The purpose of this study was to estimate the influence of the film thickness of the resin bonding layer on the tensile bond strength and on the adaptation rate to the cavo-dentin surface. Three2-step self-etching resin bonding systems (Unifil Bond: UB, Imperva Fluoro Bond: FB and Clearfil Mega Bond: MB) and three1-step selfetching resin bonding systems (AQ Bond Plus: AQP, One-Up Bond F: OUB and Reactmer Bond: RMB) were used in this study. Thickness of the bonding resin was controlled by using a three-way air syringe in accordance with the manufacturer's instructions after the application of the bonding agent. The results were as follows:
1. All systems demonstrated good bonding performances when the manufacturer's instructions were strictly obeyed. TBSs (MPa) to enamel/dentin were10.1/9.3for UB, 11.4/8.9for FB, 13.4/13.6for MB, 13.3/13.4for AQP, 12.5/12.1for OUB and13.5/11.9for RMB.2. All resin bonding systems except for AQP formed thin film by a brief strong burst of air next to application. After execution of air burst following air blow with the strength as on manufacturer's instructions, the film thickness (μm) of the bonding resin decreased from63.9to3.3for UB, from66.6to2.1for FB, from73.1to5.8for MB, from2.5to1.3for AQP, from93.5to1.1for OUB, and from68.7to2.5for RMB.
3. The bond strength to enamel was not affected by strong air in any systems.
4. When the strong air was used, TBS of OUB to dentin and the adaptation rate to dentin cavity wall of UB and OUB decreased with statistical significance.
5. It was concluded that MB, AQP and RMB were less technique-sensitive in terms of the strength of the air, since they demonstrated high TBS and adaptation rate under the strong air.
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