Amalgam

Amalgam is a direct restorative material consisting of an alloy(mixture) of silver(Ag), tin(Sn), copper(Cu), zinc(Zn) and liquid mercury(Hg)

Composition
Silver (40-70%)
Tin (26-30%)
Copper (2-30%)
Zinc (0-2%)
Mercury

Can be formulated as:
low-copper (5% copper or less) Ag3Sn + Hg = Ag2Hg3 + Sn8Hg+ Ag3Sn
or
high-copper (13%-30% copper); high copper has better corrosion resistance and greater strength/ Ag3Sn + Ag-Cu + Hg = Ag2Hg + Sn8Hg +Ag3Sn
Alloy particles can be irregularly shaped or microspheres or a combination of both(admixed)
Particles are produced by heating the metal parts and pouring into an ingot ( 400 degrees celsius) and cooled slowly (6-8hours). The ingot is cut and passed through a sieve to produce the appropriate particle size ( 60-120 length, 10-70 width, 10-35 thick MICROMETRES)

Amalgam has multiple phases
y (gamma) Ag3Sn
y1 (gamma 1) Ag2Hg3 – matrix of set amalgam
y2 (gamma 2) Sn8Hg – weakest phase
e (episilon) Cu3Sn
n (eta) Cu6Sn5

Advantages
Good wear/pressure resistance in large restorations
Easy/simple to handle
Retention provided through macromechanical cavity preparation

Disadvantages
Thermal/Electrical conductivity
Poor aesthetics
Corrosion
Expansive properties
Amalgam tattoos
Tensile Strength is lower than compressive strength
Mercury toxicity
Microleakage – gap developing between restoration and tooth surface

Indications
Large cavities
Low aesthetic areas
Heavy occlusal contacts
Regions of poor isolation
Restorations extending onto root surfaces

Contraindications
High aesthetic areas
Small/Shallow cavities
Regions which can be well isolated