Working Casts and Dies Flashcards
Working cast definition
- Replication of prepared teeth and ridge area of dental arch
- Obtained from final impression
- Used to make wax pattern made
Die
- Positive reproduction of individual tooth on which wax pattern is done
- Obtained from final impression
Materials used for die
Epoxy resin
Polyurethane
Amalgam
Gypsum type 4/5
Gypsum products
- Type 1- Impression plaster
- Type 2- Model plaster
- Type 3- Dental stone
- Type 4-Dental stone with high strength(Low abrasion resistance)
- Type 5-Dental stone with high strength and expansion
Types of die according to material
Electro deposition of metals
Flexible die material
Refractory dies
Resin
ideal properties of dies
-Produce fine impression details
-Easy manipulation
-Dimensionally stable
-Compatible with impression materials
-High abrasion resistance
-Good strength and smooth surface
Non injurious
Die preparation methods
Working cast with separated dies
Working cast with removable dies
Working cast with separated die
- Two casts from single impression
- One sectioned and other working cast
Working cast with removable dies types
- Dowel pin system-straight and curved
- Pindex system
- Di-lock system
Main characteristic of plasters
Expansion
Main constituent of gypsum
Calcium sulphate dihydrate
Impression plaster use
Removable partial dentures
Constituents of model plaster and dental stone
Mineral in nature and derived from environment
Difference between dental stone and dental stone type IV
Dental stone type IV is modified with polymers
Difference between dental stone and dental stone type IV with dental stone type V
differences in porosity(Type V has less)
Methods to increase abrasive resistance of gypsum
- Substitution of silica for water
- Treat surface with resin(epoxy)
- Impregnation of acrylic resin into die
Type V dental stone has gypsum
False-it mimics gypsum but it is actually a polymer
Epoxy resin use
Die materials to overcome low strength and abrasion resistance of die stones
What material is electroconductive?
Polyether
What is the benefit of electroplated models?
- Thinner crowns w/ even surface thickness
- Overcome the minimum thickness of casting(non precious alloys cannot be cast below-0.8 mm and precious alloys below 0.2 mm)
Function of die hardener
- Increases surface hardness of die
- Should enter applied surface
