physical and mechanical properties e lec

Question 1

which two modes are there to establish strength

Answer 1

tension and compression

Question 2

what does tension do

Answer 2

stretches the length

Question 3

what does compression do

Answer 3

shrinks the length

Question 4

what is Poisson’s ratio

Answer 4

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.

Question 5

what differences can teeth have

Answer 5

size
composition
history

Question 6

how are properties of materials determined

Answer 6

by using a machine called the universal testing machine

Question 7

how does the universal testing machine work

Answer 7

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

Question 8

what can the data be used for

Answer 8

to plot a stress strain curve

Question 9

what is a stress strain curve

Answer 9

where stress is the force/area

Question 10

what is the strain

Answer 10

change in dimension/original length

Question 11

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

Answer 11

standardise it

Question 12

what does anisotropic mean

Answer 12

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

Question 13

what does enamel consist of

Answer 13

parallel long hexagonal prisms

Question 14

what do we also need to consider

Answer 14

the history of the tooth eg any trauma

Question 15

what else makes a good experiment

Answer 15

a large enough sample size so it can be representative

Question 16

what practicalities do we consider

Answer 16

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

Question 17

the stress strain curve starts to

Answer 17

increase proportionally and then levels off

Question 18

what is on the x axis

Answer 18

strain

Question 19

what is on the y axis

Answer 19

stress

Question 20

what is the point called where the stress and strain meet

Answer 20

elastic limit, proportional limit or yield point

Question 21

what is the highest value for stress called

Answer 21

strength

Question 22

what is the slope called

Answer 22

the modulus of elasticity or youngs modulus

Question 23

what does the PDL add

Answer 23

toughness and resilience

Question 24

what can materials fail

Answer 24

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

Question 25

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

Answer 25

abfraction

Question 26

abfraction

Answer 26

leads to the enamel pooling at the base of the tooth

Question 27

fatigue is a major problem with

Answer 27

posts

Question 28

why does the post fail in a crown

Answer 28

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

Question 29

what is the study of ware

Answer 29

tribology

Question 30

what experiments are conducted in tribology

Answer 30

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

Question 31

what has changed in recent decades

Answer 31

diet

Question 32

what should be of high importance when considering restorative materials

Answer 32

ware

Question 33

what can happen to the opposing dentition

Answer 33

it can be wared out

Question 34

how does LDI test their materials

Answer 34

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

Question 35

what is the paper used in LDI to test the material

Answer 35

silicon carbide paper

Question 36

hardness

Answer 36

tends to be indicative on how a material might ware

Question 37

what is the effective field test and hardness test

Answer 37

mohs hardness scale

Question 38

what is the scale of the mohs hardness scale

Answer 38

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

Question 39

how does it work

Answer 39

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

Question 40

what technique can be problematic to test the hardness of enamel

Answer 40

indentation techniques as enamel is very thin

Question 41

what test is used to test the hardness of thin films

Answer 41

the Knop test

Question 42

what us the fracture toughness equation

Answer 42

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].

Question 43

do teeth have a different fracture structure

Answer 43

due to anisotropic

Question 44

is there a single way of determining single fracture toughness

Answer 44

no as now there is a branch of linear fracture mechanics

Question 45

what test do we use for the hardness of teeth

Answer 45

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

Question 46

what are the disadvantages of the vickers test

Answer 46

it is difficult to do

Question 47

what is the issue with teeth

Answer 47

they are a laminated composite structure and very small

Question 48

as we measure the height the pendulum travels

Answer 48

we can calculate impact energy

Question 49

how high is the instrument

Answer 49

0.5m

Question 50

what is the energy of the instrument

Answer 50

2 joule

Question 51

what is colour created by

Answer 51

by rods and cones cells which absorb different wavelengths

Question 52

what is the colour wheel extended into

Answer 52

value

Question 53

what is value

Answer 53

measure of how light and dark a colour is

Question 54

what other colour space schemes are made

Answer 54

l,a,b scheme

Question 55

when taking shades what should we consider

Answer 55

the quality of the light source- natural north light

Question 56

what is north light

Answer 56

a flat even north light