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CSA - Materials > Physical And Mechanical Properties > Flashcards

Physical And Mechanical Properties Flashcards

1
Q

How do you establish the most important property of a material?

A

Once you have defined the task a material has to fulfill

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2
Q

What are the two simple modes of stress?

A

Tension and compression

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3
Q

What what is tensile strength?

A

Stretching force

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4
Q

What is compressive strength?

A

Compressive force

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5
Q

Which forces are a combination of compressive and tensile modes?

A

Torsion, shear and flexible modes

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6
Q

What is torsion?

A

Twisting

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7
Q

What is shear strength?

A

Ability to resist forces that cause material’s internal structure to slide against itself

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8
Q

What is flexural strength?

A

Bending

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9
Q

Why is the tooth a complex material to test the strength of?

A

It is a composite - made up of multiple components

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10
Q

What does a universal testing machine do?

A

It deforms the sample tested in a known and controlled way whilst monitoring the force

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11
Q

What does anistrophic mean?

A

Having a physical property which has a different value when measured in different directions

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12
Q

Where are the loads directed in enamel?

A

Along the the length of the prism

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13
Q

What form will the material being tested in the UTM need to be in?

A

A regular and reproducible specimen

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14
Q

What could affect if a tooth is used for a sample?

A

The history of the tooth. - damage, etc

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15
Q

Describe what is shown in the elastic region

A

Initially the stress is proportional to strain

Deformation is recoverable

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16
Q

What is shown in the plastic region?

A

Permanent deformation

17
Q

What is the point where the elastic and plastic regions meet?

A

The elastic limit, proportional limit or yield point

18
Q

What is the highest value for stress termed?

A

Strength

19
Q

What is Young’s modulus?

A

The slope of the elastic region - modulus of elasticity

20
Q

What is a complaint material?

A

A material with a low stiffness

21
Q

What does a higher Young’s modulus mean?

A

The stiffer the material

22
Q

Which tooth tissue is easily deformed?

A

PDL - relatively easily elastic ally deformed.

23
Q

What is aberfraction of the tooth?

A

Where cyclic loading had lead to enamel spooling at the neck of the tooth

24
Q

Fatigue is a major problem in regards to which device?

A

Posts - used to fix crowns to devitalised teeth which have their pulps extracted

25
Q

What affects the highly ware resistant enamel?

A

Our diets and bad oral habits

26
Q

What assumptions can we make about hard materials?

A

That they have higher ware resistance and are more abrasive

27
Q

Name and explain a hardness scale

A
  • Mohs’ hardness scale
  • 1 to 10 talc to diamond
  • scratch one material with another - the less hard material is scratched
28
Q

How do we define fracture toughness?

A

The Griffith Equation

29
Q

What does the growth of a crack/fault lead to?

A

Failure

All materials have flaws/cracks

30
Q

How do you increase rapture toughness?

A

Make the path of crack more difficult

31
Q

How does the structure of the tooth increase fracture toughness but what is the issue with the nature of the tooth?

A

Cracks are deflected from common paths

Tooth is anisotropic - higher fracture toughness on one plane as oppose to another

32
Q

Explain the know test vickers test

A

An indent with equal length diagonals and cracks emanating from their tips are measured

Notoriously hard to do correctly

33
Q

How do you test fracture toughness with a biaxial flexure rig?

A
  • indent is placed opposite top loading piston
  • sample loaded till it fails maximum load
  • other variable then used to calculate fracture toughness

Unfortunately cant generate big enough disks of enamel or dentine

34
Q

How does an impact tester work?

A
  • hammer strikes specimen
  • specimen will break on absorbing some energy from the hammer
  • hammer travels less high
  • measure difference in pendulum travel - calculate energy absorbed -> impact energy
35
Q

Which wavelengths do (near) white teeth reflect?

A

All wavelengths- reasonably well

36
Q

Why does the inside colour of the tooth effect its appearance?

A

Enamel is quite translucent - esp at tips

37
Q

What does value mean?

A

How light or dark a colour is

38
Q

What is important to make sure of when matching shades/colours?

A

Quality of light source - natural north light - flat and even - possible Edith electric light

CSA - Materials (3 decks)

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