Influence of different phosphoric acids in enamel adhesion

Abstract

The aim of this study was to evaluate in vitro the shear bond strength of a composite resin after acid etching with phosphoric acid 37% with and without chlorhexidine. Thirty bovine incisors were divided into two groups (n = 15), according to the type of acid etching applied in enamel – G1 (phosphoric acid 37%) and G2 (phosphoric acid 37% with chlorhexidine 2%). The conditioning of the surface followed the manufacturers’ recommendations; after this step, there was the application of adhesive and the insertion of composite resin in a rubber matrix with a center hole of 4 mm. The specimens were submitted to analysis of shear strength in a Shimadzu AGS-X Universal Testing Machine with crosshead speed of 1 mm/min and the values measured in MPa. After the test, the Adhesive Remnant Index (ARI) was assessed. Data were analyzed by descriptive and inferential statistics, adopting a significance level of 5%. The mean shear strength reported for the two groups were, respectively, 12.02 MPa and 11.86 MPa (unpaired t-test; p-value > 0.05). As for the ARI, the most frequent scores for G1 and G2 were 3 and 5, with no statistically significant difference between groups (Mann-Whitney test; p-value > 0.05). Under the experimental conditions of the study, we conclude that the addition of chlorhexidine to phosphoric acid 37% did not affect the bond strength to the enamel surface nor the type of failure found.