Abstract: Abstract： Objective To provide the basis for the application of electronic colorimeter into shade selection in composite resin adhesive restorations. Methods Three light-curing resin composites, a total of 23 shades, were investigated. Trapezoidal specimens of 1mm, 2mm and 3mm in thickness of each shade of resin composites were prepared, 5 for each kind of thickness. Color was measured by CrystalEye spectrophotometric colorimeter against white and black backgrounds. CIE L* , a*, b* values relative to CIE source were obtained, and color difference was analyzed under the Vita classical built shade guide. The system gavethe most recommended shade and color difference ΔE was obtained. With Vita classical shade guides as a built-in, the factors of brand, background and the thickness of the resins affecting the match rate of the results of shade matching were analyzed. Results Background influenced the match rates of the results of shade matching to Tetric and Majesty, while not to Ceram X（p>0.05）. The match rate of the results of shade matching over a black background was much higher than that over a white background（p<0.001）.Thickness of the resins influenced the match rates of the results of shade matching to Tetric and Majesty（p<0.05）, while not to Ceram X（p>0.05）. As the thickness increased, the match rates of the results of shade matching showed a tendency to increase.

Key words: Light-cured composite resins, color, color difference, colorimeter