BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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