What are the 2 essential properties of impression materials?
Accurate reproduction of detail (ability to flow and wet surfaces) and dimensional stability (during solidification, removal from mouth, before being poured up).
What are the 5 non-elastic impression materials? (The rest are elastic!)
Plaster, Compound, Apaptol, Waxes, ZnO Eugenol
What's the difference in mechanical behavior between elastic and non-elastic?
Elastic allows accurate reproduction of undercuts
What's a benefit of rigid (non-elastsic) materials?
Viscous, and can displace soft tissues (elastic doesn't really)
What's the difference between reversible (thermoplastic) and irreversible (thermoset)?
Reversible/thermoplastic are reusable and set by change in temp. Irreversible/thermoset are not reusable and set by chemical reaction.
What's the difference between elastic and viscoelastic?
Viscoelastic materials have a small amount of permanent deformation, and a time dependent rebound.
When would you use non-elastic (rigid) impressiono materials?
Endentulous ridge impressions and border molding tray for denture impressions (compound and adaptol), Secondary wash impressions (ZOE), bite registration (Wax, ZOE, Plaster, Hard-setting PVS), occlusal registration for articulator bite fork (Wax, Compound, Hard-setting PVS)
What is impression plaster used for?
Used to be used for denture impressions, but now as a bite registration material
What is the point of adding starch to impression plaster?
To weaken the material to allow easier removal from the mouth
What are some examples of separating material for impression plaster?
Soap, varnish, liquid alginate solutions
What is the major benefit of impression plaster?
Short working and setting times to facilitate intraoral use
What is dental compound particularly good for?
Preliminary denture impressions and border molding trays for secondary impressions. It is particularly useful because it pushes the tongue and other soft tissues away so that an accurate mold of the endentulous ridge can be made.
What's the difference between dental compound "tray material" vs "sticks"?
Tray material is for full arch impressions, and heated in water to soften. Sticks are for border molding and stabilizing rubber dam clamps on teeth; heated in a flame.
How is adaptol different from dental compound?
They are similar, but adaptol is used specifically for border-molded custom trays. Also, Adaptol is sticker when heated, and less rigid when cooled.
What are the advantages of ZOE?
Accurate mucostatic material (low viscosity), very low distortion, cheap
What are the disadvantages of ZOE?
Messy, setting time varies due to temp and humidity, Eugenol irritating to some.