Stress distribution in molars restored with inlays or onlays with or without endodontic treatment: A three-dimensional finite element analysis

Statement of problem Previous research into the strength of endodontically treated or vital teeth restored with inlays or onlays has not determined which restoration method and material provide the most favorable stress distribution upon loading. Purpose The purpose of this study was to calculate the von Mises stresses in a mandibular first molar using a 3-dimensional (3-D) finite element model. Models compared endodontically treated and vital teeth, a variety of restorative materials, and the use of either inlays or onlays to restore teeth. Material and methods Four 3-D models of mandibular first molars were created: (1) the IV group (inlay restored, vital pulp); (2) the OV group (onlay restored, vital pulp); (3) the IE group (inlay restored, endodontically treated); and (4) the OE group (onlay restored, endodontically treated). In each group, 3 types of restorative material were tested: (1) composite resin, (2) ceramic, and (3) gold alloy. The materials had elastic moduli of 19 GPa, 65 GPa, and 96.6 GPa, respectively. Each model was subjected to a force of 45 N directed to the occlusal surface, applied either vertically or laterally (45 degrees obliquely). The stresses occurring in dentin tissue were calculated. The stress distribution patterns and the maximum von Mises stresses were calculated and compared. Results The different restorative materials exhibited similar stress distribution patterns under identical loading conditions. In each group, the gold-restored tooth exhibited the highest von Mises stress, followed by ceramic and composite resin. The maximum von Mises stress in dentin was found in the IE group (16.73 MPa), which was 5 times higher than the highest value found in the OV group (2.96 MPa). The highest stresses, which occurred at the floor of the preparation and the cervical region in dentin, were in the IE group. The stress concentration area in the IE group was also larger. Conclusions The results indicate that endodontic treatment caused higher stress concentration in dentin compared with vital teeth, but that proper restoration can minimize internal stresses. In the models, the von Mises stress values increased with the increasing elastic modulus of the restorative material. Composite resin onlays showed the best performance overall in minimizing internal stresses. As internal stresses are indicated as a prime failure mechanism of the restoration, composite resin onlays are expected to better restore structural integrity.