Light and color

Without light color

does not exist.

An object of a certain color

absorbs all light waves of all

colors and reflects only those

waves of its colour.

• Visible electromagnetic energy

• wavelength is measured in nanometers (nm) or billionths of a meter.

Light

• Sensitive only to the visible part of the electromagnetic spectrum with wavelengths of 380 to 750 nm. (a narrow band)

Eye

Ultraviolet, x rays and gamma rays

→ shorter wave length

infrared radiation →longer

wavelengths.

Pure white light →consists of relatively equal quantities

of electromagnetic energy over the visible range.

When light is passed through a prism →longer

wavelengths are bent (refracted) < the shorter ones.

It splits into its component colors.

Infrared [high wavelength ] then white light : Red, Orange,

yellow, Green, Blue, Violet : then ultraviolet

Sources of Light:

� In the morning and the

evening→ uneven

distribution of color

� Northern daylight around the noon hour on a bright

day → ideal

� Harmonious balance of the

full visible spectrum exists.

� All colors of the visible

spectrum .

� It is used as a standard for

judging light from other

sources. It is 100 in color

rending index.

� Incandescent light bulb →Emits

relatively higher concentrations of

yellow light waves than of blue and

blue-green.

� Fluorescent → Gives relatively

high concentrations of blue waves.

� Color corrected lamp→ For

shade selection

Natural Artificial

� Colour Rendering Index (CRI ): A scale of

1 to 100, indicates how well a particular light

source renders color as compared to a

specific standard source.

� Colour temperature: Related to the color

of a standard black body when heated.

Color temperature is reported in degrees

Kelvin (K).

� Northern daylight has an average color

temperature of around 6500° K & 100 CRI.

Some important light phenomena:

• 2 colors match under a light but mismatch under other source.Metamerism

• A glow of an object when illuminated and stopped when illumination source is removed.

• e.g. Enamel

• Small amount of rare-earth elements are added to porcelain powder.

Fluorescence

• Light scattering effect that creates appearance of bluish white color.

• Teeth has this properties

• High index refractive oxides in size range near wavelength of visible light.

Opalescence

Color mixing:

� Primary colors are Red, Blue , Yellow

� Combination of two primary colors gives

a secondary color:

� Red + Blue → Violet

� Blue + Yellow → Green

� Red + Yellow → Orange

Munsell

Colour

System

CIELAB

Colour

System

The most popular

method for describing

color.

The 3 attributes of

color arc called Hue.

Value and Chroma.

� This is defined as the particular variety of a color,

shade, or tint.

� Hue of an object can be red, green, yellow.

� The place of that wavelength (or wavelengths) in

the visible range of the spectrum determines the

hue of the color.

� In the Munsell color system, Hues are

divided into 10 gradations:

� Yellow

� Yellow-Red

� Red

� Red –Purple

� Purple

� Purple-Blue

� Blue,

� Blue-Green

� Green, and

� Green-yellow

� Arranged in a wheel.

� Each gradation is subdivided; for

example, red can be written 1R, 2R, 3R

. . . 9R, 10R

� These can be further subdivided. Thus a

particular Hue might be.

� Most natural teeth fall into a range

between Yellow and Yellow-Red .

� The intensity of a hue.

� Chroma ═ Saturation.

� Achromatic shades

have a Chroma near 0.

� Natural teeth are found

with Chroma ranges

from 0 to 7.

� Relative lightness or darkness of a color or the brightness of an object.

� In the Munsell method of describing color, value is divided into 10 gradations,

� 0 → black

� 10 → white.

Munsell colour System

Natural teeth range in Value from 4

to 8.

A restoration that has too high a

Value (is too bright) may be readily

detected by an observer and is a

common esthetic fault in metal-

ceramic prosthodontics.

Location of a particular shade in the color space is defined by 3 co-ordinants.

Munsell colour order system → Value, Hue, and Chroma

CIELAB colour order systems→ L*, a*, and b*. L*. This is a lightness variable proportional to Value

in the Munsell system. Represent the lightness, brightness or black/white character of the color. It describes the achromatic characteristics of the colour.

a* and b*. These coordinates describe the chromatic characteristics of the colour.

Although they do not correlate directly with Munsell’sHue and Chroma.

The a* coordinate

corresponds to the red-

purple/blue-green axis in

the Munsell color space.

+ve a* relates to a

predominantly red-purple

color.

-ve a*denotes a color

that is more blue-green.

b*coordinate

corresponds to the yellow-

purple/blue axis.

By Observers eye using

commercially available

shade guides.

Light strikes the retina of

the eye.

The rods → detect the

value while

The cones →detect the

hue and the chroma.

QuantitativelyVisually

Quantitatively using

colour measuring

instruments

e.g.

Spectrophotometer

& colorimeter.

1. Teeth → polished and moist

2. Time → At the beginning of the visit

3. Position Patient sitting in an upright position

4. From a distance of 3-6 feet

5. Operator standing between patient and light source

6. Removal of bright clothes and lipstick

7. Light grey walls of the office

8. Looking at the cervical region

9. Any surface characteristics must be recorded

10. Under different lightening conditions

11. Taking another opinion

Commercial shade guides:

The most convenient method for selecting a shade is to use one of the modern commercially available porcelain shade guides.

Each shade tab has an opaque backing colourand a neck colour, body colour, and incisalcolor.

Shade selection consists of picking the shade tab that looks the most natural and having this reproduced in a laboratory with the help of the materials and techniques recommended by the manufacturer.

There are 3 types of Shade guides

Hue – Chromashade guide

• The most widely used of which is Vita Lumen Vacuum.

• Which include 15 shades.

• Enables selection of an approximate color shade.

Mass shade guide

• e.g. Chromascop, Ivoclar.

• Gives greater accuracy, since they are more complete.

• They enable more accurate measurement of hue, value, chromaover all areas of the tooth to be copied

Vitapan 3D Master

• Concept is based on the 3D systematic and logical organizations of tooth colors.

• Allows more accurate shade selection.

• Cover the entire color spectrum of natural teeth and in the same time consume the 3 color parameters.

• Value is determined first followed by the chromaand finally the hue.

Hue selection:

� Choose the nearest hue first.

� Then select the appropriate match of chroma

and value from the tabs available.

� It may be difficult to determine a given hue

accurately if its chroma or intensity is low.

� Therefore the region with the highest chroma

(i.e.. the cervical region of canines) should be

used for initial hue selection.

Shade selection using Hue-Chroma shade guide:

Chroma selection:

� Once the hue selection has been

accomplished, a choice is made of the

best match of chroma.

� Between comparisons, glancing at a blue

object will rest the operator's eye and

helps to avoid eye fatigue.

Value selection:

Finally, value determination is made with another commercial guide.

Observation from a distance.

Standing slightly away from the chair.

Looking through squinted eyes will help in assessing the value.

Squinting → ↓ the amount of light that reaches the retina→ ↓Stimulation of the cones + ↑ sensitivity of rods to achromatic conditions.

While squinting, the observer concentrates on which disappears from sight first, the tooth or the shade tab;

The one that fades first has the lower value.

When the proper selection of value has been made, it will be the exception rather than the rule for this to coincide with the determinations for hue and chroma.

A decision must be made whether it is necessary to change the previously selected shade sample.

If the independent value determination is < than the value of the sample selected for hue and chroma, a change is necessary because it is not possible to increase the value of an object by adding surface stain (which always reduces brightness).

If the value determination is>than the hue determination, it should be decided whether this difference can be bridged through internal or surface staining of the restoration.

� The determinations of hue and chroma as

well as of value are then communicated to

the laboratory.

It is used when a fairly good match is obtainable from the commercial

shade sample. The tooth is divided into 3 regions, cervical, middle and incisal . Each

region is matched independently.

Spectrophotometers measure light reflectance (at wavelength

intervals)over the visible spectrum, and

Colorimeters:

Provide direct color coordinate

specifications without mathematical

manipulation.

These instruments have been used

extensively in dental research.

A recent introduced spectrophotometer is

capable of accurately measuring color

within small areas (1x2 mm) of a tooth.

The measurement repeatability for opaque

and translucent porcelain samples

indicated a good color accuracy.

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