Effect of oxygen inhibition on composite repair strength over time

The study was aimed at examining whether an oxygen inhibition layer is required for bonding a repairing to a pre‐existing composite, and to determine the time required for free radicals within a composite substrate to decay to the extent that the composite repair strength drops significantly. Ten slabs of Gradia Direct Anterior (GC Corp.) were divided into (1) control group: an interfacial oxygen inhibition layer was created by applying and light‐curing two layers of bonding resin (D/E Resin, Bisco) to the slabs surface in atmospheric air; (2) experimental group: the absence of an interfacial oxygen inhibition layer was obtained by light‐curing the second bonding resin layer in a nitrogen atmosphere. After 1 and 2 h, 1, 14, and 30 days of air storage, a composite repair was layered over the bonding resin. Microtensile bond strengths were measured and statistically analyzed. The curing atmosphere was not a significant factor for bond strength ( p = 0.82), and time and curing atmosphere‐time interaction were significant ( p < 0.001). The 30 day‐strengths were the lowest ( p < 0.05). An oxygen‐inhibited layer is not initially required for bonding to resin composite, and it takes more than 14 days before the bond strength between a pre‐existing and a fresh composite drops. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006