Abstract: Objective: To evaluate the optical data of the different sites of the dark color abutments covered by four different all-ceramic crowns and the color difference between the crowns and the target tab by using a digital dental spectrophotometer. Methods: Ten dark color(ND8) abutments were made and were respectively tried in four different groups of all-ceramic crowns (Procera aluminia, Procera zirconia, Lava zirconia, IPS E.max glass-ceramic lithium disilicate-reinforced monolithic crown).The color data of the cervical, body, incisal sites of the samples was recorded and analyzed by a spectrophotometer. The CIE L^*、a^*、b^* values were measured again after veneered. The color difference between the abutments covered by all-ceramic crowns and target A2 dentin tab was evaluated. Results: The L^* values of the abutments increased in four groups of all-ceramic copings, but a^*、b^* values were both decreased. There was statistical difference among four groups of copings. After veneered, the L^* values of all the copings declined slightly, the values of a^*, b^* increased significantly. When compared with A2 tab, the ΔE of the crowns was below 4. It meant the color difference which was almost clinically acceptable but was perceived by human eyes. Conclusion: Four ceramic copings were demonstrated to effectively promote the lightness and hue of the dark abutments. Though the colorimetric baseline of these copings was uneven, veneer porcelain which thickness less than 0.8~0.9mm could efficiently decrease the color difference to be clinically acceptable, but four ceramic systems were still different in colorimetric characteristics to some extent.

Key words: Spectrophotometer, All-ceramic , Color, Color difference