| ObjectiveTo make a mechanical analysis on three-dimensional finite element models of the endodontically treated premolars with medial-occlusal Cavities, which were restored by filling and crown or post-core and crown, and to provide a guideline for making restoration plans for such kind of tooth structure defect.MethodsThree-dimensional finite element models of the endodontically treated premolars with medial-occlusal Cavities were built using advanced thin-layer CT scanning and 3-dimensional computer assisted design technique, which were restored with filling and Ni-Cr metal-ceramic crown (the amalgam filling or composite resin filling) or with the three post-core systems and Ni-Cr metal-ceramic crown (Ni-Cr alloy post-core or Au alloy post-core or polythene fiber reinforced composite resin post-core ). The Von Mises Stresses and the Principal Stresses were applied for comparing the maximum stress value of dentin and stress concentration areas in models under the same simulating loads.Results(1)Three-dimensional finite element models of the endodontically treated mandibular first premolars with medial-occlusal cavities have been built.(2)The maximum Von-Mises stress values and the maximum Principal stress values of dentin of post-core and crown were lower than that of filling and crown. When different post-core materials with various elastic modules were used, the peak stress values in the cervical third region were significantly different. The result showed that metal post with high elastic module reduced the peak of dentinal stress to some extend .In groups restored with filling and crown, the peak stress values with amalgam filling were higher than that with composite resin filling.(3) The stress concentration of each model was observed at buccolingual regions. Comparing with filling and full crown restoration, the stress concentration area in the models with the post-core and crown restoration transferred to parts of root from crown. Comparing with amalgam filling, the stress concentration area in the models with composite resin filling was larger. The pattern of the stress distribution in the dentin was altered after post restoration, which was more obvious in high elastic module post-core restoration and less in low elastic module post-core restoration. The result showed that metal post with high elastic module changed the pattern of the stress distribution with high stress concentrating at the border between the post and the dentin. The stress distribution had an increasing tendency from tooth crown part to root middle part with the increasing tendency of elastic module of post-core.Conclusions(1)The generated three-dimensional finite element models of the endodontically treated mandibular first premolars with medial-occlusal Cavities are highly similar in geometry and mechanics to the real instance. With the SCT image reconstruction technique and the engineering software, oral biomechanical researches can reconstruct the model precisely,quickly and flexibly.(2) The post has protective function in odontoprosthesis. Compared with filling and crown restoration, The post-core and crown restoration is more suitable to the endodontically treated premolars with medial-occlusal cavities.(3) The elastic modulus of post-core materials affect the stress distribution pattern in dentin. The materials with elastic modulus similar to that of dentin, such as polythene fiber reinforced composite, may be more suitable for post-core restoration. The post with higher elastic modulus, such as Ni-Cr cast metal post-core system, makes larger stress concentration around post and results in catastrophic fracture.(4) If the endodontically treated premolars with medial-occlusal cavities are restored with filling and crown , amalgam filling is superior to composite resin filling.(5) The results suggest that when the premolars are restored with post-core and PFM crown, especially with Ni-Cr cast alloy post-core, it is important to assure the thickness of the buccolingual canal wall during tooth preparing. |
