Bond strength of an adhesive polymerized under nitrogen

Purpose: To evaluate the use of nitrogen, in conjunction with visible light polymerization, for improving composite-to-dentin bond strengths. Materials and Methods: Composite cylinders were bonded to dentin with Scotchbond Multi-Purpose. Immediate (Groups 1- 4) and 24-hour (Groups 5-8) strengths were determined for the following two adhesive application and two polymerization techniques: Groups 1 & 5: gentle air thinning of adhesive and polymerization with conventional visible light curing (VLC) unit; Groups 2 and 6: aggressive air thinning of adhesive and conventional VLC; Groups 3 and 7: gentle air thinning of adhesive and polymerization in nitrogen environment with modified VLC unit; and Groups 4 and 8: aggressive air thinning of adhesive and polymerization in nitrogen environment with modified VLC unit. Results: The immediate bond strengths (MPa) were: Group 1: 15.1 ± 1.8, Group 2: 6.1 ± 2.1, Group 3: 17.8 ± 3.1, Group 4: 15.8 ± 2.0. The 24-hour strengths were: Group 5: 26.7 ± 4.4, Group 6: 13.5 ± 7.5, Group 7: 24.1 ± 5.7, Group 8: 26.4 ± 4.3. Visible light polymerization of a thinned layer of adhesive resin in a nitrogen environment produced significantly higher immediate and 24-hour bond strengths than when compared to visible light polymerization in ambient air.