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BDS2 - dental material science > amalgam > Flashcards

amalgam Flashcards

1
Q

what is dental amalgam

A

an alloy formed by the reaction of
> mercury (liquid)
and
> silver, tin, copper and other metals (powder)

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2
Q

what is an alloy

A

consists of 2 or more metals

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3
Q

what are the 2 ways to classify amalgam

A

> composition

> particle size and shape

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4
Q

classify amalgam in terms of composition

A

> traditional

> copper enriched

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5
Q

what does particle size and shape of amalgam affect

A

affects handling and final properties

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6
Q

what is the the average composition of amalgam

A
  • 70% Ag
  • 25% Sn
  • 3% Cu
  • 1% Zn (a lot of today’s amalgams don’t have zinc and are zinc free - traditional amalgams have a small %)
  • 1% Hg
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7
Q

what is included in the powder constituent of amalgam

A

> silver, tin
copper
zinc
Hg in powder

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8
Q

what is the function of silver, tin

A

intermetallic compound Ag3Sn

gamma phase - reacts with mercury (Hg) to form amalgam

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9
Q

what is the function of copper

A

increases strength and hardness

added to improve material

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10
Q

what is the function of zinc

A

scavenger during production
preferentially oxidises and slag formed / removed
some amalgams are zinc free

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11
Q

what is the function of mercury in powder

A

only a few materials have this
pre-amalgated alloys so it will react faster
[silver, tin and copper then mix with amalgam grounded down]

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12
Q

what is included in the liquid constituent of amalgam

A

mercury (Hg)

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13
Q

what is the function of mercury in liquid

A

reacts with other materials

it is triple distilled = very pure

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14
Q

name 2 particle types

A

> lathe cut

> spherical, spheroidal

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15
Q

what are lathe cut particles

A

> coarse, medium, fine
formed by filing ingots
creates lots of fragments / shards / shavings

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16
Q

what are spherical, spheroidal particles

A

> range of particle sizes
formed by spraying molten metal into inert atmosphere
easier to control
form globules on surface underneath

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17
Q

what is the setting reaction of amalgam

A

Ag3Sn + Hg = Ag3Sn + Ag2Hg3 + Sn7Hg9

gamma = gamma + gamma 1 + gamma 2

powder + liquid = unreacted particles + amalgam matrix

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18
Q

what is present in the set structure of amalgam

A

> gamma
gamma 1
gamma 2

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19
Q

what is gamma

A

intermetallic silver tin (Ag3Sn)

gives good strength and corrosion resistnace

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20
Q

what is gamma 1

A

Ag2Hg3
gives good corrosion resistance
its like a soup which encapsulates the rest

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21
Q

what is gamma 2

A

Sn7Hg9
it is weaker and has poor corrosion resistance
spherical particles

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22
Q

what do voids do

A

decrease strength

increase corrosion

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23
Q

what is the tensile strength of the different amalgam components

A

> gamma = 170
gamma 1 = 30
gamma 2 = 20
= amalgam = 60

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24
Q

what is the setting dimensional changes in traditional amalgam

A

initial contraction - solution of alloy particles in mercury

then expansion - gamma 1 crystallisation

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25
what is the setting dimensional changes in modern amalgam
small contraction solid solution of mercury in Ag3Sn advantage = doesn't expand (note: expansion / contraction is <0.2% so little clinical sign)
26
what happens with zinc when it interacts with saliva / blood
Zn + H2O = ZnO + H2 bubbles of H2 formed within amalgam > pressure build up causes expansion > downward pressure causes pulpal pain > upward pressure means the restoration will sit proud of the surface forcing material to expand = not a desirable effect hence why there is zinc free materials
27
what is amalgam properties dependent on
``` > dependent on handling factors - proportioning and trituration - condensation - carving and polishing > dependent on cavity design > variations in products > affected by corrosion ```
28
name mechanical properties of amalgam
> strength > abrasion resistance > creep > biocompatibility
29
what is the abrasion resistance like for amalgam
high suitable for posterior teeth too high for deciduous teeth
30
what is the problem with creep
affects marginal integrity changes shape problem in tradiitonal materials (depends on cavity design and corrosion)
31
what is the biocompatibility of amalgam
concern over mercury toxicity
32
what factors decrease strength
undermixing too high mercury content after condensation too low condensation pressure slow rate of packing - increments don't bond (don't want undulations on surface) corrosion
33
what is creep
When a material is repeatedly stressed for long periods at low stress levels (ie stress below the elastic limit / will not cause the tooth to fracture) it may flow, resulting in permanent deformation [will change shape]
34
what does creep do to the restoration
causes the amalgam to change shape and sit proud of the tooth surface protrudes around the margins margins are exposed so when forces are applied the amalgam will fracture resulting in ditched margins
35
what is the thermal expansion of amalgam
3 times more than the tooth | expands and contracts more than the tooth so it can leaev gaps
36
what is the thermal conductivity of amalgam
high | may need to use a liner / varnish (insulator) in deep cavities to protect the pulp
37
is amalgam compatible with bonding systems
amalgam does not bond to the tooth needs mechanical retention cavity walls need to splay outwards
38
what is the handling of amalgam like
- mixing, working times and setting times are ok | - varies between types
39
what is the viscosity of amalgam like
packed (condensed) into cavity | user friendly
40
what is the aesthetics of amalgam
poor | dont use anteriorly
41
what is the radiopacity like of amalgam
yes radiopaque | will show if you have left gaps in the restoration
42
is amalgam anticariogenic
no
43
does amalgam give a smooth surface
yes if polished well | may deteriorate over time
44
what is the setting shrinkage of amalam
modern materials tend to have net overall shrinkage
45
how does corrosion happen in amalgam
gamma 2 more electronegative weakens materials (particularly at margins) corrosion products may contribute to sealing margins reduce by > copper enriched polishing margins > avoiding galvanic cells
46
what are the advantages of spherical particles
* Less mercury required * Higher tensile strength * Higher early compressive strength * Less sensitive to condensation * Easier to carve
47
what are copper enriched alloys also called and why have they this name
also called non-gamma 2 | high copper content (>6%)
48
what are the types of copper enriched
> dispersion modified - original > single composition types - introduced to increase uptake by profession
49
what is dispersion modified copper enriched amalgam
> originally Ag-Cu spheres and conventional lathe cut alloy (now some single composition dispersed alloys - spheres and lathe cut particle same composition) > originally thought spherical particles would act as a strengthening agent > but increased copper content gave beneficial modifications to setting reaction i dunno if this made sense lol love my notes x
50
what is the dispersion modified setting reaction
as conventional material 1. gamma + Hg = gamma + gamma 1 + gamma 2 2. gamma 2 + Ag-Cu = Cu6Sn5 + gamma 1 (takes several days but gets rid of gamma 2)
51
what does the dispersion modified setting reaction do to the silver copper
adds a copper tin halo to it | Cu6Sn5 goes around the Ag-Cu
52
what is the difference between single composition and dispersion modified
it goes straight to having no gamma 2 present instead of having the 2 separate reactions
53
what is in single composition formulations
powder - Ag-Sn-Cu | particle types = spherical and lathe cut
54
what is the setting reaction of the single composition formulation
Ag-Sn-Cu + Hg = Ag-Sn-Cu + gamma 1 + Cu6Sn5
55
what are the benefits of copper enriched amalgam
> higher early strength > less creep > higher corrosion resistance (will last longer) > increased durability of margins (more difficult to break down)
56
how is each amalgam material affect by creep
> traditional lathe cut = 6.3% = massive > traditional spherical = 1.1% > copper dispersion = 0.46% > copper single = 0.07%
57
what amalgam material has the best compressive strength
copper single | even after 1 day placed it is double that than any of the others
58
what is the thermal expansion coefficient of amalgam
22-28 ppm/degrees celsius
59
what are the advantages of amalgam
• Strong • User friendly ○ Especially copper enriched
60
what are the disadvantages of amalgam
``` • Corrosion • Leakage ○ Does not bond ○ Potential to creep • Poor aesthetics • Mercury ○ Perceived toxicity ○ Environmental impact ```
61
what is the advantage of encapsulated amalgam
mercury hygiene
62
what is good about traditional amalgam
lasts a long time | average = 4-5 years but can last longer than 10 years
63
what amalgam does the dental hospital do
permite has a high compressive strength lower microleakage

BDS2 - dental material science (13 decks)

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