Objective This study aimed to evaluate and compare the impacts of the postbleaching application of sodium ascorbate, alpha‐tocopherol, and quercetin on the shear bond strength (SBS) of composite resin. Material and Methods 60 extracted intact maxillary first premolars were collected and were randomly divided into five experimental groups as follows (n=12): Group A (negative control): no bleaching, Group B (positive control): bleaching with 40% hydrogen peroxide (HP), Group C: HP±10% sodium ascorbate for 10min, Group D: HP±10% alpha‐tocopherol for 10min, and Group E: HP±1% quercetin for 10min. Composite bonding was done immediately after bleaching for Groups B‐E and without any treatment for Group A. After being stored in distilled water at room temperature for 24h, all specimens were tested for SBS in the universal testing machine. One‐way analysis of variance and Tukey's post‐hoc test were used to analyze the SBS values of all groups. Results The results showed that the bonding of composite to the unbleached group exhibited the highest mean value of SBS (22.68±2.91MPa). Among the antioxidant‐treated groups, the highest SBS value was detected in quercetin‐treated specimens (15.45±1.58MPa), which was significantly different from the positive control group (p<.05). Conclusion It could be concluded that 10% quercetin applied for 10min increased the bond strength to bleached enamel, but it was not able to reverse it completely.

Objective The aim of this study was to evaluate and compare the effects of chlorhexidine, quercetin, and α‐tocopherol on the shear bond strength of universal adhesives in the short (24h) and long term (6 months). Material and Methods Ninety‐six extracted sound molars were collected and divided randomly into four groups: control (no treatment), 2% chlorhexidine, 10% α‐tocopherol, and 1% quercetin. The solutions were prepared and applied to the teeth for 60 s, followed by application of All‐Bond universal adhesive and composite build‐up. Half of the specimens in each group (n = 12) were tested for shear bond strength (SBS) after 24 h of storage and the other half were kept in distilled water for 6 months and then tested for shear bond strength. The shear bond strength test was performed and the failure modes were determined using a stereomicroscope. The data were analyzed using two‐way analysis of variance and Tukey's post hoc tests with p ˂ .05 as the significance level. Results The results of the two‐way analysis of variance test showed that there was no significant difference in immediate SBS, and after 6 months, α‐tocopherol had the lowest SBS in comparison to the control and CHX subgroups (p < .05). The t‐test showed that the shear bond strength in the α‐tocopherol and quercetin groups was significantly decreased after 6 months. Conclusion It can be concluded that the solutions used in this study had no adverse effect on immediate SBS. After 6 months, the CHX could preserve SBS in comparison to other groups.