Abstract:

Objective

Metal ceramic restorations and natural teeth have different spectral reflectance curves. Metamerism phenomenon may affect the color match of them if the light source changes. The purpose of this study was to determine the metameric color differences between natural teeth and two kinds of metal ceramic crowns.

Methods

The spectral reflectance curves and color corordinates of natural teeth and two kinds of metal ceramic full crowns of A2 shade were measured with a spectrophotometer （PR-650） according to the CIE L^*ab color scale and CIE XYZ color scale relative to illuminant D65， A， CWF and ultraviolate （UV）. Metameric index was calculated to determine the metameric color differences between natural teeth and metal ceramic restorations.

Results

CIE L^*，a^*，b^* values were influenced by the type of illuminant in both natural teeth and metal ceramic restorations. The pattern of spectral reflectance curves for natural teeth and metal ceramic restorations of A2 shade differed greatly， while there were more than 3 crossing points in each curve. The metameric indice between natural teeth and tow kinds of metal ceramic restorations under illuminant A were 2.53， 0.95， respectively， 2.95， 2.47 under illuminant CWF and 3.20， 5.07 under UV. The metameric indice between metal ceramic restorations of different brand were 1.43 under illuminant A， 0.99 under CWF and 3.74 under UV.

Conclusions

Changes in optical properties of metal ceramic restorations of A2 shade relative to the different illuminants are different from those of natural teeth， the metameric effect between natural teeth and metal ceramic restorations of A2 shade is significant. Therefore， shade matching between natural teeth and metal ceramic restorations should be performed under more than one illuminants.

Key words: Metamerism, Natural teeth, Metal ceramic crown, Illuminant