Effect of Different Porcelains and Energies on Curing Resin Cement

Objectives: This study evaluated the effect of three different energy levels on Degree of Conversion-(DC) and Knoop-microhardness-(KHN) of one resin cement through two types of 1-mm thick ceramic discs.

Methods: Shade A1 of resin cement (Variolink-II,Ivoclar-Vivadent,Amherst,NY) was used in a 0.5-mm thick ring. A BluePhase-G2 light (Ivoclar-Vivadent) was used to cure this resin cement through 1-mm thickness of A-2 Empress Esthetic-(EST) and ZrPress-(ZR) ceramic discs (Ivoclar-Vivadent).  The BluePhase-G2 light was used for three light curing times (20s, 40s, 60s) to cure the resin specimens directly on a Golden Gate Attenuated Total Reflectance FT-IR plate heated to 30°C. The DC of the resin was calculated at 100 seconds after light curing. The specimens were then removed and the Knoop-microhardness was tested at 5 minutes after light curing and again after 24-hrs 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.

Results: Three way ANOVA showed that the curing times, type of ceramic and storage time had a significant effect on the DC and KHN values. Both the Knoop Hardness and DC increased significantly after 24-hrs of storage. There was a linear relationship between DC and KHN (R²=0.99) within the range of DC and KHN studied. Overall polymerization through ZR is lower than EST especially at 20 and 40 s. Greater conversion degree and hardness occurred when the curing time was increased from 20-s to 40-s and to 60-s.  

Ceramic type	Curing Time	DC-Mean(SD)	Immediate-KHN-Mean(SD)	24Hrs-KHN-Mean(SD)
(EST)	20-Sec.	0.594(0.008)	2.98(0.23)	8.10(0.43)
	40-Sec.	0.624(0.003)	4.16(0.20)	11.20(0.71)
	60-Sec.	0.639(0.007)	4.68(0.21)	12.66(0.80)
(ZR)	20-Sec.	0.579(0.010)	2.51(0.16)	7.03(0.41)
	40-Sec.	0.616(0.007)	3.82(0.21)	9.02(0.72)
	60-Sec.	0.639(0.010)	4.75(0.21)	11.63(0.72)

Conclusions:

• There was a large and significant increase in DC and KHN within the first 24hours of light curing.
• There can be an excellent relationship between DC and KHN.
• Overall polymerization through ZR is lower than EST especially at 20 and 40 s.
• Light curing for only 20-s with the BluePhase-G2 is not recommended.