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2 Dental Materials > Structure And Properties > Flashcards

Structure And Properties Flashcards

1
Q

Dental composite definition

A

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

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2
Q

What are fibre reinforced materials?

A

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

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3
Q

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

A

Statement of manufacture

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4
Q

Statement of manufacture must contain 5 things

A
  • 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
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5
Q

Dental materials must meet standards from? 2

A

BSI - British standards institute

ISO - international standards organisation

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6
Q

The Instron universal testing machine tests which mechanical properties? 4

A

Tensile strength
Compressive strength
Diametral tensile strength
Flexural strength

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7
Q

How is tensile strength tested?

A

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

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8
Q

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

A

Causes premature cracks leading to premature failure in brittle materials

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9
Q

Draw diametral tensile strength test using instron universal testing machine

A
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10
Q

What material is the diametral tensile strength test used for?

A

Brittle materials

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11
Q

Draw the flexural strength test using instron universal testing machine

A
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12
Q

What is this point?

A

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

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13
Q

What is this point?

A

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

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14
Q

What is this point?

A

Ultimate tensile strength
The specimen fails

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15
Q

What does modulus mean?

A

The stiffness of a material

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16
Q

How do u calculate modulus using the graph?

A

Stress/strain (in the linear region of graph)

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17
Q

What is ductility?

A

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

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18
Q

How do you calculate ductility using the graph?

A

Extend the linear line and move across till it touches F

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19
Q

What is resilience?

A

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

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20
Q

How do you calculate resilience using the graph?

A
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21
Q

What is toughness?

A

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

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22
Q

How do u calculate toughness on this graph?

A
23
Q

What is fatigue?

A

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

24
Q

Do you understand this graph showing fatigue?

A
25
Q

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

A

Hardness microscope

26
Q

How does the hardness microscope measure surface hardness?

A

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

27
Q

A large hardness number means?

A small hardness number means?

A

Large = low hardness

Small = high hardness

28
Q

What hardness microscope makes this shape?

A

Vickers

29
Q

What hardness microscope makes this shape?

A

Brinell

30
Q

What hardness microscope makes this shape?

A

Knoop

31
Q

How does the shear bond strength test work?

A

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

32
Q

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

A

The two materials are separated completely

33
Q

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

A

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

34
Q

How does the impact strength test work?

A

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

35
Q

How does the surface roughness test work?

A

Profilometer runs along the surface
Measures the Ra (mean deviation of the surface profile)

Higher Ra means rougher material

36
Q

What three things r calculated in the thermal properties test?

A

Thermal conductivity (K)

Specific heat capacity (Cp)

Thermal diffusivity (D)

37
Q

What is thermal conductivity (K)?

A

Rate of heat transfer through a material

38
Q

What is specific heat capacity (Cp)?

A

Energy required to heat up a material

39
Q

What is thermal diffusivity (D)

A

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

40
Q

What is the rheological properties test?

A

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

41
Q

For rheological properties test
Viscosity is proportional to what? 2

A

Pressure / speed

42
Q

What is this type of material?

A

Dilatant material

43
Q

What is this type of material?

A

Newtonian material

44
Q

What is this type of material?

A

Pseudoplastic material

45
Q

What happens to viscosity in dilatant material?

A

Viscosity increases with applied pressure

46
Q

What happens to viscosity in Newtonian material?

A

Viscosity remains constant with applied pressure

47
Q

What happens to viscosity in pseudoplastic material?

A

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

48
Q

Remember this

A

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

49
Q

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

A

Corrosion
Solubility parameter

50
Q

What is corrosion?

A

Chemical reactivity of metals and alloys

An electrolytic property (conducts electricity)

51
Q

What is Solubility parameter

A

Solutions used to simulate various foods in a laboratory

52
Q

To test biological properties
Testing occurs at what 3 levels

A

Laboratory screening

Limited laboratory in Vivo usage testing

Human randomised controlled clinical trial

53
Q

What does laboratory screening assess? 3

A

Acute systemic toxicity

Irrational potential

Carcinogenic potential

2 Dental Materials (4 decks)

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