Demineralization effects of hydrogen peroxide on bovine enamel and relation to shear bond strength of brackets.

Materials and Methods: Four equally-sized pieces of each crown from 18 bovine incisors were randomly distributed among 7 groups (n = 10). After bleaching with 30% hydrogen peroxide for 1 h, specimens were stored in artificial saliva for 0 h, 24 h, or 1, 2, 3, or 4 weeks before bonding specimens to brackets. An unbleached group of specimens served as controls. Shear bond strength (SBS in MPa) was measured with a universal testing machine. Adhesive Remnant Index (ARI) scores were determined after failure of bracket bonds. To measure demineralized Ca2+, four 4 x 4 mm sections from each of 15 bovine incisors were randomly distributed among 4 groups (n = 15). Specimens were stored in artificial saliva for 0 h, 24 h or 7 days after bleaching and then immersed in 37% phosphoric acid solution. After 15 s, 30 s, and 60 s, 5-ml aliquots of solution were removed for spectrophotometry. Unbleached specimens served as controls.