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1. DENTAL AMALGAM
CONTENTS:
1) HISTORY
2) GENERAL CONSIDERATION
3) CLASSIFICATION AND DISCUSSION
4) METALLURGICAL PHASES
5) MANUFACTURE OF ALLOY PARTICLES
6) AMALGAMATION
7) DIMENSIONAL STABILITY
8) STRENGTH
9) CREAGT
10) TARNISH AND CORROSION
11) MANIPULATION
12) AMALGAM ‘PROBLEMS’
13) ALTERNATIVE TO AMALGAM
14) BONDED AMALGAM RESTORATIONS
15) GALLIUM BASED AMALGAM RESTORATION
16) CURRENT STATUS AND CONCLUSION
17) BIBLIOGRAPHY

2. DENTAL AMALGAM
HISTORY OF DENTAL AMALGAM: The Chinese developed a
Silver Amalgam for fillings more than 1000 years before
dentists in west. “Silver Paste” is mentioned in the
‘Materia Medica’ of Su Kung (659A.D) and again about
1108 in Ja-Kuan Pen – tsao by T’ang Shen – Wei. During
the Ming period in their material medicas, LivWen-t’ai
(1505) and lishihchen (1578) discussed its formulation:
100 parts of Mercury to 45 parts of Silver and 900 parts of
Tin. Trituration of these ingredients produced a paste said
to be as solid as silver.
- The first dental silver amalgam is supposed to have been
introduced by Bell of England in 1819 and later used by
Traveau in Paris in 1826.
- In 1833, 2 frenchman, by name of Crawcour came to
America with what they claimed was a new material for
filling teeth. A crude Amalgam, their so called, “Royal
Mineral Succedaneum” was produced from shavings of
silver cut from coins and mixed with enough Hg to make a
sloppy paste. The Crawcour’s blatant advtising and
reprehensible habit of leaving carious matter in teeth they
filled brought down upon them wrath of many of most
prominent members of profession and after a few months
were forced to return to France. Nevertheless during their
short stay they traveled widely, touting the RMs and
placing fillings in a great many mouths. Many American
dentists saw in the material an answer to their problems
with Au-foil, which was very difficult and time consuming

3. to use and many began to experiment with silver
Amalgams; though leaders of profession did not.
AMALAGAM WARs: Unfortunately it was that the young
American society of Dental Surgeons (ASDS) came into
being so soon after the crowcour brothers had created
such a stir with their new amalgams. Their bombastic
advertisement had posed a threat to more ethical and
conscientious dentists At the same time many other
untrained, often unprincipled practitioners in search of
easy money seized upon the new material, which was
easier to place in a tooth than AU.
Organised dentistry, which of that time represented
only a very tiny percentage of practicing dentists, began a
campaign/crusade against the use of Amalgam (~1841)
and their drive soon assumed the tone of religious
crusade. Proponents of Amalgamwere to be rooted out and
to this end every member of ASDS was required to sign a
pledge that it was his Opinion and firm conviction that
any Amalgam whatever is unfit for plugging of teeth and
fangs [retained roots] and I pledge myself never under any
circumstance to make use of it in my practice.
Those who refused to sign the pledge were summarily
expelled. Meanwhile Dr. Chapi A. Harris, in his opening
address to the first class of Balfimore College of Dental
Surgery (1839), said Amalgam that, “it is one of the most
abominable articles for filling teeth that could be
employed. But progress, in whatever form it takes, cannot
be so easily implemented. Many dentists – including a

4. number of highly reputable ones, soon found in Amalgam,
answer to certain difficult restorative problems. They also
felt compelled to use it to serve the needs of those too poor
to pay for Au. and also in order to complete with the
quacks, who were, using it widely. As a consequence, so
many dentists had refused to sign the pledge by 1850 that
the ASDS were forced to rescind it. But their conciliatory
action came too late and the annual meeting scheduled for
Aug’1856 had to be cancelled. Thus came to an end the 1st
National organization of dentists.
- Dr. Thomas W. Evans of Philadelphia emigrated to
France in 1847 and introduced use of silver amalgam for
fillings. He was dentist to Emperor Louis Napoleon.
- In 1870s a group of dentists led by prominent J. Foster
Flagg forming what they called a “New Departure” group,
effectively brought to an end the last hostilities of the
great “AmalgamWars”. The basic tenet of the movement
was that no single filling material could serve equally well
in every case Au had its use, so did Silver Amalgam (which
infact was claimed by the group to be more versatile
material of the two).
- A number of attempt to improve the resistance of
Amalgam to shrinkage had been made since the ‘Crawcorn’
days.
- Dr. Thomas W. Evans, who was chiefly responsible for
popularizing the use of silver Amalgam in Europe
experimented with mixture of Sn, Cd and Hg. Though he
eventually found it necessary to reintroduce Ag into the

5. mixture, tin and reduces shrinkage has remained an
essential ingredient to this day.
- At this time innovation to enhance utility of Amalgam
were brought out: Retentive pins that screwed into dentin
patented in 1871 and matrix retainers and matrices came
into scene in that same year. Johnston brothers advertised
the pins.
- In 1895, the great “Greene Vardiman Black” often called
the “father of scientific Dentistry”; announced his formula
for a truly satisfactory Amalgam. After years of
experimentation, using instruments, of his own design to
measure hardness, flow and other characteristics, Black
hit upon a mixture of metals that remained essentially
unchanged: 68% Ag with small amounts of copper, Tin and
Zinc with this new alloy, expansion, contraction can be
precisely controlled.
- In 1926 – Alfred Stock, Ph.D, a German chemist
published an article condemning amalgam restorations.
Dr. Stock himselves was exposed to high Hg levels and
recognized the danger, posed by the type of Amalgam, in
use at that time viz. a tablet had to be heated in a spoon
till beads of Hg appeared and then it was transferred to
mortar and pestle for trituration. This procedure released
significant amount of Hg vapours.
Hence a commission was established to investigate
his allegations. In 1930, this commission issued a report
that validated the safety of newer amalgam that neednot
be heated and it replaced the older formulation.

6. - In 1959, Dr. Wilmer Eames recommended a 1:1 ratio of
Hg to alloy, thus lowering the 8:5 ratio of Hg to alloy that
others had been recommending.
- In 1962, a spherical particle dental alloy was introduced.
- In 1963, Innes and Yudelis introduced a high copper-
dispersion alloy system that proved to be superior to its
low copper predecessors.
- In 1970s, Dr. Hal Huggins began promoting the theory
that Amalgam restorations caused wide variety of disease.
- In 1985, Dr. Hal Huggins published a book that detailed
his belief about Hg. toxicity. He says that Hg released by
Amalgam restorations caused a wide variety of
Neurological, CVS, Immunological, collagen, emotional and
Allergic disorders. The resulting conditions are said to
include Multiple sclerosis, depression, high/low B.P.
Tachycardi, Arthritis, lupus, Scleroderma, leukemia,
Hodgkins disease, fatigue, Mononucleosis, Gohn’s disease,
ulcers and other digestive problems. This and media hype
led to some dentists to question safety of Amalga
restoration.
- In 1995, survey reported that 8.7% of dentists wanted to
ban Amalgam use and 14.3% were undecided about its
safety.
- Other physicians like Robert Atkins M.D and Andrew
Weil M.D added fuel to the fire through books and T.V
programs during 90s.
- American council of science and health, a consumer
education and advocacy group has determined that

7. allegations against Amalgam constitute one of the greatest
unfounded health scares of recent times.
AMALGAM – An amalgam is an alloy that contains Mercury
as one of its constituents. Because Hg is liquid at room
temperature, it can be alloyed with solid metals. The
process of amalgamation in clinic consists of releasing Hg
droplets from sealed chamber within a capsule into
another chamber within capsule that contains an alloy
powder and then mixing the components together in a
device called Amalgamator. Amalgamation process
continues while segments of plastic mass are condensed
under firm pressure against the walls of prepared teeth;
and if present, a matrix band. The reaction continues
during the manipulation period in the mouth and
decreases within a few minutes as the dental amalgam
increases in strt and hardness; although the reaction can
continue for several days, the dental amalgam becomes
sufficiently strong to support moderate biting forces within
the first hour. The general descriptive reaction is as
follows: Alloy particles for Amalgam + Mercury –
Dental Amalgam + Non-reacted Alloy
Powder particles.
General considerations for Amalgam Restorations –
Because Dental Amalgam is a direct restorative
material the decision is usually a choice between Amalgam

8. and composite. Some of the following information involves
a comparative analysis between these two materials:
INDICATIONS –
1) Occlusal factors – Amalgam has somewhat greater wear
resistance than composite. It therefore may be indicated in
clinical situations that have heavy occlusal functioning. It
also may be more appropriate when a restoration restores
all of the occlusal contact for a tooth.
2) Isolation factors – unless an Amalgam restoration is to
be bonded, the isolation of the operating area is less
critical than for a composite restoration. Minor
contamination of an Amalgam during insertion may not
have as adverse an effect on final restoration as the same
would on composite restoration. However, is Amalgam is to
be bonded, isolation needs are same as that of composite.
3) Operator Ability and Commitment factors: The tooth
preparation for an Amalgam is very exacting. It requires a
specific form with uniform depths and precise marginal
form. Many failures of Amalgam restoration may be related
to inappropriate tooth preparations. The insertion and
finishing procedure for Amalgam are much easier than
composite. Instead if it is to be bonded, it is as complex as
for composite.
Clinical Indications for Direct Amalgam Restoration:
Because of the factors presented above, Amalgam is
most appropriately considered for :

9. 1) Moderate to large class I and Class II restorations
(especially including those with heavy occlusal loading
that cannot be isolated well or that extend onto the root
surface)
2) Class V restorations (Including those that are not
esthetically critical, cannot be well isolated or are located
entirely on root surface)
3) Temporary caries control Restorations (including those
teeth which are badly broken down and require a
subsequent assessment of pulpal Health before definite
treatment).
4) Foundations (including for badly broken down teeth
that will require increased retention and resistance form
in anticipation of subsequent placement of a crown or
metallic Onlay).
Contradiction:
While esthetics is subject to wide variations in
personal interpretation, most patients find the appearance
of the Amalgam restoration objectionable when compared
to composite restoration. Therefore use of Amalgam in
prominent esthetic areas of mouth is usually avoided.
These areas include anterior teeth, premolars and in some
patients – the molars. Because Amalgams requires a larger
tooth preparation than composite, most small (even
moderate) defects in posterior teeth should be restored
with composite rather than Amalgam which leads to
conservation of tooth structure.

10. Advantages :
1) Ease of use
2) High composite strt.
3) Excellent wear resistance
4) Favourable long term clinical research results
5) Lower cost than for composite restorations
6) Bonded Amalgams have “Bonding benefits:
i. Less microleakage, interfacial staining
ii. Slightly increase strt of remaining tooth
structure
iii. Minimal post operative sensitivity
iv. Some retention benefit
v. Esthetic benefit of sealing by not permitting
the Amalgam to discolour the adjacent tooth
structure.
Disadvantages:
1) Non Insulating
2) Non Esthetic
3) Test conservative
4) Weakens tooth structure (unless bonded)
5) More technique sensitive if bonded.
6) More difficult tooth preparation
7) Initial marginal leakage.

11. Classification – Major approaches to classifications of
Amalgams and Amalgam alloys are in terms of
1) Amalgam Alloy particle geometry and size
2) Copper content, and
3) Zonc content.
A general classification can be as follows:
Lathe cut low/high Cu
Silver Amalgam Admixed
Alloys
Spherical low/high Cu
Composition Morphology Eg:
Traditional
Traditional
High Cu.
High Cu.
High Cu.
Lathe cut
Spherical
Lathe cut (SC)
Spherical (SC)
Admixed
(trad + Ag-Cu
Entectic)
Aristaloy
Spheraloy
Epoque 80
Tyti
Disper alloy
ALLOY COMPOSITION: American National Institute (ANSI)
American Association (ADA) specification No. 1 requires
that Amalgams alloys contain predominantly silver and

12. tin. Unspecified amounts of other elements for eg.: Copper,
Zinc Gold and Hg are allowed in concentration less than
Ag and Sn.
Alloys that contain in excess of 0.001% Zinc are
required to be designated as ‘Zinc containing Alloys for
dental amalgam, while alloys containing 0.01% or less of
Zn are designated as ‘Zinc free alloys.
Historically amalgam alloys contained at least 65 wt%
Ag, 29 wt% tin and less than 6wt% copper, a composition
close to that of G.V Black (1896). During the 1970s many
amalgam alloys containing between 6wt% and 30wt%
copper were developed, many of these being superior in
many respects to traditional low-Cu amalgams.
TRADITIONAL AMALGAM ALLOYS:
LATHE CUT: Until 1960s, the chemical composition and
microstructure of available amalgam alloys were
essentially the same as those of the most successful
systems investigated by G.V Black (Black 1895)-
Traditional alloys were delivered to the dentist as fillings,
which were lathe cut from a cast ingot. Milling and sifting
produced the ultimate particle size distribution, as well as
the final form of Amalgam Alloy particles.
A commercial alloy evolved into a blend of different
particle sizes rather than a unimodel system, in order to
optimise packaging efficiency. The length of particles in
commercial lathe cut alloys might range from 60-120µm,
their with from 10 to 70µm and their still smaller (<30µm)
due to introduction of so called ‘Spherical alloys’.

13. Traditional alloys contain 66% to 73% of Ag by
weight; tin varies from 25 upto 29wt% and amount of
copper may be as high as 6wt% and Zn upto 2wt% upto3wt
% Hg may also be present. The structure of these
traditional alloys are essentially phase mixtures of gamma
phase of silver tin system (Ag3Sn) and the Epsilon phase of
copper tin System (Cu3Sn). Some of these alloys are still
available, but represent only a minor component of overall
Amalgam market.
SPHERICAL – The spherical alloys were introduced on the
market during 1960s. Generally their particle shape is
created by means of an Atomizing process. Although alloys
produced in this way are classified or spherical, thie r
particle shape may be irregular. Generally the maximum
particle size in a spherical powder in 40-50µm or less;
although there unusually is a particle size distribution.
Spherical traditional Amalgam lowered the necessary
Mg/alloy ratio and dramatically reduced the condensation
pressures.
HIGH COPPER BLENDED AND SINGLE COMPOSITION:
During the late 1960s, alloys with a significantly different
chemical compositions were introduced on the market. All
of these could be characterized by their high copper
content.
A first alloy of this type (Dispersalloy; Hohnson and
Johnson Dental Care Co.) (innes and Youdelis, 1963) was
a mechanical mixture of 2 parts of a traditional lathe cut
alloy with one part of spherical alloy. The chemical
composition of spherical particle was 72wt% Ag, and 28wt

14. %. Copper, it corresponds to the Eutectic composition of
silver copper system. The overall composition of this alloy
contained approximately 13% ADA specifications at that
time.
Amalgams made from this alloy, however were
clinically superior to traditional alloy with respect to
marginal integrity (Mahler et. al. 1970), and consequently,
other manufacturers developed similar composites
featuring some with a copper content greater than that
found in traditional Amalgam. At present copper content
varies upto approximately 30% by weight in some
commercial amalgam alloys.
The structure of several high copper alloys are similar
to that of Dispersalloy. They can be classified as “blended”
alloys in which traditional and high copper phases are
mechanically blended.
Another type of alloy is produced by melting together
all components of a high copper systems creating a single
composition, spherical or a lathe cut alloy, rather than a
mechanical mixture of 2 distinct powders. Depending upon
number of components involved, these systems are also
referred to as Quaternery alloys or as a ‘single
Composition System’.
Some amalgams alloy produces, in an effort to
improve clinical handling properties, supply “admixture”
types of high copper alloys. In these, the chemical
compositions and physical forms of the basic powders )
lathe cut/spherical) are varied. This system further differs
from those using Dispersalloy, in that both blended

15. components are representatives of copper Enriched alloys.
It is important to stress that all of these copper enriched
alloys contain > 10% copper by weight in form of either
silver copper eutectic or copper tin system.
Although Amalgam alloys containing many other
metals have been proposed or one investigated on an
experimental basis, at present only Indium, Palladium and
Selenium have been utilized as commercial Additives.
Palladium improves the corrosion resistance. Selenium has
been added to improve biocompatibility of amalgam.
Indium has been admixed in larger concentrations (10% by
weight) in metallic form to a high copper amalgam in order
to reduce the Hg vapour released in mastication process.
(Powell et. al., 1988; Youdelis, 1992)
TYPICAL COMPODITIONS OF AMALGAM ALLOYS. CHEM.
COMP. (Wt%):
Type Ag Sn Cu Au Others
TL
TS
HCS
HCAd
HCl
G4
70.9
72
41-61
62-69.7
43
50
23.8
26
24-30.5
15.1-18.6
29
26
2.4
1.5
12-28.3
12-22.7
25
15
1
0.5
0-0.3
0-0.9
0.3
-
-
-
In 3.4
In10
Hg 2.7
Pd 9
TL = Traditional Lathe cut, TS= Traditional Spherical, HCS
= High Cu Spherical, HCAd = Hi. Cu. Admixed, HCl= Hi Cu
lathe cut, GA = Alloy for Gallium Amalgam.

16. AMALGAM
ALLOYS
CLASSIFIC
ATION
TYPE Ag Sn Cu Zn Hg Other
New true
Dentalloy
Micro II
Dispersalloy
Tytin
Sybraloy
Cupralloy
AristalloyCR
Indiloy
Valiant
Valiant Phd
Low Cu
Low Cu
High Cu
High Cu
High Cu
High Cu
High Cu
High Cu
High Cu
High Cu
Lathe cut
Lathecut
Mixed
Spherical
Spherical
Mixed
Spherical
Lathecut
Lathecut
Mixed
70.8
70.1
69.5
59.2
41.5
62.2
58.7
60.5
49.5
52.7
25.8
1.0
17.7
27.8
30.2
15.1
28.4
24.0
30.0
29.7
24
8.6
11.9
13.0
28.3
22.7
12.9
12.1
20.0
17.4
1.0
0.3
0.9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-
-
-
-
-
-
-
3.4 In
0.5 Pd
0.5 Pd
From Osborne Int et al: JDR ’07: 983 to 98, 1978
METALLURGIC PHASES IN DENTAL AMALGAMS:
The setting reactions of alloy for dental amalgam with
Hg are usually described by metallurgic phases that are
involved. These phases are found in phase diagram for
each alloy system.

17. Symbols and Stoichimetry of phases involved in
Amalgam’s setting
Phases in Amalgam
Alloys and set Dent Amalgams
Gamma - √
Gamma 1 - √1
Gamma 2 - √2
Epsilon – ε
Eta – ŋ
Silver Copper Eutectic
Stoichio metric formula
Ag3Sn
Ag2Hg3
Sn7-8Hg
Cu3Sn
Cu6Sn3
Ag-Cu
The Influences of Ag-Sn Phases on Amalgam Properties:
In the range of compositions around the √ phase,
increases or decreases in silver influences the amount of B
and √ phases and the properties. Because the effect of
these phases is relatively pronounced, their control is
essential, if an alloy of uniform quality is to be produced.
If tin concentration exceeds 26.8 wt%, a mixture of √
phase and a tin rich phase is formed. The presence of tin
phase increases the amount of tin-Hg phase formed when
alloy is amalgamated. The tin-Hg phase lacks corrosion
resistance and is the weakest component of dental
amalgam. Amalgams of tin rich alloys display less
expansion than do silver rich alloys.
Ag-Sn alloys are quite brittle and difficult to
comminute uniformly unless a small amount of copper is

18. substituted for Ag. This atomic replacement is limited to
about 4wt% - 5wt% above which Cu3Su. Within limited
range of copper solubility, increased copper content
hardens and strengthens the Ag-Su alloy.
The use of Zn in an amalgam alloy is a subject of
controversy. Zinc is seldom present in an alloy to an
extent greater than 1wt%. Alloys Zn are more brittle and
amalgam produced tends to be less plastic during
condensation and carving. Chief function of Zinc is that of
de-oxidiser – Scavenger, viz; it acts as a scavenger during
melting, uniting with O2 to minimize formation of other
oxides.
Zinc may have some beneficial effects related to early
corrosion and marginal integrity as shown in clinical
trials. But may even cause abnormal ‘Delayed’ expansion
of amalgam if it is condensed in presence of moisture.
MANUFACTURE OF ALLOY POWDER: To make, lathe cut
powder, an annealed ingot of alloy is placed in a milling
machine or in a lathe and is fed into a cutting tool/bit.
The chips are removed are of ten needle like and some
manufacturers decrease the ship size by ball milling.
Homonizing Anneal: Because of rap[id cooling conditions
from the ascast state, an ingot of an Ag-Su alloy has a
cored structure and contains nonhomogeneous grains of
varying composition. Hence, a homogenizing Anneal
treatment is performed to establish the equilibrium phase
relationship.

19. The ingot is placed in an oven heated at temperature
below solidus for sufficient time to allow diffusion of
atoms to occur and the phases to reach equilibrium. Time
of treatment varies depending on temperature used and
size of ingot. A 24 hours time period treatment is not
unusual.
After heating, ingot is brought to room temperature
very slowly so that the proportion of phases will continue
to adjust towards room temperature equilibrium ratio. It is
quenched rapidly, phase distribution will essentially
unchanged.
For eg.: in a Ag-Su alloy, rapid quenching results in
maximum intention of β phase, whereas slow cooling
results in formation of maximum amount of the √ phase.
Particle treatment: Once the ingot has been reduced to
cuttings many manufacturers perform same type of
surface treatment of particles. Although specific treatment
are proprietary, treatment of alloy particles with acid has
been a manufacturing practice for many years. Exact
function of this step is not known, but is probably related
to preferential dissolution of specific components from the
alloy. Amalgams made from acid washed powders tend to
be more reactive than those from unwashed powders.
The stresses induced into the particle during cutting
and ball milling must be relieved or they slowly release
over time, causing a change in alloy, particularly in
amalgamation rate and dimensional change occurring
during hardening. The stress relief process involves an
annealing cycle at a moderate temperature; usually for

20. several hours at approximate 1000
C. The alloy generally
then is stable in reactivity and properties when it is stored
for an indefinite period.
Atomised powder: Atomised powder is made by melting
together the desired elements. The liquid metal is atomized
into fine spherical droplets of metal. If the droplets solidify
before hitting a surface, the spherical shape is preserved
and these powders are called ‘ Spherical Powders. Like the
lathe cut powder, these too are given a heat treatment that
coarsens the grains and slows the reaction of these
particles with Hg. These are also washed with acid. The
tiny drops of alloy are allowed to solidify in an inert
gaseous (Argon) or liquid (water) environment.
Lathe cut vs Spherical alloys – Amalgams made from
lathe cut or Admixed type tend to resist condensation
better than amalgams of spherical alloy because spherical
amalgams are extremely plastic, one cannot rely on
condensation press to establish proximal contour. A
contoured and wedged matrix band is essential to prevent,
flat proximal contours, improper contacts and overhanging
cervical margins. Also spherical alloys require less Hg
than lathe cut ones, hence do have better properties.
AMALGAMATION AND RESULTING STRUCTURE:
1) Low Copper Alloys – Amalgamation occurs when Hg
causes in contact with surface of Ag-Su particles. When a
powder is triturated, the Ag and Su in the outer portion of
particles dissolve into Hg. At the same time, Hg diffuses

21. into the alloy particles. The Hg has a limited solubility for
silver (0.035wt%) and tin (0.6wt%). When that solubility is
exceded, crystals of 2 binary metallic compounds
precipitate into mercury. These are BCC Ag2 Hg3 compound
(the √ phase) and the hexagonal close packed Sn7-8Hg
compound (the √2 phase). Since the solubility of Ag in Hg
is much lower than that of tin, the √1 phase ppts first and
√2 phase pptr later. Immediately after trituration, the alloy
powder coexist liquid Hg, giving the mix a plastic
consistency. As remaining Hg dissolves, √1 and √2 crystals
grow and finally as Hg is exhausted, amalgam hardens. As
the particles become covered with newly formed crystals
(mostly √1), the reaction rate decreases. Since the alloy is
mixed with Hg in a ratio of 1:1 or lower, this amount of Hg
is less to completely conserve all the alloy particles
consequently, unconsumed particles are present in set
amalgam.
Alloy particles (now smaller, because their surfaces
have dissolved in Hg) are surrounded and bound together
by solid √1 and √2 crystals Thus a typical low Cu amalgam
is a ‘composite’ in which unconsumed alloy particles are
embedded in √1 and √2 phases.
The reaction can be expressed as :
Alloy particles (β + √) + Hg - √1+ √2 + unconsumed alloy
particles (β m+√).
The physical properties of hardened amalgam depend on
the relative percentages of each of microstructural phases.
The unconsumed Ag3Sn particles have maximum and
strong effect. The more of this phase is retained, the

22. stronger is the amalgam. While weakest is √2 phase with
hardness approximately 10% of √1 phase whereas the √
phase hardness is somewhat higher than √1.
The interface between √ phase and matrix is
important. The maximum amounts of √ phase will not
strengthen the alloy unless the particles are bound to the
matrix.
2) HIGH COPPER ALLOYS –
a) ADMIXED ALLOYS – These are mixture / blend of
spherical silver – copper (Ag-Cu) eutectic alloy (71.9wt%)
Ag. And 28.1wt%. copper) particles and lathe cut low
copper Amalgam alloy particles.
When Hg reacts with admixed powder, silver dissolves
into Hg from, Ag-Cu alloy particles and both silver and tin
dissolves into the Hg from the Ag-Su alloy particles; The
tin in solution diffuses to the surface of Ag-Cu alloy
particles and reacts with copper phase to form the ‘n-
phase (Cu3Su5). A layer of n-crystals forms around
unconsumed Ag-Cu alloy particles. This n-layer also
contains some √1 crystals. The √1 crystals form
simultaneously with n phase and surrounds both n
covered Ag-Cu particles and Ag-Sn particles.
As in low copper amalgams, √1 is the matrix phase.
The reaction can be expressed as:
Alloy particles (β+√) + Ag-Cu entectic + Hg - √1 + n +
unconsumed alloy of both type of particles.

23. Note that √2 phase is formed simultaneously as n phase,
but is replaced by the latter. For this the net copper
conclusion should be aleast 12% in the alloy powder. Some
set admixed amalgams do contain √2, although percentage
is much smaller than low – Cu amalgams.
b) SINGLE COMPOSITION ALLOYS – number of
phases found in each single composition alloy particle
includes, β phase (Ag-Sn), ‫ﻻﻻ‬(Ag3Sn) and Є (Cu3Su). Some of
alloys may also contain ŋ(Cu6Sn5), Atomised particles
have dendritic microstructure with fine lamellar.
When Hg is triturated with Hg, Ag and Sn from Ag-
Su phases dissolves in Hg, little Cu too dissolves in Hg.
The √1crystals forms the matrix with the unconsumed
particles ŋ crystals are found as meshes of rod crystals at
the surface of alloy particles as well as in matrix and also
are much larger than ŋ- crystals of admixed alloys. The
reaction:
Ag-Sn-Cu alloy particles + Hg - √1th + uncons. all
pont. In single composition, little or none of √2 phase is
formed. Preferential corrosion of n(Cu6Su5) phase
reportedly has been shown to be significant both in vivo
(Marshall et. al., 1980) and in vitro (Averette et. al., 1978)
studies.
Recently evidence has been presented for presence of
an additional tin-Mercury phase, delta – 2 (Sarkar, 1994
a), at the grain boundaries of resulting √1- network. This
ohase results from lower tin concentration in last Hg
solidify. Since it is located a grain boundaries, it will have
significant influence indetermining the structure sensitive

24. properties of Amalgam. Since Copper and tin will
preferentially combine in dental – amalgam, higher Cu –
concentration will also reduce formation of 2
phase. It is
also possible that through solid solution, indium may
increase the stability of √1phase (Sarkar, 1994)
- In relation to preferential corrosion of n phase, G. M.
Grrener and K. Gurgot studied the effect of addition of
palladium on enhancement of corrosion resistance of High
Cu amalgam and also its effect on its mechanical property.
They used low % Pd. They concluded that,
1) Addition of Pd has no effect on mechanical
property of High Cu. Amalgation with creep,
produced being < 1%
2) Addition of Pd lead to increase in corrosion
resistance.
- JDR vol 61 No. 7, 1982, pg 1192-1194
DIMENSIONAL STABILITY – ideally an Amalgam should set
with no change in dimensions and their stable for life of
restoration. However a variety of factors influence both
initial dimensions on setting and long term dimensional
stability, as follows;
a) Dimensional change : ADA spe. No. 1 requires that
Amalgam should neither contract nor expand more than
20µm/cm measured at 370
C between 5 minutes and 24
hours after beginning of trituration, with a device which is
accurate to atleast 0.5µm.

25. Theory of dimensional change: Classic picture of
dimensional change is one in which specimen undergoes
an initial contraction for about 20 minutes after beginning
of trituration and then begins to expand.
a) Contraction: 1) initial dissolution of alloy particles.
2) Growth of √1crystals.
3) Low mercury: Alloy ratio
4) High condensation pressures.
5) Longer trituration time.
6) Smaller particle size alloys
7) Mechanical trituration
b) Expansion: 1) Continued growth of √1 crystals
2) Excess Mercury
3) Hand trituration
4) Larger particle size alloys (used in past)
b) Effect of Moisture Contamination: Occurs in Zinc
containing low copper and high copper Amalgam only
when they are contaminated by moisture during
trituration or condensation. Expansion starts, usually,
after 3-5 days and may continue for months, reaching
values greater than 400 µm (4%) and is known as
Delayed / secondary expansion.
c) Effect of Creep: Amalgam Creeep is plastic deformation
principally due to very slow metallurgic phase
transformations that involve diffusion controlled reaction
and produce volume increases.

26. STRENGTH
A prime requisite for any restorative material is a strength
sufficient to resist #. Fracturing especially at margins
hastens corrosion, sec. caries and subsequent failure.
Comparison of Compressive Strength and Creep of a
low copp. And high – Cu Amalgam
Amalgam Comp. Strt.
(MPa)
Creep (%) Tensile strt
(24h) MPa
1h 7 days
Low Copper*
Admix+
Sing Comp‡
145
137
262
343
431
510
2.0
0.4
0.13
60
48
64
* - fine cut C.D., Caulk Company, Milford
+ - Dispensalloy, Johnson and Johnson Dental Products
‡
- Tytin S.S., Whiye Dental Manufaturig Company
Specimen used is comparable with a typical Amalgam
restorations dimension wise.

27. 2) Physical Properties of Amalgam – Table in Craig and
Powers.
a) Product Hg in Mix
(%)
Comp strt (MPa)
1h[0.5mm/min]
Comp. Strt (MPa) 7
day
Creep
(%)
0.2mm/min 0.05mm/min
- Low copper
i) fine cut
caulk Co.
ii) Spherical
- Caulk Sph
- Kerr Sph
- Shofu Sph
- HIGH COPPER
i) Admixed
Dispersalloy
ii) Sing. Comp
- Sybraloy
-Tytin
53.7
46.2
48.5
48.0
50.0
46.0
43.0
45
141
88
132
118
252
292
302
366
380
364
387
455
516
227
289
299
305
340
452
443
6.3
1.5
1.3
0.5
0.45
0.05
0.09

28. Product Ten. strt (0.5mm/min) (MPa) Dim change
(µm/cm)15 min 7 days
- LOW COPPER
i) fine cut
caulk Co.
ii) Spherical
- Caulk sph
- Kerr sph
- Shofu sph
- HIGH COPPER
i) Admixed
Dispensalloy
ii) Unicompositional
- Sybraloy
- Tytin
3.2
4.7
3.2
4.6
3.0
8.5
8.1
51
55
55
58
43
49
56
-19.7
-10.6
-14.8
-9.6
-1.9
-8.8
-8.1
- Adapted from Malhotra, Asgar, JADA 96: 447, 1978.
- All these figures are recorded as Amalgam is subjected to
a particle rate of loading because sudden application of
heavy force can # the amalgam.
From both the tables, its clear the amalgam has strong
compressive strt and much weaker tensile strength. Hence
cavity design should maximize compression and minimize
tension or shear forces.

29. Transverse strength: The values are sometimes referred
to as Modulus of Rupture. Since Amalgam are brittle
materials they withstand little deformation during
Transverse Strength testing. Main factors related to high
values of deformation are 1) Slow rates of load application
2) High creep 3) high temperature of testing. Hence, High
Cu; Amal with low Creep should be supported by bases
with high moduli to minimize deformation and transverse,
failure.
- Strength of various phases: This is very important and
is studied by initiation and propagation of crack in set
Amalgam. The strongest to weakest phases are as follows:
(low Copper) 1) Unreacted Alloy Particles (r)
2) √1 phase 3) √2 phase
- Elastic modulus: When determined at low rates of
loading. Such as 0.025 mm/min, values in range of 11-20
GPa are obtained. High Copp. Alloys tend to be stiffer than
low copper alloys.
- Effect of various factors on strength:
i) Trituration: Under and over trituration decreases strt of
both low and high copper amalgams.
ii) Mercury content: Mercury in excess of 54-55% markedly
decreases strt of both low and high copper Amal.
iii) Condensation: Greater the condensation pressure,
increased is the strt – lathe cut, while for spherical,
lighter pressures produces adequate strt.
iv) Porosities: Porosities decreases strt.

30. v) Amalgam Hardening Rate: Even if a fast hardening
Amalgam is used, its strength is likely to be low initially.
Patient should be cautioned not to subject the restoration
to high biting stresses for atleast hours after placement.
By that time, a typical Amalgam has reached atleast 70%
of its strt.
- CREEP : Creep rates have been found to correlate with
Marginal breakdown of traditional low copper amalgams
i.e., higher the creep, greater the degree of marginal
breakdown. However for high Cu. Amalgams, creep is not
necessarily a good predictor of marginal # It is prudent to
select an alloy that has creep rate below level of 3% as in
ADA specification No. 1.
The √1 phase has been found to exert a primary influence
on low copper Amalgam creep rates. Creep rates increase
with larger √1 volume fractions and decrease with larger √1
grain sizes. The presence of √2 is associated with higher
creep rates. In addition to absence of √2, very low creep
rates in single composition high Cu- amalgams may be
associated with ŋ rods, which act as barriers to
deformation of √1 phase.
Also those manipulative factors that maximized strt,
minimize creep rates.
- Expansion due to creep: Mercuroscopic Expansion

31. TARNISH AND CORROSION
Amalgam restoration often tarnish and corrode in oral
environment. The degree of tarnish and resulting
discolorations appear to be dependent on individuals oral
environment and to a certain extent on particular alloy
employed. Electrochemical studies indicate some
passivation offering protection against further corrosion,
occurs as a result of Tarnish.
A tendency towards tarnish, although unaesthetic
because of black silver supfide, does not necessarily imply
that active corrosion and early failure of restoration will
occur.
- Traditional Amalgams and high copper Amalgams show
two kinds of corrosion – a) Chemical b) Electrochemical
Traditional Amalgams are susceptible to corrosion
with chlorides attacking the gamma – 2 phase. This phase
corrodes according to:
8Sn7Hg + 21O2 + 4H2O + 28 Cl-
- 14Sn4(OH)6Cl2 + 8Hg
This process then leads to 2 deteriorating effects:
1) The corrosion of interconnected √2 further weakens
the Amalgam particularly the tensile strt.
2) Hg liberated by corrosion process can react with
remaining unreacted √ to produce additional reaction
prod (√1 + √2).
The formation of these 2 phases could produce an
additional reaction i.e., additional dimensional change
(Mercuroscopic Expansion), leading to unsupported

32. amalgam at margin which can easily # in tension. The
entire mechanism has been associated with phenomenon
of Amalgam ditching which was quite prevalent in clinical
use of traditional Amalgam. The liberation of Hg has also
created additional biocompatibility concerns.
In high copper Alloys, little or none of √2 phase is
formed due to formation of emphase (Cu6Sn5) which was
more corrosion resistant. However, the eta prime phase is
also prover to be susceptible to corrosion in oral cavity;
4Cu6Sn5+19O2+18H2O+12Cl-
- 6[CuCl2 3Cu(OH)2]+20SnO
This reaction will not subsequently affect the strength of
highcopper Amalgam because eta phase is not an
interconnecting phase. However eta phase’s corrosion has
raised questions regarding biocompatibility of high copper
Amalgams.
However addition of Palladium to high copper
Amalgams have produced hope against corrosion of eta
phase. It is shown that Palladium is soluble in √1 with
resultant improvement in behaviour. Recent studies have
shown that Hg is released during free corrosion of
Amalgam invitro in various salivas. Over short term this
Hg burden was found to be in range, of 4-20µg/day or
about same value as dietry intake and over longer periods,
it was lower than dietry intake. Invivo, however, natural
buffering capacity of saliva, along with attendant organic
protelus may appreciably lower corrosion kinetics.
- Electro chemical Corrosion: This is an important
mechanism of Amalgam corrosion and has potential to

33. occur virtually anywhere on or within a set Amalgam. This
occurs whenever chemically different sites act as anode
and cathode. Also it requires that the sites be connected
by an electrical circuit in of an electrolyte typically saliva.
The anode corrodes, producing soluble and insoluble
reaction products.
If an amalgam is indirect contact with an adjacent
metallic restoration such as Gold crown, Amalgam acts as
Anode in circuit . This type of corrosion is called ‘Galvonic
Corrosion’ and is associated with presence of
macroscopically different electrode sites. A high copper
Amalgam is cathode with reference to a conventional
Amalgam. These concerns are being expressed that if a
high Cu restoration are placed in the mouth with
traditional restoration in contact with it, corrosion and
failure would be accelerated in latter.
The same process may occur microscopically (local
galvanic corrosion or structure selective corrosion) ecause
of electrochemical difference of different phases. Residual
alloy particles act as strongest cathodes. Su-Hg or Cu-Su
reaction product phases are strongest Anodes in low
copper and high copper respectively. Local electrochemical
cells also may arise whenever a portion of Amalgam is
covered by plaque/soft tissue. The covered area has locally
lowered O2 and/or higher hydrogen ion concentration
making it behave more Anodically and corrode. Cracks and
crevices produce similar conditions and preferentially
corrode (concentration cell corrosion or crevice corrosion)
regious within an Amalgam that are under stress also

34. display a greater propensity for corrosion. So in a Cl I
dental amalgams, electro chemical corrosion events are as
follows;
1) local galvanic corrosion between Amalgam Phases along
all surfaces of Amalgam.
2) Stress corrosion during occlusion with opponent tooth
surface
3) Concentration cell corrosion within margins with tooth
surface.
4) Concentration cell corrosion below plaque on amalgam
surface (causing pitting).
In Cl II restoration events are same as Cl I, in
addition there is corrosion at interproximal contacts with
adjacent metal crowns. In Cl III restoration, events are
same as Cl I restoration.
Electro chemical corrosion is not a process of Hg
liberation, Hg reacts with unreacted Alloy particles.
MANIPULATION OF AMALGAM
1) Selection of an alloy: This involves a number of factors
including setting time, particle size and shape and
composition particularly as it relates to elemination of √ 2
phase and the presence or absence of zinc. It is estimated
that more than 90% of dental Amalgam currently placed
are high copper alloys. The majority of alloy selected are
unicompositional (spherical) and Admixe with Admixed
being favoured slightly.

35. Also the further processes of Inserting, Condensing,
Carving, Finishing also affect the Amalgam alloy selection.
2) Proportions of Alloy to Mercury: Up until the early
60s it was necessary to use an amount of mercury
considerably in excess of that desirable in final
restorations to achieve smooth, plastic Amalgam mixes
because of deleterious effects of Hg on physical and
Mechanical properties of Amalgam, Hg was used only to an
acceptable level. Excess Hg was removed by squeezing the
mixed Amalgam after trituration in a cloth, muslin cloth or
guaze piece or by working the excess Hg to the top during
condensation of restoration, which was subsequently
removed. But there was a considerable chance of error as
amount of Hg removed – varied.
However in 1960, Lames described the ‘No squeeze Cloth’
Technique or ‘Minimal Mercury technique’ or after his
name, ‘The Lames technique: He suggested that sufficient
Hg be present in original mix to provide a coherent and
plastic mass after trituration, but be low enough that Hg
level of restoration is at acceptable level without need to
remove an appreciable amount by condensation.
The amount of alloy and Hg to be used can be
described as Mercury: Alloy ratio. The recommended ratio
being 1:1 i.e., 50% Hg. However some alloys require less
than 50% Hg, some require more than 50%., the
percentage varies between 43-54%.

36. With spherical alloys, recommended amount of Hg is
closer to 42%. Percentage of Hg used depends upon how
the alloy particles can be packed together.
Another transitional approach includes redesigning
Amalgam to have much less initial Hg. If alloy particle
sizes are judiciously chosen to pack together well, it is
possible to minimize the Hg required for mixing to 15-25%
range. Clinical properties of this alloys are unknown.
The ADA in combination with National Institute on
standards and Technology (ADA-NIST) has patented a Hg
free direct filling alloy based on Ag-coated Ag-Sn particles
that can be self welded by compaction (Hand
consolidation) to create an restoration.
Initially Automatic Mechanical dispensers for alloy
and Hg have been used in the past. But with
recommendation of “No touch” procedures for handling
alloy and Hg, the capsules with preproportional amounts
of alloy and Hg have been substituted for dispensers.
- Size of Mix: Manufacturers commonly supply capsules
containing 400, 600 or 800 mg of alloy with appropriate
amount of Hg, colour coded for ease of identification. Also
capsule with 100 mg of alloy is available for large amount
of amalgam if needed for core building on severely broken
tooth.

37. AMALGAMATION:
1) Hand Trituration: Is done using a Mortar and Pestle.
In this it is difficult to follow the manufacturer’s
direction explicitly with reference to pressure, rpm,
etc. A general recommendation is that mixing should
be continued until the Amalgam has a shiny
appearance, adheres to the sides of mortar and curls
over slightly at the top.
2) Mechanical Trituration: Mechanical Amalgamation
saves a lot of time and standarises the procedure. It
is carried out by an ‘Amalgamator’. A large number of
commercial brands of Amalgamators are available.
The basic principle of operation is comparable for
most of them. – A capsule serves as a ‘motor’. A
cylindrical metal/plastic piston of smaller diameter
than capsule is inserted in it and serves as ’pestle’.
Reusable capsules also usually contain an
appropriate pestle.
The alloy and mercury are dispensed into the
capsule or of a disposable capsule system is being
used, capsule may require activation. When capsule
has been secured in the machine and the machine
has been turned on, the arms holding the capsule
oscillate at high speed, Hence trituration is
accomplished. There is an automatic timer for
controlling length of mixing time and most modern
amalgamators have two or more operating speeds.
New Amalgamators must have hoods that cover
the reciprocating arm holding the capsule, this is to

38. confine Hg that might be sprayed into the room or a
capsule that might be thrown from the Amalgamator
during trituration. Eg.: of Amalgamators, Promix,
Antomix, Varimix, etc. Antomix has plastic cards for
particular alloys an size of mix, which when inserted
into the slot, sets the amalgamator for correct speed
and time.
3) Consistency of Mix: Undermixing, Normal mixing,
overmixing can result variations in condition of
trituration of alloy and H. These 3 mixes have
different appearances and respond differently to
subsequent manipulation. The undermixed A,algam
appears dull, grainy and appears crumbly, also leaves
a rough surface after carving, increasing
susceptibility to tarnish. Adequately mixed Amalgam
appears shiny and separates in a single mass from
capsule. Such a mix is warm (not hot) when removed
from capsule, also leaves a smooth surface on carving
which will retain its luster after polishing. Over
triturated mix appears soupy and tends to stick to
the inside of capsule.
These 3 mixes have characteristically different
mechanical property of dimensional change. Strength
and creep.
INSERTION AND CONDENSATION: The principle objective
of Insertion is to condense the amalgam to adapt it to the
preparation walls and matrix and produce a restoration
free of voids and have as low as possible Hg content in

39. restoration to improve strength and decrease corrosion. An
amalgam carrier is used to insert Amalgam into the cavity.
After mixing, condensation should be promptly initiated as
longer the time lapse between mixing and condensation,
weaker is the Amalgam. In addition Hg content and creep
of amalgams are increased. Condensation of partially set
material probably #s and break up the matrix that has
already formed and can also introduce voids in it or even
produce layering.
Condensation can be Hand or Mechanical Condensation.
a) Hand Condesation: i) Procedure. Ii) Condensation
pressure.
b) Mechanical Condensation: Procedure is same as that for
hand condensation except here condensation is done by
Anatomatic device. Various mechanisms are used, some
use impact force, while others use rapid vibration, less
energy is needed, hence is less fatiguing than hand
condensation.
CARVING AND FINISHING:
a) Precarve Burnishing -
b) Carving – The restoration should be carved to reproduce
proper tooth anatomy. The objective is to simulate the
anatomy rather than to reproduce extremely fine details. If
carving is too deep, amalgam bulk at margins in reduced,
and hence may # under masticatory stress.
c) Post carve Burnishing –

40. - Finishing and Polishing – Most Amalgams do not require
finishing and polishing. However, these procedures are
occasionally necessary to, i) complete the carving, ii) refine
the anatomy iii) refine the marginal integrity iv) Enhance
the surface texture of restoration.
Additional finishing and polishing procedures are not
attempted within 24 hours of insertion, because
crystallization is not complete. An amalgam restoration is
less prove to Tarnish and corrosion, if a smooth
homogeneous surface is achieved.
Polishing of High Cu. Amalgams is less important than for
low copper Amalgams as formers are less prove to tarnish
and marginal breakdown.
- Repairing and Amalgam Restoration – If an amalgam
restoration # during insertion, the defective area must be
reprepared as if were a small restoration.
Appropriate depth and retention form must be generated,
sometimes, entirely within existing amalgam restoration. If
necessary another matrix must be placed. A new mix of
Amalgam can be condensed directly into the defect and
will adhere to the amalgam already present, if o
intermediary material has been place between 2 amalgams.
Therefore sealer material can be placed on any exposed
dentin, but should not be place on amalgam preparation
walls. If amalgam has been bonded, carefully condition
and apply adhesive to the adhesive to the exposed tooth
structure in the preparation.

41. In such cases, the bond between new and old
amalgam is important. The flexural strt. of repaired
amalgam is less than 50% of that of unrepaired amalgam.
The bond is a source of weakness, factors such as
corrosion and saliva contamination at the interface
presents formidable barriers that interface with bonding of
old and new amalgam.
Repair, of amalgam restorations probably falls into
the category of hazardous procedure. Repair should be
attempted only if the area involved is small, one that is
not subjected to high stresses, capable of adequately
supporting and retaining 2 restorations parts.
- C. Leelawat, W. Scherer, J. Chang, A. Scherlman, T
Vijayaraghvan, studied the microleakage (invitro) patterns
when fresh amalgam was added to existing one. They foun
no change in microleakage patterns. But incidence were
significantly decreased when fresh Amalgam was bonded to
existing one.
- J. Esthetic Dent. Mar-Apr’92 Vol 4 (2), 41-45.
- C. Leelawat, W. Scherer, J. Chang, A. Scherlman, T
Vijayaraghvan and J. le Geros studied the invitro shean
and flexural strt when fresh amalgam was bonded to
existing one. They found a significant improvement in
performance of restoration.
- J. Esthetic Dent. Mar-Apr’92 Vol 4 (2), 46-49.

42. - AMALGAM ‘PROBLEMS’: following are the ‘problems’
that can be encountered when amalgam restorations are
evaluated;
1) Amalgam “blues” – Discoloured areas seen through
enamel either due to leaching of corrosion products into
dentinal tubules or from the colour of underlying Amalgam
seen through translucent (undermined) enamel.
2) Proximal overhangs – Are diagnosed visually, tactilely
and xgphically. Is a plaque trap and obstacle to
maintenance of good oral hygiene and may result in
inflammation of adjacent soft tissue.
3) Marginal Ditching – Also called as “Ditched” restoration.
May be caused due to a) Improper cavity preparation or
finishing. B) Excess Mercury C) Creep.
Shallow ditching less than 0.5mm deep usually is not a
reason for restoration. However, if it is too deep, has to be
restored.
4) Voids – occurs at margins due to a) Improper
condensation b) Material pulling away or breaking from
marginal area when carving bonded Amalgam. If the void
is 0.3mm deep and is located in gingival 1/3rds
of tooth
crown, then restoration is judged as defective and should
be repaired / replaced.
5) Fracture lines – May occur across the occlusal
surface or in Isthmus reg. May be mistaken with an
“Abutted Restoration”.
6) Abnormal Anatomic Contours – should be
recontoured or replaced.

43. 7) Marginal Ridge Incompatibility – May cause food
impaction, restoration is defective and should be
recontoured.
8) Improper Proximal Contact –
9) Recurrent caries –
10) Improper Occlusal contacts –
ALTERNATIVES TO AMALGAM : As given by :
1) B. M. Eley – BDJ July’97 vol 183 No. 1 pg. 11-14.
2) Theodore Croll – Quintissence Int’ Nov’98 vol29 No.
11 Pg. 697 to 703.
Alternatives may be classified as Metal alloys and tooth
col. Alternatives.
1) Metal alloys – 1) Gold – Cast gold only real alternative
to Amalgam in moderate to larger cavities. Has superior
qualities, but is very technique sensitive. Expensive about
7-8 times than equivalent restoration for smaller
restorations, gold foil can be used, but is difficult, time
consuming, technique sensitive and expensive.
2) Consolidated Silver Alloy : In 1994, another metal
alternative was developed which consisted of Ag particles
suspended in dilute acid solutions. The acid treatment
cleaned the surface by removing oxides or other adsorbed
layers silver particles, thus enabling their consolidation
and cold welding. This acid assisted consolidation took
place at room temperatures under moderate pressures.

44. Physical properties showed high rupture strt than
Amalgam, however composite strt and hardness values
were lower than those found for Amalgam. It is still under
laboratory studies and is not commercially available.
- S. B. Geiger, D. Gurbator, M. P. Dariel, F. Eichmiller, R.
Liberuran, M. Ratzker – Oper Dent Mar-Apr’99 vol 24. No.
2. Pg – 103 to 108.
3) Gallium Alloys : 16 times more expensive than similar
amount of mercury-based Amalgam. Both the commercially
available brands are much more sticky when mixed and
hence are more difficult to pack in a cavity. Needs PTFE
(TEFLON) instruments to overcome this ‘mushy and sticky’
problem.
- High levels of corrosion, high levels of expansion leading
to even tooth #, unknown toxicology of Ga. Hence all these
make it inferior, much more costly, much more difficult to
use than Hg based Amalgams.
II) TOOTH COLOURED ALTERNATIVES – Patients demand
for Esthetic Restoration has stimulated the development of
new tooth coloured restorative materials, which are:
1) GICs 2) Composites 3) Resin modified GICs 4)
Compomers 5) Ceramics.
All of these have shorter life span than Amalgam. And only
composites and ceramics can be considered to restore
small occlusal cavities in permanent posterior teeth.

45. i) Composites : Expensive (3 times the cost at insertion),
Polymerisation shrinkage, Wear (increases with size),
demands total isolation, Acid etch bonding can break
causing Microleakage, shorter clinical life than Amalgam.
Indications for posterior cavities are :
Should e small cavity, must not involve