the mandibular displacement from the front to the rear was gradually reduced, and clockwise rotation was appeared. CONCLUSIONS: The results indicate that maxillary protraction appliance has reaction force on TMJ and jaw. With increasing of loading forces, reaction forces and deformation increase. At the same time, chin deformation may occur and the mandible has clockwise rotation.

Key words: 3-D FEM, TMJ, Protraction, Reaction force