Quiz 3-physical Properties Flashcards
incident light
reflected, absorbed, or transmitted
opacity of dentin and enamel
dentin is more opaque
translucency
diffused transmission of light; light is dispersed (not transmitted)
opaque
no passage; scattering within may happen
refraction
light changes direction in a second medium
seeing color
- source emits light onto
- object
- color that we see is reflected off to the observer
3 indices of color
Hue, Value, and chroma
Hue
The dominant color of the object (red,yellow, or blue)
Hue of teeth
yellow to yellow-red
value
the lightness or darkness of a color (0 is black and 10 is white) teeth=6-8
Value of natural teeth
6-8
Chroma
the intensity of a color; is the object rich in color or pale?
0=achromatic and 18=saturated
teeth are weak
Color Content
different light sources have different wavelength components
better a light source matches standard
higher ranking
color rendition index
a measure of how well a light source renders color compared to standard (N daylight)
light source for color matching
> 90 CRI
Intensity
low level light and high level cause loss of color
ideal intensity is
1500-2500 lux
surroundings
modify the type of light reaching the object
Gloss
object; how much light is reflected off the object (moisture, roughness)
Individual response
normal people see different colors
color vision
5% of men and .5% of women have color deficiencies
receptor fatigue
causes a complementary color to be seen (red square, see blue square left behind)
munsell system
plots 3 values of color on a scale; compare to color tabs
Spectrophotometer
measures wavelength intensity reflected or transmitted
Colorimeter-CIE
Commission international de l’eclarage; international org concerned with light and color
L in LaB
L= luminance from 0-100
A and b in LaB
Red=+a and green -a
+b=yellow and -b = blue
Can give C lab coordinates
colorimeters and specs
Dental shade guide tabs
organized sequence of models
metamerism
when two objects appear to match under one light but not under another-metamers
Fluorescence
the object emits light when illuminated by a specific light source; in real teeth so necessary in restorations
Thermoconductivity
Quantity of heat in C/S passing through a body of 1cm thick with a cross-section of 1cm squared when temp diff is 1 C (conductors have high values)
Thermal diffusivity
rate at which body with a nonuniform temp approaches equilibrium
liner
layer of cement lining a filling/crown to prevent direct heat transfer to patient
coefficient of thermal expansion (CTE)
change in length over original length x the change in temp
dental importance of CTE
change in temp causing a change in shape of restoration
electrical conductivity and restivity
measure of ability to conduct electric current
dentin vs enamel conductor
dentin better for electricity
carious teeth as conductors
less conductive
Corrosion
deteriation by chemical or electrochemical rxn
stimulants of corrosion
wet, salt, acids, warm, stress
Anode
needed for corrosion; the surface where the corrosion occurs
Cathode
needed for corrosion; where reduction rxns take place
Electrolyte
needed for corrosion; a solution that conducts electricity-supplies the ions
electromotive series
based on thermodynamics, ranking of relative corrosion resistance in metals; ideal in water and practical in Cl solns
passivity
certain metals; limit corrosion, protects the metal or alloy from corrosion
Electromotive series
resistance to corrosion
uniform attack
corrosion all over
Crevice Corrosion
i.e. oxygen depletion; results in specific areas of corrosion (think food on a restoration)
Galvanic Corrsosion
when two metals are in physical contact (touching or soln between them) -Gold crown and amalgam in mouth; less noble (amalgam) will corrode and release ions
Noble
higher (gold); protected from corrosion
Anotic/Active
Low (mercury, silver, copper) will corrode and release ions
Dental importance of corrosion
- Harm
a. think mercury-do not want released
Allergens-nickel released
palladium allergen too - esthetics compromised
tarnish
surface discoloration which can be linked to corrosion
other objects that tarnish
polymer materials
