Choose :

1. Which type of porosity causes discoloration?

a) Localized shrinkage porosity

b) Pin hole porosity
c) External porosity
d) Gas inclusions

2. What is the typical shape of porosity caused by gas?

a) Irregular
b) Spherical
c) Cylindrical
d) Cuboidal

3. What is the cause of back pressure porosity?

a) Solidification shrinkage
b) Gas inclusions
c) Air trapped in the mold
d) Suck back porosity

4. How can shrink pot porosity be avoided?

a) Using a thin sprue

b) Attaching the sprue to the thinnest portion of the pattern
c) Using a sprue of correct thickness
d) Using multiple sprues

5. Where should the sprue be attached to prevent shrink pot porosity?

a) Thinnest portion of the pattern

b) Thickest portion of the pattern
c) Anywhere on the pattern
d) At the edge of the pattern

6. What is recommended to do at the point of attachment of the sprue to prevent shrink pot
porosity?

a) Narrowing the sprue

b) Enlarging the sprue
c) Flaring the sprue
d) Removing the sprue immediately

7_ Which factor does not contribute to incomplete casting?

a) Insufficient alloy
b) Proper heating of the mold
c) Premature solidification of the alloy
d) Back pressure of gasses

8_ Which method is used to melt the alloy before casting in the Torch melting / Centrifugal
casting machine?

a) Induction heating
b) Torch flame
c) Resistance heating
d) Spring action

9_ There are four types are available for casting crucibles !!

a. Clay
b. Carbon
c. Copper
d. A & B

10_ In ............. , special equipment is used to the facilitate the operation .

a. Vacuum investing
b. Hand investing
c. mixed investment
d. Neither one is correct

12_ Casting & Melting requires ......... source to melt the alloy casting .
a. cold
b. Heat
c. Moderate temperature
d. Zero temperature

13_ Which of the casting defects ?

A. Surface smoothness
B. Complete casting
C. Incomplete casting
D. Wax soft

14_ phosphate bonded investment away from........ring. (6:7 , 6:8 , 3:4 mm ) .

15_ ..........liner is placed inside the ring .(plastic , ceramic, metal ring ).

16_ ceramic paper liner should be

( long , medium, short).

17_Gypsum bonded investment away from..........ring ( 6:7 , 6:8 , 3:4 ).

18_The surface of most cast , soldered , or otherwise heated metal dental appliances is
cleaned by ................ to restore the normal surface condition .

a) warming the structure in suitablesolutions .

b) mechanical polishing .
c) other treatment of the alloy .
d) all of them .

True or false:

1. External porosity can lead to discoloration.( )

2. Pin hole porosity is typically irregular in shape.( )

3. Back pressure porosity occurs due to air trapped in the mold.( )

4. Shrink pot porosity occurs when the sprue solidifies before the rest of the casting.( )

5. Attaching the sprue to the thickest portion of the pattern can help avoid shrink pot
porosity.( )

6_ Placing a reservoir close to the pattern is a method to prevent shrink pot porosity.( )

7_ Gas blow holes in casting are caused by insufficient alloy. ( )

8_Incomplete casting can occur when the mold is heated to the casting temperature. (
)

9_ Sprues blocked with foreign bodies can lead to incomplete casting. ( )

10_ Heat sources for casting machines can include the reducing flame of a torch.( )

11_ Casting machines utilize only air pressure for the casting process ( )

12_ During investing of the pattern , the correct water powder ratio of the investment mix , a
required number of spatulation turns, and a proper investing technique are nunessential to
obtain acceptable casting results . ( )

13_ There are three methods of investing the wax pattern .( )

14_ In vacum investing , special equipment is used to facilitate the investing operation . (
)

15_ We must not follow the manufacturer's instructions in the case of manual investment
and vacuum investment . ( )
16_If storage is necessary store it in a refrigerator ( )

17_ Manipulation of the wax at its softening temp invest the pattern at the earliest (
)

18_ When using gypsum bonded investment should be 3:4 away from ring ( ).

19_solid rings permit the investment to expand laterally during setting and hygroscopic
expansion of the mold( ).

20_ plastic paper liner is cut to fit the inside of metal ring and is held in place with the finger (
).

21_ Shouldn't touch or adapted further with a finger because this reduces its cushioning
effect ( ).

22_the ring must be shaken to remove the excess water ( ).

23_ when the ceramic paper liner short at end of ring , the investment is locked into the ring
and uniform expansion of the cavity occurs( ).

24_ Phosphate bonded investment is faster than gypsum bonded investment after burn out
or before burn out ( ).

25_ We should follow heat of type of investment to avoid cracking and flaking( ).

26_ When putting metal in warmer sulfuric acid we shouldn't use steel or stainless tweezer (
).

27_ Rate of heating has influence on hardness and on over all dimensions of the investment
(. )

28_ Accelerated casting method reduce the time of both bench set of the investment &
burnout ( )

Complete:

1_ What is one common cause of surface roughness in castings?

2_ It is a device which uses heat source to melt the alloy casting force (......................... )

3_ Casting machines use :

_
_
_

4_ There are two methods of investing the wax pattern : ................... and ...................... .

5_ Technique ............... and ................. requires a heat source to melt the alloy casting force
.

6_ Three fuel sources are used for casting Torch ; .......... , ........... , ............ .

7_ Casting defects are .............. ,............... ,............. ,.......... ,..................... ,............

8_.............is process by which the sprued wax pattern is embedded in a material called
investment .

9_ investment must be able to withstand....... , ...........of casting, and must ........to the
pattern in away such as........ , ................are exactly reproduced.

10_ there are two types of material used for casting wax pattern.................. , ............. .

11_ There are two types of expansion ................ , .................. .

12_ Heat is used while burning out depend on.............,................... .

13_ Heat of phosphate bonded investment is..............., gypsum bonded investment

is...............

14_ Type of tweezer is used to remove metal are............. or ............ .

15_ surface tarnish or oxidation can be removed by the process of ..................... .