Effect of phosphoric acid etching prior to self-etching primer application on adhesion of resin composite to enamel and dentin

Purpose: To investigate the effect of phosphoric acid etching prior to the application of self-etching primer on the adhesion of resin composite to tooth substrates. Materials and Methods: Bovine teeth were randomly divided in four groups of 20 samples each. Tooth surface conditions were as follows: Group 1: enamel ground with 600-grit SiC paper; Group 2: ground enamel was etched with 35% phosphoric acid gel for 15 seconds, water-rinsed and completely dried; Group 3: ground dentin; Group 4: dentin etched using the same method as Group 2. The samples in each group were divided in two subgroups of 10 each. UniFil Bond (UB) and Clearfil SE Bond (SE) were applied as adhesive systems with self-etching primers, and a layer of resin composite (AP-X) was placed and light-cured for 40 seconds. The tensile bond strengths (TBS) were measured and the resin-tooth interfaces were observed with scanning electron microscopy. Results: The mean TBS values were 11.2 MPa (Group 1-UB), 14.3 MPa (Group 1-SE), 16.3 MPa (Group 2-UB), 20.5 MPa (Group 2-SE), 13.4 MPa (Group 3-UB), 16.7 MPa (Group 3-SE), 9.3 MPa (Group 4-UB) and 12.6 MPa (Group 4-SE). Two-way ANOVA and Scheffe's F test showed that the enamel etching significantly increased the TBS values but dentin etching significantly decreased the TBS values.