[Bond strength of multilayer-cured composites]

SEM studies of six visible light-cured composites showed no difference between the morphology of the layered area and of the compact zones, unless the inhibited layers are removed from the polymerized portions. Only in plugable materials did the removal of these layers result in an increased formation of air bubbles and in an interface of 10-20 microns thickness interspersed with cavities. The transverse strength of these specimens was in part approx. 35% less than in the control material. In all materials studied removal of the inhibited layers at their points of attachment resulted in an average decrease of transverse strength by 26%. When the inhibited layers were left in place this reduction was rarely more than 17%, on an average less than 13%. This slight reduction in the transverse strength of attached specimens with the inhibited layer retained may be attributed to the ability of this layer to polymerize when reirradiated after the exclusion of oxygen.