Effect of prolonged application times on the durability of resin–dentin bonds

Objectives To examine the effect of prolonged application time on the early and 3-year resin–dentin microtensile bond strength. Methods Water/ethanol (Single Bond [SB]) and acetone-based systems (One Step [OS]) were employed. A flat superficial dentin surface was exposed in third human molars by wet abrasion. The adhesives were applied to a delimited area of 52 mm2 on wet surfaces, for 40, 90, 150 and 300 s. Four teeth were assigned for each experimental condition. Composite build-ups were constructed incrementally. After water storage at 37 °C for 24 h, teeth were sectioned to obtain sticks with cross-sectional areas of 0.8 mm2 to be tested in tension (0.5 mm/min) either immediately (IM) or after 3 years (3Y) of water storage. The microtensile bond strength (μTBS) values were analyzed by two way repeated measures ANOVA and Tukeyʹs test (α = 0.05). Results The 90- and 150-s groups achieved the highest IM μTBS for OS (p < 0.01). For SB, the highest IM μTBS values were observed after 300-s application (p < 0.01). Significant decreases in μTBS were observed for OS in the 40- and 90-s groups after 3Y, except for the 150-s group. With regard to SB, after 3Y significant drops in μTBS values were observed for the 40- and 150-s groups, except for the 300-s group. Significance Prolonged application times can increase the immediate μTBS of two-step etch-and-rinse adhesive systems and make the adhesive layer more stable over time.