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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
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 up causing expansion = downward pressure causing pulpal pain = upward- restoration sitting proud of surface
28
What handling factors is amalgam dependent on?
proportion & tituration 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 hour and after 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)
- undermixing - too high Hg content after condensation - 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 depends on: = cavity design = corrosion
35
What is meant by creep?
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
What are 4 examples of materials than 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 to a tooth?
- 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
What is the thermal conductivity of amalgam?
- 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
Does amalgam bond to teeth?
no, needs mechanical retention for restoration to stay
42
How is the handling of amalgam?
It is reasonable, 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, of polished well - may deteriorate over time
48
What is the setting shrinkage property like for amalgam?
modern materials tent to have net overall shrinkage
49
Corrosion weakens materials. Where does this particularly happen on teeeth?
At margins
50
How can corrosion of amalgam be reduced? (3)
- copper enriched, polishing margins - avoiding galvanic cells
51
What are the advantages of spherical amalgam particles
- less Hg required - higher tensile strength - higher compressive strength - less sensitive to condensation - easier to carve
52
What is tensile strength?
The max loas a material can support without fracture when being stretched, divided by the original cross- sectional area of 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 (introduced 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 though 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 modifies 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)
- 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
In which type of amalgam is compressive strength after 1 day the highest?
Cu single composition formulas
66
In which type of amalgam is compressive strength after 1 day the lowest?
lathe cut amalgams
67
What is the creep % for Cu single composition amalgams?
0.07%
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 / celcius - enamel = 11 so 2-3x enamel
71
What are the advantages of using amalgam?
- strong - user friendly (especially if copper enriched)
72
What are the disadvantages of using amalgam? (4)
- 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

JK BDS2 CDS DMS (4 decks)

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