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BDS2 - DMS > Amalgam > Flashcards

Amalgam Flashcards

1
Q

Dental amalgam is an <i>alloy</i>. 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?

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 the amalgam?

A
  • This is am 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
  • Coarse, medium, fine
  • Like a shaving (creates all sorts of fragments of irregular shape)
  • Formed by filing 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 points)

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 p 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? (3 points)

A
  • Proportioning & trituration
  • 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) an hour and 2) 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 points)

A
  • Undermixing
  • Too high Hg content after conden sation
  • 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 d epends on:

Cavity design

Corrosion

35
Q

What is meant by creep?

A
  • When a material is repeatedly stressed for long periods at low stress levels i.e. stress is below the elastic limit, it may flow, resulting in permanent deformation
36
Q

What are 4 examples of materials that 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 t o a tooth?

A
  • Three times 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 heat 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? (mixing, working times, setting times)

A
  • It is reasonable

- This 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, if polished well

- May deteriorate over time

48
Q

What is the setting shrinkage property like for amalgam?

A
  • Modern materials tend to have net overall shrinkage
49
Q

Corriosion weakens materials. Where does this particularly happen on teeth?

A
  • At margins
50
Q

How can corrosion of amalgam be reduced? (3 points)

A
  • Copper enriched, polishing margins

- Avoiding galvanic cells

51
Q

What are the advantages of spherical amalgam particles? (5 points)

A
  • Less Hg required
  • Higher tensile strength
  • Higher early compressive strength
  • Less sensitive to condensation
  • Easier to carve
52
Q

What is tensile strength?

A
  • The max load a material can support without fracture when being stretched, divided by the original cross-sectional area if 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 (introduces 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 thought 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 modified setting reaction (for copper enriched amalgam)?

A
  1. As conventional material:

Gamma + Hg -> Gamma + gamma 1 +gamma 2

  1. 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 points)

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

What is the creep % for Cu single composition amalgams?

A
  • 0.07%
66
Q

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

A
  • Cu single composition formulas
67
Q

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

A
  • Lathe cut amalgams
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/Celsius

Enamel = 11, so 2-3x enamel

71
Q

What are the advantages of using amalgam? (2 points)

A
  • Strong

- User friendly (especially if use copper enriched)

72
Q

What are the disadvantages of using amalgam? (4 points)

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
  1. 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

BDS2 - DMS (14 decks)

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