Thermal stresses in porcelain veneered lithium disilicate and zirconia dental crowns: Comparative analysis using a validated viscoelastic finite element model

This study aims to investigate the effects of material compatibility, variable cooling rates, and crown geometry on thermal stress development in porcelain-veneered lithium disilicate (PVLD) and porcelain-veneered zirconia (PVZ) dental crown systems, and subsequently anticipate parameters for their optimum performance. An anatomically correct 3D crown model was developed from STL files generated using 3D scans of the experimental crown sample. Next, the viscoelastic finite element model (VFEM) based on the 3D crown model was developed and validated for anatomically correct bilayer PVLD and PVZ crown systems. The Vicker's indentation method was used on experimental PVLD and PVZ crown samples to validate the simulated thermal stress results from the VFEM. The validated VFEM was then used to predict thermal transient and residual stresses within the dental crown systems. The comparison between thermal residual stress profiles in PVLD and PVZ crowns showed that the interfacial stress concentrations were comparatively lower for PVLD crowns. However, the PVLD crowns also experienced prominent tensile stresses in the veneer layer. Furthermore, the rapid cooling protocol was seen to cause intensification of compressive stresses on the exterior veneer surface for both PVLD and PVZ crowns which can enhance resistance against crack growth. But faster cooling rates also caused rapid stress evolution which may cause material defects within the crown. This study highlights the importance of material compatibility by comparing stress distribution within the PVLD and PVZ crowns. Moreover, the post-firing cooling protocols showed significant effects on overall thermal stress distribution and consequently, the long-term dental crown performance.