amalgam

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Dental amalgam
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Amalgam terminology

• Amalgam an alloy containing mercury as a major
  ingrediet
• Dental amalgam an alloy mercury with Ag-Sn
• Dental amalgam alloy a Ag-Sn alloy (to be mixed
  with mercury )

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Applications

• As a permanent filling material in
• class 1 and 2 cavities
  
  class 5 cavities where esthetics are not
  concerned
• for making dies
• In retrograde fillings
• As a core material

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Classification

• Copper content high copper or low copper
• Zinc content zinc containing or zinc free
  alloys
• Shape of the alloy spherical, lathe cut
• No of alloyed metals binary , tertiary ,
  quaternary
• Size of alloy microcut , macrocut

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Composition

• Low copper silver -63-70
• tin -26-29
• copper - 2-5
• zinc - 0- 2
• High copper are of two type
• 1 Admixed 2 Single
  composition
• Ag 69 Ag
  40 60
• Sn 17 Sn
  22 30
• cu - 13 cu
  13 30
• Zn 1 zn
  0 -4
• 
  indium or palladium in small
• 
  amounts

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Function of each component

• Silver (Ag)
• increases strength
• increases expansion
• Decreases creep
• Tin (Sn)
• Decreases resistance to tarnish and corrosion
• decreased strength
• increases setting time
• Copper (Cu)
• - increases hardness and strength
• - increases setting expansion
• Mercury (Hg)
• - activates the reaction
• zinc (zn)
• - acts as deoxidizer
• - causes delayed expansion ( conditioned )

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Basic Setting reactions

• Low copper
• High copper
• In high copper gamma 2 phase is eliminated
• Gamma phase is the stronger phase of amalgam
• Gamma two phase is the weakest nd least stable to
  corrosion process.

Ag3Sn Ag-Cu Hg Þ Ag3Sn Ag-Cu Ag2Hg3
Cu6Sn5
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Material-Related Variables

• Dimensional change
• Strength
• Corrosion
• Creep

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Dimensional Change

• Most high-copper amalgams undergo a net
  contraction
• Contraction leaves marginal gap
• initial leakage
• post-operative sensitivity
• reduced with corrosion over time
• Net contraction
• condensation technique
• greater condensation higher contraction
• trituration time
• overtrituration causes higher contraction

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Strength

• Develops slowly
• 1 hr 40 to 60 of maximum
• 24 hrs 90 of maximum
• Higher compressive vs. tensile strength
• Weak in thin sections
• unsupported edges fracture

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creep

• Slow deformation of amalgam placed under a
  constant load
• load less than that necessary to produce fracture
• Gamma 2 dramatically affects creep rate

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Amalgam Properties
7 days
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