FIXED PROS - Shade Selection Flashcards
why is shade selection important?
aesthetics
- satisfies the patient and dentist
what are the 3 variables describing how light is perceived to be reflected from the tooth surface?
hue
value
chroma
what is the hue?
describing the most dominant shade of the tooth
A = red-yellow
B = yellow
C = grey
D = red-yellow-grey
what is the chroma?
the saturation of the colour
= the intensity of the hue
what is the value?
the lightness or darkness of the shade
what are the limitations of the shade guide?
- colours differ for each company
- guide is not universal for all restorations
- must use the same shade guide used by the lab - for crowns, dentures
what 3 factors influence the shade decision?
the object
the observer
illumination
how can the object influence shade decision?
the light can be reflected, absorbed or transmitted through/off the object
what is the reflection called if the object surface is smooth? what’s the equation?
specular
angle of incidence = angle of reflection
what is diffusion?
when the surface is rough and reflected light is scattered
what is the illumination?
the standard light source defined by its specific spectral power distribution
what is the most important light source to use?
daylight = sunlight+skylight
what characteristics does the image have from the brain POV? (4)
- invertion
- spherical aberration - shape can be different
- chromatic aberration - lens has to separate the colours
- blind spots = gaps in the image field
describe vision in low light.
- rod cells are activated
= scotopic vision
what are rod cells responsible for?
providing a monochromatic perception
- good vision in low light
in low light, when is full sensitivity achieved?
after 30 mins
describe vision in high light levels.
- cone cells are activated
= photopic vision
role of cone cells.
provide full colour vision
what time of day is ideal for shade selection and matching? why?
- morning or start of appointment
- because eye fatigue is minimal
what is the ideal distance from the oral cavity for shade matching?
61-183cm
from 2-6 feet
what level should the patient be sat at for shade matching?
same level as operators eyes
what lighting is best for shade selection?
mid-day light
what things from the environment should be avoided in order to choose shade selection?
- bright-coloured surroundings
= if the patient has bright clothing, use a mask - no lipstick
- surfaces with high gloss disturbs the glare
what colour background is ideal?
grey
what should be the condition of the teeth for shade selection?
- tooth and adjacent should be free of plaque, other deposits, stains
- moist tooth, dehydration makes the tooth whiter
