Degree of Conversion of Different Shades of Ceramic-Resin Cement systems

Objectives: The aim of this research was to evaluate the degree of monomer conversion of different resin cement shades when photocured under different feldthpathic ceramic shades. Methods: Three VITA VM7 ceramic shades (0M1, 2M2 and 5M3) and two resin cement shades (Variolink II, A3 Yellow and transparent) were studied. The resin cement specimens were light cured under a ceramic block (5 mm x 5 mm x 2 mm) for 20 or 40 seconds. Specimens photocured without the ceramic block were used as control. Sixteen groups (n=3) were evaluated. Micro-ATR FTIR spectrometry was used to evaluate the extent of polymerization of the different specimen conditions after 24 hours. The degree of conversion (DC) was calculated as a percentage of experimentally polymerized versus maximally polymerized composite. Statistical analysis of the data was evaluated using ANOVA and a Tukey b rank order test at p=0.05. Results: The %DC of both resin cement shades cured under ceramic 5M3 was significantly lower than the other groups (control, 0M1 and 2M2) at p<0.05. Similarly the A3 Yellow photocured for 40 s under all ceramic shades exhibited significantly lower %DC than the other groups at p<0.05. The %DC of 0M1 groups exhibited no significant difference from 2M2 groups (p > 0.05), with the exception of the transparent resin cement photocured for 40 s under 2M2 and 5M3 ceramics. Conclusion: Photocuring under 2 mm ceramic showed that the increase in chroma saturation significantly decreased resin cement DC; which suggests that a chemical cure resin cement should be applied when a dark feldspathic ceramic restoration is used.