Evaluation of the effect of different filling materials applied to internal root resorption cavities of various sizes on stress distribution by finite element analysis

Evaluation of the effect of different filling materials applied to ınternal root resorption cavities of various sizes on stress distribution by finite element analysis The aim of this thesis is to examine the distribution of stresses on teeth, supporting tissues, and the materials used after filling resorption cavities in maxillary incisor teeth with different sizes of internal root resorption using various materials (gutta-percha, MTA, Biodentine), and to provide data that may assist in clinical practice. In this study, a micro-computed tomography scan of a single maxillary incisor tooth, which was caries-free, restoration-free, and had completed root development, was used to create a three-dimensional model. A 3D finite element model was generated from this scan, referencing the maxillary incisor dimensions from Wheeler's dental atlas. Cortical and trabecular bone, lamina dura, and periodontal ligament supporting the maxillary central incisor were modeled. The physical properties of the cementum layer were neglected due to its similarity to dentin and its very thin structure. While the initial model represented a healthy tooth as the control model, internal root resorption cavities with diameters of 1.5 mm, 2.5 mm, 3.5 mm, and 4.5 mm were created in the middle third of the root canal for other control models. In the treated models, internal resorption cavities of different sizes were restored with different materials (gutta-percha, MTA, Biodentine), while the apical and coronal thirds of the resorption cavity were filled with gutta-percha. A total of 17 models, including control groups, were subjected to a force of 100 N applied 2 mm apically from the incisal edge, at a 135-degree angle to the long axis of the tooth. The von Mises stress distributions on dentin, periodontal ligament, and the materials used to fill the internal root resorption cavities were evaluated, while the maximum and minimum principal stress distributions on dentin, cortical and trabecular bone were examined. Additionally, the maximum displacements occurring around the resorption cavities were assessed. When analyzing the stress distributions resulting from the applied force, the least stress in the dentin was observed in the healthy tooth model, while the highest stress was seen in the untreated model with a 4.5 mm internal root resorption cavity. As the size of the internal root resorption increased, there was generally an increase in stress values. The stress distributions in the dentin approached that of a healthy tooth when the internal root resorptions were treated. When examining the stress distributions on dentin, cortical and trabecular bone, and periodontal ligament, the highest stress values were observed in models treated with gutta-percha, followed by models treated with MTA, while the lowest stress was found in models treated with Biodentine. It was also determined that the stress accumulated on the material was highest in the models treated with Biodentine, followed by those treated with MTA, and the lowest stress was in the models treated with gutta-percha. Internal root resorption caused an increase in stress values in the dentin. The increase in the size of the resorption cavity generally resulted in increased stress on the tooth and adjacent supporting structures. The use of Biodentine and MTA, which have a higher modulus of elasticity, in the repair of internal root resorption resulted in more absorption of the applied force, transmitting less stress to the dentin compared to gutta-percha. Keywords: Biodentine, Gutta-percha, Internal root resorption, MTA, Finite elements, Stress analysis