Amalgam

Question 1

why is there concern amalgam has health risks

Answer 1

role of mercury in disease causation with its systemic distribution and accumulation in the body

Question 2

what is amalgam

Answer 2

an alloy formed by the reaction of:

• mercury (liquid)
• silver, tin, copper and other metals (powder)

Question 3

when was the ‘first amalagm war’

Answer 3

1840s (american society of dental surgeons banned use of amalgam)

Question 4

when was the second amalagm war

Answer 4

1970s-1990s

mercury fear - health and environment

Question 5

how is amalgam classified

Answer 5

by composition and by particle shape and size

Question 6

what are the different types of composition of amaglam

Answer 6

• tradtional

- copper enriched

Question 7

what are the different types of particle shape and size of amalgam

Answer 7

• originally applied to traditional but now also to copper enriched
• affects handling and final properties

Question 8

what is amalgam composed of

Answer 8

• Ag (70%)
• Sn (25%)
• Cu (3%)
• Zn (most today don’t have zinc) (1%)
• Hg (1%)

Question 9

what is the function of silver, tin in the powder

Answer 9

intermetallic compound (Ag3Sn)
- gamma phase, reacts with Hg liquid to form amalgam

Question 10

what is the function of copper in the powder

Answer 10

increases strength and hardness

Question 11

what is/ was the function of zinc in powder

Answer 11

it was there to oxidise rather than have the other metals oxidise (sacrifical lamb)

Question 12

what is the function of Hg in powder

Answer 12

“pre-amalgamated” alloys react faster

Question 13

what proportion of weight of amalgam is powder and liquid

Answer 13

powder: 50%
liquid: 50%

Question 14

what is the function of Hg in liquid

Answer 14

• triple distilled (very pure)

- reacts with other metals

Question 15

what are the different particle types in amalgam

Answer 15

Lathe cut

• coarse, medium, fine
• formed by filling ingots

Sperical, spheroidal

• range of particle sizes
• formed by spraying molten metal into inert atmosphere

Question 16

Describe the setting reaction of amalgam

Answer 16

silver + tin –> unreacted silver/tin + tin/mercury

Question 17

describe the set structure of amalgam

Answer 17

gamma (silver/tin)
- good strength and corrosion resistance

gamma 1 (silver/mercury)
- good corrosion resistance

gamma 2 (tin/mercury)
- weak and poor corrosion resistance

Question 18

what do voids do to the set structure

Answer 18

decrease strength and increase corrosion

Question 19

what is the tensile strength of gamma

Answer 19

170MPa

Question 20

what is the tensile strength of gamma 1

Answer 20

30MPa

Question 21

what is the tensile strength of gamma 2

Answer 21

20MPa

Question 22

What is the mean strength of amalgam

Answer 22

60MPa

Question 23

how do setting dimensional changes differ between traditional and modern amalgams

Answer 23

Traditional (big changes in expansion)

• intial contraction (solution of alloy particles in Hg)
• expansion (gamma 1 crystallisation

Modern (expansion/contraction is <0.2% so little clinical sign)

• small contraction
• solid solution of Hg in Ag3Sn

Question 24

why do we now have zinc free materials

Answer 24

It can react with saliva to get zinc oxide and hydrogen, so bubbles of hydrogen formed within amalgam

• pressure build up causes expansion
• downward pressure cause pulpal pain
• upward - restoration sitting proud of surface

Question 25

what do properties of amalgam depend upon

Answer 25

- handling factors - cavity design - products - corrosion

Question 26

What is the strength like of amalgam

Answer 26

early: fairly poor | later (>24hrs): OK

Question 27

what is the abrasion resistance like of amalgam

Answer 27

- high, suitable for posterior teeth | - too high for deciduous

Question 28

what factors decrease the strength of amalgam

Answer 28

- undermixing - too high Hg content after condenstaion - too low condensation pressure - slow rate of packing (increments do not bond) - corrosion

Question 29

What is 'creep'

Answer 29

when a material is repeatedly stressed for long periods at low stress levels (i.e. stress is below elastic limit) it may flow, resulting in permanent deformation

Question 30

why is creep a problem for amalgam

Answer 30

- amalgam is visco-elastic - high in traditional materials - affects marginal integrity n. b. also marginal integrity depends on cavity design and corrosion

Question 31

what materials are affected by creep

Answer 31

amalgam alloys waxes plastics

Question 32

how does creep affect amalgam

Answer 32

- amalgam fits cavity, force is low magnitude force and is applied frequently - amalgam changes shape, sitting proud of tooth surface - amalgam vulnerable to fracture at margins (ditched margins)

Question 33

what is the biocompatibility of amalgam like

Answer 33

so far it's safe to use but concern about mercury toxicity

Question 34

what is the thermal expansion of amalgam like

Answer 34

x3 of tooth

Question 35

what is the thermal conductivity of amalgam like

Answer 35

high, may need to use liner/ varnish in deep cavities

Question 36

does amalgam bond to tooth

Answer 36

no

Question 37

how do we get amalgam to stay in place

Answer 37

needs mechanical retention

Question 38

what are the handling properties of amalgam like

Answer 38

mixing, working and setting times are OK, varies between types

Question 39

what is the viscosity properties of amalgam like

Answer 39

packed (condensed) into cavity - user friendly

Question 40

aesthetics of amalgam

Answer 40

poor

Question 41

radiopaque?

Answer 41

yes

Question 42

anticariogenic?

Answer 42

no

Question 43

smooth surface?

Answer 43

yes, if polished well, may deteriorate over time

Question 44

setting shrinkage?

Answer 44

modern materials tend to have net overall shrinkage

Question 45

what part of the set structure is the most electronegative and why is that important

Answer 45

gamma 2 weakens material particularly at margins corrosion

Question 46

how do we reduce corrosive properties of amalgam

Answer 46

- copper enriched, polishing margins | - avoiding galvanic cells

Question 47

what are advantages of spherical particles

Answer 47

- less Hg required - higher tensile strength - higher early compressive strength - less sensitive to condensation - easier to carve

Question 48

what are copper enriched alloys also called?

Answer 48

non-gamma2 higher copper copper enriched

Question 49

what proportion of copper enriched alloys are copper

Answer 49

>6%

Question 50

what are the different types of copper enriched alloys

Answer 50

- dispersion modified (original type) | - single composition types (introduced to increase uptake by profession)

Question 51

how many reactions happen in dispersion modified copper enriched alloys

Answer 51

2

Question 52

what are dispersion modified copper enriched alloys made of

Answer 52

Ag-Cu spheres + conventional lathe cut alloy

Question 53

What are the two reactions that happen in dispersion modified copper enriched alloys

Answer 53

1. gamma + Hg --> gamm + gamma 1 + gamma 2 | 2. gamma 2 + Ag-Cu --> Cu6Sn5 + gamma 1 takes several days

Question 54

how is Ag-Cu and Cu6Sn5 arranged in dispersion modified setting reaction

Answer 54

Ag-Cu as a sphere Cu6Sn5 as halo around spheres (also gamma 1 and gamma present)

Question 55

in single composition formulations (Cu enriched) what is the powder composed of

Answer 55

Ag, Sn, Cu - copper 12-30% - particle types: spherical and lathe cut

Question 56

in single composition formulations (Cu enriched) what is the setting reaction

Answer 56

Ag-Sn-Cu + Hg --> Ag-Sn-Cu + gamma 1 + Cu6Sn5 | no gamma 2

Question 57

what are the benefits of copper enriched alloys

Answer 57

- higher early strength - less creep - higher corrosion resistance - increased durability of margins

Question 58

out of trad-lathe, trad-spherical, Cu dispersion and Cu single, what are the % creep values

Answer 58

trad-lathe (6.3%) trad-spherical (1.1%) Cu dispersion (0.46%) Cu single (0.07%)

Question 59

how do the compressive strength values change between the 4 alloys between day 1 and day 7

Answer 59

lathe (45-302 MPa) spherical (120-370) CU dispersion (118-387) Cu single (272-485)

Question 60

what is the thermal expansion coefficient of amalgam compared to enamel and dentine

Answer 60

Amalgam (22-28ppm/oC) enamel (11) dentine (8)

Question 61

advantages of amalgam

Answer 61

strong | user friendly

Question 62

disadvantages of amalgam

Answer 62

- corrosion - leakage (doesn't bond) - poor aesthetics - mercury (pereived toxicity and environmental impact)

Question 63

which amalgam should we use?

Answer 63

Encapsulated - Hg hygiene Trad alloys - served well, lifetime in excess of 10 years - but av lifetime 4-5 years (?) Copper enriched - some clinical trials showing material is superior GDH&S - we use permite

Question 64

what are the properties of permite

Answer 64

- non-gamma 2, spherical and lathe cut - huge compressive strength quickly (260MPa in 1hr, 500MPa in 24hrs) - very low microleakage compared to other brands (0.04 ml/min) - compressive strength(500) - tensile strength (60) - elastic modulus (30) - hardness (100)

Question 65

how does amalgam compare to other composites failure rate after 8 years

Answer 65

much better than all composites (lower failure rate)