Impression Materials
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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 Flavourings 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?
Polyethers Addition silicones
What measurements of grooves should be replicated that indicate an effective product? (with regards to surface detail)
20 - 50 micrometres.