Objetives: The aim of this study was to evaluate the effect of different ceramic spacer shades on the Knoop hardness (KH) of dual-cure resin cements (RelyX ARC RLX, 3M ESPE; Variolink II VLK, Ivoclar Vivadent) cured for 20 seconds with an LED light-curing unit.
Materials: Eight groups (n equals 15) were tested as follows: RelyX Control (light-cured without ceramic spacer); RelyX-2M2 ceramic spacer; RelyX-5M3 ceramic spacer; RelyX self-cured. Similar conditions were used with Variolink II cement. A microhardness tester was used to measure the KH values. Specimens were subjected to five 50 g/15 s indentations following curing at 0, 1, 2, 3, 4, 6, 24, 168, and 336 hours in order to determine the point at which the cements reach the maximum KH values.
Results: Control groups exhibited significantly higher KH values than the other groups (P less than 0.001) at 0 h following light curing. The KH values for RelyX-2M2 were not significantly different than the control group (P greater than 0.05) after 336 hours. All groups tested with 5M3 spacers had KH values that were not significantly different from the groups with self-cure mode, P greater than 0.05. The KH values for RelyX self-cure cement were significantly higher than Variolink II self-cure, P equals 0.003. RelyX-2M2 had KH values that were not significantly different from that of Variolink-2M2, P greater than 0.05.
Conclusions: Ceramic spacer shades have tremendous effect on the KH values of RelyX and Variolink II. Darker ceramic shades (5M3 spacers) interfere with the absorption of light by the cements tested. In addition, the chemical portion in the self-cured mode is not sufficient to achieve optimum microhardness.