Influence of oxygen‐inhibited layer on dentin bond strength of chemical‐cured resin composite

This study evaluated the influence of an oxygen‐inhibited layer on the surface free energies of three single‐step self‐etch adhesives and on the bond strength of chemical‐cured resin. Adhesives were applied to bovine dentin and light irradiated, and the oxygen‐inhibited layer was either retained or removed. Surface free energies were determined by measuring the contact angles of test liquids placed on the cured adhesives. Dentin bond strengths of chemical‐cured resin with and without the oxygen‐inhibited layer were measured. Ultrastructural observation of the restorative–dentin interface was made by scanning electron microscopy. For all surfaces, values of the estimated surface tension component, Lifshitz‐Van der Waals force (γ_S^LW), were relatively constant. Values for the Lewis acid (γ_S⁺) component increased slightly when the oxygen‐inhibited layer was removed, whereas those of the Lewis base (γ_S^?) component decreased significantly. The bond strength of the chemical‐cured resin composite was significantly higher in specimens without an oxygen‐inhibited layer (7.6–8.0 MPa) than in those with an oxygen‐inhibited layer (4.8–5.2 MPa). Small gaps between adhesive and resin composite were found for the group with an oxygen‐inhibited layer. These results indicate that the absence of an oxygen‐inhibited layer in single‐step self‐etch adhesives promotes higher dentin bond strength of the chemical‐cured resin.