Impact of thermal properties of veneering ceramics on the fracture load of layered Ce-TZP/A nanocomposite frameworks

OBJECTIVES: The aim of this in vitro study was to assess the influence of thermal properties of veneering ceramics on the fracture load of layered ceria stabilized zirconia/alumina nanocomposite (Ce-TZP/A) single crowns. METHODS: Ce-TZP/A single crown frameworks (nanoZr) were veneered with 5 different veneering ceramics for zirconia (Cerabien ZR, IPS e.max, Triceram, Vintage ZR, VM9). In addition, veneering ceramics for alumina (Allux) and for the metal-ceramic technique (Reflex) were included in order to cover a wide range of coefficients of thermal expansion. Fracture load of the crowns was assessed in a shear test (n=10). Glass transition temperatures (T(g)) of the ceramics as well as the coefficients of thermal expansion of the ceramics (alpha(veneer)) and Ce-TZP/A (alpha(core)) between 25 and 500 degrees C were determined (n=6). RESULTS: Fracture load ranged from 574.0+/-97.1N (IPS e.max) to 1009.6+/-150.0N (VM9). Deltaalpha=alpha(core)-alpha(veneer) and DeltaT=T(g)-25 degrees C (DeltaT in K) were calculated. The fracture load was strongly correlated to Deltaalpha DeltaT with a maximum at Deltaalpha DeltaT approximately 580 x 10(-6). SIGNIFICANCE: The overall fracture load of veneered Ce-TZP/A crowns is correlated to the thermal properties of the respective veneering ceramic.