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BDS2 Dental Material Science > Amalgam > Flashcards

Amalgam Flashcards

1
Q

what type of material is amalgam?

A

an alloy

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2
Q

how can amalgam be classified?

A

by its:

  • composition
  • particle shape & size
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3
Q

what are the different compositions of amalgam?

A
  • traditional

- copper enriched

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4
Q

what materials is amalgam composed of?

A
  • Ag (silver)
  • Sn (tin)
  • Cu (copper)
  • Zn (zinc)
  • Hg (mercury)
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5
Q

what makes up the powder aspect of amalgam?

A
  • silver-tin (Ag3Sn)
  • copper
  • zinc
  • mercury in powder
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6
Q

what is the liquid aspect of amalgam composed of?

A

Hg (mercury)

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7
Q

what is the function of the silver-tin compound found in amalgam?

A

it reacts with the Hg liquid to form amalgam

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8
Q

what is the function of copper in the makeup of amalgam?

A

increases strength and hardness of material

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9
Q

how can the mercury found in amalgam be described?

A

very pure (triple distilled)

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10
Q

what are the different particle types that amalgam can be composed of?

A
  • Iathe cut

- Spherical, spheroidal

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11
Q

what is the setting reaction of amalgam?

A

Ag3Sn + Hg —> Ag3Sn + Ag2Hg3 + Sn7Hg9

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12
Q

what is the gamma phase of the amalgam setting reaction?

A

Ag3Sn

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13
Q

what is the gamma 2 phase of the amalgam setting reaction?

A

Ag2Hg3

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14
Q

what is the gamma-2 phase of the amalgam setting reaction?

A

Sn7Hg9 (tin-mercury)

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15
Q

what are the characteristics of the gamma phase of the amalgam setting reaction?

A
  • good strength

- good corrosion resistance

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16
Q

what are the characteristics of the gamma-1 phase of the amalgam setting reaction?

A
  • good corrosion resistance
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17
Q

what are the characteristics of the gamma-2 phase of amalgam?

A
  • weak and poor corrosion resistance
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18
Q

what is the average tensile strength of amalgam?

A

60MPa

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19
Q

what amalgam phase has the highest tensile strength?

A

gamma phase

20
Q

what amalgam phase has the lowest tensile strength?

A

gamma-2 phase

21
Q

why is zinc not commonly used in amalgams anymore?

A
  • zinc can interact with saliva/blood
  • bubbles of H2 formed within amalgam
  • pressure buildup causes expansion
    (downward pressure causes pulpal pain, upwards pressure causes restoration to sit proud of surface)
22
Q

what handling factors may affect the properties of amalgam?

A
  • proportioning and titration
  • condensation/how well it is packed into cavity
  • carving and polishing
23
Q

what are the amalgam properties dependant on?

A
  • handling factors
  • cavity design
  • affected by corrosion
24
Q

what type of amalgam particles are better? why is this?

A

spherical particles

  • less Hg required
  • higher tensile strength
  • higher early compressive strength
  • less sensitive to condensation
  • easier to carve
25
Q

what type of cavities are amalgam restorations particularly suited to? why is this?

A
  • cavities in posterior teeth

- high abrasion resistance

26
Q

what factors may decrease the strength of an amalgam restoration?

A
  • undermining
  • low condensation pressure (when packing into cavity)
  • slow rate of packing
  • corrosion
27
Q

why is creep a problem in amalgam restorations?

A

affects marginal integrity & can contribute to microleakage

28
Q

what is creep?

A

when a material experiences:

  • low level stress levels (below elastic limit stress) which are applied repeatedly over a prolonged time period
  • causes material to flow resulting in permanent deformation
29
Q

how might ditching occur in amalgam restorations?

A
  • low magnitude forces are applied to amalgam repeatedly
  • amalgam flows and changes shape
  • amalgam sitting proud of tooth surface
  • prone to fracture, resulting in ditched margins
30
Q

what is the thermal expansion of amalgam? is this good or bad?

A

x3 of tooth

- not ideal & may lead to margin gaps

31
Q

what is the thermal conductivity of amalgam? is this good or bad?

A
  • high which is bad

- may need to use a liner in deep cavities

32
Q

what is the thermal diffusivity of amalgam? what does this mean for the material?

A
  • high
  • when a transient thermal stimuli is applied amalgams temperature rises quickly
  • can damage the pulp
33
Q

what are the bonding properties of amalgam?

A
  • does not bond to tooth

- needs mechanical retention from undercuts

34
Q

what type of cavity prep requires removal of MORE tooth surface, composite or amalgam?

A

amalgam!

35
Q

what type of amalgam particles require less force when packing into the cavity?

A

spherical particles

36
Q

what amalgam phase is most likely to experience corrosion?

A

gamma-2 phase

37
Q

how can corrosion be reduced in amalgam materials?

A
  • enrich with copper
  • polish margins
  • avoid galvanic cells
38
Q

what is copper enriched amalgam?

A

amalgam with:

  • non gamma 2 phase
  • high copper (copper>6%)
39
Q

what are the two types of copper enriched amalgam materials?

A
  • dispersion modified (original)

- single composition types

40
Q

what does an increased copper content provide amalgam?

A
  • higher early strength
  • less creep
  • higher corrosion resistance
  • increased durability of margins
41
Q

what is the setting reaction of single composition copper enriched amalgam?

A

AgSnCu + Hg —> AgSnCu + Ag2Hg3 + Cu6Sn5

42
Q

what type of amalgam (both original and copper enriched) has the highest compressive strength?

A

Cu single composition

43
Q

what material has a higher compressive strength, amalgam or composite?

A

amalgam

44
Q

how does the elastic modulus of amalgam compare to that of enamel?

A
  • lower elastic modulus

- amalgam is less rigid than enamel

45
Q

what are the advances of amalgam as a restorative material?

A
  • strong
  • hard
  • durable
  • radiopaque
  • use friendly
46
Q

what are some disadvantages of amalgam as a restorative material?

A
  • corrosion
  • leakage (does not bond)
  • poor aesthetics
  • mercury (perceived toxicity, environmental)
47
Q

what can be done to an amalgam cavity prep to avoid ditching?

A
  • ensure the CSMA is between 90-120 degrees
  • if the CSMA is less than this then there is an insufficient bulk of amalgam which would make it more susceptible to fracture
  • if it is more there are undermined enamel margins also making it more susceptible to fracture

BDS2 Dental Material Science (13 decks)

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