Admixed high copper alloy powder contains:

  # Admixed high copper alloy powder contains:

A. 9-20% copper

B. 13-20% copper

C. 9-30% copper

D. 13-30% copper

The correct answer is A. 9-20% copper.

In low copper alloys, copper is less than 6% by weight. In high copper single composition alloys, 13-30% copper by weight is present whereas in high copper admixed alloys, 9-20% copper is present.



Back pressure porosity can be avoided by:

  # Back pressure porosity can be avoided by:

A. Using asbestos liners

B. Placing the sprue at least one quarter inch away from the end of casting ring

C. Preventing rapid heating of investment

D. Using a short and wide sprue

The correct answer is B. Placing the sprue at least one quarter inch away from the end of casting ring

Entrapped air bubbles on the inner surface of the casting, sometimes referred to as back-pressure porosity, can produce large concave depressions. This is caused by the inability of the air in the mold to escape through the pores in the investment or by the pressure gradient that displaces the air pocket toward the end of the investment via the molten sprue and button. The incidence of entrapped air can be increased by the use of the dense modern investments.

All castings probably contain a certain amount of porosity, as exemplified by the photomicrographs. This should be minimized because it may adversely affect the physical properties of the casting. Proper burnout, an adequate mold and casting temperature, a sufficiently high casting pressure, and a proper investment L/P ratio can minimize or eliminate entrapped air porosity. It is good practice to make sure that the thickness of investment between the tip of the pattern and the end of the ring is not greater than 6 mm. 



Dull aching, continuous pain is transmitted by which of these nerve fibers

  # Dull aching, continuous pain is transmitted by which of these nerve fibers?

A. A delta fibers

B. B fibers

C. C fibers

D. A alpha fibers

The correct answer is C. C fibers.

C fibers transmit late, dull pain due to its high threshold. The C fibers are unmyelinated, have slower conduction velocity and are associated with a dull, aching or burning sensation.



First number in the instrument formula indicates:

  # First number in the instrument formula indicates:

A. Length of the blade in centimeters

B. 1/10th of the width

C. Angulation of the blade in degrees

D. Primary cutting edge angle

The correct answer is B. 1/10th of the width.

The complete instrument formula (four numbers) is expressed as the blade width (1) in 0.1-mm increments, cutting edge angle (2) in centigrades, blade length (3) in millimeters, and blade angle (4) in

centigrades.

Reference: Sturdevant's, 2018, Mosby