Effect of herbal antioxidants on the shear bond strength of composite resin to bleached enamel at different time intervals

Background: Anterior tooth discolorations can be treated conservatively and noninvasively through bleaching to achieve the desired esthetic outcomes. However, bleaching along with composite resin is advisable for certain clinical cases for optimum results. However, shear bond strength (SBS) of composite resin to the bleached tooth gets significantly lowered. Before placing the composite restoration, the bleached enamel needs to be treated with antioxidant agents to increase its SBS. The study aims to evaluate and compare the effect of herbal antioxidants on SBS of composite resin to bleached enamel at different time intervals.

Materials and methods: Sixty extracted single-rooted maxillary incisors postdecoronation, keeping their labial surfaces up were mounted in cold-cure acrylic resin. The samples were randomly divided into: Group I - unbleached; Group II - 10% pine bark extract for 10 min postbleaching; Group III - 10% pine bark extract for 20 min postbleaching; Group IV - application of 10% rosemary extract for 10 min postbleaching, Group V - application of 10% rosemary extract for 20 min postbleaching; Group VI - no application of antioxidant. 35% hydrogen peroxide was used for bleaching all the samples except those which served as negative control. Later composite cylinder 4 mm in diameter and length were built on prepared enamel. The maximum load at failure was recorded using the universal testing machine.

Statistical analysis: Data were analyzed using the analysis of variance and Tukey's t-test with significance level of P < 0.05.

Results: Highest load was exhibited by Group I. Group V showed satisfactory shear strength followed by Groups IV, III, II, and VI.

Conclusion: Both 10% rosemary and 10% pine bark extracts showed better results when applied for 20 min as compared to 10 min application. Increased duration of antioxidant application increases the SBS.