Definitive casts and dies Flashcards
What are two other terms that synonymous with master cast?
- Definitive cast
- Working cast
What is a replica or copy of the prepared tooth or teeth, ridge areas, and other parts of the dental arch known as?
-Master cast
What is a die?
-Positive reproduction of the prepared tooth
T/F The master cast must accurately represent both prepared and unprepared tooth surfaces
True
What must the unprepared teeth immediately adjacent to the prepared teeth be free of the meet the master cast requirements?
- Voids
- Defects
- Irregularities
All contacting surfaces of opposing teeth in MI and any tooth surfaces involved in anterior guidance must be free of what to meet mast cast requirements?
- Free of defects
- Allow for precise articulation
T/F All relevant soft tissues must be accurately reproduced, especially edentulous ridges that will be involved in fixed prostheses
True
For die requirements all _______ areas must be accessible.
Marginal
Epoxy resin is _____ abrasion resistant that gypsum.
More
Epoxy resin is ____ expensive than gypsum
More
What type of impression material must be used for an epoxy resin?
- PVS
- Polyether
What type of impression material must be used for a polyurethane?
- PVS
- Polyether
Polyurethane is ____ abrasion resistant than gypsum
-More
Electroplated is ______ distorted
Easily
What is electroplated incompatible with?
- Polyether
- Polysulfide
With flexible silicone or polyether the restoration is ___ separated from die.
Easily
Gypsum is _______ abraided.
-Easily
Gypsum is also known as what?
-Calcium sulfate dihydrate (mined this way)
What is calcination?
-The turning of dihydrate gypsum into dental stone (anhydrite)
When is the Beta-hemihydrate produced?
-When gypsum is heated in an open ketlle type to produce Type I and Type II Dental plaster or stone
Type I and Type II dental stone are what type of hemihydrate?
-Beta
Type II Dental stone is what type of hemihydrate?
-Alpha
What is alpha-hemihydrate also referred to as?
-Hydrocal
When is alpha-hemihydrate produced?
-When gypsum is dehydrated under pressure in the presence of water vapor
How is Densite produced?
-Gypsum is boiled in 30% CaCl solutions
Type IV, and V dental stone is what?
-Densite
What do you use type I stone for?
-Impression plasters and Mounting stone
What is Type II stone used for?
-Model plasters
What is type III stone used for?
-Model stones
What is Type IV stone used for?
-Die stones
What is Type V stone used for?
-Die stones
What properties does Type IV stone have?
- High strength
- Low expansion
What properties does Type V stone have?
- High strength
- High expansion
What has the lowest expansion?
-Type I mounting stone
What is plaster of Paris?
-Type I dental stone
What type of stone do you used for Diagnostic casts, -working casts for Removable complete dentures?
Type III
What is the theoretical lowest required volume of water needed to hydrate 100g of hemihydrate?
- 18.6 mL
Which type of hemihydrate crystals are smaller, more prismatic and regular in shape?
-Alpha
Which type of hemihydrate crystals are larger, more porous and irregular in shape?
-Beta
Which type of hemihydrate required more water?
-Beta
Which type of hemihydrate produces a harder and stronger set structure?
-Alpha
What does adding more water to the mix do to the set time?
-Increase the set time
What can decrease the set time of the materials?
- 2% K2SO4
- Slurry mix
- Increase water temp
If you spatulate more quickly what does it to do the set time?
-Decrease
T/F The high strength dental stone contains the least amount of excess water
True
How long after mixing and pouring is the gypsum usually at its maximum wet strength?
-1 - 2 hours
What is wet strength?
-The strength measured when excess water remains in the hardened mass of stone
What is dry strength?
-Stone is its strength with all of the excess water removed.
The dry strength is approximately ______ that of the wet strength?
-Twice
What is hardness?
-Surface measurement of the resistance of one material to be deformed by indenting or scratching by another material
T/F Surface hardness always correlates with abrasion resistance.
False
-They dont always correlate