Hydrocolloids +Alginates Flashcards
What is a solution and what is suspension
Solution= Homogenous
Suspension=Heterogenous
What are hydrocolloids based on?
Colloid suspension of polysaccharide
What is the order of polysaccharides in the sol state?
Random (less viscous)
What is the order of polysaccharides in the gel state?
Ordered (viscous)
What can be added to hydrocolloid to reduce flexibility?
Inert powder
Define Syneresis
Water loss. Gel molecules come together and squeeze water to the surface.
What happens when we reheat a gel state Agar
Bonds break, goes back to sol state (Reversible hydrocolloid)
What happens when hydrocolloids are placed in the mouth
Placed in the mouth is sol state and records details and leaves in gel state
ingredients in alginate:
Calcium Salt
Alginate Salt
Trisodium phosphate
Purpose of calcium salt/?
Cross links the alginate chains to help form the gel
How do we get retention of alginate imp
- adhesive on tray
- perforated tray
why do we shake the alginate back
To mix up the components properly before use and get a uniform mix
What does sodium alginate become when the reaction starts?
Calcium alginate as there is cross linking
What are the 5 key positives of alginate
- Non toxic
- Easy to mix
- Cheap and shelf life
- Surface detail
- Can control setting via temp of water
Issues with alginate
- must be cast up quickly as it can distort over time
- Tears easily
- messy
- unstable in moisture and heat
- Incompatibility with denture stones
