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Fixed > Invesring And Casting > Flashcards

Invesring And Casting Flashcards

1
Q

List steps of investing and casting

A

1-spruing
2-investing
3-casting

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2
Q

Sprue: is ..

A

a channel through which the wax pattern is eliminated& the molten alloy is Pushed to fill the mould cavity completely

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3
Q

Sprue former: is …

A

a wax , plastic, or metal rod used to produce sprue channel with Desired shape and size.

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4
Q

Basic requirement of sprue

A

1-The sprue must allow complete escapement of molten wax

2-Easy flow of the molten alloy

3-The metal within it must remain molten until complete solidification

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5
Q

The metal within it must remain molten until complete solidification of the molten Alloy of the mold cavity, why ?

A

act as a reservoir to compensate for the shrinkage that Occurs during solidification of the casting

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6
Q

Wax (sprue) advantages

A

it melt at same temperature of wax pattern

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7
Q

Plastic (sprue) advantages , disadvantages

A

Used when spruing long span fixed partial dentures

plastic sprue formers soften at higher temperature than the wax pattern

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8
Q

Location of sprue former

A

Attached to the thickest non-functional cusp on the wax pattern , thin area causes localized shrinkage porosity

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9
Q

Diameter of sprue former

A

2.5mm(10-gauge)s for molar and metal-ceramic patterns

smaller 2mm(12-gauge) for premolars and partial coverage restorations.

sprue former should be thicker than the thickest portion of the wax pattern

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10
Q

If the sprue former diameter is too small the result ….

If too large diameter …..

A

(suck-back) porosity

spread the molten alloy faster before The gases eliminated from the mold cavity (incomplete casting.)

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11
Q

using air-pressure casting Machine It is preferred to use ….

A

narrower diameter sprue formers

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12
Q

Angulations of sprue former

A

The sprue former should be attached at 45 to the surface of the wax pattern and should not attached at right angle

Because the molten alloy when enter to the mold change the direction and lead To development of turbulence which will cause porosity

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13
Q

Attachment of sprue former to wax pattern ?

A

by adding drop of sticky wax

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14
Q

Reservoir

A

It is apiece of wax attached to the sprue former , and placed as close to the wax pattern as possible to compensate the solidification shrinkage

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15
Q

Accessory spruing is

A

vent to allow escape of the air& gases from the mold during casting

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16
Q

Length of sprue former

A

6-8mm should be left from the end of the ring in case of gypsum-bonded

3-4mm in phosphate –bonded investment.

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17
Q

highest point of the wax pattern should be at…. Distance from the end of the ring.

A

6.0mm

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18
Q

If the sprue too short it will

A

increase the thickness of the Investment bridge, so during casting the air inside the mold will not escape readily through the thick bridge and result in back-pressure porosity.

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19
Q

If the sprue too long

A

the investment bridge will be very thin And may fracture due to casting force of the molten alloy And if the sprue too thin and long the alloy may solidify Before complete fill of the mold.

20
Q

Sprue former should be (in shape )

A

straight as possible to minimize turbulence as the alloy Enter the mold.

21
Q

There are two basic designs of sprue formers;

A

Direct spruing: in which the sprue former provides direct connection between the wax pattern and crucible former.

Indirect spruing: in which the wax pattern connect indirectly to the crucible former by bar .

22
Q

For Single small size restoration the design is

A

straight single and direct
Sprue used for casting

23
Q

in spruing anterior teeth for metal-ceramic restoration the sprue is

A

attached to the thin area of the wax pattern

24
Q

For single large size restorations…….. is recommended

A

double spruing , Direct double V-shaped sprue former (noble alloy)

25
Q

Indirect double sprue former design for…

A

large restorations casted With base metal alloy

26
Q

Direct spruing are preferred for……..

Indirect spruing are preferred for……….

A

air-pressure casting machine

casting base metal alloy

27
Q

Crucible former

A

Base of the casting ring during investing

28
Q

If the ring liner is absent

A

the investment will expand in inward direction towards the mold cavity leading to distortion of the restoration.

29
Q

Before investing the wax pattern should be sprayed by… which act as ….

A

wetting agent (Debubblizer) to Act as surface tension reducer

30
Q

Requirements of dental casting investment

A

1-accuratly wet the wax pattern produce its details
2-withstand high temperature of burn out of wax
3-high strength enough to with-stand casting pressure
4-sufficient porosity to allow air escapement during casting
5-chemical stability at high temperature of casting
6-have total amount of expansion (setting-hygroscopic-thermal)
7-has minimum setting expansion to prevent wax pattern distortion
8-easy recovery of casting

31
Q

GYPSUM BONDED INVESTMENT, used for casting of gold alloys because

A

A-it is not chemically stable above 650
B-produce expansion suitable for shrinkage of the gold

32
Q

PHOSPHATE BOMDED INVESTMENT , used for casting of high melting alloys e.g. base metal alloys because

A

1-it is chemically stable up to 1100c
2-it produce thermal expansion higher than gypsum bonded investment

33
Q

gypsum and phosphate bonded investment are available in two forms:

A

Conventional type ((750c for gypsum-950c for phosphate))

Heat sock type

34
Q

Silicate Bonded Investments used with

A

Base metal alloys such as chrom-cobalt and steel needs high temperatures for melting 1250-1400 and silica can be heated up to 1200c

35
Q

Investing techniques:

A

I- Brush technique II-Vacuum technique

36
Q

Brush technique produce better casting because.

A

it can reduce the air entrapment and the investment wet the pattern very well

37
Q

Reducing zone:

A

hottest zone which blue in color

38
Q

zone used to melt the alloy

A

The reducing zone

39
Q

There are two types of blow torch:

A

1-Gas-air torch , used for melting of gold alloy

2-Gas-oxygen torch , used for melting of base metal and porcelain fusion

40
Q

Casting machines

A

1-air pressure casting machine
2-vacuum casting machine both of them used with gold alloy
3-centrifugal casting machine used for gold and base metal alloy

41
Q

The crucible may be….. which used for……., or …..used for…….

A

ceramic , base metal alloy

graphite, gold alloy melting

42
Q

finishing can be divided to zones:

A

Zone-1-internal margin
any defect at this area usually need remake of restoration

Zone-2-internal surface

Zone-3-the sprue

Zone-4-proximal contacts

Zone-5-occlusal surface

Zone-6-axial walls

Zone-7-External margins

43
Q

List Casting defects

A

1-Incomplete casting
2-Suk-back porosity
3-Rough casting
4-Large nodule
5-Multiple nodule
6-fins
7-Marginal discrepancy

44
Q

Inclusion porosity …….

Back-pressure porosity…..

A

-particles of investment dislodged during casting

-due to improper air escapement through the pores of investment During casting due to:
1-lake of pores in investment
2-improper investment bridge thickness (more than 8mm)
3-too short sprue

45
Q

Under-sized restoration =

Over sized restoration =

A

-new restoration should be done
* difference in solidification (less/more)

Fixed (10 decks)

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