| Objective: Endodonticly treated posterior teeth should receive cuspal coverage. When a large portion of the coronal structure is lost, three post and core techniques, including conventional cast post-cores, prefabricated post-cores and filling post-cores, were usually applied in such cases to provide necessary retention and resistance for a crown. However, there were only a limited number of reports on the stress analysis and comparison of those techniques. Therefore, this study was designed to evaluate dental stress of several residual roots, which were restored with distinct post-core techniques and loaded by different force.Methods: Three 3D finite element models of the restored first mandibular molars were constructed by CT image reconstruction technique. Then MIMICS software was used to separate the areas and finish 3D calculation. GEOMAGIC software was also applied to modify and generate a NURBS surface in each patch. All components of the models were assembled under the ANSYS preprocessor. Specific materials parameters were selected to simulate the various restoration and dentin status. Then these models were been solved and the stress distribution and peak value of dentin were be studied.Results: The 3D finite element models of restored first mandible molars were successfully established, which were consistent to the situation observed in the clinical environment. The stress distribution analysis indicated that: (1) restoration methods: for the different teeth treated with cast Ni-Cr post-cores, prefabricated Ni-Cr post and composite resin cores ,amalgam post-cores, peak values of the dentin stress decreased in that order. The teeth treated with custom cast post-cores, had the maximal peak value, and the stress concentration area was around the terminal part of the post. For the teeth restored with prefabricated posts and various cores, the peak values of the dentin stress were less than that restored with a system in which only core materials was used to create post and core. For prefabricated ones, the stress concentration area was around the terminal part of the post and the cervical part, nevertheless, for the filling ones, mostly the cervical part shown the peak value. (2)Materials: for the restoration with cast post-core, peak values of dentin stress were decreased when the elasticity module of post-core materials was reduced. And the stress distribution was homogeneous throughout the whole body. For the restoration with prefabricated post-core, peak values of dentin stress were increased by the elasticity module of core materials was reduced. And the difference of the stress distribution between post and core was distinct. For the restoration with Fill post-core, the smallest dentin stress peak value was occurred when it was restored by the material with middle elasticity module, and the stress concentration area was located inside the post-core. When the elasticity module of the material decreased, this area would move to the cervical portion. (3)Loading: when force was loaded on the center of occlusal surface, the peak value of stress occurred, and stress concentration area also appeared on the distal side of the root. When the force was moved away form the central part, the peak value would decrease, and the area with high stress on the exterior surface of the root would be expanded. (4) Residual dentin: The amount of residual dentin has little influence on the stress value and distribution, when adopted materials of high elasticity module. While used materials of low elasticity module, it's necessary to preserve residual dentin as much.Conclusion : (1) It was a practical and accurate way to establish three-dimensional finite element models by CT image reconstruction technique and reverse engineering software MIMICS and GEOMAGIC. (2)Loading was an important factor to affect the peak value and distribution of dentin stress. (3)We should choose the compatible technique and materials to restore endodonticly treated teeth, according to the distribution of their healthy dentin. |
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