Structure And Properties

Question 1

Dental composite definition

Answer 1

Combination of materials in which the individual retain their identity and which possess different properties to the components acting alone

Question 2

What are fibre reinforced materials?

Answer 2

Type of composite consisting of fibres of a high strength and modulus bonded/embedded to a matrix

Question 3

The medical devices directive says that u must offer to a patient receiving dental appliance what?

Answer 3

Statement of manufacture

Question 4

Statement of manufacture must contain 5 things

Answer 4

• Patients name and confirmation appliance is for them
• Prescribers name and registered address
• Technicians name and registered address
• Description of appliance
• Confirmation that is meets legal requirements

Question 5

Dental materials must meet standards from? 2

Answer 5

BSI - British standards institute

ISO - international standards organisation

Question 6

The Instron universal testing machine tests which mechanical properties? 4

Answer 6

Tensile strength
Compressive strength
Diametral tensile strength
Flexural strength

Question 7

How is tensile strength tested?

Answer 7

Pulling force applied to elongate rod, rod is stretched till it breaks at a force F newtons

Question 8

Why is the compressive strength test not recommended for some materials?

Answer 8

Causes premature cracks leading to premature failure in brittle materials

Question 9

Draw diametral tensile strength test using instron universal testing machine

Answer 9

Question 10

What material is the diametral tensile strength test used for?

Answer 10

Brittle materials

Question 11

Draw the flexural strength test using instron universal testing machine

Answer 11

Question 12

What is this point?

Answer 12

Yield
Point at which the specimen begins to get disrupted, the specimen can withstand everything up until this point

Question 13

What is this point?

Answer 13

Fail
After it has failed as the mechanism isn’t fast enough to record fail

Question 14

What is this point?

Answer 14

Ultimate tensile strength
The specimen fails

Question 15

What does modulus mean?

Answer 15

The stiffness of a material

Question 16

How do u calculate modulus using the graph?

Answer 16

Stress/strain (in the linear region of graph)

Question 17

What is ductility?

Answer 17

The ability of the material to be drawn out into a wire

Question 18

How do you calculate ductility using the graph?

Answer 18

Extend the linear line and move across till it touches F

Question 19

What is resilience?

Answer 19

Energy absorbed by the material in undergoing plastic deformation up to the elastic limit

Question 20

How do you calculate resilience using the graph?

Answer 20

Question 21

What is toughness?

Answer 21

Total amount of energy a material can absorb up to the point of fracture
High value = tough
Low value = brittle

Question 22

How do u calculate toughness on this graph?

Answer 22

Question 23

What is fatigue?

Answer 23

Application of cyclical on/off loading for a defined number of cycles

Question 24

Do you understand this graph showing fatigue?

Question 25

What is used to measure the surface hardness of a material?

Answer 25

Hardness microscope

Question 26

How does the hardness microscope measure surface hardness?

Answer 26

Apply and indent or under a load onto a material Measure the height and width Look up in book to get hardness number

Question 27

A large hardness number means? A small hardness number means?

Answer 27

Large = low hardness Small = high hardness

Question 28

What hardness microscope makes this shape?

Answer 28

Vickers

Question 29

What hardness microscope makes this shape?

Answer 29

Brinell

Question 30

What hardness microscope makes this shape?

Answer 30

Knoop

Question 31

How does the shear bond strength test work?

Answer 31

2 materials stuck together Try to separate by shearing (sliding) them apart

Question 32

In the shear bond strength test what does adhesive failure mean?

Answer 32

The two materials are separated completely

Question 33

In the shear bond strength test what does cohesive failure mean?

Answer 33

The union remains intact but the force has caused one of the materials to fracture separating them

Question 34

How does the impact strength test work?

Answer 34

Pendulum swings and fractured the specimen, the pendulum continues its swing round The lower the pendulum swings after fracture the greater the impact strength as more energy is consumed by the specimen

Question 35

How does the surface roughness test work?

Answer 35

Profilometer runs along the surface Measures the Ra (mean deviation of the surface profile) Higher Ra means rougher material

Question 36

What three things r calculated in the thermal properties test?

Answer 36

Thermal conductivity (K) Specific heat capacity (Cp) Thermal diffusivity (D)

Question 37

What is thermal conductivity (K)?

Answer 37

Rate of heat transfer through a material

Question 38

What is specific heat capacity (Cp)?

Answer 38

Energy required to heat up a material

Question 39

What is thermal diffusivity (D)

Answer 39

The rate that temperature will rise within a material when heat is applied to its surface

Question 40

What is the rheological properties test?

Answer 40

Study of viscosity and how it varies with Rate of shear ( how fast push plunger down) And time

Question 41

For rheological properties test Viscosity is proportional to what? 2

Answer 41

Pressure / speed

Question 42

What is this type of material?

Answer 42

Dilatant material

Question 43

What is this type of material?

Answer 43

Newtonian material

Question 44

What is this type of material?

Answer 44

Pseudoplastic material

Question 45

What happens to viscosity in dilatant material?

Answer 45

Viscosity increases with applied pressure

Question 46

What happens to viscosity in Newtonian material?

Answer 46

Viscosity remains constant with applied pressure

Question 47

What happens to viscosity in pseudoplastic material?

Answer 47

Viscosity decreases with applied pressure and, unless setting, increases when pressure decreases

Question 48

Remember this

Answer 48

Thermal expansion and contraction of a material must match as closely as possible to tooth surface being replaced

Question 49

What are the 2 chemical properties that are tested for a material?

Answer 49

Corrosion Solubility parameter

Question 50

What is corrosion?

Answer 50

Chemical reactivity of metals and alloys An electrolytic property (conducts electricity)

Question 51

What is Solubility parameter

Answer 51

Solutions used to simulate various foods in a laboratory

Question 52

To test biological properties Testing occurs at what 3 levels

Answer 52

Laboratory screening Limited laboratory in Vivo usage testing Human randomised controlled clinical trial

Question 53

What does laboratory screening assess? 3

Answer 53

Acute systemic toxicity Irrational potential Carcinogenic potential