Bond Strengths of Self-etching Adhesives To Pre-etched Enamel

Self-etching (SE) adhesive systems are less effective at etching enamel than etch-and-rinse (ER) systems and generally produce lower bond strengths. Objective: To investigate whether pre-etching enamel with phosphoric acid will raise bond strengths for four SE adhesives to levels comparable with an ER adhesive. Methods: Four SE adhesive systems were investigated: Adper Prompt-L-Pop, Clearfil SE, Clearfil S3 and Xeno IV. These were compared to the ER adhesive system, Single Bond (SB). In all testing, human enamel surfaces were ground and polished (4000 grit) to expose flat enamel areas and Z100 resin composite was used when forming bonds. Each of the five adhesive systems was applied to the enamel using recommended procedures to form five groups of 10 specimens. The four SE systems were also applied to enamel surfaces that had been etched with 35% phosphoric acid (15 sec), rinsed and dried (n=10 per group). The resin composite was applied and light cured and specimens were stored in water (37°C) for 24 hours. An Ultradent bonding assembly was used to determine shear bond strengths. Additional enamel specimens were prepared for SEM examination. Etch morphology specimens were made by applying the SE agents as recommended and then rinsing with acetone and water, and by dissolving the enamel from bonded specimens, the resin morphology could be examined by SEM. Results: All four SE adhesives produced significantly lower bond strengths (p<0.05) than SB when recommended procedures were used and the resin penetration was notably less than for SB. With enamel pre-etching, all four SE adhesives demonstrated significantly increased bond strengths (p<0.05) that were statistically similar to SB (p<0.05), and the resin morphology was similar to that of SB. Conclusions: The results suggest that weaker etching is responsible for the lower bond strengths of SE adhesive systems to enamel.