Abstract
Purpose: We investigated how various frame materials, porcelain firing temperature and heating rate influenced the fracture toughness of the veneer porcelain used for zirconia all-ceramic restorations.
Methods: The fracture toughness was evaluated according to the ISO 15732 standard. The veneer porcelain for the zirconia all-ceramic restorations was fired on 0.4- and 0.8-mm-thick zirconia frames (ZAC) at moderate firing schedules, and fired on ZAC(0.4) at low, moderate, and high temperatures and at slow, moderate, and fast heating rates. Veneer porcelain fired on metal frames for porcelain-fused-to-metal (PFM) ceramic restorations was also evaluated as a control. The data were analyzed using 2-way ANOVA and the Tukey-Kramer HSD test (ɑ = 0.05).
Results:
The effects of the ZAC and PFM frame thicknesses and the firing temperature on the fracture toughness of the veneer porcelain were not significantly different. The fracture toughness of the sample heated fast on the ZAC was significantly lower than that of the samples heated at slow and moderate rates (p < 0.05). The fracture toughness of the sample heated slowly on the PFM was significantly higher than that of the samples heated at moderate and fast rates (p < 0.05).
Conclusions: The results suggest that the effects of the ZAC frame thickness and firing temperature on the fracture toughness of the veneer porcelain were not significantly different; however, the heating rate significantly influenced the fracture toughness.
