Effects of warm air-drying and spreading on resin bonding

The purpose of this study was to compare the effect on resin-to-enamel bonding produced by warm air from a hair dryer, and to correlate changes in resin bond strength with resin tag structure. Herculite-XR resin composite and Bondlite bonding resin were used. The three technique variables were the type of air used for drying, air dryer distance, and drying and spreading time. Control samples were dried and the bonding resin spread with a dental air syringe, whereas warm air from a hair dryer was used on the experimental samples. The bond strength (MPa) was determined in shear at a crosshead speed of 1 mm/min. Following bond strength evaluation, the teeth were immersed in 10% HCl for enamel dissolution and the resin tag structure was examined with the SEM. ANOVA analyses of shear bond strengths were performed. Warm air-drying and spreading for 15 seconds at 6 cm and 5 seconds at 6 cm respectively, produced statistically greater shear bond strengths (x = 20.4 +/- 4.4 MPa, P less than 0.05). The other drying time/distance combinations, including the control (x = 14.4 +/- 3.3 MPa), were not statistically different. Differences in resin tag structure were qualitatively evident under the SEM, with sharp tags produced by the warm air-drying and spreading techniques, compared to the blunt tags created by syringe air-drying and spreading. Warm air-drying and spreading significantly improved the bond strength. No apparent correlation exists between bond strength and tag length.