Proper bonding to dentin depends on efficient infiltration of resin into the demineralized microporous collagen and formation of hybrid layer. Grape Seed Extract (GSE) has up to 97% PA and can potentially stimulate collagen cross linking and increase the stiffness of dentin. This study was designed to evaluate the efficacy of GSE on composite-dentin bond strength in different times and concentrations. In this experimental study, 60 freshly sound extracted teeth selected. The dentin surface of each specimen was acid-etched with 37% Phosphoric acid gel for 15 seconds and then they were rinsed for 10 s with distilled water. All teeth were divided to five groups (each group consists of 12 teeth). In control group GSE was not applied and in other groups different concentrations of GSE were applied for different times. The micro-shear bond strength of composite-dentin interface was evaluated using universal testing machine at a crosshead speed of 1 mm/min. Data were statistically analyzed using ANOVA test by SPSS software ver.15 ( α=0.05). The highest bond strength of one-day group was 17.28 MPa and the lowest bond strength in one-hour and one-minute group was 3.70 MPa. The difference between control group and one-day group, one-hour group and oneminute group was significant (p values 0.002, 0.024 and 0.012 respectively). Mann-Whitney revealed also that there was no significant difference between the experimental groups. We concluded that the produced GSE material could not improve the bond strength between adhesive and dentin
