The thermal contraction mismatch between materials is an important indicator for estimating thermal processing stresses in ceramic prostheses.   Objective: This in-vitro study tested the hypothesis that the viscoelastic option of the ANSYS finite element program can accurately predict thermally induced stresses that cause failure in ceramic core and veneer combinations.  Methods: Open-ended cylindrical forms (9mm, 11mm ID) with three wall thicknesses were cast in wax.  Empress 2 (E2C) and an experimental core ceramic (EXC) were hot pressed per the manufacturer's recommendation using the cylindrical wax patterns (n=72).  Each core cylinder was veneered with one dental ceramic producing a total of 2mm thickness upon completion (n=3 per thickness). All observed fractures indicated failure.  The cylinders were modeled with 8-node axisymmetric thermal and viscoelastic elements.  Results: Calculated stresses for the eight ceramic systems made are:

Finite element analyses yielded low stresses (<13 MPa) for Empress 2 and Eris and much higher stresses (>70 MPa) for the cylinders that failed even at the wash coat stage (Vita and Finesse). Conclusion: This study demonstrated that viscoelastic finite element analysis may be used to predict the likelihood of fracture based on thermal contraction data.  Supported by NIH/NIDCR- DE06672.