Effect of alloy type and surface conditioning on roughness and bond strength of metal brackets

The effect of 5 different surface conditioning methods on bonding of metal brackets to cast dental alloys was examined. The surface conditioning methods were fine (30-µm) or rough (125-µm) diamond bur, sandblasting (50-µm or 110-µm aluminum oxide [Al2O3]), and silica coating (30-µm silica). Fifty disc-shaped specimens of 5 different alloys (gold-silver, palladium-silver, nickel-chromium, cobaltchromium, and titanium) were ground with 1200-grit silicone carbide abrasive and polished before being reused for each conditioning method. Polished surfaces were used as negative controls. After measuring surface roughness (RZ), metal brackets were bonded to the conditioned alloys with a self-curing resin composite. Specimens were thermocycled (5000 times, 5°–55°C, 30 seconds), and shear bond tests were performed. Significantly higher (P .001) surface roughnesses were observed with use of the rough diamond bur (RZ ~33 µm), 110-µm Al2 O3 (RZ ~14 µm), and fine diamond bur (RZ ~10 µm), compared with the controls (RZ ~1 µm). Silica coating (RZ ~4 µm) and 50-µm Al2 O3 (RZ ~4 µm) demonstrated no significant difference (P > .001) in roughness when compared with the controls. The control group showed no resistance to shear forces (0 MPa). Bond values were greater (19 MPa) when silica coating was used, compared with 50-µm Al2O3 (7 MPa) and 110-µm Al2O3 (8 MPa) for all alloys tested. However, interaction between alloys and conditioning methods exhibited significant differences (P > .0001)