An amalgam is an alloy that contains mercury as one
of its constituents.
• DENTAL AMALGAM
An alloy of mercury, silver, copper and tin which may
also contain palladium ,zinc and other elements to
improve handling characteristics and clinical
The general term amalgam is also used as a synonym
by the dental professionals
• INITIATED IN 1841 ALSO KNOWN AS THE ‘FIRST AMALGAM WAR’
• DR. CHAPIN A. HARRIS (1839) SAID AMALGAM IS AN ABOMINABLE ARTICLE
FOR DENTAL FILLING.
• 1843-RESOLUTION BY AMERICAN SOCIETY OF DENTAL SURGEONS THAT
AMALGAM USE IS MALPRACTICE.
• 1845- PLEDGE BY THIS ORGANISATION NOT TO USE AMALGAM.
• 1850-PLEDGE RESCINDED. MARKED END OF AMALGAM WAR OFFICIALY.
• INVESTIGATIONS WERE BEGUN ON AMALGAM COMPOSITION IN GERMANY
,U.S. & FRANCE.
• THE QUESTION OF AMALGAM COMPOSITION WAS FINALLY SETTLED IN 1895
BY DR. G.V. BLACK . (67.5% Ag; 27.5% Sn; 5% Cu).
• The Second Amalgam War was started by a German
chemist, professor Alfred Stock in the mid 1920’s when Stock
claimed to have evidence showing that mercury could be
absorbed from dental amalgams and that this led to serious
health problems. Stock reported that nearly all dentists had
excess mercury in their urine.
• He reported that mercury levels in urine of 7 patients with
amalgam ranged from 0.1 to 40 mg/L
• The current controversy, sometimes termed the “Third
Amalgam War” began primarily through the seminars,
writings and videotapes of H.A. Huggins, a dentist from
Colorado Springs. He was convinced that mercury released
from dental amalgam was responsible for a plethora of
human diseases affecting the cardiovascular and nervous
• 1991- Issue reported by a major television
• NIH- NIDR & FDA Reexamined the issue ---- concluded that there is no
basis for the claim
• Moderate to large Class I & II restorations.
• Class V restorations
• Caries control restoration
• For making dies.
• Earlier as retrograde rootcanal filling material.
• In clinical situations involving heavy occlusal
• In less optimum conditions of moisture
• Operator ability.
• Anterior teeth and clearly visible surfaces of
• Remaining tooth structure requires support /
would require extensive preparation to
• Treatment of incipient / early primary fissure
1. Ease of use
2. High compressive strength
3. Excellent wear resistance
4. Favorable long-term clinical results
5. Lower cost than for composite restorations
6. Bonded amalgams have "bonding" benefits:
• Less microleakage
• Less interfacial staining
• Minimal postoperative sensitivity
• Some retention benefits
• Esthetic benefit of sealing by not permitting the amalgam to
discolor the adjacent tooth structure
3. Less conservative (more removal of tooth
structure during tooth preparation)
4. More difficult tooth preparation
5. Weakens tooth structure (unless bonded)
6. More technique sensitive if bonded
7. Initial marginal leakage
DENTAL AMALGAM ALLOY
• An alloy of silver, copper, tin and other
elements that is formulated and processed in
the form of powder particles or as
• Also known as alloy for dental amalgam.
GENERATIONS OF AMALGAM ALLOY
• FIRST GENERATION
Amalgam that was studied and recommended
- Composed of 3 parts silver & 1 part tin.
Addition of zinc and copper to the first generation
Admixture of spherical Ag ₃ – Cu eutectic alloy to the original alloy powder
Alloying of copper to silver and tin , up to 29% form a ternary alloy in which
most of the tin is firmly bonded to copper.
Alloying of silver, copper , tin and indium creates a true quaternary alloy, in
which almost none of the tin is available to react with mercury.
Alloying of palladium (10%),silver(62%), copper(28%),to form a eutectic alloy
which is lathe cut and blended into 1st , 2nd or 3rd generation amalgam in the
ratio of 1:2.
Classification of Amalgam Alloy
According to no. of alloyed metals
– Binary alloys (Ag-Sn)
– Ternary alloys (Ag-Sn-Cu)
– Quaternary (Ag-Sn-Cu-In)
Acc to particle size
– Fine cut
– Coarse cut
Acc to copper content
– Low copper <6%
– High copper >6%
Acc to zinc content
– Zinc containing >0.01%
– Zinc free <0.01%
Acc to shape of produced particles
– Spherical (Smooth-surfaced)
– Lathe-cut (Irregular shaped)
Acc to alloy Content
Acc to presence of noble metals
• ADA Specification No. 1 require that amalgam alloy should be
predominantly silver and tin.
• Unspecified amounts of other elements like copper ,zinc , gold
and mercury are allowed in concentration less than silver or
• ZINC containing alloy- more than 0.01%
• ZINC free alloy- less than 0.01%
EFFECTS OF VARIOUS COMPONENTS
SILVER COPPER TIN
Increases strength Increases Strength Controls reaction rate
Increases Expansion Increases Expansion Decreases strength
Decreases flow Decreases flow Decreases Expansion
Decreases setting time Increases Flow
Decreases plasticity Increases plasticity
Manufacture of alloy powder
Milling/Lathe cutting Atomizing
Differences between Lathe-cut and
Lathe – cut Spherical
1. Require more mercury (50%)
2. Require more condensation
3. Require smaller condenser
4. Less ease in carving and
5. Less overhangs and strong
1. Require less mercury (42%)
2. Require less condensation
3. Require broader condenser
4. Smooth surface during
carving & burnishing
5. Overhangs and weak
METALLURGICAL PHASES IN
• Phases in amalgam alloys
and set dental amalgam
• Stiochiometric formula
LOW COPPER ALLOY
• LOWCOPPER contains
COPPER - 2-5%
ZINC - 0.8%
ALSO CALLED CONVENTIONAL AMALGAM ALLOY
• The physical properties of the
hardened amalgam depend
on the relative percentage of
each of the microstructural
• The more unconsumed Ag-Sn
particles found in the final
structure , the stronger the
• The weakest component is
the g₂ phase.
• The hardness of Sn₇₋₈ Hg
( g₂ ) is 10% the
hardness of Ag₂ Hg₃ ( g ₁ ).
HIGH COPPER ALLOY
• HIGH CORROSION RESISTANCE
• COPPER content 12 - 30%
• TWO TYPES- ADMIXED
- SINGLE COMPOSITION
ADMIXED AMALGAM ALLOY
• Introduced in 1963 by INNES AND YOUDELIS.
• Ag-Cu eutectic alloy (71.9% Ag and 28.1% Cu) particles are added
to lathe cut low copper amalgam alloy particles.
• STRONGER- Due to increase in residual alloy particle & decrease in
• Contains 30-55% spherical high copper particle.
• REACTION :
• ALLOY PARTICLES (b+g) + Ag-Cu eutectic + Hg g₁
+ h + UNCONSUMED ALLOY OF BOTH TYPES OF
•When Hg reacts with an admixed powder, Ag dissolves
into the mercury from Ag-Cu alloy particles .
• Both Ag and Sn dissolve into the Hg from the Ag-Sn
•The Sn in solution diffuses to the surfaces of the Ag-
Cu alloy and reacts with Cu to form h phase (Cu₆Sn₅)
• A layer of h crystals forms around unconsumed Ag-Cu
•The layer also contains some g₁ crystals.
•g₁ forms simultaneously with h on the surface of h
covered Ag-Cu alloy & Ag-Sn lathe cut alloy
• ELIMINATION OF g 2 PHASE :
• REACTION 1 :
• Ag₃Sn (Excess γ phase) +Ag-Cu (Silver-Copper Eutectic) +
Hg Ag₂Hg₃ (g ₁ Phase) + Sn₇₋₈Hg (g ₂ Phase)
+Ag₃Sn ( unreacted γ Phase) + Ag-Cu
(unreacted Eutectic phase)
• REACTION 2 :
• Ag-Cu (unreacted Eutectic phase) + Sn₇₋₈Hg (γ 2 Phase)
Ag₂Hg₃ + Cu₆Sn₅ ( η phase )
The second reaction occurs at mouth temperature for 1-2
weeks and γ2 phase is thus nearly eliminated.
• DEVELOPED BY ASGAR IN 1974.
• EACH PARTICLE OF THIS ALLOY HAS THE SAME CHEMICAL
• SILVER -60%
SMALL AMOUNTS OF INDIUM AND PALLADIUM SEEN IN SOME
• COPPER CONTENT VARIES BETWEEN 13-30%
• Ag-Sn-Cu ALLOY PARTICLES + Hg
g1 + h+ UNCONSUMED ALLOY PARTICLES.
•When triturted with MERCURY, SILVER
& TIN from Ag-Sn dissolve.
•Little copper dissolve in Hg.
• g1 crystals grow forming a matrix
that binds the unreacted alloy particles
• h crystals(Cu₆Sn₅)- Form a mesh at
the surface of alloy particles and are
also dispersed in the matrix.
FUNCTION OF THE η PHASE
• Strengthen the bond between alloy particles
and γ₁ phase.
• Interlocks the γ₁ phase thus improving the
amalgams resistance to deformation.
• ANSI/ADA NO-1 requires that amalgam should
neither contract nor expand more than 20 µm / cm,
measured at 37˚C, between 5 mins and 24 hrs after
the beginning of trituration , with a device that is
accurate to atleast 0.5 μm.
• Classically, amalgam initially undergoes contraction for about 20
min after the beginning of trituration and then begins to expand.
• Initial contraction is due to the dissolving of the alloy particles in
Hg and resultant formation of γ₁ phase.
• On availability of sufficient Hg, the γ₁ crystals grow & impinge
against each other resulting in expansion.
• Most modern amalgams, exhibit net contraction as their
manipulation involves minimum Hg technique.
Factors affecting dimensional change:
a) Increased γ phase or β phase, increased expansion
b) Increased traces of Tin, decreased expansion
2) Particle size: Decreased particle size, there is contraction
3) Particle shape: Smoother shape (as in spherical type) there is better
wetting with Hg causing in faster amalgamation resulting in
4) Hg/Alloy ratio: Increased Hg/Alloy ratio -Increased expansion
5) Trituration: Rapid trituration and longer trituration results in contraction because of
– Faster amalgamation
– Decrease in particle size
– Pushing of Hg between particles
– Prevention of outward growth of crystals
6) Condensation: Increased condensation pressure causes closer contact of Hg with alloy
particles and squeezing of excess Hg from the mix resulting in contraction.
• Expansion that occurs due to reaction of Hg with
alloy components is termed Primary expansion
or Mercuroscopic expansion.
• Mercuroscopic Expansion: Release of mercury
from γ2 phase during electrochemical corrosion
results in additional formation of phases on
reaction with unreacted γ phase, causing further
• Expansion that occurs after 1 to 7 days due to
moisture contamination during trituration or
condensation before the amalgam mass is set, is
termed Secondary expansion or Delayed
• Alloys containing Zn, if contaminated with
moisture during trituration or condensation,
a large expansion occurs.
• This is due to release of H₂ gas within the
restoration creating an internal pressure of
nearly 2,000 psi.
The gas is formed as follows:
Zn + H₂O ZnO + H₂
• Starts after 3-5 days , continue for months
reaching values greater than 400μm.
Effects of dimensional change
• Expansion >> 4%
• Pressure on pulp causing pain
• High point leading to occlusal interference causing pain
• Pressure on cavity walls resulting in tooth fracture and pain.
• Greater susceptibility to corrosion
• Expansion over the cavity margins causes fracture of the restoration
• Contraction >> than 50µ/cm
• Secondary caries
• Plaque accumulation
Factors affecting strength of Dental Amalgam
Increased trituration within limits increases strength
(due to increased coherence of matrix crystals).
Increased trituration beyond limits decreases strength
( due to cracking of formed crystals decreasing coherence).
• Hg/Alloy ratio:
Increased Hg/Alloy ratio, decreased strength, because
increased Hg results in
– Decreased unreacted γ phase
– Increased γ2 phase
– Increased residual Hg (weakest phase) within
• Condensation pressure Increased pressure (3-
4lb/ square inch) within limits results in increased
• Microstructure of amalgam:
– Increased γ and γ1 phases there is increased
– Presence of η phase there is increased strength
– Increased γ2 phase, there is decreased strength
• Particle size: Decreased size ( 15 -35 m)
results in increased strength (due to
increased surface area / unit volume)
• Particle shape: Regular uniform shape result
in increased strength (due to more
wettability, more coherent mass, less
• Effect of amalgam hardening rate: The ADA
specification stipulates a minimum compressive
strength of 80 Mpa at 1 hour.
Defn:-Time dependent plastic deformation that is produced by a
TYPES : 1) STATIC 2) DYNAMIC
SIGNIFICANCE OF CREEP ON AMALGAM :
Creep rate has been found to correlate with
marginal breakdown of traditional low-Cu
• However for High-Cu amalgams , the Creep rates
are less(< 0.1%) .
• Creep occurs because of grain boundary sliding.
• η crystals on γ1 grains prevent grain boundary
sliding and therefore are responsible for
decreased creep values of high copper alloys.
Factors affecting Creep
• Microstructure of amalgam
– Increased γ1 fraction, increased creep
– Increased γ2 fraction, increased creep
– Increased grain size of γ1, decreased creep
– Presence of η phase, decreased creep
• Hg/Alloy ratio: Increased Hg/Alloy ratio, increased
creep (due to more residual Hg)
• Condensation pressure: Increased pressure within
limits, decreased creep (due to less residual Hg)
• Delay between trituration and condensation:
TARNISH & CORROSION
• Amalgam undergoes 2 types of corrosion:-
Chemical & Electrochemical
• Chemical corrosion results in formation of
surface Silver sulfide layer.
• Electrochemical corrosion –
Galvanic, Crevice & Stress Corrosion.
• The most common corrosion products of
traditional amalgam alloys are oxides &
oxychlorides of tin.
• Along the margins SnO helps to seal the space
against microleakage. Thus, dental amalgam
behaves as a self sealing restoration.
• Electrochemical corrosion of high-copper
amalgams produce both Cu & Sn oxides &
MERCURY : ALLOY RATIO/PROPORTIONING
For conventional mercury-added systems , TWO TECHNIQUES
are used for achieving mercury reduction in the final
Methods of Dispensing Alloy
A wide variety of
mercury and alloy
• Automatic mechanical
• Preweighed pellets-
method of dispensing
capsules -alloy and Hg
separated by disk or
• To dissolve alloy particles in Hg so as to obtain a plastic
mass of amalgam which can be condensed into the cavity.
• To remove oxide film coated on the alloy particles.
• To pulverize the alloy particles for proper wetting by Hg.
• With mortar and pestle (trituration pressure 2-3 psi)
• With mechanical amalgamator
• Factors affecting trituration
• Speed - number of unit movements/ unit time
• Weight of the capsule and the pestle
• Duration of trituration
• Difference in the size between the pestle and the encasing capsule.
• It is a continuation of trituration.
• Can be accomplished in two ways:-
a) By kneading the plastic amalgam mix in a
piece of rubber dam.
b) By triturating the mix in a pestle free
capsule for 2-3 seconds after the specified
• To condense unattacked g particles closely together
• To adapt amalgam to the cavity walls.
• To remove excess Hg.
• To bring Hg on the top of each increment so as to bind the increments to one
another (increasing dryness technique).
• To increase the density of the restoration by development of an uniform
compact mass with minimal voids.
• To increase the rate of hardening so that carving operation need not be
• Hand condensation
• Mechanical condensation( impact type of force , rapid
• Condensation pressure: 3 to 4 lb/sq inch.
To produce a restoration with -
• Proper physiological contours.
• Minimal flash (no overhangs).
• Functional, non-interfering occlusal anatomy.
• Adequate, compatible marginal ridges.
• Proper size, location, extent and inter-relationship of contact areas.
• Physiologically compatible embrasures.
• No interference with integrity of periodontium.
• Method: Performed by using various varieties of amalgam
carvers available ( like Hollenbeck's carver). Carving is always from
the tooth surface to the restoration surface. This is done to avoid
removal of amalgam at the margins.
• To further decrease the size and number of voids.
• To express excess Hg on the surface of the amalgam
• To adapt amalgam to the cavosurface anatomy.
• Method: Performed using Beaver tail
burnisher or Sprately burnisher. From
amalgam to tooth.
FINISHING & POLISHING
• To remove amalgam flash that has been left behind during
• To remove superficial scratches and irregularities:
decreases fatigue failure, decreases concentration cell
corrosion and decreases accumulation or adherence of
• To make the restoration aesthetically more appealing.
DENTAL MERCURY HYGIENE
1) Ventilation: Provide proper ventilation in the work place by
having fresh air exchanges and periodic replacement of filters,
which may act as traps for mercury.
2) Monitor office: Monitor the mercury vapor level in the office
periodically. This may be done by using dosimeter
badges(Limit-50μg/m³in 8hr shift over 40hr work week).
3) Monitor personnel: Monitor office personnel by periodic
4) Office design: Use proper work area design to facilitate spill
containment and cleanup.
5) Pre-capsulated alloys: Use pre-capsulated alloys to eliminate the
possibility of a bulk mercury spill. Otherwise store bulk
mercury properly in unbreakable containers on stable surfaces.
6) Amalgamator cover: Use an amalgamator fitted with a cover.
7) Handling care: Use care in handling amalgam. Avoid skin
contact with mercury or freshly mixed amalgam. Avoid dry
8) Evacuation systems: Use high volume evacuation when
finishing or removing amalgam. Evacuation system
have traps or filters. Check, clean or replace traps and
9) Masks: Change mask as necessary when removing
10) Recycling: Store amalgam scrap under radiographic fixer
solution in a covered container. Recycle amalgam
scraps through refiners.
11) Contaminated items: Dispose of mercury contaminated
items in sealed bags according to applicable regulations.
12) Spills: Clean up spilled mercury properly by using
bottles, tapes or fresh mixes of amalgam to pick-up
droplets: or use commercial clean up kits. Do not use
household vacuum cleaner.
13) Clothing: Wear professional clothing only in dental
14) Select an appropriate alloy: Proper mercury/alloy ratio
to avoid the need to remove excess mercury before
GALLIUM BASED ALLOY
• Gallium was discovered in 1875. It is a metal with similar
atomic structures and characteristics to mercury and has a
melting temperature of 29°C. Hence, by 1928 Puttkammer
suggested gallium as a substitute for mercury.
• Recently, 2 Gallium based restorative alloys have become
1. Gallium Alloy GF II ; 2. Galloy
• Handling characteristics of this alloy is not favorable.
• High level of corrosion is seen which causes loss of strength
marginal disintegration and marginal fracture in chunks.
• Dimensional change of 21.5%.
• Poor biocompatibility.
MERCURY FREE DIRECT FILLING ALLOY:-
Ag coated Ag-Sn particles which can be self-compacted.
To compensate for some of the disadvantages presented by amalgam a clinical
technique that bonds amalgam to enamel and dentin was introduced by
Baldwin as long back as 1897.
I. It permits more conservative cavity preparations because it does not always
require additional mechanical retention.
II. It eliminates the use of retentive pins
III. It reduces marginal leakage to minimum.
IV. It reinforces tooth structure weakened by caries and cavity preparation.
V. It reduces the incidence of postoperative sensitivity
VI. It reduces the incidence of marginal fracture.
i. It has not been in use long enough to allow a proper evaluation of its clinical performance.
ii. It increases the cost of amalgam restoration
iii. It increases the time to perform a conventional amalgam and may be technique sensitive.
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