Elastomeric Impression Materials

Question 1

What are the two main types of elastomeric materials?

Answer 1

1. Polyether

2. Addition silicone

Question 2

What two events must occur in the impression material to provide an effective impression?

Answer 2

1. Elastic strain

2. Elastic recovery

Question 3

What properties should be considered when assessing impression materials?

Answer 3

1. Flow/viscosity
2. Surface detail (reproduction)
3. Wettability (contact angle)
4. Elastic recovery (%)
5. Stiffness (flexibility)
6. Tear strength
7. Mixing time
8. Working time

Question 4

What is the ISO standard for impression materials?

Answer 4

• grooves/indentations of 20-50 microns (depending on material viscosity) are replicated

Question 5

What properties are ideal for good quality of surface interaction between material and tooth/soft tissue surfaces?

Answer 5

1. Viscosity - must be able to flow readily

2. Surface wetting - must make intimate contact with teeth/mucosa

Question 6

What properties are ideal for providing an accurate impression?

Answer 6

1. Surface reproduction

2. Visco-elasticity/elastic recovery

Question 7

What properties are ideal for dealing with removal and undercuts?

Answer 7

1. Tear/tensile strength

2. Rigidity (flexibility)

Question 8

Explain how viscosity effects surface detail reproduction

Answer 8

• viscosity is a measure of materials ability to flow
• this determines a material’s potential for making close contact with hard/soft tissue surfaces
- therefore effecting how well it records surface detail

Question 9

Define surface wetting

Answer 9

• ability of impression material to make intimate contact with teeth/mucosa surfaces

Question 10

What are the standard notch dimensions used to test impression materials?

Answer 10

1. 20 microns
2. 50 microns
3. 75 microns

Question 11

How does a faster load release effect strain and permanent deformation of impression materials?

Answer 11

1. Reduces maximum strain value

2. Decreases level of permanent deformation

Question 12

What level of viscoelasticity is preferred in impression materials?

Answer 12

1. Low viscoelasticity as this results in small deformation

Question 13

Define tear strength

Answer 13

Stress material will withstand before fracturing

Question 14

What level of rigidity is desirable for impression materials?

Why?

Answer 14

Low rigidity in order to ease its removal from undercut/interdental regions

Question 15

How do the setting and working times compare in polyethers and addition silicones?

Answer 15

1. Addition silicones have a slightly longer setting time

2. Addition silicones have double the working time of polyethers

Question 16

What 5 general rules should you follow when selecting an impression material?

Answer 16

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