Hardness development of dual-cured resin cements through different thicknesses of ceramics.

This study investigated the Knoop hardness of a thin layer in three dual-cured resin cements (Linkmax HV, Nexus 2, and Variolink II HV) irradiated through or not through different thicknesses (1 through 5 mm) of a machinable ceramic. Hardness was recorded at a series of time intervals up to five days, starting from the end of a light irradiation period. Increase in hardness was more rapid over the first 0.5 hour; thereafter it continued at a low rate until maximum hardness was attained. Ceramic thickness had a significant influence on hardness in all dual-cured resin cements, especially when ceramic thickness was more than 4 mm. In addition, it was noted that the polymerization of Nexus 2 seemed to be more dependent on light exposure compared with the other two materials. Variolink II HV and Linkmax HV, on the other hand, seemed to indicate the potential of being compensated by chemical curing to some degree.