Chapter 16 Gypsum and Wax Products

Chapter 16  Gypsum and Wax Products

Complete Chapter Questions And Answers
 

Sample Questions

MULTIPLE CHOICE

1. Which of the following is true concerning the chemical properties of gypsum materials?
a.
Chemically, the mineral gypsum is a hemihydrate of calcium carbonate.
b.
To form the raw material into a powder, the manufacturer heats it and adds water.
c.
When the dihydrate is again mixed with water, a product with a viscosity capable of flowing is produced.
d.
The amount of water required to mix the calcium sulfate hemihydrate is greater than the amount required for the chemical reaction.

ANS: D
The amount of water required to mix the calcium sulfate hemihydrate is greater than the amount required for the chemical reaction. Chemically, the mineral gypsum is a dihydrate of calcium sulfate and is mined as a solid mass. To form the raw material into a powder, the manufacturer heats this dihydrate, which causes it to lose water. It is then ground to produce a powdered hemihydrate. When the hemihydrate is again mixed with water, a product with a viscosity capable of flowing is produced.

REF: p. 279 TOP: Properties and Behaviors of Gypsum Products (Chemical Products)

2. Which of the following dental gypsum products will require the least water for mixing and will have the highest final density?
a.
Impression plaster (Type I)
b.
Model plaster (Type II)
c.
Dental stone (Type III)
d.
Dental stone, high strength (Type IV)

ANS: D
High-strength dental stone will require the least water for mixing and will have the highest final density. Model plaster is formed if the heating process occurs in open vats at a temperature of approximately 115° C. Dental stone is produced if the heating process is done under pressure and at a higher temperature. A further increase in pressure and further refining of the powder by grinding result in an even denser stone known as high-strength or die stone.

REF: p. 279 TOP: Properties and Behaviors of Gypsum Products (Chemical Products)

3. β-Hemihydrate is commonly used for:
a.
die stone.
b.
working casts.
c.
diagnostic models.
d.
dental investment.

ANS: C
β-Hemihydrate, or model plaster, is commonly used for diagnostic casts (study models). The product of the heating process is porous and irregular in shape. α-Hemihydrate is produced if the heating process is done under pressure and at a higher temperature. It is called dental stone and is a more uniformly shaped and less porous form of hemihydrate than β-hemihydrate. Dental stone is used for working casts. A further increase in pressure and further refining of the powder by grinding result in an even denser stone, known as high-strength or die stone. When stone is mixed with silica, it forms dental investment.

REF: p. 279 TOP: Properties and Behaviors of Gypsum Products (Chemical Products)

4. Which material is able to withstand the high heat and stress produced when molten metal is forced into molds to form indirect restorations?
a.
Dental investment
b.
Model plaster
c.
Dental stone
d.
Die stone

ANS: A
Dental investment is a material able to withstand the high heat and stress produced when molten metal is forced into molds to form indirect restorations. It is created when dental stone is mixed with silica.

REF: p. 279 TOP: Properties and Behaviors of Gypsum Products (Chemical Products)