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

Purpose: 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.

Methods: 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.

Results: 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.

Clinical significance: 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.