TOOTH COLOR AND REFLECTANCE AS RELATED TO LIGHT-SCATTERING AND ENAMELHARDNESS

Tooth color is determined by the paths of light inside the tooth and a bsorption along these paths. This paper tests the hypothesis that, sin ce the paths are determined by scattering, a relation between color an d scattering coefficients exists. One hundred and two extracted inciso rs were fixed in formalin, mounted in a standardized position in brass holders, and pumiced. A facet was prepared near the incisal edge on t he labial plane to allow for Knoop hardness measurements with a 500-gr am load. Light scattering by the enamel was measured in a 45 degrees/0 degrees geometry; light scattering by both enamel and dentin was meas ured in a 0 degrees/0 degrees geometry. The reflection spectrum of the tooth was measured from the labial plane with a spectroradiometer in a 45 degrees/0 degrees geometry, with standard illuminant A and standa rd illuminant D65. To include all volume-reflected light, we used enti re-tooth illumination and small-area measurement. CIELAB color coordin ates were calculated from the spectra. Neither spectra nor coordinates showed evidence of a contribution of fluorescence to tooth color. Ave raged values and standard deviations for L,a*,b*, were 69.9 (4.1), 1. 22 (1.4), and 17.9 (2.9), respectively. Both scattering coefficients a veraged to 0.6 (0.4) mm(-1); Knoop hardness number was, on average, 27 1 (39) kg/mm(2). L correlated with a* (r = -0.51), with the enamel sc attering coefficient (r = 0.60), and slightly with hardness (r = 0.17, p = 0.03). The colors of 28 teeth from which the enamel was removed c orrelated strongly with the colors of the complete tooth. This study q uantitatively confirms that tooth color is determined mainly by dentin , with enamel playing only a minor role through scattering at waveleng ths in the blue range.