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2c. BDS2 CDS DMS > 35. Amalgam > Flashcards

35. Amalgam Flashcards

1
Q

L35: What toxic element does amalgam contain?

A

Mercury (no proof amalgam fillings pose a health risk)

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2
Q

L35: What type of metal is amalgam?

A

An alloy (metal containing 2 or more types of metals)

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3
Q

L35: What is the composition of amalgam?

A
  • Mercury (Hg) (liquid);

- Silver, tin, copper and other metals (powder).

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4
Q

L35: How are different amalgams classified?

A
  • Composition: traditional or copper enriched;

- Particle shape and size.

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5
Q

L35: What is the function of silver and tin in amalgam?

A
  • Intermetallic compounds;

- Gamma (g) phase, interacts with Hg liquid to form amalgam.

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6
Q

L35: What is the function of copper in amalgam?

A

Increases strength and hardness

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7
Q

L35: What is the function of zinc in amalgam?

A
  • Scavenger during production;
  • Preferentially oxidises and then slag formed/ removed.

[some zinc free]

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8
Q

L35: What is the function of mercury (powder), in amalgam?

A

‘Pre-amalgamated’ alloys, react faster

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9
Q

L35: What is the function of mercury (liquid), in amalgam?

A
  • Triple distilled (very pure);

- Reacts with other metals.

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10
Q

L35: What are the two particle types of amalgam?

A
  • Lathe cut (coarse/ medium or fine, formed by filing ingots);
  • Shperical/ spheroidal (range of particle sizes, formed by spraying molten metal into inert atmosphere).
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11
Q

L35: What is the overall setting reaction equation for amalgam?

A

Ag3Sn + Hg > Ag3Sn (unreacted particles, g) + Ag2Hg3 (g1) + Sn7Hg9 (g2) (amalgam matrix)

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12
Q

L35: How do gamma phases differ with regards to strength and corrosion resistance?

A

g: good strength and corrosion resistance;
g1: good corrosion resistance;
g2: weak and poor corrosion resistance.

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13
Q

L35: Which gamma phase has the greatest tensile strength?

A

g

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14
Q

L35: What is the average tensile strength of amalgam?

A

60 MPa

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15
Q

L35: When modern amalgam sets, are there any dimensional changes and if so how do these differ to traditional amalgams?

A
  • Small contraction;

- Traditional: initial contraction followed by expansion due to g1 crystallisation.

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16
Q

L35: Why are zinc-free amalgams sometimes favoured?

A
  • Interaction with saliva/ blood;
  • Zn + H2O > ZnO + H2;
  • Bubbles of hydrogen formed within amalgam;
  • Pressure build up causes expansion;
  • Downward pressure causes pulpal pain;
  • Upward, restoration sitting proud of surface.
17
Q

L35: What are amalgam properties dependent on?

A
  • Handling factors: proportioning and trituration, condensation, carving and polishing;
  • Cavity design;
  • Product variation;
  • Corrosion.
18
Q

L35: What mechanical properties do amalgams have?

A
  • Strength: compressive;

- High abrasion resistance (good for posterior teeth, too high for deciduous teeth).

19
Q

L35: What factors can decrease the strength of amalgam restorations?

A
  • Undermixing;
  • Too high Hg content for condensation;
  • Too low condensation pressure;
  • Slow rate of packing (increments not bound);
  • Corrosion.
20
Q

L35: What is material creep?

A

When a material is repeatedly stressed for long periods at low stress levels (below elastic limit), it may flow and result in permanent deformation

21
Q

L35: How does creep effect amalgam restorations?

A
  • Affects marginal integrity (also depends on cavity design and corrosion);
  • Change of shape at restoration boundaries and vulnerable to fracture.
22
Q

L35: Describe the thermal expansion and conductivity of amalgam.

A
  • Both high;
  • Expansion 3x as much as tooth;
  • Conductive so may require use of cavity liner/ varnish in deep cavities.
23
Q

L35: How do amalgam restorations ‘bond’ to teeth?

A
  • Do not bond;

- Require mechanical retention (undercuts).

24
Q

L35: Describe the handling/ viscosity of amalgam.

A
  • Mixing, working and setting times ok (varies between types);
  • Viscosity, packed and condensed into cavity.
25
Q

L35: Describe the aesthetics, radiopacity, anticariogenicity, smooth surface and setting shrinkage properties of amalgam.

A
  • Aesthetics: poor;
  • Radiopaque: yes;
  • Anticariogenic: no;
  • Smooth surface: yes (if polished well);
  • Setting shrinkage: small (modern only).
26
Q

L35: How is corrosion of amalgam material reduced?

A
  • Addition of copper (copper enrichment);

- Polishing margins.

27
Q

L35: What are the advantages of spherical particles?

A
  • Less Hg required;
  • Higher tensile strength;
  • Higher early compressive strength;
  • Less sensitive to condensation;
  • Easier to carve.
28
Q

L35: How does copper effect the setting reaction of amalgam alloys?

A

Beneficial modifications to the setting reaction

  1. As conventional material (g + Hg > g + g1 + g2)
  2. g2 +Ag-Cu > Cu6Sn5 + g1 (takes several days)

Ag-Cu particles, surrounded by Cu6Sn5 ‘halo’ - stronger

29
Q

L35: What are the benefits of copper enriched amalgams?

A
  • Higher early strength;
  • Less creep;
  • Higher corrosion resistance;
  • Increased durability of margins.
30
Q

L35: How do the compressive strengths of different amalgam compositions differ?

A
  • Traditional lathe (45, 302);
  • Traditional spherical (120, 370);
  • Cu dispersion (118, 387);
  • Cu single (272, 485).

[first number: after 1 day, second number: after 2 days]

31
Q

L35: Compare the thermal expansion coefficients for dentine, enamel, ceramic, GIC, gold alloy, amalgam, composite.

A 
Enamel: 11
Dentine: 8
Ceramic: 8-14
GIC: 10-11
Gold alloy: 12-15
Amalgam: 22-28
Composite: 25-68

ppm/ degrees C

32
Q

L35: What is permite amalgam?

A

Non-gamma 2, spherical and lathe cut

33
Q

L35: What is the typical tensile strength of permite amalgam and how does this change over 1hr-24hr-7 days?

A

1 hour: 28 MPa
24 hours: 54 MPa
7 days: NA

34
Q

L35: Compare the mechanical properties (compressive strength, tensile strength, elastic modulus and hardness) of different restorative materials.

A

See screenshot on desktop!

35
Q

L35: How does the rate of microleakage differ between permite and other amalgams?

A

Significantly less! 0.04 ml/min, some up to 1.97ml/min

36
Q

L35: How does the failure rate of amalgam restorations compare to other restorative materials?

A
  • Lowest failure rate;
  • 5.8% over 8 years;
  • Composites: 13.7% on average.

2c. BDS2 CDS DMS (12 decks)

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