INVESTING AND CASTING PROCEDURE (dls Flashcards
(48 cards)
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SPRUING
The sprue must allow the molten wax to escape from the mold.
T
T/ f
SPRUING
The sprue must enable the molten metal to flow into the mold with as little turbulence as possible.
T
T/ f
SPRUING
The metal within it must remain molten slightly longer than the alloy that has filled the mold. This provides a reservoir to compensate for the shrinkage that occurs during solidification of the casting alloy.
T
The sprue can be made from?
wax, plastic, or metal.
T/ F
Wax sprues are preferred for most castings because they melt at the same rate as the pattern.
T
DIAMETER
• Metals and metal-ceramic patterns: __mm sprue
2.5
DIAMETER
Premolar and partial coverage restorations: ___mm sprue
2.0
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LOCATION
• The sprue should be attached to the bulkiest noncritical part of the pattern, away from margins and occlusal contacts.
T
T/ F
LOCATION
Normally, the largest nonfunctional cusp is used.
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RUCIBLE FORMER
• The sprue is attached to a _____ “sprue former”, usually made of rubber, which serves as a base for the casting ring during investing
crucible former
The casting ring serves as a ___ for the investment while it sets and restricts the setting expansion of the mold.
container
CASTING AND RING LINER
Therefore, a liner is placed ____ the ring to allow for more expansion of the investment material during setting and
burnout since the liner is somewhat compressible.
inside
CASTING AND RING LINER
• In case of wetting the liner, the absorbed water help in
______expansion.
• The amount of expansion depends on the number of the
liners used.
hygroscopic
have a carcinogenic potential (used earlier)
A. Asbestos liner
B. Non-asbestos
Asbestos liners
• Cellulose paper liner
A. Asbestos liner
B. Non-asbestos
A
• Cermic ring liner (alumino-silicate fibrous material)
A. Asbestos liner
B. Non-asbestos
B
Combination of cellulose and ceramic ring liner
A. Asbestos liner
B. Non-asbestos
B
No liner»_space; expansion is toward the center of the mold»_space;_____
distorted cast
for high melting base metal alloys used in casting partial removable dentures
Silica bonded
INVESTING
ARMAMENTARIUM: [9]
• Vacuum mixer and bowl
• Vibrator
• Investment powder (gypsum or phosphate bonded)
• Water or colloidal silica
• Spatula
• Brush
• Surfactant graduated cylinder
• Crucible former
• Casting ring and liner
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INVESTING PROCEDURE:
BRUSH TECHNIQUE
Select the correct program on the mixing unit in accordance with the manufacturer’s instructions
T
BURNOUT (WAX ELIMINATION)
- After the ring is filled to the rim, allow the investment to set. If the hygroscopic technique is used, place the ring in a ____ (100°F) water bath for 1 hour.
37°C
BURNOUT (WAX ELIMINATION)
Reexamine the ring for any residual particles, and then place it with the sprue facing ___ in the furnace on a ribbed tray. The tray allows the molten wax to flow out freely.
down
BURNOUT (WAX ELIMINATION)
Heat the furnace to ___°C (392°F), and hold this temperature for 30 minutes. Most of the wax is by then eliminated.
200
