Chapter 11 Casting Metals, Solders, and Wrought Metal Alloys

Chapter 11  Casting Metals, Solders, and Wrought Metal Alloys

Complete Chapter Questions And Answers
 

Sample Questions

MULTIPLE CHOICE

1. Which of the following statements is true of noble dental casting alloys?
a.
They require gold and must contain at least 25% noble metals by weight.
b.
They do not require gold and require less than 25% by weight of noble metals.
c.
They do not require any gold but must contain at least 25% noble metals by weight.
d.
They must contain at least 60% by weight of noble alloys, of which gold must account for at least 40% by weight.

ANS: A
Noble dental casting alloys do not require any gold but must contain at least 25% noble metals by weight. High-noble alloys must contain at least 60% by weight of noble alloys, of which gold must account for at least 40% by weight. Base-metal alloys do not require gold and require less than 25% by weight of noble metals.

REF: p. 171 TOP: Casting Alloys (All-Metal Castings)

2. Which description is correct regarding palladium?
a.
Is more expensive than gold
b.
Has poor corrosion resistance
c.
Increases the hardness of the alloy
d.
Is a precious metal but it is not considered noble

ANS: C
Palladium increases the hardness of the alloy. It is widely used because it has good corrosion resistance and is less expensive than gold. Platinum and palladium are noble metals that are sometimes referred to as precious metals because of their high monetary value. Although silver is considered to be a precious metal, it is not considered noble because of its corrosion in the oral cavity.

REF: p. 171 TOP: Casting Alloys (Other Noble Metals for Casting Alloys)

3. Which of the following is a noble metal used for dental casting alloys?
a.
Silver (Ag)
b.
Platinum (Pt)
c.
Copper (Cu)
d.
Titanium (Ti)

ANS: B
Platinum, palladium, and gold are noble metals used for dental casting alloys. The primary base metals used in casting alloys are copper, nickel, silver, zinc, tin, and titanium. Copper and silver are often added to gold alloys to increase their hardness. Zinc is added to reduce oxidation when the alloy is cast. Because of their low cost, base metals have also been called nonprecious metals. Although they are not considered to be as good as the noble metals, the base metals are essential for many applications in dentistry.

REF: p. 171 TOP: Casting Alloys (Other Noble Metals for Casting Alloys)

4. Which of the following is true concerning grain formation in dental casting alloys?
a.
Reheating gold-based alloys will degrade the physical properties.
b.
Reheating base-metal alloys will not degrade the physical properties.
c.
Large crystals produce more desirable properties in the metal alloy than small crystals do.
d.
Iridium or ruthenium is added to gold-base alloys to keep the crystals from growing too large.

ANS: D
Iridium or ruthenium is added to gold-base alloys to keep the crystals from growing too large. Small crystals produce more desirable properties in the metal alloy than large crystals do. Reheating gold-based alloys (called annealing) can improve some of the properties. However, with base-metal alloys, reheating will degrade the physical properties.

REF: p. 172 TOP: Casting Alloys (Crystal Formation [Grains])