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BDS2 CDS DMS > 6. Amalgam > Flashcards

6. Amalgam Flashcards

1
Q

Dental amalgam is an alloy formed by the reaction on (2)

A

Mercury (liquid)

Powder (silver, tin, copper, other metals)

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2
Q

Classifications of amalgam are based on (2)

A

Composition

Particle shape and size

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3
Q

Types of compositions of amalgam (2)

A

Traditional

Copper-enriched

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4
Q

Function of silver and tin in amalgam powder (2)

A

Intermetallic

Gamma phase reacts with mercury liquid to form amalgam

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5
Q

Function of copper in amalgam powder

A

Increases strength and hardness

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6
Q

Function of zinc in amalgam powder

A

Scavenger during production - oxidises preferentially and slag formed/removed
Most products are now zinc free

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7
Q

Function of mercury in amalgam powder

A

Few particles - pre-amalgamated alloys - increases reaction speed

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8
Q

Function of mercury in amalgam liquid

A 
Reacts with other metals
Triple distilled (very pure)
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9
Q

Types of particles in amalgam (2)

A

Lathe cut

Spherical, spheroidal

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10
Q

Features of lathe cut amalgam particles (2)

A

Coarse, medium, fine

Formed by filling ingots

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11
Q

Features of spherical amalgam particles (2)

A

Range of particle sizes

Formed by spraying molten metal into inert atmosphere

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12
Q

Amalgam setting reaction

A

Ag3Sn + Hg –> Ag3Sn + Ag2Hg3 + Sn7Hg9

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13
Q

Amalgam setting reaction gamma

A

Gamma –> gamma + gamma 1 + gamma 2

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14
Q

Amalgam setting reaction particle types

A

Powder + liquid –> unreacted particles + amalgam matrix

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15
Q

Gamma phase shows (2)

A

Good strength

Good corrosion resistance

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16
Q

Gamma 1 shows

A

Good corrosion resistance

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17
Q

Gamma 2 shows (2)

A

Weak strength

Weak corrosion resistance

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18
Q

Effect of voids on strength and corrosion (2)

A

Decrease strength

Increase corrosion

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19
Q

Effect of removing gamma 2 on amalgam

A

Amalgam will be made stronger

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20
Q

Tensile strengths of amalgam components (4)

A

Gamma - 170MPa
Amalgam - 60MPa
Gamma 1 - 30MPa
Gamma 2 - 20MPa

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21
Q

Types of setting dimensional changes of amalgam (2)

A

Traditional

Modern

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22
Q

Features of traditional amalgam setting changes (2)

A

Initial contraction - solution of alloy particles in Hg

Expansion - gamma 1 crystallisation

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23
Q

Features of modern amalgam setting changes (2)

A

sSmall contraction

Solid solution of Hg in Ag3Sn

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24
Q

Why are amalgam materials now usually zinc free

A

Due to reaction of zinc with saliva/blood

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25
Q

Reaction of zinc with saliva/blood

A

Zn + H2O –> ZnO + H2

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26
Q

Effects of hydrogen gas formed within amalgam (3)

A

Pressure build-up causes expansion
Downward pressure causes pulpal pain
Upward pressure causes the restoration to protrude

27
Q

Compressive strength of traditional amalgam (2)

A

Early (<1hr) strength is quite poor

Late (>24hrs) strength is sufficient

28
Q

Features of amalgam abrasion resistance (2)

A

High - suitable for posterior teeth

Too high for deciduous teeth

29
Q

Factors that decrease amalgam strength (5)

A

Under mixing
Mercury content after condensation is too high
Condensation pressure is too low
Slow rate of packing (increments do not bond)
Corrosion

30
Q

Definition of creep (2)

A

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

31
Q

What materials does creep effect (4)

A

Amalgam
Alloys
Waxes
Plastics

32
Q

Is creep high or low in amalgam and why

A

High in traditional materials because amalgam is viscoelastic

33
Q

Marginal integrity depends on (3)

A

Creep
Cavity design
Corrosion

34
Q

Biocompatibility issues of amalgam (2)

A

Concerns about mercury toxicity

Disposal of mercury and amalgam

35
Q

Thermal propertjes of amalgam (2)

A

High thermal expansion (3x greater than tooth tissue)

High thermal conductivity (liners required in deep cavities)

36
Q

Bonding mechanism of amalgam

A

Mechanical retention (from cavity design)

37
Q

Handling properties of amalgam

A

Acceptable mixing, working and setting times

Must have thick viscosity (packed

38
Q

Features of amalgam viscosity (2)

A

Must be thick enough to be packed and hold its shape in cavities
Must be viscous enough to adapt (not flow) to cavity shape

39
Q

Other amalgam properties (5)

A 
Poor aesthetics
Radiopaque
Not anticariogenic
Smooth surfaces if polished well
Modern materials tend to have net overall shrinkage (ditching)
40
Q

Features of gamma 2 phase (2)

A

Most electronegative

Weakens material, particularly at margins

41
Q

Method for increasing strength and decreasing corrosion of gamma 2 phase

A

Silver copper is mixed with gamma 2, increasing strength and decreasing corrosion

42
Q

Methods of reducing corrosion (3)

A

Mixing AgCu with gamma 2
Polishing margins
Avoiding galvanic cells

43
Q

Advantages of spherical particles (5)

A 
Less mercury required
Higher tensile strength
Higher early compressive strength
Less sensitive to condensation
Easier to carve
44
Q

Features of copper-enriched alloys of amalgam (2)

A

Non-gamma 2/higher copper alloys

Contain Cu >6%

45
Q

Types of copper-enriched amalgam (2)

A 
Dispersion modified (original)
Single composition
46
Q

Features of dispersion modified type of copper-enriched amalgam (2)

A

Originally Ag-Cu spheres

Originally conventional lathe-cut alloys

47
Q

Features of single composition dispersed alloys (3)

A

Spheres and lathe-cut particles of the same composition
Powder - Ag-Sn-Cu
Copper - 12-30%

48
Q

Setting reaction of dispersion modified copper-enriched amalgam (2)

A

Gamma + Hg –> gamma + gamma 1 + gamm 2

Gamma 2 + Ag-Cu –> Cu6Sn5 + gamma 1

49
Q

Setting reaction of single composition copper-enriched amalgam (2)

A

Ag-Sn-Cu + Hg –> Ag-Sn-Cu + gamma 1 + Cu6Sn5

50
Q

Benefits of copper-enriched amalgam (4)

A

Higher early strength
Less creep
Higher corrosion resistance
Increased durability of margins

51
Q

Creep (%) of amalgam types (4)

A

Traditional lathe-cut - 6.3%
Traditional spherical - 1.1%
Cu-enriched dispersion modified - 0.46%
Cu-enrinched single composition - 0.07%

52
Q

Compressive strength of amalgam types after one day (4)

A

Traditional lathe-cut - 45MPa
Traditional spherical - 120MPa
Cu-enriched dispersion modified - 118MPa
Cu-enrinched single composition - 272MPa

53
Q

Compressive strength of amalgam types after seven days (4)

A

Traditional lathe-cut - 302MPa
Traditional spherical - 370MPa
Cu-enriched dispersion modified - 387MPa
Cu-enrinched single composition - 485MPa

54
Q

Advantages of amalgam (2)

A

Strong

User friendly

55
Q

Disadvantages of amalgam (4)

A

Corrosion
Leakage (does not bond)
Poor aesthetics
Mercury (perceived toxicity and environmental impact)

56
Q

Types of amalgam and decision between them (3)

A

Encapsulated - Hg hygiene
Traditional alloys - served well (lifetime 10+yes; average 4-5yrs)
Copper-enriched - superior material

57
Q

Type of amalgam used in GDH

58
Q

Reasons for Permite amalgam use in GDH (5)

A 
High compressive strength
Low microleakage
Small dimension changes
Low creep
High tensile strength
59
Q

Compressive strengths of amalgam and hybrid composite (2)

A

Amalgam - 350MPa
Hybrid composite - 300MPa
Amalgam > hybrid composite

60
Q

Tensile strengths of amalgam and hybrid composite (2)

A

Amalgam - 60MPa
Hybrid composite - 50MPa
Amalgam > hybrid composite

61
Q

Elastic modulus’s of amalgam and hybrid composite (2)

A

Amalgam - 30GPa
Hybrid composite - 14GPa
Amalgam > hybrid composite

62
Q

Hardness of amalgam and hybrid composite (2)

A

Amalgam - 100VHN
Hybrid composite - 90VHN
Amalgam > hybrid composite

63
Q

Posterior failure rate of composite and amalgam after 8yrs (2)

A 
Amalgam - 5.8%
All composites - 13.7%
Coarse hybrid composite - 9.3%
Fine hybrid composite - 15.4%
Microfilled composite - 16.4%

BDS2 CDS DMS (15 decks)

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