Module 1: Gypsum (Lab)

Calcium Sulfate Dihydrate

Gypsum is chemically known as?

Gypsum

Calcium sulfate dihydrate is also known as?

Calcination

Through ___________, gypsum is converted to calcium sulfate hemihydrate depending upon the temperature used.

Calcium Sulfate Hemihydrate

Through calcination, gypsum is converted to _______ _______ ___________ depending upon the temperature used.

Beta Hemihydrate - Alpha Hemihydrate

Calcium sulfate hemihydrate can either be (2)?

Beta Hemihydrate

This hemihydrate is also known as dental plaster.

Beta Hemihydrate

Hemihydrate obtained by heating the gypsum in a kettle in open air at a temperature of 110-120 degrees centigrade.

Alpha Hemihydrate

This hemihydrate is also known as cast stone.

Alpha Hemihydrate

Hemihydrate obtained by heating in an autoclave at a temperature of 120-130 degrees centigrade.

Dental Plaster

Which has a bigger particle size, dental plaster or dental stone?

Dental Plaster

Which material needs more water during mixing, dental plaster or dental stone?

Setting TIme

The length of time it takes for the materials to harden from the time of their mixing.

Initial Setting Time

The time when the material starts to harden.

Final Setting Time

The time when the material has completely hardened.

Water-Powder Ratio

Refers to the quotient obtained when the volume of water is divided by the weight of the powder.

Longer

Does the setting time take longer or shorter when more water is added?

Mixing

Accomplished by rotating the spatula in the material to help break up any remaining clumps and enhance the wetting of the powder. 

Yes

Does the setting time become faster when the mixing is faster (within practical limits).

Yes

Does higher temperature speed up the setting time?

50 degrees centigrade

The setting time becomes retarded if it exceeds this temperature.

Accelerators - Retarders

What are the 2 types of modifiers?

Accelerator

Modifier which decreases the setting time.

Retarder

Modifier which increases the setting time.

Accelerator

What type of modifier is potassium sulfate?

Retarder

What type of modifier is potassium borax?

Dental Plaster - Dental Stone - Dental Investment - Impression Plaster

What are the 4 gypsum products important to dentistry?

Hand Spatulation - Mechanical Spatulation

What are the 2 ways of spatulating dental plaster?