Physical and Mechanical Properties Flashcards
Name some physical and mechanical properties we look at when we investigate polymers
- Strength
- Stress:stain relationship
- Fatigue
- Ware and hardness
- Fracture toughness
- Impact strength
- Aesthetics
List the 2 ways you can measure strength
1 Tension
2. Compression
Wha p we need to consider/ do before we take measurements of a tooth?
- First try and standardises the specimen
- Consider whether to test the whole tooth or the components enamel or dentine
- consider that the structure of teeth is not the same in each direction enamel and dentine are anisotropic.
- Consider the history of the tooth
Wha lines does enamel consist of?
Parallel long acicular hexagonal prism aligned such that loads are directed along the enamel prism
What is the elastic limit?
The point where the elastic and plastic regions meet
What are other names for the elastic limit ?
proportional limit or yield point.
What does th highest value for stress show?
It is tired the strength
What is the slop of theistic region Called?
It is termed the modulus of elasticity or Youngs modulus
What does a high Young’s modulus show?
thh the material is stiff
How are teeth held in the mouth?
They are mounted in bone fundamentally
What adds resilience to the tooth’s support system?
The periodontal ligament
Why can materials catastrophically fail at stresses well below their ultimate strength?
Due to cyclical load
What can cyclical load lead to in teeth?
alleged to lead to the enamel spooling (flaking) at the neck of the tooth.
(This is called aberfraction)
What are “post”?
these are devices used to fix crowns to devitalised teeth which have their pulps extracted.
What is the study of ware called?
Tribology
How do test the ware of restorative materials ?
- By simply rubbing them against a standard abrasive material such as silicon carbide paper.
- We will then contrast that with enamel samples.
What is harness usually an indicator of?
Indicator of how a material might ware
What qualities do harder materials tend to have?
tend to be more ware resistant and also more abrasive.
Name a hardness scale
Mohs’ hardness scale
Knop hardness
Describe the points on Mohs’ hardness scale
There are 10 points
1 is Talc
10 is diamond
How would you perform Mohs’ test
Scratch 1 material with another with the less hard material being scratched
How would you perform Knops test
Use diamond coproduce an indent in the material you are trying to measure
What important trauma do teeth go through on. daily?
Impact
Name the equation that defines fracture toughness?
Griffiths equation
