Elastomers

Question 1

Advantage of speed set alginate?

Answer 1

High level of patient comfort

Question 2

Define thixotrophy

Answer 2

Progressive decrease viscosity

Question 3

Advantage of enhanced thixotrophy?

Answer 3

Gives greater accuracy of impression without excessive flow

Question 4

Advantage of high elasticity in relation to undercuts?

Answer 4

Copes with the most severe undercuts

Question 5

What limits syneresis (release of water)

Answer 5

Dimensional stability (controlled by pH balance in the formula)

Question 6

Examples of elastomeric impression materials? (2)

Answer 6

1. Polyether

2. Addition silicones

Question 7

Accessing material properties checklist includes (8)

Answer 7

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

Question 8

Name an example of an addition silicone

Answer 8

Polyvinylsiloxane

Question 9

What is the purpose of ISO standards

Answer 9

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

Question 10

What is the ISO standard for impression materials?

Answer 10

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

Question 11

List 3 of the best features of the virtual Polyvinylsiloxane

Answer 11

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

Question 12

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

Answer 12

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

Question 13

What properties lead to impression accuracy? (2)

Answer 13

1. Surface reproduction

2. Visco-elasticity/elastic recovery

Question 14

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

Answer 14

1. Tear/tensile strength

2. Rigidity (removal)

Question 15

Define viscosity

Answer 15

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

Question 16

Define surface wetting

Answer 16

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

Question 17

Why is 100% elastic recovery ideal?

Answer 17

Recovery from deformation
No permanent strain
IDEAL BEHAVIOUR

Question 18

How does less load time lead to less overall permanent strain

Answer 18

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

Question 19

Why is low viscoelasticity ideal?

Answer 19

Small deformation

Question 20

Define tear strength

Answer 20

Stress material will withstand before fracturing

Question 21

Why should an impression material ideally have low rigidity?

Answer 21

• Impression material should be flexible not rigid

- To ease its removal from undercut/interdental regions

Question 22

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

Answer 22

Addition silicones