Evaluation the Effect of Rosmarinic Acid as an Antioxidant Agent on Shear Bond Strength of Resin Composite to Bleached Enamel.

Background: Tooth bleaching, a routine esthetic dental procedure, can compromise bond strength to enamel and dentin, especially if composite restorations are bonded immediately post-bleaching due to residual peroxide and free radicals. To address this, various treatments, including antioxidants like sodium ascorbate (SA), have been used, though SA may increase bacterial accumulation. Rosmarinic acid (RA), an alternative antioxidant, offers additional antibacterial and adhesive benefits. This study evaluates the effect of RA application time on shear bond strength (SBS) in bleached enamel, comparing its efficacy with SA under varying treatment durations. Three null hypotheses regarding RA's impact on SBS are tested.

Material and methods: The labial surfaces of 60 freshly extracted bovine incisors were randomly assigned into 6 groups and subjected to a specific surface treatment as follows: no bleaching procedure (NBL), bleaching with 38% hydrogen peroxide (BL), BL+ 10% sodium ascorbate for 10 min (SA), BL+ RA for 10 seconds (RA1), 60 seconds (RA2) and 10 min (RA3). The resin composite was bonded to enamels s immediately after these treatments. After storage in water for 24 hours, the bonded samples were mounted on a universal testing machine and loaded to the fracture point. Data analysis was performed using Kolmogorov-Smirnov, Lilliefors, One-way analysis of variance and Games-Howell tests.

Results: The NBL group had the highest SBS, comparable only to SA (P= 0.908). SA outperformed all RA groups (P< 0.001). RA3 showed the lowest SBS, significantly lower than RA1 (P= 0.011). The main fracture mode in all research groups was adhesive failure.

Conclusions: Rosmarinic acid was not able to reverse the bond strength to enamel immediately after the bleaching process, regardless of the duration of application. Key words:Antioxidant agents, Dental bleaching, Enamel, Rosmarinic acid, Shear bond strength.