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BDS2 - DMS > Partial Denture Alloys > Flashcards

Partial Denture Alloys Flashcards

1
Q

What are the ideal properties for partial denture alloys? (7 points)

A
  • Rigid (YM)
  • Strong (UTS, EL)
  • Hard
  • Ductile
  • Precise casting (shrinkage)
  • Melting point ( will indictae what type of investment material you will use in the process)
  • Density
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2
Q

What are 4 examples of partial denture alloys?

A
  • ADA type IV gold
  • Which gold (Ag-Pd)
  • Co-Cr
  • Titanium
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3
Q

What do we want the base of a RPD to be like?

A
  • High YM - to maintain shape in use

- High EL - to avoid plastic deformation

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4
Q

What do we want the clasp of an RPD to be like?

A
  • Lower YM - to allow flexure over tooth

- High EL - maintain elasticity over wide range of movement

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5
Q

What is pure gold used for in dentistry?

A

Class III and Class IV cavities

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6
Q

What are type I gold alloys used for?

A
  • Simple alloys
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7
Q

What are type II gold alloys used for?

A

Larger (2-3 surface) inlays

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8
Q

What are type III gold alloys used for?

A

Crown and bridge alloys

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9
Q

What are type IV gold alloys used for?

A

Partial dentures

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10
Q

What is the composition of type IV gold? (6 points)

A
  • Au
  • Ag
  • Cu
  • Zn
  • Pd
  • Pt
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11
Q

What % of Au is present in type IV gold?

A

65%

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12
Q

What % of Ag is present in type IV gold?

A

14%

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13
Q

What % of

Cu is present in type IV gold?

A

14%

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14
Q

What % of Zn is present in type IV gold?

A

2%

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15
Q

What % of Pd is present in type IV gold?

A

3%

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16
Q

What % of Pt is present in type IV gold?

A

2%

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17
Q

What effect doe the presence of copper have on type IV alloy? (8 points)

A
  • Solid solution in all proportions
  • Solution hardening
  • Order hardening - if 40%-80% gold and correct hea t treatment
  • Reduced melting point
  • No coring - solidus close to liquidus
  • Imparts red colour (if sufficient quantity)
  • Reduces density
  • Base metal - can corrode if too much
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18
Q

What effect does the presence of silver have on type IV alloy? (6 points)

A
  • Solid solution in all proportions
  • Solution hardening
  • Precipitation hardening with COPPER & heat treatment
  • Can allow tarnishing
  • Molten silver absorbs gas - creates porosity
  • Whitens alloy - compensates for copper
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19
Q

Can the presence of silver in type IV gold alloy cause coring?

A
  • Yes
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20
Q

What effect does the presence of platinum have on type IV alloy? (4 points)

A
  • Solid solution with gold
  • Solution hardening
  • Fine grain structure (better mechanical properties)
  • Coring can occur (wide liqui dous - solidus gap)
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21
Q

What effect does the presence of palladium have on type IV alloy? (4 points)

A
  • Similar to Pt but less expensive
  • LESS CORING than Pt
  • COARSER GRAINS than Pt
  • ABSORBS GASSES when molten - porous casting
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22
Q

What effect does the presence of zinc have on type IV alloy?

A

Scavenger

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23
Q

What effect does the presence of nickel have on type IV alloy?

A
  • Increases hardness & strength (wrought alloys)
24
Q

What effect does the presence of indium have on type IV alloy?

A
  • Fine grain structure
25
Q

What is the process of heat treatment of Type IV gold alloy? (4 points)

A

1) Quench after casting (fine grains)
2) Homogenising anneal (700 degrees, 10 mins) as some degree of coring has been created previously
3) If cold worked - stress relief anneal
4) Heat harden - (order and precipitation) -> 450 degrees cool slowly (15-30 mins) to 200 degrees then quench

(all of these processes try to improve the properties of the partial denture)

26
Q

What are CoCr alloys used for? (3 points)

A
  • Wires
  • Surgical implants
  • Cast partial dentures
27
Q

What is involved in the composition of CoCr alloy? (5 points)

A
  • Co
  • Cr
  • Ni
  • Mo
  • C
28
Q

What is the % composition of Co in a CoCr alloy?

A

54%

29
Q

What is the % composition of Cr in a CoCr alloy?

A

25%

30
Q

What is the % composition of Ni in a CoCr alloy?

A

15%

31
Q

What is the % composition of Mo in a CoCr alloy?

A

5%

32
Q

What is the % composition of C in a CoCr alloy?

A

0.4%

33
Q

What effects does the presence of cobalt in a CoCr alloy have? (3 points)

A
  • Forms solid solution with Cr
  • Increased strength, hardness, rigidity
  • CORING possible
34
Q

What effects does the presence of cobalt in a CoCr alloy have? (4 points)

A
  • Forms solid solution with Co
  • Increased strength, hardness, rigidity
  • Coring possible
  • Forms passive layer - corrosive resistance
35
Q

What effects does the presence of nickel in a CoCr alloy have? (4 points)

A
  • Replaces some Co
  • Improves ductility
  • Slight reduction in strength
  • Sensitivity: 6% females, 2% males
36
Q

What effects does the presence of carbon in a CoCr alloy have?

A
  • Undesirable, carbide grain boundaries hard and brittle

- Ideally wouldn’t have any carbon at all but during the casting process some of it is inevitable

37
Q

What effects does the presence of Mo in a CoCr alloy have? (2 points)

A

Reduces grain size - hence increases strength

38
Q

What effects does the presence of W (Tungsten) in a CoCr alloy have? (3 points)

A
  • Increases strength
  • Al - increases PL
  • Others: scavengers
39
Q

What is the temperature of investment material and give 2 examples of these in making a CoCr alloy?

A
  • High temp: 1200-1400 degrees

- Hence - silica or phosphate bonded

40
Q

How is a CoCr alloy melted?

A
  • Electric induction preferred

- Oxyacetylene - avo id carbon pickup

41
Q

How should casting of a CoCr alloy be carried out? (3 points)

A
  • Centrifugal force required
  • Avoid overheating - coarse grains
  • Cooling too fast or slow - carbides - brittle
42
Q

What 4 things can be used to finish/polish CoCr?

A
  • Sandblast
  • Electroplate
  • Abrasive wheel
  • Polishing buff
43
Q

Which is harder gold or CoCr?

A

CoCR

  • It wears in the mouth better
44
Q

What is the elongation/ductility of CoCr like? (4 points)

A
  • Low ductility (4%)
  • Work hardens rapidly
  • Adjustment difficult
  • Precision casting
45
Q

What are 4 uses if titanium in dentistry?

A
  • Implants
  • Partial dentures (cast)
  • Crown & bridge (cast)
  • MAxillo-facial skull plates
46
Q

What is one of the main key advantages of using titanium?

A

Good biocompatibility

47
Q

Does titanium have good or bad corrosion resistance?

A

Good (passive oxide layer)

48
Q

What are parts of titanium joined by?

A

Laser welding

49
Q

What is the best RPD alloy in terms of elongation?

A
  • Titanium - but it is V expensive
50
Q

Which RPD alloy has the best UTS?

A

Stainless steel

51
Q

What is the best RPD alloy in term of density?

A

Titanium

52
Q

What is the best RPD alloy in relation to rigidity (YM)?

A
  • Ag-Pd

- Closely followed by Au (hard) and titanium

53
Q

What is the best RPD alloy in relation to hardness?

A
  • CoCr is very hard

- Gold is not as difficult to polish but will wear down more easily

54
Q

What is the best RPD alloy in terms of shrinkage?

A

Gold (hard)

55
Q

Look at property comparison table in lecture

A

:)

BDS2 - DMS (14 decks)

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