BACKGROUND:During the restoration of residual molar crown, a little part of tooth is still remained commonly. After the restoration, with various forces, stress distribution affects directly the results after restoration. Finite element method is gradually applied in stress analysis on artificial tooth.OBJECTIVE: To establish the three-dimensional (3-D) finite element model of post-inlay restoration of the first residual mandibular molar crown so as to provide experimental data for improving model establishment of complicated teeth and analysis on the property of stress distribution of restoring methods.DESIGN: Repeated observation and measurement were given.SETTING: Department of Stomatology and Department of Radiology of First Hospital affiliated to Sun Yat-sen University;Department of Solid Mechanics,College of Traffics and Communications, South China University of Technology; Department of Restoration of Guanghua College of Stomatology.MATERIALS: The experiment was performed in Department of Solid Mechanics, College of Traffics and Communications of South China University of Technology from November 2003 to December 2004. Six first mandibular molars on the right side with normal morphology in vitro were collected, and Toshiba Xpress/SX spiral CT machine, image photo synthesis software and finite element analysis software ANSYS were applied in the experiment.METHODS: 1 of the 6 first mandibular molars on the right side with normal morphology in vitro was selected for pulpectomy, which was the best in density and near to clinical requirement in morphology. With pulpectomy, the prosthesis of braking-lock post-inlay restoration was prepared. Spiral CT-cross scanning was performed in premolar crown before the restoration, the residual crown with post-inlay in main root canal after restoration and the residual crown with braking-lock second post-inlay restoration. With image photosynthesis software, 3-D digital model of residual tooth and metal part was established and the entire tooth model was prepared after adhesion of two parts. In order to provide better boundary conditions of simulated natural tooth in practice, alveolar bone was considered. Under Mesh order in ANSYS software, automatic mesh generation was performed in the model directly.MAIN OUTCOME MEASURES: Establishment of 3-D finite element models of residual tooth before restoration, post inlay, and alveolar bone and tooth after restoration and the results of mesh generation.RESULTS: By establishing 3-D finite element models of residual tooth before restoration, post inlay, alveolar bone and tooth after restoration and automatic mesh generation, there were altogether 117720 units and 20988nodes. Good geometric similarity presents between the construction model of 3-D finite element model and solid tissue.CONCLUSION: Combination of 3-D finite-element model with spiral Ctcross technology establishes complex dental models, simulates practical conditions authentically and is good in operation.

Objective: To compare the in vitro biocompatibility of bone marrow mesenchymal cells on polyetheretherketone (PEEK) and titanium (Ti) surfaces. Methods : PEEK and Ti foils with thicknesses of 1 mm and diameters of 10 mm were prepared. First, bone marrow mesenchymal cells were separated and purified by the whole bone marrow adherent culture method in vitro. Then, osteogenesis-induced bone marrow mesenchymal cells were cultivated on the surfaces of the PEEK and Ti foils. Scanning electron microscopy (SEM), the Alamar Blue test, an alkaline phosphatase (ALP) kit and Alizarin Red staining were used to analyze calcium nodules and compare the adhesion, proliferation and osteogenic differentiation ability of bone marrow mesenchymal cells on the surfaces of the PEEK and Ti foils. Results : ① The morphology of the bone marrow mesenchymal cells cultured on the PEEK and Ti foils at 1 h, 4 h and 24 h showed no significant differences. ② In the 1 h, 3 h, 1 d and 3 d cultures of the bone marrow mesenchymal cells inoculated on the surfaces of the foils, the number of living cells in the PEEK group was greater than that in the Ti group (P < 0.05). ③ In the 7 d and 14 d osteogenesis-induced cultures of the inoculated bone marrow mesenchymal cells, the ALP activity of the PEEK group cells was significantly greater than that of the Ti group cells (P < 0.05). ④ Semiquantitative analysis after Alizarin Red staining showed that the mineralization degree of the bone marrow mesenchymal cells induced by osteoblasts was greater in the PEEK group than in the Ti group (P < 0.05). Conclusion PEEK has better in vitro biocompatibility than Ti and can better promote cell adhesion, proliferation and osteogenic differentiation compared with Ti, and so it is expected to become a new dental implant material.