Effects of applying procyanidins on the bond strength of bleached dentin to composite resin

To study the influence of procyanidins on the bonding strength of dentin bleached by carbamide peroxide to composite resin.

By applying different treatments to dentin bonding interfaces, 120 human third molars were randomly divided into 12 groups (n = 10): W group (no bleaching+deionized water), Wa group (no bleaching+deionized water+aging), WT1 group (no bleaching+5% procyanidins for 1 min), WT1a group (no bleaching+5% procyanidins for 1 min+aging), WT2 group (no bleaching+5% procyanidins for 5 min), WT2a group (no bleaching+5% procyanidins for 5 min+aging), C group (carbamide peroxide+deionized water), Ca group (carbamide peroxide+deionized water+aging), CT1 group (carbamide peroxide+5% procyanidins for 1 min), CT1a group (carbamide peroxide+5% procyanidins for 1 min+aging), CT2 group (carbamide peroxide+5% procyanidins for 5 min), and CT2a group (carbamide peroxide+5% procyanidins for 5 min+aging). The bond strength to composite resin was measured by universal mechanical testing machine, microstructure and the nanoleakages were measured by scanning electron microscope immediately or after the thermal cycling aging test.

The immediate bond strength of the bleached groups pretreated with procyanidins for 1 min (P＜0.001) and 5 min (P＜0.001) was higher than that of Group C, and the difference was statistically significant. Meanwhile, there was no statistically significant difference between Group CT1 and Group CT2 (P = 1.000). After the thermal cycles, the bond strength of each group declined. The differences between Group W and Group Wa (P＜0.001) and Group C and Group Ca (P＜0.001) were statistically significant, but no significant differences between Group CT1 and Group CT1a (P = 0.052) or Group CT2 and Group CT2a (P = 0.053) were found. The main effects of“aging”(P＜0.001), “bleaching”(P＜0.001) and“procyanidins”(P＜0.001) and the second-order interaction effects of“bleaching * procyanidins”(P = 0.008), “bleaching * aging”(P = 0.024), and“aging * procyanidins”(P＜0.001) were statistically significant. SEM observations showed that the hybrid layers in Groups C, CT1 and CT2 were not clear, and the hybrid layers in Groups Ca, CT1a and CT2a were partially destroyed and disintegrated. Under backscattering mode, it was observed that there were a large number of silver nitrate particles in the hybrid layer of Group Ca, and the residual silver ions in the hybrid layer of Groups CT1a and CT2a were decreased.

Pretreatment with 5% procyanidins for 1 min can improve the immediate bond strength of dentin bleached by carbamide peroxide to composite resin and maintain bonding durability.