Silica coating of Ni-Cr alloy resulted in higher shear bond strength than those of other surface treatments.

Up to now, there is no any experience about the application of dental lasers to bond resin composites to metal surfaces in dentistry. The aim of this preliminary study was to evaluate if the laser irradiation of ceramic-covered alloy surface would improve the bond strength of resin to metal, and if different parameters of laser output may influence the strength of this bond. Fifty three cylinders (thickness of 5 mm and diameter of 10 mm) were made up of a commercially available nickel-chromium alloy by lost-wax technique. Forty prepared specimens were divided into four groups. Five specimens in each group were covered by slurry of dental opaque porcelain and irradiated by Nd:YAG laser using different output parameters for each group. Other five specimens in each group were treated using the same laser parameters without porcelain covering. Five sandblasted specimen served as control group. Panavia F2.0 was bonded on the metal surfaces using polyethylene tubes. In ceramic-coated specimens, silane was applied to achieve chemical bond between silica particles and resin cement. All specimens were thermocycled and subjected to shear bond strength (SBS) test (50 kgf at 0.5 mm/min). Two specimens of each ceramic-coated laser-treated groups were studied using scanning electron microscopy and wavelength dispersive X-ray spectroscopy which showed stabilization of silica particles on the metal surface. ANOVA procedure showed that although shear bond strength was significantly higher in porcelain-covered laser treated samples, but the effect of power output of laser irradiation was not significant (P = 0.917). There were no statistically significant difference between SBS in control samples and laser treated specimens without porcelain covering. It can be concluded that Nd:YAG laser surface treatment may improve the silica coating of alloy surface to achieve better resin-metal bond.