Resin-dentin shear bond strength and interfacial ultrastructure with and without a hybrid layer

The purpose of this study was (1) to evaluate the effect of a 2-minute exposure of 5% NaOCl following acid conditioning of the dentin on the shear bond strength for two adhesive systems and (2) to examine the ultrastructure of the resin-dentin interface under SEM. The mesial and distal surfaces of 28 extracted human third molars were ground to expose dentin,then polished with 600-grit SIG. Teeth were randomly assigned to four test groups (n=14) and received the following treatments: Scotchbond Multi-Purpose (SBMP) - Samples were conditioned with 37% phosphoric acid, rinsed and left moist,SBMP primer and adhesive were applied according to the manufacturer's directions, and Restorative Z-100 composite resin was bonded to the dentin surface. SBMP/NaOCl - The same procedures were followed as for SBMP except the surfaces were treated with 5% NaOCl for 2 minutes, after acid conditioning. All-Bond 2 (AB2) - The same technique was followed as for SBMP, using AB2 according to the manufacturer's recommendations. AB2/NaOCl - The same procedure was followed as for SBMP/NaOCl,using AB2. Specimens were thermocycled in a water bath 300 times between 5 degrees-55 degrees C, then sheared in a Zwick Universal Testing Machine. A one-way ANOVA and Duncan's Multiple Range Test were used for statistical analysis of the data. A 2-minute exposure of dentin to 5% NaOCl following acid conditioning of the dentin had no significant effect on the dentin shear bond strength for Scotchbond Multi-Purpose, but significantly increased the bond strength of All-Bond 2 specimens. The interfacial structure of the dentin to resin bond for two dentin treatments and two adhesive systems was studied morphologically under the scanning electron microscope. Argon ion beam etching and acid demineralization clearly revealed the hybrid layer for the conventional treatment with phosphoric acid and indicated an absence of this resin-impregnated collagen network in those specimens treated with both phosphoric acid and NaOCl.