EFFECT OF DIFFERENT THICKNESSES AND TWO SHADES OF TWO CERAMIC MATERIALS ON THE DEGREE OF CONVERSION OF A LIGHT CURED RESIN CEMENT

Statement of the problem: The success of a ceramic restoration depends primarily on the durability of the bond between ceramic and luting agent, and respectively between luting agent and enamel and dentin. When using composite resin as a luting material, the bond strength will be determined by achieving adequate resin polymerization which is affected by ceramic shade and thickness that interferes with light transmittance resulting in a decrease in the total energy reaching the luting cement.
Objective: This research was designed to evaluate the degree of monomer conversion of light cured resin cement under two ceramic materials (Lithium Disilicate, ultra translucent zirconia) using Different thicknesses (0.4 mm, 0.7mm, 1.0 mm). The degree of conversion is measured by FTIR (Fourier transform infrared spectroscopy).
Materials and methods: light cure resin cement (rely X veneer, 3M) was used as manufacturer’s instructions with film thickness of 0.1mm, and cured for 20 seconds using Bluephase (Ivoclar Vivadent) 1200 mW/cm2 curing done through 14×14 specimens of two types of materials (ulta-translucent zirconia katana UT, lithium disilicate e-max) with two shades (A1, A3) and different thicknesses (0.4 mm ,0.7mm, 1 mm). Then the degree of conversion of each sample evaluated using Fourier transform infrared spectroscope, (Nicolet 6700)
Results: One-Way ANOVA revealed no significant difference between different thicknesses of the ceramic material on the degree of conversion of resin cement (P>0.05). While there was a significant difference between different shades of the ceramics on its degree of conversion (P≤0.05). ceramics with the shade A3 showed lower degree of conversion than ceramics with the shade A1, and there was a significant differences between the two types of ceramic materials on the degree of conversion of resin cement with the lithium disilicate material showing a higher degree of conversion than the ultra-translucent zirconia (P≤0.05).
Conclusion: Thicknesses up to 1.0 mm has no significant effect on the polymerization of resin cements, Lighter shades transmit more light to the underlying cement than darker ones, Lithium disilicate has higher translucency and allow more conversion of monomer to polymer in the underlying cement.