INVESTING AND CASTING PROCEDURE (dls Flashcards
T/ f
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
T/ F
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.
T
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
T/ f
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
BURNOUT (WAX ELIMINATION)
Increase the heat to the final burnout temperature (generally 650°C [1202°F] or 480°C [896°F] if a hygroscopic technique is used and hold that temperature for ___ minutes.
45
When the casting ring is transferred to the casting machine, a quick visual check of the sprue in shaded light is helpful to see whether it is properly heated. It should be a ____ color.
cherry-red
CASTING ARMAMENTARIUM:
[6]
• Broken-arm (Kerr) centrifugal casting machine
• Crucible
• Blowtorch
• Protective colored goggles
• Tongs Casting alloy
• Flux
CASTING Procedure
The crucible is preheated, particularly over the trajectory that will be in contact with the alloy, and the alloy is added.
1
CASTING Procedure
The mold is placed in the cradle of the casting machine
2
CASTING Procedure
The mold is kept on the alloy with the reducing flame until
the crucible is moved into position
3
CASTING Procedure
The casting machine arm is then rested to amke the casting
4
CASTING Procedure
After the red glow has disappeared from the button, the
casting ring is plunged under running cold water into a large
rubber bowl
5
CASTING Procedure
Oxides are removed by pickling in % hydrochloric acid (or
preferably, a non-fuming substitute)
6
CASTING Procedure
A knife to trim the investment at the bottom end of then ring
7
CASTING Procedure
The other end is not trimmed because of the risk of
damaging the margin. When the ring liner is exposed, the
investment can be pushed out of the ring.
8
CASTING Procedure
It is then broken apart under running water ( bacausee it is
still hot)
9
CASTING Procedure
The remaining investment is carefully removed with a small
blunt instrument
10
Incomplete wax elimination
Problem?
Rough casting
Improper pattern position Narrow, long sprue
P?
Large nodules
Particle of investment dislodged during casting
P?
Multiple nodules
Wax pattern distortion
Uneven expansion
P?
Nodules on occlusal surface
Improper water-to- powder ratio Improper mixing time Improper burnout temperature
P?
Fins
Wax pattern too thin Cool mold or melted alloy Inadequate metal
P?
Incomplete casting
Incomplete wax elimination
P?
Incomplete casting with shiny, rounded defect
Improper pattern position
Narrow, long sprue
P?
Solidification shrinkage (“suck- back”) porosity
Particle of investment dislodged during casting
P?
Inclusion porosity
Wax pattern distortion
Uneven expansion
P?
Marginal discrepancy
Improper water-to- powder ratio Improper mixing time Improper burnout temperature
P?
Inadequate or excessive expansion
