Dental amalgam is an alloy used in dental restorations that is a mixture of mercury and other metals such as silver, tin, and copper. It has been used in dentistry since the 1800s. The document discusses the history, composition, manufacturing process, setting reactions, properties and strengths of dental amalgam. It provides details on the phases that form during setting and how composition affects properties such as strength, expansion and corrosion resistance. High copper amalgams have higher strengths compared to low copper amalgams. Proper manipulation of the amalgam is important to achieve optimal strength.

1. DENTAL AMALGAM

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

3. 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)

4. 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”.

5. 1826 : O. Taveau (Paris) – used combination of
Ag & Hg to form silver paste.
1833 : Crawcour Bros. (USA) – Royal Mineral
succedanem.
1843 : Resolution passed by American Society of
Dental Surgeons declaring the use of amalgam
as malpractice – FIRST AMALGAM WAR.

6. 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.
1855 : Elisha Townsend – Ag-Sn-Hg alloy.

7. 1895 : G.V. Black – systematic study on
properties & manipulation of amalgam & its
relation to cavity preparation.
1926 : 2nd AMALGAM WAR – Dr. A. Stock became
poisoned with Hg through 25 years of exposure.
1930 : ADA specification No.1 for amalgam
revised in 1934, 1960 & 1970.

8. 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%)

9. 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

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

11. 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

12. 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

13. 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%

14. 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

15. 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 .

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

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

18. 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 &
Sn forms.
• Point C  intermetallic compound Ag3Sn 
forms by peritectic reaction

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

20. • Sn rich alloy  less expansion than Ag rich
• Alloys without Zn  more brittle & less
plastic
• Indium & palladium, < 1%  enhances
physical, mechanical & corrosion resistance

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

22. 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 
phase retained.

23. 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.

24. Particle Treatment
 Related to preferential dissolution of specific
components from alloy.
 Acid washed powder  More reactive
 Stress induced during ball milling relieved
otherwise  causes changes in alloy
characteristics
 Stress relief  Annealing cycle  100°C
several hrs  Stable in reactivity  increased
shelf life

25. 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

26. 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

27. SETTING REACTIONS
LOW COPPER
 On trituration Sn & Ag dissolve into Hg .
 Hg has limited solubility for Ag 0.035 wt% & 0.06
wt% for Sn .
 When solubility exceeds, crystals of 2 binary metallic
compds. ppt. into Hg .
 These are body centered cubic Ag2Hg3 (1) & hexagonal
Sn7Hg ( 2) .
 Solubility of Ag< Sn Therefore, 1 ppt.

28.  After trituration - alloy powder coexists with
liquid Hg - plastic consistency of mix .
 Remaining Hg dissolves alloy particles (Ag-Sn)
covered with newly formed 1 crystals - Rxn.
rate decreases  alloy hardens .
 Hg insufficient to completely consume alloy 
unconsumed particles present in set amalgam .
 Low Cu amalgam  unconsumed particles
embedded in 1 & 2 phases .
 Alloy particles ( β +  )+ Hg - 1 + 2 +
unconsumed alloy.

30.  Dominating phase in well condensed low copper amalgam is  1 (54
% - 56%) ; unreacted alloy (27%-35%) &  2 (11% - 13%) .
 More the unconsumed alloy , more strong the amalgam .
 Weakest phase   2  least stable in corrosive environment
 Interface between  & 1 matrix important .
  phase strengthens amalgam when bound to matrix .
  > 1 >  2 .

31. HIGH COPPER -- ADMIXED
 Mixture of lathe cut low Cu alloy & spherical .
 Amalgam made from this alloy stronger .
 Ag – Cu particles + Ag – Sn particles  strong fillers  increase
residual alloy + decrease matrix  strengthening amalgam matrix
increase resistance to marginal breakdown
 30 wt. % - 55 wt. %  spherical high Cu alloy
 Ag Cu alloy  2 phases
- Ag rich
- Cu rich

32. • Admixed alloy + Hg :
- Ag dissolves in Hg
from Ag – Cu alloy
- Ag + Sn dissolves in
Hg from Ag - Sn alloy
• Sn in solution diffuses to surface of Ag-Cu
particles
• Sn + Cu  Cu6 Sn5 ( phase)
• Layer of  crystals forms around
unconsumed Ag-Cu alloy particles

33. • 1 forms simultaneously with  phase
• Alloy particles (ß+) + Ag-Cu Eutectic + Hg
 1 +  + unconsumed alloy of both types
of particles
• 2 eliminated & replaced by  therefore Sn
not available for reaction
• To accomplish this net Cu concentration at
least 12% in alloy powder.

34. Single Composition
Phases found are :
• Ag – Sn (ß)
• Ag3 Sn ()
• Cu3 Sn ()
• Cu6 Sn5 ()
• On trituration :- Ag & Sn phase dissolves in
Hg
• Little Cu dissolves in Hg
• 1 crystals grow  binds together partially
dissolve alloy partilces

35. •  crystals – meshes of rod like crystals at
surface of alloy particles and in matrix
• Difference of solubility of Ag, Sn & Cu in Hg
plays an important role
• Solubility of Hg in Sn 170 times more than
Cu & 17 times more than Ag
• i.e. Sn more soluble than Ag, Ag more
soluble than Cu & Cu least soluble in Hg

36. DIFFERENCE BETWEEN LOW Cu & HIGH Cu
Have irregular shapes Have spherical smooth
surface
Made by milling Produced by atomization
Requires more mercury for
mixing & have poor
properties
Requires less mercury &
have better properties
Mix is less plastic & heavy
condensation pressures
Mix is more plastic and is
not sensitive to
condensation pressure

37. 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

38. Initial Contraction
 Alloy – Hg mixed  contraction results
 Hg absorbed  inter particular spaces of
alloy
 Reaction continues – alloy dissolves in Hg
become smaller ; 1 phase grows
 Contraction continues as growth of 1
continues ; this continues in the first
20min
 As 1 grows they impinge against one
another
 Impingement of 1 tends to oppose
contraction

39. Expansion
 Sufficient Hg present provides plastic mix
 Expansion occurs when 1 crystals impinge
upon one another
 Rigid 1 matrix formed - growth of 1
cannot force matrix to expand
 1 crystals grow into interstices containing
Hg ; consuming Hg & providing continued
reaction
 Low Hg/alloy ratio & high condensation
pressure favours contraction
 Procedures that accelerate setting &
consumption of Hg favours contraction
 Measurement of dimensional change of
modern amalgam reveal net contraction

40. Mercuroscopic Expansion
 Interface between matrix and  phase
important
 Unconsumed  phase not strengthen
amalgam unless bound to matrix
 Expansion of amalgam at margins
promoted by Hg released from 2 phase
 This Hg re-react with  phase 
mercuroscopic expansion

41. Delayed contraction
 After rigid 1 matrix formed growth of 1
cannot force matrix to expand
 1 crystals grow into interstices
containing Hg
 This leads delayed contraction mass 
absorption of unreacted Hg
Factors favouring contraction :
• Low Hg / alloy ratio
• High condensation pressure  squeezes
out Hg

42. • 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

43. STRENGTH
 ANSI / ADA specification No.1 for amalgam
alloy minimum allowable compressive
strength 1hr after setting when a
cylindrical specimen is compressed at a
rate of 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

44. Measurement of Strength
 Under compressive stress using specimens
of dimension comparable to the volume of
typical amalgam restoration
 Satisfactory amalgam strength  310MPa
 When manipulated properly 7 day
compressive strength  more than 310MPa
 Tensile stresses easily produced
 Amalgam cannot withstand high tensile /
bending stresses

45. 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

46. Factors affecting strength
 Trituration
- Over trituration or under trituration
decreases strength of both old &
new high Cu alloys
- Maximum strength achieved when
mixing continue till coherent mass of
matrix with interfaces formed

47. - Further trituration  cracks in
crystals & interfaces  drop in
strength of set amalgam
 Effect of Hg content
- Sufficient Hg mixed in alloy  each
alloy particle wetted thoroughly
otherwise dry granular mix  rough
pitted surface
- If sufficient Hg not present 
insufficient matrix formation 
decreased strength
- Hg/ alloy ratio 48-52 %

48.  Effect of Condensation
- Lathe cut  increased condensation
required to squeeze out Hg
- Increase condensation pressure 
decrease porosity & increased
strength
- Spherical alloy  light condensation
pressure to reach adequate strength
 Porosities
- Cannot be avoided in an
agglomerated mass
- Result in area of stress concentration
; propagation cracks ; corrosion &
fracture of restoration

49. 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%

50. Influence of microstructure on creep
 1 exert primary influence on low Cu
amalgam creep rates
 Creep increases with 1 vol. fractions &
decreases with larger 1 grain size.
 2  higher creep rates

51. Effect of Manipulative variables on Creep
 Hg / alloy ratio minimized
 Condensation pressure maximized for lathe
cut or admixed
 Timing of trituration

52. 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.

53. - Reduce original Hg / alloy ratio (Eames
Tech/Minimal Hg Tech) [1:1]
• Sufficient Hg provides coherent
plastic mass
• Hg content of finished restoration
comparable to original Hg alloy
ratio
• Usually 50% with lesser amounts
with spherical alloys
• Technique reduces contact and
contamination with metallic Hg

54. 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
 Recommended ratio for lathe cut alloys  1:1
(50% Hg)
 Recommended amount of Hg for spherical
alloys  42%
 If Hg content low mix dry & grainy with
insufficient matrix
 Wide variety of Hg & alloy dispensers
available

55. • Dispensers based on volumetric
proportioning
• Pre-weighed pellets or tablets
• Disposable capsule
 Hg is measured by volume
 Dispenser held vertically

56. 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  Trituration
traditionally Mortar & Pestle were used.
 Mechanical device amalgamator saves
time & standardizes procedure

57.  Amalgamator:3 speeds :- Low- 3200 to 3400
Medium-3700 to 3800
High – 4000 to 4400
Principle of Operation
• Capsule serves as a mortar
• Cylindrical metal / plastic piston – pestle
• Alloy & Hg dispensed into capsule
• Capsule secured in machine & turned on
• Arms holding capsule oscillate – trituration
accomplished
• Automatic timer for control of mixing time

59.  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

61. 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.

62. CONSISTENCY
 Attainment of a proper mix controlled by
timing trituration
 Grainy Mix  under triturated
Mixing Variables
 Under mixing
• Appears dull
• Crumbly and grainy in consistency
• Rough surface after carving
• Mercury in excess/ hardens rapidly
• Strength is less
• Prone to tarnish and corrosion

63.  Over Triturated
• Wet & plastic
• Difficult to remove from capsule
• Working time decreased
• Sets rapidly
• Increased contraction & increased creep
• Decrease strength

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

65. 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)

66. • Irregular shaped alloy – small tip
condenser (1-2mm) increased
condensation force – vertical direction
• Spherical alloy – large tip condenser-
lateral direction condensation & vertical
with vibration
• Admixed alloy  small – medium, medium
to high force & vertical & lateral direction

67. 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

68. • 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

69. 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

70. 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

72. 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

73. • Burnishing alone not provide scratch free &
retention free surface
• Slow speed handpieces  finishing &
polishing amalgam
• Restoration surface finished initially with
fine prophylactic paste applied with cotton
pellet / non ribbed rubber cup  light
pressure
• If amalgam hardened
- Contour with slow speed green
stones or diamond bur, brown &
green rubber points
- Mixture of fine pumice & water /
alcohol with a rotary brush or
felt wheel

74. 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. Zn can produce ZnO layer on the
occlusal surface
 Corrosion  chemical or electrochemical
process by which metal undergoes actual
deterioration by reaction with environment

75. Corrosion of Amalgam
 2 phase most prone phase to corrosion
whereas 1 phase is resistant
 Low copper
- 2 reaction product  penetrate
matrix because of intercrystaline
contacts between blades  corrosion
proceeds from the outside amalgam,
along crystals connecting new
crystals at intercrystaline contacts

76. - 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

77.  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

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

79. 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

80. • Collects within restoration; increases
internal pressure  amalgam to creep 
expansion
• Starts 3 – 5 days after placing restoration
• Reaching values greater than 400µ (4%)
• Contamination occurs any time during
manipulation & insertion
• Severe expansion cause pressure on pulp
 severe pain
• Pressure centered can go upto 2000 lb/sq
inch

82. Marginal Ditching
 Secondary expansion  throughout clinical
life of an amalgam
 On non-occlusal surface entire restoration
may appear extruded.
 On extruded surface the abrasion and
attrition tend to limit the overall extrusion.
 Occlusal margins become fracture
susceptible ledges elevated from natural
contours of enamel
 Extrusion at margins is promoted by
electrochemical corrosion (Mercuroscopic
expansion)

83.  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’

84. 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

85. 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

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

88. 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

89. 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

90. 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

91. 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

92. 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

93. 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

94. 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’

95. 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% .

96. 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

97. 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

98.  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 .

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