RESUMO
<p><b>OBJECTIVE</b>To make a mechanical analysis on three-dimensional finite element models of the mandibular first molar defect restored with post core and all-ceramic crown, and to provide a guideline for planning restoration for such kind of tooth structure defect.</p><p><b>METHODS</b>Cone-beam CT based three dimensional finite element models of post and core restored first mandibular molars were established, with 6 different ferrule designs (the ferrule with only 180 axial wall on different locations). The von Misses criterion was applied for comparing the maximum von Misses stress value of dentin and stress concentration areas in six models which restored with fiber post or cast NiGr alloy post core or Au alloy post core under the maximum, vertical, inclined and horizontal direct loads.</p><p><b>RESULTS</b>The restoration effects in six models were compared, and the maximum von Misses stress concentration areas were not obviously different. The maximum von Misses stress value of NiCr alloy post core and crown was 62.81 MPa. Under horizontal load, the maximum von Misses stress value of dentin increased remarkably.</p><p><b>CONCLUSIONS</b>The location of residual dentin has little influence on the stress distribution, when restored by post core and crown. Au alloy post core and crown or fiber post core and crown are superior to NiCr alloy post core and crown.</p>