Effect of double layering and prolonged application time on MTBS of water/ethanol-based self-etch adhesives to dentin

One way of possibly improving bond strength is by changing the application mode of self-etch adhesives. The current study evaluated the resin-dentin microtensile bond strength (MTBS) promoted by two- and one-step self-etching adhesives after different bonding application procedures. Flat dentin surfaces from extracted human molars were bonded: 1) according to the manufacturers' instructions, 2) duplicating the number of adhesive coats and 3) doubling the application time of the acidic primers. Two-step (Clearfil SE Bond/SEB and Resulcin AquaPrime/RE) and one-step (Etch & Prime 3.0/EP and One-Up Bond F/OUB) self-etch adhesives were used. Resin-dentin beams were tested in tension at 0.5 mm/minute. Selected debonded beams were observed under scanning electron microscopy (SEM). MTBS data were analyzed by ANOVA and multiple comparison tests (p < 0.05). The highest MTBS was always attained with SEB, regardless of the bonding procedure. RE, EP and OUB showed similar MTBS when bonded as per the manufacturers' instructions. The MTBS of OUB increased after doubling the application time and duplicating the adhesive coats. The two-step self-etch adhesives were insensible to changes in bonding application procedures. Attempts to improve the bonding performance of water/ethanol-based self-etching systems by using different bonding application parameters were system-specific and only effectively detected in one-step adhesive systems.