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JK BDS2 CDS DMS > Amalgam > Flashcards

Amalgam Flashcards

1
Q

Dental amalgam is an alloy. It is formed by the reaction of what materials?

A
  • Mercury (liquid)
  • silver, tin, copper and other metals (powder)
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2
Q

What is an alloy?

A

A material made from the mixing of 2 or more metals

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3
Q

What are the 2 different ways in which you can classify amalgam?

A
  • By composition
  • By particle size and shape
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4
Q

When classifying amalgams by composition. What are the 2 different possible compositions of amalgam?

A
  • traditional
  • copper enriched
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5
Q

Why do we sometimes classify amalgams into particle shape and size?

A

as this affects the handling and final properties

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6
Q

What is the composition of amalgam?? (ask about this)

A
  • Ag- silver = 70%
  • Sn - Tin = 25%
  • Cu -Copper = 3%
  • Zn - Zinc - 1%
  • Hg - Mercury - 1%
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7
Q

What are the functions of silver and tin in amalgam?

A

This is an intermetallic compound which reacts with Hg liquid to form amalgam- this is the gamma phase

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8
Q

What is the function of copper in the amalgam?

A

Increases strength and hardness (ensures that the material lasts longer)

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9
Q

What is the function of zinc in the amalgam?

A
  • scavenger during production- preferentially oxidise’s and slag formed/removed - some zinc free

(Zn oxidises to prevent the other materials from oxidising)

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10
Q

What is special about ‘pre-amalgamated’ alloys?

A

They react faster

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11
Q

What makes the liquid Hg in amalgam very pure?

A

It is triple distilled

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12
Q

What is the function of liquid Hg in amalgam?

A

reacts with other metals

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13
Q

What is a lathe cut particle and how is it formed?

A
  • Course, medium, fine
  • like a shaving (creates all sorts of fragments of irregular shape)
  • formed by filling ingots
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14
Q

What is an ingot?

A

A loose term applied to any mass of material specifically cast from a molten state of known composition, weight, shape and physical dimension

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15
Q

What is a spherical/spheroidal particle and how is it formed?

A
  • range of particle sizes
  • formed by spraying molten metal into the inert atmosphere and so they produce globules as they hit the surface underneath
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16
Q

What is the setting reaction of amalgam?

A

Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
- Powder + liquid -> unreacted particles + amalgam matrix

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17
Q

What properties does gamma in the set structure of amalgam have ? (2)

A
  • good strength
  • good corrosion resistance
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18
Q

What property does gamma 1 in the set structure of amalgam have?

A

good corrosion resistance

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19
Q

What properties does gamma 2 in the set structure of amalgam have?

A

weak and poor corrosion resistance

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20
Q

What do voids in the set structure of amalgam cause?

A

decreases strength and increases corrosion

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21
Q

What is the mean tensile strength of the gamma component of amalgam?

A

170MPa

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22
Q

What is the mean tensile strength of the gamma-1 component of amalgam?

A

30MPa

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23
Q

What is the mean tensile strength of the gamma-2 component of amalgam?

A

20MPa

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24
Q

What is the mean tensile strength of amalgam?

A

60MPa

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25
Q

In relation to expansion and contraction during setting dimensional changes of amalgam, what happens in traditional amalgam?

A
  • initial contraction -solution of alloy particles in Hg
  • Expansion- gamma crystallisation
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26
Q

In relation to expansion and contraction during setting dimensional changes of amalgam, what happens in modern amalgam?

A
  • Small contraction
  • solid solution of Hg in Ag3Sn
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27
Q

Why do we use zinc free amalgams for restoration material?

A
  • zinc interacts with saliva and water to produce zinc oxide and hydrogen
  • the bubbles of hydrogen formed within amalgam will do the following:

= pressure build up causing expansion
= downward pressure causing pulpal pain
= upward- restoration sitting proud of surface

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28
Q

What handling factors is amalgam dependent on?

A

proportion & tituration
condensation
carving & polishing

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29
Q

Is amalgam dependent on cavity design?

A

Yes

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30
Q

Will amalgam be affected by corrosion?

A

Yes

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31
Q

What is the compressive strength of traditional amalgams like: after 1 hour and after 24 hours

A
  • one hour - poor (ish)
  • 24 hours = ok
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32
Q

What is the abrasion resistance of amalgam (hard material that resists the surface layer being removed)?

A
  • High, suitable for posterior teeth
  • too high for deciduous
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33
Q

What factors have an effect on decreasing the strength of amalgam? (5)

A
  • undermixing
  • too high Hg content after condensation
  • too low condensation pressure
  • slow rate of packing (so increments do not bond)
  • corrosion
34
Q

Why can creep be a problem with traditional amalgams?

A
  • affects the marginal integrity as the material changes shape when it undergoes creep
  • NB marginal integrity also depends on:

= cavity design
= corrosion

35
Q

What is meant by creep?

A

When a material is repeatedly stressed for long period of time at low stress levels:

e.g. stress is below the elastic limit, it may flow, resulting in permanent deformation

36
Q

What are 4 examples of materials than can be affected by creep?

A
  • amalgam
  • alloys
  • waxes
  • plastics
37
Q

What is biocompatibility?

A
  • the quality of not having toxic or injurious effects on biological systems
38
Q

What is the concern over the biocompatibility of mercury?

A

Concern over mercury toxicity

39
Q

What is the thermal expansion of amalgam compared to a tooth?

A
  • three time that of a tooth
  • ideally want thermal expansion of amalgam to be the same as enamel-> as amalgam warms up it expands more than the tooth tissue which may cause a gap
40
Q

What is the thermal conductivity of amalgam?

A
  • high, may need to use a liner/varnish in deep cavities
  • this is because the head reaching the dental pulp may be an issue
41
Q

Does amalgam bond to teeth?

A

no, needs mechanical retention for restoration to stay

42
Q

How is the handling of amalgam?

A

It is reasonable, varies between types

43
Q

How is the viscosity of amalgam?

A

Quite easy to pack (condense) into cavity it is ‘user friendly)

44
Q

How are the aesthetic properties of amalgam?

A

poor

45
Q

How are the radiopaque properties of amalgam?

A

amalgam is radiopaque

46
Q

Does amalgam have anti-cariogenic properties?

A

No

47
Q

Does amalgam have smooth surface properties?

A

Yes, of polished well
- may deteriorate over time

48
Q

What is the setting shrinkage property like for amalgam?

A

modern materials tent to have net overall shrinkage

49
Q

Corrosion weakens materials. Where does this particularly happen on teeeth?

A

At margins

50
Q

How can corrosion of amalgam be reduced? (3)

A
  • copper enriched, polishing margins
  • avoiding galvanic cells
51
Q

What are the advantages of spherical amalgam particles

A
  • less Hg required
  • higher tensile strength
  • higher compressive strength
  • less sensitive to condensation
  • easier to carve
52
Q

What is tensile strength?

A

The max loas a material can support without fracture when being stretched, divided by the original cross- sectional area of the material

53
Q

What are 2 names that can be used to describe copper enriched alloys and what % of copper is in these?

A
  • Non-gamma 2
    -high copper
  • Copper >6%
54
Q

What are the 2 types of copper enriched alloys?

A
  • dispersion modified (original)
  • single composition types (introduced to increase uptake by profession)
55
Q

Originally, what were dispersion modified copper enriched alloys made from?

A
  • Ag-Cu spheres + conventional lathe cut alloy
56
Q

What was original though about dispersion modified copper enriched alloys?

A

Originally thought the spherical particles would act as a strengthening agent BUT increased copper content gave beneficial modifications to the setting reaction

57
Q

What is the dispersion modifies setting reaction (for copper enriched amalgam)?

A
  1. As conventional material:
    Gamma + Hg -> Gamma + gamma 1 +gamma 2
  2. Gamma 2 + Ag-Cu -> Cu6Sn5 + gamma 1
    - If add copper, it will react with the gamma 2
    - Produces copper tin and some gamma 1 so have no gamma 2 left
    * note - after the reaction silver copper has a halo which is copper tin (Cu6Sn5)
58
Q

In single composition formulations (of copper enriched amalgams) what is the copper percentage in the powder?

A

12-30%

59
Q

In single composition formulations (of copper enriched amalgams) what are the particle types present?

A
  • spherical
  • lathe cut
60
Q

What is the setting reaction for single composition formulations for copper enriched amalgams?

A

Ag-Sn-Cu + Hg -> Ag-Sn-Cu + gamma 1 + Cu6Sn5
-notice no gamma 2

61
Q

What are the benefits of copper enriched amalgams? (4)

A
  • higher early strength (developed within the first hour)
  • less creep
  • higher corrosion resistance (so will last longer)
  • increased durability of margins (margins more difficult to break down)
62
Q

What is the creep % for traditional lathe cut amalgams?

A

6.3%

63
Q

What is the creep % for traditional spherical amalgams?

A

1.1%

64
Q

What is the creep % for Cu dispersion modified amalgams ?

A

0.46%

65
Q

In which type of amalgam is compressive strength after 1 day the highest?

A

Cu single composition formulas

66
Q

In which type of amalgam is compressive strength after 1 day the lowest?

A

lathe cut amalgams

67
Q

What is the creep % for Cu single composition amalgams?

A

0.07%

68
Q

In which type of amalgam is compressive strength after 7 days the highest ?

A

Cu single composition formulations

69
Q

In which type of amalgam is compressive strength after 1 day the lowest?

A

lathe cut amalgams

70
Q

What is the thermal expansion coefficient of amalgam?

A

22-28 ppm / celcius
- enamel = 11 so 2-3x enamel

71
Q

What are the advantages of using amalgam?

A
  • strong
  • user friendly (especially if copper enriched)
72
Q

What are the disadvantages of using amalgam? (4)

A
  • creep
  • leakage -does not bond
  • poor aesthetics
  • mercury -> perceived toxicity/ environmental impact
73
Q

Why should amalgam be encapsulated?

A

Hg hygiene

74
Q

What is the life expectancy of traditional amalgams?

A

lifetime in excess of 10 years but average lifetime 4-5 years

75
Q

What is the compressive strength of PERMITE after 24 hours?

A

500MPa
- so much more likely to survive for a longer period of time and resist larger forces than other amalgams

76
Q

What is the tensile strength of amalgam (Permite)?

A

60MPa

77
Q

What is the elastic modulus of amalgam (Permite)?

A

30GPa

78
Q

What is the hardness of amalgam (Permite)?

A

100 (VHN)

79
Q

What is the microleakage of amalgam (Permite)?

A

0.04 ml/min
- much better than many other amalgams

80
Q

What is the failure rate of amalgam like compared to other restorative materials ?

A

Low compared to other materials

JK BDS2 CDS DMS (4 decks)

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