Regional bond strengths of self-etching/self-priming adhesive systems

The purpose of this study was to measure the regional tensile bond strengths (TBS) at various portions of human tooth enamel and dentin, and to observe the resin-dentin interfaces of two commercially available self-etching/self-priming adhesive systems by scanning electron microscopy (SEM). Twelve extracted human cuspid teeth were used to measure TBS and four additional teeth were used for scanning electron microscopy (SEM). Outer enamel and dentin were removed from the labial tooth surfaces to form a long cavity preparation into middle dentin extending from the mid-crown to the apex of the root within the same tooth. Either Clearfil Liner Bond 2 (LB 2, Kuraray) or Fluoro Bond (FB, Shofu) was bonded to the surfaces, and covered with resin-composite. The resin-bonded teeth were serially sliced at right angles to the long axis of the tooth, and the bonded surfaces were trimmed to give a bonded cross-sectional surface area of 1 mm² for TBS tests. LB 2 and FB showed significantly higher TBS in coronal, cervical and middle root dentin than that in enamel and apical root dentin. SEM showed that the thickness of the hybrid layer of both systems was about 1.0 μm in coronal, cervical and middle root dentin, and less than 0.5 μm in apical root dentin. These results suggested that the self-etching/self-priming systems produce good adhesion in coronal, cervical and middle root dentin by creating thin hybrid and transitional layers, but bonding to enamel and apical root dentin should be improved.