Visible light cured resin cements are recommended for luting ceramic veneers. This requires that the curing light penetrate through the veneer to fully polymerize the cement film. Objectives: The purpose of this study was to determine the degree of conversion (DC) of a light cured cement cured through various ceramic thicknesses and using different light outputs and curing times. Methods: Specimens of Empress I were fabricated in wafers 5mm x 5mm and 0.5, 1.5 and 2.5 mm in thickness and surface shaded Vita A-2. Variolink Base cement (transparent) was placed between glass slides using mylar strips and a thin film was generated by applying pressure. The films were polymerized for 20 and 40 seconds using a Spectrum 800 curing light at 300 mW/cm² and 600 mW/cm². DC was determined after 24 hours using micro-FTIR (Nicolet 560 ESP) (n=4). Direct DC values were determined using a percentage of carbon double bonds (1638cm-1) compared to a reference aromatic peak (1608 cm-1). Data were evaluated with a 3-way ANOVA (factors: thickness, power, time) and post-hoc Tukey's test. Results: (% double bond conversion)

All factors were significant for DC (p<0.05). Cure decreased with increasing ceramic thickness and decreasing power and time (p<0.05). Conclusions: DC was significantly affected by increased ceramic thickness. High light output and extended curing times are needed to cure this cement through the ceramic. Light-cured only cements may be contraindicated when used with thick veneers or crowns. Supported by the Health Future Foundation.