Amalgam Flashcards

(80 cards)

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
In relation to expansion and contraction during setting dimensional changes of amalgam, what happens in traditional amalgam?
- Initial contraction - solution of alloy particles in Hg | - Expansion - Gamma crystallisation
26
In relation to expansion and contraction during setting dimensional changes of amalgam, what happens in modern amalgam?
- Small contraction | - Solid solution of Hg in Ag3Sn
27
Why do we use zinc free amalgams for restoration material?
- 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
28
What handling factors is amalgam dependent on? (3 points)
- Proportioning & trituration - Condensation - Carving & polishing
29
Is amalgam dependent on cavity design?
- Yes 
30
Will amalgam be affected by corrosion?
- Yes
31
What is the compressive strength of traditional amalgams like after 1) an hour and 2) 24 hours?
- One hour = poor(ish) | - 24 hours = ok
32
What is the abrasion resistance of amalgam (hard material that resists the surface layer being removed)?
- High, suitable for posterior teeth | - Too high for deciduous
33
What factors have an effect on decreasing the strength of amalgam? (5 points)
- Undermixing - Too high Hg content after conden sation - Too low condensation pressure - Slow rate of packing (so increments do not bond) - Corrosion
34
Why can creep be a problem with traditional amalgams?
- Affects the marginal integrity as the material changes shape when it undergoes creep - NB marginal integrity also d epends on: Cavity design Corrosion
35
What is meant by creep?
- 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
What are 4 examples of materials that can be affected by creep?
- Amalgam - Alloys - Waxes - Plastics
37
What is biocompatibility?
- The quality of not having toxic or injurious effects on biological systems 
38
What is the concern over the biocompatibility of mercury?
- Concern over mercury toxicity
39
What is the thermal expansion of amalgam compared t o a tooth?
- 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
What is the thermal conductivity of amalgam?
- 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
Does amalgam bond to teeth?
- No, needs mechanical retention for restoration to stay 
42
How is the handling of amalgam? (mixing, working times, setting times)
- It is reasonable | - This varies between types
43
How is the viscosity of amalgam?
- Quite easy to pack (condense) into cavity - it is 'user friendly'
44
How are the aesthetic properties of amalgam?
- Poor
45
How are the radiopaque properties of amalgam?
- Amalgam is radiopaque
46
Does amalgam have anti-cariogenic properties?
- No
47
Does amalgam have smooth surface properties?
- Yes, if polished well | - May deteriorate over time
48
What is the setting shrinkage property like for amalgam?
- Modern materials tend to have net overall shrinkage 
49
Corriosion weakens materials. Where does this particularly happen on teeth?
- At margins 
50
How can corrosion of amalgam be reduced? (3 points)
- Copper enriched, polishing margins | - Avoiding galvanic cells
51
What are the advantages of spherical amalgam particles? (5 points)
- Less Hg required - Higher tensile strength - Higher early compressive strength - Less sensitive to condensation - Easier to carve
52
What is tensile strength?
- The max load a material can support without fracture when being stretched, divided by the original cross-sectional area if the material 
53
What are 2 names that can be used to describe copper enriched alloys and what % of copper is in these?
- Non-gamma 2 - High copper - Copper > 6%
54
What are the 2 types of copper enriched alloys?
- Dispersion modified (original) | - Single composition types (introduces to increase uptake by profession)
55
Originally, what were dispersion modified copper enriched alloys made from? 
- Ag-Cu spheres + conventional lathe cut alloy 
56
What was original thought about dispersion modified copper enriched alloys?
- Originally thought the spherical particles would act as a strengthening agent BUT increased copper content gave beneficial modifications to the setting reaction 
57
What is the dispersion modified setting reaction (for copper enriched amalgam)?
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
In single composition formulations (of copper enriched amalgams) what is the copper percentage in the powder?
12%-30%
59
In single composition formulations (of copper enriched amalgams) what are the particle types present?
- Spherical | - Lathe cut
60
What is the setting reaction for single composition formulations for copper enriched amalgams?
- Ag-Sn-Cu + Hg -> Ag-Sn-Cu + gamma 1 + Cu6Sn5 | notice no gamma 2
61
What are the benefits of copper enriched amalgams? (4 points)
- 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
What is the creep % for traditional lathe cut amalgams?
- 6.3%
63
What is the creep % for traditional spherical amalgams?
1.1%
64
What is the creep % for Cu dispersion modified amalgams?
0.46%
65
What is the creep % for Cu single composition amalgams?
- 0.07%
66
In which type of amalgam is compressive strength after 1 day the highest?
- Cu single composition formulas
67
In which type of amalgam is compressive strength after 1 day the lowest?
- Lathe cut amalgams 
68
In which type of amalgam is compressive strength after 7 days the highest?
- Cu single composition formulations 
69
In which type of amalgam is compressive strength after 1 day the lowest?
- Lathe cut amalgams 
70
What is the thermal expansion coefficient of amalgam?
- 22-28 ppm/Celsius | Enamel = 11, so 2-3x enamel
71
What are the advantages of using amalgam? (2 points)
- Strong | - User friendly (especially if use copper enriched)
72
What are the disadvantages of using amalgam? (4 points)
- Creep - Leakage - does not bond - Poor aesthetics - Mercury: * perceived toxicity * Environmental impact
73
Why should amalgam be encapsulated?
- Hg hygiene 
74
What is the life expectancy of traditional amalgams?
- Lifetime in excess of 10 years but average lifetime 4-5 years 
75
What is the compressive strength of PERMITE after 24 hours?
- 500MPa | so much more likely to survive for a longer period of time and resist larger forces than other amalgams
76
What is the tensile strength of amalgam (Permite)?
- 60MPa
77
What is the elastic modulus of amalgam (Permite)?
- 30GPa
78
What is the hardness of amalgam (Permite)?
100 (VHN)
79
What is the microleakage of amalgam (Permite)?
0. 04 ml/min | - Much better than many other amalgams
80
What is the failure rate of amalgam like compared to other restorative materials?
- Low compared to other materials