Microhardness of Dual-Cured Resin Cements Through Ceramic

Objectives: To evaluate the Knoop hardness of dual-curing resin cements (RelyX Unicem, 3M ESPE, and Variolink II, Ivoclar Vivadent) light-cured directly or through ceramic discs.

Methods: The cements were inserted in perforated polytetrafluorethylene matrix between Mylar strips. Light-curing was performed using a conventional (QTH) light (XL 2500, 3M ESPE, 400mW/cm2), and two LEDs light-curing units (Ultrablue Is, DMC Equip. Ltd., 400mW/cm2; Elipar Free Light 2, 3M ESPE, 1200mW/cm2), all for 40 seconds. In the experimental groups, the light-curing of the dual-curing resin cements was performed through ceramic discs (ProCAD, Ivoclar Vivadent). In the control groups, the light-curing was performed without ceramic discs. After 24 hours, microhardness measurements (HMV 2, Shimadzu) were performed on the top and bottom surfaces of specimens with 1mm thickness (five indentations per surface with a 25g load for 30sec). Data were submitted to 4-way ANOVA and Tukey's test (p=0.05).

Results: Light-curing with Elipar Free Light 2 resulted in significantly higher mean hardness values (40.9±5.8 KHN) (p =.01) than XL 2500 (35.4±7.3 KHN) and LED Ultrablue Is (35.7±6.1 KHN) which were not significantly different. Light-curing through ceramic discs resulted in significantly lower mean hardness values (34.2±5.7 KHN) than that of the groups without ceramic (40.5±6.6 KHN, p=.01). RelyX Unicem resulted in significantly higher mean hardness values (38.2±7.7 KHN) (p =.03) than Variolink II (36.5±5.9 KHN). In general, hardness measurements found on the top surface of all groups (39.8±5.5 KHN) was higher (p = .01) than on the bottom 34.9±7.2 KHN.

Conclusion: The presence of the ceramic discs reduced by 15.5% the mean hardness values of the resin cements. The intensity of the light source was more important than the type of curing unit. In general, RelyX Unicem specimens showed higher mean hardness values than Variolink II specimens.