This presentation describes the optical properties of dental materials, the different types of colour models, how colour is produced, dimensions of colour, problems in colour perception, shade guides available in markets and rules in shade selection

1. OPTICAL PROPERTIES OF DENTAL
MATERIALS AND SHADE
SELECTION
Dr Hrishita
MDS- Part 1

2. COLOUR
Colour is the result of the physical modification of light by colourants
as observed by the human eye and interpreted by the brain-
Billmeyer and Saltzman
Colour is the sensation resulting from stimulation of the retina of the
eye by light waves of certain lengths- Webster

3. LIGHT
Light is a form of visible energy that is a part of the electromagnetic
spectrum and possesses specific wavelengths
Wavelengths are measured in nanometers or billionth of a meter
The wavelength of visible light that can be perceived by the human
eye is 380-750nm

4. PHYSICS OF COLOUR

5. In order for colour to exist there needs to be interaction between 3
elements
LIGHT
OBJECT
VIEWER
COLOUR

6. The wavelengths of visible spectrum are perceived by the three types of
color receptors (called cones) in the human eye- Photopic Vision
Only perceived as variations of red, green, and blue light
Newton’s observation was white light contains all colors. If an object
appears to be a particular color, this means that the light reaching our
eyes when viewing that object has somehow been changed by the object.

7. EMISSION
Emission is defined as production of light from a source through a
chemical or physical process
To create perfectly white light, a light source would have to emit
exactly the same amount of each wavelength
No light source can emit perfectly white light
This affects color perception since there are only certain wavelengths
are produced by the light source to interact with an object

8. INTERACTION OF EMITTED LIGHT WITH AN
OBJECT
Reflection
Refraction
Absorption
Transmission
Diffraction
Scattering

9. REFLECTION
Reflected light rays are those rays which bounce back from the surface
of the object being hit instead of being transmitted or absorbed.
2 types:
oSpecular reflection
oDiffuse reflection

10. TYPES OF REFLECTION

11. REFRACTION
The splitting of white light by a prism into different colours is due to
refraction

12. ABSORPTION
Absorption is the process by which a matter takes up the energy of a
electromagnetic radiation
 Object
Absorb energy of light
Excite electrons to higher energy arrangement
Then electrons come back to stable energy position giving out heat

13. A material will absorb only a particular
wavelength of light, which corresponds
exactly to the amount of energy required
to excite its electrons
The rest of the wavelengths are not
absorbed are the wavelengths that form
the colour perceived

14. TRANSMISSION
Transmission occurs when light passes through a transparent or
translucent material
If the material is completely transparent, all light is transmitted, and
the color white is perceived. If the material is completely opaque, all
light is absorbed, and the color black is perceived

15. DIFFRACTION
Diffraction is a type of
interaction between all types
of waves with the objects

16. SCATTERING
Scattering occurs when any object changes the direction of the light
beam

17. TRANSPARENT TRANSLUCENT OPAQUE
A medium is said to be
transparent when it allows
maximum transmission of
light without any distortion
A medium is said to be
translucent when it allows
transmission of light in a
diffuse manner
A medium is said to be
opaque when it transmits no
light, whatsoever
None of the transmitted
light is scattered
10% of the transmitted
light is scattered
No light is transmitted
through the material
A clear window glass A frosted glass A brick wall

18. Light is emitted from a light source
This light may reach the eye directly, or it may either strike or pass
through an object
If the light interacts with an object, some of the light is absorbed by the
object
The wavelengths that are not absorbed are either reflected or
transmitted directly to the eye and are perceived by the rods and cones
in the eye
Processed and recognized by the brain as a specific color

19. RGB COLOUR MODEL
Colour creation by emitting
wavelengths that are mixes of
RED,GREEN,BLUE light to stimulate
the cones in eyes
When the additive primary colours
are combined they produce WHITE
So called as Additive primary
colours
The secondary colours are CYAN,
YELLOW and MAGENTA
Seen in electronic media

20. CMY COLOUR MODEL
For media that reflect and transmit light off
their surfaces
The primary colors in these color systems are
those created by the absorption of one of the
RGB wavelengths and the reflection/transmission
of CYAN, MAGENTA & YELLOW
The absence (or subtraction) of these three
colors results in WHITE-SUBTRACTIVE
PRIMARY COLOURS
Because dentists work with pigments when
dealing with porcelain, the easiest system for
clinicians to use is the subtractive system
(Freedman, 2012)

21. COLOUR IN DENTISTRY
PIGMENT COLOURS
DIMENSION OF COLOUR
oHue
o Value
o Chroma
oPrimary Colours
o Secondary Colours
o Complimentary Colours

22. HUE
Dominant colour of the object
Represents the dominant wavelength present
In the younger permanent dentition, hue tends to be similar throughout
the mouth. With aging, variations in hue often occur because of intrinsic
and extrinsic staining from restorative materials, foods, beverages,
smoking, and other influences (Aschheim, 2015)

23. CHROMA
It is the degree of saturation or intensity of hue
It is only present with hue
For example, to increase the chroma of a porcelain restoration, more of
that hue is added

24. VALUE
Value is the relative lightness or darkness of a colour
It is not the quantity of the colour “gray”, but rather the quality of
brightness on a gray scale-Gray scale value
 Value is the most important factor in shade matching. If the value
blends, small variations in hue and chroma will not be noticeable (Preston
JD, 1980)

25. PRIMARY COLOURS
RED, YELLOW, BLUE
These colours are perceived when one
of the RGB wavelength is absorbed
Red is perceived when green is
absorbed; yellow is perceived when
blue is absorbed; and blue is perceived
when red is absorbed

26. SECONDARY COLOURS
Orange, Green, Violet
The secondary colors are formed
by combining two of the primary
colors
Red and yellow create orange;
yellow and blue create green; and
blue and red create violet

27. COMPLIMENTARY COLOURS
Complementary colors are those that,
when combined in equal proportions,
will form gray that absorbs and
reflects all wavelengths in equal
amounts
They neutralize each other and form
gray
This is clinically significant because
complementary colors can be combined
to lower the value of excessively
bright restorations

28. COLOUR OF HUMAN TEETH
Dr. E. B. Clark indicated the Hue ranged from 6 YR (yellow-red) to 9.3
Y (yellow), the Value ranged from 4 to 8, and the Chroma ranged from
0 to 7
Lemire and Burk found a Hue range from 8.9 YR to 3.3 Y, a Value
range of 5.8 to 8, and a Chroma range from 0.8 to 3.4
 Goodkind and Schwabacher identified the Hue range as 4.5 YR to 2.6
Y, the Value range as 5.7 to 8.5, and the Chroma range from 1.1 to 5
Studies indicate that human teeth are in the yellow-red to yellow
portion of the spectrum, they are relatively high in Value (light or
bright), and they have a relatively low Chroma (not too much colour
intensity)

29. OPTICAL TRIAD
Fluorescence
Opalescence
Translucency

30. FLUORESCENCE
Fluorescence by definition is the absorption of
light by a material and the spontaneous emission
of light in a longer wavelength (McLaren, 1997)
Natural tooth has fluorescing qualities and is
believed to have because of the organic content
It absorbs wavelengths between 300 to 400nm
i.e ultraviolet radiations
This energy is then released as radiations of
longer wavelengths 400-500nm (yellow white
fluorescence) and the tooth appears to be a light
source
With the characteristic of fluorescence,
restorations look brighter and more alive

31. OPALESCENCE
Translucent materials have the property of opalescence, which give
them a milky white appearance : opal stone
Enamel: highly mineralised tissue
Counter opalescence

32. TRANSLUCENCY
4th dimension of colour
Not addressed by Munsell
But one of the most important factors for esthetics
The degree to which light is transmitted rather than absorbed or reflected
The incisal edges of natural teeth are translucent
Inclusion of Translucency in restorations to avoid opaque dead appearance
Lab technicians can use a densitometer to measure the amount of light that is
transmitted through a restoration or shade tab

33. MEASUREMENT OF COLOUR
 Colour systems
oMunsell System
oCIE L*a*b system

34. MUNSELL SYSTEM
 Created by AH Munsell in 1915
 Still considered the standard today
 Cylindrical Coordinate system
 In this system colour is divided into
three parameters—value, chroma and
hue
 Munsell notation: H V/C
 eg. Purple colour of medium value and
high chroma “ 5P 5/10”
 Matching denture base acrylics,
gingival porcelains

35. CIE L*A*B SYSTEM
 Adams Coordinate system
 3 coordinates:
o L*= Vertical axis and represents the
value
o a= Horizontal axis and it is the
measurement along the red green line
o b= Rectangular axis and it is the
measurement along the yellow blue line
 Numerical representation
 Any colour in this system is represented
by a unique point in space determined by
the amount of coordinates relative to
different axes used in the system

36. FACTORS AFFECTING COLOUR PERCEPTION
 There are many variables that affect how a colour is perceived
 The lighting conditions, the environment, and the viewer all play vital
roles in colour perception and evaluation in the clinic

37. ILLUMINATION & LIGHT INTENSITY
Colour can be neither accurately perceived nor correctly evaluated
without proper illumination
 Quantity as well as quality of illumination is important
The intensity of light is the most common regulator of pupil diameter,
which is a crucial factor in accurate shade matching
This is achieved by maintaining a lighting intensity of 150 to 200 foot-
candles, as verified by a light meter (Carsten,2003)

38. LIGHT TYPE COLOUR
TEMPERATURE (K)
LIGHT SOURCE
A 2856 INCANDESCENT BULB
B 4860 MIDDAY SUNLIGHT
C 6770 AVERAGE NORTHERN
SUNLIGHT
D 6500 AVERAGE DAYLIGHT
E 3000 FLUORESCENT TUBE
(WARM WHITE)
DIFFERENT TYPES OF LIGHT AND THEIR
DESIGNATION AS GIVEN BY CIE

39. CLINICAL LIGHTING CHALLENGES
LIGHTING CONFLICT
METAMERISM
BEZOLD BRUCKE EFFECT

40. Light coming through the window mixes with fluorescent light coming
from the hallway and the colour corrected light in the dental operatory.
It is the job of the clinician to determine the accurate shade amidst
these various lighting conflicts
LIGHTING CONFLICTS

41.  If the clinician or the lab technician has access to a natural light
source, it is best to perform shade matching at 10 am or 2 pm on a
clear, bright day when the ideal colour temperature of 5,000 K is
present
 Colour-corrected lighting tubes that burn at about 5,000 K (D50
illuminants) should be installed when only artificial lighting is available
(i.e., when there is no natural light)
 A lighting intensity of 175 + or - 25 foot-candles must be maintained
(verified by colour temperature meter)
 A colour temperature meter should be used periodically to verify
that a colour temperature of 5,000 K is achieved in the shade-
matching area
 Dust and dirt should be cleaned from lighting tubes and diffusers
routinely, since the presence of dust may alter the quantity and quality
of emitted light

42. METAMERISM
It is defined as a phenomenon when colour of two objects appear to
match under one set of viewing conditions but differ under different
set of conditions like a change in light source
This occurs because a certain light source produces only certain
wavelengths to interact with an object and thus the same object will
appear to be different colors when viewed using different light
sources

43. BEZOLD BRUCKE EFFECT
At low light levels, the rods of the human eye are more dominant than
the cones and colour perception is lost
At the same time, when the light is too bright, colour appears to
change
This phenomenon is known as Bezold Brucke effect

44. PROBLEMS IN COLOUR PERCEPTION
Colour Blindness- A person with color blindness has trouble seeing red,
green, blue, or mixtures of these colors
o It is a X linked recessive disorder
o affects males more commonly than females
 Aging- Detrimental to colour matching because cornea and lens of eyes
become yellow with age, imparting yellow brown bias
 Fatigue- Tired eyes cannot perceive colour as accurately as alert eyes can
 Binocular Difference- Perception variance between right and left eye
o Place tab on the same side of the tooth to be matched

45. Patient position- Patient should be upright with his mouth at the
observer’s eye level
Selection distance- 3 to 6 feet from the oral cavity
Time of selection- 10 AM & 2 PM are considered the best time for
shade selection in natural light because the temperature of natural llight
at that time is 5000K
Surroundings- Distracting surroundings should be avoided like bright
walls, bright clothes and loud cosmetics as they interfere with colour
perception
oTo avoid distractions in the oral cavity a neutral 18% grey card may
be used

46. SHADE SELECTION STEPS
The patient is in upright position, mouth at dentist eye level
Selection should be made when subject tooth and adjacent teeth are clean
Should be done before any intraoral procedures are started
Hold the shade tab as close to the tooth as possible
Selection is done at the start of the appointment

47. Cosmetics should be removed and bright coloured clothes covered
View in many light source as possible and from varying distances
Do not stare for more than 5 seconds
Move your eyes away and look at a neutral colour (light blue or grey)

48. COMMERCIAL SHADE GUIDES
 Most convenient and common method of making
shade selections
 Guides consist of shade tabs
o Metal backing
o Opaque porcelain
o Neck, body, and incisal color
 Select tab with the most natural
intraoral appearance

49. COMMERCIAL SHADE GUIDES
 Vita Classic
 Vitapan 3D Master
 Chromascop (Ivoclar Vivadent)
 Extended Range Shade Guides

50. VITA CLASSIC SHADE GUIDE
A B C D
 Very popular shade guide
 Tabs of similar hue are clustered into letter
groups
o A (red-yellow)
o B (yellow)
o C (grey)
o D (red-yellow-gray)
 Chroma is designated
with numerical values
 A3 = hue of red-yellow, chroma of 3

51. Red-Yellow Yellow Gray
Red-Yellow-
Gray

52. HUE SELECTION
 Four categories representing hue
 Operator should select hue closest to that of
natural tooth
 Use area of tooth highest in chroma for hue
selection
o Difficult to select hue for teeth low in
chroma

53. CHROMA SELECTION
 Hue selection done; eg. B
 Chroma is selected from gradations within the B
tabs
o B1, B2, B3, B4
 Several comparisons should be made
o Avoid retinal fatigue
o Rest eyes between comparisons (blue-gray)

54. VALUE SELECTION
 Use of second, value ordered shade
guide is recommended
 Value oriented shade guide
o B1, A1, B2, D2, A2, C1, C2,
D4, A3,D3, B3, A3.5, B4, C3,
A4, C4
 Value best determined by
squinting with comparisons
made at arms length
o Decreases light coming in the eye
o Diminishes cone sensitivity,
increases rod sensitivity
o Tooth fading first has a lower
value

55. FINAL CHECK
 Potential Problem
Following value selection, tabs selected for hue and chroma may not
coincide with shade tab selected for value
 Possible Findings / Solutions
 Value of shade tab < natural teeth
o Select new shade tab with higher value
o Cannot increase value of restoration with extrinsic staining
o Will only increase opacity, decrease light transmission
 Value of shade tab > natural teeth
o Select new shade tab with lower value
o Bridge difference with intrinsic or extrinsic staining

56. VITAPAN 3D-MASTER SHADE GUIDE

57. VITA-3D – STEP 1
 Determine the lightness level (value)
 Hold shade guide to patient’s mouth at
arms length
 Start with darkest group moving right
to left
 Select Value group 1, 2, 3, 4, or 5

58. VITA-3D – STEP 2
 Selection of chroma
 From your selected Value group, remove
the middle tab (M) and spread the
samples out like a fan
 Select one of the three shade
samples to determine chroma

59. VITA-3D – STEP 3
 Determine the hue
 Check whether the natural
tooth is more yellowish or
more reddish than the
shade sample selected

60. VITA-3D – VALUE MODIFICATION
 For more precise shade,
intermediate levels for value is
selected
o 2.5M2 = value between
2M2 and 3M2

61. VITA-3D – CHROMA MODIFICATION
 For more precise shade,
intermediate levels for chroma can
be selected
o 3M1.5 = chroma between 3M1
and 3M2

62. VITA-3D – HUE MODIFICATION
 For more precise shade,
intermediate levels for
hue can be selected
o 3M2 / 3L2.5 = hue
between 3M2 and
3L2.5
2.5

63. CHROMASCOP
 The tabs are initially divided based on
hue
 Chromascop uses a three-digit
numbering system consisting of five
groups of four tabs, as follow:
o Group 100 = White
o Group 200 = Yellow
o Group 300 = Orange
o Group 400 = Gray
o Group 500 = Brown
 Chroma and value are communicated by
a system of numbers:
o 10 = Least chromatic, highest value
o 40 = Most chromatic, lowest value

64. EXTENDED RANGE SHADE GUIDES
 Most shade guides do not cover all the colours
in the natural dentition
 Some porcelain systems extend the typical
range
o Bleached shades
o Dentin shades
o Custom shade guides

65. BLEACHED GUIDE
The progression of lightening in natural teeth was found to be identical to
the order suggested by Bleached guide (Ontiveros, et al., 2009)

66. SHADE MAPPING
 Recommended even when good custom shade match
exists
 Tooth is divided into
o Three regions
o Nine segments
 Each region is matched independently
 Further characterizations are sketched on
diagram, may include
o Craze lines
o Hypocalcifications
o Proximal discolorations
o Translucency

67. CONCLUSION
 Although limitations in materials and techniques may make a perfect colour
match impossible, a harmonious restoration can almost be achieved
 Shade selection should be approached in a methodical and
organized manner
 This will enable the practitioner to make the best choice and
communicate it accurately to the laboratory
 An understanding of the science of colour and colour perception is
crucial to the success in the ever expanding field of aesthetic
restorative dentistry

68. REFERENCES
Stephen Chu- Fundamentals of Colour: Shade Matching and
Communication
Dental Phillips
Materials used in dentistry- S. Mahalaxmi