Shade Selection Flashcards
Define colour
A sensation induced in the eye by electromagnetic waves of a certain frequency
How bu are visible rays?
380nm-780nm
What is needed to create colour?
- Light source
- Sample or object to interact with the light source
- Light sensor and image processor
In the context of dentistry what do we need to create colour?
- Illuminant (dental light)
- Object (patients teeth)
- Observer (dentist)
What happens when light strikes an object
The light can be REFLECTED and/or ABSORBED and/or TRANSMITTED
Describe how and when light is reflected
If a light beam strikes an opaque block if the surface is smooth and specular (mirror like) and the angle of incident is equal to the angle of reflection then light is reflected
What happens if light hits an opaque block that has a rough surface?
Then the reflected light diffuses and is scattered from the surface
Are natural teeth fully opaque
No they are also translucent
What happens if light hits a translucent block?
Some of the light that is not reflected may be transmitted
Some of this transmitted light may be absorbed, diffracted or re emitted
What determines the colour fo an object?
The extent of reflection and/or absorption and/or transmission of white light in the object
Define light source
A physical emitter of light eg candle, lamp, the sun
Define illuminant
Standard light source defined by its specific spectral power distribution
Name the most important light source we can use
Day light
What is day light
Sunlight and skylight
What is the problem with using daylight to shade selection
Daylight varies considerably through out the day
Name the illuminant that is closest to sunlight in terms of spectral power distribution
D65 fluorescent tubes
Name some common fluorescent lamps
- Artificial daylight
- Natural de luxe
- TL84
- Warm white de luxe
- Warm white
What is the minimum colour rendering index we need to be able to shade match effectively
At least 90
Name the 3 fluorescent lamps that have a colour rendering index over 90
- Artificial daylight
- Natural de luxe
- TL84
What problems does the brain have to correct when a visual signal is sent from the retinas
Has to fix the fact that:
- The image in inverted
- The image has chromatic and spherical aberration
- There are 2 gaps in the image felid arising from the blind spot of each eye
Name the 2 cells in our eyes that aid us in forming an image
Cones and rods
What are rod cells sensitive to
Low light levels
Describe scotopic vision
- When light level are low
- Only rod cells are sensitive
- Provides a monochromatic or light/dark perception
- Full sensitivity is achieved after 30 mins
How long does it take for rod cells to reach full sensitivity
30 mins
What are cone cells sensitive to?
Medium to high levels of light
Describe photopic vision
- When light levels are medium to high
- Only cone cells are sensitive
- Provides full colour vision
How long does it take for cones to become stable and give an accurate image
Several minutes are requires
How does the eye deal with initial over stimulation of cone cells
The response of the eye changes over time due to the chromatic adaption effect
What is the chromatic adaption effect
The fact that the sensitivity of a highly stimulated cone decreases over a period of time
This means it requires several minutes for a response to become stable
Name the shade guide we use on clinics
Vita shade guide
Using the vita shade guide which is the lightest shade and which is the darkest
Lightest: B1
Darkest: C4
What is the trend in the A groups in a vita shade guide
The A groups are the brown shades
They increase in chroma from A1 to A4
What is the trend in the B groups in a vita shade guide
The B groups are the yellow shades
They increase in yellow chroma from B1 to B4
What is the trend in the C groups in a vita shade guide
The C groups are the grey shades
They increase in grey chroma from C1 to C4
What is the trend in the D groups in a vita shade guide
The D groups are the reddish shades
They increase in yellow chroma from D2 to D4
What is the vita shade guide usually used to colour match?
Crowns
What is used to shade guide composites
Denstply shade guide
What do yo need to take into account when selecting a shade?
- Retinal fatigue
- We have poor colour memory
- Simultaneous contrast effects
- Colour vision defects
What is retinal fatigue
Our eyes can become tired and when they doit can be very hard to distinguish colours
How can we overcome retinal fatigue
Try and look at something blue or grey before colour matching (eg dental bib)
What is Simultaneous contrast effects
The fact that are ours are influenced by the colours around us and this can change the way we see the same colour in different areas
Who is more likely to suffer from colour blindness men or women
Men
How many men and women suffer from red green colour blindness
1 in 13 men
1 in 300 women
Name some new machines that have been invented to aid us with shade selection
- Colourometre
- Specticleometre
- IKam
How does the Colourometre work
It is placed on the tooth and records the amount of green red and blue in the tooth
It then uses this data and gives us a corresponding vita shade guide colour for the tooth
What are the drawbacks of the Colourometre
The tooth isn’t a uniform shade and the Colourometre doesn’t account for multiple shades in the tooth
How does the Specticleometre work
It takes an image of the teeth you want to work on
This image can then be built up and analysed on a computer to see the various colours of the tooth
How does the IKam system work
2 images of the patients dentition is recorded under a colour corrected light source (d65 tube): one image is a gloss image and the other is a cross polymerised image
Describe the gloss image taken using an IKam system
It used by the technician to assess the morphology of the tooth and how the crown will sit in the mouth
Describe the cross polymerised image taken using an IKam system
It is a colour corrected image that has all the reflections taken out so that you can see the colour of the teeth properly
Vision in low lights is termed?
scotopic vision
Vision in medium to high light is termed?
photopic vision
