2. Physical Properties of Dental Materials Flashcards
(41 cards)
Physical Properties of Dental Materials
____ Properties
____ Properties
____ Properties
Thermal
Rheologic
Optical
Physical Properties
Properties of a material based on ____ laws
How materials respond to changes in their ____
Laws of mechanics, optics, thermodynamics, electricity, magnetism, radiation etc.
physical
environments
Thermal Properties
thermal ____
thermal ____
thermal ____
conductivity
diffusivity
expansions
Thermal Conductivity
The ease with which heat is ____ through a material
— ____ Vibrations, Motion of electrons
Heat passing through a body, 1cm thick and 1cm2 cross-section per second when the temp. diff. is 1oC
Units: ____ (W.m-1.K-1)
transferred
lattice
cal/cm.sec.celsius
Thermal Conductivity
____ are better heat conductors than ____
Large metallic restorations require an ____ to protect the pulp
Heat flows from ____ temp points to ____ temp points
metals non-metals insulating cement base high low
Relative Values of Thermal Conductivity
Metallic materials have higher ____ than non-metallic materials
Cover the base of preparations with non-metallic materials (____) before you place the metallic restoration above it
thermal conductivities
zinc oxide
Thermal Diffusivity (h)
The ____ at which the temp. of a body changes as heat passes through it
The transfer of heat from a hot to a cold source depends on both ____ and ____ and ____.
kappa = Conductivity (cm2/s) ; Cp= Heat capacity (cal/g.C); p = Density (g/cm3)
____ doesn’t take into account the specific heat and density; thermal diffusivity does take it into account
rate thermal conductivity density specific heat thermal conductivity
Specific heat (Cp)
- Quantity of heat to raise the temp of a unit volume of a material by \_\_\_\_ degree C - Units: \_\_\_\_
1
cal/gm^-1 oC
Relative Values of Diffusivity
Metallic materials are highly ____; and non-metallic materials are ____ (low conducting)
conducting
insulating
Considerations for Insulation
Lining efficiency is proportional to the ____, divided by the square root of the ____
____ based is desired when placing restorations
thickness of insulating material
thermal diffusivity
highly thick
Coefficient of Thermal Expansion
Change in ____ per unit of the original length (of an object) when its temperature is raised 1 oC.
The coefficient (alpha) increases with ____
length
temperature
Thermal Expansion
Clinical Consequences
- ____ around restorations
- Shrinkage of ____
- Differential shrinkage of ____
Filling material with high thermal expansion; if patients eats cold ice, the filling will ____ and the margins will be eliminated resulting in leakage
Two materials of PFM crowns expand and contract to ____, must be wary of fractures
leakage wax patterns PFM crowns shrink different degrees
Relative Values of Coefficient of Thermal Expansion
Heat all to same degree; the dotted line is the amount of expansion you will observe (____ expands the highest)
Amalgam is ____ tooth, composite is ____ tooth, and acrylic is ____ tooth structure
acrylic
2x
3x
8x
Biological Consequences
____ along tooth/restoration interface
Corrosion products from ____ reduce microleakage
microleakage
amalgam
Rheology (Flow Properties)
Study of ____ of materials
Viscosity is the ____ to flow of a material under an applied stress
High viscosity implies ____ flow
flow
resistance
slow
Viscosity
Two plates with liquid in between them; apply force resulting in velocity (v)
Based on force applied you can determine the ____ (____)
____ > velocity of the top plate divided by the distance between
Based on the two > determine the ____ (____)
shear stress
MPa
shear strain rate
viscosity
centipoise
Some Typical Values of Viscosity
Pure water at 20oC = ____ cp
Light body polysulfide = ____ cp at 45oC
Heavy body polysulfide = ____ cp at 36oC
1.0
281,000
1,360,000
Rheologic Behavior Fluids
Moving the top plate, moves at a velocity (v); distance and area are fixed > the only things change are the force and velocity
If you apply a force on top plate, and the movement is proportional (velocity) > you can plot shear stress (F) and strain rate (velocity) > if force and velocity are ____, you get a straight line between > force is occurring in a ____
If plate is moving rapidly (little force, lots of velocity) > fluid is behaving as ____ (shear thinning > as you increase the shear the material acts as if it was very thin)
____ (velocity decreases as you increase the force) is opposite to pseudoplastic > plate begins to move, you need much higher forces to continue to get it to move
Plastic > when you apply a force it doesn’t move until you hit a ____ of force
propertional newtonion fluid pseudoplastic fluid dilatant threshold
Rheologic Behavior Fluids
Newtonian Fluid
eg. ____
Pseudoplastic Fluid
(Shear thinning)
eg.
____
ZnPO4 cement
Znpolycarboxylate
Viscosity (Other flow behavior)
Thixotropic Behavior
Viscosity that is dependent on ____
Molecular ____ during mixing
Thixotropic manner > viscosity changes upon previous deformation (mixing paint, for example); you break up the ____ as you deform the material, thereby making it less ____
previous deformation
rearrangement
secondary molecular bonds
viscous
Flow and Cementation of Crowns
Flow behavior of cement determines pressure needed for ____
If cement is pseudoplastic > little force on crown and it goes easily and becomes ____ (you probably want a pseudoplastic cement in your practice)
If newtonian > force and pressure and ____
complete eating
well seated
proportional
Color and Esthetics in Dentistry
Electromagnetic radiation from the sun
Light is electromagnetic radiation of wavelength ____ nm
Primary colors : ____
400-700
red, blue, green
Visible light
Spectrum of white (visible) light
Wavelength range
____ nm
Wavelength of maximum visual perception -____nm
Range is ____nm for wavelength of maximum visual perception
400-700
555
540-570
Spectral Distribution of Light
Different light sources have different wavelength distribution
Combine both ____ and ____, you form daylight
Tungsten lamp > strong ____ component
typical direct sunlight
blue sky light
red
