Effects of immersion time and frequency of water exchange on durability of etch-and-rinse adhesive

This study evaluated the immediate and long-term bond strength to dentin (microtensile bond strength, μTBS) and silver nitrate uptake (SNU) of a three- and two-step etch-and-rinse adhesive under different water immersion times and frequency of water exchange. The adhesives and composite resin were applied according to the manufacturer's instructions in a flat occlusal demineralized dentin of 48 molars. Teeth were assigned to four groups of immersion time (immediate and 1, 3, and 6 months), sectioned to obtain resin-dentin beams, and then subdivided into three groups of water exchange (daily, weekly, and monthly) before being tested in tension. Two resin-dentin beams from each tooth were immersed in silver nitrate and analyzed by SEM. Significant difference in μTBS and SNU was detected for both adhesives (p ≤ 0.0001 for the cross-product interaction). For Adper Single Bond 2, the most pronounced reductions of μTBS were observed for the daily exchange groups in all times. For Adper Scotchbond Multi Purpose, 1-month immersion period was not capable to induce degradation of the dentin bonds, except when the water was exchanged daily. For both adhesives, all storage regimens showed increased SNU results only after 6-month water storage; this being more pronounced for daily water exchange groups. For both adhesives, the highest SNU was observed in the daily water exchange group. The daily water exchange is a fast and reliable in vitro aging method for testing the durability of the adhesive interface produced by adhesive systems.