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BDS 2: Dental Materials > Dental Amalgams > Flashcards

Dental Amalgams Flashcards

1
Q

Define amalgam

A

When mercury is mixed with another metal

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2
Q

What metal is mercury mixed with in dental amalgams?

A

Mercury + silver tin alloy

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3
Q

List the chemical symbols for the following;

  • Silver
  • Tin
  • Copper
  • Zinc
  • Palladium
  • Indium
  • Mercury
A
  • Ag
  • Sn
  • Cu
  • Zn
  • Pd
  • In
  • Hg
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4
Q

What is the composition of conventional amalgam? (5)

What intermettalic compound is found in the composition?

A
  • Silver (67-74%)
  • Tin (25-28%)
  • Copper (0-6%)
  • Zinc (0-2%)
  • Mercury

(Alloy contains gamma phase Ag3Sn An intermetallic compound)

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5
Q

What are other names for conventional amalgam? (2)

A
  • Traditional amalgam

- Low copper amalgam

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6
Q

What is the composition of high copper amalgam? (7)

A
  • Silver (40-70%)
  • Tin (21-30%)
  • Copper (12-30%)
  • Zinc (0-1%)
  • Palladium (0-0.5%)
  • Indium (0-4%)
  • Mercury
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7
Q

Give an example of a single ternary alloy used in high copper amalgams?
What are its components?

A
  • Tytin

- Ag-Sn-Cu

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8
Q

What are the components of a quaternary alloy used in high copper amalgams?

A

Ag-Sn-Cu-In

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9
Q

What does silver do in dental amalgams?

Increase (3)
Decreases (2)

A
  • Increases strength
  • Increases tarnish and corrosion resistance
  • Increases expansion
  • Decreases flow and creep
  • Decreases setting time
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10
Q

What does tin do in dental amalgams?

Increase (2)
Decreases (3)

A
  • Increases setting time
  • Increases flow and creep
  • Decreases strength
  • Decreases tarnish and corrosion resistance
  • Decreases expansion
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11
Q

What does copper do in dental amalgams?

Increase (3)
Decreases (2)

A
  • Increases strength + hardness
  • Increases tarnish and corrosion resistance
  • Increases expansion
  • Decreases flow and creep
  • Decreases setting time
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12
Q

What is the function of zinc in copper amalgams?

A

Acts as a scavenger

decreases oxidation of other metals

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13
Q

What is the function of mercury in copper amalgams?

A

Activates reaction

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14
Q

What does palladium increase in copper amalgams? (2)

A
  • Increases strength

- Increases tarnish and corrosion resistance

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15
Q

What does indium do in dental amalgams?

Increase (3)
Decreases (2)

A
  • Increases strength
  • Increases setting time
  • Increases expansion
  • Decreases flow and creep
  • Decreases surface tension and so the amount of mercury required is less
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16
Q

When the alloys for the amalgams are ‘lathe-cut’ what process need to occur to form the gamma phase of the alloy?

What are the alloy particles cut from?

At what temperature do particles anneal?

What is surface treated with to increase reactivity?

A
  • Needs homogenising to form gamma phase
    (400°C for up to 8 hours)
  • Particles cut from ingot
  • Annealed at 100°C to relieve internal strains
  • Surface treated with acid to increase reactivity
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17
Q

How are spherical alloy particles produced?

What is surface treated with to increase reactivity?

A
  • Spherical particles are produced by atomising molten alloy in an inert atmosphere
  • Acid washed to increase reactivity
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18
Q

What are the advantages of using spherical particles over lathe-cut? (5)

A
  • Require less mercury
  • Require less mixing time
  • Require lower condensation pressures
  • Harden more rapidly
  • Smoother surface for restoration
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19
Q

What are the new mercury intermetallic compounds formed after mixing of low copper amalgam? (2)

A
  • Ag2Hg3

- Sn7Hg

20
Q

What is 30% of set low copper amalgam formed of?

A

Unreacted Ag3Sn

strongest phase

21
Q

What is 60% of set low copper amalgam formed of?

A

Ag2Hg3

2nd strongest phase

22
Q

What is 10% of set low copper amalgam formed of?

A

Sn7Hg

weakest phase

23
Q

Explain the series of dimensional changes of amalgams

A
  • Initial shrinkage due to alloy dissolution
  • Expansion occurs from growth of crystalline phases
  • Stable after 6-8 hours
24
Q

How does mercury content affect expansion of amalgams?

A

The higher the mercury content the higher the expansion

25
Q

What factors of dental amalgams increase shrinkage? (4)

A
  • Smaller particle size
  • Higher Hg:Alloy
  • Trituration time longer and more rapid
  • Condensation pressure higher
26
Q

What is a Trituration?

A
  • Mechanical mixer
  • 3000 rpm
  • 5-20 seconds
27
Q

What is the gamma phase?

A

Ag3Sn

28
Q

What is epsilon phase?

A

Cu3Sn

29
Q

What is gamma 2 phase?

A

Sn7-8Hg

30
Q

What is eta phase?

A

Cu6Sn5

31
Q

If amalgam is under-trituated what would you see?

A

Dull, dry and crumbly mix

32
Q

If amalgam is over-trituated what would you see?

A

Shiny, hot, wet mix, sticks to capsule

33
Q

Why are amalgams condensed? (3)

A
  • Removes excess mercury
  • Prevent voids
  • Give optimum marginal adaptation
34
Q

Why may delayed expansion of the amalgam occur?

A
  • If a zinc containing alloy becomes contaminated with water
  • Hydrogen is evolved.
  • Which causes an expansion
35
Q

What is tarnish of amalgams?

What compound causes this?

A

Surface discolouration caused by black silver sulphide

36
Q

Put the phases in order of corrosion resistance

A 
Ag2Hg3 (gamma 1)
Ag3Sn (gamma) 
Ag3Cu2 
Cu3Sn (epsilon) 
Cu6Sn5 (eta) 
Sn7-8Hg (gamma 2)
37
Q

What is galvanic corrosion?

A

When there are 2 opposing dissimilar metals and one corrodes the other

38
Q

What is crevice corrosion?

A

Plaque build-up increases electronegativity with respect to clean surface. Causing the plaque surface to corrode

39
Q

What is stress corrosion?

A

Occurs under a sustained tensile force in corrosive environment

40
Q

What is the longevity of amalgams?

A

12 years

41
Q

What are some disadvantages of amalgams? (6)

A
  • Non adhesive
  • Conducts heat/electricity
  • Corrosion/Tarnish
  • Poor aesthetics
  • Brittle
  • Viscoelastic
42
Q

How can the quality of the amalgam be controlled by the dentist? (5)

A
  • Trituration procedures
  • Cavity designs
  • Condensation technique
  • Marginal integrity
  • Anatomy
43
Q

What is an amalgam tattoo?

A

Accidental implantation of silver containing compounds into oral mucosal tissue.

(Grayish/black pigmentation)

44
Q

Why aren’t gallium alloys used anymore? (4)

A
  • Poor corrosion resistance
  • Prone to delayed expansion
  • Expensive
  • Very wet mix and difficult to handle
45
Q

What are fluoridated amalgams?

A
  • Contains fluoride containing glass particles

- More susceptible to erosion

BDS 2: Dental Materials (13 decks)

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