Final Exam: Impression Materials

Question 1

4. What are the two examples of elastic aqueous hydrocolloids that were covered?

Answer 1

Agar and alginate

Question 2

4. Aqueous hydrocolloids (agar and alginate) both exhibit the property of syneresis. What is syneresis?

Answer 2

Once an impression is made and the mold is taken out of the mouth, the surface will interact and exude water to the air, resulting in outer contraction over time. This is due to fibril cross linking continuing.

Question 3

4. Aqueous hydrocolloids (agar and alginate) both exhibit the property of imbibition. What is imbibition?

Answer 3

If an impression is placed in water, it will take up water and expand.

Question 4

43. What is one very notable advantage of the non-aqueous elastomer “Addition silicone” material (Vinyl polysiloxane)?

Answer 4

It can be used for multiple casts

Question 5

52. What is a notable disadvantage to using the non-aqueous elastomer “Polyether” material?

Answer 5

Very short working time

Most stiff and precise though, so used for crown and bridge impressions

Question 6

54. Rank the following materials in order of stiffness, starting with the most stiffest material:
    - Addition silicone, condensation silicone, hydrocolloids, polyether, polysulfide

Answer 6

1. Polyether (most stiff)
2. Addition silicone
3. Condensation silicone
4. Polysulfide and hydrocolloids (least stiff)

Most important thing to remember is that polyether is most stiff - I don’t think we’ll be asked to reproduce the order

Question 7

43. What impression material can you use more than once and still get an accurate impression?

Answer 7

Addition silicone (vinyl polysiloxane)

Question 8

46. Pick the aqueous hydrocolloids
    - Addition silicones
    - Agar
    - Alginate
    - Condensation silicone
    - Polyether
    - Polysulfide

Answer 8

Aqueous hydrocolloids - agar and alginate

Non-aqueous elastomers