Gypsum Flashcards
What is a die?
Positive reproduction of a tooth from an impression that has been prepared to accept a restoration
What is a model?
Cast dimensionally accurate reproduction in a positive form of areas of the oral cavity
What are the ideal properties of model and die materials?
Dimensionally accurate Easy to use Accurate reproduction of fine detail Inert Good strength Inexpensive Abrasion resistant Good colour contrast
What are the model and die materials that we use?
Gypsum
What type of structure does model gypsum have and what is it?
Monoclinic spade lattice structure
Calcium sulphate hemihydrate
What are the three types of gypsum?
Beta
Alpha
Alpha modified
What is beta form? And what colour ?
Plaster of paris and is white
What is the structure of the beta form? When is it used? What properties does it have?
Large irregular orthorhombic crystals
Rudimentary procedures
Soft, short setting time, high porosity
40-50ml water to 100gms
What is the alpha form?
Kafir D
Dental stone
yellow and ah small regular prismatic particles
25-35ml to 100gms
Alpha modified is what type of gypsum?
Artificial stone coloured
Large crystals
Die for crown Nd bridge
20-35ml water to 100gms
Why is die stone better than dental stone?
GORE Good colour contracts Optimum stengh when VAccum Reasonbly inexpensive Excellent working time
What is the Setting expansion of gypsum reduced by?
Potassium sulphate
Sodium chloride
Borax
What is the setting time of gypsum reduces by?
Reduced :Borax postasuim citrate ans sodium chloride
Increased: more than 20% gypsum! potassium sulphate and sodium chloride
