1. Which of the following gypsum products is used as ‘die material’ ;

A. Type 1
B. Type 2
C. Type 3
D. Type 4

Answer D

2. Binder in investment;

A. Quartz
B. Silica
C. Crystobalite
D. None

Answer D
Binder : 25% to 35% of α-calcium sulfate hemihydrate is used
-To react with water and on hydration binds the silica together.
-To impart sufficient strength to the mould and
-To contribute to the mould expansion by its setting expansion.

• Casting gold-containing alloys with melting ranges below 1000 °C
• Material is heated at temperatures sufficiently high
  

  – 200-400 °C: shrink considerably
  – 400 °C – 700 °C : slight expansion takes place between
  – Above : decomposition and the release of sulfur dioxide causing contamination of alloy

3. In the investment for gold, the strength is provided by;

A. Silica
B. Gypsum
C. Crystobalite
D. Carbon

Answer B

4. Dental investment is the plaster mixed with fillers like;

A. Silica
B. zinc
C. Glass
D. Chalk powder

Answer A

5. A refractory cast is made up of;

A. Diestone
B. Investment
C. Plaster
D. Stone

Answer B

6. Gypsum bonded investment should NOT be heated above;

A. 700 degree C
B. 750 degree C
C. 800 degree C
D. 900 degree C

Answer B

7. The correct sequence of dimensional change occuring when gypsum investments are heated above 1000 degree C is;

A. Expansion, contraction, marked expansion
B. Expansion, shrinkage
C. Contraction, expansion
D. Shrinkage, expansion, marked contraction

Answer D

8. Normal setting expansion of gypsum bonded investments is;

A. 0.1 to 0.5%
B. 0.5 to 1%
C. 1 to 1.5%
D. 1.5 to 2%

Answer A
NORMAL SETTING EXPANSION
– silica particles probably interfere with the intermeshing and interlocking of the crystals
– thrust of the crystals is outward during growth,
– Soft wax and thin pattern may get distorted,

9. Silica sol________?

A. Is applied to the walls of the investment to produce hygroscopic expansion
B. Increase the strength and the setting expansion of the phosphate-bonded investment
C. Acts as a retarder in the silica bonded investments
D. Acts as a refractory in the Silica bonded investments

Answer:B

10. Casting shrinkage is compensated by_______?

A. Thermal expansion
B. Hygroscopic expansion
C. Wax expansion
D. All of the above

Answer:D