Effect of overlay on resin cement shade on hardness

Objectives: To study Knoop hardness (KHN) of different shades of a resin cement light-cured either directly or through ceramic discs, and evaluated either immediately or 24 hours after light exposure.
Methods: Specimens (5.0 mm diameter, 1.0 mm thick) of a resin cement (Variolink Veneer) were made using 7 different shades: LV -1, -2, -3, MV 0, HV +1, HV +2, and HV +3. Specimens were fabricated in a elastomeric mold, covered with a mylar strip, and a 0.7mm thick ceramic disc (IPS e.max Press) was placed over top, and the cement was light-activated for 20 seconds using a LED curing light (Radii-cal). As control, no overlay was placed. (N=10) Specimens were wet-sectioned and the microhardness (KHN) was measured (50g load applied for 15 seconds) immediately or after 24h storage at 37^o C. Five indentations were made at 100 µm depths from the top surface and averaged to represent hardness at a given depth. Data were submitted to ANOVA and Tukey’s test (α=0.05).
Results: Table presents the data. Resin cement shade significantly affects KH. Indirect activation significantly lowered hardness. Hardness significantly increased after 24 h for all cements shades, relative to immediate values.
Conclusions: The resin cement shade and the presence of a ceramic indirect restoration have a significant effect on the KH. Cement microhardness significantly increases after 24h for all cements shades relative to immediate.