Dept of Cons & Endodontics
KVG Dental College, Sullia
• Alloy production
• Alloy manipulation
• What is an amalgam failure?
• What types of failure?
• Why failure?
• 618-907 AD- Tang dynasty in China, according to Geir
Bjørklund, an active proponent of mercury free dentistry
• In Germany by Dr. Strockerus in about 1528
• In 1603, German Tobias Kreilius boiled a concoction of copper,
acids and mercury which was poured as a hot liquid onto
• In 1819, first dental amalgam was probably introduced in
England, ‘Bell’s putty’, by Thomas Bell, by mixing metals with
mercury at room temperature
• In 1826, Taveau, from France described a silver paste filling material
• 1833 the Crawcour brothers, two Frenchmen, brought amalgam to the
• 1844 it was reported that fifty percent of all dental restorations
placed in upstate New York consisted of amalgam. At that point the
use of dental amalgam was declared to be malpractice, and the
American Society of Dental Surgeons (ASDS), the only US dental
association at the time, forced all of its members to sign a pledge to
abstain from using the mercury fillings. This was the beginning of what
are known as the first dental amalgam war.
• The war ended in 1856 with the rescission of the old association.
• The American Dental Association was founded in its place in 1859, which
has since then strongly defended dental amalgam from allegations of
being too risky from the health standpoint.
• Taft's text was published in 1859, Harris' in 1863. They stated that
beginning in the early 19th century, eleven types of metallic fillings
were used in teeth damaged by dental caries. The simple process of
rolling metal into pellets to be placed into cavities was common. These
pellets were made of some of the aforementioned materials like gold,
lead, platinum, silver and amalgam as well as aluminum.
• Sir Louis Regnart-"Father of Amalgam". He improved on a boiled
mineral cement by adding mercury, which greatly reduced the high
temperature originally needed to pour the cement onto a tooth.
• 1895-G V Black, a Chicago dentist standardized cavity preparation and
• The ratio of the mercury to the remaining metallic mixture in dental
amalgam has not been always 50:50. It was as high as 66:33 in 1930.
• 1930: ADA spec no 1
• In 1959, Eames introduced minimal mercury technique, with reduced
mercury alloy ratio
• Two texts used by American dentists of this time were, "A Practical Treatise
on Operative Dentistry" written by J Taft, and "The Principles and Practice
of Dental Surgery", written by Chapin A Harris.
BEFORE REACTIONBEFORE REACTION AFTER REACTIONAFTER REACTION
AMALGAM = an alloy containing Hg as the major ingredient.
DENTALAMALGAM = an alloy of Hg with Ag-Sn.
DENTALAMALGAM ALLOY = a Ag-Sn alloy (to be mixed with Hg).
Melting / Casting / Comminution IRREGULAR Particles
Melting / Spray Atomization SPHERICAL PARTICLES
“Cast ingots --> filed into powder on a lathe- Comminution
Irregular particles = lathe cut = filings
Particles are polycrystalline
Homogenization heat treatment to remove coring
Annealing heat treatment of filings to relieve cold work
Hot alloy sprayed into cold air
Particles spherodize and solidify
Spheres are acid-washed
Generally spheres are Heat Treated
Decreased with time and advent of spherical alloy powders
* Eutectic alloy- is a mixture of chemical compounds or
elements that has a single chemical composition that solidifies at
a lower temperature than any other composition made up of the
same ingredients. This is called eutectic composition and the
temperature at which it solidifies is known as eutectic
• Peritectic alloy similar to eutectic alloy, here, a liquid and
solid phase of fixed proportions react at a fixed temperature to
yield a single phase. The solid product forms at the interface
between the two reactants, and forms a diffusion barrier and
causes reactions to proceed much more slowly than eutectic.
• Ternary- a complex formed by interaction of three molecules
Addition of Noble metals- GENERATIONS
First generation- GV Black
3 part silver + 1 part tin, peritectic alloy
Alloy product of reaction between the beta-phase of solid solution of tin in
silver with liquid phase of silver & tin. This is defined as gamma phase.
Cu (admixture)- upto 4%, decrease plasticity and increase hardness &
strength of alloy
Zn- traces- deoxidizer or scavenger for alloy, decrease brittleness.
Ag3-Cu eutectic alloy (admixture/blending)
Alloying of Cu to silver & tin- upto 29% ternary alloy, most of tin
firmly bonded to Cu.
Alloying of silver, copper, tin & indium true quaternary alloy, none of
tin is available to react with mercury.
Alloying of palladium (10%), silver (62%) and copper (28%), to form a
eutectic alloy lathe-cut and blended into 1st, 2nd or 3rd gen amalgam-
ratio 1:2 set amalgam, exhibits highest nobility
THE ORGINAL GAMMA PHASE (i.e., Ag3Sn or the alloy
powder) which has not been completely dissolved in mercury.
Mechanically strongest phase, for this reason it should occupy the
maximum available space in the volume of the restoration.
GAMMA-1 Phase (Ag2Hg3) is one of the amalgamation
products that form the matrix. It is the noblest phase i.e., Most
resistant to tarnish & corrosion. Effort, made to make this phase
occupy maximum space in bonding matrix of final product.
GAMMA-2 Phase (Sn7 Hg8)
It is the phase which is the least resistant to tarnish &
corrosion & every effort is made minimize its volume percentage in
the matrix. Most of amalgam failures, due to this phase.
- Unreacted residual mercury, present in isolated areas within the amalgam mass.
- Mechanically weakest phase & when a certain volume limit exceeds, there
will be drastic drop in the strength & hardness in addition to increase in creep &
flow of restoration.
VOIDS (porous) PHASE
- Due to entrapment of air bubbles, in the process of building the amalgam
restoration, despite any meticulous procedures.
- Such voids act as a nidus not only for internal corrosion, but also leads to stress
concentration & propagation which ultimately leads to early failure of structure
The trace element phase
In which copper & zinc might be found either as separate phases or combined
with Ag, Sn & Hg.
Cu- increase strength, brittleness, hardness and proportional limits of amalgam
Zn- increase deformability, ultimate strengths, resistance to oxidation of final
In terms of the serviceability of final restoration, the most important
components of the mass.
This especially to the interphases between the 3 components namely
gamma, gamma-1 & gamma-2.
In the final restoration, the more continuous they are better is the
bonding between the primary phases. Consequently, the more coherent &
the more resistant to environmental variable the restoration will be.
EPSILON Phase (Cu3Sn)
AgSn alloys are quite brittle & difficult to comminute uniformly unless a
small amount of copper is substituted for silver. This atomic replacement is
limited to about 4-5 wt%, above which Cu3Sn is formed within the limited
range of copper solubility, increased copper content hardens & strengthen
the AgSn alloy.
ETA Phase (Cu6Sn5)
• The crystals are found as meshes of rod crystals at the surfaces of
the alloy particles as well as dispersed in the matrix.
• Meshed ETA crystals on unconsumed alloy particles may
strengthen bonding between the alloy particles & 1 grains.
Crystals dispersed between 1 grains may interlock 1 grains. This
interlocking is believed to improve the amalgam’s resistance to
deformation in high copper alloys.
I. According to the number of alloyed metals
Only 2 alloys namely silver & tin
Along with silver & tin copper was added to increase the
strength of the alloy.
Indium was added to the above which act as a grain refiner.
II. According to the shape of powdered particles
spherical: alloy shape which has smooth surfaced spheres.
Lathe cut: irregular shapes ranging from spindles to shavings.
spheroidal: spherical with irregular spheres
III. According to the powder particle size
IV. According to the copper content
Low copper alloys, which contain less than 4% of copper
High copper alloys, which contain more than 10% of
copper & has improved physical properties & corrosion resistant.
V. According to whether the powder consists of unmixed or
Certain amalgam made of only one alloy, others have one or
more alloys or more alloys (blended) to the basic alloy e.g.;
adding copper to the basic binary silver –tin alloys.
• A failing amalgam filling can be defined as a filling that has been
a contributory cause of secondary injury in the organ of the tooth
i.e, the tooth itself and its surrounding connective tissue.
( Knud Dreyer Jorgensen, Amalgams in dentistry, Dental Materials Research: Proceedings of the 50th
Anniversary Symposium, Oct 6-8. 1969 Issue 354, By United States. National Bureau of Standards,
American Dental Association)
absorption of Hg
into alloy powder
Expansion, due to
formation & growth
of matrix crystals,
reaches a plateau
with cessation of
contraction of mass,
• Factors affecting:
• Constituents- More gamma phase- greater possibility of expansion
- Greater traces of tin, less expansion
• Mercury- More Hg, more prolonged second stage of amalgamation
- Greater amount of matrix crystals (gamma, gamma 1 or
gamma 2), produces more expansion
• Particle size- smaller size more surface area per unit volume first
stage, dissolution occurs rapidly marked contraction second stage
also rapid expansion plateau achieved too quickly (before cavity
filled)- apparent expansion may not be noticed stage 3 contraction
maybe more noticed.
Trituration- more energy used, smaller particles will be made more
mechanical force will be present pushing mercury in between
particles discourage expansion
• More trituration energy, greater distribution of forming matrix
crystals all over mix, preventing outward growth, which creates
expansion of second stage.
• More trituration energy, faster amalgamation proceeds, plateau of
expansion curve occur before completely filling cavity
preparation no apparent expansion, possibly limited contraction
Condensation- more energy used, into condensing amalgam into
cavity preparation, closer original particles of powder are brought
together at expense of expanding matrix crystals.
• Increased condensation energy, also squeezes more Hg out of the
mix less formation of matrix crystals, inducing more contraction.
• More regular the particle shape is and smoother its surfaces are,
faster and more effectively the mercury can wet the powder
• Makes faster amalgamation process in all stages, maximum
expansion occurs before filling cavity, with no apparent expansion.
• Moisture- esp affects Zn containing amalgam.
• Water from any source(saliva, blood, respiration etc) + Zn (in
amalgam) ZnO + Hydrogen gases
• Takes place- 24-72 hours after amalgam insertion.
• Hydrogen gases, accumulate, exert pressure- upto 2000 PSI.
• Protrusion of entire restoration outside cavity, increased
microleakage space around restoration, restoration perforation,
blister formation on restoration surface, increased flow & creep,
pulpal pressure pain, delayed expansion- 400 µ/cm3
• Amalgam loses 15% strength when temp elevated from room to
• Loses 50% strength when temperature elevated to 60% (hot
• More energy used, more continuous interphases between matrix
crystals & original particles, more evenly distributed matrix crystals
over mix more coherent mass greater strength
• If trituration, continued after complete matrix crystals formation,
excess energy will crack crystals & interphases drop in strength
Mercury- weakest phase, liquid room temp., cannot resist any slip or
dislocation within amalgam caused by external loading
• Residual mercury- increase in Hg content from 53%- 55%, causes
drop in compressive strength, more than 50%
• More energy used, less residual mercury, higher relative
percentage of strong original particles in restoration.
• More continuous interphase between original particles & forming
• More even distribution of gamma1 or gamma 1-gamma 2 matrix
crystals more consistent strength throughout restoration mass
*condensation of an amalgam mass after formation of matrix
crystals does not diminish strength as trituration does, because there
is more resistance to crystal displacement during condensation than
• Important to minimize the number & size of pores
• Keep them away from critical areas of the restoration
• Pores facilitate stress concentration, propagation of cracks,
corrosion and fatigue failures of amalgam structures
• Porosity of 1% reduces amalgam strength as 10% excessive
• Results from the fact that different phases of amalgam do not
completely wet each other simultaneously during amalgam
• Under-trituration, under condensation, irregular shaped particles of
alloy powder, miscalculated diameter varieties of powder particles
to occupy available spaces, insertion of too large increments into
cavity preparation, delayed insertion after trituration or a
generally non-wetting, non-plastic mass of amalgam.
Particle size & shape-
• Alloy particles, more regular & smooth- more wettable
• Will react & combine more efficiently
• Resultant, less interrupted interphases create a more coherent and strong
• Smaller the diameter of the original particles, greater will be the strength
of the set amalgam.
• 1 day specimen- substantial increase in strength, average particle
diameter 12 or less microns
• 1 week specimen- substantial increase when average particle diameter
16 or less microns
• 1 day specimen- marked increase in strength when average particle
diameter 18 microns or less
• 1 week specimen- same increase when average particle diameter 12
microns or less
• Closer original particles of alloy are- stronger end product will be
• When average interparticle distance is 38 microns or less,
noticeable increase in compressive strength in 24 hr sample
• 1 week sample- 32 microns or less
• Tensile strength- 28 microns or less, marked increase in 24 hr
• 39 microns or less, marked increase in one week specimen
• A solid state dispersion within amalgam mass of another phase,
with one which has a different shape & dimension than original
phases, can distort original space lattices, precipitating
interferences with slip increasing amalgam strength
• Eg:- addition of Cu or addition of Ag-Cu eutectic or Ag-Cu-
Palladium near-eutectic alloys
• Net result- greatly enhanced strength
Gamma 2 phase
• Mechanically, second Weakest phase
• Corrosion ability
• Reduction or prevention of its formation- increase strength of
amalgam, especially age strength
• Decreasing corrosion activity within an amalgam restoration will
protect the adhesive integrity between the multiple phases, thus
preventing the strength from deteriorating.
Measured during setting of amalgam Measured after amalgam sets
Reflects change in dimension of amalgam
Reflects constant change in dimension
under either static or dynamic loading
Markedly pronounced after
More energy used to condense, less the
creep, mercury increase will increase
Dispersion or elimination of gamma-2 can
Lesser the creep, better will be the
marginal integrity & longevity of the
• ‘It is mainly the operator who causes the amalgam restoration to
be a success or failure’
• The choice between spherical, spheroidal or lathe-cut alloy
particles can be related to the type of patient population the
dentist is involved with.
• Spherical particle alloy- quick strength attainment
- Require fast operator
- exhibit more flow
- deformation with time
• Choice between zinc containing & zinc free-
Zinc containing- problems in presence of moisture
Zinc free- less plastic, less workable, more susceptible to oxidation, so
should be used in cases only where elimination of moisture is
impossible, eg:- root apices, subgingival lesions
Marzouk, 1st edition
Proportioning of alloy & mercury
*consider manufacturer’s recommendation which is based on metallurgical condition, thermal
treatment, powder particle specification
High mercury technique (increasing
Minimum mercury/ Eame’s
Initial amalgam mix contains a little
more Hg than needed for the powder
(52-53%), producing a very plastic mix
Initial amalgam mix contains equal
amounts of mercury and powder alloy
Necessary to continue squeezing the
mercury out of the mix increments being
introduced to build up the restoration, so
that each increment will be drier than
the previous one
Necessary to squeeze mercury out of the
mix during the incremental build-up of
50% or less mercury only will be in the
final restoration, with obvious
• Restorations to be retained with multiple auxillary means of
retention (pins, internal boxes, grooves)- need wetting or plastic
consistency of amalgam increasing dryness technique
• A very large restoration which needs more than one mix
increasing dryness technique
• Proportioning is done by weight and not by volume- volume is
misleading because of trapped air and voids in mass
• Choice between pre-weighed, pre-proportioned alloy mercury
capsules or weight proportioning oneself in the office
• Do not leave previous mixes
remnants in the capsule, as this
will get incorporated into a new
mix without proper binding or
plasticity, weakening the final
• Scratches in the capsules may
trap mercury or traces of old
mixes, compromising quality of
• Cracks in the capsules that leak
mercury will pollute the office
and reduce mercury in the mix,
sometimes with undesirable
• Improper case selection
• Improper selection of alloy and mercury
• Improper Cavity preparation
• Improper manipulation of alloy
• Improper Pulp protection
• Improper Matrix adaptation
• Extensive loss of tooth structure and
• Poor retention and resistance form
• Areas of high masticatory loads
• Parafunctional habits
• Extensive/open contacts
• Improper outline form
• Cavity outline in stress bearing areas
• Improper resistance form
• Improper retention form
• Improper convenience form
• Inadequate occlusal extension- include pits & fissures
• Inadequate extension of the proximal box- if proximal box walls
are not adequately extended into embrasures they are not
amenable to cleaning secondary caries
• Overextension of cavity preparation walls- 1/4th the intercuspal
distance facio-lingual width
• If cavity preparation extends to half the intercuspal distance,
capping of cusps should be considered, if cavity preparation
extends to 2/3rd, cusp capping becomes mandatory.
• Minimum thickness in cusp capping should be 2mm over functional
cusps and 1.5mm over non-functional cusps.
Minimum depth of 1.5mm to provide bulk
Flat pulpal floor
Butt joints in regions where occlusal stresses encountered
Round off axio pulpal line angle
Failure to diverge mesial & distal walls of occlusal cavity
Retentive devices should be prepared entirely in dentin without
Incomplete removal of carious tooth structure
• Matrix should be stable after it has been applied-
if unstable, distorted restoration, gross marginal
• Cervical excess can irritate peridontium
• Unstable matrix- proper condensation cannot be
carried out soft amalgam filled with voids
• If large cavity, demands working time
exceeds 3-4 mins, use multiple mixes
• Elimination of Hg by excessive
squeezing, may reduce strength
• Very small plugger holes- punch holes in
• Very large plugger holes- may not
condense amalgam in corners
• Light tapping- to remove Hg to surface,
adequate condensation pressure
RESIN COATED AMALGAM
• To overcome the limitation of microleakage with amalgams, a
coating of unfilled resin over the restoration margins and the
adjacent enamel, after etching the enamel, has been tried.
Although the resin may eventually wear away, it delays
microleakage until corrosion products begin to fill the tooth
• Mertz-fairhurst and others evaluated bonded and sealed
composite restorations placed directly over frank cavitated
lesions extending into dentin versus sealed conservative
amalgam restorations and conventional unsealed amalgam
restorations. The results indicate that both types of sealed
restorations exhibited superior clinical performance and
longevity compared with unsealed amalgam restorations over a
period of 10 years
• Fluoride, being cariostatic, has been included in amalgam to deal with
the problem of recurrent caries associated with amalgam restorations.
The problem with this method is that the fluoride is not delivered long
enough to provide maximum benefit.
• Several studies investigated fluoride levels released from amalgam.
These studies concluded that a fluoride containing amalgam may release
fluoride for several weeks after insertion of the material in mouth.
• As an increase of up to 10–20-fold in the fluoride content of whole
saliva could be measured, the fluoride release from this amalgam seems
to be considerable during the first week.
• An anticariogenic action of fluoride amalgam could be explained by its
ability to deposit fluoride in the hard tissues around the fillings and to
increase the fluoride content of plaque and saliva, subsequently
affecting remineralization. In this way, fluoride from amalgam could have
a favorable effect not only on caries around the filling but on any initial
enamel demineralization. The fluoride amalgam thus serves as a “slow
• Conventional amalgam is an obturating material as it merely fills the
space of prepared cavity, and thus, does not restore the fracture
resistance of the tooth, which was lost during cavity preparations. In
addition, the provision for adequate resistance and retention form for
amalgams may require removal of healthy tooth structure. Further, since
amalgam does not bond to tooth structure, microleakage immediately
after insertion is inevitable. So, to overcome these disadvantages of
amalgam, adhesive systems that reliably bond to enamel and dentin have
• Amalgam bond is based on a dentinal bonding system developed in
Japan by Nakabayashi and co-workers. The bond strengths recorded in
studies have varied, approximately 12–15 MPa, and seem to be
routinely achievable. Using a spherical amalgam in one study of bonded
amalgam, Summitt and colleagues reported mean bond strength of 27
MPa. The authors believed that this higher bond strength was achieved
because the bonding material was refrigerated until immediately before
• Bond strengths achieved with admixed alloys tend to be slightly
lower than those with spherical alloys. One study compared post-
insertion sensitivity of teeth with bonded amalgams to that of teeth
with pin-retained amalgams. After 6 months, teeth with bonded
amalgams were less sensitive than teeth with pin-retained
amalgams. This difference in sensitivity was not present 1 year after
insertion. This is possibly because of corrosion products in
nonbonded amalgam restorations filling the interface, and thus,
decreasing microleakage and sensitivity.
• If bonding proves successful over the long term, method of
mechanical retention can be eliminated, thus reducing the potential
for further damage to tooth structure that occurs with pin placement
or use of amalgapins. If mechanical retention is not needed, cavity
design can allow more sound tooth structure to be preserved.
CONSOLIDATED SILVER ALLOY SYSTEM
• One amalgam substitute being tested is a consolidated silver alloy
system developed at the National Institute of Standards and
• It uses a fluoroboric acid solution to keep the surface of the silver
alloy particles clean.
• The alloy, in a spherical form, is condensed into a prepared cavity
in a manner similar to that for placing compacted gold. One
problem associated with the insertion of this material is that the
alloy strain hardens, so it is difficult to compact it adequately to
eliminate internal voids and to achieve good adaptation to the
cavity without using excessive force.
FUTURE OF DENTAL AMALGAM
• The prediction that amalgam would not last until the end of the
20th century was wrong.
• Its unaesthetic appearance, its inability to bond tooth, concerns
about the mercury and versatility of other materials have not
not led to the elimination of this inexpensive and durable
material. As other materials and techniques improve, the use of
amalgam will likely continue to diminish, and it will eventually
disappear from the scene.
• Yet, amalgam continues to be the best bargain in the
restorative armamentarium because of its durability and
technique insensitivity. Amalgam will probably disappear
eventually, but its disappearance will be brought about by a
better and more aesthetic material, rather than by concerns
over health hazards. When it does disappear, it will have
served dentistry and patients well for more than 200 years.
• Dental Materials Research: Proceedings of the 50th Anniversary Symposium,
Oct 6-8. 1969 Issue 354, By United States. National Bureau of Standards,
American Dental Association
• Dental amalgam: An update
Ramesh Bharti, Kulvinder Kaur Wadhwani, Aseem Prakash Tikku, and Anil Chandra
J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208
• Textbook of dental materials by Sharmila Hussain
• Dental materials: Prep manual for under graduates by Patil
• Sturdevant’s Art and Science of Operative Dentistry
• Operative dentistry- modern theory and practice- Marzouk, Simonton, Gross- 1st
• Essentials of Operative Dentistry- Anand Sherwood
• Textbook of operative dentistry- Vimal K Sikri
• Skinner’s Science of Dental Materials- 9th edition
• Pictures- various sources from the internet