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CSA > clinical aspects of amalgam > Flashcards

clinical aspects of amalgam Flashcards

Components and chemistry ◦ Properties ◦ Relating properties to clinical use ◦ Compare with other materials ◦ Safety

1
Q

what is amalgam

A

an alloy of mercury with another metal or other metals

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2
Q

what is dental amalgam

A

consists of silver mercury and tin with some other metals to modify the properties

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3
Q

what is the chemical equation of amalgam

A

Ag + Sn —> Ag3Sn

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4
Q

what is the shape of amalgam

A

lathe cut

spherical

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5
Q

what is amalgam currently stored in

A

in a capsule and the mercury and the amalgam alloy are separated by a membrane but is ruptured before being placed in the amalgamator

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6
Q

what are the three possible stages of the dissolved metals

A

Ag+Sn—->Ag3Sn known as the gamma phase
Ag+ Hg—-> Ag2Hg3 known as the gamma phase 1
Hg+ Sn —->Sn7Hg known as the gamma phase 2

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7
Q

what is gamma 2 responsible for

A

corrosion
creep
decrease in strength

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8
Q

what does the addition of copper

A

AgCu + Sn7Hg ( gamma 2) = Cu6Sn5 +Ag2Hg3 ( gamma 1)

reduces the gamma 2 phase

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9
Q

what is the typical modern amalgam powder composed of

A

silver
tin
copper
zinc

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10
Q

what is the % by weight of silver

A

65 min

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11
Q

what is the % by weight of tin

A

29 max

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12
Q

what is the % by weight of copper

A

6-13 max

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13
Q

what is the % by weight of zinc

A

2 max

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14
Q

what is the powder:liquid ratio

A

Ideally final amalgam restoration should contain <50% mercury

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15
Q

how much mercury should be added to make the mixture movable

A

more than 50% to make it movable

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16
Q

what happens if there less than 50% mercury in the filling

A

it makes the amalgam very dry

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17
Q

what happens when the amalgam is packed

A

the mercury is drawn to the top and the excess is scraped away during carving

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18
Q

what do we use to pack the amalgam

A

the condenser

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19
Q

what layer lies on top of the restoration

A

the mercury rich layer which we can then scrap away

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20
Q

what are the properties of spherical amalgam

A

softer more flowable

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21
Q

what are the properties of lathe cut amalgam

A

less flowable,

good for building up large amounts of missing tooth structure

22
Q

what do we typically use

A

ADMIXED

23
Q

advantages of amalgam

A 
good compressive strength 
good wear resistance 
easy to use
kind to opposing teeth
chemical set
cheap
radiopaque
24
Q

disadvantages of amalgam

A

do not stick to teeth
weak in thin sections minimum is 2mm depth
thermal conductor
unaesthetic

25
Q

what type of reaction can we get with amalgam fillings

A

lichenoid reactions

localised allergic reaction- red, white blotchy where the amalgam is located

26
Q

how do we treat lichenoid reactions on the buccal surface

A

remove the amalgam filling and can replace with GIC/composite

27
Q

what do we need to consider with amalgam fillings

A

they can act as a Plaque retention factor if there are overhangs

28
Q

when do we use amalgam

A

class 1 and class 2 restorations
where heavy occlusal force is there
where aesthetics are not important
building up teeth before the tooth is crowned

29
Q

how do we prepare teeth for an amalgam restoration

A

undercut
no unsupported enamel- wider at the base than the top
cavo surface angle should be greater than 90
the amalgam margin angle should be less than 70

30
Q

how do we create an undercut

A

if we use the pear shaped bur in the HS and drill across the longitudinal axis of the tooth it should naturally create a undercut

31
Q

what is retention

A

the prevention of the amalgam cavity being pulled out by vertical forces
macro mechanical

32
Q

what is resistance

A

the prevention of the amalgam cavity being moved by lateral forces

33
Q

what is the amalgam margin angle

A

where the restoration meets the prepared surface

34
Q

what do we do if were missing a total cusp

A

we can use a pin but we DO NOT use them any longer

35
Q

what are the disadvantages of a pin

A

could damage the pulp

if too close to the enamel it can cause the tooth cusp to fracture

36
Q

what can we use instead of pins

A

pits and grooves- cut directly into the tooth to allow for the amalgam to macromechanically bond

37
Q

what is bonding

A

the active substances (MDP or 4-META) form a hybrid layer with dentine and chemical bond to amalgam

38
Q

what are the disadvantages of polishing

A

the heat generated from polishing might damage the pulp

39
Q

will polishing improve the life expectancy

A

NO

40
Q

in the 1998 study what is the median age at replacement for amalgam

A

15 years

41
Q

in the 1998 study what is the median age at replacement for composite

A

8 years

42
Q

how long does it take for amalgam to fully set

A

24 hours

43
Q

how many amalgams were studied in the 2001 study

A

1800

44
Q

how many composites were studied in the 2001 study

A

1500

45
Q

in the 2001 study what was the average life span for amalgam

A

12 years

46
Q

in the 2001 study what was the average life span for composite

A

5 years

47
Q

what is the risk of secondary caries in the composite group

A

3.5 x

48
Q

is mercury vapour safe

A

highly toxic

49
Q

how is mercury vapour taken in

A

ingested

released when chewing or brushing

50
Q

describe the toxicity of amalgam

A

When mercury enters the environment it can be converted by bacteria into methyl mercury (MeHg) in fresh and salt water
Methyl mercury is highly poisonous

51
Q

which governments have banned mercury

A

sweden and germany

52
Q

what do we need to do with mercury in the clinical skills lab

A

Report mercury spills
Put empty capsules and waste amalgam in the receptacles provided
Clean the heads into the designated sink( dirty sink) (This has a separator on it)

CSA (51 decks)

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