The purpose of this in vitro study was to evaluate the effect of two types of modified CAD/CAM restorative material and its thickness, together with the type of resin luting cement, and its method of curing on color difference (∆E) and VHN as an indicator of the degree of polymerization of resin luting cement.
Materials and methods: A total of 36 groups were used in this study (n=5) where, 32 Groups representing the each of the two different resin luting cement materials, under each of the two different modified CAD/CAM materials interface with four different materials thicknesses (0.5 mm, 0.7 mm, 0.9 mm and 1.2 mm) and polymerized with either conventional halogen or LED light curing system. Another four groups were prepared representing the control groups for each resin luting cement and light curing unit used. ∆E Measurement: Specimens in all groups was measured just after polymerization at the top of the specimens after removal of the ceramic face and Mylar strip to be compared with stored in dry boxes in darkened incubator at 37˚C for one week to be subjected to the color measurement again at the surface of the specimens. Micro Hardness Measurement : The resin luting cement specimens were subjected to micro-hardness tester (WilsonÒ Hardness Tester, Model Tukon 1102, Buehler, Lake Bluff, IL, USA). The data obtained from the means of ∆E and VHN test were subjected to analysis of variance (ANOVA) followed by Tukey's test at a 5% level of significance.
Results: Four-Way ANOVA was used to test the four main effects namely, type of indirect esthetic restorative material and its thickness, together with the type of resin luting cement, and its method of curing the types of resin luting cement, the mode of curing. The first main effect (type of modified CAD/CAM material) had two levels namely, Lava Ultimate, and Vita Enamic. The second main effect (modified CAD/CAM material thickness) had four levels namely, 0.5 mm, 0.7 mm, 0.9 mm and 1.2 mm. The third main effect (type of resin luting cement) had two levels namely Vario Link Dual and Nexus 3 LC. The fourth main effect (type of light curing unit) had two levels namely QTH and LED.
Conclusion: Within the limitation of this study, it could be concluded that, the thickness of the CAD/CAM material and the type of the resin luting cement had a higher effect on the ∆E and micro-hardness, hence the degree of maturation, of resin luting cement than did either the type of tested CAD/CAM materials or the curing units.