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DMT > Gold alloys and semi-precious alloys > Flashcards

Gold alloys and semi-precious alloys Flashcards

1
Q

Define noble

A

Metals that do not oxidise easily

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2
Q

Examples of noble metals

A

Gold, platinum and palladium

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3
Q

Define precious

A

Related to how valuable the metal is

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4
Q

Examples of precious metals

A

Gold, platinum and silver

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5
Q

Why is gold good for restoring teeth?

A

Ductile - easily shape to fill cavity
Soft - easily distorted
Stable/un-reactive
Coefficient of thermal expansion similar to tooth

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6
Q

Advantages of gold foil

A

Ductile so conform to fit cavity

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7
Q

Disadvantages of gold foil

A

Expensive
Never fully dense = marginal staining
Poor mechanical properties so limited to small cavities

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8
Q

Advantages of gold alloys

A

Cheaper

Harder

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9
Q

Alloys are less ductile than pure gold, what does this mean for restorations?

A

Can’t be shaped to fit cavity, must now be done by casting

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10
Q

How are dental gold alloys classified?

A

Type I = soft
Type II = medium
Type III = hard
Type IV = extra hard

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11
Q

Through what process do gold alloys improve mechanical strength and hardness?

A

Solution hardening

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12
Q

What is quenching?

A

Mold placed in cool liquid and liquid metal poured into this = increased rate of cooling

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13
Q

Effect of quenching?

A

Improve mechanical properties

smaller grains = higher yield strength

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14
Q

Consequence of quenching

A

Cooling down quickly leads to coring

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15
Q

Effect of coring?

A

Effects corrosion resistance

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16
Q

How is coring removed?

A

Homogenization

17
Q

How are dental alloys cast? What is the effect of this?

A

Quenching

Small grains = increase yield strength but also coring = homogenisation

18
Q

How can properties of gold alloys be improved?

A

Solution hardening
Precipitation hardening
Order hardening
Work hardening

19
Q

What is order hardening?

A

Controlled Cu and Au content - heat treatment

20
Q

What type of gold alloy may be used for small occlusal restorations?

A

Pure gold or Type I alloys (inlays)

21
Q

What type of gold alloy may be used for medium stress bearing applications like large inlays?

A

Type II

22
Q

What type of gold alloy may be used for high stress bearing applications like full crowns, denture components

A

Type III and IV

Hardening

23
Q

Advantages of medium/low gold content materials?

A

Cheap
Whitish appearance
Similar properties to type III and IV gold alloys = strong, rigid

24
Q

Disadvantages of medium/low gold content?

A

Lower density than high gold content = less accurate

25
Q

Properties of silver/palladium

A

Lower density than gold alloys = less accurate
Oxygen dissolves in molten alloy = porous
Adequate corrosion resistance
Similar to type III gold alloys

DMT (11 decks)

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