Comparison of stress distributions in post-core supported full crown and endocrone restorations using different CAD/CAM materials in mandibular molars with excessive crown destruction, with finite element analysis

In order for endodontically treated teeth to maintain a good prognosis for many years, they must continue to function with a successful prosthetic treatment. Root canal treatment and restorations after; In order to provide a homogeneous tensile force distribution along the root and dentin, the elastic properties of the lost dentin tissue should be restored by using materials whose properties are close to the biomechanical properties of dentin. Factors such as the quality and adaptation of the restoration, the preservation of the remaining dental tissues, and the adequacy of the bond between the tooth and the prosthetic materials are important for the success of the treatment. Considering the developments in adhesive dentistry and CAD/CAM technology, the use of endocrone restorations, which are more conservative compared to post-core full-crown restorations, has increased, especially in teeth with excessive material loss in recent years. In scientific studies, it is seen that all-ceramic, composite or hybrid materials, which are common in endocrown and post-core supported full-crown restorations, produced from materials with improved aesthetic and mechanical properties, are used quite frequently. Considering the studies, the prognosis of these materials in teeth with excessive crown destruction, root canal treatment and different restoration types is not known exactly. The aim of our study; to evaluate the stress distributions created by vertical and oblique forces applied in the dental tissues and restorations in endocrone and post-core full-crown restorations made using different materials on mandibular first molars with excessive substance destruction and root canal treatment, using three-dimensional finite element stress analysis method and to evaluate their mechanical performance. This study was carried out in cooperation with Ankara University Faculty of Dentistry and Tinus Engineering. In the research, a total of 12 models were created in the virtual environment by modeling two different restoration types, three different restoration materials and two different strength types. Arrangement of the three-dimensional mesh structure and its transformation into a mathematically appropriate solid mesh structure, creation of three-dimensional finite element analysis models and finite element stress analysis process; Performed on HP workstations with INTEL Xeon E-2286 processor clocked at 2.40 GHz and 64 GB ECC memory. Obtaining .stl model from tomography data was done in 3DSlicer software. Obtaining .stl model from tomography data was done in 3DSlicer software. In our study, three-dimensional finite element geometric modeling was made using the images of the lower left 1st molar tooth at different angles in the Wheeler dental atlas. In our research, dental tissues; enamel, dentin, periodontal ligament, cortical and cancellous bone. Geometric models of endocrown and full-crown restorations applied with gutta-percha, glass fiber post, resin cement, composite resin and lithium disilicate glass ceramic [IPS e.max CAD (Ivoclar Vivadent, Schaan, Liechtenstein)], hybrid ceramic [Vita Enamic (Vita Zahnfabrik, Bad Säckingen, Almanya)] and zirconia reinforced lithium silicate [Vita Suprinity (Vita Zahnfabrik, Bad Säckingen, Almanya)], CAD/CAM materials used for restoration were made. A total of 300 N force was applied from 5 different regions on the occlusal surfaces of the teeth in the vertical or oblique direction. Stress distributions of each model were analyzed by 3D SESA method; Von Mises stresses and maximum principal stresses of endocrown, full crown, dentin, enamel and resin cement were evaluated using color images. Under vertical and oblique force loading conditions, the stress intensity occurring in endocrowns was in the retention cavities, whereas more stress accumulation was observed in the areas contacting the steps in full-crown restorations. Among the CAD/CAM materials used, the highest stress values in restorations were found in the IPS e.max CAD group, and the lowest values were found in the Vita Enamic material. Under vertical forces, the highest stress values were found in endocrowns, while oblique loading was found in full-crown restorations. Under vertical forces, the highest stress values were found in endocrowns, while oblique loading was found in full-crown restorations. In vertical force application, the highest maximum principal tensile stress value found in resin cements was observed in endocrown using IPS e.max CAD, while Vita Enamic full-crown restorations were found in oblique forces. Maximum principal stress values in enamel and dentin in all vertical and oblique forces are generally higher in full crown groups restored with Vita Enamic. It has been observed that the stresses spread over a wider area under angular forces compared to vertical forces.