Effects of self-curing activator and curing protocol on the bond strength of composite core buildups.

Abstract

To determine the effect of the polymerization mode of simplified bonding systems and the corresponding core buildup resin composite on the bond strength to dentin. Composite core buildups were bonded to flat prepared dentin surfaces of 320 human molars using a two-step etch-and-rinse (Excite, ER) and a two-step self-etching (AdheSE, SE) bonding system. Bonding systems were used both with and without their respective self-curing activators (Excite DSC, ER+SC; AdheSE DC, SE+SC). Six curing protocols for the dual-curing composite (MultiCore Flow) were examined: self-curing for 5 min (a); irradiation with light from each aspect for 10 s (b), 20 s (c), and 40 s (d); and irradiation with light from the occlusal aspect only for 60 s (e) and 120 s (f). Shear bond strengths were measured immediately after curing. Additional measurements were performed after water storage of the specimens for 24 h at 37°C. These specimens had been cured according the curing protocols given in the manufacturer's instructions (groups a and d). Failure modes were analyzed using scanning electron microscopy. Immediate bond strengths were significantly different among the bonding systems (p < 0.001): SE > ER > ER+SC > SE+SC. Immediate bond strengths of ER and SE were significantly lower when the composite was self-cured (p < 0.05). The use of SC activators reduced the bond strength and promoted adhesive failures to dentin. A severe incompatibility problem was observed between the composite and SE+SC. Dentin bonding of dual-curing composite core buildups in combination with simplified bonding systems is still unsatisfactory, even when SC activators are employed. For adequate bonding to dentin, polymerization of the dual-curing composite should always be light initiated.