Adhesion of metal brackets to glassy matrix and hybrid CAD/CAM materials after different physico-chemical surface conditioning

This study compared the adhesion of metal brackets bonded to different CAD/CAM materials after various surface conditioning methods. CAD/CAM blocks (N = 204, n = 17 per group) of (a) VITA Mark II (VM), (b) IPS e.max CAD (IP), (c) Lava Ultimate (LU), and (d) VITA ENAMIC (VE) were conditioned with one of the following methods: C-Control: (fine diamond bur); CJ: (fine diamond bur + air-abrasion with 30 μm SiO₂ + silane), and HF: (fine diamond bur +9.5% hydrofluoric acid + silane). Metal brackets were bonded to the conditioned surfaces of the specimens, stored in artificial saliva for 24 h at 37 °C and thermocycled (×1000). Subsequently, the brackets were debonded under shear in a Universal Testing Machine (1 mm/min). Failure types were analyzed under scanning electron microscope. Data were analyzed using two-way ANOVA and Tukey’s tests (α = 0.05). Two-parameter Weibull distribution values, including the Weibull modulus, scale, and shape, were calculated. Mean bond strength (MPa) values were significantly affected by the surface conditioning method (p < 0.001) but not the CAD/CAM material type (p = 0.052). Bond strengths for all CJ and HF-conditioned specimens were twofold higher (11.83 ± 1.95 ? 9.44 ± 1.63) than those for control specimens with all materials (4.73 ± 0.93 ? 6.02 ± 0.69). Lower mean values were obtained in LU-CJ (9.78 ± 1.61) and LU-HF (9.44 ± 1.63) than those for other groups (11.83 ± 1.95 ? 10.93 ± 1.33) groups (p < 0.05). Weibull distribution showed higher shape values for VM-CJ (11.26) and VM-HF (8.87) than those for other groups (0.82–1.83). In control groups, exclusively adhesive and after conditioning mainly mixed failures were observed. Chairside silica coating or HF conditioning significantly improved metal bracket adhesion to both glassy matrix and hybrid CAD/CAM materials tested, with the most reliable adhesion being observed for feldspathic ceramic.