MOD 08 - Gypsum (Type IV & V)

High strength

• Type IV, Class II stone, Densite, Improved dental stone, modified alpha hemihydrate, and die stone

• Strongest and most expensive

• Making cast or dies for crowns, bridge, and inlay fabrication

Principle requisites for high strength

Strength, Abrasion, Resistance, Hardness, Minimal setting expansion

• Mnemonics: Strong athletes run hard miles

hard surface is necessary in type iv because

tooth prep is covered with wax and carved flush with margins of die

This instrument is used in Type IV, thus it must be resistant to abrasion

Sharp Instrument

Advantage of type IV

surface resists to abrasion

Average dry surface gypsum hardness solution in type IV

92

Type V

• Dental stone, High strength, High expansion

• Used for inlays, onlays bcs expansion leads to unnacceptability tightly fit

• Strength is achieved by lowering w:p

• Higher setting expansion to aid compensationg for alloy solidication shrinkage

• Setting expansion is increased, since few base metal alloys have greater tendency of shrinkage

How to make Type V

• Calcined by boiling it in 30% CaCl

• Washed away or autoclave by sodium succinate 0.5%

• Results to more shorter and thicker

• Residual CaCl and sodium succinate is removed by washing powder with hot water

fill out the properties of gypsums: