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3rd Yr- CSB- Extra-coronal restorations > Shade Selection > Flashcards

Shade Selection Flashcards

1
Q

Define colour

A

A sensation induced in the eye by electromagnetic waves of a certain frequency

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2
Q

How bu are visible rays?

A

380nm-780nm

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3
Q

What is needed to create colour?

A
  1. Light source
  2. Sample or object to interact with the light source
  3. Light sensor and image processor
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4
Q

In the context of dentistry what do we need to create colour?

A
  1. Illuminant (dental light)
  2. Object (patients teeth)
  3. Observer (dentist)
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5
Q

What happens when light strikes an object

A

The light can be REFLECTED and/or ABSORBED and/or TRANSMITTED

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6
Q

Describe how and when light is reflected

A

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

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7
Q

What happens if light hits an opaque block that has a rough surface?

A

Then the reflected light diffuses and is scattered from the surface

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8
Q

Are natural teeth fully opaque

A

No they are also translucent

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9
Q

What happens if light hits a translucent block?

A

Some of the light that is not reflected may be transmitted

Some of this transmitted light may be absorbed, diffracted or re emitted

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10
Q

What determines the colour fo an object?

A

The extent of reflection and/or absorption and/or transmission of white light in the object

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11
Q

Define light source

A

A physical emitter of light eg candle, lamp, the sun

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12
Q

Define illuminant

A

Standard light source defined by its specific spectral power distribution

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13
Q

Name the most important light source we can use

A

Day light

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14
Q

What is day light

A

Sunlight and skylight

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15
Q

What is the problem with using daylight to shade selection

A

Daylight varies considerably through out the day

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16
Q

Name the illuminant that is closest to sunlight in terms of spectral power distribution

A

D65 fluorescent tubes

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17
Q

Name some common fluorescent lamps

A
  1. Artificial daylight
  2. Natural de luxe
  3. TL84
  4. Warm white de luxe
  5. Warm white
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18
Q

What is the minimum colour rendering index we need to be able to shade match effectively

A

At least 90

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19
Q

Name the 3 fluorescent lamps that have a colour rendering index over 90

A
  1. Artificial daylight
  2. Natural de luxe
  3. TL84
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20
Q

What problems does the brain have to correct when a visual signal is sent from the retinas

A

Has to fix the fact that:

  1. The image in inverted
  2. The image has chromatic and spherical aberration
  3. There are 2 gaps in the image felid arising from the blind spot of each eye
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21
Q

Name the 2 cells in our eyes that aid us in forming an image

A

Cones and rods

22
Q

What are rod cells sensitive to

A

Low light levels

23
Q

Describe scotopic vision

A
  1. When light level are low
  2. Only rod cells are sensitive
  3. Provides a monochromatic or light/dark perception
  4. Full sensitivity is achieved after 30 mins
24
Q

How long does it take for rod cells to reach full sensitivity

A

30 mins

25
Q

What are cone cells sensitive to?

A

Medium to high levels of light

26
Q

Describe photopic vision

A
  1. When light levels are medium to high
  2. Only cone cells are sensitive
  3. Provides full colour vision
27
Q

How long does it take for cones to become stable and give an accurate image

A

Several minutes are requires

28
Q

How does the eye deal with initial over stimulation of cone cells

A

The response of the eye changes over time due to the chromatic adaption effect

29
Q

What is the chromatic adaption effect

A

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

30
Q

Name the shade guide we use on clinics

A

Vita shade guide

31
Q

Using the vita shade guide which is the lightest shade and which is the darkest

A

Lightest: B1
Darkest: C4

32
Q

What is the trend in the A groups in a vita shade guide

A

The A groups are the brown shades

They increase in chroma from A1 to A4

33
Q

What is the trend in the B groups in a vita shade guide

A

The B groups are the yellow shades

They increase in yellow chroma from B1 to B4

34
Q

What is the trend in the C groups in a vita shade guide

A

The C groups are the grey shades

They increase in grey chroma from C1 to C4

35
Q

What is the trend in the D groups in a vita shade guide

A

The D groups are the reddish shades

They increase in yellow chroma from D2 to D4

36
Q

What is the vita shade guide usually used to colour match?

A

Crowns

37
Q

What is used to shade guide composites

A

Denstply shade guide

38
Q

What do yo need to take into account when selecting a shade?

A
  1. Retinal fatigue
  2. We have poor colour memory
  3. Simultaneous contrast effects
  4. Colour vision defects
39
Q

What is retinal fatigue

A

Our eyes can become tired and when they doit can be very hard to distinguish colours

40
Q

How can we overcome retinal fatigue

A

Try and look at something blue or grey before colour matching (eg dental bib)

41
Q

What is Simultaneous contrast effects

A

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

42
Q

Who is more likely to suffer from colour blindness men or women

A

Men

43
Q

How many men and women suffer from red green colour blindness

A

1 in 13 men

1 in 300 women

44
Q

Name some new machines that have been invented to aid us with shade selection

A
  1. Colourometre
  2. Specticleometre
  3. IKam
45
Q

How does the Colourometre work

A

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

46
Q

What are the drawbacks of the Colourometre

A

The tooth isn’t a uniform shade and the Colourometre doesn’t account for multiple shades in the tooth

47
Q

How does the Specticleometre work

A

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

48
Q

How does the IKam system work

A

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

49
Q

Describe the gloss image taken using an IKam system

A

It used by the technician to assess the morphology of the tooth and how the crown will sit in the mouth

50
Q

Describe the cross polymerised image taken using an IKam system

A

It is a colour corrected image that has all the reflections taken out so that you can see the colour of the teeth properly

51
Q

Vision in low lights is termed?

A

scotopic vision

52
Q

Vision in medium to high light is termed?

A

photopic vision

3rd Yr- CSB- Extra-coronal restorations (11 decks)

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