Effect of Three Antioxidants on the Shear Bond Strength of Composite Resin to Bleached Enamel: An In Vitro Study

Introduction Vital tooth bleaching is a widely accepted minimally invasive treatment for the management of tooth discoloration. However, residual oxygen radicals generated during bleaching adversely affect the polymerization of resin-based restorative materials, resulting in reduced bond strength when adhesive procedures are performed immediately after bleaching. Antioxidant agents have been proposed as a means of neutralizing residual free radicals and restoring bonding effectiveness. Objective The objective of this study is to compare the effects of 6.5% proanthocyanidin, 10% sodium ascorbate, and 10% selenium on the shear bond strength (SBS) of composite resin bonded to enamel following in-office bleaching. Materials and methods Seventy-five extracted permanent maxillary anterior teeth were selected and subjected to in-office bleaching using 37.5% hydrogen peroxide. Specimens were randomly allocated into five groups (n = 15): immediate bonding after bleaching, delayed bonding after three weeks, 6.5% proanthocyanidin treatment, 10% sodium ascorbate treatment, and 10% selenium treatment. Following surface treatment, enamel specimens were etched with 37% phosphoric acid, bonded using Adper™ Single Bond 2 (3M ESPE, St. Paul, MN, USA), and restored with Filtek Z250 XT (3M ESPE, St. Paul, MN, USA) composite resin. SBS was evaluated using a universal testing machine (UTM) at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey's post hoc test, with statistical significance set at p < 0.05. Results The highest mean SBS was observed in the proanthocyanidin group (45.52 ± 1.37 MPa), followed by sodium ascorbate (31.11 ± 1.98 MPa), delayed bonding (30.39 ± 1.51 MPa), selenium (15.95 ± 0.82 MPa), and immediate bonding (11.17 ± 1.66 MPa). The ANOVA demonstrated marked differences across the experimental groups (F = 1209.846, p < 0.001). Proanthocyanidin exhibited significantly higher SBS than all other groups. Conclusion Application of antioxidants after bleaching significantly improved the bond strength of composite resin to enamel. Among the tested antioxidants, 6.5% proanthocyanidin demonstrated the greatest efficacy in restoring SBS, followed by sodium ascorbate. Selenium exhibited comparatively limited effectiveness. Proanthocyanidin may serve as a clinically useful adjunct for immediate restorative procedures following bleaching.