[Three-dimensional finite element stress analysis of supporting bone of mandibular posterior fixed bridge. Part III. Comparative analysis with stress of the cortical bone beneath different pontics of fixed bridge].

OBJECTIVE: To analysis stress of the cortical bone beneath different pontics of mandibular posterior fixed bridge by using three-dimentional finite element method.

METHODS: According to the measured data, the characters of all components of fixed bridge and the supporting tissues, and the principals of finite element, the three-dimentional finite element model was developed on the basis of an adult mandible. The model consisted of 1363 nodes and 1134 elements after the fixed bridge was placed. Three different pontics were designed. Young's mudulus and Poisson's ratio were obtained from the literature for each type of tissue or materials in the model. The surfaces of pontic next to the mucosa beneath the pontic consisted of nine elements and the contact area were respectively reduced 1/3. It was assumed all materials in the model were homogeneous, isotropic and linearly elastic. One vertical load of 20 kg and one horizontal load of 20 kg were applied respectively on the occlusal surface of the abutments and the pontics of three different fixed bridge. Three-dimentional finite element stress analysis was used to calculate the epsilon max and the epsilon min of the cortical bone beneath pontics of fixed bridge.

RESULTS: Under the vertical loading, the cortical bone beneath the pontics appeared compressive stresses, the stress values of the cortical bone beneath the pontics were respectively -0.211(-)-0.119 (epsilon max, kg/mm2), -0.355(-)-0.201 (epsilon min), -0.224(-)-0.125 (epsilon max), -0.375(-)-0.215 (epsilon min), -0.239(-)-0.133 (epsilon max), -0.395(-)-0.228 (epsilon min). Under the horizontal loading, the cortical bone beneath the pontics exhibited tensile stresses and compressive stresses. The stress values of the cortical bone beneath the pontics were respectively -0.004-0.283 (epsilon max, kg/mm2), -0.249(-)-0.009 (epsilon min), -0.0042-0.301 (epsilon max), -0.264(-)-0.0095 (epsilon min), -0.0045-0.322 (epsilon max), -0.281(-)-0.0101 (epsilon min). The stress in the cortical bone beneath the pontics increased when the area of contact was reduced, the stress values changed in 5%-7%, but the rules of stress distribution of three different pontics were similar.

CONCLUSION: Stress values in the cortical bone beneath three pontics are small, and the change of stress in the cortical bone beneath the different pontics of mandibular posterior fixed bridge is small too.