90. Elastomeric Impression Materials

Question 1

L90: What two factors are there to consider when choosing an impression material?

Answer 1

• Material characteristics;

- Clinical performance (patient acceptance and ease of use).

Question 2

L90: What properties contribute to patient acceptance?

Answer 2

• Time to set;

- Taste

Question 3

L90: What material characteristics should be considered?

Answer 3

• Viscosity (ability to flow over tissues);
• Surface wetting;
• Level of accuracy;
• Level of elasticity (to capture undercuts);
• Elastic recovery;
• Tear strength;
• Dimensional stability.

Question 4

L90: In an ideal elastomeric impression material, how viscoelastic do you want the material to be and why?

Answer 4

• Low viscoelasticity;
• Better elastic recovery;
• Small deformation (permanent strain).

Question 5

L90: What is wettability?

Answer 5

Contact to tooth tissues

Question 6

L90: What is tear strength?

Answer 6

A measure of how well a material can withstand tearing under an applied force

Question 7

L90: What is rigidity?

Answer 7

Stress/ strain ratio, i.e. the amount of stress required to cause a material to change shape

Question 8

L90: To meet current ISO standards, what level of detail must impression materials be able to distinguish between?

Answer 8

20 or 50 um, depending on material viscosity

Question 9

L90: How can permanent strain be minimised when removing an impression from the oral cavity?

Answer 9

Sharp pull - reduced load time - less overall permanent strain

Question 10

L90: How do working and setting times vary between polyethers and addition silicones?

Answer 10

Polyethers offer a slightly quicker setting time (1 minute quicker), but there is only a 2 minute working time as opposed to 4 with addition silicones

Question 11

L90: What type of material are elastomeric impression materials?

Answer 11

Elastomers

Question 12

L90: What are the two major types of elastomeric impression materials used?

Answer 12

• Polyethers;

- Addition silicones.