The Nature Of Color - Dental Tribune International (Page 2 of 4) in pdf

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Describing Color

the “norm color system”. Red

Color can be described in at

components of a color are tailed

least three different ways:

along the X- (horizontal) axis and

• Spectrophotometry describes

green components along the

the physical characteristics of

Y- (vertical) axis. Every color is

a color (eg, the spectral re-

assigned a particular point and

flectance of a surface at differ-

the spectral purity of colors de-

ent wavelengths).

creases as you move left along

• Colorimetry describes what a

the coordinate plane. What is not

color matches with.

taken into consideration in this

• The Munsell system describes

model is brightness.

what the color looks like.

CIE L*A*B *

The Munsell Color System

A three-dimensional model

Figs. 9 & 10: Color temperature illustrating high temperature blue and low temperature red.

This system was proposed

with the color differences per-

by the American AH Munsell in

ceived corresponding to dis-

1905 and revised in 1943. The

tances when measured calori-

system defines three attributes

metrically. The a-axis extends

of color: H (hue), C (chroma), and

from green (-a) to red (+a); b axis

V (value). Color matching in den-

from blue (-b) to yellow (+b).

tistry is based on this system.

Brightness (I) increases from the

Munsell established numerical

bottom to top (Figure 14).

scales with visually uniform

Chromatic &

steps for each of these attributes.

Achromatic colors

Hue is that attribute of a color

by which we distinguish red from

Achromatic colors are white,

green, blue from yellow etc.

black and grey in between. They

Munsell called red, yellow,

lack the attributes of hue and

green, blue and purple principal

saturation. Chromatic colors are

hues and placed them at equal

everything that we perceive as

Fig. 11:Value scale and chart graduated from 0 to 10. A black or low value is represented by 0. 10 represents a white or high

value with the mid-tones being grey.

intervals around a circle. He in-

having “color”; everything other

Fig. 12: Chromatic scale, extending from weakly saturated on the left to densely saturated chroma on the right.

serted five intermediate hues:

than white, black or grey.

Color of the Natural Tooth

• Yellow-red

• Green-yellow

In describing the color of a

• Blue-green

natural tooth we find there are

• Purple-blue

two additional attributes. In ad-

• Red-purple

dition to hue, chroma and value,

we discover the attributes of

This makes ten hues in all.

opalescence and fluorescence.

The definitions of the first three

Value indicates the lightness

attributes are identical to those

of a color. The scale of value

defined by Munsell, but each can

ranges from 0 for pure black to 10

be qualified further:

for pure white. Black, white and

Hue: The primary source of

the greys between them are called

color is dentine and the hue of

neutral colors. They have no hue.

a vital, healthy tooth is in the

Colors that have a hue are called

yellow to yellow-red range

chromatic colors (Figure 11).

Chroma: In natural teeth the

Chroma is the degree of

chroma is dictated primarily by

Fig. 13: Munsell Color Space. Vertical axis represents value extending from black on the bottom to white on top, with grey

departure of a color from the

dentine but is influenced by the

in the middle. The color wheel arranged around the axis represents the hues and chroma increases outwards and perpen-

neutral color of the same value.

translucency and thickness of

dicular to the vertical axis. Thus, hue, chroma and value can be observed at various combinations.

Colors of low chroma are some-

enamel. The thinner the enamel,

Fig. 14: CIE L*A*B scale. Lightness is calculated on the vertical or L scale und huelchroma along the ab axis.

times called weak, while those

the less the effect on the chroma.

This gives rise to the three pri-

opposite to each other. Each color

of high chroma are said to be

Thus, in the cervical area, with its

page 8

mary colors:

has a complementary or opposite

highly saturated, strong or vivid

thin enamel, the chroma appears

qualities are utilized in infrared

hue, so that on the color wheel we

(Figure 12).

densely saturated. The thicker

lamps. Beyond this are electro-

• 400–500 nm = blue

have three complementary pairs.

the enamel, the more the chroma

Munsell Color Space

magnetic rays with increasing

• 500–600 nm = green

Just as positive and negative

is masked giving rise to a diffuse

wavelengths and decreasing fre-

• 600–700 nm = red

magnets attract each other, com-

Hue, value and chroma can

chromatic appearance.

quencies; these include radio

plementary colors also attract.

be varied independently and the

Value: In natural teeth this

waves.

All colors encountered in na-

Figure 8 graphically shows the

colors can be arranged in a three-

is primarily influenced by the

Human color recognition de-

ture can be reproduced by com-

relationship between the three

dimensional space. The neutral

quality and thickness of enamel.

pends upon light, objects that re-

bining light of these three wave-

primary colors of red, green and

colors are arranged in the verti-

The thicker the enamel, the

flect light and the viewer’s eyes

lengths in varying intensities:

blue and the three primary lights

cal line called the neutral axis.

greater the optical effects result-

and brain. The color of a self-lu-

of cyan, magenta and yellow.

Black is at the bottom, white at

ing in a higher value. Thick,

minous object is called self-lumi-

• 100%= white light

the top and all greys are in be-

dense, opaque dentine has the

Color Temperature

nous color and can be natural or

•

0% = black

tween. Hues are displayed at var-

effect of lowering the enamel

artificial. The color of an illumi-

• 50% = grey (Figure 7)

Color is intimately related

ious angles around the neutral

value (Figures 15, 16 & 17).

nated object is called object color

to temperature. Color T

is ex-

axis and chroma arranged per-

Opalescene: In a natural

The Color Wheel &

and can arise from reflected or

pressed in Kelvins. The higher

pendicular to the axis increasing

tooth, this is an effect produced in

Complementary Colors

scattered light. The energy car-

the color T

, the closer to blue

outward (Figure 13).

enamel and is due to different re-

ried by waves (which are approx-

If we arrange all these col-

the color is; the lower the color

fractory indices of the various or-

CIE XYZ

imately 400–700 nm) stimulates

ors around a circle we have a color

, the closer the color is to red.

ganic and inorganic components

the receptors in the human

wheel. Looking at the color wheel

The sun at noon is 5.000 Kelvin

In 1931 the CIE developed

of enamel as well as the ability

retina, producing color stimuli.

we can see that certain colors fall

(Figures 9 & 10).

the XYZ color system, also called

of hydroxyapatite crystal to scat-

ter incident light. The result is

that the long wavelengths are

transmitted through the tooth

whilst the short wavelengths are

reflected, producing a bluish

gleam. The effects vary from blue

to grey to white gleaming areas

(Figure 18).

Fluorescence: This effect oc-

curs when a body absorbs lumi-

nous energy and then diffuses

it back to the visible spectrum.

In nature this is caused by ul-

traviolet light striking pigments

in the dentine enamel interface

resulting in light emission rang-

ing from intense white to light

blue.

Figs. 15, 16 & 17:Variations in value in natural teeth. Low value giving a grey appearance, mid-value giving a cream appearance and high value giving a white appearance.

The Nature Of Color - Dental Tribune International Page 2

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