Could a higher crosslink concentration affect the bond strength of fiberglass post using different modes of universal adhesive?

Grape seed extract (GSE) is a proanthocyanidin-rich plant-derived agents and have been shown to increase dentin biomechanical properties and resistance of dentin collagen to degradation. High GSE concentrations had never been studied for bond strength (μTBS) maily in root canal dentin. This study investigated the effect of high concentrations of GSE in a shorter clinical time on the bond strength of fiberglass posts through the application of Universal adhesive in two modes (etch-and-rinse and self-etching). Seventy-two single-rooted bovine teeth were prepared and divided randomly into six groups (n = 12) according to surface treatment and application mode of Universal adhesive. Two groups were etched with 37% phosphoric acid to expose collagen fibrils and a biomodification agent was applied next at two different higher concentrations (30% and 50% GSE), for 1 min. For the other two groups, GSE was previously applied and after Single Bond adhesive was used in self-etching system mode. The other sample were divided in two groups without GSE application, in the total-etch and self-conditioning of universal adhesive. Then, the fiber posts were enveloped with composite resin and cemented with RelyX Ultimate. The samples were sectioned in discs with thickness of 1 mm and submitted to the push-out test at 0.5 mm/min. Two teeth from each group were prepared for confocal electron microscopy to understand the adhesive behavior on dentin biomodified by GSE. The data presented homogeneity and were statistically analyzed using two-way ANOVA and Bonferroni`s complementary analysis (α = 0.01). The 50% GSE used with the self-etching system maintained the μTBS values when compared to its control group (p > 0.0172). The values of etch-and-rinse groups reduced after using 30% and 50% GSE (p < 0.0001), but were similar among each other (p = 1.00). Based on the confocal images and μTBS values we can suggest that higher GSE concentration promotes buffering of collagen fibrils when the dentin was previously demineralized with phosphoric acid. However, when GSE was used as self-etching mode, it could lead the GSE particles along with adhesive, keeping μTBS values similar to the control group.