dental amalgam e lec

Question 1

what is amalgam

Answer 1

a combination of different things eg an alloy containing mercury

Question 2

which industries is amalgam used in

Answer 2

more than just dental industries

Question 3

how is gold extracted

Answer 3

extraction of gold from an ore

Question 4

why are companies reducing their use of amalgam

Answer 4

because of the environmental impact the release of mercurious compounds.

Question 5

what state is mercury in at room temp

Answer 5

liquid

Question 6

what temp does mercury freeze at

Answer 6

-39C

Question 7

what is mercury used in

Answer 7

thermometers, manometers, tilt switches, treatment for STDs

Question 8

what temp does mercury form alloys

Answer 8

room temperature

Question 9

what is the most damaging form of mercury

Answer 9

organic compounds and mercury vapours

Question 10

how is mercury considered safe

Answer 10

when rendered with an alloy or inter metallic compound

Question 11

when does mercury become inert

Answer 11

when it is placed

Question 12

what is the maximum exposure levels per week

Answer 12

300mg per week

Question 13

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

Answer 13

25mg/m3

Question 14

how can mercury enter the body

Answer 14

absorbed
ingested
inhaled

Question 15

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

Answer 15

60 days

Question 16

what is mercury presented in to the clinician

Answer 16

into a pre prepared capsule for health and safety reasons

Question 17

what might a typical modern alloy contain

Answer 17

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

Question 18

what is the amalgam alloy made from

Answer 18

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

Question 19

what is the ratio of silver to tin in amalgam alloys

Answer 19

Ratio of 73% : 17% by weight

Question 20

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

Answer 20

Ag3Sn which is known as the gama phase!

Question 21

what year was the amalgam settled in

Answer 21

1855

Question 22

why is zinc added to the amalgam alloy

Answer 22

it is not clear

Question 23

what was amalgams first made from in 1500-1840s

Answer 23

large amounts of silver coins which has silver and cooper

Question 24

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

Answer 24

90-95% wt

Question 25

how does silver set

Answer 25

slow but and was hard

Question 26

how does tin set

Answer 26

rapidly but does not harden

Question 27

how does copper set

Answer 27

it set but wasn't hard

Question 28

what is the equation of mercury and amalgam alloy reaction

Answer 28

Hg + Ag Sn (γ)( gamma phase)

Question 29

what is the product of the mercury and amalgam reaction

Answer 29

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

Question 30

what do the gamma 1 and gamma 2 phase do

Answer 30

they precipitate out of the liquid and are not soluble

Question 31

what is the gamma 1 structure referred to as

Answer 31

the matrix and holds the whole composite together

Question 32

what is the gamma 2 phase susceptible to

Answer 32

corrosion

Question 33

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

Answer 33

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

Question 34

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

Answer 34

that it distorts restorations and leads to marginal failure

Question 35

what are remaining products of corrosion

Answer 35

tin based

Question 36

what is the dangers of the products of corrosion

Answer 36

can be lost to the body and increase mercury exposure | also causes staining of the surrounding tissues

Question 37

how was dental amalgam mixed in the start

Answer 37

mixed with a mortar and pestle

Question 38

how was the process improved from mixing it by hand

Answer 38

the introduction of amalgamators which automatically mixed the alloy and mercury

Question 39

how are amalgam and mercury now mixed

Answer 39

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

Question 40

what is the shape of the amalgam alloy

Answer 40

spherical

Question 41

what is the lathe cut

Answer 41

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

Question 42

how are spherical amalgam alloys made

Answer 42

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

Question 43

how do we get rid of corrosion

Answer 43

to increase the amount of copper

Question 44

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

Answer 44

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

Question 45

what happens to the additional copper

Answer 45

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

Question 46

what do the crystals of Cu6Sn5

Answer 46

fine rod like

Question 47

what do we have to consider about dental amalgams

Answer 47

``` 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 ```

Question 48

what is the compressive strength of amalgam

Answer 48

350MPA

Question 49

what is the tensile strength of amalgam

Answer 49

35 MPA

Question 50

why is the spherical cut of amalgam alloy better

Answer 50

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

Question 51

what is creep

Answer 51

the material flows as a response to the various stresses

Question 52

at what temp does the gamma phase 1 start to melt

Answer 52

80C