Optical Properties of Dental Materials
Esthetic effects are sometimes produced in a restoration by incorporating
colored pigments in nonmetallic materials such as resin composites,
denture acrylics, silicone maxillofacial materials, and dental ceramics.
The color observed when pigments are mixed results from the selective
absorption by the pigments and the reflection of certain colors.
Opacity is a property of materials that prevents the passage of light. When
all of the colors of the spectrum from a white light source such as sunlight
are reflected from an object with the same intensity as received, the object
appears white. When all the spectrum colors are absorbed equally, the
object appears black. An opaque material may absorb some of the light
and reflect the remainder. If, for example, red, orange, yellow, blue, and
violet are absorbed, the material appears green in reflected white light.
opacity
translucency
Translucency is a property of substances that permits the passage of light,
but disperses the light, so objects cannot be seen through the material.
Some translucent materials used in dentistry are ceramics, resin
composites, and denture plastics.
Transparency is a property of material allows the passage of light in such
a manner that little distortion takes place and objects may be clearly seen
through them.
Transparent substances such as glass may be colored if they absorb certain
wavelengths and transmit others. For example, if a piece of glass absorbed
all wavelengths except red, it would appear red by transmitted light. If a
light beam containing no red wavelengths were shone on the glass, it
would appear opaque, because the remaining wavelengths would be
absorbed.
The index of refraction for any substance is the ratio of the velocity of
light in a vacuum (or air) to its velocity in the medium.