How Does "Touch and Cure" Resin Cement Effect on Nanoindentation Hardness?

Objectives: To investigate nanoindentation hardness of three dual cure resin cement in the different period of time.
Methods: Three flat dentin surface polished with #600-SiC were obtained from caries-free human premolars. Each tooth was randomly assigned to three groups: 1. G-CEM(CSL), 2. Panavia V5(PVL); both are “Touch and cure” resin cement, 3. RelyX Ultimate(RXL). For all groups, primer or an adhesive was applied according to the manufacturer’s instruction without light-cured(Table1). Then 4-mm resin cement was built up and light-cured from 5 directions for 20 seconds each. After 24-hrs of distilled water storage at 37^oC, for making approximately 1.0-mm testing specimens, teeth were sectioned at the middle of mesio-distal direction along the long axis of the teeth and perpendicular to the resin-dentin interface. The interfaces of the specimens were sequentially polished with SiC and diamond paste down to 1-µm particle size. Hardness test was performed at two time periods; 3 and 72 hours after polishing. The hardness values of resin cement were measured with an ultramicrohardness tester at each 20-µm interval distance from the resin-dentin interfaces until 200-µm depth. Four indentations were tested within each depth level. In total, 40 indentations(n=40) were performed on the specimen per each time testing period. Game-Howell test (α=0.05) was used to statistically analyzed the hardness value as the variable among different cement(CSL, PVL, and RXL) and time period(3 and 72 hrs).
Results: CSL at 72 hrs showed the highest hardness value among all groups. When time periods were compared, only the hardness value of CSL showed statistical differences(Table2). For touch and cure resin cement, CS shows higher hardness value than PVL in both 3 and 72 hrs.
Conclusions: The hardness value of dual cure resin cement was affected by the period of time.