Are Universal Adhesives Effective for Bonding to Zirconia in the Long Term?

Background: The bond capacity of universal adhesives should be comparable to a specific primer for zirconia. Thus, this study evaluated the bond strength to zirconia of four universal adhesives and a zirconia primer over long-term storage. Materials and Methods: The surfaces of 75 samples of zirconia were sandblasted with 50 μm aluminum oxide particles and then divided into groups (n = 15): G1 – Single Bond Universal (SBU); G2 – All Bond Universal; G3 – Peak Universal Bond; G4 – Ambar Universal (AU), and G5 – Z-Prime Plus (ZP). A cone of resin composite was constructed on the applied materials. The samples were submitted to a tensile bond strength test after 24 h using a universal testing machine. Then, the remaining materials were removed from the sample surfaces, and the surfaces were polished and sandblasted again as previously described to obtain the same groups. These new samples were stored in distilled water at 37°C for 12 months and then submitted to a tensile bond strength test. The data were analyzed by two-way analysis of variance and Tukey's test (α =0.05). Results: The material factor (P = 0.001) and the storage factor (P = 0.001) were significant, and the interaction was not significant (P = 0.117). According to Tukey's test, bond strength mean values (in MPa) followed by distinct letters were significantly different. After 24 h, G5 = 21.12 A, G1 = 20.55 A, G4 = 19.19 AB, G2 = 14.22 B, and G3 = 8.44 C. After 12 months, G1 = 7.37 A, G5 = 5.61 AB, G4 = 4.97 B, G2 = 3.32 C, and G3 = 1.93 D. After 12 months of storage, all groups' bond strength significantly decreased. Conclusions: SBU and AU had bond strengths comparable to ZP after 24 h. No material resisted water degradation.