Load-bearing capacity and failure types of anterior zirconia crowns veneered with overpressing and layering techniques

Objectives. The aim of this study was to test whether the load bearing capacity of anterior zirconia crowns veneered with overpressed or layered, is similar and to evaluate the failure types. Methods. Standardized zirconia frameworks were fabricated and randomly divided into 8 groups (N = 120, n = 15 per test group). Four groups were veneered with one of the layered veneering porcelains: Zirox, GC Initial ZR, VITA VM9 or IPS e.max Ceram and the other four groups were veneered with overpressed veneering porcelains: PressX Zr, GC Initial LF, VITA PM9 or IPS e.max ZirPress. The crowns were cemented on their corresponding CoCr abutment and the specimens were loaded at an angle of 45 degrees in a Universal Testing Machine to determine the fracture load. Data were analyzed using one-way and two-way ANOVA, followed by a post hoc Scheffe test, t-test and Weibull analysis (alpha = 0.05). Results. Within three manufacturers of veneering porcelain, fracture load values were not statistically significant between overpressed and layered porcelain systems. Within one manufacturer of veneering porcelain, the overpressed crowns (IPS e.max ZirPress: 1519 +/- 334 N) demonstrated significantly higher (p < 0.05) fracture load than that of the layered one (IPS e.max Ceram: 894 +/- 160 N). Except with IPS e.max ZirPress, where exclusively only chipping of the veneering porcelain was observed, all other porcelain systems showed predominantly framework fractures together with fracture of the veneering porcelain. Conclusion. Overpressed veneering porcelains for zirconia frameworks exhibited similar or better fracture load compared with layered ones. (C) 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.