Analyses of multilayered dental ceramics subjected to biaxial flexure tests

The purpose of this study was to formulate explicitly the equation to relate the biaxial strength of multilayered dental ceramics to the fracture load for multilayered discs subjected to biaxial flexure tests.

Analytical modeling showed that the solutions for multilayered discs subjected to biaxial flexure tests could be obtained from the existing solutions for monolayered systems by replacing the neutral surface position and the flexural rigidity of monolayers with those of multilayers. Finite element analyses were performed on porcelain/zirconia bilayered discs subjected to piston-on-ring and ring-on-ring tests to verify the analytical results.

Good agreement was obtained between (i) present analytical results and Roark's formulas for stresses at the top and the bottom surfaces of bimetallic discs subjected to bending, and (ii) present analytical and finite element results for porcelain/zirconia bilayered discs subjected to piston-on-ring and ring-on-ring tests.

The present closed-form solutions provide a basis for evaluating the biaxial strength of multilayered dental ceramics. Depending upon the strength of the individual layers and the stress distribution through the thickness of the multilayer during tests, cracking can initiate from any layer under tension.