Viscoelastic finite element stress analysis of the thermal compatibility of dental bilayer ceramic systems.

Purpose: The aim of this study was to test the hypothesis that viscoelastic finite element analyses can reliably predict the effect of geometry on maximum tensile stresses in bilayer screening tests that are used to determine thermal compatibility.

Materials And Methods: Three-dimensional viscoelastic finite element models of a beam, cylinder, disk, sphere, central incisor crown, molar crown, and posterior three-unit fixed partial denture (FPD) were used to calculate residual stresses after simulated bench cooling. Four compatible and four incompatible systems were evaluated.

Result: The highest residual tensile stresses for all material combinations were associated with the three-unit FPD. Residual tensile stresses ranged from 5.4 MPa in the disk for a compatible combination to 262 MPa in the three-unit FPD for an incompatible system. Residual tensile stresses in the three-unit FPD ranged from 16.8 MPa to 44.0 MPa for the compatible systems and from 175 MPa to 262 MPa for the incompatible systems.

Conclusion: Based on finite element calculations, it is predicted that all-ceramic dental prostheses with an average thermal contraction mismatch (500 degrees C to 25 degrees C) greater than +/- 1.0 ppm/K will likely exhibit a relatively high percentage of failures in clinical use compared with systems having smaller thermal contraction mismatch between core and veneering ceramics.