Can degradation of adhesive interfaces due to water storage affect stress distributions? A finite-element stress analysis study

Purpose: The aim of this finite-element stress analysis (FEA) was to determine the effect of degradation due to water storage on stress distributions in root-filled premolar models restored with composite using either a self-etch (SE) or an etch-and-rinse (E & R) adhesive. Materials and Methods: Four premolar FEA models including root filling, MOD cavity, and composite restorations were created. The cavities were assumed to be treated by SE or E & R adhesives and stored in water for 18 months. The elastic properties of the adhesive-dentin interface after 24-h and 18-month water storage were obtained from the literature and applied to the FEA models. A 300-N load was applied on the functional cusps of the models. The SolidWorks/Cosmosworks structural analysis program was used and the results were presented considering the von Mises stresses. Results: Stresses in the cervical region increased over time on the load-application side of the main tooth models (SE: 84.11 MPa to 87.51 MPa; E & R: 100.24 MPa to 120.8 MPa). When the adhesive interfaces (hybrid layer, adhesive layer) and dentin were evaluated separately, the stresses near the root canal orifices increased over time in both models; however, this change was more noticeable in the E & R models. Stresses at the cavity corners decreased in the E & R model (within the adhesive layer), while SE models showed the opposite (within the hybrid layer). Conclusion: Change in the elastic modulus of the adhesive layer, hybrid layer, and dentin due to water storage has an effect on stresses in root-filled premolar models. The location and the level of the stresses differed depending on the adhesive used.