Describe how a natural tooth's characteristics concerning light reflection and refraction is replicated within a PFM crown.
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Dental Technology Mapa Mental sobre Describe how a natural tooth's characteristics concerning light reflection and refraction is replicated within a PFM crown., criado por Alice Dolman em 04-05-2019.
Describe how a natural tooth's characteristics concerning
light reflection and refraction is replicated within a PFM
crown.
In ceramics the greatest light scattering effect is achieved by an increasing difference in refractive index
between particles and the main bulk of the porcelain phase.
Porcelain itself can be regarded as optically heterogeneous i.e. it is a
transparent medium, containing small particle such as metallic oxides
(opacifiers), crystals or glassy grains of dissimilar refractive indices to
the porcelain.
When a beam of light enters such a system, a portion of beam is
scattered, and the intensity of the beam is reduced.
The scattering is strongly dependant on particle size, so that the maximum
scattering occurs at a particle size of the same magnitude as the radiation
wave-length.
In order to increase the light scattering in dental ceramics and simulate the prismatic effect of human enamels, it
is necessary to introduce opacifiers, crystals or a second phase of porcelain powder to the basic frit.
During the building up process of different porcelain
layers, a porcelain with a better ability to reflect light
is used to stimulate dentine. A porcelain with a better
ability of scattering light is used to mimic enamel to
allow translucency of the prosthesis around the incisal edges.
Refraction will occur as light passes through the internal (eg,
cracks) and external surfaces of the tooth. An example of an
internal surface within a porcelain-bonded restoration is the
interface between a pressed coping and the superficial veneering
porcelain.
opaque porcelains increase the
brightness/value reflecting a higher degree
of light. Without this layer the metal
substructure will be more visible, or harder
to cover.
An uneven surface to the opaque layer increases
the degree of light scattering in the crown.