Microhardness, atomic force microscopy and profilometry of dental enamel conditioned with acetic and phosphoric acids

To compare the microhardness, microroughness, and topography of the enamel surface via Vickers microhardness, atomic force microscopy (AFM), and profilometry values before and after the use of 32% and 37% acetic acid and 32% phosphoric acid.

Four groups were established: Group 1: control group; Group 2: phosphoric acid gel (Scotchbond Universal Etchant) at 32%; Group 3: 32% acetic acid gel; and Group 4: 37% acetic acid gel. The microhardness was determined with a Vickers indenter (VHN). The topography and microroughness of the enamel were analyzed using 3D images obtained via AFM in tapping mode. Microroughness was determined using a contact profilometer. An ANOVA and paired t-test was used to compare the average VHN and microroughness both before and after the etching of the enamel surface.

Statistically significant differences were found for average microhardness after the conditioning of the enamel surface of the four groups (P< 0.001). The roughness obtained via AFM revealed differences among the four groups after the use of the three different acid gels. The profilometry assay showed significant post-conditioning differences among all groups. Conditioning with 32% acetic acid partially modified the characteristics of the enamel surface to a greater extent than conditioning with 37% phosphoric acid; furthermore, the use of acetic acid generated microretentions that could be effective for adhesion.

Acetic acid, an organic biodegradable acid less corrosive than phosphoric acid, can be used to modify the characteristics of the enamel surface, such as microhardness, topography, and microroughness.