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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
Reaction of zinc with saliva/blood
Zn + H2O --> ZnO + H2
26
Effects of hydrogen gas formed within amalgam (3)
Pressure build-up causes expansion Downward pressure causes pulpal pain Upward pressure causes the restoration to protrude
27
Compressive strength of traditional amalgam (2)
Early (<1hr) strength is quite poor | Late (>24hrs) strength is sufficient
28
Features of amalgam abrasion resistance (2)
High - suitable for posterior teeth | Too high for deciduous teeth
29
Factors that decrease amalgam strength (5)
Under mixing Mercury content after condensation is too high Condensation pressure is too low Slow rate of packing (increments do not bond) Corrosion
30
Definition of creep (2)
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
What materials does creep effect (4)
Amalgam Alloys Waxes Plastics
32
Is creep high or low in amalgam and why
High in traditional materials because amalgam is viscoelastic
33
Marginal integrity depends on (3)
Creep Cavity design Corrosion
34
Biocompatibility issues of amalgam (2)
Concerns about mercury toxicity | Disposal of mercury and amalgam
35
Thermal propertjes of amalgam (2)
High thermal expansion (3x greater than tooth tissue) | High thermal conductivity (liners required in deep cavities)
36
Bonding mechanism of amalgam
Mechanical retention (from cavity design)
37
Handling properties of amalgam
Acceptable mixing, working and setting times | Must have thick viscosity (packed
38
Features of amalgam viscosity (2)
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
Other amalgam properties (5)
``` Poor aesthetics Radiopaque Not anticariogenic Smooth surfaces if polished well Modern materials tend to have net overall shrinkage (ditching) ```
40
Features of gamma 2 phase (2)
Most electronegative | Weakens material, particularly at margins
41
Method for increasing strength and decreasing corrosion of gamma 2 phase
Silver copper is mixed with gamma 2, increasing strength and decreasing corrosion
42
Methods of reducing corrosion (3)
Mixing AgCu with gamma 2 Polishing margins Avoiding galvanic cells
43
Advantages of spherical particles (5)
``` Less mercury required Higher tensile strength Higher early compressive strength Less sensitive to condensation Easier to carve ```
44
Features of copper-enriched alloys of amalgam (2)
Non-gamma 2/higher copper alloys | Contain Cu >6%
45
Types of copper-enriched amalgam (2)
``` Dispersion modified (original) Single composition ```
46
Features of dispersion modified type of copper-enriched amalgam (2)
Originally Ag-Cu spheres | Originally conventional lathe-cut alloys
47
Features of single composition dispersed alloys (3)
Spheres and lathe-cut particles of the same composition Powder - Ag-Sn-Cu Copper - 12-30%
48
Setting reaction of dispersion modified copper-enriched amalgam (2)
Gamma + Hg --> gamma + gamma 1 + gamm 2 | Gamma 2 + Ag-Cu --> Cu6Sn5 + gamma 1
49
Setting reaction of single composition copper-enriched amalgam (2)
Ag-Sn-Cu + Hg --> Ag-Sn-Cu + gamma 1 + Cu6Sn5
50
Benefits of copper-enriched amalgam (4)
Higher early strength Less creep Higher corrosion resistance Increased durability of margins
51
Creep (%) of amalgam types (4)
Traditional lathe-cut - 6.3% Traditional spherical - 1.1% Cu-enriched dispersion modified - 0.46% Cu-enrinched single composition - 0.07%
52
Compressive strength of amalgam types after one day (4)
Traditional lathe-cut - 45MPa Traditional spherical - 120MPa Cu-enriched dispersion modified - 118MPa Cu-enrinched single composition - 272MPa
53
Compressive strength of amalgam types after seven days (4)
Traditional lathe-cut - 302MPa Traditional spherical - 370MPa Cu-enriched dispersion modified - 387MPa Cu-enrinched single composition - 485MPa
54
Advantages of amalgam (2)
Strong | User friendly
55
Disadvantages of amalgam (4)
Corrosion Leakage (does not bond) Poor aesthetics Mercury (perceived toxicity and environmental impact)
56
Types of amalgam and decision between them (3)
Encapsulated - Hg hygiene Traditional alloys - served well (lifetime 10+yes; average 4-5yrs) Copper-enriched - superior material
57
Type of amalgam used in GDH
Permite
58
Reasons for Permite amalgam use in GDH (5)
``` High compressive strength Low microleakage Small dimension changes Low creep High tensile strength ```
59
Compressive strengths of amalgam and hybrid composite (2)
Amalgam - 350MPa Hybrid composite - 300MPa Amalgam > hybrid composite
60
Tensile strengths of amalgam and hybrid composite (2)
Amalgam - 60MPa Hybrid composite - 50MPa Amalgam > hybrid composite
61
Elastic modulus's of amalgam and hybrid composite (2)
Amalgam - 30GPa Hybrid composite - 14GPa Amalgam > hybrid composite
62
Hardness of amalgam and hybrid composite (2)
Amalgam - 100VHN Hybrid composite - 90VHN Amalgam > hybrid composite
63
Posterior failure rate of composite and amalgam after 8yrs (2)
``` 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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