Early bond strengths of dual-cured core composite resin by self-curing

Objectives: For root canal restoration, dual-cured type composite resin and bonding agent are generally used, because it is difficult to reach the light irradiation on deep area. Meanwhile, clinically, contouring for core preparation may occur a few minutes after the core-buildup. In those clinical cases, it is important that having proper bond strength of no-light irradiation area in early timing. The purpose of this study was to evaluate early shear bond strength of dual-cured core composite resins using bonding agent to dentin by self-curing mode.

Methods: Three dual-cured core composite resins [UniFilCore (UC, GC), Trial core composite resin UCA-106 (GC) and Clearfil DC Core Automix (DC, Kuraray Medical inc.)] were examined. Bovine teeth were polished with wet silicon carbide paper (#600), in order to expose the dentin surface. Bonding system for each product was applied to exposed dentin surfaces according to the manufacturers' instructions without light-curing and each core composite resin was placed on the bonding surface. These bonded specimens immersed in water at 37-degrees Centigrade for 5min, 10min and 24 hours and then were subjected to shear bond strength (SBS) testing with a crosshead speed of 1 mm/min. Statistical analysis was performed using t-test (p-value<0.01).

Results: Mean values of the shear bond strength (SBS) including standard deviations after each time immersed in water at 37-degrees Centigrade were shown as follows; (tests per material; n=5).

	SBS to dentin (MPa)
	Self-curing			Light-curing
	5min	10min	24hrs	24hrs
UC	5.18(1.27)	7.70(1.59)	10.99(4.41)	21.88(2.33)
UCA-106	3.28(0.39)	6.43(2.19)	11.35(4.22)	21.71(2.23)
DC	N.D.	1.32(0.20)	1.75(0.37)	21.45(2.66)

The shear bond strength by self-curing after 10min and 24hrs for UCA-106 and UC was significantly higher than those for DC (p<0.01).

Conclusion: The Self-curing SBS were lower than Light-curing SBS for three materials. UCA-106 and UC had significantly higher SBS compared to DC.