Comparative evaluation of effects of commercially available and natural antioxidants on shear bond strength of composite resin to bleached enamel: An in vitro study

Introduction: Following bleaching with commercially available bleaching agents, various antioxidants are used to reverse the bond strength of enamel. Aim: The aim of this study was to compare and evaluate the effect of 5% grape seed extract, 5% oregano seed extract, and commercially available antioxidants on the bond strength of bleached enamel with a commercial 35% hydrogen peroxide H202 bleaching agent. Materials and Methods: In this experimental in vitro study, labial enamel surface of 50 extracted human maxillary central incisors was randomly divided into 5 groups based on antioxidants used as follows: Group 1 ( n = 10) positive control group no usage of bleaching agent Group 2 ( n = 10) bleaching with 35% hydrogen peroxide gel for 10 min, without the use of antioxidants. Group 3 ( n = 10) bleaching followed by use of 5% sodium ascorbic acid solution Group 4; ( n = 10) bleaching followed by use of 5% proanthocyanidin solution (oligomeric proanthocyanidin complex - Grape seed extract) Group 5; ( n = 10) bleaching followed by use of 5% oregano seeds extract. After the bleaching procedure, composite resin cylinders were bonded incrementally on the labial surface and stored in artificial saliva at 37°C for 24 h. The samples were subjected to shear bond strength (SBS) under a universal testing machine. Results and Discussion: The experiment investigated the impact of different treatments on tooth enamel, specifically focusing on the effects of bleaching with and without antioxidants. The negative control group, where no bleaching was performed, exhibited an average enamel hardness. In contrast, the positive control group, subjected to bleaching without any antioxidant intervention, demonstrated a significantly lower mean enamel hardness. Introducing antioxidants along with bleaching agents showed interesting results. The group treated with sodium ascorbic acid as an antioxidant exhibited an average enamel hardness of 13.31, ranging from 11.96 to 15.60. Similarly, the grape seed extract group had a mean hardness of 14.13 and a range from 12.08 to 15.60. The oregano seed extract group showed the highest average hardness among the antioxidant-treated groups, with a mean of 17.14 and a range from 15.75 to 18.20. Among the antioxidant-treated groups, the oregano seed extract groups consistently showed the highest SBS, followed by the grape and Na ascorbic acid groups. Conclusion: Within the constraints of this in vitro research, it can be inferred that 5% oregano seed extract can be used to reverse the reduced bond strength and may be an alternative to delayed bonding after bleaching affects the bond strength of composite resin to the enamel, even when compared to the commercially available antioxidant.