Self-etching primer versus hydrofluoric acid and air-abrasion: effects on flexural and resin bond strengths of resin-based CAD/CAM material

This study aimed to evaluate the effect of self-etching primer (Monobond Etch '' MEP), hydrofluoric acid (HF), and air-abrasion (A) protocols on shear bond strength (SBS) of resin cement and flexural strength (FS) of nanoparticle-filled resin-based CAD/CAM material. Bar- and rectangular-shaped specimens (n = 130 for each) were obtained from a resin-based material (Cerasmart 270). The specimens were divided into 13 subgroups according to surface treatments: Control (C); HF for 60, 90, and 120 s; MEP for 60, 90, and 120 s; air-abrasion for 10, 15, and 20 s; air-abrasion followed by HF; air-abrasion followed by MEP; HF followed by MEP. Surface roughness (Ra) values were measured using a profilometer (Surftest SJ-210) by applying 9 readings per specimen. One specimen per group was examined by atomic force microscopy (AFM; Multimode 8) in a 20 mu m x 20 mu m area, and scanning electron microscopy (SEM; EVO LS-10) under x1000 magnification. FS and SBS data were obtained using a universal test device (Marestek) at a crosshead speed of 1 mm/min. Air-abraded groups showed the highest Ra (A10: 1.331 +/- 0.213; A15: 1.409 +/- 0.110; A20: 1.491 +/- 0.111; A + HF: 1.415 +/- 0.138; A + MEP: 1.309 +/- 0.071 mu m) and the lowest FS values (A10: 122.59 +/- 16.80; A15: 118.94 +/- 11.74; A20: 117.22 +/- 11.18; A + HF: 114.42 +/- 18.09; A + MEP: 128.98 +/- 19.74 MPa). FS values of HF- and/or MEP-applied groups were statistically similar to the control group (C: 167.37 +/- 27.02; HF60: 186.74 +/- 30.66; HF90: 162.79 +/- 29.31; HF120: 184.11 +/- 17.18; MEP60: 171.98 +/- 29.65; MEP90: 162.49 +/- 20.38; MEP120: 173.55 +/- 22.50; HF + MEP: 175.09 +/- 21.64 MPa). SBS values of MEP-applied groups were higher than those of HF-etched groups with the same duration. Significant differences in SBS values were found after etching protocols with different durations (HF60: 4.14 +/- 0.64; HF90: 4.48 +/- 0.33; HF120: 6.76 +/- 1.65; MEP60: 6.24 +/- 1.23; MEP90: 9.92 +/- 1.25; MEP120: 10.22 +/- 1.27 MPa). Prolonged MEP application (90 s and 120 s) can be the preferred surface treatment for resin-based CAD/CAM materials. However, air-abrasion may adversely affect its mechanical properties.