1. LATHE-CUT ALLOY POWDER
Main Constituent Metals (Ag, Sn, Cu & Zn)
Homogenizing Heat Treatment
Milling Machine / lathe
to produce filings
& further broken down by
Acid treatment Stress – Relief protocols
2. ATOMIZED POWDER (SPHERICAL ALLOY) :
Molten alloy is forced under inert gas through fine crack in the
crucible in to the chamber. If the droplets solidify before hitting a surface,
the spherical shape is preserved.
Acid treatment Heat treatment
• Average Particle size of modern powder ranges from 15-35 micro
PHASES OF AMALGAM
PHASES FORMULA HARDNESS (VHN)
1. r Ag3 Sn 250 – 270
2. r1 Ag2 Hg3 App. 120
3. r2 Sn7-8 Hg App. 15
4. e Cu3 Sn ------
5. n Cu6 Sn5 ---------
6. silver-copper Ag-Cu ------
KINETICS OF AMALGAMATION
• LOW COPPER ALLOYS :
When Powder (Ag3 Sn) is triturated with
mercury, 2 processes occur:
1.Ag & Sn in the outer portion of particles dissolve into Hg.
2. Hg diffuses into alloy particles.
• Hg has a limited solubility of Ag (0.035wt%) & Sn (0.6wt%)
• When the solubility in Hg is exceeded, 2 binary metallic
compounds precipitate in to Hg. They are:
1. Body centered cubic Ag2 Hg3 (r1) phase
2. Hexagonal Sn7-8 Hg (r2) phase.
• Later r1 & r2 crystals grow as the remaining Hg dissolves the alloy
particles. As Hg disappears, amalgam hardens.
• Alloy & Hg in about 1:1 ratio, there is insufficient Hg to completely
consume original alloy particles. As a result unconsumed particles
are present in the set amalgam (of about 27% of original r phase)
• HIGH COPPER ALLOYS:
1. ADMIXED ALLOY:
In 1963,Innes & Youdelis added spherical Ag-Cu
eutectic alloy (71.9 wt% Ag & 28.1 wt% Cu) particles to lathe-cut low
copper amalgam alloy. This has resulted in increased residual alloy
particles & decreased matrix.
• Total Cu content ranges from 9wt% - 20wt%.
• When Hg reacts with Admixed powder :
a) Ag from Ag-Cu particles dissolves Hg.
b) Ag & Sn from Ag3 Sn dissolves Hg.
c) Sn from Ag3 Sn diffuses Ag-Cu alloy particles and reacts with
copper n-phase(Cu6Sn5) around unconsumed Ag-Cu.
• Reaction is summarized as:
Ag3 Sn +Ag-Cu eutectic +Hg r1 + n (Cu6 Sn5) + unconsumed alloy
• Here r2 phase is eliminated.
2. SINGLE COMPOSITON ALLOY :
• First alloy of this type contained of 60 wt% Ag, 27 wt% Sn
& 13 wt% Cu
• Total Cu content ranges from 13- 30 wt%.
• The alloy particle is composed of a very fine distribution of Ag3 Sn (r) and
Cu3 Sn (e).
• Simplified reaction with Hg:
Ag3 Sn (r) + Cu3 Sn (e) + Hg Cu6 Sn5(n) +Ag2 Hg3 (r1)
• Here also r2 phase is eliminated.
• CHOICE OF ALLOY
• CHOICE OF MECURY
• PROPORTIONING OF Hg to Alloy
• TRITURATION & METHODS
• INSERTION OF AMALGAM
1. HAND CONDENSATION
2. MACHANICAL CONDENSATION
• PRE-CARVE BURNISHING
• FINISHING & POLISHING.
CHOICE OF ALLOY
• The factors to be considered are:
1. Alloy composition
2. Particle shape
3. Particle size
4. Speed of set
5. Pre amalgamated or standard alloy
6. Zinc containing or zinc free alloy.
• The generally accepted specifications for amalgam alloy require the
composition of the constituent metals to be :
65% min. Ag
29% max. Sn
6% max. Cu
2% max. Zn
• Use of disperse alloy has the advantage of its greater tarnish & corrosion
resistance, improved compressive and edge strength with consequent
reduction in marginal failure leading to ditching.
• Jerman(1970) found that by adding 1.5% SnF to the alloy ,there was an
increased fluoride content of the enamel adjacent to the restoration with an
associated reduction in the enamel solubility. But there is no evidence that
there is continuous leaching of fluoride from the set amalgam.
• The disadvantage of lathe-cut particles is that, although they are
similar in size as a result of sieving, they are not necessarily
similar in shape.
• Advantages of spherical particle:
1. Easier to produce
2. Less sensitive to manipulative variables Eg: Breaking up during
3. Superior 1-hr and final compressive strengths & tensile strengths.
4. Increased plasticity of the mix with mecury.
• The original particle size alters the character of the finished , carved
& polished surface.
• Smaller the particle size:
1) Higher the 1hr & 24hr strength
2) lesser the expansion
3) more easily adopted to the cavity walls
4) much less pitted, when carved
5) more easily polished.
• Use of fine cut amalgam alloy particle is advocated.
SPEED OF SET
• Setting time of an alloy is accelerated by increasing the Ag
• Min. Content of Ag is 65% in ADA. SP.
1. Quick setting alloys (Ag— 66.7%-74.3%)
2. Slow setting alloys (Ag— 43-48%)
• Advantages of fast setting alloy:
a) reduces chair side time
b) allow to fill approximal cavities at one appointment.
• Disadvantage: Rapid crystallization limits removal of Hg from
successive condensed portions of amalgam already in the cavity.
CHOICE OF MERCURY
• The most recent British standard sp. for dental mercury is B.S.4227
• Mercury complying with the requirements of British &USA
Pharmacopoeia or ADA sp.no.6 should be used.
• Hg must contain <0.02% by mass, non-volatile residue & there
must be no visible surface contamination.
• It should have a mirror like surface.
• Contaminated Hg by the metals amalgam alloy can only be purified
by “Distillation procedures”
• Tarnished Hg which comes out from wet mixes after trituration with
amalgam alloy can be cleaned by :
1) Passing through pin pricked hole in filter-paper held
in a glass filter funnel & allowed to drop in to a
carefully cleaned glass dispenser.
2)Through clean chamois skin to restore its previous
PROPORTIONING MECURY TO
• Philips and Swartz(1949) have shown that regardless of the amount
squeezed away in the squeeze cloth or removed by condensation,
the more the Hg used in the original mix the greater is the amount
that will remain in the restoration.
• Philips and Boyd(1947) have shown that as the Hg:alloy ratio is
increased, the % of residual Hg also increases proportionally. For
each additional 15% of Hg used in the original mix, there is an
avg increase of 1-1.5% residual Hg.
• The residual Hg content of the final restoration should be between
• Traditionally Hg:alloy ratio were 7:5 & 8:5 by weight or even higher.
• Eames (1959) has fathered the change from using increased
Hg:Alloy ratio to using Hg:Alloy ratio of 1:1,which can only be
triturated in a mechanical amalgamator. This technique also known
as “NO SQUEEZE CLOTH TECHNIQUE” or “MINIMAL MERCURY
• Eames etal (1961) recognized the advantage of a more plastic mix
and advise when using a 1:1 ratio of Hg & alloy to over triturate
• The problem then arises which is the best method of dispensing the
correct proportions of Hg to alloy.
• The Various methods of proportioning alloy & Hg are:
eg: Crescent and Ash balances
eg: Baker proportioner
eg: S.S.White sigrens
Amalcap capsules with mercury in cap
have now been developed
which will, in one appliance,
dispense & triturate the alloy
• The more common method of dispensing alloy & Hg is the
Automatic release type of dispenser which proportions
• Ryge etal (1958) have analyzed the accuracy of 12 different
methods of obtaining the desired proportions of alloy & Hg.
According to them, the best method of obtaining an accurate
Hg:alloy ratio was to use pre-dispensed alloy produced by
manufacturer together with a good Hg volume dispenser.
• Hg dispenser should be held vertically and not at 45o. It should
be half filled.
• The purpose of trituration is to bring the particles of alloy into contact with
• Prior to 1940’s Amalgam was triturated by hand in a mortar & pestle.
• Its objectives are :
1) to get workable mass in minimum time
2) to remove oxide layer from powder
3) to reduce particle size, increase surface area & thus increasing the rate of
4) to keep the r1 & r2 crystals as minimum as possible yet bind the particles.
• Methods of trituration are:
1)Mortar & pestle
2) Rubber thumb-stall
3) Mechanical amalgamation / Amalgamator.
Mortar pestle method
• Is the oldest method used.
• Suggested by Dr.Marcus.L.Ward.
• Here pestle is held in a pen grasp with 2-3 pounds load and
rapid convenient circular motion is used until a shiny,
homogeneous mass is obtained.
• WORK = PESTLE SPEED X PESTLE LOAD X TIME
• Need 60-120s for trituration.
RUBBER THUMB-STALL METHOD:
• In 1934, Mary Gayler advocated this method.
• This technique has the advantage not destroying the original particle size,
but a higher Hg : alloy ratio is used to obtain amalgamation in 1minute.
• Types of motion:
1) Off-centre-centrifugal action
2) Reciprocating figure of “8”.
1) Trituration is achieved rapidly (20-25sec)
2) More standard mix can be obtained.
TESTING OF MIX
• Is a continuation of trituration.
• Enhances uniformity, coherence & handling ease.
• In the mortar & pestle method due to continuous folding off the mass
from the side of the mortar to the centre, a layered mass is
developed. This is made more cohesive by hand mulling.
Mix is kneeded in a piece
of rubber dam
or between finger & palm
• Large egg shaped burnisher is used.
1) Less Hg
3) r2 phase
• To produce restoration with proper
physiological & anatomical contour.
• Use sharp instrument.
• Don’t attempt to produce deep anatomical
fissure (Mahler’ 58).
• Marginal ridge – wide, round & carved to
the level of adjacent marginal ridge
• Use large spoon excavator - Gross
FINISHING & POLISHING
• Finishing: process which continues the
carving objectives, removes flash &
• Polishing: process which creates a
corrosion resistant layer by removing
scratches & irregularites from the surface.
• # 12-15 bladed steel burs (worn)
• Rhein trimmers (gingival area)
• # 12 BP bald or Blacks knives
• Fused Alumina white stone (marginal
• Water resistant strip (cervical areas)
• Done usually after 24 hrs
• Polish all surfaces of restoration
• Amalgam line (Mosteller” 57)
• Fine sand paper discs (Buccal & lingual
embrasures of proximal surfaces)
• Linen strips (Proximal surface below the
• Gingival excess of amalgam:
1) E.V.A prophylaxis system with safe sided
& safe edged diamond tip
2) Ultra sonic scaler points
• Smooth, highly polished matrix band
• Final polishing :SnO or Whitening made
into paste with alcohol, applied with bristle
or goat hair brush.
• Temperature should not be raised >65o
PROPERTIES OF AMALGAM
Effect of moisture contamination
1) DIMENSIONAL CHANGES
• Amalgam undergoes dimensional changes in 3 stages:
• According to ADAsp.1, Amalgam should neither contract
nor expand more than 20micro.m/cm at 37o between
5mnts & 24hrs after beginning of trituration
• Measured by Interferometer
• Factors affecting dimensional changes:
3) Particle size
• Moisture contamination:
Delayed expansion: Occurs due to contamination of Zn
containing alloys with water during trituration or
Zn+H2O ZnO + H2
Reaches about >400micro.m
• Its clinical consideration:
1) Protrusion of restoration out of cavity
# of restoration
2) Increased flow & creep
3) causes pulpalgia (2000psi)
4) decreases compressive strength
• Management :
Use Zn free alloys
• By Jorgensen
• Results from when Hg released from corrosion
of r2 phase reacts with remaining alloy particles.
Sn8Hg + 1/2 O2+ H2O + Cl- Sn4(OH)6Cl2 +
• Causes further weakening of the restoration
• Amalgam has high compressive strength & low
• The compressive strength of a satisfactory amalgam
should be atleast 310MPa.
• ADA SP. Stipulates a minimum compressive strength of
80MPa at 1hr.
• Factors affecting strength:
5)Particle shape &size
• Is a time dependent plastic deformation of crystalline
material under the influence of a static or dynamic
• Can be correlated with marginal breakdown.
• Creep rate: 1)Low Cu---0.8-8%
2)High Cu--- <0.1%
• Factors affecting creep:
1)Higher condensation forces Creep
& Elimination of r2 phase
2) Excess Hg Creep
TARNISH & CORROSION
• Amalgam often tarnish &corrode in oral environment
• Tendency towards tarnish is unaesthetic due to formation
of black AgS
• Corrosion occurs in the interface between tooth &
• Corrosion products Oxides & chlorides of Sn
• Galvanism (differences in EMF)
• Higher Hg:Alloy ratio corrosion
• Smooth& homogeneous surface minimizes tarnish
• THERMAL PROPERTY:
-- GOOD CONDUCTOR OF HEAT
-- Cf. Of thermal exp, is 3 times greater than
-- If RDT is <2mm, protection of pulp is
• ELASTIC MODULUS:
--High Cu alloys are more stiffer than low Cu
-- 62 GPa
• FORMS OF Hg:
Organic & Inorganic
Most toxic organic forms are Methyl
Hg & Ethyl Hg
Least toxic form of Hg – Inorganic.
• Concentration of Hg:
OSHA has set a threshold limit value of
• Max allowable Hg level in blood 3 micro
• Chronic exposure – assessed by urinary
1000 Pronounced symptoms
500 Mild to Moderate
100 Subtle changes
25 No known Health effects
4 Upper limit of urinary Hg
• Sources of Hg exposure – Dental office:
Amalgam raw materials being stored
During trituration, insertion & intraoral
During finishing & polishing
During Amalgam removal
Dental Hg hygiene recommendations
• Train all personals regarding potential hazard of
Hg vapor & make them aware of its potential
• Working in well ventilated spaces
• Periodically monitor dental operatory
atmosphere for Hg vapor (DOSIMETERS & Hg
• Facilitate Hg spill contamination cleanup
• USE only Pre-capsulated alloys
• USE Amalgamator with enclosed arm
• AVOID skin contact with Hg / freshly mixed
• USE high volume evacuation
• Store all scrap amalgam in tightly closed
• Recycle amalgam scrap when feasible
• Dispose Hg contaminated items in sealed bags
• USE trap bottles / tape / freshly mixed amalgam
to pick up spilled Hg
AMALGAM BONDING SYSTEM
• Used to seal underlying tooth structure &
bond the amalgam to enamel & dentin
• 4-META based bonding systems are used
• It is important to develop micro-mechanical
bonding since no chemical
• Hence bonding system is applied in much
Bonding systems used:
• Amalgam bond plus (parkell)
• Panavia (Kuraray)
• Scotch bond multi-purpose plus(3M-ESPE)
• Potential advantages:
Decreased micro leakage
Improved resistance form
Decreased post-operative sensitivity
• Primary indication:
when weakened tooth structure remains &
bonding may improve the overall resistance form
of the restored tooth.
GALLIUM BASED ALLOYS
• Gallium has similar atomic structure and characteristics
• They consist of Gallium(65%), Indium, Tin, copper,
• 16 Times more experience
• Very sticky
• High level of corrosion
• High level of expansion (1% or 60 mMts/ cm)
• Toxicology unknown
• Two types of Gallium alloys :
• Palladium – Ga – Sn Ag-cu powder mixed with
liquid of Ga-In-Sn
• SKINNER”S- Science of dental materials
• Sturdevant”s Art & science of operative dentistry
• Operative dentistry- Modern theory &practice
• Pickard”s manual of operative dentistry
• Operative dentistry-Gillmore & Lund
• Clinical restorative materials & techniques
-- Karl. F. Leinfelder
• Bonding of amalgam restoration, oper dent,
2000, 25 ,121-129.