Objective       To determine the effect of the thickness and translucency of cast-ceramic on the curing efficiency of dual-cured resin cement.       Methods       Ceramic restorations (IPSe. max) with different translucencies

including high translucency (HTA2)

low translucency (LTA2)

medium opacity (MO1)

and high opacity (HO1)

were made into wafers at 6.0 mm in diameter and at 0.5

1

2

3 and 4 mm in thickness respectively (n=20). The experimental group had the ceramic restorations positioned between the dual-cured resin cement (Variolink Ⅱ) and light source during polymerization. In the control group there was no ceramic restoration

and light curing was performed using light-emitting diodes (LED) as light source. The degree of conversion was evaluated using Fourier transform infrared (FT-IR) spectrometer

and the Knoop hardness test was performed on the cement layer.       Results       The degree of conversion and the hardness of dual-cured resin cement were decreased with the increase of thickness and the decrease of translucency（P0.05）

and in dual-cured control group they were the highest (except 0.5 mm groups of HTA2). At the same translucency

the hardness showed statistical difference between different thickness groups except 1.0 mm groups and 2.0 mm groups of HTA2 and LTA2（P0.05）. For the wafers at the same thickness

the hardness of dual-cured resin cement presented no statistical difference between HTA2 and LTA2

between HO1 and MO1（P0.05）. However

the hardness of resin cement of HTA2 and LTA2 was significantly higher than that of HO1 and MO1 （P0.05）.       Conclusion      Ceramic thickness and translucency have great influence on the hardness of dual-cured resin cement

and the curing efficiency is decreased with the increase of thickness and decrease of translucency.