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Cylinders of microfil and small-particle light-cured composite resin were bonded to the flattened labial enamel surface of young bovine incisor teeth which had previously been subjected to four different treatments: (1) teeth immersed in 35% hydrogen peroxide (HP) for 60 min and etched (E) with 37% phosphoric acid gel for 60 sec; (2) teeth immersed in saline (S) for 60 min and E for 60 sec; (3) teeth E for 60 sec and immersed in HP for 60 min; and (4) teeth E for 60 sec, immersed in S for 60 min. Specimens were stored in water at 37 degrees for one and seven days prior to tension- and shear-testing. A total of 256 teeth was tested--eight teeth in each group for each day, for each resin, and for each test. Statistical analysis of the results indicated that there was a highly significant reduction in adhesive bond strength of the resins when the enamel was exposed to HP as compared with S. SEM examination of randomly selected fractured test specimens indicated that this reduction in adhesive bond strength occurred primarily at the bonding resin-enamel interface. Less significant differences in bond strength were noted in the control specimens, with regard to resin type, time of storage, and the etching order.

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Cylinders of small‐particle light‐cured composite resin were bonded to the superficial dentin layer of young bovine incisors that had previously been subjected to 4 different treatments: 1) immersed in 35% hydrogen peroxide for 60 min, then etched with 37% phosphoric acid gel for 60 s; 2) immersed in saline for 60 min, then etched with 37% phosphoric acid gel; 3) etched with 37% phosphoric acid gel for 60 s, then immersed in 35% hydrogen peroxide for 60 min; and 4) etched with 37% phosphoric acid gel, then immersed in saline for 60 min. Specimens were stored in water at 37°C for 1 and 7 d prior to tension and shear testing. A total of 128 teeth were tested: 8 teeth in each group, for each day and for each test. No measurable adhesion of resin to peroxide‐treated dentin was observed and statistical analysis of the test results indicated that this represented a highly significant reduction in the bond strength as compared with values obtained when resin bonded to saline‐treated dentin was tested. SEM examination of randomly selected fracture test specimens indicated that the bond failure was both cohesive and adhesive in nature, suggesting that peroxide treatment adversely affects the setting of bonding resin and its adhesion to a filled resin.