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Dental Materials > Week 2 Mechanical and Physical Properties > Flashcards

Week 2 Mechanical and Physical Properties Flashcards

1
Q

Stresses from thermal expansion can?

A

stresses from thermal expansion can rupture adhesive bonds; divide by 11.4 so we can compare to tooth; closer to 1 is good

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2
Q

thermal diffusivity

A

heat transfer when temperature fluctuates

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3
Q

thermal conductivity? What does high K value mean?

A

steady state heat transfer (equilibrium achieves); higher value for k equals higher heat transfer; *enamel and dentin have LOW k= good bc we won’t feel every change in temperature

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4
Q

color fatigue

A

eye decreases its response spectrum when continually stimulated; quickly glance between shade and tooth

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5
Q

metamerism

A

different light sources produce different shade matches; *use northern daylight or color corrected lights

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6
Q

shade guides

A

hand held color matching guides

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7
Q

Lab*color measurement system

A 
L= white (top) and black (bottom) axis
a= red (+) and green (-) axis
b= yellow (+) and blue (-) axis
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8
Q

Munsell color measurement system

A

3D coordinate system has a point for color based on hue, chroma and value
Hue: color, wavelength
Chroma: degree of color saturation, more intense closer to circle’s edge
Value: lightness or darkness of a shade

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9
Q

Flow

A

*amorphous material under constant applied force

Ex: waxes, glasses, plastics

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10
Q

Creep

A

*solid
plastic deformation
-time and temp dependent
-static or dynamic stress

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11
Q

viscosity

A

How thick aa material is –ability of liquid to resist flow

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12
Q

rheology

A

flow of matter

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13
Q

2-body abrasion

A

1 surface slides against another, rough surfaces often wear faster, hardness indirectly involved

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14
Q

3-body abrasion

A

loose particles in a liquid or gas medium with wear rates proportional to: applied pressure, speed of particles, lubrication, and hardness of particles

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15
Q

hardness? Hardness tests?

A

resistance to scratching or indentation

Tests= BHN, Rockwell, Vickers, Knopp, Shore

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16
Q

fatigue

A

material failure at LOW stresses due to repeated loading. # of stress cycles is important, surface cracks appear, failure is abrupt, dynamic vs. static

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17
Q

impact strength

A

energy required to cause fracture with a sudden, single blow, not a strength at all but an ENERGY, very different results from regular impact

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18
Q

resilience

A

amount of energy absorbed before elastic limit is exceeded, area under elastic strain

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19
Q

toughness

A

total energy required to fracture a material (elastic + plastic energy = toughness), total area under curve

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20
Q

brittleness

A

failure occurs with little or no permanent deformation (no plastic strain, opposite of malleable)

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21
Q

malleability

A

related to amount of COMPRESSIVE plastic strain (high plastic strain, opposite of brittle)

22
Q

ductility

A

amount of TENSILE plastic strain

23
Q

strength

A

maximum stress achieved

24
Q

permanent deformation

A

=plastic strain reached, occurs when SS curve is no longer linear (starts to curve), object no longer returns to original form

25
Q

compliance

A

inverse slope of force-elongation curve (related to flexibility but based on shape)

26
Q

flexibility

A

inverse of elastic modulus (1/E)

27
Q

Hooke’s Law explains

A

linear proportionality between elastic stress and strain, E is slope of SS curve; Modulus of Elasticity

28
Q

yield strength

A

the stress value where an offset line intersects the SS curve (0.1% or 0.2%)

29
Q

proportional limit

A

the stress point at which the stress strain curve deviates from linearity and begins the area of plastic strain

30
Q

elastic limit

A

stress that just exceeds the elastic strain limit

31
Q

plastic strain

A

atoms are permanently displaced when stress is applied. Do NOT recover to original state

32
Q

elastic strain

A

atoms return to original positions when stress is removed, it IS recovered

33
Q

Poisson’s ratio

A

relates strain change in all 3 dimensions when a stress is applied along one axis, *remember forces are vectors so you have both magnitude and direction

34
Q

stress definition and explain equation

A

RESISTANCE of a material TO APPLIED FORCE
*stress=load/area
larger area=lower stress; larger load=more stress

35
Q

define strain? another term for strain?

A

is change in shape when force applied. also deforamtion (dimensionless)

36
Q

tensile

A

pulled on strain (think fishing line)

37
Q

compressive

A

pushing on object, atoms pushed together

38
Q

shear

A

atoms/objects sliding past each other

39
Q

torsional

A

twisting motion, atoms twist against something causing friction

40
Q

diametral tension

A

compression test for brittle material

41
Q

modulus of elasticity/Young’s modulus

A

represents stiffness, proportionally constant between stress and strain (or the slope) of the linear portion of S-S curve

42
Q

stress-strain diagram

A

shows how stress and strain are related for a given material

43
Q

flexure is what type of bend?

A

3/4 point bend, generating multiple types of stress with 1 or 2 applied forces

44
Q

yield point

A

elastic limit has been reached and is going into plastic strain, deformation is occurring

45
Q

percent elongation tests what?

A

test to measure ductility

46
Q

ultimate strength

A

maximum stress a material can withstand

47
Q

What is color?

A

psychological response to eletromagnetic radiation affected by light, object and individual

48
Q

What is color hue?

A

the color itself determined by dominant wavelength

49
Q

what is color value?

A

lightness or darkness of a shade

50
Q

Chroma

A

degree of color saturation, more intense closer to circle’s edge

51
Q

heat capacity

A

of heat units needed to change (1 mol of) a materail 1 degree

52
Q

specific heat

A

ofheat units needed to change (1 gram of) a material 1 degree

Dental Materials (17 decks)

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