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Hydrofluoric acid etching modifies the cementation surface of ceramic restorations, which is the same surface where failure is initiated. Information regarding the influence of hydrofluoric acid etching on the cyclic loads to failure of ceramic crowns is lacking.The purpose of this in vitro study was to evaluate the influence of different hydrofluoric acid concentrations on the fatigue failure loads of feldspathic ceramic crowns.Eighty feldspathic ceramic crowns were cemented with resin cement to identical simplified complete crown preparations machined in a dentin-like polymer. The preparations were etched with 10% hydrofluoric acid for 60 seconds and received a primer coating. Before cementation, the intaglio of the ceramic crowns was treated with 1 of 4 surface conditionings (n=20): nonconditioned (control, CTRL), or etched for 60 seconds with different hydrofluoric acid concentrations: 1% (HF1), 5% (HF5), and 10% (HF10). A silane coupling agent was applied on this surface of all crowns, which were cemented to the preparations. Each crown was cyclically loaded in water with a G10 epoxy-glass piston positioned in the center of the occlusal surface. Fatigue failure loads of ceramic crowns were obtained by the staircase approach after 500 000 cycles at 20 Hz. Mean failure loads were analyzed by 1-way ANOVA and the Tukey test (α=.05).Mean failure loads of groups CTRL (245.0 ±15.1 N), HF1 (242.5 ±24.7 N), and HF10 (255.7 ±53.8 N) were statistically similar (P>.05), while that of the HF5 group (216.7 ±22.5 N) was significantly lower (P<.05).HF5 acid had a negative effect on the fatigue loads of the tested feldspathic ceramic crowns, while HF1 and HF10 acids did not change the fatigue resistance.