Methods: A total of 96 standardized class 5 cavities (1.5×2×3 mm) were prepared on the buccal surface of sound extracted human premolars and molars with both enamel and dentin margins and were randomly assigned to three groups as follows: Group A, Filtek P90 (silorane) with its dedicated adhesive system (P90 system adhesive); Group B, Adper Prompt L-Pop with Filtek Z250; Group C, Adper Prompt L-Pop with Filtek Z350XT. The teeth were subjected to thermocycling regime (1000×, 5–55ºC) and half of them received bleaching (38% carbamide peroxide, 15 min, twice a day, 14 days) and half of them received no bleaching (Control). Then dye penetration of tooth sections were evaluated following 24 hours immersion in 2% basic fuschin. Statistical analysis was performed with Kruskal-Wallis and Mann-Whitney U test at 95% significance level.
Results: There was not any significant differences between composites in control groups either in enamel (P=0.867) and dentin (P=0.59) margins. After bleaching, microleakage of Z250 and Z350 did not significantly change (P>0.05) in relation to control but the microleakage of P90 significantly increased in both enamel (P=0.042) and dentin (P=0.002) margins. Bleaching increased the microleakage of Z350 and P90 more than Z250 (P<0.05).
Conclusions: There was not any significant difference between bleaching and control subgroups of two metacrylate-based composites either in enamel or dentin margins. Microleakage of silorane-based composite significantly increased after bleaching.