Amalgam
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what is amalgam?
alloy formed by the reaction of mercury, silver, tin, copper and other metals
how do you classify amalgam?
composition, particle shape and size
what are the 2 compositions of amaglam?
traditional and copper enriched
what does particle shape and size influence?
handling and final properties
what are the powder components of amalgam?
silver, tin, copper, Zn, Hg in powder
what does the silver tin component do?
reacts with Hg liquid to form amalgam. it is the gamma phase
what does the copper component do?
increase strength and hardness
what does the zinc component do?
scavenger during production
what does the mercury liquid component do?
reacts with other metals
what are the different particle types?
lathe cut, spherical and spheroidal
what are the properties of lathe cut materials?
coarse, medium, fine, formed by filling ingots
what are the properties of spherical and spheroidal materials?
range of particle sizes, formed by spraying molten metal into inert atmosphere
simplify the amalgam setting reaction
silver tin powder reacts with mercury liquid to give silver tin unreacted products and amalgam matrix (silver mercury and tin mercury)
what is the gamma 1 phase?
silver mercury
what is the gamma phase?
silver tin
what is gamma 2 phase?
tin mercury
which gamma phase has weak and poor corrosion resistance?
gamma 2 phase
what is the final impact of setting on the dimensions of amalgam?
small contraction
if there is zinc in amalgam and it comes into contact with saliva/blood what can happen?
bubbles of hydrogen within amalgam, expansion due to pressure, pulpal pain due to pressure, upward pressure causing restoration to sit proud on surface
what are amalgam properties dependent on?
handling factors, cavity design, corrosion, types of products
what are the advantages of spherical particles?
less Hg required, higher tensile strength, higher early compressive strength, less sensitive to condensation, easier to carve
comment on the mechanical properties (strength, abrasion resistance) of amalgam
strength is okay, high abrasion resistance
what factors decrease strength?
undermixing, too high Hg content after condensation, too low condensation pressure, slow rate of packing, corrosion
what does creep affect?
marginal integrity