Influence of bleaching and antioxidant agent on microtensile bond strength of resin based composite to enamel

The purpose of this investigation was to determine the effect of bleaching agent (10% carbamide peroxide) and antioxidant (10% sodium ascorbate) on the microtensile bond strength (μTBS) of resin based composite to enamel. Sixteen extracted human molar teeth were divided into three bleaching groups of 10% carbamide peroxide and an unbleached control group. The specimens in group 1 were bonded immediately after bleaching; group 2 were treated with antioxidant; group 3 were immersed for 3 h in distilled water, whereas the unbleached specimens in group 4 had no treatment (control) before bonding. The enamel was etched using 36% phosphoric acid, and was bonded to light polymerized resin composite. The tooth and resin composite assembly was sectioned to produce specimen of 1.0 mm² cross-section. Specimens were subjected to microtensile testing and fractographic analysis using scanning electron microscopy. The data was analyzed using one-way analysis of variance and Tukey–Kramer multiple comparisons test (P = 0.05). The specimen bonded immediately after bleaching revealed significantly lower μTBS (22.33 ± 8.46) compared to those of the control group (30.77 ± 8.01). The bleached specimen treated with antioxidant had μTBS (31.27 ± 6.92) similar to the control group. The majority of failures were at the adhesive interface, however the control group had greater cohesive failures. μTBS reduced significantly when resin based composite was bonded to prebleached enamel with carbamide peroxide (P < 0.001). Furthermore, application of antioxidant to bleached enamel restored the μTBS to levels similar to unbleached enamel (P < 0.001).