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PROSTHO > INVESTING AND CASTING PROCEDURE (dls > Flashcards

INVESTING AND CASTING PROCEDURE (dls Flashcards

1
Q

T/ f

SPRUING

The sprue must allow the molten wax to escape from the mold.

A

T

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2
Q

T/ f

SPRUING

The sprue must enable the molten metal to flow into the mold with as little turbulence as possible.

A

T

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3
Q

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.

A

T

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4
Q

The sprue can be made from?

A

wax, plastic, or metal.

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5
Q

T/ F

Wax sprues are preferred for most castings because they melt at the same rate as the pattern.

A

T

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6
Q

DIAMETER
• Metals and metal-ceramic patterns: __mm sprue

A

2.5

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7
Q

DIAMETER

Premolar and partial coverage restorations: ___mm sprue

A

2.0

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8
Q

T/ F

LOCATION
• The sprue should be attached to the bulkiest noncritical part of the pattern, away from margins and occlusal contacts.

A

T

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9
Q

T/ F

LOCATION

Normally, the largest nonfunctional cusp is used.

A

T

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10
Q

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

A

crucible former

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11
Q

The casting ring serves as a ___ for the investment while it sets and restricts the setting expansion of the mold.

A

container

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12
Q

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.

A

inside

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13
Q

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.

A

hygroscopic

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14
Q

have a carcinogenic potential (used earlier)

A. Asbestos liner
B. Non-asbestos

A

Asbestos liners

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15
Q

• Cellulose paper liner

A. Asbestos liner
B. Non-asbestos

A

A

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16
Q

• Cermic ring liner (alumino-silicate fibrous material)

A. Asbestos liner
B. Non-asbestos

A

B

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17
Q

Combination of cellulose and ceramic ring liner

A. Asbestos liner
B. Non-asbestos

A

B

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18
Q

No liner&raquo_space; expansion is toward the center of the mold&raquo_space;_____

A

distorted cast

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19
Q

for high melting base metal alloys used in casting partial removable dentures

A

Silica bonded

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20
Q

INVESTING
ARMAMENTARIUM: [9]

A

• 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

21
Q

T/ f

INVESTING PROCEDURE:
BRUSH TECHNIQUE
Select the correct program on the mixing unit in accordance with the manufacturer’s instructions

A

T

22
Q

BURNOUT (WAX ELIMINATION)

  1. 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.
A

37°C

23
Q

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.

A

down

24
Q

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.

A

200

25
Q

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.

A

45

26
Q

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.

A

cherry-red

27
Q

CASTING ARMAMENTARIUM:
[6]

A

• Broken-arm (Kerr) centrifugal casting machine
• Crucible
• Blowtorch
• Protective colored goggles
• Tongs Casting alloy
• Flux

28
Q

CASTING Procedure

The crucible is preheated, particularly over the trajectory that will be in contact with the alloy, and the alloy is added.

A

1

29
Q

CASTING Procedure

The mold is placed in the cradle of the casting machine

A

2

30
Q

CASTING Procedure

The mold is kept on the alloy with the reducing flame until
the crucible is moved into position

A

3

31
Q

CASTING Procedure

The casting machine arm is then rested to amke the casting

A

4

32
Q

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

A

5

33
Q

CASTING Procedure

Oxides are removed by pickling in % hydrochloric acid (or
preferably, a non-fuming substitute)

A

6

34
Q

CASTING Procedure

A knife to trim the investment at the bottom end of then ring

A

7

35
Q

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.

A

8

36
Q

CASTING Procedure

It is then broken apart under running water ( bacausee it is
still hot)

A

9

37
Q

CASTING Procedure

The remaining investment is carefully removed with a small
blunt instrument

A

10

38
Q

Incomplete wax elimination
Problem?

A

Rough casting

39
Q

Improper pattern position Narrow, long sprue

P?

A

Large nodules

40
Q

Particle of investment dislodged during casting

P?

A

Multiple nodules

41
Q

Wax pattern distortion
Uneven expansion

P?

A

Nodules on occlusal surface

42
Q

Improper water-to- powder ratio Improper mixing time Improper burnout temperature

P?

A

Fins

43
Q

Wax pattern too thin Cool mold or melted alloy Inadequate metal
P?

A

Incomplete casting

44
Q

Incomplete wax elimination

P?

A

Incomplete casting with shiny, rounded defect

45
Q

Improper pattern position
Narrow, long sprue

P?

A

Solidification shrinkage (“suck- back”) porosity

46
Q

Particle of investment dislodged during casting

P?

A

Inclusion porosity

47
Q

Wax pattern distortion
Uneven expansion

P?

A

Marginal discrepancy

48
Q

Improper water-to- powder ratio Improper mixing time Improper burnout temperature

P?

A

Inadequate or excessive expansion

PROSTHO (17 decks)

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