Nafiseh Elmamooz - Assistant professor, Oral and dental disease research center, Kerman University of Medical sciences, Kerman, Iran.
Ali Eskandarizadeh - Associate professor, Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran
Elina Rahmanian - Resident of Operative Dentistry, Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran
Shahriar Sarvareh Azimzadeh - Resident of Orthodontics, Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran

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.      

ceramic veneer thickness, degree of conversion, luting resin cements