Effect of thermal misfit between different veneering ceramics and zirconia frameworks on in vitro fracture load of single crowns.

Thermal misfit is deemed as one reason for the chipping of veneered zirconia restorations. Aim of the present study was to assess the effect of thermal misfit on the fracture load of veneered zirconia frameworks and to evaluate the applicability of a universal veneering ceramic for both zirconia and titanium frameworks. Fracture loads of zirconia and titanium frameworks veneered with different ceramics were measured. Differences in the thermal expansion coefficients of core and veneer (Delta alpha), as well as differences between glass transition temperatures of the veneering ceramics and room temperature (Delta T)--which is considered as the effective temperature range for stress formation, were determined. In the zirconia group, fracture load ranged from 818.0 +/- 127.2 to 935.2 +/- 186.3 N without significant differences (Student's t-test, p < 0.05). Moreover, zirconia and titanium crowns veneered with the universal veneering ceramic revealed high fracture load. Results also showed a correlation to the product Delta alpha x Delta T, such that if 185 x 10(-6) < Delta alpha x Delta T < 1120 x 10(-6), a veneering ceramic adapted for titanium might be likewise applicable for zirconia.