evaluating the effect of ceramic veneer thickness on degree of conversion in three luting resin cements

compare the effect of different ceramic thicknesses on degree of conversion (dc) of 3 light-cured resin cements. methods: in this experimental in-vitro study, the degree of conversion of three light-cured resin cements, variolink veneer (ivoclar, liechtenstein), relyx veneer (3m espe, usa) and choice2 (bisco, usa) were evaluated beneath feldespatic ceramic discs (vita vmk master) with a same shade,  2m2, in different thicknesses (0.5, 1, 2 and3 mm) using ftir. the light curing unit used was optilux 501, with an intensity of 600 mw/cm2 and exposure duration of 40 seconds. three specimens of each cement group were examined in each condition. the obtained data was submitted to kolmogorov-smirnov and also checked for absence of skewness and kurtosis for normal distribution. after that, anova test was used for comparison between experimental groups (tukey hsd). results: in all the three used cements, dc decreased as ceramic thickness increased. this reduction was not significant when using 0.5 and 1 mm ceramic discs, however, it was significant between 1, 2, and 3mm discs(p<0.05). there was no difference within the cements’ dc when exposed through ceramic discs of 0.5, 1, and 2mm, but the rely x veneer cement had a lower dc compared to variolink veneer and choice2 when the thickness increased to 3mm(p<0.05). conclusion: it is not advisable to use light-cured resin cements beneath 3 mm thick ceramics and the use of rely x veneer is not recommended as the ceramic thickness increases.