Objectives: The aim of this study was to investigate the rubbing action on micro-tensile bond strength (MTBS) and interfacial morphology of a newly developed one-step adhesive system bonded to dentin. Methods: Flat mid-coronal dentin surfaces were exposed from extracted human third molars, and wet-sanded by 600-grit silicone carbide sandpaper for 60 sec. The surfaces which were wet enough as were seen by naked eyes were treated using a one-step adhesive (Absolute, Dentsply-Sankin) with or without 10 sec rubbing action. The adhesive-treated surfaces were coated with a low-viscosity resin (Protect Liner F, Kuraray) and subjected to TEM observation according to the method reported by Van Meerbeek et al (J Dent Res 77, 50-59, 1998). Additionally, the adhesive-treated surfaces were bonded with resin composite (Xeno CF paste, Dentsply-Sankin) and stored in 37 C water for 24 hrs. The bonded specimens were sectioned into 0.7 mm thick slabs, trimmed into an hourglass shape, and finally subjected to MTBS testing. Results: TEM observations of specimens treated with rubbing showed a hybrid-layer (HL) of 2-3 um thickness in the resin/dentin interface, scattered hydroxyapatite crystals (HAp) around collagen fibrils at the area near the bottom of HL, and a shag-carpet appearance with filler particles at the top of HL. Specimens treated without rubbing action showed a 1.5-2 um thick HL and scattered HAp around collagen fibrils near the bottom of HL, but the shag-carpet appearance was not observed. For MTBS, rubbed specimens revealed MTBS of 29.9 MPa (n=18), which was significantly higher than the value (18.1 MPa (n=16)) of un-rubbed specimens (t-test, p<0.01). Conclusion: It is concluded that, within this adhesive used, the rubbing action improves the bonding effectiveness from the viewpoint of bond strength and interfacial morphology. (Supported by Grant-in-Aid for Scientific Research #15592013 from the Ministry of Education, Japan)

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