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CSA > physical and mechanical properties e lec > Flashcards

physical and mechanical properties e lec Flashcards

we will discuss strength - different modes stress fatigue ware and hardness fracture toughness impact strength aesthetics

1
Q

which two modes are there to establish strength

A

tension and compression

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2
Q

what does tension do

A

stretches the length

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3
Q

what does compression do

A

shrinks the length

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4
Q

what is Poisson’s ratio

A

ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative.

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5
Q

what differences can teeth have

A

size
composition
history

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6
Q

how are properties of materials determined

A

by using a machine called the universal testing machine

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7
Q

how does the universal testing machine work

A

by deforming the sample in a known and controlled manner whilst monitoring the force

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8
Q

what can the data be used for

A

to plot a stress strain curve

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9
Q

what is a stress strain curve

A

where stress is the force/area

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10
Q

what is the strain

A

change in dimension/original length

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11
Q

what should we try to do when carrying out a test to the specimen

A

standardise it

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12
Q

what does anisotropic mean

A

having a physical property which has a different value when measured in different directions.

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13
Q

what does enamel consist of

A

parallel long hexagonal prisms

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14
Q

what do we also need to consider

A

the history of the tooth eg any trauma

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15
Q

what else makes a good experiment

A

a large enough sample size so it can be representative

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16
Q

what practicalities do we consider

A

eg if we need to grip the sample how do we not damage it

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17
Q

the stress strain curve starts to

A

increase proportionally and then levels off

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18
Q

what is on the x axis

A

strain

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19
Q

what is on the y axis

A

stress

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20
Q

what is the point called where the stress and strain meet

A

elastic limit, proportional limit or yield point

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21
Q

what is the highest value for stress called

A

strength

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22
Q

what is the slope called

A

the modulus of elasticity or youngs modulus

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23
Q

what does the PDL add

A

toughness and resilience

24
Q

what can materials fail

A

at stresses well below the ultimate strength; this is usually due to cyclical loading

25
Q

stresses well below the ultimate strength can be seen in teeth by a condition called

A

abfraction

26
Q

abfraction

A

leads to the enamel pooling at the base of the tooth

27
Q

fatigue is a major problem with

A

posts

28
Q

why does the post fail in a crown

A

poorly designed post and core leads to a failure of the cement which allows the post to flex resulting in the post becoming fatigued.

29
Q

what is the study of ware

A

tribology

30
Q

what experiments are conducted in tribology

A

our limbs are joined and conducted with low friction collagen fibres which regenerate
also have high resistance collagen free enamel coatings on our teeth

31
Q

what has changed in recent decades

A

diet

32
Q

what should be of high importance when considering restorative materials

A

ware

33
Q

what can happen to the opposing dentition

A

it can be wared out

34
Q

how does LDI test their materials

A

by rubbing the material against standard abrasive material such as silicon carbide paper

35
Q

what is the paper used in LDI to test the material

A

silicon carbide paper

36
Q

hardness

A

tends to be indicative on how a material might ware

37
Q

what is the effective field test and hardness test

A

mohs hardness scale

38
Q

what is the scale of the mohs hardness scale

A

ten points on the scale with talc at 1 and diamond at 10

39
Q

how does it work

A

we scratch the material together and the less hard one becomes scratched

40
Q

what technique can be problematic to test the hardness of enamel

A

indentation techniques as enamel is very thin

41
Q

what test is used to test the hardness of thin films

A

the Knop test

42
Q

what us the fracture toughness equation

A

defined by the Griffith equation
Sigma is now joined by a subscript f indicating stress at failure. [a] is for crack size, all materials have flaws or cracks in them and when a material fails it is due to the growth of this crack [a].

43
Q

do teeth have a different fracture structure

A

due to anisotropic

44
Q

is there a single way of determining single fracture toughness

A

no as now there is a branch of linear fracture mechanics

45
Q

what test do we use for the hardness of teeth

A

it is a version of the knops test called the vickers test

46
Q

what are the disadvantages of the vickers test

A

it is difficult to do

47
Q

what is the issue with teeth

A

they are a laminated composite structure and very small

48
Q

as we measure the height the pendulum travels

A

we can calculate impact energy

49
Q

how high is the instrument

A

0.5m

50
Q

what is the energy of the instrument

A

2 joule

51
Q

what is colour created by

A

by rods and cones cells which absorb different wavelengths

52
Q

what is the colour wheel extended into

A

value

53
Q

what is value

A

measure of how light and dark a colour is

54
Q

what other colour space schemes are made

A

l,a,b scheme

55
Q

when taking shades what should we consider

A

the quality of the light source- natural north light

56
Q

what is north light

A

a flat even north light

CSA (51 decks)

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