Does sandblasting improve bond strength between nano-ceramic resin and two different luting composites?

Purpose: To assess the influence of a sandblasting surface treatment on the shear bond strength (SBS) between a recently introduced Resin Nano-Ceramic (RNC) CAD/CAM material and two resin cements. Methods: 40 RNC blocks were divided into two groups (n=20): a control (C) and a test group (S_50) to which air abrasion (50 μm, 0.28 MPa, and 10s) was applied. Each group was divided into two subgroups (n=10) according to the applied luting material: a self-etch dual-cure resin cement (LP) and a dual-cure resin cement (LR). SBSs were determined with a universal testing machine at a crosshead speed of 0.5 mm/min. Fracture patterns were evaluated by a stereomicroscope (25x) and classified into adhesive, cohesive and mixed. One-way ANOVA test (α=.01) was used to establish differences between groups, considering SBS as dependent and the type of surface treatment as independent variable. Results: Mean SBS values (MPa) and standard deviations (SD) for the experimental groups were: [C-LP]: 8.68 (1.16); [C-LR]: 15.32 (3.93); [S_50-LP]: 13.91 (2.58); [S_50-LR]: 15.77 (4.12). A statistically significant difference (p<0.001) was found between [C-LP] and the other three groups. Sandblasting positively affected (p<0.01) the self- adhesive cement adhesion to nano-ceramic resin. Group C_LP showed 100% of adhesive fractures, while S_50_LP had some cohesive (20%) and mixed fractures (10%). The fracture pattern of group C_LR was 60% cohesive, 20% adhesive and 20% mixed, while group S_50-LR showed 100% of cohesive failure. Conclusion: Within the limitations of this study, sandblasting of the RNC surface is recommended when the tested self-adhesive resin cement is used for luting, in order to significantly improve bond strength values. For the luting agent LR - associated with a universal adhesive system - satisfactory adhesion values were achieved regardless an air abrasion pre-treatment.