Effect of Curing Light on the Polymerization of Resin Cement

Objective: Adequate polymerization of resin cement under ceramic restorations is an important factor to obtain adequate physical and biological properties. This study examined the effect of selecting single-peak vs. polywave emission LED curing light on the Degree of Conversion-(DC) and Knoop-microhardness-(KHN) of resin cement when they were light cured through a ceramic disc.

Method:  Two shades-(A1&A4) of resin cement (Variolink-II, Ivoclar-Vivadent) were used in a 0.5mm thick ring. The top surfaces were covered with a Mylar strip and further covered with a disc of 1mm thick shade A2 Empress Esthetic ceramic. The specimens were light cured using an Elipar-S10-(3m-ESPE, single-peak LED) delivering 13.6-J/cm², or the BluePhase-G2-(Ivoclar-Vivadent,polywave-LED) delivering 9.8-J/cm² of energy.

Both lights were used for 20s to cure the resin specimens directly on the surface of a Golden Gate Attenuated Total Reflectance FT-IR plate that was heated to 30°C. The DC of the resin was calculated after 100-seconds. The specimens were removed and the KHN was immediately tested, and again after 24-hours storage in the dark at 37°C and 100% humidity. Five specimens were made and tested in each group. The DC and KHN results were analyzed with ANOVA and Fischer’s PLSD at α = 0.05.

Result: The choice of curing light had no significant effect on the DC and only a small effect on the immediate and 24-hrs KHN values. Shade A4 harder and better DC than A1.

Shade	Light Type	DC-Mean-(SD)	Immediate-KHN-Mean(SD)	24-HRS –KHN-Mean(SD)
A1	Polywave	0.594( 0.008)(a)	2.98(0.23)	8.10(0.43)(d)
	Single	0.605( 0.008)(a)	2.71(0.30)	8.30(0.43)(d)
A4	Polywave	0.611(0.011)(b)	3.37(0.17)(c)	9.09(0.52)
	Single	0.619(0.006)(b)	3.45(0.20)(c)	8.77(0.44)
Letters in parentheses = Homogeneous subsets-(Fischer’s α=0.05)

 Conclusion:  The small differences in the DC and KHN values achieved using the Single-Peak and Polywave curing lights are probably not clinically significant and either light could be used. Shade A4 was slightly harder than A1.