EFFECT OF WATER LEACHING ON THE ADHESION OF COMPOSITE RESIN TO BLEACHED AND UNBLEACHED BOVINE ENAMEL

Standarized cylinders of light-cured composite resin were bonded to the ground labial enamel surface of bovine incisor teeth that had been immersed in double-distilled water for 7 days after having been (a) immersed in hydrogen peroxide for 5, 30, or 60 min, then etched for 60 s with 37% phosphoric acid; (b) immersed in saline for 5, 30, or 60 min, then etched for 60 s with 37% phosphoric acid; (c) etched with 37% phosphoric acid for 60 s, then immersed in hydrogen peroxide for 5, 30, or 60 min; or (d) etched with 37% phosphoric acid for 60 s, then immersed in saline for 5, 30, or 60 min. The enamel surface was washed with water for 1 min and dried with compressed air for 30 s prior to applying the resin. The tooth and applied resin were stored in water at 37-degrees-C for 1 day prior to shear and tensile testing. A total of 192 specimens was used, 8 for each enamel preparation mode, for each time period, and for each test. Test values were tabulated and statistically analyzed. Analysis of variance revealed significantly higher bond strength values (p < 0.005) for hydrogen peroxide-treated as compared with saline-treated specimens. A significant interaction was also noted between test solution and etching order. Scanning electron microscopic examination of failed shear- and tensile-tested specimens revealed no significant solution-related differences in the fracture pattern or the resin quality. It was concluded that exposure of peroxide-treated enamel to water at 37-degrees-C for 7 days eliminates the reduction in bond strength that attends the immediate application of resin to peroxide-bleached enamel. The increase in bond strength that is associated with some peroxide-exposed specimens is thought to arise from improved surface conditioning or cleansing.