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Fixed Prosth > New Material for Final > Flashcards

New Material for Final Flashcards

1
Q

Minimum distance from top of wax pattern to top of casting ring

A

6 mm

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2
Q

Sprue and shrinkage of metal

A

The metal within the sprue must remain molten slightly longer than the metal in the mold. This provides a reservoir to compensate for the shrinkage that occurs during solidification of the casting alloy.

Bulges in the sprue
Want the last part to cool to be in the sprue

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3
Q

Sprue materials

A

Wax
Plastic (Rigid)
Hollow plastic (Allows for better escape of the wax during burnout)
Metal

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4
Q

Purposes of the Sprue

A

Allows molten wax to escape the mold
Allows molten metal to flow into mold
Provides reservoir of metal to compensate for shrinkage during solidification

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5
Q

Sprue sizes for
Molars
Premolars and partial coverage castings

A

Molars: 10 gauge (2.5 mm diameter)

Premolars and partial coverage castings: 12 gauge (2.0 mm diameter)

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6
Q

Good sprue characteristics

A

Generally, larger is better, provides better reservoir of metal
Built in reservoirs
Attached to bulkiest, non-critical part of pattern
Creates path of least resistance and turbulence
Place at an angle so molten metal doesn’t have to flow in a direction opposite of centrifugal force

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7
Q

Attachment of sprue

A

Should be carefully smoothed to minimize turbulence
Should not be restricted (necking) - can increase chances of casting porosity and can reduce mold filling
Should not be excessively wide - causes this portion to solidify last and create ‘suck-back’ or ‘shrink-spot’ porosity’

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8
Q

Crucible Former

A

Usually made of rubber for easy separation from investment and casting ring
Attaches to other end of the sprue
Creates funnel shape through which the molten metal flows

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9
Q

Purposes of Casting Ring

A

Surrounds wax pattern? and confines investment while it sets and restricts the setting expansion

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10
Q

Ring liner

A

allows for investment expansion

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11
Q

Investment made of

A

Refractory Material - usually silica
Binder Material - provides strength
Additives

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12
Q

Refractory materials

A

Silica - silicon dioxide - SiO2
Quartz
Cristobalite

Filler material

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13
Q

Modifiers

A

Accelerators
Retarders
Dimension Control
Coloring Agents

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14
Q

Types of Investment

A

Gypsum Bonded
Phosphate Bonded
Ethyl-Silica Bonded

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15
Q

Gypsum Bonded Investments not stable above what temp

A

650 C

1200 F

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16
Q

Gypsum Bonded Investments used for which gold alloys

A

I
II
III
IV

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17
Q

What is the refractory material for Gypsum Bonded investments

A

Cristobalite or quartz

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18
Q

Which Investment type is easiest to work with

why

A

Gypsum Bonded Investment
Best surface reproduction, smoother castings
Softer investment, easier to retrieve casting
More porous, facilitating more complete mold filling

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19
Q

What happens during burn out on Gypsum bonded investments

A

SiO2 undergoes alpha to beta phase change

Thermal expansion

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20
Q

What is the binder in Gypsum-bonded investments

A

Gypsum

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21
Q

What is responsible for thermal expansion in investments

A

The refractory material - like cristobalite and quartz

this is during wax elimination

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22
Q

Types of expansion of Gypsum-bonded investments that can be manipulated to obtain desired size of casting

A

Setting Expansion
Hygroscopic expansion
Thermal expansion

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23
Q

What factors increase expansion during investment setting

A

Less water
Casting Ring liners, more liners = more expansion
Two ring liners
Prolonged Spatulation
Water Bath (100F for 1 hour immediately after investing) - Hygroscopic Expansion
Use Dry Ring Liner
Use Ringless investment Technique

Stone and investment both expand

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24
Q

What contracts during casting process

A

Wax pattern

Cooling alloy

25
Q

It is bad to have a casting that is slightly oversized

A

False

advantageous for accurate seating

26
Q

First place to look if crown is not seating properly - most common problem area

A

Interproximal contacts

27
Q

Order from most to least expansion

A 
Hygroscopic expansion (under water submersion or wet liner)
2 liners
Semihygroscopic expansion
1 liner
Normal setting expansion
28
Q

Factors that reduce expansion with gypsum bonded investments

A

Add water to the mix

Eliminate the casting ring liner

29
Q

Phosphate bonded investments

Most are mixed with what for what reason

A

Mixed with suspension of colloidal silica in water
Adding water to colloidal suspension increases working time and decreases expansion

some mixed with water alone

30
Q

Binder of phosphate bonded investments

A

consists of magnesium oxide and ammonium phosphate

31
Q

Temperature characteristic of phosphate bonded investments

Used for what materials

A

Stable at much higher burn out temperatures

Suitable for metal-ceramic alloys which typically fuse around 2550 F

32
Q

Expansion of phosphate bonded investment

A

more silica refractory material which creates more expansion in burn out oven
Compensates for additional shrinkage of metal as it cools from a higher casting temperature

33
Q

Ethyl-Silica Bonded Investments

A

Used for high-melting base metal alloys

Partial denture frameworks

34
Q

Quenching
what
used for what

A

Casting is placed in water when the button no longer has a red glow

Interferes with the crystalline lattice of the alloy

Results in a softer, more malleable alloy

35
Q

Different Casting Alloys

A 
Types: I
II
III
IV
Metal Ceramic Alloys
Base metal alloys - don't use
36
Q

Properties and uses of Casting Alloy Type I

A

Soft

Simple Inlays

37
Q

Properties and uses of Casting Alloy Type II

A

Medium hardness

Complex inlays, onlays, single unit crowns

38
Q

Properties and uses of Casting Alloy Type III

A

Hard

Crowns and Fixed Dental prostheses

39
Q

Properties and uses of Casting Alloy Type IV

A

Extra hard

Partial denture frameworks

40
Q

Fusing Temperature

A

Melting point of the alloy

41
Q

Fusing temperature of gold alloys

A

plus or minus 1700 F

925 C

42
Q

Fusing temperature of Metal-ceramic allys

A

plus or minus 2550 F

1400C

43
Q

More copper in gold alloy results in

A

more yellow color

44
Q

Gold is more biocompatible, avoid what metal

A

Ni

45
Q

In karat parts, what is pure, 75%

in Fineness

A

24 karat - pure
18 karat - 75%

1000 fine - pure gold
750 fine - 75% gold

46
Q

Alloy weight
Pennyweight
pound

A

20 dwt/pennyweight = 1 oz.

12 oz. - 1 lb

47
Q

Six zones of evaluation

A
  1. Intaglio surface - including internal margin
  2. Sprue Area
  3. Proximal Contacts
  4. Occlusal Surface
  5. Axial Walls
  6. External Margin
48
Q

First place to look in first zone

A

Internal margin
start over if defected
Do not try on die until entire intaglio surface is free of irregularities

49
Q

Where should casting contact tooth or die when placed

A

Only on margin area, because of die spacer

space of 25-35 microns

50
Q

Use what, and take away how much when removing defects on intaglio surface
Micro etch

A

Use small carbide burr to remove slightly more than the defect itself
micro-etch entire intaglio surface

51
Q

Forcing casting onto die

A

never force casting onto die

52
Q

Internal marking agents

A 
Liqua-mark (water-soluble die)
AccuFilm IV (solvent-based die)
Occlude (powdered spray)
Rouge in Turpentine
Fit checker (elastomeric detection paste)
53
Q

How to remove sprue

A

Section sprue circumferentially with carborundum disc

Bend and twist remaining attachment

54
Q

Proximal contacts should be broad in which directions

A

All directions

Articulating paper can be used when contacts need to be reduced

55
Q

Before adjusting occlusal surface

A

check thickness of casting with Iwanson thickness gauge

56
Q

Contacts on occlusal surface should not be where

A

On inclines in either MI or excursions

Should be centrum type contacts

57
Q

Benefit of a highly polished surface

A

Enables patient to carry out optimum plaque control

58
Q

the best marginal adaptation of gold alloy is done where

A

directly on the tooth

an advantage of partial coverage inlays, onlays, 3/4 and 7/8 crowns

Fixed Prosth (2 decks)

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