The strength of layering technique in visible light-cured composites

Despite the extensive use of the layering technique in light-cured restorations there is limited information for the interfacial strength when curing is accomplished in air and an inhibited zone is formed on the first layer. This study analyzed the nature of the inhibited zone to determine the interfacial topography, evaluated the shear interlayer bond strength in the presence of the inhibited layer, and assessed the effect of various interfacial treatments on bonding. Two microfilled, one hybrid, and three small-particle composite resins were included in the study. According to the results, the inhibited zone is primarily composed of catalyst-free monomer. The presence of this zone reduces bond strength, creating interfacial discontinuities. Removal of the inhibited layer by an organic solvent of low boiling point results in the highest strength and better interfacial topography from the tested treatments.