Impression Materials

Question 1

What are the components of Alginate powder?

Answer 1

Sodium alginate
Calcium sulphate
INERT FILLER - gives cohesion and strength (70%)
Modifiers - improve surface quality
Flavourings
TRI-SODIUMPHOSPHATE - DELAYS formation of alginate gel

Question 2

What are the 2 states a hydrocolloid can exist in?

Answer 2

SOL - viscous liquid state
GEL - jelly-like consistency state where fine particles form framework which encapsulate a liquid through capillary force

Question 3

What is the difference between muco-static and muco-compressive?

Answer 3

Muco-static – a fluid material that displaces soft tissues slightly (alginate) – gives impression of un-displaced mucosa
Muco-compressive – VISCOUS (high viscosity elastomer) – DISPLACES soft tissue when it is pressed against patient’s dentition – gives impression of mucosa under load.

Question 4

What is the ideal viscosity for an elastomer?

Answer 4

LOW - so it can make close contact with the tooth and the surface detail recorded is more accurate.

Question 5

What is viscoelasticity and how does this relate to elastomers?

Answer 5

Viscoelasticity is how elastic a material is - how much the impression will return to normal after removal - they ALWAYS EXHIBIT PERMANENT DEFORMATION.
You want a material with the smallest permanent deformation.

Question 6

What are the key properties of IM?

Answer 6

Low viscosity
Low thermal expansion coefficient
Extent of viscoelasticity - want one with the smallest permanent deformation

Question 7

What are the 2 types of elastomers used in GDH?

Answer 7

Polyethers

Addition silicones

Question 8

What measurements of grooves should be replicated that indicate an effective product? (with regards to surface detail)

Answer 8

20 - 50 micrometres.