The effect of elapsed time following bleaching on enamel bond strength of resin composite

Recent studies have concluded that carbamide peroxide bleaching agents sign ificantly affect the bond strength of composite to bleached enamel. This st udy evaluated the effects of bleaching regimen with different carbamide per oxide concentrations and post-treatment times on composite bond strength to enamel. Two hundred and four flat buccal and lingual enamel surfaces obtai ned from erupted sound third molars were randomly divided into 17 groups (n =12). Sixteen experimental groups comprised the evaluation of four carbamid e peroxide home bleaching agents (Opalescence 10%-20 % and Whiteness 10%-16 %) and four time intervals after bleaching (one day, one, two and three wee ks). Specimens of control group were not submitted to bleaching and were st ored in artificial saliva at 37 degrees C for 10 days. The specimens of exp erimental groups were exposed to one daily application of carbamide peroxid e for six hours for 10 consecutive days. After each daily treatment and pos t-bleaching, the specimens were stored in artificial saliva solution. Bonds were formed with Scothbond MP and Z-100 composite resin, and shear bond te st was carried out 24 hours after adhesive-composite application. Two-way A NOVA showed that the bond strengths were significantly different (p <0.05). For the first two weeks post-bleaching, the bond strengths of resin to ena mel were low. After a lapse of three weeks, the bond strength returned to t hat of the untreated control group. Increased concentration did not prolong the time needed prior to bonding.