Infuence of oxygen inhibition on the surface free energy and enamel bond strength of self-etch adhesives

Abstract

We compared the surface free energies and enamel bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The adhesives were applied to the enamel surfaces of bovine incisors, light irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free energies and their components (γ SLW, γ S+, and γ S-) were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component γ SLW was relatively constant. The value of the γ S+ component increased slightly when the oxygen-inhibited layer was removed, whereas that of the γ S- component decreased signifcantly. The enamel bond strengths of the self-etch adhesives were signifcantly lower in the specimens without an oxygen-inhibited layer. The oxygen-inhibited layer therefore appeared to promote higher enamel bond strength.