The effect of phosphoric acid concentration on resin tag length and bond strength of a photo-cured resin to acid-etched enamel

Abstract

Objectives: To determine the relationship between depth of penetration and tensile bond strength of a photo-cured resin to phosphoric acid etched enamel, and the efficacy of enamel etchants that are less aggressive than a concentration of 10% H 3PO 4. Methods: The tensile bond strength and length of tags produced by a photo-cured (20 s) resin consisting of pre-polymerized TMPT/silica in 3% HNPM–TEGDMA on acid-etched enamel was determined. The enamel etchants tested were various concentrations (3–65%) of phosphoric acid. The resin was applied to enamel samples that had been abraded with No. 600-grit SiC paper and acid etched (30 s) to create test specimens that were loaded to fracture on a testing device. The HCl-treated, then cut specimens, were examined under scanning electron micrcoscopy and light microscopy. Results: The tensile bond strength (10 MPa) of resin to enamel, pre-treated with various acid concentrations did not vary significantly. But resin tag length was found to decrease significantly from 22 μm for 35% H 3PO 4 to 12 μm for 20% H 3PO 4 to 9 μm for 5, 10 and 65% H 3PO 4 to 5 μm for 3% H 3PO 4. Significance: These findings suggest that the length of the tags created by the tested photo-cured resin on phosphoric acid-etched enamel contributes little to the bond strength of the test specimens, and that the adhesive strength of the resin to H 3PO 4 etched enamel is mainly attributable to the resin's ability to penetrate between the enamel crystallites and rods. Further, enamel pre-treatment by phosphoric acid etchants of concentrations lower than 10% may be satisfactorily employed. The use of less aggressive acid concentrations might minimize any potential adverse effects to enamel substrates.