Principles of color and optical effects in dentistry

1. Color and Optical effects
in dentistry
By
Mohamed Mahmoud Abdul-Monem
Assistant lecturer
Dental Biomaterials Department
Alexandria University
Egypt
Mohamed_mahmoud.biomaterials@yahoo.com

2. Nature of light and the role of human vision
• LIGHT is electromagnetic radiation that can be
detected by human eye.
• The eye is sensitive to wavelengths from
approximately 400nm(violet) to 700 nm(dark
red).
• For an object to be visible ,it must reflect or
transmit light incident on it from an external
source.

4. • The incident light is usually polychromatic; a
mixture of various wavelengths (white light).
• Light from an object that is incident on the eye is
focused in the retina (cone shaped cells which are
sensitive to red, blue and green )and converted to nerve
impulses that are transmitted to the brain.
• Constant stimulation by a single color may result
in color fatigue and decrease in eye’s response.

6. Nature of object under view
• The nature of the restorative material under
view, determines how that material will
appear.
• Light interacts with an object through :
reflection ,absorption ,refraction or
transmission.
• These phenomena determine the opacity,
translucency or transparency of an object.

7. • Opacity is related to the amount of light a
material can absorb and/or scatter.
• The opposite of opacity is translucency.
• Transparent materials absorb no light and
transmit 100% of light that passes through
them.

10. • Light reflected from rough surface scatters in
many directions because it is reflected at
many angles by the un even surface.
• This leads to an appearance that ranges from
mirror like for a perfectly smooth surface
(specular reflectance) to flat,dull
appearance(diffuse reflectance) as chalk.

12. 3D of color
• Color perception is described by
three objective variables : hue
,value and chroma .These
variables constitute the 3D of
color space.
• Hue : The dominant color of an
object. ( red, green, blue).
• Value (gray scale) : value
increases towards the high end
(lighter) and decreases towards
the low end (darker).
• Chroma: degree of saturation of a
particular hue.

13. L*a*b* color space
• Color chart based on
Comission
Internationale de
l’eclairage.
• L* represents value
• a* measurement along
red-green axis
• b* measurement along
yellow-blue axis

15. Color matching
Shade guide
Hue
A B C D
A red-brown
B red-yellow
C gray
D red-gray
Value
1 2 3 4
1 lightest
4 darkest

16. • Arrangement from lightest to darkest
• B1,A1,B2,D2
• A2,C1,C2,D4
• A3,D3,B3,A3.5
• B4,C3,A4,C4

17. Vita 3D Master shade guide

21. • To ensure maximum esthetic results :
• Shade guide
• Drawings
• Photographs
• Subjective preference of patient

22. Effect of observer on color matching
• Factors interfering with true perception of
color :
• Low or high light levels
• Fatigue of color receptors
• Sex
• Age
• Memory
• Cultural background.

23. • At low light levels,the rods in the retina are
more dominant than cones and color
perception is lost.
• As brightness becomes more intense,color
appears to change(Bezold-Brucke effect).

24. • If the patient is observed
under an intense-colored
background,the dentist
may select a tooth shade
with hue shifted towards
the complementary color
of the background.
• For example a blue
background shifts color
selection towards yellow.

25. The effect of light source on color
matching
• The appearance of an object is dependant on the
nature of the light in which it is viewed.
• Daylight, incandescent light and fluorescent
lamps are common light sources in the clinic or
lab.
• Metamerism: Objects that appear to be color
matched under one type of light may appear
different under another type.
• Thus color matching should be done under two
or more different light sources,one of which
should be daylight

27. Fluorescence
• Natural tooth absorbs light at wavelengths too
short to be visible to the eye.
• Wavelengths between 300-400 nm (Near UV
radiation).
• The energy that the tooth absorbs is
converted into light with longer wavelengths
and the tooth itself becomes a light source.

28. • The emitted light is a
blue-white color (400-
450 nm)
• Fluorescence makes a
definite contribution to
the brightness and vital
appearance of human
teeth.

29. Thank YOU