Lifetime prediction of zirconia and metal ceramic crowns loaded on marginal ridges

Objective. To evaluate the fatigue life of zirconia-veneered and metal-ceramic crowns comprised by an even thickness or a modified framework design when loaded on marginal ridges. Methods. Eighty marginal ridges were present after fabrication of forty molar crowns cemented onto composite-resin replicas and divided (n = 20/each), in the following groups: metal-ceramic with even thickness (MCev) or with a modified framework design (MCm, lingual collar with proximal struts); porcelain-fused to zirconia with even thickness (PFZev) or with the modified framework design (PFZm). Each marginal ridge (mesial and distal) was subjected to cyclic loading separately with a lithium disilicate indenter for 10(6) cycles or until fracture. Kruskal-Wallis and Wilcoxon matched pair test (p < 0.05) evaluated both marginal ridges. Every 125,000 cycles, the test was interrupted for damage inspection. Weibull distribution (90% confidence bounds) determined the probability of survival (reliability). Results. Weibull 2-parameter contour-plot showed significantly higher fatigue life for PFZev compared to MC, and comparable with PFZm. A significant decrease in reliability was observed between groups from 625,000 until 10(6) cycles. Metal-ceramic groups presented significantly lower probability of survival at 10(6) cycles (MCev = 0.66% and MCm = 4.73%) compared to PFZm (23.41%) and PFZev (36.68%). Fractographic marks showed a consistent fracture origin and direction of crack propagation. Reliability was higher for porcelain-fused to zirconia than for metal ceramic crowns, regardless of framework design. Significance. Zirconia-veneered crowns presented decreased fracture rates compared to metal ceramics, even when loaded at marginal ridges, regardless of framework design. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.