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Dental Material Science BDS2 > Impression Materials > Flashcards

Flashcards in Impression Materials Deck (8)
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What are the components of Alginate powder?

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


What are the 2 states a hydrocolloid can exist in?

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


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

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.


What is the ideal viscosity for an elastomer?

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


What is viscoelasticity and how does this relate to elastomers?

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.


What are the key properties of IM?

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


What are the 2 types of elastomers used in GDH?

Addition silicones


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

20 - 50 micrometres.