Effect of 10% Carbamide Peroxide on Resin Composite - Enamel Bond

Objectives: To determine the effect of bleaching with 10% carbamide peroxide (CP) on tensile bond strength and the composite-enamel interface. Methods: 60 extracted mandibular molars were selected, randomly divided into 3 groups: (1st) untreated, preserved in distilled water (control group); (2nd) treated with 10% CP (Nupro Gold 10%, Denstply) for 40 hours and (3rd) treated with 10% CP for 40 hours and followed by immersing in distilled water for 72 hours. Fifteen teeth from each group were randomly selected for tensile bonding test. A 3x3 mm² composite (Z100, 3M) was bonded on flat enamel surface. Tensile bond strength was determined using a universal testing machine. Five teeth from each group were prepared for scanning electron microscopy (SEM). Teeth were restored by Z100 with Single Bond on polished-enamel surface and followed by sectioning through the middle part of bonded composite using a water-cooled slow-speed diamond disk. Bond strength data was analysed using One-way ANOVA. Results: Means and SEs of bond strength of 1st, 2nd and 3rd group were 19.77±1.05 MPa, 10.98±1.07 MPa, 16.25±0.96 MPa, respectively. Bond strengths were decreased significantly after bleaching (p<0.001). There was a significant increase in bod strength when specimens were immersed for 72 hours after bleaching (p=0.002). There was no significant difference between 1st and 3rd groups (p=0.061). SEM results: resin layer without resin tags were observed at the composite-enamel interface in 2nd group. In the 3rd group, hybrid layer and resin tags were seen in most samples, however tags were poorly defined and penetrated to a lesser depth compared to the control group. Conclusions: 10% CP has adverse effects on the resin composite - enamel bond strength, however after 72 hours the bond strength was similar to that of unbleached teeth.