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32 Cards in this Set
- Front
- Back
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Thermal Properties:
Heat conduction(metals vs. ceramics, polymers) |
Metals>polymers/ceramics
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Thermal Conductivity:
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Rate of heat flow per unit temp. gradient for a given time
unit: cal/sec/C/cm Amount of heat which passes through a certain material at a given time/distance/area |
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Specfific Heat:
table |
cal/g/c
Table! |
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Thermal Diffusivity
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Time rate of temp change at 1 point due to heat source at another point
thermal conductivity(K)/ Specific Heat(Cp) x p(density) Time it takes to change the temperature of a given material |
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Thermal diffusivity Table
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memorize?
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Thermal Expansion: Coefficient
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Change in length/ initial length x change in time
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Thermal Expansion application? percolation?
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TE of restorative material doesn't match tooth-->leakage of oral fluids(Percolation)
Percolation decreases with time as space filled with corrosion products |
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Coefficient thermal expansion table
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memorize?
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Optical Properties
Definition? Color? |
Reflectance of light from object reaching photodetector of eye
Color: light source Object Observer |
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Color Visible light chart
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Purple 400-blue 500-yellow 600, orange/red-700
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Color Sensitivity
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extremes less(blue,purple), most sensitive: green/yellow(550)
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Color Variables
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1 Hue(dominant color)
2. Chroma:(strength of hue 3. Value: Brightness or darkness of object |
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Munsell Color system
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1. Letter/number combo
2. Poor stability 3. Inconenient 4. range of tooth shades only small portion |
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VITA Shade
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Widely used
Hue: A(red-brown) B(red-yellow), C(grey), D(reddish-grey) Value:light-darker chromas: intensity(A1-A4) |
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Influence of Light
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Metamerism
Fluoresecense |
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Metamerism
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Different colors under different light sources
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Fluorescene
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Tooth enamel absorbs at 300-400nm, releases at 400-450nm
Brightness/vital appearance of human tooth |
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Translucency
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ability of light to travel through material(Dentin opaque, enamel transparent/lucent)
difference absorption/scattering = differ opacity |
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Surface Texture
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Smooth= shiny
Rough= matte |
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Mechanical Properties
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Applied load = stresses/strains
Must be greater than max value to prevent fracture |
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Stress formula
types? |
Applied Force/Cross sectional area
Force: axial: elongation/shrink Shear: Shear Twisting: torsion Bending: bending |
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Strain formula
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change in length/intial length
Poissons dental material table? |
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Stress-Strain Curves
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apply forces and determine value of stress/strain
slope during linear= elastic modulus(stress/strain(alpha/e)) elastic modulus table |
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Stress-Strain Curves:
Proportional Limit/Yield Strength/Ultimate Strength(tensile/compressive) |
PL=max stress at which stress is proportional to strain, above plastic deformation
YS: stress at which material strain changes from elastic deformation to plastic deformation(perm) Ultimate strength: stress at which fracture occurs. Tensile: fracture from tensile stress Compressive: fracture from compression See graph, PL =end of linear portion, Y.S. = variable |
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Resilience
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Amout of energy that a material can absorb without undergoing any permanent deformation(Area under linear elastic portion)
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Toughness
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Total amount of energy b4 fracture
area under entier SS curve |
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Tarnish
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surface discoloration via formation of deposits
easily removed |
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Corrosion
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Chemical rxn b/w material and environment
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Electrochemical Corrsion
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Anode: Oxidation
Cathoide: Reduction Electrolyte: supply ions needed at cathode, takes away corrsion products at anode high electrode potential = noble cathode low= active anodic |
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Galvanic Corrosion
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Combinations of dissimilar metals in direct contact.
difference in potential = galvanic current less noble material corrodes/loses ions to more noble(cathode) |
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galvanic shock in dentistry
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dental amalgam+gold inlay
Silver force+gold inlay Aluminum foil +gold inlay Electrolyte= saliva/tissue fluids |
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Crevice Corrsion
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Pits of restoration covered with food.
Base= anode Surface = cathode POLISH |
