Do resin cement viscosity and ceramic surface etching influence the fatigue performance of bonded lithium disilicate glass-ceramic crowns?

OBJECTIVE: To assess the effects of a resin cement in high and low viscosity and distinct conditioning of the intaglio surface of lithium disilicate glass-ceramic crowns on fatigue performance of the crowns. METHODS: Prosthetic preparations (full-crown) in resin epoxy and crowns in lithium disilicate glass-ceramic were machined and allocated considering 2 factors (n = 10): "surface treatment" (HF - 5% hydrofluoric acid etching, followed by silane application; or E&P-self-etching ceramic primer) and "resin cement" (high or low viscosity). The preparations were etched with 10% hydrofluoric acid and an adhesive was applied. The intaglio surfaces of the ceramic crowns were treated as aforementioned (HF or E&P) and luted with high or low viscosity. The bonded sets were subjected to fatigue testing (step-stress approach: initial load of 200 N, step-size of 50 N, 10,000 cycles/step, 20 Hz) and complementary analyses (fractographic, topographic, and cross-sectional bonded interfacial zone analyses) were performed. RESULTS: Treatment with HF and silane with high viscosity resin cement (955 N/156,000 cycles) and E&P with low viscosity resin cement (1090 N/183,000 cycles) showed the best fatigue performance (statistical similarity between them). The failures originated from defects of the cement-ceramic interface, and the HF treatment induced a more pronounced topographical alteration. SIGNIFICANCE: Distinct topographical patterns from the HF and E&P treatments induced better fatigue results for the specific viscosity of the resin cement. Therefore, the fatigue performance depended on the existing topography, type of intaglio surface's defects/irregularities after surface treatment, and how the luting agent filled the irregularities.