The restoration of teeth having different amounts of root dentin loss:stress analysis and fatigue analysis using the finite element method

In this study, for the restoration of teeth with different amounts of root dentin loss, stress analysis were performed for the stresses generated at; root dentin, post materials and the cement layer between post materials and root dentin. Following the stress analysis, fatigue testing of the post materials were performed for each post material which is used for the restoration of teeth with different amounts of root dentin loss, using the 3D finite element stress analysis method according to the results of the stress analysis.For the dynamic stress analysis and fatigue testing, 4 different 3 dimensional models of the lower first premolar tooth, simulating 4 different root dentin loss amounts(clinical scenarios 1,2,3,4) were performed using the Rhinoceros 4.0 software. Each of these models received; cast gold post-core, carbon fiber post and composite core, glass fiber post and composite core, polyethylene fiber and composite core, prefabricated titanium post and composite core and one piece zirconia post-core for their restorations. Following the post-core applications, all models received metal fused to porcelain crowns for their final restorations.Following the complete restorations of the 3D models, dynamic load application performed with a load of 125 N at 1 Hz frequency with 45 degrees along the tooth?s long axis for each of the models, using the finite element stress analysis method. The results obtained from the dynamic stress analysis were loaded to the Fatigue Wizard software for the fatigue testing of each of the post materials. The results obtained from the stress analysis and the fatigue tests were evaluated to determine the most suitable post-core application for the restoration of the teeth having root dentin loss.In the first and second clinical scenarios, the use of the rigid post materials (cast gold post-core and one piece zirconia post-core) developed lower stress values at the dentin layer, compared with the use of fiber posts. When the stresses generated at; dentin, post materials and the cement layer between the post materials and the root dentin were evaluated together for the restoration of teeth having minimum amounts of root dentin loss, lower stress values were obtained from the models receiving glass fiber and polyethylene fiber posts. Greater stress values were obtained from the models of the third and fourth clinical scenarios, which have greater amounts of root dentin loss. For the third clinical scenario, which have a greater amount of root dentin loss, but the marginal preparation line around the tooth is on the sound dentin, lowest stress values at the dentin layer were obtained from the models restored with cast gold post-core and one piece zirconia post-core. For the fourth clinical scenario, which has a marginal preparation line supported by core material and dentin, lowest stress values at the dentin layer were obtained from the models restored with glass fiber and polyethylene fiber posts.According to the fatigue testing results performed for all of the clinical scenarios, best results were obtained from the models restored with glass fiber posts. Lowest results were obtained from the models restored with one piece zirconia post-core. It was concluded that, related to the results of fatigue tests, the clinical survival rate of the use of glass fiber and polyethylene fiber posts would be better, compared with the use of cast gold post-core and one piece zirconia post-core.