Microtensile Bond Strength and Interfacial Characterization of 11 Contemporary Adhesives Bonded to Bur-cut Dentin

OBJECTIVES: This study evaluated mechanically and ultra-morphologically 11 different adhesive systems bonded to dentin. METHODS: The microtensile bond strength (microTBS) of 11 contemporary adhesives, including two three-step etch&rinse, three two-step etch&rinse, two two-step self-etch and four one-step self-etch adhesives to dentin, were measured. The resultant interfacial ultra-structure at dentin was characterized by transmission electron microscopy (TEM). Human third molars had their superficial dentin surface exposed, after which a standardized smear layer was produced using a medium-grit diamond bur. The selected adhesives were applied according to their respective manufacturer's instructions for microTBS measurement after storage in water at 37 degrees C for 24 hours or for TEM interfacial characterization. RESULTS: The microTBS varied from 11.1 to 63.6 MPa; the highest bond strengths were obtained with the three-step etch&rinse adhesives and the lowest with one-step self-etch adhesives. TEM evaluation showed very different interaction patterns, especially for the self-etch adhesives. "Mild" self-etch adhesives demineralized the dentin surface sufficiently to provide micro-mechanical retention, while preserving hydroxyapatite within the hybrid layer to enable additional chemical interaction. CONCLUSIONS: When bonded to dentin, the adhesives with simplified application procedures (in particular, one-step self-etch adhesives) still underperform as compared to conventional three-step adhesives. "Mild" two-step self-etch adhesives that provide additional chemical bonding appear to most optimally combine bonding effectiveness with a simplified application protocol.