Chapter 8 Impressions Flashcards
What is a model vs a cast?
A model is a representation that may or may not be the same size
A cast is meant to be a near exact replication in size
What is a cast of a single tooth called?
A die
T/F a cast can have one die ot multiple dies?
True
What are impression trays used for?
carry and support the material
What are the different types of impression trays?
- Stock tray
- custom impression trays
- stock edentulous
- Bite registration
What are the qualities of impression material ?
- excellent detail reproduction
- good tear strength
- no distortions when removed from the mouth
What are the different types of classification of impression materials in inelastic rigid?
- impression plaster
- wax and dental compound
- Zinc oxide-eugenol (ZOE)
What are the different types of classification of impression materials in elastic ?
Alginate
Agar
Polysulfide
Polyvinyl Siloxane (PVS)
Polyether
What is alginate?
Irreversible hydrocolloid
Hydrophilic
hygienist mostly deals with this type
what does alginate contain?
- silica filler to give body
- calcium sulfate (reactor)
- sodium phosphate as retarder
- colorants
- flavor
What are the advantages of alginate?
- Hydrophilic (loves water)- reduces air bubbles from oral fluids and pouring dental stone
What are the disadvantage of alginate?
- water evaporates and impressions shrinks (SYNERSIS)
- CAN ABSORB WATER AND SWELL (imbibition)
What is syneresis?
loses water and shrinks
What is imbibition ?
Takes on/uptake of water and swells
What are the two phases of alginate?
- Sol
- Gel
