BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI
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Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 53<br />
translucency appears lighter and reveals more of the backing in the color. It is<br />
important to notice that the translucency decreases with the increasing<br />
scattering.<br />
The opacity represents the opposite of the translucency. Light scattering<br />
in a material is the result of scattering centers (eg air bubbles, opacifiers such as<br />
titanium dioxide, the filler particles in a resin composite matrix) that cause the<br />
incident light to be scattered in all directions. The effect of scattering depends<br />
on different factors as: the size, the shape, the number of the scattering centers.<br />
Scattering is also dependent on the difference in refractive indices between the<br />
scattering centers and the matrix in which the centers are located..<br />
Another optical property, capable to produce a lustrous appearance, is<br />
represented by the surface gloss. Usually, a high surface gloss is associated with<br />
smooth surfaces. For example, in dental composite resin, the surface gloss<br />
decreases with the increasing surface roughness. High gloss reduces the effect<br />
of a color difference, because the color of the reflected light is more prominent.<br />
In a restorative dental material, high gloss also lightens the color appearance.<br />
Fluorescence represents the emission of light by an object at<br />
wavelengths different from those of incident light. After the removal of the<br />
incident light, the emission ceases immediately. Porcelains used in dental<br />
laboratory are fluorescent under ultraviolet light and the quality of the<br />
fluorescence depends on the brand of porcelain (O’Brien, 2008).<br />
At their turn, each of the mentioned factors (color, translucency, gloss,<br />
fluorescence), as perceived by an observer, can be influenced by: the light<br />
source (illuminant), the inherent optical parameters of the materials that dictate<br />
the interaction of the light from the illuminant with the material; the<br />
interpretation of the observer.<br />
In Fig. 2 is represented the interaction between the light source, the object<br />
(dental material) and the observer.<br />
Surroundings in a dental office may influence and modify the actual light<br />
reaching the object. The color of walls, clothing, soft tissues (eg.lips) contribute<br />
to the color of the light incident on teeth, shade guides and restorative materials<br />
(O’Brien, 2008).<br />
In dental medicine are utilized color systems to describe the color<br />
parameters of different dental materials.<br />
The Munsell color system is a three-dimensional system which has as<br />
coordinates : hue (is the attribute of color that makes it appear blue, yellow or<br />
red), value (is the lightness or darkness of a color and it is the most important<br />
color factor in tooth color matching), and chroma (is the intensity of a color;<br />
that is, the amount of hue saturation) (O’Brien, 2008; McCabe & Walls, 2008).<br />
In Fig. 3 is represented the Munsell three-dimensional color system.<br />
Others color systems are the CIE (Commission Internationale de<br />
l’Eclairage) color systems.