6. Small band gap
1.8eV, light
absorption, opaque
Medium band gap 1.8-
3eV, light transmission
and reflection,
translucent
Large band gap
>3eV, light
transmission,
transparent
7. Enamel: transmits up to 70% of light,
reflected light gives luster
Dentin: less translucent than enamel
and can transmit up to 30%, primary
source of color due to reflection
ADJ: light is reflected to enamel or
refracted into dentin
9. Scattering
• To calculate transmitted
light, the coefficient of
absorption and
coefficient of scattering
must be calculated.
• Scattering anisotropy
factor (-1 dentin and
zirconia, 0 glass, +1
enamel)
10. 2- Opalescence
• Similar to opal
stone
• Blue with
reflected light
and orange with
transmitted light
(light scattering)
11. • Results from HA crystals (enamel)which
are smaller than the light wavelength
which could be imitated by oxides
12.
13. 3- Fluorescence
• Absorbing non-visible light and
emanating light of different
wavelengths
• Teeth fluoresce under
ultraviolet radiation due to
fluors or proteins in the dentin
giving a blue color
• Gives vitality to the tooth
14. • Rare earths, such as
europium, terbium,
cerium, and ytterbium,
are currently used as
luminophores to provide
ceramic materials with
fluorescence.
• Luminaries by VITA allow
light reflection to the
overlying structures to
give fluorescence.
18. • The color difference (∆E)
between 2 objects can
be determined by
comparing the
differences between the
respective coordinate
values for each object
• Perceptibility and
acceptability thresholds
20. • Non-metallic, inorganic
structures primarily containing
compounds of oxygen with
one or more metallic or semi-
metallic elements
• Amorphous or crystalline
Ceramics
22. 1- Glasses and
porcelains
• Amorphous structure
• Feldspar (potassium),
quartz (silica) and kaolin
• Metal oxide pigments
• Different fusion
temperatures
• Weak and brittle
23. • Chromium or chrome-alumina
(pink)
• Iron oxide (black) or platinum
(Grey)
• Cobalt oxide (Blue)
• Titanium oxide (yellow brown)
• Iron/nickel oxide (brown)
24. • Pure glass is transparent and allows 98% of light to
pass, therefore opaque materials are added to make it
semi-translucent like the tooth.
• Dental porcelains are translucent because there are no
free electrons (transmission > reflection and
absorption)
• Problems arise from the substructure
25. Porcelain fused to
metal (PFM)
• Increased light reflectivity from the opaque
porcelains that are used to mask the metal
coping
• Opaque porcelain> body porcelain> incisal
porcelain
• Transmission only in the body of the porcelain
• Looks less vital due to low light transmission
Color is not a property of the object, but of the light that enters our eyes from it.
Electromagnetic wave from 400-700 nm
The light that doesn’t pass is reflected and gives color
Transparent transmits, opaque absorbs and translucent does all
Enamel is translucent while dentin is opaque
Adj has light due to back reflection
Micro grooves cause diffuse reflection
This decrease was due to the increase of the refractive index of enamel caused by the water outflow and air intake on the outskirts of the prisms causing less hydration
Negative is back scatter, positive is forward scatter and zero is no scatter of single crystals
Since HA is destroyed by caries it appears black by trans illumination
Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves.
UV light of flash and composite
Hue is the wavelength, chroma is the saturation, value is brightness
In natural teeth, the value is characteristic for the enamel, while the chroma and hue characterize dentine. The younger individuals, less exposed to the wear caused by the acids in the diet and brushing, present enamel thicker than older individuals, and consequently lighter teeth. As wear is accentuated and the thickness of the enamel layer decreases, the translucency of the enamel increase, enabling chroma and hue, characteristics concerning the dentine, become more obvious.
3.7 is acceptable although color difference is seen
1 is perciptable
Hue, chroma and value are used for colored objects but for dental objects translucency is the fourth parameter
spectrophotometer
More crystals therefore better mechanical props
High potassium alumino silicate and low kaolin to give translucency
Sodium and potassium are fluxes and opacifiers
Blue for enamel, translucent
No free electrons opposite to metals
A natural tooth diffuses and transmits light, whereas a PFM restoration violates this property. It will only diffuse and reflect the light in the body area. As a result, PFM restorations often look brighter in the mouth
