Effects of Hydrofluoric Acid Concentration and Etching Time on the Bond Strength to Ceramic-coated Zirconia

Purpose: To evaluate the effects of different hydrofluoric acid (HF) concentrations and etching times on the surface topography, roughness, and resin bond strength to ceramic-coated zirconia (CC), and to compare them with the effects of alumina air-abrasion combined with 10-MDP (AA). Materials and Methods: AA and CC specimens were divided into 12 groups (N = 10). The CC groups were etched with HF at different concentrations (5% or 9.5%) for various durations (0 min, 1 min, 2 min, 3 min, 5 min or 10 min). The surface morphology was analyzed using SEM. Energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) were performed for chemical and crystalline-phase analyses. Surface roughness (Ra) and shear bond strength (SBS) were recorded and statistically analyzed. Results: The SBS of CC groups initially increased, but then decreased with etching time for both HF acid concentrations. The 9.5% HF group displayed more marked topographical changes and higher Ra compared with the 5% HF group for the same etching period. Mean SBS was lower in the AA group compared with the CC groups etched with 5% HF for 2-10 min and 9.5% HF for 1-3 min (p < 0.05). Conclusions: Different HF concentrations and etching times influenced the surface topography, roughness, and resin bond strength of/to ceramic-coated zirconia. Etching with 5% HF for 5 min and with 9.5% HF for 2 min, respectively, provided the highest SBS.