Effect of bleaching agents on surface free energy parameters of resin composite coated with saliva biofilm.

PURPOSE: To assess the effect of 10% carbamide peroxide and 10% hydrogen peroxide bleaching preparations on the surface free energy of resin composite with and without saliva biofilm coating. METHODS: 72 light-cured resin composite samples were used. The samples were either coated with fresh human saliva or left uncoated. Each sample was placed in a plastic assay tube containing 2 ml of either 10% carbamide peroxide (CP), 10% hydrogen peroxide (HP), or phosphate buffer solution. The tubes containing the composite samples were then placed in a dry incubator at 37 degrees C for 1- and 3-day time intervals. After each time interval the samples were rinsed with distilled water and subjected to wetting measurements using a captive bubble technique. Measurements were taken in triplicate and determination of contact angles done by using film negatives on an enlarger. The differences between pre-treatment and post-treatment measurements and between samples coated with saliva and non-coated samples were analyzed statistically for each time period and treatment group. RESULTS: 10% CP reduced octane contact angle of all exposed composite groups after 1 day of treatment regardless of saliva coating. Differences between the pre-bleached and post-bleached groups were statistically significant only for octane contact angles measured in saliva-coated samples (P < 0.05). 10% CP reduced both the octane and air contact angles of all exposed composite surfaces after 3 days of treatment. The reduction was statistically significant only for octane contact angles measured in the saliva-coated samples (P < 0.05). Additionally, 10% CP significantly reduced the surface free energy of saliva-coated samples after 1-day treatment as compared to non-coated samples. 10% HP reduced octane contact angle of all exposed composite groups after 1 day of treatment regardless of saliva coating. The differences between the pre-bleached and post-bleached groups were statistically significant only for octane contact angles measured in the saliva-coated samples (P < 0.05). 10% HP reduced both the octane and air contact angles of all exposed resin composite surface samples after 3 days of treatment regardless of saliva coating. However, the differences between the groups were not statistically significant.