Gypsum Products (general info) Quiz 2 Flashcards
What is gypsum?
naturally occuring mineral which is mined from the earth’s crust
What happens when gypsum is heated? What’s the process called?
it is calcinated. Water is driven off through a process called calcining
What are the final products when gypsum is calcinated?
plaster and stone
Examples of dentalgypsum
1) impression plaster
2) plaster
3) stone
4) binder in investments
What is plaster used for?
models
What is stone used for?
models, dies
What are investments?
investment is the mold into which metals are cast
What does it mean that gypsum is a “binder in investment”?
gypsum product serves as the matrix which holds the investment together (Ex: cement in concrete)
What is a model or caste?
replicas of oral structures
What are models or casts used for?
1) indirect restorative procedures
2) diagnosis and treatment planning
3) records (for orthodontic treatment progress)
Dies
are a removable part of a model which are typically used to replicate a single tooth
What is gypsums chemical format?
calcium sulfate CaSO4*2H2O
Write the heating equation from dihydrate to hemihydrate
CaSO42H2O —–> CaSO41/2H2O+3/2H2O
How is plaster formed? Characteristics?
by heating gypsum in the air at 110-120C. Porous and irregularly shaped particles
How is stone formed? Characteristics?
By heating gypsum in the air at 120-130C in an autoclave. Dense and regularly shaped particles
What the importance of the autoclave when making stone from gypsum?
generates steam and pressure. Makes more regularly shaped particles
How is die stone made? Characteristics?
process varies depending on manufacturer but similar to making stone. Harder and denser than stone
What is die stone used for?
dies in crowns and bridge construction
Once gypsum products are formed, they are ground into?
various sized powder particles
Manufacturers control?
1) particle size
2) particle distribution
3) packing density of the gypsum product
Order of least to most porous?
die stone -> stone -> plaster
Order of most reguarly shaped to least?
die stone -> stone -> plaster
Order of lowest packing density to most?
plaster -> stone -> die stone
