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CSA > dental amalgam e lec > Flashcards

dental amalgam e lec Flashcards

1
Q

what is amalgam

A

a combination of different things eg an alloy containing mercury

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2
Q

which industries is amalgam used in

A

more than just dental industries

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3
Q

how is gold extracted

A

extraction of gold from an ore

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4
Q

why are companies reducing their use of amalgam

A

because of the environmental impact the release of mercurious compounds.

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5
Q

what state is mercury in at room temp

A

liquid

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6
Q

what temp does mercury freeze at

A

-39C

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7
Q

what is mercury used in

A

thermometers, manometers, tilt switches, treatment for STDs

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8
Q

what temp does mercury form alloys

A

room temperature

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9
Q

what is the most damaging form of mercury

A

organic compounds and mercury vapours

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10
Q

how is mercury considered safe

A

when rendered with an alloy or inter metallic compound

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11
Q

when does mercury become inert

A

when it is placed

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12
Q

what is the maximum exposure levels per week

A

300mg per week

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13
Q

what is the maximum exposure levels in the air regarding the conc of mercury vapour

A

25mg/m3

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14
Q

how can mercury enter the body

A

absorbed
ingested
inhaled

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15
Q

how long does it take to half the amount of mercury in th body

A

60 days

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16
Q

what is mercury presented in to the clinician

A

into a pre prepared capsule for health and safety reasons

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17
Q

what might a typical modern alloy contain

A

69 %wt Ag, 19 %wt Sn, 11 %wt Cu and 1 %wt Zn.

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18
Q

what is the amalgam alloy made from

A

silver and tin with some small additions of copper < 6 %

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19
Q

what is the ratio of silver to tin in amalgam alloys

A

Ratio of 73% : 17% by weight

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20
Q

what intermediate alloy is formed of silver and tin in the amalgam alloy

A

Ag3Sn which is known as the gama phase!

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21
Q

what year was the amalgam settled in

A

1855

22
Q

why is zinc added to the amalgam alloy

A

it is not clear

23
Q

what was amalgams first made from in 1500-1840s

A

large amounts of silver coins which has silver and cooper

24
Q

what was the percentage by weight of the silver in these coins

A

90-95% wt

25
Q

how does silver set

A

slow but and was hard

26
Q

how does tin set

A

rapidly but does not harden

27
Q

how does copper set

A

it set but wasn’t hard

28
Q

what is the equation of mercury and amalgam alloy reaction

A

Hg + Ag Sn (γ)( gamma phase)

29
Q

what is the product of the mercury and amalgam reaction

A

Ag3Sn (γ) + Ag Hg (γ ) + Sn Hg (γ ) 2 3 1 7 2

30
Q

what do the gamma 1 and gamma 2 phase do

A

they precipitate out of the liquid and are not soluble

31
Q

what is the gamma 1 structure referred to as

A

the matrix and holds the whole composite together

32
Q

what is the gamma 2 phase susceptible to

A

corrosion

33
Q

what does traditional thinking say about the gamma 2 phase being corroded

A

that it is not a bad thing as it will prevent leakage of the margins

34
Q

what do we now know about the gamma 2 phase and corrosion

A

that it distorts restorations and leads to marginal failure

35
Q

what are remaining products of corrosion

A

tin based

36
Q

what is the dangers of the products of corrosion

A

can be lost to the body and increase mercury exposure

also causes staining of the surrounding tissues

37
Q

how was dental amalgam mixed in the start

A

mixed with a mortar and pestle

38
Q

how was the process improved from mixing it by hand

A

the introduction of amalgamators which automatically mixed the alloy and mercury

39
Q

how are amalgam and mercury now mixed

A

more recently this has been further refined by the use of encapsulated amalgams

40
Q

what is the shape of the amalgam alloy

A

spherical

41
Q

what is the lathe cut

A

chips of amalgam alloy which are irregularly cut and do not readily flow

42
Q

how are spherical amalgam alloys made

A

spraying liquid alloy into air or water, the latter produced a more varied morphology.

43
Q

how do we get rid of corrosion

A

to increase the amount of copper

44
Q

what happens because we have increased the copper % to 12%

A

second reaction with the gamma 2 phase forming the products gamma 1 and Cu6Sn5.
Cu6Sn5 + Ag2Hg3 (γ1)

45
Q

what happens to the additional copper

A

into the amalgam alloy such that the alloy is of two intermetallic compounds Ag3Sn and Cu3Sn,

46
Q

what do the crystals of Cu6Sn5

A

fine rod like

47
Q

what do we have to consider about dental amalgams

A 
Doesn't adhere to tooth   
 Not aesthetic
   Base or liner- need therapeutic liner or base material 
   Poor tensile strength
   Polishing 24 hours later.    
Long lasting
   Lathe cut or Spherical
   Creep
48
Q

what is the compressive strength of amalgam

A

350MPA

49
Q

what is the tensile strength of amalgam

A

35 MPA

50
Q

why is the spherical cut of amalgam alloy better

A

Spherical is thought to lead to the amalgam flowing better during condensation and also to a reduction in the amount of Hg needed to make a workable material

51
Q

what is creep

A

the material flows as a response to the various stresses

52
Q

at what temp does the gamma phase 1 start to melt

A

80C

CSA (51 decks)

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