Influence of Surface Nano-roughness of Dental Alumina Ceramic on Bond Strength to Dual-Cure Resin Cements

The goal of this research is to evaluate the effect of sandblasting and silica coating on the nano-roughness and on the microtensile bond strength (MTBS) of glass-infiltrated alumina bonded to different resin cements. Six slabs of In-Ceram Alumina (Vita) were randomly treated according to the following groups: (1) no treatment; (2) sandblasting (125 μm Al2O3-particles); and (3) tribochemical silica-coating (50 μm silanated silica particles). Nano-roughness (Ra) was assessed under an atomic force microscope (AFM). Such surface treatments were also applied to nine In-Ceram Alumina CAD/CAM blocks. Ceramic blocks were duplicated in composite resin, and composite samples were bonded to the conditioned surfaces. Each pre-treatment group was divided into three subgroups depending on the resin cement system: (1) Clearfil Ceramic Primer plus Clearfil Esthetic Cement (CEC, Kuraray); (2) RelyX Unicem (RXU, 3M); and (3) Calibra Silane plus Calibra Resin Cement (CAL, Dentsply). After 24 h, the bonded specimens were cut into 1±0.2 mm2 sticks. The MTBS values (MPa) were obtained using a universal testing machine (crosshead speed: 0.5 mm/min). Failure modes were recorded using a scanning electron microscope (SEM). Nano-roughness and MTBS data were analyzed by ANOVA and Student–Newman–Keuls tests (α =0.05). No significant changes in nano-roughness occurred after conditioning. The MTBS of CEC and RXU were comparable despite the surface treatment. All CAL-sticks debonded prematurely. Ceramic pre-treatments, such as sandblasting or silica coating, do not affect the alumina's surface nano-roughness or bond strength. The MDP monomers dissolved in the CEC Primer and the functional dimethacrylate monomers present in the self-adhesive RXU may be the key to successful bonds to alumina.