Amalgam part 1

Amalgam
DR.RACHAEL GUPTA
POSTGRADUATE

Contents
Introduction
History of amalgam
Amalgam wars
Classification
Components of amalgam
Setting reaction
Manufacture of alloy powder
Properties of amalgam
Manipulation of amalgam
Recent advances in amalgam
Side effects of mercury
Conclusion

Introduction
Dental amalgam is one of the most
versatile restorative materials used in
dentistry.
It constitutes approximately 75% of all restorative materials
used by dentists before.
It has served as a dental restoration for more than
165 years.
J Conserv Dent. 2010 Oct;13(4):204-8.
Dental amalgam: An update

No adequate economic alternative for dental amalgam.
The combination of
reliable long-term performance in load bearing situations
low cost
is unmatched by other dental restorative material.

Acceptable
Biocompatibility
Less
technique
sensitive
Cost effective
and long life
AMALGAM POPULARITY

Over the last few years improvements in
composition have led to -
Reduced
marginal
failure due to
decreased creep
and corrosion
Early seal
between
the tooth and
restoration
But development of alternatives based on ceramics and composites , and questions on its safety
have led to its decline

The variables for amalgam’s
appearance
Cavity design &
prepation
Selection of
alloy & its
manipulation
with mercury
Contouring &
finishing
procedures
Age of the
restoration &
its
environment
Amalgam: past,present & future
JADA,Vol.86,April 1973

What is amalgam????
a.mal.gam: any alloy of mercury with any another metal [silver
amalgam is used as a dental filling]
Word amalgam is derived from greek name emolient’ which means paste.
Source: Webster’s New World Dictionary

Dental amalgam is an alloy made by
mixing mercury with a silver tin
amalgam alloy (Ag-Sn)
Amalgam alloy is a silver tin alloy to which varying amounts of
copper(Cu) and small amounts of zinc(Zn) have
been added
Sturdevant’s Art & Science of Operative dentistry..5th ed; 152

INDICATIONS OF AMALGAM
 Moderate to large Class I and Class II restorations.
 Class V restorations in unaesthetic areas especially when
access is limited and moisture control is difficult and for areas
that are significantly deep gingivally.
 Class 3 in unaesthetic areas eg.distal aspect of canine
especially if
Preparation is extensive with minimal facial involvement

CONTRAINDICATIONS OF AMALGAM
 Anterior teeth where esthetics is a prime concern
 Esthetically prominent areas of posterior teeth.
 Small classes I and II restorations that can be well isolated.
 Small class VI restorations

ADVANTAGES OF AMALGAM
Ease of use, Easy to manipulate
Relatively cost effective
ease of placement-excellent wear resistance
prevent marginal leakage after period of time – maintains anatomical forms
Well condensed and triturated amalgam has good compressive strength.
Relatively not technique sensitive.

DISADVANTAGES OF AMALGAM
Unnatural appearance (non esthetic)
Tarnish and corrosion
Metallic taste
Discoloration of tooth structure
Lack of chemical or mechanical adhesion to the tooth structure.
Mercury toxicity
Promotes plaque adhesion

HISTORY OF AMALGAM
A Chinese medical text(Material medica) mentions using a “silver paste”, a type of amalgam,
to fill teeth in the 7th century -by Su Kung in 659 AD
In Europe, J Stokers, a municipal physician in Germany, recommended amalgam as a filling
material in 1528
Later, Li Shihchen (1578) - a dental mixture of 100 parts mercury with 45 parts silver and 900
parts tin
In the 18th century, John Hill, an Englishman, described mercury as, “It penetrates the
substance of all metals, and dissolves, and makes them brittle.”

Dental silver amalgam was probably introduced in
England by Joseph Bell, a British chemist, in 1819, and
was known as ‘Bell’s putty’.
In 1818, Louis Nicolas Regnart, a Parisian physician invented amalgam by the
addition of one-tenth by weight of mercury to another metal or metals.

1833
-- Crawcours brothers introduced their
“Royal Mineral Succedaneum” to America
--mixed shaved French
silver coins and mercury.

In 1877, Foster Flagg published the results of his laboratory tests and 5-year
clinical observation of new alloys with 60% of silver and 40% of tin as major
constituents in 1881 and thus predated by some 15 years the work of G.V.
Black
The universal acceptance of amalgam
as a restorative material resulted from
investigations of G V Black in 1895,
1896, 1908
By combining the principles of cavity design,
extension of the cavity into “immune” areas and the
development of an alloy with the composition of
68.5% silver, 25.5% tin, 5% gold, 1% zinc, Black
advanced amalgams into modern times

Traditional or conventional amalgam
alloys were produced by early dental
manufactures (S S White) &
predominated from 1900 untill 1970.the
basic composition was 65%Ag, 30%Sn,
5%Cu,& less than 1%zinc
ADA specification No 1 was adapted for amalgam in
1929.

Extensive studies of the setting reaction of dental amalgams (Gayler
in 1937) & found that in the coarse filling alloys of that time, copper
contents greater than 6% produced excessive expansion
Gayler ML. Dental amalgams. J Inst Metals. 1937;60:407–19
This was later challenged by Greener in 1970’s
Greener EH. Amalgam-yesterday, today and tomorrow. Oper
Dent. 1979;4:24–35

In 1959, Dr. Wilmer Eames
recommended a 1:1 ratio of
mercury to alloy, thus lowering
the 8:5 ratio of mercury to alloy
that others had recommended.
Eames WB. Preparation and condensation of amalgam with low mercury alloy ratio.
J Am Dent Assoc. 1959;58:78–83

In 1962, a spherical particle dental alloy
was introduced by Innes
This was followed in 1963 by a high copper
dispersion alloy system that proved to be
superior to its low copper
1970’s
• first single composition spherical
• Tytin (Kerr)
• ternary system (silver/tin/copper)
1980’s- mercury free alloys introduced

AMALGAM WARS-the controversy
In 1841, the American Society of Dental
Surgeons declared that
“the use of amalgam constitutes
malpractice”
AMALGAM USE DECLINED
The amalgam controversy-an evidence based analysis ;
JADA,Vol.132,march 2001

1842-a belief prevailed that amalgam exerted “a
influence upon the fluids of the mouth and
gives rise to an unhealthy action in the gums.”
1844- the society’s members were warned that they
were to sign a pledge “NEVER TO USE amalgam” or they
would risk being expelled from the membership

Townsend - gave his personal directions for
preparing the amalgam, known as “Townsend’s
Amalgam”.
In 1858, Townsend reversed his stance on amalgam
and recommended removal of teeth that could not be
saved by gold.

1924 - Alfred Stock became poisoned with mercury & published papers on the
dangers of mercury in Dentistry
1934 - German physicians - no health risk from Amalgams
In December 2003, Dr. Frederick miller, - Amalgam is a SAFE, AFFORDABLE, AND
DURABLE MATERIAL.”

The second amalgam war….
In mid 1920's a German dentist, Professor A. Stock started
the so called "second amalgam war".
He claimed to have
evidence showing that mercury could be absorbed from
dental amalgam, which leads to serious health problems.
He also expressed concerns over health of dentists, stating
that nearly all dentists had excess mercury in their urine

3rd amalgam war in 1980s
It was the Neurobiologist Mats Hanson, Assosiate
professor in physiology at Lund University in
Sweden, who in 1981 started the fight against the
authorities

"Third Amalgam War' began in 1980 primarily
through the seminars and writings of Dr.Huggins, a
practicing dentist in Colorado.
 He was convinced that mercury released from dental
amalgam was responsible for human diseases affecting
the cardiovascular system and nervous system
 Also stated that patients claimed recoveries from
multiple sclerosis, and other
diseases as a result of removing their dental amalgam
fillings.

STATEMENT ON AMALGAM-ADA
"No controlled studies have been published demonstrating systemic adverse effects from amalgam
restorations-FDI & WHO;1997
“based on available scientific information, amalgam continues to be a safe and effective restorative
material.“-ADA;1998
"There currently appears to be no justification for discontinuing the use of dental amalgam.“-
ADA;1998
“The current data are insufficient to support an association between mercury release from dental
amalgam and the various complaints that have been attributed to this restoration material”-LSRO
&FDA;2004
“there were no statistically significant differences in adverse neuropsychological or renal effects
observed over the 5-year period in children whose caries are restored using dental amalgam or
composite materials- Journal of the American Medical Association (JAMA) and Environmental
Health Perspectives;2006
amalgam is a valuable, viable and safe choice for dental patients-ADA;2009
material is a safe and effective restorative option for patients-FDA;2009

Classification of Amalgam
A) According to the number of Alloyed
Metals
Number
of
alloyed
metal
Binary alloy
(Ag-Sn)
Tertiary
alloy
(Ag-Sn-
Cu)
Quarternary
alloy
(Ag-Sn-
Cu,indium)
Sturdevant’s Art & Science of Operative Dentistry;
5th ed

B) According to shape of powdered particle
Lathecut
-irregular shapes
Spherical-
smooth surface spheres
Admixed
5th ed

C) According to copper content
Low copper
amalgam(<0-6%)
High copper
amalgam(>6-
13%)
5th ed

D)According to zinc content
Zinc containing
alloy
(>0.01-2%)
Non zinc
containing alloy
(<0-0.01%)
5th ed

1st generation
2nd generation
3rd generation
4th generation
5th generation
6th generation
E)Generations based on the
improvement in composition
was that of G. V Black i.e. 3
parts silver one part tin (peritectic alloy).
3 parts silver, 1 part tin, 4% copper. 1 % zinc,
First generation + Spherical amalgam –
copper eutectic alloy
Adding copper upto 29% to original
silver and tin powder to form ternary alloy. So that tin is
bounded to copper.
Quatemary alloy i.e. Silver, tin, copper
and indium.
(consisting eutectic alloy).
Marzouk-operative dentistry

Composition of amalgam
Conventional Amalgam Alloys: (G.V. Black’s:
Silver- tin alloy or Low copper alloy).
 Low copper alloys are available as (Lathe -cut and Pulverized) and
spherical particles.
Low copper composition:
 Silver : 63-70%
 Tin : 26-28%
 Copper : 2- 5%
 Zinc : 0-2%

Components of dental amalgam
Other
Zinc
Indium
Palladium
Silver Tin
Copper Mercury
Basic
Phillip’s Science of Dental Materials;11th ed

Silver(Ag)
Decreases creep & setting time
Decreases corrosion
Increases hardness & edge strength
Increase tarnishing

Tin(Sn)
Low strength
Larger contraction
Decreases expansion
Increased corrosion
Increased plasticity
Increased setting time

Copper(Cu)
Decreases plasticity
Increases hardness strength of alloy
Reduce creep
Reduce tarnish & corrosion

Zinc(Zn)
Decreases brittleness
Acts as a deoxidizer
Less marginal breakdown

Indium(In)
decreases surface tension
• reduces amount of mercury
necessary
• reduces emitted mercury vapor
reduces creep and
marginal breakdown
increases strength
example
• Indisperse (Indisperse Distributing
Company)
• 5% indium*
operative dentistry journal1992 Sep-Oct;17(5):196-202
• Palladium (Pd)
– reduced corrosion
– greater luster
Mahler J Dent Res 1990

Palladium pellets placed in an amalgam
restoration were effective in reducing the
amount of mercury vapor released in the
7 days following placement.
Dental Materials Volume 15, Issue 6, November 1999, Pages 382-389
The optimal palladium content in γ1 seems to be in
the range between 0.50 and 0.75 wt%.
Biomaterials, Volume 18, Issue 13, July 1997, Pages 939-946

Mercury (Hg) - only pure metal that is liquid
at room temperature

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
 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.

Admixed alloy powder:
 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.
Admixed alloy powder:
Composition:
Silver-69 %
Copper-13 %
Tin-17 %
Zinc-1 %

 Amalgam made from these powders are stronger than amalgam made from lathe cut low copper
alloys because of strength of Ag-Cu eutectic alloy particles.
 Ag-Cu particles probably act as strong fillers strengthening the amalgam matrix.
 Total copper content ranges from 9-20%.
Single composition alloy
(Unicomposition):
It is so called as it contains particles of same composition.
Usually spherical single composition alloys are used.
1. Ternary alloy in spherical form, silver 60%, tin 25%,
copper 15%.
2.Quaternary alloy in spheroidal form containing Silver:
59%, copper 13%, tin: 24%, indium 4%.

AMALGAMATION REACTION/ SETTING
REACTION
Low copper conventional amalgam alloy
 Dissolution and precipitation
 Hg dissolves Ag and Sn from alloy
 Intermetallic compounds
formed
Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg
gamma gamma gamma 1 gamma 2

3
• Gamma () = Ag Sn
– unreacted alloy
– strongest phase and corrodes the least
– forms 30% of volume of set amalgam
– Occupy maximum space in volume of restoration
1
• Gamma 1 ( ) = AgHg2 3
– matrix for unreacted alloy and 2nd strongest
phase
– Most resistant to tarnish and corrosion
– 60% of volume
CRAIG’s Restorative Dental Materials;12th ed

 Gamma 2 (2) = Sn8Hg
 weakest and softest phase
 corrodes fast, voids form
 10% of volume
 volume decreases with time due to corrosion

High copper admixed alloy
2. Sn8Hg + AgCu 
(2)
Cu6Sn5 + Ag2Hg3 + Ag3Sn
( ) (1 ) ( )
1. Ag3Sn + AgCu + Hg  Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu
( ) (1 ) (2 ) ( )
Initial reaction
Final reaction

Eta () phase
 Strength the bond betwwen alloy particles and gamma 1 phase
 Interlocks gamma1 phase thus improving amalgam resistance to
deformation
 Resistance to tarnish and corrosion

High copper
unicompositional alloy
Ag3Sn + Cu3Sn + Hg  Cu6Sn5 + Ag2Hg3
( ) (  ) (  ) (1 )
Epsilon –reduces creep, and prevent formation of gamma 2 phase

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 lathe-cut to produce the particles, ball-
milled to reduce their size
The particles are 60-120µm in length, 10-70µm in width
& 10-35µm in thickness(Irregular in shape)
Manufacture of alloy powder
Ll athe cut alloy powder
Materials science for dentistry;9th ed
B.W.Darvell

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
Materials science for dentistry;9th ed
B.W.Darvell
Spherical alloy powder

PARTICLE SIZE
• Greater amount of
mercury to form an
acceptable amalgam
Tiny particles
• More rapid hardening
and a greater early
strength
Small-to-
average
particle size
• A rough surface
• Corrosion
Larger
particles

Properties of amalgam
contains certain requirements:-
1. Maximum creep value of 3%
e
2. Minimum Compressive strength of 80 MPa at 1 hr
when a cylindrical specimen is compressed at a rot
of 0.25mm/minute
• ADA specification No.1 for amalgam alloy
3. Dimensional change between 5 min & 24 hrs after
trituration, should fall within a range of ±20µm/cm
at 37 ̊C.

DIMENSIONAL CHANGES
Stage -1: Initial contraction, occurs for about 20 minutes after beginning of
trituration. Contraction results as the alloy particles dissolve in mercury.
Contraction, which occurs, is no
greater than 4.5 μcm.
Stage -2: Expansion- this occurs due to formation and
growth of the crystal matrix around the unconsumed
alloy particles.
Stage -3: Limited delayed contraction. Absorption of
unreacted mercury
Marzouk 0operative dentistry
Properties
When mercury is combined with amalgam it undergoes three distinct dimensional changes
Dimensional change between 5 min & 24 hrs
after trituration, should fall within a
range of ±20µm/cm at 37 ̊C.

Immediately after packing a rapid
contraction may be observed, followed
by a slower expansion, and then a slight
& slower contraction(amalgam setting
dimensional change curve
20µm 20µm 20µm 20µm
Materials science for dentistry;9th ed B.W.Darvell

If amalgam expanded during hardening,
leakage around the margins of
restorations would be eliminated.

Factors that affect the dimensional changes:
1) Particle size and shape:
 More regular the particle shape, more smoother the surface area.
 Faster and more effectively the mercury can wet the powder particles and faster amalgamation
occurs in all stages with no apparent expansion.
2) Mercury:
 More mercury , more will be the expansion, as more crystals will grow.
 Low mercury: alloy ratio favors contraction
3) Manipulation:
During trituration, if more energy is used for manipulation, the smaller the particles will become
mercury will be pushed between the particles, discouraging expansion.
More the condensation pressure used during condensation, closer the particles are brought
together; more mercury is expressed out of mix inducing more contraction.

Moisture contamination (Delayed Expansion):
 Certain zinc containing low copper or high copper amalgam alloys which get contaminated by
moisture during manipulation results in delayed expansion or secondary expansion
 This expansion usually starts after 24 hrs, reach at peak within 3-5 days & may continue for months
reaching values >400µm
 Zinc reacts with water, forming zinc oxide and hydrogen gases.
Complications that may result due to delayed
expansion are:
 Protrusion of the entire restoration out of the cavity.
 Increased micro leakage space around the restoration.
 Restoration perforations.
 Increased flow and creep.
 Pulpal pressure pain.
Such pain may be experienced 10-12 days after the
insertion of the restoration

STRENGTH
A) Compressive strength
• Amalgam is strongest in compression and weaker in
tension and shear
The prepared cavity design and manipulation should
allow for the restoration to receive compression forces
and minimum tension and shear forces.
The compressive strength of a satisfactory amalgam
restoration should be atleast 310 MPa.

Compressive Strengths of Low-Copper
and High Copper Amalgam
Amalgam Compressive Strength
(MPa)
1 h 7 day
Low copper 145 343
Admix 137 431
Single
Composition 262 510

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

Product Tensile strength (Mpa)
15min 7 days
LOW COPPER ALLOYS
a) Lathe cut
b) spherical
3.2 51
4.7 55
HIGH COPPER ALLOYS
a) Admixed
b) Unicompositional
3.0 43
8.5 56
Tensile strengths of amalgam

Factors affecting strength
- depends on the type of amalgam alloy, the
trituration time & the speed of amalgamator
- either under or overtrituration decreases
the strength in both traditional & high
copper amalgams
1) Effect of trituration

2) Effect of mercury content
dry granular
mixrough & pitted
surfacecorrosion
high mercury
contentmore γ2
phase
low mercury
contentmore
unreacted AgSn
particlesimparts
strength to
restoration
sufficient mercury should be
mixed with the alloy to wet
each particle of the alloy
Introduction
History
Amalgam wars
Classification

-in lathe cut alloys, higher condensation pressure
results in higher compressive strength,
particularly the early strength(at 1 hr)
-on the other hand spherical amalgams condensed
with lighter pressures produce adequate
strength
3) Effect of condensation

-voids & porosities reduces strength
-porosity is caused by:-
a. decreased plasticity of the mix (due to
low Hg/alloy ratio, delayed
condensation, undertrituration)
b. inadequate condensation pressure(results in
inappropriate adaptation at the margins &
increase number of voids)
4) Effect of porosity

-amalgams do not gain strength as rapidly as
might be desired
-at the end of 20min,compressive strength may
be only 6% of 1 wk strength
-ADA stipulates a min of 80MPa at 1 hr
5) Effect of rate of
hardening

-the 1 hr compressive strength of high Cu
single composition amalgams is relatively
high compared with admixed high Cu
amalgams
-patients should be cautioned not to
subject the restoration to high bitting
stresses for atleast 8 hrs after placement
,by that time a typical amalgam has
reached at least 70% of its strength

even after 6 months ,some
amalgams may still be increasing in
strength, suggesting that the
reactions between matrix phases
& the alloy particles may continue
indefinitely

CREEP
• Defined as time dependent strain or deformation
produced by stress(as in Phillips)
Time dependent plastic deformation
When a metal is placed under stress, it will undergo plastic
deformation.

• Higher the creep, the greater is the degree of
marginal deterioration(ditching)
• According to ADA sp. No.1 creep should
be below 3%
• creep values:-
-low copper amalgam:0.8-8%
-high copper amalgam:0.1-1%

Factors influencing creep:
Large 1 volume fraction
Larger 1 grainsizes
smaller 1 grainsizes
2 associated with high
creep rates.
Phases of
amalgam
restorations
High CREEP Low CREEP
 phase which act as
barrier to deformation of
1 phase in single
compositional
Materials science for dentistry;9th ed B.W.Darvell0

For increased strength & low creep values:-
Mercury alloy ratio should be minimum
Condensation pressure should be
maximum for lathe cut or admixed alloys
Careful attention should be given towards
timing of trituration & condensation
Effect of manipulative variables

Thermal expansion
coefficient E 10-6 / C
Thermal conductivity
K 10-6 /C(mm2/s)
Amalgam 22-28 9.4
Composite resin 20-60 0.25
GIC 10-11 0.15-0.35
Tooth 11.4 0.18-0.47
E = volume expansion for unit rise in temperature
K = quantity of heat passing per s through a block of unit thickness
and cross sectional area for a temp. difference of 1C

CHEMICAL PROPERTIES
Dental amalgam restorations undergo both
chemical and electrochemical corrosion.
TARNISH AND CORROSION

The degree of tarnish depends on :
i. The oral environment
ii. The type of alloy used

In dental practice , a limited amount of corrosion
around the margins of amalgam restorations may
be beneficial, since the corrosion products tends to
seal the marginal gap & inhibit the ingress of fluids
& bacteria
But excessive corrosion can lead to increased
porosity, reduced marginal integrity, loss of
strength & the release of metallic products into
the oral environment

•Occurs most notably on the
occlusal surface and produces a
black amalgam silver tarnish film
•Corrosion products are mainly
oxides and chlorides of tin.
Chemical Corrosion :

Electrochemical corrosion
Chemically different sites act as anode or
cathode.
Electrolyte (saliva)
The anode corrodes, producing soluble and
insoluble reaction products.
Ag2Hg3 phase has the highest corrosion resistance,
followed by Ag3Sn, Ag-Cu, Cu3Sn, Cu6Sn5 and Sn7-8Hg.

The average depth of corrosion for most
amalgam alloys is 100-500 m.
Most corrodible phase is tin-mercury or 2
phase
Even though, a relatively small portion (1-13%)
of the amalgam mass consists of the 2 phase,
in an oral environment, the structure of such an
amalgam will contain a higher percentage of
corroded phase

The corrosion results in the formation of tin oxychloride,
from
the tin in 2 and also liberates Hg.
Sn7-8Hg + 1/202 + H2O +Cl-  Sn4 (OH) 6 Cl2 +
Tin oxychloride
Hg
( Mercuroscopic Expansion )

THE HIGH COPPER ADMIXED AND
UNICOMPOSITION ALLOY
•No 2 phase in the final set mass.
•The η phase formed with high copper alloys is not an
interconnected phase such as the 2 phase, and it has better
corrosion resistance.
• η phase is the least corrosion resistant phase in high
copper amalgam - corrosion product CuCl2.3Cu (OH)2
Cu6Sn5 + 1/202 +H2O + Cl-  CuCl2.3Cu (OH)2 +SnO.

• Surface tarnish of low copper amalgams is
more associated with γ than γ1 phase,
whereas in high copper amalgams surface
tarnish is related to the copper rich phases,ή
& silver-copper eutectic

Local electrochemical cells may arise
whenever a portion of amalgam is covered
by plaque on soft tissue. It behaves
anodically and corrodes. If these occur in
cracks or crevice, it is called crevice
corrosion.
•Regions 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.
Crevice Corrosion:
Stress Corrosion:

Factors related to excess tarnish & corrosion
High residual
mercury
Surface texture-
small scratches &
exposed voids
Contact of
dissimilar metals,
eg. gold & amalgam
Moisture
contamination
during
condensation
Type of alloy-low cu
alloy>high cu alloy

• Smoothening & polishing the
restoration
• Correct mercury/alloy ratio & proper
manipulation
• Avoid dissimilar metals including
mixing of high & low copper amalgams
Corrosion of amalgam can
be reduced by:-

Cavity preparation of amalgam
 Class 1 cavity preparation of amalgam
Narrow occlusal table – buccolingual dimension of cavity is
reduced
0.5mm pulpal to DEJ
Maximum intercuspal width should be minimum
Walls should be parallel or slightly convergent
Outline form should limit to the central pit, its buccal and
lingual grooves and triangular fossa
Pulpal floor should be flat or slightly concave
Total depth of the cavity – 1.5
All pits and fissures should be included
Intercuspal width
Kennedy’s operative pediatric dentistry 4th edition

Steps:
External outline form
Start preparation with a no.330 bur, perpendicular to occlusal
surface- mesial to distal
Include all deep and defective grooves
Contour the outline parallel to mesial and distal marginal ridges
Width of cavity – 1/3rd intercuspal width
Internal outline form
0.50 mm into the dentin – 330 bur
Round line angles – no.330 bur
Converging walls
Sharp cavosurface angle – 169L bur

Common errors in Class I
amalgam restorations
1. Preparing cavity too deep
2. Carving the anatomy of amalgam too deep
3. Undercarving that leads to fracture
4. Not including all susceptible fissures

Class II amalgam
Depth: This should be 0.5 mm below dentino-
enamel junction or 1.5 mm from the cavosurface
(i.e.. 'a'.)
Isthmus: This should be between 1/4 of the inter
cuspal distance (approximately 1.5 mm)
All the internal angles should be rounded
Pulpal floor: Pulpal floor should be slightly
concave.
Buccal and lingual walls: should be converging so
making the cavity retentive. Also, the cavosurface
angle needs to be a right angle to ensure
maximum strength at the enamel-amalgam
junction.
Gingival floor: should be located just below the
contact area with the adjacent tooth. But
supragingivally. Kennedy’s operative pediatric dentistry 4th edition

Axial wall: The width of the floor of the box should
be approximately 1 mm. follows external contour of
tooth.
Buccal and lingual walls: These should be
convergent, parallel to the appropriate external
surface and make a cavo surface angle of 90
degree.
Axio-pulpal line angle: This should be rounded
which gives the maximum thickness of amalgam
with the minimum of stress in this area.

Tuesday,
June26,
2018
PROXIMAL BOX OF DECIDUOUS TEETH
• Box converges occlusally
• Minimal flare to prevent weakening of enamel
walls
• Isthmus 1/4th to 1/5th inter cuspal
width
•Rounded axio-pulpal angle grooved to
increase retention
•No bevel in gingival seat
•Depth minimal to prevent pulp
exposure at cervial constriction
•Wide gingival floor

Mesiodistal view of correct class 2 preparation

DIAGRAM ILLUSTRATING THE INCREASED DANGER OF
PULP EXPOSURE WHEN THE GINGIVAL WALL IS
CARRIED TOO DEEPLY

Kennedy (1997) contraindicated the idea of dovetail
lock, as in primary teeth occlusal fissures are
prepared which produces curved shape that provides
retention.
Rodda recommended 1mm depth of cavity because
the distance between the mesial surface of
mandibular 1st molar and pulp horn is only 1.6 mm.

Messer and Levering reported that SSCs placed in 4 your old and younger children showed a
success rate approximately twice that of class II amalgam restoration up to 10 years.
Roberts and Sherriff reported that after 5 year, one third of class II amalgams placed in primary
teeth had failed or required replacement, whereas only 8% of SSCs required retreatment.
Paul S. Casamassimo, Henry W. Fields Jr., Dennis J. McTigue, Arthur Nowak. Pediatric
Dentistry: Infancy through Adolescence.5th edition. Saunders: Elsevier ; 2013

Class 3 cavity preparation
Primary incisor teeth: when contact areas are open
Outline form- triangular with base at gingival aspect
Buccal and lingual wall parallel to external surface of tooth to meet an apex
Pear shaped bur used to prepare cavity
Gingival cavity wall –incline slightly occlusally
-parallel to enamel rods
-undercut for mechanical retention
Cavity depth 0.5 pulpal to DEJ

 If contacts are closed
For aesthetic access is from palatal surface
Dovetail /lock–aid in retention of restoration
-dovetail should extend middle of the tooth -resistance to lateral displacement
Interproximal areas – c shaped letter when observed
Open end of C should meet retentive lock/dovetail
Inclination of incisal and gingival towards incisal edge llal to enamel rods
Primary canine teeth
Palatal lock – maxillary canine
Facial lock – mandibular canine (depend on biting forces)

Class 5 cavity preparation
 Kidney shaped; gently curved outline form acceptable
 Sharp outline form at mesial and distal margins
 No.330 bur used cut cavity
 Dentinal undercuts are given for mechanical retention

Problems with amalgam restorations:
Accounts for anatomic or morphologic structural characteristics.
Fracture of isthmus in Class II amalgam restorations
Marginal failure in the proximal box, due to excessive flare of the cavosurface
angle
Failure to remove all caries or to extend the cavity into caries susceptible areas

Differences in amalgam cavity preparation in primary and
permanent tooth
Primary tooth Permanent tooth
Intercuspal width should not more
than one third
One forth or 1.5 mm
Cavity depth : 1.5 mm Minimulm: 1.5 to 2 mm
Proximal box
•No gingival bevel
•Gingival floor incline occlussaly
•Retentive groove is not indicated
Proximal box:
•Gingival bevel should be given
•Gingival floor is perpendicular to
axial wall
•Retentive groove for secondary
retention form
Width of proximal box : 1mm Proximal box should be 0.2- 0.8 mm
in dentine

Differences in amalgam and composite cavity
preparation in primary and permanent tooth
Amalgam composite
Outline form Include the fault and adjacent
suspicious areas
Include fault but do not
extend to the adjacent
suspicious areas
Pulpal depth Minimum 1.5 1-2 pulpal floor usually not uniform
Axial depth 0.2 to 0.5 mm inside Dej Only extent of the defect, not uniform
Cavosurface
marginal
90 degree 90 degree
Primary retention
form
Occlusal dovetail and convergence Etching and bonding
Secondary
resistance
Box shape cavity, groove, slots,
locks
Grooves only large or root surface preparations.
Box for large cavity
Pulp protection Varnish, base Dentine boding
agent

REFERENCES
• PHILLIPS’ Science of Dental Materials;11th ed Kenneth J.
Anusavice
• CRAIG’s Restorative Dental Materials;12th ed John M.
Powers, Ronald L. Sakaguchi
• Materials science for dentistry;9th ed B.W.Darvell
• Sturdevant’s Art & Science of Operative Dentistry; ed; Roberson,
Heymann, Swift
• fundamentals of operative dentistry, a contemporary approach; 3rd
ed
Summitt, Robbins, Hilton, Schwartz
• Essentials of operative dentistry; I Anand
Sherwood
• Marzouk operative dentistry
• Kennedy’s opediatric operative dentistry

• Dental amalgam: An update
J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208
• The amalgam controversy-an evidence based analysis ;
• Effect of admixed indium on the clinical success of amalgam restorations
. operative dentistry journal1992 Sep-Oct;17(5):196-202
• American Dental Association (ADA) Council on Scientific Affairs, “Statement on dental amalgam,”
2011,
• Dental Materials Volume 15, Issue 6, November 1999, Pages 382-389
• Biomaterials, Volume 18, Issue 13, July 1997, Pages 939-946
• Journal of Endodontics
Volume 9, Issue 12 , Pages 551-553, December 1983
• Corrosion sealing of amalgam restorations -in vitro study Oper Dent.
2009 May-Jun;34(3):312-20.

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