clinical aspects of amalgam

Question 1

what is amalgam

Answer 1

an alloy of mercury with another metal or other metals

Question 2

what is dental amalgam

Answer 2

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

Question 3

what is the chemical equation of amalgam

Answer 3

Ag + Sn —> Ag3Sn

Question 4

what is the shape of amalgam

Answer 4

lathe cut

spherical

Question 5

what is amalgam currently stored in

Answer 5

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

Question 6

what are the three possible stages of the dissolved metals

Answer 6

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

Question 7

what is gamma 2 responsible for

Answer 7

corrosion
creep
decrease in strength

Question 8

what does the addition of copper

Answer 8

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

reduces the gamma 2 phase

Question 9

what is the typical modern amalgam powder composed of

Answer 9

silver
tin
copper
zinc

Question 10

what is the % by weight of silver

Answer 10

65 min

Question 11

what is the % by weight of tin

Answer 11

29 max

Question 12

what is the % by weight of copper

Answer 12

6-13 max

Question 13

what is the % by weight of zinc

Answer 13

2 max

Question 14

what is the powder:liquid ratio

Answer 14

Ideally final amalgam restoration should contain <50% mercury

Question 15

how much mercury should be added to make the mixture movable

Answer 15

more than 50% to make it movable

Question 16

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

Answer 16

it makes the amalgam very dry

Question 17

what happens when the amalgam is packed

Answer 17

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

Question 18

what do we use to pack the amalgam

Answer 18

the condenser

Question 19

what layer lies on top of the restoration

Answer 19

the mercury rich layer which we can then scrap away

Question 20

what are the properties of spherical amalgam

Answer 20

softer more flowable

Question 21

what are the properties of lathe cut amalgam

Answer 21

less flowable,

good for building up large amounts of missing tooth structure

Question 22

what do we typically use

Answer 22

ADMIXED

Question 23

advantages of amalgam

Answer 23

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

Question 24

disadvantages of amalgam

Answer 24

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

Question 25

what type of reaction can we get with amalgam fillings

Answer 25

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

Question 26

how do we treat lichenoid reactions on the buccal surface

Answer 26

remove the amalgam filling and can replace with GIC/composite

Question 27

what do we need to consider with amalgam fillings

Answer 27

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

Question 28

when do we use amalgam

Answer 28

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

Question 29

how do we prepare teeth for an amalgam restoration

Answer 29

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

Question 30

how do we create an undercut

Answer 30

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

Question 31

what is retention

Answer 31

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

Question 32

what is resistance

Answer 32

the prevention of the amalgam cavity being moved by lateral forces

Question 33

what is the amalgam margin angle

Answer 33

where the restoration meets the prepared surface

Question 34

what do we do if were missing a total cusp

Answer 34

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

Question 35

what are the disadvantages of a pin

Answer 35

could damage the pulp | if too close to the enamel it can cause the tooth cusp to fracture

Question 36

what can we use instead of pins

Answer 36

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

Question 37

what is bonding

Answer 37

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

Question 38

what are the disadvantages of polishing

Answer 38

the heat generated from polishing might damage the pulp

Question 39

will polishing improve the life expectancy

Answer 39

NO

Question 40

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

Answer 40

15 years

Question 41

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

Answer 41

8 years

Question 42

how long does it take for amalgam to fully set

Answer 42

24 hours

Question 43

how many amalgams were studied in the 2001 study

Answer 43

1800

Question 44

how many composites were studied in the 2001 study

Answer 44

1500

Question 45

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

Answer 45

12 years

Question 46

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

Answer 46

5 years

Question 47

what is the risk of secondary caries in the composite group

Answer 47

3.5 x

Question 48

is mercury vapour safe

Answer 48

highly toxic

Question 49

how is mercury vapour taken in

Answer 49

ingested | released when chewing or brushing

Question 50

describe the toxicity of amalgam

Answer 50

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

Question 51

which governments have banned mercury

Answer 51

sweden and germany

Question 52

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

Answer 52

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)