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

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.

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 10⁶ 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).

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 10⁶ cycles. Metal-ceramic groups presented significantly lower probability of survival at 10⁶ 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.

Zirconia-veneered crowns presented decreased fracture rates compared to metal ceramics, even when loaded at marginal ridges, regardless of framework design.