Amalgam
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what is the composition of traditional amalgam? 6
powder - silver, tin, copper, zinc, mercury liquid - mercury
what is the function of the constituents of traditional amalgam? 6
silver/tin - gamma phase, reacts with liquid Hg to form amalgam copper - increases strength and hardness zinc - reacts with oxygen mercury powder - accelerate the tting reaction mercury liquid - very pure and reacts with metals
what are the different particle types? how are they formed? and describe them 2
lathe cut - coarse, medium, fine, formed by filing ingots spherical - range of sizes, formed by spraying molten metal into inert atmosphere
what is the setting reaction of amalgam in simple terms?
Ag3Sn(γ) + Hg -> Ag3Sn(γ) + Ag2Hg3(γ1) + Sn7Hg9(γ2) Ag2Hg3(γ1) + Sn7Hg9(γ2) is the amalgam matrix
describe each gamma phase in amalgam’s structure 3
γ - good strength and corrosion resistance γ1 - good corrosion resistance γ2 - weak and poor corrosion resistance γ1 holds γ and γ2 together
what is the difference in setting dimensional changes with traditional and modern mixed amalgams?
traditional amalgam initially contracts then expands modern amalgam contracts a small amount then maintains it traditional = hand mixed, modern = mechnically mixed
why is zinc used less in amalgam?
interacts with saliva/blood * Zn + H2O -> ZnO + H2 bubbles of H2 formed within amalgam * pressure build up causes expansion * downward pressure causes pulpal pain
what are the advantages of spherical particles? 5
less Hg required higher tensile strength higher early compressive strength less sensitive to condensation easier to carve
what factors decrease the strength of amalgam? 5
undermixing too high Hg content after condensation too low condensation pressure slow rate of packing - increments don’t bond corrosion
what is creep?
when a material experiences low-level stresses that are applied repeatedly over a period of time
is amalgam biocompatible?
yes because there is no evidence that it harms humans
what are the thermal properties of amalgam?
thermal expansion - 3x greater than tooth tissue thermal conductivity - high so may need a liner in deep cavities thermal diffusivity - high so when a thermal stimuli is applied, amalgam’s temperature rises quickly and can damage the pulp
what is used to mix amalgam? describe it
amalgamator/capsule mixer * capsule is loaded with amalgam powder and liquid mercury separated by a membrane * once started, membrane is punctured and ultrasonic vibrations ensure even mixing
what can provide the conditions for corrosion of amalgam? 3
saliva, pH changes, drinks consumption
how do you decrease amalgam’s corrosivity?
copper enriched, polished margins avoiding galvanic cells
what are the different types of copper enriched amalgam? 2
dispersion modified single composition types
what is the composition of dispersion modified copper enriched amalgam?
• Ag-Cu spheres added to conventional lathe cut alloy • γ and γ1 particles present • Cu6Sn5 forms a halo around Ag/Cu spheres • all γ2 is consumed so less corrosive
what is the setting reaction for dispersion modified copper enriched amalgam?
• γ + Hg -> γ + γ1 + γ2 • γ2 + Ag-Cu -> Cu6Sn5 + γ1
what is the composition of single composition copper enriched amalgam?
powder Ag - Sn - Cu liquid Hg particles are lathe cut or spherical
what is the setting reaction for single composition copper enriched amalgam?
Ag-Sn-Cu + Hg -> Ag-Sn-Cu + γ1 + Cu6Sn5
what are the benefits of copper enriched? 4
stronger at early stages and in long term less creep higher corrosion resistance increased durability of margins
what are the advantages of amalgam? 5
strong hard durable radiopaque user friendly
what are the disadvantages of amalgam? 4
corrosion leakage - doesn’t bond to tooth poor aesthetics mercury - toxic
what are the properties of amalgam? 13
• high strength • high abrasion resistance • susceptible to creep • setting shrinkage • thermal expansion • high thermal conductivity • high thermal diffusivity • corrosive • biocompatible • poor aesthetics • radiopaque • not anticariogenic • smooth surface if polished but can deteriorate