Elastomers Flashcards

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1
Q

Advantage of speed set alginate?

A

High level of patient comfort

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2
Q

Define thixotrophy

A

Progressive decrease viscosity

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3
Q

Advantage of enhanced thixotrophy?

A

Gives greater accuracy of impression without excessive flow

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4
Q

Advantage of high elasticity in relation to undercuts?

A

Copes with the most severe undercuts

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5
Q

What limits syneresis (release of water)

A

Dimensional stability (controlled by pH balance in the formula)

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6
Q

Examples of elastomeric impression materials? (2)

A
  1. Polyether

2. Addition silicones

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7
Q

Accessing material properties checklist includes (8)

A
  1. Flow/viscosity
  2. Surface detail
  3. Wettability
  4. Elastic recovery
  5. Stiffness
  6. Tear strength
  7. Mixing time
  8. Working time
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8
Q

Name an example of an addition silicone

A

Polyvinylsiloxane

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9
Q

What is the purpose of ISO standards

A

Assesses properties of a product to see if it meets acceptable requirements for safe and effective use

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10
Q

What is the ISO standard for impression materials?

A

That grooves/indentations of either 20um or 50um (depending on material viscosity) are replicated

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11
Q

List 3 of the best features of the virtual Polyvinylsiloxane

A
  1. Excellent detail reproduction
  2. Superior elastic recovery
  3. High tear strength
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12
Q

What does superior elastic recovery mean in response to virtual impressions?

A

Easy to remove from the patients mouth and elastically recover from the deformation of removal

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13
Q

What properties lead to impression accuracy? (2)

A
  1. Surface reproduction

2. Visco-elasticity/elastic recovery

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14
Q

What properties allow us to deal with removal and undercuts? (2)

A
  1. Tear/tensile strength

2. Rigidity (removal)

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15
Q

Define viscosity

A

A materials ability to flow
Determines a materials potential for how well it records surface detail (making close contact with hard/soft tissue surfaces)

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16
Q

Define surface wetting

A

Impression material must make intimate contact with teeth/mucosa surfaces - so all surface is replicated

17
Q

Why is 100% elastic recovery ideal?

A

Recovery from deformation
No permanent strain
IDEAL BEHAVIOUR

18
Q

How does less load time lead to less overall permanent strain

A

If load time is less - impression is removed with a sharp pull
Therefore there is a less overall permanent strain (lower deformation)

19
Q

Why is low viscoelasticity ideal?

A

Small deformation

20
Q

Define tear strength

A

Stress material will withstand before fracturing

21
Q

Why should an impression material ideally have low rigidity?

A
  • Impression material should be flexible not rigid

- To ease its removal from undercut/interdental regions

22
Q

Do polyethers or addition silicones have a longer setting and working time?

A

Addition silicones