Elastomers Flashcards

1
Q

How are elastomers formed? How does this form its properties?

A

Polymerisation and cross linking of polymer chains

Cross linking
- generates elastic properties

Polymerisation can produce byproducts such as water or alcohol which affects dimensional stability

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2
Q

Give an example of some elastomers

A

Polysulphides

Silicones

Polyethers

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3
Q

How do you assess a material?

A

Surface detail

Flow/viscosity

Contact angle

Elastic recovery

Stiffness

Tear strength

Mixing time and working time

Setting shrinkage

Dimensional stability

Thermal expansion

Biocompatibility

Shark fin test (flow under pressure)

Shore A hardness

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4
Q

What are the ideal properties of an impression material?

A

Low viscosity

Low contact angle

High wettability

Low viscoelasticity

Low stiffness

Low thermal expansion

Low polymerisation shrinkage

High tear resistance

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5
Q

Why must IMs maintain a high quality of surface interaction between material and tissues? How achieved?

A

To get high accuracy

  • low contact angle and high wettability is needed so the IM makes contact with as much tooth/mucosa as possible
  • viscous so it flows readily
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6
Q

Why does an IM need accuracy? How achieved? What size of notch can an IM record in a tooth?

A

50um

Needs accuracy so the impression is as close as an exact replica as possible

  • achieved through viscosity
  • visco-elastic recovery into its normal position after removal from undercuts / patients mouth
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7
Q

How does an impression material deal with removal and undercuts?

A
  • High shark fin test so the material will readily flow into undercuts and sulci
  • high tear strength so material doesn’t tear when removing from undercuts
  • have low rigidity so it can be easily removed
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8
Q

Why does an IM need dimensional stability?

A
  • so little to no setting shrinkage affecting accuracy of impression
  • thermal expansion / contraction should be close to mouth and room temperature so that accuracy is not affected during setting
  • so that dimensions do not change in storage
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9
Q

What material has a better setting time and working time out of polyethers and addition silicones?

A

Polyethers

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