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Flashcards in Impression Materials Deck (8)
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1
Q

What are the components of Alginate powder?

A

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

2
Q

What are the 2 states a hydrocolloid can exist in?

A

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

3
Q

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

A

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.

4
Q

What is the ideal viscosity for an elastomer?

A

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

5
Q

What is viscoelasticity and how does this relate to elastomers?

A

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.

6
Q

What are the key properties of IM?

A

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

7
Q

What are the 2 types of elastomers used in GDH?

A

Polyethers

Addition silicones

8
Q

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

A

20 - 50 micrometres.