TENSILE BOND STRENGTH AND SEM EVALUATION OF CARIES-AFFECTED DENTIN USING DENTIN ADHESIVES

Tensile bond strength measurements are commonly used for the evaluatio n of dentin adhesive systems. Most tests are performed using extracted non-carious human or bovine dentin. However, the adhesion of resins t o caries-affected dentin is still unclear. The objectives of this stud y were to test the hypothesis that bonding to caries-affected dentin i s inferior to bonding to normal dentin, and that the quality of the hy brid layer plays a major role in creating good adhesion. We used a mic ro-tensile bond strength test to compare test bond strengths made to e ither caries-affected dentin or normal dentin, using three commercial adhesive systems (All Bond 2, Scotchbond Multi-Purpose, and Clearfil L iner Bond II). For scanning electron microscopy, the polished interfac es between the adhesive bond and dentin were subjected to brief exposu re to 10% phosphoric acid solution and 5% sodium hypochlorite, so that the quality of the hybrid layers could be observed. Bonding to normal dentin with either All Bond 2 (26.9 +/- 8.8 MPa) or Clearfil Liner Bo nd II (29.5 +/- 10.9 MPa) showed tensile bond strengths higher than th ose to caries-affected dentin (13.0 +/- 3.6 MPa and 14.0 +/- 4.3 MPa, respectively). The tensile bond strengths obtained with Scotchbond Mul ti-Purpose were similar in normal and caries-affected dentin (20.3 +/- 5.5 MPa and 18.5 +/- 4.0 MPa, respectively). The hybrid layers create d by All Bond 2 in normal dentin and by Clearfil Liner Bond II in norm al or caries-affected dentin showed phosphoric acid and sodium hypochl orite resistance, whereas the hybrid layers created by All Bond 2 in c aries-affected dentin and those created by Scotchbond Multi-Purpose to normal and caries-affected dentin showed partial susceptibility to th e acid and sodium hypochlorite treatment. The results indicate that th e strength of adhesion to dentin depends upon both the adhesive system used and the type of dentin. Moreover, the quality of the hybrid laye r may not always contribute significantly to tensile bond strength.