Amalgam Flashcards
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
what is creep
when a material experiences low level stress levels which are applied repeatedly over a prolonged period
what can creep result in?
permanent deformation
what is the biocompatibility issue with amalgam?
mercury toxicity
what is the thermal expansion of amalgam in relation to tooth substance?
x3 of the tooth
comment on the thermal conductivity of the tooth?
high may need to use liner/varnish in deep cavities
comment on the thermal diffusivity of the tooth?
high so when a transient thermal stimuli is applied amalgam’s temperature rises quickly
comment on the bonding of amalgam?
it does not bond but instead needs mechanical retention
how does amalgam corrode?
gamma 2 phase weakens material particularly at margins
how is corrosion reduced?
copper enriched, polishing margins, avoiding galvanic cells
is amalgam radiopaque?
yes
what is the difference between normal amalgam and copper enriched amalgam?
copper enriched has no gamma 2 phase and has high copper content
what are the types of copper enriched amalgam?
dispersion modified and single composition types
what is the setting reaction of dispersion modified amalgam?
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
what is the setting reaction for single composition formulations?
silver tin copper and mercury produce silver tin copper, gamma 1 and copper tin with 1 reaction only
what are the benefits of copper enriched amalgam?
higher early strength, less creep, higher corrosion resistance, increased durability of margins
what is the compressive strength of amalgam?
500MPa
what is the thermal expansion coefficient of amalgam?
22-28
comment on the posterior restoration failure of amalgam compared to composites
amalgam has significantly less failures
what are the advantages of amalgam?
strong, hard, durable, radiopaque, user friendly
what are the disadvantages of amalgam?
corrosion, leakage, poor aesthetics, mercury
