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Pres Res unit 1-materials Flashcards

(65 cards)

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1
Q

Occlusal Force trend

A

decreases from molars to incisors

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2
Q

everyday chewing force

A

10N

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3
Q

movement of teeth during chewing

A

axial and horizontal

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4
Q

Force is defined by

A

point of application, magnitude, and direction of application

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5
Q

average max biting force

A

756N

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6
Q

Stress Strain Curves

A

A certain amt of force is required to move an object (rubberband) a distance deltaL; divide Force and deformation are devided by the cross-section of area and the length so that the force is independent of size since it changes

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7
Q

stress is equal to and units

A

force/area in Pascals (1MPa=1,000,000 Pa) Pa=N/m^2

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8
Q

shearing

A

forces on diff planes in opposite directions (i.e. force on top to left and force on bottom to right)

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9
Q

Torsion

A

twisting

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10
Q

Strain

A

no units, deformation/length; undergoes change in length

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11
Q

Elastic

A

deformation will not be permanent (rubber band)

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12
Q

Plastic

A

permanent deformation; relocation of atoms

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13
Q

universal testing machine

A

produces stress-strain curves

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14
Q

stress strain curve

A

will determine elasticity vs placitity

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15
Q

Elastic limit

A

looks at material, to determine the boundary between elastic and plastic

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16
Q

Proportional limit

A

use a machine to determine the boundary between elastic and plastic

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17
Q

Stress-strain curve

A

the stress value at which a material exhibits a specified permanent strain

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18
Q

ceramic materials

A

break before they permanently deform, such as ceramics

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19
Q

Ultimate tensile strength

A

the max stress a material can withstand before failure in tension

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20
Q

Fracture Strength

A

the stress at which a material fractures; not necessarily equal to ultimate strenght

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21
Q

Elastic Modulus/Young’s modulas

A

represents the stiffness within the elastic range E=theta/E=stress/strain

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22
Q

Stiffness of Cobalt chrome

A

good/stiff

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23
Q

Acrylic resin and composite resin stiffness

A

not very (relative)

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24
Q

Brittle materials in dentistry (not ductile)

A

Amalgam, composites, cements, and ceramics

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25
Ductility
ability of a plastic to be deformed
26
Dutility trend
gold silver most | Lead tin least
27
Resilience
resistance to deformation., energy absorbed per V material
28
Toughness
resistance of a material to fracture, or energy absorbed
29
Stress strain comparisons
see charts Brittle-straight line Ductile- curved line Taller line-strong Shorter line-weak Does not go far in x direction/high slope-stiff Further in x-flexible (not much slope) Tough- will bend a lot before breaking Resielent- graph will not bend, stays elastic Tough-graph will bend, becomes plastic but hard to fracture
30
Ultimate compression strenght
amt of stress to compress a material
31
impact strength
energy required to fracture a material under impact force
32
diametral compression test
indirect tensile test, test brittle materials for tensile strength
33
shear strength
max stress before failure in shear mode; used for bond strength testing
34
Bending creates
areas of compression (of side angle getting smaller); neutral axis on object; larger angle is under tension (more likely to fail)
35
cantilever Bending Test
tests bending, force applied down
36
Bending moment
force x distance (basically torque)
37
Flexural strength
denture materials and ortho wires, transverse strength, 3 point bend test
38
Torsion
twistin, important in endo files for root canals, shear stretch
39
Fatique
progressive fracture under repeating loading
40
Stress to cycles to failure
shows endurance limit, may fail over long periods of small or larger stress
41
Factors Affecting Fatique
environment: temp, humidity, pH Surface features Material history
42
Fracture Toughness
A measure of material's resistance to a brittle fracture when a crack is present; good for brittle materials (flaws in metal are more forgiving than ceramics)
43
Viscoelasticity
has elastic and flow qualities; some elastic and plastic deformation is possible;
44
Creep
Viscoelastc property-time dependent strain of a material under a static/constant stress
45
Stress Relaxation
Viscoelastic- reduction in stress in a material subjected to constant strain- think ortho bands which apply less force after application
46
Hardness
resistance to permanent surface indentation
47
Brinell Hardness Test
used for metals; hardened steel ball indenter is used and diameter is measured
48
Rockwell Hardness Test
Used for metals and plastics; a ball or cone used
49
Vickers Hardness Test
microscopic, for metals and plastics-softer material loses out-porcelain hardest
50
Knoop Hardness Test
micro indentation test , rhombic based pyramidal diamond
51
Wear
loss of material; relocation
52
Bruxism
pathological form of wear
53
Abrasive two body wear
to surfaces rubbing, grinding
54
abrasive three body
food between two teeth
55
corrosive wear
wear coupled with a chemical attack
56
Rheology
study of flow of matter
57
Viscosity
fluids resistance to flow
58
newtonian fluid
viscosity remains constant (water)
59
Plastic
no flow until a certain shear stress is reached (yield point) toothpaste
60
Psuedoplastic
decreasing viscosity as shear rate increases (stir faster and it gets thinner/easier)
61
Dilatant
viscosity increases with a shear rate (harder to mix as you stir)
62
Thixotropic
Time dependent decreasing in viscosity, has yield point, curve is not reversible (ketchup bottle)
63
Burnishing
closing the metal margin of a metal crown-recovery of elastic strain but NOT plastic
64
Barcol
additional hardness test-resin composites
65
Shore
used for rubber

Pres/Res (14 decks)

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