4. Dental amalgam is one of the most
versatile restorative materials used in
dentistry.
It constitutes
approximately 75%
of all restorative
materials used by
dentists.
It has served as a
dental restoration
for more than 165
years.
But development of alternatives
based on ceramics and
composites , and questions on its
safety have led to its decline.
5. Amalgam -An alloy containing mercury
Dental Amalgam – An alloy of mercury silver copper and tin,
which may also contain palladium, zinc and other elements to
improve handling characteristics and clinical performance
Dental amalgam Alloy – An alloy of silver copper and tin that is
formulated and processed in the form of powder particles or
compressed pellets.
6.
7. 659 AD
• Amalgam -- First used by Chinese. There is a mention of silver
mercury paste by Sukung in the Chinese medicine and later by Li
schichan
1819
• First use of room temp mixed amalgam- Bell in
England (Bell’s putty)
1840
• AMALGAM WAR- I
1895
• G.V. Black developed a formula for modern amalgam
alloy -67% silver, 27% tin, 5% copper, 1% zinc.
8. 1926
• AMALGAM WAR –II
1959
• Dr. Wilmer Eames recommended a 1:1 ratio of
mercury to alloy.
1970
• Change from hand trituration to mechanical
trituration
1973
• AMALGAM WAR – III
9. 1979
• Gay and workers found mercury vapor in breath of patients
with amalgam fillings.
1984
• Human autopsy demonstrated the mercury found in brain
and kidneys were related to the amalgam fillings in the teeth.
1990
• Media was involved when the TV show “is there a poison in
your mouth?” came out.
1991
• Dental amalgam mercury syndrome groups started being
active.
• August 1991- national institute of health technology
concluded amalgam was safe.
11. In 1845, American society of Dental surgeons condemned the use
of all filling materials other than gold as toxic, there by igniting
the first amalgam war.
WHAT ENDED THE WAR?
• Professional and consumer demand.
• In 1859, the leaders of the profession regrouped to
form the American Dental Association.
• Between 1860 and 1890, many experiments were
done to improve amalgam filling materials.
• It was the classical work of GV Black in 1895 that a
systemic study was done on properties &
appropriate manipulation of amalgam.
12. Controversy over amalgam gained surface again in 1926,
a German physician, Dr. Alfred Stock, showed that mercury
escaped from the fillings in the form of dangerous vapours that can
cause significant medical damage.
13. During this Second Amalgam War, the American Dental
Association vigorously defended silver amalgam and its
widespread use was continued.
Remarkably, the Food and Drug Administration (FDA) has
separately approved the mercury and the alloy powder for
dental use.
Unfortunately now came the second world war over Europe
& " the second amalgam war" fell in forgetfulness.
14. It was neurobiologist, Mats Hanson, Associate professor at
the university of Sweden who in 1981 again started the
fight against the authorities.
But it began primarily through seminars ,writings,&
videotapes of Dr H. A. Higgins, a dentist from Colorado
Springs.
15. Pressure from mounting clinical evidence forced the ADA to finally
publicly concede that mercury vapor does escape from the amalgam
filling into the patients mouth.
But the ADA remained adamant that mercury in patients' mouths is
safe, and in 1986 it changed its code of ethics, making it unethical for a
dentist to recommend the removal of amalgam because of mercury
But problem flared in 1990’s by the telecast of television program ‘60
minutes’ in CBC television
16. The amalgam war continues to rage on today.
There is presently a congressional bill in The United States House of
Representatives (H.R. 4163) introduced by Rep. Diane Watson (D-CA)
and Rep. Dan Burton (R-IN) to ban the continued use dental amalgam
fillings.
Norway banned dental amalgam in 2008
Sweden banned the use of dental amalgam for almost all purposes in
2009
Denmark, Estonia, Finland, and Italy use it for less than 5% of tooth
restorations.
Japan and Switzerland have also restricted or almost banned dental
amalgam.
France has recommended that alternative mercury-free dental materials
CURRENT STATUS ON AMALGAM WAR
17. In December of 2016,
three EU institutions (the European Parliament, the
European Commission and the Council of the European
Union)
reached a provisional agreement to ban dental amalgam
fillings for children under 15 and pregnant and breastfeeding
women as of July 1, 2018,
and to consider banning dental amalgam completely by 2030
18. SPECIFICATION NO. 1
ANSI/ADA STANDARD NO. 6—DENTAL
MERCURY: 1987 (REAFFIRMED 2005)
ADA SPECIFICATION
19.
20. CLASSIFICATION BY MARZOUK
According to number of alloy metals
1. Binary alloys
(Silver-Tin)
2.Ternary alloys
(Silver-Tin-Copper)
3. Quaternary
alloys
(Silver-Tin-
Copper-Indium).
21. According to the shape of the powdered
particles
1. Spherical shape
(Smooth surfaced
spheres)
2. Lathe cut
(Irregular ranging
from spindles to
shavings)
3. Combination of
spherical and lathe
cut
(Admixed)
24. According to copper content of
powder
1. Low copper content
alloy - Less than 4%
2. High copper content
alloy - more than 10%
25. According to zinc content
1. Zn free (<0.01%) 2. Zn containing (>0.01%)
26. Generations of amalgam
According to compositional changes of succeeding generations of
amalgam
1. First generation amalgam was that of G. V Black i.e. 3 parts silver one
part tin (peritectic alloy).
2. Second generation amalgam alloys - 3 parts silver, 1 part tin, 4%
copper to decrease the plasticity and to increase the hardness and
strength. 1 % zinc, acts as a oxygen scavenger and to decrease the
brittleness.
3. Third generation: First generation + Spherical amalgam – copper
eutectic alloy.
4. Fourth generation: Adding copper upto 29% to original silver and tin
powder to form ternary alloy. So that tin is bounded to copper.
5. Fifth generation: Quatenary alloy i.e. Silver, tin, copper and indium.
6. Sixth generation: consisting eutectic alloy which includes palladium,
27.
28. composition
Conventional Amalgam Alloys:
(G.V. Black’s: Silver- tin alloy or Low copper alloy).
Low copper alloys are available as comminuted
particles (Lathe -cut and Pulverized) and spherical
particles.
Low copper composition:
Silver : 63-70%
Tin : 26-28%
Copper : 2- 5%
Zinc : 0-2%
29. ROLE OF INDIVIDUAL COMPONENT
SILVER
Constitutes approximately
2/3rd of conventional
amalgam alloy.
Adds to strength of finished
amalgam restoration.
Decreases flow and creep of
amalgam.
Offers resistance to tarnish.
Increases expansion on setting
30. Since Silver caused expansion on setting the
element tin was added to Silver.
Tin reduces both the rate of the reaction
and the expansion to optimal values.
Second largest component and contributes
¼th of amalgam alloy.
Readily combines with mercury to form
gama-2 phase, which is the weakest phase
and contributes to failure of amalgam
restoration.
Reduce the expansion but at the same time
decreases the strength of amalgam.
tin
31. copper
Since tin decreases the strength of
amalgam copper was added to
increase its strength.
Contributes mainly hardness and
strength of the amalgam.
Tends to decrease the flow and
increases the setting expansion
32. zinc
Acts as Scavenger of foreign
substances such as oxides in the
alloy powder.
Helps in decreasing marginal
failure.
The most serious problem with
zinc is delayed expansion, because
of which zinc free alloys are
preferred now a days.
33. Indium
It helps to increase the plasticity and
the resistance to deformation
It reduces the surface tension, thus
reducing the amount of mercury
required for the reaction.
It reduces the amount of mercury
vapour emitted.
It increases strength.
It reduces the creep and marginal
breakdown.
34. palladium
It increase the plasticity and the
resistance to deformation
It reduces corrosion.
It adds lustre to amalgam.
It also whitens the material.
35. INDICATIONS
Class I and class II cavities-moderate
to large restorations.
Class 3 in unaesthetic areas e.g. distal
aspect of canine, especially if
preparation is extensive with minimal
facial involvement.
Class 5 lesions in non-esthetic areas
especially when access is limited and
moisture control is difficult and for
areas that are significantly deep
gingivally
As a core build up material.
36. Can be used for cuspal restorations (with pins
usually)
As a die material
In teeth that act as an abutment for removable
appliances
In cases of heavy occlusal forces.
37. CONTRAINDICATIONS
Anterior teeth where esthetics is a prime
concern.
Esthetically prominent areas of posterior teeth.
Small –to-moderate classes I and II restorations
that can be well isolated.
Small class VI restorations
39. HOMOGENIZING ANNEAL
An ingot of silver-tin alloy has cored structure and contains non-
homogenous grains of varying composition.
Hence, a homogenising heat treatment is performed to re-establish the
equilibrium phase.
The ingot is placed in an oven and heated a temperature below the
solidus for sufficient amount of time to allow diffusion of the atoms and
the phases to reach equilibrium.
The time of heat treatment may be more than 24 hours.
The ingot is withdrawn from the oven and then quickly quenched. Thus
the equilibrium achieved remains essentially unchanged.
Thus in a Ag-Sn alloy, rapid quenching of the alloy results in maximum
amount of β phase retained, where as slow cooling results in the
formation of maximum amount of γ phase.
40. Produced by cooling molten 72% Ag and
28% Sn and forming an ingot (The ingot
may be 3-4 cm in diameter and 20 -30 cm in
length)
Alloy is heated for 8 hours at 400°C for
homogeneous distribution of silver and tin
Ingot is placed in a milling machine or lathe
and is fed into the cutting tool. The chips
removed are often needle like and then ball
milled to reduce their size
The particles are 60-120µm in length, 10-
70µm in width & 10-35µm in
thickness(Irregular in shape)
MANUFACTURING PROCESS- LATHE CUT
41. Produced by atomizing the molten alloy in a
chamber filled with an inert gas- argon
Molten metal falls through a distance of
approximately 30 feet and cools
Results in characteristic spherical particle
shapes.
If particles are allowed to cool before they
contact the surface of chamber, they are
spherical in shape.
If they are allowed to cool on contact with
the surface they are flake shaped. Particle
size ranges form 5 to 40 microns
MANUFACTURING PROCESS- SPHERICAL
42. Acid washed – Preferential dissolution of specific
components – acid washed powders more reactive
than unwashed powders
Age hardening is basically a stress relief process.
It makes the alloy stable in its reactivity and property
for indefinite period of time – improves shelf life.
Generally done by heating them 60 to 100 ̊c for 1 to 6
hours
PARTICAL TREATMENT
43. HIGH COPPER AMALGAM ALLOY
(COPPER ENRICHED ALLOYS)
To overcome the inferior properties of low copper amalgam alloy
-- shorter working time, more dimensional change, difficult to
finish, set late, high residual mercury, high creep & lower early
strength, low fracture resistant
Youdelis and Innes in 1963 introduced high copper content
amalgam alloys. They increased the copper content from earlier
used 5% to 12%.
Copper enriched alloys are of two types:
1) Admixed alloy powder.
2) Single composition alloy powder.
44. Also called as blended alloys.
Contain 2 parts by weight of conventional composition lathe
cut particles plus one part by weight of spheres of a silver
copper eutectic alloy.
Made by mixing particles of silver and tin with particles of
silver and copper.
The silver tin particle is usually formed by the lathe cut
method, whereas the silver copper particle is usually
spherical in shape.
admixed ALLOY
45. Single composition alloy
UNICOMPOSITIONAL ALLOY
It is so called as it contains particles of same
composition.
Asgar – 1974
Usually Spherical in nature
Copper Content is 13 – 30 %.
47. amalgamation
It is a process of alloying of mercury which is in the
liquid state to Ag- Sn i.e. Silver- Tin metal alloy
being in the solid state.
48. LOW COPPER ALLOYS:
Amalgamation occurs when mercury
contacts the surface of the silver-tin
alloy particles.
The silver and tin dissolve into the
mercury.
METALLURGICAL
PROCESSES IN
AMALGAMATION
Ag₃Sn + Hg Ag₂Hg₃ +Sn8hg+
Ag3Sn
γ γ₂
γ ₁ Β+γ
49. Gamma (γ) = Ag3Sn
Unreacted alloy
Strongest phase and
corrodes the least Forms 30%
of volume of set amalgam
50. Gamma 1 (γ ₁) = Ag2Hg3
Matrix for unreacted alloy and
2nd strongest phase
60% of volume
51. Gamma 2 (γ₂) = Sn8Hg
Weakest and softest phase
Corrodes fast, voids form
Corrosion yields Hg which reacts
with more gamma
10% of volume
Volume decreases with time due
to corrosion
52. Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag2Hg3 + Sn8Hg + Ag-Cu
γ γ ₁ γ₂
ADMIXED HIGH-COPPER
ALLOYS:
Ag dissolves into the Hg from the Ag-Cu alloy
particles.
Both Ag and Sn dissolve into Hg from the Ag-
Sn alloy particles. (same as in low-Cu
alloy)
Sn in solution diffuses to the surface of Ag-Cu
alloy particles and reacts with the Cu to
form the h phase (Cu6Sn5) (therefore,
the Sn7-8Hg or g2 is eliminated
53. Final reaction:
γ₂ η γ ₁
Sn8Hg + Ag-Cu Cu6Sn5 + Ag2Hg3 + Ag-Cu
A layer of η forms around
unconsumed Ag-Cu particles.
γ ₁ phase is the matrix.
The final structure composes of
the γ phase, Ag-Cu particles γ₁
matrix, and η reaction layers.
54. SINGLE COMPOSITION HIGH-COPPER
ALLOYS:
Ag3Sn + Cu3Sn + Hg Ag2Hg3 + Cu6Sn5 +Ag3Sn + Cu3Sn
γ γ ₁ γ
η є
Phases found in each single-
composition alloy particle are
γ (Ag3Sn), and є (Cu3Sn).
η crystals are found as
meshes of rod crystals at the
surfaces of alloy particles, as
well as dispersed in the
matrix.
γ₂ is eliminated.
55. • Ease of use, Easy to manipulate
• Relatively inexpensive
• Excellent wear resistance
• Restoration is completed within one sitting
without requiring much chair side time.
• Well condensed and triturated amalgam has
good compressive strength.
ADVANTAGES
56. • Unnatural appearance (non esthetic)
• Tarnish and corrosion
• Metallic taste and galvanic shock
• Discoloration of tooth structure
• Lack of chemical or mechanical adhesion to the tooth
structure.
• Mercury toxicity
• Promotes plaque adhesion
• Delayed expansion
• Weakens tooth structure (unless bonded).
DISADVANTAGES
57.
58. ADA specification No.1 for amalgam lists following
physical properties as a measure of quality of the
amalgam:
1. Strength
2. Creep
3. Dimensional changes
4. Modulus of elasticity
59. A) COMPRESSIVE STRENGTH:
Amalgam is strongest in compression & much weaker in
tension & shear.
When subject to a rapid application of stress either in tension or
compression a dental amalgam does not exhibit significant
deformation or elongation & as a result functions as a brittle
material.
High copper single composition materials have the highest
early compressive strength of more than 250 MPa at 1 hr.
While it is lowest for the low copper lathe cut alloy (145 MPa).
STRENGTH:
60. High values for early compressive strength are advantage for
an amalgam, because they reduce the possibility of fracture by
application of prematurely high occlusal forces by the patient
before the final strength is reached.
The compressive strength at 7 days is again highest for the
high copper single composition alloys, with only modest
differences in the other alloys.
Tooth preparation should be done in such a way that they are
subjected to more of compressive stresses and less of tensile
stresses.
The compressive strength of a satisfactory amalgam
restoration should be at least 310 MPa
61. COMPRESSIVE STRENGTHS OF LOW-
COPPER AND HIGH COPPER AMALGAM
Amalgam Compressive strength (MPa)
1 hr 7 days
Low copper 145 343
Admixed 137 431
Single
composition
262 510
62. B) TENSILE STRENGTH
Amalgam is much weaker in tension.
Tensile strengths of amalgam are only a fraction of their
compressive strengths
Cavity design should be constructed to reduce tensile stresses
resulting from biting forces
High early tensile strengths are important – resist fracture by
prematurely applied biting forces.
Both low & high copper amalgams have tensile strength that
range between 48-70 MPa
63. TENSILE STRENGTHS OF AMALGAM
Amalgam Tensile strength – 24 hrs
(MPa)
Low copper 60
Admixed 48
Single composition 64
64. Creep is defined as time dependent strain or deformation
produced by stress (Phillips)
Creep of dental amalgam is a slow progressive permanent
deformation of set amalgam which occurs under constant
stress (static creep) or intermittent stress (dynamic creep)
Creep is related to marginal breakdown of low copper
amalgams
Higher the creep, the greater is the degree of marginal
deterioration (ditching)
It is measured after the amalgam has set.
CREEP AND FLOW
65. Severe contraction leads to plaque accumulation &
secondary caries
Expansion leads to postoperative pain & splitting of
tooth
If amalgam expanded during hardening, leakage
around the margins of restorations would be
eliminated.
Largest dimensional change -19.7µg/cm- low cu
lathe cut alloy.
Lowest -1.9µm/cm – high cu admixed alloy.
DIMENSIONAL CHANGE
66. High copper alloys tend to be stiffer than low
copper alloys
When rate of loading increased, values of approx
62 Gpa have been obtained
MODULUS OF ELASTICITY:
67.
68. Historically, the only way to achieve smooth & plastic amalgam
mixes was to use an amount of mercury considerably in excess
than that is final restoration.
But due the deleterious effects of mercury, manipulative
procedures were employed to reduce the amount of mercury.
Two techniques were employed for achieving this,
By squeezing/ wringing
amalgam into cloth.
Through
condensation of
69. Thus the most obvious method was to reduce the original
mercury/alloy ratio.
This is known as MINIMAL MERCURY TECHNIQUE/ EAMES
TECHNIQUE.
The Eames technique suggests, mercury and alloy in the ratio of 1:1.
Conventional – lathe cut alloys require 50% mercury, where as
modern high copper i.e. spherical alloys require relatively less
amount of mercury i.e. about 42%
Spherical alloys have lower volume and less surface tension hence
require less mount of mercury to wet the particles.
70. To use the appropriate amount of mercury and alloy a wide variety
of mercury and alloy dispensers are made available:
• Automatic
mechanical mercury
dispensers.
• Pre-weighed pellets.
71. • Pre-proportioned capsules
Now-a-days widely used.
These contain pre-proportioned aliquots of alloy &
mercury.
Also called as pre-capsulated amalgam.
72. They are further available as:
• Reusable capsules
These are available with Friction fit & screw cap lids
73. Newer SELF ACTIVATING CAPSULES have been
developed that allow mercury to enter into the
compartment within the first few oscillation of
amalgamator.
74. Advantages of pre-proportioned capsules:
Convenient to use.
Eliminates the chance of mercury spill.
Disadvantages:
Expensive
Cannot make minor adjustments in the ratio
for personal preference.
75. Trituration
Process of mixing the amalgam alloy particles with mercury.
Earlier it was done by hand trituration
A mortar and a pestle was used for this purpose.
The inner surface of the mortar was roughened to increase
friction
Usually a period of 25-40 seconds is enough for mixing.
The pressure applied was about 2-3psi.
76. mulling
• It is a continuation of trituration.
It increases the homogeneity of mass to get a
single consistent mix.
• Can be accomplished as follows:
1. During hand trituration:
• By kneading the plastic amalgam mix in a
piece of rubber dam.
2. During mechanical trituration:
• By triturating the mix in a pestle free capsule
for 2-3 seconds after the specified time.
77. Refers to the incremental placement of the amalgam into
the prepared cavity and compression of each increment
into the others.
Amalgam should be condensed into the cavity within 3
min after trituration.
condensation
78. Aims of Condensation:
Adapt amalgam to the margins, walls and line angles of the
cavity.
Minimize voids and layering between increments within the
amalgam.
Develop maximum physical properties.
Remove excess mercury to leave an optimal alloy: mercury
ratio.
Purpose of Condensation:
To get a continuous homogenous mass that is well adapted to
all margins, walls and line angles.
Best carried out using hand instruments.
79. Hand condensation:
Hand condensers are used for this purpose.
Irregular shaped alloys –
Condensers with relatively small tip, 1 to 2 mm
High condensation forces in vertical direction
As much mercury-rich mass as possible should be removed
Spherical amalgam alloys-
Condensers with large tips are used.
Condensed in lateral direction
80. Mechanical condensation:
Mechanical condensers are used for this purpose.
Useful for condensing irregular shaped alloys when high
condensation forces are required.
Less fatiguing to the dentist.
Need was eliminated with the advent of spherical alloys.
Tend to lead to unreliable
production of heat and
mercury vapor,
both of which are undesirable.
82. CONDENSATION PRESSURE –
A force of 15 lb i.e. 66.75 N is recommended to be applied to
each increment.
Where as it is seen that practitioners apply a force of only 3-4
lb i.e. 17.8 N
83. burnishing
First Burnishing (Pre-carve Burnishing):
It is a continuation of condensation.
Carried out using a large burnisher for 15 seconds
Use light force and move from the centre of the restoration
outwards to the margins.
Advantages of pre-carve burnishing:
Increases adaptation of amalgam to the cavity walls and
margins.
Brings the mercury to the surface.
84. carving
Using remaining enamel as a guide, carve gently from
enamel towards the centre and recreate the lost anatomy
of the tooth.
Amalgam should be hard enough to offer resistance to
carving instrument
A scarping or "ringing" (amalgam crying)
should he heard.
If carving is started too soon, amalgam will
pull away from margins.
85. Objectives of carving :
To produce:
A restoration with no overhangs
A restoration with the proper physiological contours.
A restoration with minimal flash.
A restoration with adequate, compatible marginal
ridges.
A restoration with proper size, location, extend and
interrelationship of contact areas.
86. Final Burnish (Post carve burnishing)
Following carving, check the occlusion and carry out a brief
final burnish.
Use a large burnisher at a low load and burnish outwards
towards the margins
Improves smoothness
Heat generation should be avoided
If temp raises above 60C, causes release
of mercury accelerates corrosion &
fracture at margins
87. Finishing can be defined as the process, which continues
the carving objectives, removes flash and overhangs and
corrects minimal enamel undercuts.
Polishing is the process which creates a corrosion resistant
layer by removing scratches and irregularities from the
surface.
Can be done using descending grade abrasive, eg. rubber
mounted stone or rubber cups.
A metallic lustre, is always done with a polishing agent
(precipitated chalk, tin or zinc oxide).
Finishing & polishing
88. Objective of finishing and polishing :
• Removal of superficial scratches and irregularities
Advantages:
• Minimizes fatigue failure of the amalgam
• Minimizes corrosion
• Prevents the adherence of plaque
Should be done 24 hours after insertion, however, some new alloys
can be polished after 8-12 hours still others require only a 30-
minute wait after insertion
91. DIMENSIONAL
CHANGE
When mercury is combined with amalgam it undergoes three
distinct dimensional changes:
Stage -1
• Initial contraction, occurs
in the first 20 mins.
• Occurs due to the
dissolution of alloy
particles in mercury.
• Severe contraction leads
to plaque accumulation
& secondary caries
Stage -2
• Expansion- this occurs
due to formation and
growth of the crystal
matrix around the
unconsumed alloy
particles.
• Expansion leads to
postoperative pain &
splitting of tooth
Stage -3
• Limited delayed
contraction.
92. 16.6% of restorations fail- expansion.
The impingement of growing crystals one on another will cause
outward forces which will result in some expansion (crystal
growth pressure)
If sufficient Hg is present to produce a plastic matrix, expansion
occurs as a result of growth of γ ₁ crystals & vice versa
According U.S Bureau of standards a dimensional change on
setting, value of 5 - 10µm allowable.
expansion
93. Dr Grey - 1920
Takes place after 24 hours. Zinc containing amalgam when
contaminated with moisture during trituration or condensation
can result in delayed expansion.
This expansion can be for 3-5 days to months reaching values
greater than 400µm
Also called as secondary expansion.
Hydrogen is produced by the electrolytic action involving zinc
and water which does not combine in amalgam but rather
collects within the restoration increasing the internal pressure
causing amalgam to expand.
Zn + H2O ZnO + H2
DELAYED EXPANSION:
94. COMPLICATIONS DUE TO DELAYED EXPANSION ARE:
Protrusion of the entire restoration out of the cavity.
Increased micro leakage space around the restoration.
Restoration fracture.
Such pain may be experienced 10-12 days after the insertion
of the restoration.
95. Surface discolouration on a metallic
surface without the loss of structure. (
sulphide layer)
It depends on oral environment and type
of alloy.
In case of low copper alloys, gamma
phase is responsible.
For high copper alloys, eta and Ag-Cu
eutectic are responsible.
Does not cause any detrimental effect on
the amalgam
tarnish
96. Actual deterioration of metal by reaction with its environment.
Tin oxychloride is the corrosion product formed.
Excessive corrosion can lead to:
Increased porosity.
Reduced marginal integrity.
Loss of strength.
Release of metallic products in to the oral
environment.
corrosion
97. Types of Corrosion:
1. Galvanic corrosion:
• Dental amalgam is in direct contact with an adjacent metallic
restoration such as gold crown
2. Crevice Corrosion:
• Local electrochemical cells may arise whenever a portion of
amalgam is covered by plaque on soft tissue.
• The covered area has a lower oxygen and higher hydrogen ion
concentration making it behave anodically and corrode.
3. Stress Corrosion:
• Regions within the dental amalgam that are under stress
display a greater probability for corrosion, thus resulting in
stress corrosion.
• For occlusal dental amalgam greatest combination of stress
and corrosion occurs along the margins
98. Corrosion products from the tin in γ 2 phase include tin
oxychloride.
Due to corrosion, mercury gets released.
This mercury then reacts with unreacted gamma particles and
produces additional γ 1 and γ 2 phases which results in some
expansion called as MERCUROSCOPIC EXPANSION.
This results in porosity and reduction in strength.
Corrosion on surface of amalgam restorations usually occurs to a
depth of about 100 – 500 micrometres.
Phosphate buffering ability of saliva is known to inhibit this
process and provide protection against corrosion.
99. SELF SEALING ABILITY OF AMALGAM
Though corrosion and corrosion products are
detrimental to a restoration, it is advantageous in
amalgam restorations.
Since amalgam doesn’t bond to the tooth, the corrosion
products seal the amalgam and tooth interference.
This is seen more in low copper amalgam than high
copper amalgam.
101. To compensate for some of the disadvantages presented by amalgam a
clinical technique that bonds amalgam to enamel and dentin was
introduced by Baldwin as long back as 1897.
Advantages:
• It permits more conservative cavity preparations because it does
not require additional mechanical retention.
• It reduces marginal leakage to minimum.
• It reinforces weakened tooth structure
• It reduces the incidence of postoperative sensitivity
• It reduces the incidence of marginal fracture.
Disadvantages:
• Expensive
• Time consuming
• Technique sensitive
BONDED AMALGAM RESTORATIONS :
102. GALLIUM – AN ALTERNATIVE TO
AMALGAM:
As early as 1956, Smith and Caul and co-workers claimed that a gallium
based alloy could serve as a possible alternative to dental amalgam.
They found that mixing gallium with either nickel or copper and tin
produced a pliable mass that could be condensed into a prepared cavity,
which, after setting, had physical properties suitable for a restorative
material.
Commercial brands are: Galloy, Bayswater, Gallium GF, Gallium GF II
Disadvantages:
• Handling characteristics of this alloy is unfavourable.
• High level of corrosion
• Dimensional change of 21.5%.
• Poor biocompatibility.
• Expensive
103. 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
restoration interface.
RESIN COATED AMALGAM:
104. Fluoride, being cariostatic, has been included in amalgam to deal
with the problem of recurrent caries associated with amalgam
restorations.
It was proposed by Innes and Youdelis in 1966, Serman in 1970 and
Stone in 1971
Several studies concluded that a fluoride containing amalgam may
release fluoride for several weeks after insertion of the material in
mouth.
The fluoride release from this amalgam seems to be considerable
only during the first week.
The problem with this method is that the fluoride is not delivered
long enough to provide maximum benefit.
FLUORIDATED AMALGAM :
105. Powell et al in 1989 added pure indium powder with high
copper alloy and triturated it with mercury.
A significant decrease in mercury evaporation was seen.
Youdelis found that less mercury is required for mixing
amalgam when 10% Indium is present.
Johnson GH et al : indium containing high copper alloy
exhibited low creep and increase in strength.
INDIUM CONTAINING AMALGAM :
106. One amalgam substitute being tested is a consolidated silver alloy
system developed at the National Institute of Standards and
Technology.
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.
The 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.
CONSOLIDATED SILVER ALLOY SYSTEM:
107. An experimentation was done which involved discarding the mercury
content of amalgam and replacing it with a silver solution and unsialinized
titanium dioxide ceramic nanoparticles for strength, with a favourable,
easy to manipulate consistency.
Prepared maxillary premolar controls were filled with amalgam and
compared to an experimental group filled with the novel material.
Both groups were then thermocycled, cross-sectioned, and studied
through scanning electron microscopy (SEM).
It was concluded that the addition of the silver solution and ceramic
nanoparticles to mercury-free regular-set alloy yielded a product that
exhibits improved marginal adaptation with less application of
condensation pressure, when compared to regular-set amalgam
MERCURY FREE AMALGAM:
108. Dental amalgam has served as an excellent and versatile restorative
material for many years.
Although there is evidence of a decrease in its use in the world,
amalgam’s cost, durability and ease of manipulation have persuaded
many dentists to continue to use it as their first choice for restoring
posterior teeth.
There is still no adequate economic alternative for dental amalgam.
Amalgam will probably disappear eventually, but its disappearance will
be brought about by a better and more esthetic 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.
Conclusion:
109. REFERENCES:
J Conserv Dent. 2010 Oct;13(4):204-8. Dental amalgam: An update
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march
2001
Mertz-Fairhurst EJ, Curtis JW, Jr, Ergle JW, Rueggeberg RA, Adair SM.
Ultraconservative and cariostatic sealed restorations: Results at year 10. J
Am Dent Assoc. 1998;129:55– 66.
Summitt JB, Burgess JO, Osborne JW, Berry TG, Robbins JW. Two year
evaluation of amalgam bond plus and pin-retained amalgam restorations
(abstract 1529) J Dent Res. 1998;77:297.
Bharti R, Wadhwani KK, Tikku AP, Chandra A. Dental amalgam: An update.
Journal of conservative dentistry: JCD. 2010 Oct;13(4):204.
PHILLIPS’ Science of Dental Materials;11th ed Kenneth J. Anusavice
CRAIG’s Restorative Dental Materials;12th ed John M. Powers, Ronald L.
Sakaguchi
