The role of etching in bonding to enamel: a comparison of self-etching and etch-and-rinse adhesive systems

Abstract

Objective: Etch and resin infiltration morphologies were compared for three self-etch adhesive (SEA) systems and eleven model etch-and-rinse (ERA) systems using various phosphoric acid (PA) concentrations with Adper Single Bond Plus (SB) adhesive. Matches for the morphologies were made between each SEA system and one of the PA/SB systems and bond strength measurements were made for all the systems. The hypothesis was that similar morphology would result in similar bond strength assuming micro-mechanical bonding is the mechanism of adhesion.

Methods: Three specimens were prepared on polished (4000 grit) human enamel for each adhesive system to examine etch and resin infiltration morphology by SEM. For the latter, the adhesive systems were bonded using recommended methods and the enamel was dissolved in acid to reveal the resin. The etch patterns for the SEA systems were determined by rinsing off the material with water and acetone. Polished (4000 grit) human enamel was used with each adhesive system to determine 24-h resin composite to enamel shear bond strengths (SBS). A minimum of 10 specimens were used for each group. Data were analyzed by a one factor ANOVA and Fisher's PLSD post hoc test.

Results: The SBS to polished enamel for two of the three SEA systems were statistically significantly greater (p<0.05) than the PA/SB matched systems, indicating that chemical bonding might be partly responsible for the measured bond strength. All three SEA systems provided statistically lower (p<0.05) SBS values than the PA/SB systems with PA concentrations between 2.5% and 40%.

Significance: Although chemical bonding may be present for some SEA systems it does not provide enough increase in bond strength to compete with the bond produced by ERA systems using phosphoric acid etching of enamel.