Effects of mechanical properties of adhesive resins on bond strength to dentin

Objectives: The purpose of this study was to evaluate the relationship between the micro-tensile bond strength to dentin and mechanical properties of the cured adhesive resins. Methods: Coronal dentin surfaces of extracted human teeth were treated with four commercial self-etching priming systems (Clearfil SE Bond; UniFil Bond; Tokuso Mac-Bond II; and Imperva Fluoro Bond) and bonded with a resin composite. After 24 h storage in water at 37degreesC, the bonded specimens were trimmed and subjected to micro-tensile bond strength testing at a cross-head speed of 1 mm/min. Debonded surfaces were observed under a FE-SEM. For testing mechanical properties, 0.7-mm thick slabs of each adhesive resin were prepared, light-cured, and stored dry at the room temperature for 24 h. After trimming, ultimate micro-tensile strength was measured. The nano-hardness and Young's modulus were also evaluated using cured adhesives that were prepared in the same manner as described above. Results: The micro-tensile bond strengths to dentin and ultimate micro-tensile strengths of the resins were not significantly different among all systems (P > 0.05). However, the nano-hardness and Young's modulus of Clearfil SE Bond and Imperva Fluoro Bond adhesive resins were significantly higher than those of UniFil Bond and Tokuso Mae-Bond II resins (P < 0.05). The micro-tensile bond strength significantly correlated with the ultimate micro-tensile strength of the resins (r(2) = 0.77; P < 0.05), but was not correlated with the nano-hardness or Young's modulus (P > 0.05). SEM observation of the debonded surfaces revealed a mixed type of fracture with a combination of interfacial and cohesive failure within the adhesive resin. Significance: The four self-etching priming systems exhibited similar dentin bond strengths, which also correlates with the ultimate strength of the adhesive resins. (C) 2002 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.