Method: A light-curing resin composite (Filtek Supreme XTE Universal Restorative System, A3E, 3M Espe) sample (1mm thickness, 6 mm diameter) was light-cured for 30 seconds (Bluephase 20i, HIP mode 1200 mW/cm2, Ivoclar-Vivadent) through two shades (A1 and A3), two translucencies (HT and LT) and six thicknesses (0.5, 1, 2, 3, 4 and 5 mm) of ceramic (Empress CAD, Ivoclar Vivadent) and laboratory resin composite (Lava Ultimate, 3M Espe). Control samples were directly cured without the presence of ceramic. The degree of conversion was first determined (at 24h, three measurements) with Raman Spectroscopy (Alpha 300R, 632 nm, WiTec Gmbh) on top of the resin composite sample. The swelling ratio was then determined from measurements of absorption and solubility in an ethanol/water mixture (75/25%) for each sample. Statistical analysis was performed with ANOVA and MANOVA for shade-translucency, thickness and material.
Result: The degree of conversion was affected by the thickness and shade-translucency of the restoration whatever the material used. The 3 mm thickness is a critical treshold for the polymerization depth. The swelling ratio was affected by the thickness and shade-translucency but also by the material used.
Conclusion: The polymerization is greatly reduced from 3 mm deep with Empress-CAD and Ultimate blocks. Further studies are needed to analyze the irradiation time and material temperature parameters.