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1

Physical Properties of Dental Materials

____ Properties
____ Properties
____ Properties

Thermal
Rheologic
Optical

2

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

3

Thermal Properties

thermal ____
thermal ____
thermal ____

conductivity
diffusivity
expansions

4

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

5

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

6

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

7

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

8

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

9

Relative Values of Diffusivity

Metallic materials are highly ____; and non-metallic materials are ____ (low conducting)

conducting
insulating

10

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

11

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

12

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

13

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

14

Biological Consequences

____ along tooth/restoration interface

Corrosion products from ____ reduce microleakage

microleakage
amalgam

15

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

16

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

17

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

18

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

19

Rheologic Behavior Fluids

Newtonian Fluid
eg. ____

Pseudoplastic Fluid
(Shear thinning)
eg.
____

ZnPO4 cement
Znpolycarboxylate

20

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

21

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

22

Color and Esthetics in Dentistry

Electromagnetic radiation from the sun

Light is electromagnetic radiation of wavelength ____ nm

Primary colors : ____

400-700
red, blue, green

23

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

24

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

25

Spectral Distribution of Light

Fluorescent Light

Neylite

Vitalight

Neylite and Vitalight > made to simulate ____

natural daylight

26

The Color Wheel

Primary colors: ____

Complementary colors: Colors ____ each other on color wheel.

red, blue, green
opposite

27

The Color Wheels

Light mixture (Additive) color system
Pigment mixture system
Primary colors - blue, green, red
Complementary to blue: ____; red: ____; green: ____

We are using the ____ system (the square on top)

additive

yellow
cyan
magenta

Additive

28

Color Measurement Systems

____ System
Hue (circumferential)
Chroma (diameter)
Value (horizontal)

Munsell

29

The Color Solid

The three dimensions of color

Value = ____ from top to bottom

Chroma increases from ____ to ____

Hue changes ____

decreases
center
outward
circumferentially

30

Color Measurement Systems


In addition to the hue-value-chroma system, there exists another system (____)

Value = central axis; chroma = diameter axis; hue = circumfertial

Lab color system