Effect of quercetin pretreatment on the immediate and aged bond strength of bleached dentin

This in vitro study aimed to investigate the effect of quercetin pretreatment on the bond strength of bleached dentin. Human dentin blocks (2 × 2 × 1 mm) were prepared and randomly divided into 5 groups (n = 16): deionized water pretreatment + no bleaching treatment (DNB); deionized water pretreatment + bleaching treatment (DYB); 75 μg/mL quercetin pretreatment + bleaching (Q75B); 150 μg/mL quercetin pretreatment + bleaching (Q150B); and 300 μg/mL quercetin pretreatment + bleaching (Q300B). The surfaces of superficial dentin (bonding surfaces) were treated with the respective solutions for 2 min, and then the surfaces opposite to the bonding surfaces (near pulp, bleaching surfaces) were subjected to bleaching treatment with 40% hydrogen peroxide (Ultradent, USA) for two 15-min sessions (groups DYB, Q75B, Q150B, and Q300B). After the bleaching procedure, the bonding surfaces were bonded with resin cements (Panavia V5, Kuraray, Japan). The bonded specimens were then divided into 2 subgroups (n = 8): the aging group (subgroup T), which was subjected to 10,000 thermocycles, and the nonaging group (subgroup N), which was not subjected to thermocycling. The microshear bond strength (μSBS) was obtained using a universal testing machine (AGS-X, Shimadzu, Tokyo, Japan). Additional dentin blocks (5 × 5 × 1 mm) were prepared and treated the same as the groups DYB, Q75B, Q150B, and Q300B (n = 8) to evaluate the color change, defined as groups CC_DYB, CC_Q75B, CC_Q150B, and CC_Q300B, respectively. Color evaluation was performed using a spectrophotometer (Vita Easyshade Advance 4.0, Vident, USA) to obtain a baseline and again at the end of the bleaching treatment. The data were analyzed via two-way analysis of variance (ANOVA) and Tukey's post-hoc test (α = 0.05). For the immediate bond strength, the specimens in the groups Q75B, Q150B, and Q300B showed significantly higher μSBS values than those in the group DYB (all P < 0.05). No significant differences in the μSBS values were found among the groups Q75B, Q150B, Q300B, and DNB, respectively (all P > 0.05). For the aged bond strength, both the groups Q150B and Q300B exhibited significantly higher μSBS values than groups DYB and DNB (all P < 0.05), whereas no significance differences were found between groups Q150B and Q300B (P = 1.00) or between the groups DYB and DNB (P = 1.00). No significant differences were observed in the △E values among all the groups tested (P = 0.80). Therefore, the application of quercetin for 2 min prior to the bleaching procedure preserved the immediate bond strength and improved the aged bond strength of bleached dentin while maintaining the effectiveness of bleaching.