Study Of The Stress Distribution In The Temporomandibular Joint Affected By Tooth Wear With The Three-dimensional Finite Element Method

Tooth wear progresses throughout one's life. Mild wear has positive physiological significance. But severe wear does negative effect on people's oral health. The problems associated with the dentition wearing out will assume as great importance as the problems of caries and periodontal disease. Tooth wear is popularly found in dental clinical practice. There are some studys on the TMJ affected by tooth wear. But the results are different. On the one hand, loss of occlusal vertical dimension (OVD), change of occlusion, stress in the TMJ increasing and articular pathological change could result from severe wear. On the other hand, there was no associations between wear levels and symptoms of temporomandibular disorders (TMD). There are many reseach papers about the TMJ in every aspect. And biomechanical study of the TMJ is increasingly reported, including the study with finite element method. But the finite element model(FEM) of the TMJ constructed in previous study is not perfect. There is no report of the model, including the TMJ, masticatory muscles, mandible and lower teeth, which is made by maxillofical magnetic resonance(MR) images of volunteer, the direction and origin of the muscle forces are determinedaccording to the 3D ontic model of the mandible and the masticatory muscles derived from the same MR images. There is also no study on the stress distribution in the TMJ affected by tooth wear to our knowledge.In this study, we developed a 3D FEM including the TMJ, masticatory muscles, mandible and lower teeth, based on the MR images of the healthy volunteer. We investigated stress distribution in the nomal and the TMJ affected by tooth wear during clenching, using finite element analysis. And we determined the biomechanical change in the TMJ, especially in the disc and the condyle, and the pathophysiological progression in the TMJ affected by tooth wear. This study was divided into three sections.Part One: Construction of the 3D finite element model of the TMJ, the masticatory muscles, the mandible and the lower teethObjectives To construct the 3D FEM of the TMJ including articular disc, articular cartilage, cortical bone and cancellous bone, the masticatory muscles, the mandible and the lower teeth. Then to make use of the model into the biomechanical study of the TMJ subsequently. Material and methods A series of coronal MR images of the healthy volunteer's bilateral TMJ were taken in closed position with maximal intercuspation by using Genesis-Signa Twin02 magnet of American GE Corporation, head loop and 3D-SPGR programm. After transferring 60 MR images to the SUN computer workstation and applying the 3D reconstruction function, we made the 3D images of the TMJ, mandible and lowerteeth. 60 MR images were scanned by the AGFA-Arcus II scanner, and saved as BMP files in the computer. The outlines of the articular disc, the lower teeth, cortical bone and cancellous bone of the mandible, the masticatory muscles, were drew respectively applying the same coordinate system. Fourty points proportionally distributed on each outline were selected and turned into data files using COLOR and POINTS software designed by BUAA 405 Room. Then the data files were opened in UG, a CAD software, to construct 3D ontic model. In the meantime they were also read in the finite element software-ANSYSG. 1 to upbuild the FEM made up of linear brick elements, each element with eight nodes, and meshed by researcher. The materials of the FEM were hypothesized linear elastical material. The magnitude, direction and origin of muscle forces were determined according to the ontic model of the mandible and the masticatory muscles derived from UG. Results The morphology of 3D FEM including the TMJ, the mandible, the masticatory muscles and the lower teeth is as fine as the 3D MR images. The TMJ consists of cortical bone and articular cartilage of the glenoid fossa, articular disc, cortical and cancellous bone and articular cartilage of the condyle. Masticatory muscles consist of the masseter muscle, temporal muscle, medial...