17955695
Descripción
Mapa Mental por Alice Dolman, actualizado hace más de 1 año
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Creado por Alice Dolman
hace más de 5 años
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How is light reflected and
refractedwithin a natural tooth?
- Human enamel contains approx.. 97% by weight mineral matter, mostly in the form of
hydroxyapatite. The hydroxyapatite crystals in enamel are extremely small
- Hydroxyapatite crystals align in organized, tightly packed masses to form prismatic
enamel rods. Refraction will occur as light passes through each enamel rod and also at
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.
- The enamel rods or prisms are bound together with organic material (the collagen
matrix) which represents approximately 1% of total mass.
- Enamel is therefore very translucent and may transmit up to 70% light through a 1mm thick section.
By contrast the dentine only contains about 70% hydroxyapatite and the apatite crystals are much
smaller than in enamel. Consequently they have an even greater surface area/volume ratio, it is still
translucent but will generally not transmit much more than 30% light.
- Enamel is therefore very translucent and may transmit up to 70% light through a 1mm thick section.
By contrast the dentine only contains about 70% hydroxyapatite and the apatite crystals are much
smaller than in enamel. Consequently they have an even greater surface area/volume ratio, it is still
translucent but will generally not transmit much more than 30% light.
- Hydroxyapatite crystals align in organized, tightly packed masses to form prismatic
enamel rods. Refraction will occur as light passes through each enamel rod and also at
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.
- Colour
- When light shines on your teeth, it is scattered and reflected in the
enamel, creating the colour of your teeth. If you have plaque on your
enamel, your enamel will reflect less light and look darker. If your
dentin (the layer under your enamel) is darker, it may show through
the enamel and create a darker appearance.
- The total colour effect is derived from a combination of
light directly reflected from the tooth surface combined
with the light that has been reflected from the dentine
which has already undergone some internal reflection.
- The dentine is the prime source of colour
and the reflected light emitted via the
enamel are modified by the thickness and
degree of translucency of the enamel and
the dark oral background.
- When light shines on your teeth, it is scattered and reflected in the
enamel, creating the colour of your teeth. If you have plaque on your
enamel, your enamel will reflect less light and look darker. If your
dentin (the layer under your enamel) is darker, it may show through
the enamel and create a darker appearance.
- Translucency
- Translucency in human enamel is influenced by the reflection and
refraction of light in enamel rods.
- as the enamel approaches the tip of the
incisal edge, the amount of light transmitted
will increase to a degree where it almost
becomes transparent.
- as the enamel approaches the tip of the
incisal edge, the amount of light transmitted
will increase to a degree where it almost
becomes transparent.
- Translucent enamel displays the characteristic of opalescence.
Opalescence causes tooth enamel to reflect blue light back to the
observer. Blue light tends to bend/refract more or to scatter within
the enamel body. Longer red-yellow wavelengths do not bend as
much in the enamel;
- Translucency in human enamel is influenced by the reflection and
refraction of light in enamel rods.
- Chroma
- chroma of a natural tooth comes mainly from the dentin, and the
thickness and opacity of the overlying enamel determines how much
chromatic influence the dentin has. When the enamel is thin at the
gingival third but thick incisally, a chroma gradient is created. Increasing
opacity of the enamel, as seen with dehydration and bleaching, can
exaggerate the chroma gradient.
- chroma of a natural tooth comes mainly from the dentin, and the
thickness and opacity of the overlying enamel determines how much
chromatic influence the dentin has. When the enamel is thin at the
gingival third but thick incisally, a chroma gradient is created. Increasing
opacity of the enamel, as seen with dehydration and bleaching, can
exaggerate the chroma gradient.
- When light enters a natural tooth it gets bounced around the enamel like a
fiber-optic cable. If one side of a tooth is illuminated with a curing light, the
entire crown is lit. When light travels from one translucent material to
another, light will be either reflected at the surface, or it will pass through the
surface but bends (refracts) as it passes.
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