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 37°C, 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 Youngʹs 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 Youngʹs modulus of Clearfil SE Bond and Imperva Fluoro Bond adhesive resins were significantly higher than those of UniFil Bond and Tokuso Mac-Bond II resins (P<0.05). The micro-tensile bond strength significantly correlated with the ultimate micro-tensile strength of the resins (r2=0.77; P<0.05), but was not correlated with the nano-hardness or Youngʹs 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.