The Effect of Dimension and Geometrical Shape of Prefabricated Post and the Material of Crown on the Stress Levels and Distributions in the Root of Restored Molar Tooth Using Finite Element Method

Statement of Problem: Researchers are often looking for appropriate treatments while considering esthetic aspects and health. In endodontically treated teeth afflicted with severe damage or complete loss of the coronal structure, a post is usually inserted in the root canal to provide intra-canal retention of the restorations. Therefore, it seems that it is necessary to investigate the stress distribution in the restored teeth with different post algorithms. In this study, the effects of post geometry and its dimensions on the stress distributions and levels in the root of molar teeth repaired by post-core crown (Ceramic, Alumina and Nickel-chrome) were studied using finite element method. An extracted intact mandibular second molar tooth was embedded in a cylindrical acrylic resin mould and then were sliced. The sections generated in this way were photographed and the images were transferred into the Solidworks software. After tooth modeling, Posts and crowns were designed. Then, the samples were exposed to a uniform distributed load of 240 N with the load angle of 45 degree which was applied over the occlusal area. In order to simulate the surrounding area of the tooth and also the periodontal ligament space, the bone was also modeled. Numerical results revealed that in the prefabricated post restoration, there was a stress concentration in the cervical region. The maximum value of normal stress (32.3 MPa) was seen in the parallel post with 1.4 diameter (D1.4), and the minimum value (26.7 MPa) was observed in the double tapered post (N0.1). It was observed that the increase in the modulus of elasticity from 100 to 300 causes an increase in normal stress from 69.5 to 38.5 MPa and in tensile stress from 69.5 to 38.5 MPa. Numerical analysis showed that the maximum stress concentration in post core crown restoration increased when the posts with 1.4 mm diameter or post with double taper were used. The stress values decreased with the decrease in the post modulus of elasticity. The maximum stress in the residual dentin decreased by an increase in the post diameter. Besides, the maximum stress on the residual dentine changed irregularly by the change in the tapered post diameter. Also, it was found that crowns material did not have any considerable effect on the stress concentration.