Fatigue resistance of Y-TZP/porcelain crowns

Purpose: Following the tendency of all-ceramic crowns, Y-TZP stands out for its biomechanical properties. The literature describes several possibilities of Y-TZP surface treatment aiming to improve the adhesion to substrate, but there is still a controversy about the long-term effects of them. However, clinical studies (which do not analyze those treatments) observe that mostly failures occur cohesively in porcelain and not for lack of adhesion to the substrate. To evaluate the effects of some surface treatments and cementing agents of Y-TZP/porcelain crowns, this study evaluated the fatigue resistance in a simplified model in order to reduce bias and better study the materials themselves. Methods and materials: For this, 90 preparations were machined in epoxy resin that received Y-TZP frameworks made by CAD/CAM system and veneered by feldspathic ceramic. Six groups were tested (n=15): PN, ZP and GI – cleaning with isopropyl alcohol; OG – overglaze applying; AO – 125 m Al2O3 sandblasting; CJ – 30 m SiO2 sandblasting. The crowns from the ZP group were cemented with zinc phosphate and the crowns from GI group were cemented with glass ionomer, while the remaining crowns were cemented using Panavia F (Kuraray). The fatigue resistance was evaluated using stepwise stress until failure: 5k cycles at 200N followed by 10k cycles at 800, 1000, 1200 and 1400N. The cement thickness and failure modes were analyzed in stereomicroscope and scanning electronmicroscopy, and the results were statistically analyzed by Kaplan–Meier and Mantel-Cox log rank tests (5%), 1-way ANOVA and Tukey’s test andWeibull nonparametric test. Results: The adhesively cemented crowns showed higher fatigue resistance when compared to the non-adhesively crowns, but the treated crowns were also similar to the nonadhesive ones.Weibull’s analysis indicated that all specimens had a higher ratio of late to early failures. The predominantly failure mode was the chipping of the veneer. Conclusion: It can be concluded that the surface treatments didn’t influenced the fatigue resistance of Y-TZPporcelain crowns, but the adhesively luting is recommended in this case.