Elastomeric Impression Materials

Question 1

What are the types of elastomers

Answer 1

Polyether

Additional silicones

Question 2

How should you select an impression material based on

Answer 2

material characteristics
clinical performance (patient acceptance, ease of use)

Question 3

What material properties should you look at

Answer 3

flow/viscosity
surface detail (reproduction)
wettability
elastic recovery (%) 
stiffness (flexibility)
tear strength 
mixing time
working time

Question 4

What is polyvinylsiloxane

Answer 4

additional silicone

Question 5

What is the ISO standard for impression materials

Answer 5

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

Question 6

What does superior elastic recovery allow

Answer 6

easy to remove from the patient’s mouth and elastically recover from the deformation of removal

Question 7

What does high tear strength allow

Answer 7

The excellent tear resistance reduces the risk of tearing fine margins

Question 8

What does good wettability allow

Answer 8

They spread easily and adapt smoothly to dentine and moist oral tissue

Question 9

What are the ideal properties for impressions materials to achieve a good quality of surface interaction between material and tooth/soft tissue surfaces

Answer 9

viscosity
surface wetting
contact angle

Question 10

What are the ideal properties for accuracy

Answer 10

surface reproduction (ISO) 
visco-elasticity/elastic recovery

Question 11

What are the ideal properties for dealing with removal and undercuts

Answer 11

tear/tensile strength

rigidity (flexibility)

Question 12

What are ISO standards designed to do

Answer 12

exclude unsafe and poorly performing materials from the market

Question 13

What is viscosity

Answer 13

a measure of material’s ability to flow

Question 14

What is surface wetting

Answer 14

must make intimate contact with teeth mucosa

Question 15

What is the contact angle

Answer 15

determines how well material envelops the hard/soft tissue surface (to record fine detail)

Question 16

What does viscosity determine

Answer 16

determines a material potential for making close contact with hard/soft tissue surfaces
so how well it records

Question 17

What does viscosity range from

Answer 17

low, medium, high

Question 18

Why is surface wetting important

Answer 18

so all surfaces are replicated

Question 19

What is the ideal behavior regarding elasticity

Answer 19

100% elastic recovery

Question 20

When is viscoelastic behavior observed

Answer 20

when impression material have been stretched/compressed on removal from out, fails to return to its original dimensions/shape
i.e there is permanent deformation

Question 21

What is the ideal viscoelasticity

Answer 21

small deformation

Question 22

What is tear strength

Answer 22

stress material will withstand before fracturing

important in the material in the undercut

Question 23

What is rigidity

Answer 23

stress/strain
large stress needed to cause the material to change shape
ideally the impression material is flexible

Question 24

If a material has low rigidity what does this allow

Answer 24

to ease its removal from undercut/interdental regions

Question 25

Which has a lower setting time - polyethers or addition silicones

Answer 25

polyether

Question 26

Which has a lower working time - polyethers or addition silicones

Answer 26

polyether

Question 27

How should you make a decision as to what material you are going to use

Answer 27

1. Know the key properties of the material
2. Review product specification data
3. Know typical values expected for specific properties
4. Identify properties not mentioned
5. Reject claims not supported with scientific and/or clinical data