Residual Stress Determination in Anatomically Correct All-Ceramic and Metalloceramic Crowns

Objective: to simulate the residual stress developed in anatomically correct all-ceramic and metalloceramic crowns after porcelain veneering high temperature processing.

Methods: The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing proximal walls by 1.5 mm and occlusal surface by 2.0 mm. A crown comprising a core (0.5mm thickness) and a porcelain veneer layer of a 5-cusp first lower molar configuration was designed to match the preparation, and was imported to a thermal simulation software (ProEngineer, Needham, MA). The solids were meshed, and materials properties (density, Poisson's ratio, elastic modulus, coefficient of thermal expansion-CTE) were assigned for the porcelain veneer and three different core materials (zirconia, alumina, and metal). The assemblies were cooled from 900C to room temperature (25C), and maximum principal stresses (MPS) were determined for the core and veneer solids.

Results: Tensile stress states were observed at the core regions close to the core-veneer interface for the zirconia and metal cores (highest), whereas moderate compression was observed for the alumina core. Conversely, compressive stress states were observed at the veneer regions close to the core-veneer interface for zirconia and metal (highest) cores, and a tensile stress state was observed for the alumina core.

Compressive stress state at the core chamfer margin region, and veneer cervical region was only observed for the zirconia core.

Conclusion: CTE mismatch resulted in high residual stresses for all samples regardless of a positive or negative CTE mismatch between core and veneer material. The crown complex configuration also resulted in regions of high stress concentration at the occlusal region of the core-veneer interface. Supported by NIDCR-DE109676