A Comparative Finite Element Study on the Biomechanical Effect of Implant Crown Screw Access Channel Filled by Direct vs. Indirect Restoration Materials

Abstract

Background: The restorative material used to seal the screw access channel in screw-retained implant-supported crowns may influence the biomechanical behavior and mechanical performance of the restoration. Objective: To evaluate the influence of different screw access channel restorative materials on stress distribution and deformation in porcelain-fused-to-metal (PFM) and monolithic zirconia implant-supported crowns using three-dimensional finite element analysis (FEA). Materials and Methods: Three-dimensional finite element models of screw-retained PFM and monolithic zirconia implant-supported crowns were developed. Four restorative materials—direct composite resin, resin matrix ceramic (RMC), lithium disilicate (LDS), and zirconia inlays—were used to restore the screw access channel. Each model was subjected to 200 N vertical and oblique occlusal loads. Equivalent von Mises (EVM) stress and total deformation were calculated and compared among the different restorative materials and crown types. Results: In PFM crowns, lithium disilicate and zirconia inlays produced lower stress transfer under vertical loading than direct composite resin and resin matrix ceramic. Under oblique loading, the differences in stress distribution among restorative materials were less pronounced. Zirconia inlays exhibited the highest internal stress concentrations but the lowest deformation, whereas direct composite resin demonstrated the greatest deformation. In monolithic zirconia crowns, deformation values were comparable among zirconia, lithium disilicate, and resin matrix ceramic inlays, indicating that the high stiffness of the zirconia crown largely governed the biomechanical response. Conclusions: Both the crown material and the restorative material used to seal the screw access channel affected the biomechanical performance of implant-supported restorations. Lithium disilicate and zirconia demonstrated more favorable mechanical behavior than direct composite resin, which exhibited greater deformation. These findings suggest that indirect restorative materials may provide biomechanical advantages over direct composite resin, particularly in restorations subjected to higher occlusal loads.