shade selection Flashcards
what is the definition of colour
a sensation of light induced in the eye by EM waves of certain frequency
what is the frequency of colour
380-780nm
what is needed to make colour
- Sample
- Light source
Light sensor + image projector
- Light source
what do we need in the context of dentistry to make light
- Object
- Illuminant
Observer
- Illuminant
what can happen to light when it strikes an object
reflected
absorbed
transmitted
when does the angle of incidence and the angle of reflection equal
if the surface is smooth
what is seen if the angle of incidence and the angle of reflection is the same
specular reflection
what can happen if the surface is slightly rough
diffusion of light
what do natural teeth show when they are wet
specular reflection
what type of light shall we use to correctly shade match
clinic light as natural daylight changes in the day
what are the two types of vision
scotopic vision
photopic vision
what is scotopic vision
Only rod cells are sensitive at low light levels
Light/dark perception / monochromatic
Full sensitivity after 30 mins
what is photopic vision
Cone cells sensitive
Full colour range
how does chromatic adaption occur
Caused by the response of the eye changing with time
Several minutes are required for the cone cells to become stable
what shade guide to dentists use
VITA shade guide
how is the vita shade guide used
Which is split into 4 groups: A - brown shades A1-->A4 increasing the depth of colour B - yellow group C - grey group D - reddish hue
how do dentists use the shade guide
1, first decide what group the tooth is in
2. then check with the other teeth
be mindful of retinal fatigue
what is retinal fatigue
hard to identify colours after a while so we can fix this by looking at a neutral colour for a little while eg blue beds
what are the disadvantages of the vita shade guide
The tooth doesn’t have a uniform colour from the cervical to the incisal edge
So not the perfect solution
what equipment can we use to get a more accurate colour guide
Spectrophotometer
Enabled an image to be built up
And a weather map can be build up of different colours
