Amalgam

Question 1

what is amalgam?

Answer 1

alloy formed by the reaction of mercury, silver, tin, copper and other metals

Question 2

how do you classify amalgam?

Answer 2

composition, particle shape and size

Question 3

what are the 2 compositions of amaglam?

Answer 3

traditional and copper enriched

Question 4

what does particle shape and size influence?

Answer 4

handling and final properties

Question 5

what are the powder components of amalgam?

Answer 5

silver, tin, copper, Zn, Hg in powder

Question 6

what does the silver tin component do?

Answer 6

reacts with Hg liquid to form amalgam. it is the gamma phase

Question 7

what does the copper component do?

Answer 7

increase strength and hardness

Question 8

what does the zinc component do?

Answer 8

scavenger during production

Question 9

what does the mercury liquid component do?

Answer 9

reacts with other metals

Question 10

what are the different particle types?

Answer 10

lathe cut, spherical and spheroidal

Question 11

what are the properties of lathe cut materials?

Answer 11

coarse, medium, fine, formed by filling ingots

Question 12

what are the properties of spherical and spheroidal materials?

Answer 12

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

Question 13

simplify the amalgam setting reaction

Answer 13

silver tin powder reacts with mercury liquid to give silver tin unreacted products and amalgam matrix (silver mercury and tin mercury)

Question 14

what is the gamma 1 phase?

Answer 14

silver mercury

Question 15

what is the gamma phase?

Answer 15

silver tin

Question 16

what is gamma 2 phase?

Answer 16

tin mercury

Question 17

which gamma phase has weak and poor corrosion resistance?

Answer 17

gamma 2 phase

Question 18

what is the final impact of setting on the dimensions of amalgam?

Answer 18

small contraction

Question 19

if there is zinc in amalgam and it comes into contact with saliva/blood what can happen?

Answer 19

bubbles of hydrogen within amalgam, expansion due to pressure, pulpal pain due to pressure, upward pressure causing restoration to sit proud on surface

Question 20

what are amalgam properties dependent on?

Answer 20

handling factors, cavity design, corrosion, types of products

Question 21

what are the advantages of spherical particles?

Answer 21

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

Question 22

comment on the mechanical properties (strength, abrasion resistance) of amalgam

Answer 22

strength is okay, high abrasion resistance

Question 23

what factors decrease strength?

Answer 23

undermixing, too high Hg content after condensation, too low condensation pressure, slow rate of packing, corrosion

Question 24

what does creep affect?

Answer 24

marginal integrity

Question 25

what is creep

Answer 25

when a material experiences low level stress levels which are applied repeatedly over a prolonged period

Question 26

what can creep result in?

Answer 26

permanent deformation

Question 27

what is the biocompatibility issue with amalgam?

Answer 27

mercury toxicity

Question 28

what is the thermal expansion of amalgam in relation to tooth substance?

Answer 28

x3 of the tooth

Question 29

comment on the thermal conductivity of the tooth?

Answer 29

high may need to use liner/varnish in deep cavities

Question 30

comment on the thermal diffusivity of the tooth?

Answer 30

high so when a transient thermal stimuli is applied amalgam’s temperature rises quickly

Question 31

comment on the bonding of amalgam?

Answer 31

it does not bond but instead needs mechanical retention

Question 32

how does amalgam corrode?

Answer 32

gamma 2 phase weakens material particularly at margins

Question 33

how is corrosion reduced?

Answer 33

copper enriched, polishing margins, avoiding galvanic cells

Question 34

is amalgam radiopaque?

Answer 34

yes

Question 35

what is the difference between normal amalgam and copper enriched amalgam?

Answer 35

copper enriched has no gamma 2 phase and has high copper content

Question 36

what are the types of copper enriched amalgam?

Answer 36

dispersion modified and single composition types

Question 37

what is the setting reaction of dispersion modified amalgam?

Answer 37

first step is the same as conventional material and then theres another reaction which turns gamma 2 and silver copper into copper tin and gamma 1

Question 38

what is the setting reaction for single composition formulations?

Answer 38

silver tin copper and mercury produce silver tin copper, gamma 1 and copper tin with 1 reaction only

Question 39

what are the benefits of copper enriched amalgam?

Answer 39

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

Question 40

what is the compressive strength of amalgam?

Answer 40

500MPa

Question 41

what is the thermal expansion coefficient of amalgam?

Answer 41

22-28

Question 42

comment on the posterior restoration failure of amalgam compared to composites

Answer 42

amalgam has significantly less failures

Question 43

what are the advantages of amalgam?

Answer 43

strong, hard, durable, radiopaque, user friendly

Question 44

what are the disadvantages of amalgam?

Answer 44

corrosion, leakage, poor aesthetics, mercury