6- Colour

What 3 main factors condition colour? What is colour?

Light, object, observant

Light strikes an object and will absorb a certain wavelengths and reflect other

What wavelength range roughly represents visible light from blue to red? What range is visible to eye?

About 400 nm (blue/UV side) to 700 nm (red/infrared side)

360-720nm

What is reflection?

Light aiming on non-transparent surface and changes direction

What artificial light sources should be avoided vs used?

Incandescent- alter chromatic appreciation

Fluorescent or LED better- provides ideal observation conditions

What is refraction? What does it depend on? (2)

Some light is reflected, the rest passes through the object and changes direction

Depends on density of the object and wavelength of incident light

What is translucency, how does it apply to teeth?

Gradient between transparent and opaque

Increased translucency of crown, lowers value- less light returns to eye

What does the translucency of enamel depend on?(5)

Angle of incidence

Surface texture

Luster (gloss/shine)

Wavelength

Level of dehydration

What is fluorescence? Where does it occur in the tooth and why?

Ability to absorb light energy and then emit (give off) light at a longer wavelength

Occurs mainly in dentin due to more organic material

The more dentin fluoresces, lower the chroma

Fluorescent powders added to crowns to increases amount of light returned- blocks discolourations and decreases chroma

What is opalescence? In enamel…

Material appears to be one colour when light reflected from it, another when light transmitted through it- transilluminates reds and scatters blue within- so appears blueish

Enamel opalescent effects brighten tooth- give optical depth and vitality

What is phosphorescence?

Duration of light emission lasts after stimuli removed

What is metamerism? How to avoid this issue?

Different colour according to light source- two colours look the same under one light source but look different under another light source

By selecting shade in diff conditions- daylight and fluorescent

How does the observant perceive colour? When staring at a colour for a while what happens and how can you avoid?

Cones in the macula interpret colour

Rods in periphery interpret brightness or luminosity

When staring at colour for a while- ability to perceive tone decreases (adaptation)- negative persisting image- AFTERIMAGE

avoid by looking a blue cardboard for 5 secs

Hue, value, chroma

Colour tone- how we distinguish groups of colours

Relative lightness/darkness- max value (white) vs min (black)- middle 1/3> cervical > incisal

Saturation- canine most saturated, determined by dentin

What 2 groups are the colours of the visible spectrum classified into?

Primary- blue, yellow, red

Secondary- violet, orange

Tooth colour in dentin goes from- yellow, reddish yellow, orange

What objective methods can be used to select shade?

Spectrophotometer

Colorimeter

What factors may influence subjective methods to select shade?

Clinic

Patient- opinion, wet and clean teeth, eliminate distractors (glasses)

Observer- must be between patient and light source, at beginning of visit, try many times, quick observations

What are 4 limitations of shade/colour guides?

It does not cover the entire scale of natural teeth

The order of colours does not follow logical arrangement

The materials are different from the ceramic powders

Porcelain from the guides are thicker than the crown

What’s the 4 colour technique? (vitapan classic)

Lumin-VACUUM guide from VITA CLASSIC

Guide ordered by hue, saturation and luminosity

4 colours- saturation 1-4

A-D- hue

A- yellow-orange- young, CI, LI

B- yellow- middle age

C- yellow- gray- mature

D- red-gray

Use diff guide for luminosity

How is VITAPAN 3D master ordered?

Value (1 most white - 5), chroma (1 least saturated - 3), hue

(More accurate)

1. Determine correct lightness 0-5

2. Select chroma

3. Select hue- on L yellow- on R reddish

Comparison between VITA classical and 3d master

When should you select the shade?(5)

Before anaesthesia and tooth prep

Natural light between 10am and 2pm

Look for 5 secs at a time

Eyes narrow

Orient on central 1/3

What’s the order you should determine shade select procedure? What to consider?

Brightness, saturation, hue

Close eyes a little and determine luminosity

Consider texture , natural light, orient on central 1/3