Amalgam modified/cosmetic dentistry courses

DENTAL AMALGAM
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INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

CONTENTSCONTENTS
1. INTRODUCTION .1. INTRODUCTION .
2. HISTORY .2. HISTORY .
3. CLASSIFICATION & COMPOSITION .3. CLASSIFICATION & COMPOSITION .
4 . MODE OF SUPPLY4 . MODE OF SUPPLY
5 .5 . METALLURGIC PHASES.METALLURGIC PHASES.
6. MANUFACTURE .6. MANUFACTURE .
7. SETTING REACTIONS.7. SETTING REACTIONS.
8. PROPERTIES.8. PROPERTIES.
9. MANIPULATION .9. MANIPULATION .
10. FAILURE OF RESTORATIONS .10. FAILURE OF RESTORATIONS .
11. MERCURY TOXICITY .11. MERCURY TOXICITY .
12. DEVELOPMENTS IN AMALGAM .12. DEVELOPMENTS IN AMALGAM .
13. BONDED AMALGAM RESTORATIONS .13. BONDED AMALGAM RESTORATIONS .
14. CONCLUSION14. CONCLUSION ..

INTRODUCTION
“Amalgam” derived from Greek word
“Emolient” which means paste.
Amalgam is an alloy of 2 or more metals in
which one of the constituents is essentially Hg.
Dental amalgam is an alloy of Hg, Ag, Cu &
Sn which may contain Zn, Pd & other elements
to improve handling characteristics & clinical
performance. (Kenneth. J. Anusavice)

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HISTORY
1800 : (France) – D’ Arcets mineral cement
– 1st
dental amalgam alloy of Bi, Pb, Sn & Hg
plasticized at 100°C
1818 : Regnert – Increased amount of Hg &
lower plasticizing temp to 68°C.
1819 : Bell (Eng) – First use of - room
temperature mixed amalgam “Bell’s Putty”.

1843 : Resolution passed by American Society of
Dental Surgeons declaring the use of amalgam
as malpractice – FIRST AMALGAM WAR.
1845 : Amalgam pledge adopted by the same
society.

1855 : 1st amalgam war ended by breakup of
society
In late 1800’s improved amalgams of
Elisha Townsend, J.F. Flag & G.V. Black – widely
used.
1926 : 2nd
AMALGAM WAR – Dr. A. Stock became
poisoned with Hg through 25 years of exposure.

1963 : Innes & Youdelis – High Cu alloy
1973 : Dr. Olympio Pinto 1981 : Dr. H.A. Higgins
3rd
AMALGAM WAR.
Dr. Pinto held a variety of diseases from
leukemia to bowel disorders – mimicked by
patients reaction to Hg.
1977 : ANSI – Specification No.1 for amalgam
reapproved as No.1 a in 1985.

CLASSIFICATION
I. Based on No. of alloyed materials
 Binary : Ag – Sn
 Ternary : Ag – Sn – Cu
 Quarternary : Ag-Sn-Cu-In
II. Based on Cu content
 High Cu (6-30%)
 Low Cu (Less than 6%)

III. Based on Zn content
 Zn free (less than 0.01%)
 Zn containing (0.01% or more)
IV. Based on Powder Particle size
 Microcut
 Fine cut
 Coarse cut

v.v. Based on composition .Based on composition .
 Unicomposition (Same chemical composition )Unicomposition (Same chemical composition )
 Admixed (spherical eutectic high Cu + lathe cutAdmixed (spherical eutectic high Cu + lathe cut
low Cu) .low Cu) .
VI. Based on shape of powdered particles .VI. Based on shape of powdered particles .
 Spherical.Spherical.
 Lathe cut .Lathe cut .
 Spheroidal.Spheroidal.

VII. Based on addition of noble metals
 Palladium
 Gold
 Platinum
 Indium
VIII. Based on generation
1st
Generation – 3 parts Ag +1 part Sn (Peritectic)
2nd
Generation–3 parts Ag+1 part Sn+Cu + 1% Zn

3rd Generation – blending spherical Ag-Cu
(Eutectic) to original powder
4th
Generation – Alloy Cu to Ag & Sn upto 29%
ternary alloy
5th
Generation - Ag + Cu + Sn + In
6th
Generation – Alloy Pd (10%), Ag (62%) &
Cu(25%) to 1st
, 2nd
, 3rd
generation

COMPOSITION
1. Low Cu alloy : Ag - 65%
Sn - 29%
Cu - 2 – 5% (< 6%)
Zn - 0 – 2%
2. High Cu alloy :
Admixed
Ag - 65 – 70%
Sn - 17%
Cu - 9 – 20%
Zn - 1 – 2%

Single composition
Ag - 60%
Sn - 27%
Cu - 13 – 30%
Zn - 0 - 2%
Functions of Individual Alloying Metals
1. SILVER
• Whitens alloy
• Decreases Creep
• Increases strength
• Increases setting expansion
• Increase tarnish corrosion
• Decrease setting time

2. TIN
• Decreases setting expansion
• Decreases Strength
• Decrease tarnish resistance
• Increases setting time
3. COPPER
• Decreases brittleness
• Increases hardness
• Increases setting expansion
4. ZINC
• Scavenger
• Increases plasticity
• Decreases tarnish & corrosion
• Prevents oxidation of alloy during
manufacture .

5. PALLADIUM
Increases hardness
• Whitens alloy
6. MERCURY
• Sometimes present in alloy powder in
range of 2 – 3% - PRE AMALGAMATED
ALLOY

MODE OF SUPPLY
 Bulk powder
 Alloy & Hg in disposable capsules
 Pre-weighed alloy as tablets
 Pre-proportioned capsules

METALLURGIC PHASES OF AMALGAM
Silver Tin Alloy
• Silver (73%), Tin (27%) cooled below
480°C  inter metallic compound Ag3Sn is
formed
• Concentration
of Sn < 26%
ß1 phase  solid solution of
Ag & Hg forms.
• Point C  intermetallic compound Ag3Sn 
forms by peritectic reaction

Influence of Ag-Sn phase on amalgam
• In the range of compositions around γ
phase increase or decrease in Ag influences
amount of ß or γ phase & properties of alloy
• If silver content > 73%  setting time
shortened
• If Sn content >27%  mixture of γ phase &
Sn rich phase formed
• Sn7 Hg phase lacks corrosion resistance,
weakest phase

MANUFACTURE
Lathe Cut Powder
Annealed ingot of
alloy  Milling
machine / lathe  cutting
tool / bit.
Chips  needle like
 ball milling

After heating  ingot brought to room temp.
Ingot withdrawn rapidly & quickly quenched 
phase distribution unchanged.
Ingot cooled slowly  proportion of phase
continue to adjust towards room temp equilibrium
ratio.
Ag. Sn : Rapid – Quenching – Maxm amount of ß
phase retained.
Slow cooling  maxm. Amount of
γ
phase retained.

Homogenizing Anneal
Rapid cooling ingot  cored structure
contains non homogenous grains.
Homogenizing Heat treatment  Re-
establishes equilibrium phase relationship.
Ingot–Oven– heated at a temp below solidus.
Time of heat treatment varies but 24 hr at selected
temperature is not unusual.

Atomized Powder
 Melting together desired
elements
 Liquid metal atomized into
fine spherical droplets ; If
droplets solidify before hitting
the surface  Spherical
 Given heat treatment
 Washed with acid

Particle size
 Controlled by manufacturer
 Average particle size = 15 – 35 µm
 Small particle size : increase surface area/vol
increase amount of Hg
 Small average particle size  more rapid
hardening of amalgam  great early strength
 Particle size distribution affects character of
finished surface

SETTING REACTIONS
LOW COPPER
 On trituration Sn & Ag dissolve into Hg .
 Hg has limited solubility for Ag 0.035 wt% & 0.6
wt% for Sn .
 When solubility exceeds, crystals of 2 binary metallic
compds. ppt. into Hg .
 These are body centered cubic Ag2Hg3 (γ1) & hexagonal
Sn7Hg ( γ2) .
 Solubility of Ag< Sn Therefore, γ1 ppt.

HIGH COPPER --HIGH COPPER -- ADMIXEDADMIXED
 Mixture of lathe cut low Cu alloy & spherical .Mixture of lathe cut low Cu alloy & spherical .
 Amalgam made from this alloy stronger .Amalgam made from this alloy stronger .
 Ag – Cu particles + Ag – Sn particlesAg – Cu particles + Ag – Sn particles  strong fillersstrong fillers  increaseincrease
residual alloy + decrease matrixresidual alloy + decrease matrix  strengthening amalgam matrixstrengthening amalgam matrix
increase resistance to marginal breakdownincrease resistance to marginal breakdown
 30 wt. % - 55 wt. %30 wt. % - 55 wt. %  spherical high Cu alloyspherical high Cu alloy
 Ag Cu alloyAg Cu alloy  2 phases2 phases
-- Ag richAg rich
-- Cu richCu rich

Single Composition
Phases found are :
• Ag – Sn (ß)
• Ag3 Sn (γ)
• Cu3 Sn (ε)
• Cu6 Sn5 (η)
• On trituration :- Ag & Sn phase dissolves in
Hg
• Little Cu dissolves in Hg
• γ1 crystals grow  binds together partially
dissolve alloy partilceswww.indiandentalacademy.comwww.indiandentalacademy.com

PROPERTIES
1. Dimensional Change
Theory of Dimensional Change
During setting amalgam undergoes 3
distinct successive dimensional changes
 Stage I : Initial contraction
 Stage II : Expansion
 Stage III : Contraction

Initial Contraction
 Alloy – Hg mixed  contraction results
 Hg absorbed  inter particular spaces of
alloy
 Reaction continues – alloy dissolves in Hg
become smaller ; γ1 phase grows
 Contraction continues as growth of γ1
continues ; this continues in the first 20min

Expansion
 Sufficient Hg present provides plastic mix
 Expansion occurs when γ1 crystals impinge
upon one another
 Rigid γ1 matrix formed - growth of γ1
cannot force matrix to expand

Mercuroscopic Expansion
 Secondary expansion  throughout
clinical life of an amalgam
Expansion of amalgam at margins is also
promoted by Hg released from γ 2 phase .
This Hg re-reacts with gamma phase 
MERCUROSCOPIC EXPANSION

Delayed contraction
 After rigid γ1 matrix formed growth of γ1
cannot force matrix to expand
Factors favouring contraction :
• Low Hg / alloy ratio
• High condensation pressure  squeezes
out Hg

• Smaller particle size  more surface area
• Longer trituration time  particles made
smaller
• Greater traces of Sn in alloy
Factors favouring expansion
• Greater Ag – increased expansion
• Greater Cu - increased expansion
• More Hg / alloy ratio

STRENGTH
 ANSI / ADA specification No.1 for amalgam
alloy minimum allowable compressive
strength 1hr /0.25mm/min is 80MPa
 Lack of strength to resist masticatory
forces  inherent weakness
 Most common fracture of amalgam 
margins (Marginal Breakdown) Hastens
corrosion & lead to 2° caries

Compressive Strength
 Most favourable strength characteristic
 1 hr & 7 day compressive strength for
amalgam
Amalgam 1hr 7 day
Low Cu 145 343
Admix 137 431
Single comp. 262 510

Factors affecting strengthFactors affecting strength
 Trituration
Effect of Hg content
- Hg/ alloy ratio 48-52 %
Effect of Condensation
Porosities

CREEP
Significance on amalgam performance
 Creep rate correlate with marginal
breakdown of low Cu amalgams
 Creep rate of high Cu amalgams 0.4%
 Creep rate below 3% specified in
ANSI/ADA specification No.1
 Creep rate of low Cu amalgam range
between 0.8 – 8%

MANIPULATION
Hg / Alloy Ratio
 To achieve smooth plastic amalgam mixes 
Hg used in excess
 Excess Hg has deleterious effects
 To reduce amount of Hg
- Excess Hg squeezed out
- Increasing dryness technique :
Hg expressed in increasing amounts
from each successive increment with each new
increment serving as a Blotter.

Proportioning
 Amount of alloy & Hg to use  Hg/alloy ratio
 Signifies parts by weight of Hg & Alloy
 Mix of amalgam with Hg/alloy ratio 6:5
contains 54.5% Hg


TRITURATION
Objective of Trituration :
 Attain workable plastic mass
 Rub of oxide films from alloy particles
 To pulverize pellets into particles
 To dissolve alloy in Hg for formation of
matrix crystals
 To keep matrix crystals as small as possible
 Mixing of alloy with Hg.
 Mechanical device

 Amalgamator:3 speeds :- Low- 3200 to 3400
Medium-3700 to 3800
High – 4000 to 4400

 Capsule
- Friction fit
- Screw cap led
 Wide variety capsule pestle combination
available
- One piece construction : No Hg released
 Diameter & length of pestle < dimensions of
capsule

MULLING
 Continuation of trituration causes mix to
cohere
 Mix enveloped in a dry piece of rubber dam
vigorously rubbed of one hand and palm of
another hand for 2 – 5 seconds
 After mechanical trituration mix removed &
triturated in pestle free capsule for 2-3 sec.

CONSISTENCY
 Attainment of a proper mix controlled by
timing trituration
 Grainy Mix
Mixing Variables
 Under mixing
 Over Triturated

 Normal Mix
• Wet & plastic
• Smooth, soft consistency with shiny
surface
• Good strength
• Mix is warm when removed from the
capsule
• Carved surface retain lusture

CONDENSATION
• Compacts alloy so that greatest possible
density attained
• Hg rich amalgam brought on top of each
increment
• Delayed condensation  weaker amalgam
• Good isolation in zinc containing alloy
• Ultrasonic condensers not recommended
• Increases strength, decreases creep
(7-10MPa) www.indiandentalacademy.comwww.indiandentalacademy.com

Hand Condensation
• Never touch with bare hands
• Increments carried & inserted by amalgam
carrier.
• Condenser point forced into amalgam 
avoids voids, adapt to wall
• Shiny surface after condensation of each
increment
• Continued till cavity overfilled

• Well condensed amalgam  proper
consistency of mix
• Larger increment  more difficult adapt
Mechanical Condensation
• Done by automatic device
• Impact type of forces or vibration forces

Condensation pressure :-
• P ∝1/surface area
• Area of condenser point and forced applied
 condensation pressure
• Smaller the condenser greater the pressure
• 3 – 4 lb average force applied – condenser
point 2mm diameter

BURNISHING
• Process of marginal adaptation of amalgam
• Ball burnisher used in light strokes from
amalgam towards tooth surface
• Undue pressure & heat generation avoided
during burnishing

CARVING, FINISHING & POLISHING
• Objective carving  simulate tooth
anatomy
• Prevents over hanging restorations at
proximal surface
• If carving too deep at marginal areas 
fracture
• Amalgam ready for carving soon after
condensation
• Carving proceeds in direction parallel or
slightly towards the margin of tooth

FAILURE OF RESTORATIONS
Tarnish & Corrosion
 Tarnish  process in which a metal surface
loses its lusture and gets discolored
 Surface discoloration  formation of
oxides, sulphides or chloride on the surface.
 Corrosion  chemical or electrochemical
process by which metal undergoes actual
deterioration by reaction with environment

Corrosion of Amalgam
 γ2 phase most prone phase to corrosion
whereas γ1 phase is resistant
 Low copper
- γ2 reaction product  penetrate
matrix because of intercrystaline
contacts between blades  corrosion
proceeds from the outside amalgam,
along crystals connecting new
crystals at intercrystaline contacts

- Penetrating corrosion  generates a
porous, spongy amalgam with
minimum restoration
 High copper
- Sn-Hg particles replaced by Cu-Sn
phase.
- Cu-Sn phase corrosion prone, but less
when compared to Sn-Hg
- In Cu-Sn penetrating corrosion does
not takes place

 Corrosion
- Chemical corrosion (Dry corrosion)
- Electrochemical corrosion (Wet
corrosion)
• Electrochemical corrosion  chemically
different sites act as anode and cathode
• Residual amalgam alloy acts as cathode
whereas Sn-Hg or Cu-Sn acts as anodes

Electrochemical corrosion
 Galvanic corrosion
- Macroscopic
- Microscopic
 Stress corrosion
 Concentration cell corrosion
Average corrosion depth = 100 – 500µm

Delayed expansion (Secondary expansion)
 Associated with Zn amalgam
 Reaction of Zn with water
 Absent in non Zn amalgam
 H2 produced by electrolytic action
involving Zn + H2O
Zn + H2O  ZnO + H2 ↑
 H2 not combines with amalgam

Marginal Ditching
 Most common evidence of degradation
of amalgam is marginal fracture.
 Combination of brittleness, low tensile
strength and electrochemical corrosion 
marginal fracture.
 At some point occlusal stresses of
opposing tooth contact creates local
fractures produces a ditch  marginal
ditching.
Measured on basis of ‘Mahler’s Scale’

Amalgam Blues
 Discolored area seen through enamel in
teeth having amalgam restoration
 Bluish hue results from
- Leaching of corrosion products of
amalgam into the dentinal tubules
- From colour of underlying amalgam
seen through translucent enamel

Amalgam Tattoo
 Macular bluish gray or black lesions on the
buccal mucosa, gingiva or palate, present
in vicinity of teeth with large amalgam
restorations.
 Due to
- Iatrogenic mishap
- Fragments gets deposited from
multiple tooth extractions containing
amalgams

MERCURY TOXICITY
In nature Hg exists in three forms
 Elemental (Hg°)
 Inorganic – Mercurous (Hg+1
) & Mercuric
(Hg+2
)
 Organic – Methyl, ethyl & Phenyl mercury
salts

Hg released from dental restorations
 Hg vapour can be kept low
- Care in preparation of
amalgam.
- Avoiding ultrasonic condensor
- Adequate water spray & high
volume suction during cutting or
polishing.
- Use of rubber dam.
 Magnitude & proportion of the
released mercury level ∝ surface
area of the restoration
 Hg release by high Cu < low Cu.

Safe & Threshold levels of Mercury
 Maximum level of occupational exposure
considered safe is 50mg Hg/m3
of air
 Maximum allowed concentration in blood –
5ng/ml of blood
 Maximum allowed concentration in urine –
15mg/1 to 20mg / 1 of urine
 Threshold value for workers in mercury
industry – 350 to 500mg Hg/m3
of air

ENVIRONMENTAL HAZARDS OF MERCURY
Minamata Disease
 Tragedy of Minamata Bay in the 1950’s .
 Symptoms of Hg poisoning during this
incident were : (1) ataxic gait (2) convulsions
(3) numbness in mouth & limbs (4) difficulty in
speaking

DEVELOPMENTS IN AMALGAM
Gallium Alloys
 Gallium was one of the substitutes
suggested for mercury by Puttkammer
(1928)
 This direct filling material contains no
mercury.
 Based on ability of liquid gallium to wet
surfaces of many solids like Hg, gallium is liquid
at room temperature

Disadvantages
1. Low resistance to corrosion
2. Gallium alloy & high Cu amalgam placed
in oral cavity, galvanic corrosion with
preferential corrosion of gallium alloy.
3. Difficult handling  wetting & adhesive
property
4. Gallium alloy dark residue on gloves
5. High cost

Hg free direct filling silver alloys
 Daniel et al (1994)
 Ag particles suspended in dil. Acid solution
 Physical properties showed higher rupture
strength than amalgam .
 Consolidated silver – cold welded system –
rotary instrument for contouring & finishing

Indium containing alloy & binary mercury –
Indium liquid alloy
 Powell et al in 1989
 Pure indium powder admixed into dispersed
phase high Cu alloy .
 Decrease in mercury evaporation
 As the amount of indium increased from 0 to
14%  decrease in Hg vapour .
 Commercially available in name of
‘Indisperse’

Fluoride containing amalgam
 Innes & Youdelis 1966, Jerman in 1970 &
Stoner et al 1971
- Dilution of salt crystals that are in
contact with cavity wall
- By corrosion that liberates fluorides
contained in the mass of amalgam.
e.g. Fluoralloy – Dentoria SA, France
Low Mercury Amalgam
 In these amalgams, mercury is used as
low as at 15 to 25% .

BONDED AMALGAM RESTORATIONS
 Introduced by Baldwin in 1897
 Condensation of amalgam on to and into
the unset zinc phosphate cement
 Adhesive cements such as zinc
polycarboxylate & GIC, suggested substitutes
for zinc phosphate cement

Advantages
 Conservative preparation .
 Increased fracture resistance of the tooth
 Reduced micro leakage,lower incidence of
recurrent caries, post operative pain
& pulpal damage
 Conservative repair of existing restorations

 In 1986 Varga et al employed 4-META &
Panavia Ex Resin as the intermediate bonding
agents.
 Masaka (1989)  Panvia Ex be abandoned in
in favour of 4 – META .
 “AMALGAMBOND” was developed .

CONCLUSIONCONCLUSION
Amalgam has provided valuable and comparativelyAmalgam has provided valuable and comparatively
inexpensive service to patients longer than anyinexpensive service to patients longer than any
other material available .other material available .
It has many positive attributes andIt has many positive attributes and
remains an important part of dentist’s restorativeremains an important part of dentist’s restorative
resource .resource .
Mercury free alloys are likely to beMercury free alloys are likely to be
available to provide the advantages of amalgamavailable to provide the advantages of amalgam
without environmental concerns about mercury .without environmental concerns about mercury .

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