2. AMALGAM
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.
Phillips’ Science of dental materials, 11/e Anusavice.
3. HISTORY
• 1800’s – mineral cement – first dental amalgam
• First use of room temp mixed amalgam- Bell in England
1819 (Bell’s putty) and Taveau in France (1826) –
advocated a mixture of silver and mercury as a filling
material – produced amalgam by grinding silver coins with
mercury.
• 1833 – Introduction of Royal Mineral Succedaneum to USA
as substitute for gold – Crawcour Brothers
• 1848 – AMALGAM WAR
• 1860’S -1870’S – Elisa townsend and Flagg did a lot of
work to improve Dental Amalgam
4. HISTORY
• 1920 – Dr Grey – Delayed expansion
• 1926 – ADA sp no 1 assigned to amalgam
• 1926 - Second amalgam war – Europe – as a result of
the writings of Alfred Stock, a prof of Chemistry – 25
years of exposure – published papers on the dangers of
mercury vapor. But he used Cu amalgam tablets that
were heated up and produced a significant amount of
mercury on top that vaporized readily.
• 1960 – Eames proportion
Mackert JR. Dental Amalgam and mercury. JADA 1991;122:54-71.
5. HISTORY
• 1963 – Innes and Youdelis – High Cu admixed alloy
• Current controversy – termed Third amalgam war – due
to writings of Dr Hal Huggins – 1973
• 1979 – Gay and workers found mercury vapor in breath
of patients with amalgam fillings following chewing
Mackert JR. Dental Amalgam and mercury. JADA 1991;122:54-71.
6. ADA SPECIFICATION
• SPECIFICATION NO. 1 FOR ALLOY FOR DENTAL
AMALGAM, APPROVED BY ANSI IN 1977.
• ANSI/ADA STANDARD NO. 6—DENTAL MERCURY:
1987 (REAFFIRMED 2005)
7. ADA SPECIFICATION NO.1
• Amalgam alloys should contain silver and tin
(predominantly)
• Copper, zinc, gold and mercury (unspecified amounts)
• Alloys which contain in excess of 0.01% of zinc –
zinc containing alloy
8. Creep
(Max %)
Comp Strength of 1
Hour
(Min/Mpa)
Dimensional
Changes between 5
MIN & 24 Hours
(Range %)
3.0 80 + 20µm/cm
• ADA allows small quantities of mercury to be
present in the alloy
- Pre amalgamated alloys
Phillips’ Science of dental materials, 11/e Anusavice.
9. ADA SPECIFICATION NO.6
• Should be triple distilled and pure
• The contaminants should be less than 0.02% of non-
volatile residue
• Dull surface of mercury is suggestive of contamination.
Phillips’ Science of dental materials, 11/e Anusavice.
10. Alloy Composition
• True dental amalgam science began in 1896 by
G.V.BLACK
• COMPOSITION:
• Silver – 65%
• Tin - 29%
• Copper – 6%
• During 1970s many amalgam alloys containing 6-
30% of Cu developed.
11. Property of Individual
Component
PROPERTY INGREDIENT
Silver Tin Copper Zinc
Strength Increases Decreases Increases
Resistance
to corrosion
Increases
Decreases
Hardness Increases
Expansion Increases Decreases Increases
Flow Decreases Increases Decreases
Color Imparts
Setting time Decreases Increases Decreases
Workability Increases Increases
Cleanliness Increases
12. METALLURGICAL PHASES IN
DENTAL AMALGAM
Phases in Amalgam Alloys Stoichiometric Formula
γ (Gamma) Ag3Sn
γ1 Ag2Hg3
γ2 Sn7-8Hg
ε (Epsilon) Cu3Sn
η (Eta) Cu6Sn5
Silver Copper eutectic Ag-Cu
13. METALLURGICAL PHASES IN
DENTAL AMALGAM
• Body centered cubic γ1 has mercury to silver ratio 3:2.
• while hexagonal γ2 phase has mercury tin ratio 1:6.
• Majority of the mercury in set amalgam is in the γ1
phase and minority is in γ2 phase.
• 30% of set amalgam is unreacted γ phase particles
14. Tensile strength of phases of amalgam
Phases in Amalgam Alloys Tensile strength (Mpa)
γ (Gamma) 170
γ1 30
γ2 20
Amalgam 60
15. Ag-Sn Phase
• The more silver rich β phase is crystallographically
similar to γ phase but is a solid solution of silver and
tin.
• If Sn > 26.8%, - leads to formation of more of γ2 phase
that lacks corrosion resistance and is the weakest
component of dental amalgam.
• If Sn < 26%, β phase forms – detrimental to the final
properties of amalgam
Craig,s Restorative Dental Materials, 12/e
16. CLASSIFICATION
Based on the particle shape
1. Lathe cut powder
2. Spherical alloy powder
3. Admixed alloy powder
Based on copper content
1. Low copper alloys – less than 6%
2. High copper alloys – 13 – 30 %
Based on zinc content
1. Zinc containing alloys – 0.01%
2. Non – zinc containing alloys – less than 0.01%
17. PRODUCTION OF SILVER
ALLOY – LATHE CUT
• Metal ingredients heated and protected from oxidation
until melted.
• An annealed ingot of the alloy powder is reduced in a
lathe and ball milled.
• Homogenizing heat treatment done to reestablish the
equilibrium phase.
• Ingot is placed in an oven, heated to a temperature
below the solidus temperature to allow diffusion of the
atom to occur and reach an equilibrium.
• Time - generally atleast for 24 hours.
• Allowed to cool to room temperature.
• Slow cooling results in more formation of gamma phase
Phillips’ Science of dental materials, 11/e Anusavice.
18. PRODUCTION OF SPHERICAL
ALLOY – Atomization
Desired elements
melted together to
form molten alloy
Sprayed under high
pressure of inert gas
through a fine crack in a
crucible into a large
chamber
Depending on the difference in the surface energy
of molten alloy and inert gas, the alloy may be
spherical or somewhat irregular
If the droplets solidify before hitting the
surface the spherical shape is maintained.
Spherical particles
size varies from 15-
35µm
Craig,s Restorative Dental Materials, 12/e
20. TREATMENT
• Acid washed – Preferential dissolution of specific
components – acid washed powders more reactive than
unwashed powders.
• Aging is basically a stress relief process and makes it
stable in its reactivity and property for indefinite period
of time – improves shelf life - involves annealing cycle
of several hours at approximately 100 ̊C
• Generally done by heating them 60 to 100 ̊c for 1 to 6
hours
21. Amalgamation Reaction –
Low Copper Alloys
• During the reaction, the formation of body centered
cubic form of Ag2Hg3 and hexagonal Sn7-8Hg occurs.
22. • γ1 forms first and then γ2
• Alloy is mixed with mercury in the ratio of 1:1
• Mercury is insufficient to completely consume the
alloy particles
24. ADMIXED ALLOYS
• 1963 innes and youdelis added silver copper
eutectic alloy particles ( 71.9% of Ag and 28.1%
Cu) to lathe cut low copper alloys
• The AgCu particles acts as strong fillers in
strengthening the amalgam matrix.
• contains 30 to 55% of spherical powder.
• copper content - 9 to 20%
25. • Ag from AgCu Eutectic, Ag and Sn from the
AgSn alloy dissolves in the Hg.
• The Sn in solution diffuses to the surface of the
AgCu eutectic, reacts with Cu to form the η phase
(Cu6Sn5).
• η phase forms around the unconsumed AgCu alloy
particles.
• γ1 is formed simultaneously and surrounds the η
covered Ag Cu particles and the unreacted AgSn
lathe cut particles
• γ1 is the matrix phase which binds the
unconsumed alloy particles
• γ2 is actually formed along with η phase but is
eliminated during hardening for which we need net
28. UNICOMPOSITIONAL ALLOYS
• Usually Spherical in nature
• Cu Content 13 – 30 %.
• Initially γ1 phase is formed
• Very little Cu dissolves in Hg.
• The γ1 crystals grow forming a matrix that binds the
partially dissolved alloy particles.
• The η particles are formed at the surface of the alloy
particles.
• These η particles are much larger than the η crystals of
the admixed alloy
29. Two kinds of η crystals are formed
1. Polyhedral crystals between the unconsumed particles
2. Meshes of η rod particles which cover the unconsumed
particles. These meshes of η crystals strengthen the bond
between the alloy particles, γ1 phase and η crystals. η
crystal interlock between the γ1 grains. This interlocking
improves the amalgam resistance to deformation.
30.
31. • γ + ε (Cu3Sn)+Hg γ1 + η + Unreacted γ
and ε
• γ2 phase is eliminated in both admixed and spherical
alloy
33. DIMEMSIONAL CHANGE
• Ideally an amalgam with no change in dimension and
stable throughout is preferred.
• Expansion
• Contraction
34. DIMEMSIONAL CHANGE
• Its is measured between 5 – 24
hours after beginning of
trituration with an equipment
accurate to measure 0.5µ AT
37 ̊C
• Value - + 20µ/cm
35. • INITIAL CONTRACTION - Alloys dissolve in
mercury and becomes smaller in size.
• This is due to the initial volume of silver mercury
being more than the final volume of gamma 1 phase.
• EXPANSION - γ1 is formed and impingement of γ1
produces an outward pressure
• Once a rigid matrix of γ1 is formed the growth of
γ1 crystals cannot force the matrix to expand.
36. FACTORS FAVOURING
CONTRACTION
• Less mercury content
• Higher condensation pressure
• Longer trituration time which hastens the
reaction
• Smaller particle size.
37. DELAYED EXPANSION
• Dr Grey - 1920
• Any expansion which 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.
38. STRENGTH
• Resistance to compressive forces - most favorable
strength feature of amalgam
• Amalgam is strong in compression but weak in tensile
AMALGAM COMP.STRENGTH(MPa)
1 HOUR 7 DAYS
TENSILE STRENGTH
24 HOURS MPa
LOW COPPER 145 343 60
ADMIXED 137 431 48
SPHERICAL SINGLE 262 510 64
COMPOSITION
39. STRENGTH
• One hour compressive strength of spherical amalgam
is almost double of the other 2 amalgams
• Both low and high copper amalgams have less tensile
strength
• Tooth preparation should be done in such a way that
they are subjected to more of compressive stresses
and less of tensile stresses.
40. FACTORS AFFECTING STRENGTH
Trituration
Both under and over trituration reduces the strength
Mercury content:
• Sufficient mercury should be there to coat the
particles.
• If the mercury content increases beyond 54% the
strength reduces markedly
41. FACTORS AFFECTING STRENGTH
Condensation:
• For lathe cut amalgam, greater the condensation
pressure higher the compressive strength.
• Spherical amalgam - light condensation pressure
produces adequate strength.
Porosity:
If time lapse between trituration and condensation is
more, porosities are more and strength is less.
42. CREEP
• It is measured by placing a
cylindrical specimen of 8mm
length and 4mm diameter 7
days after preparation.
• A static stress of 36 MPa is
applied at 37 ̊c
• The change in length that
occurs between the 1st and
the 4th hour is divided by
the original length and
multiplied by 100.
44. CREEP
• Presence of γ2 phase increases the creep rate.
• High copper amalgam that has little or no γ2 have
low creep values.
• In low copper amalgam γ1 grains tend to slide. The
γ2 phase which is present in between the γ1 is
extremely plastic makes way for the sliding of γ1
grains
45. CREEP
• In high copper amalgam eta
crystals slows the sliding of
γ1 grains.
• The η crystals are
embedded between the γ1
grains and interlock the γ1
grains
• η phase inhibits the grain
boundary sliding and
thereby reduces the creep
rate.
46. FACTORS AFFECTING CREEP
• Trituration:
Both over and under trituration increases the creep
Increased condensation pressure decreases creep
• Mercury content:
High mercury content increases creep.
Mercury content beyond 46% produces sudden
increase in creep (mahler et al)
47. TARNISH AND CORROSION
• Amalgam restoration often undergo tarnish and
corrosion.
• Tarnish – surface discolouration
Depends on Oral environment and type of alloy
Produces unesthetic black silver sulphide.
48. TARNISH AND CORROSION
• Corrosion – electro chemical reaction leads to
• Porosity, Reduced
• marginal integrity and
• Loss of strength
• Electro chemical studies show
• γ1 phase has the highest corrosive resistance
followed by γ, AgCu, ε and η
• Least resistance to corrosion is γ2 phase.
• γ2 phase crystals are long and blade like, penetrating
throughout the matrix. They form a penetrating matrix
because of the intercrystalline contact between the blades.
Hence this phase is more prone for corrosion producing
penetrating corrosion.
49. TARNISH AND CORROSION
• Amalgam corrodes eventhough silver and mercury are
corrosion resistant elements.
• γ2 is more electronegative than γ and γ1 phases. So this
induces galvanic corrosion.
• Corrosion of amalgam decreases over time because the
surface of amalgam becomes more noble. (Sutow et al
2007)
50. Low copper amalgam
γ2 phase the corrosive products are
Sn oxy Chloride+ SnO2 + SnCl + Hg
Hg reacts with γ forms γ1 + γ2
High copper amalgam
• η phase has the least corrosive resistance but has
better resistance than γ2
• cu6sn5(η) the corrosive products are
• CuCl2 + Cu(OH)2 + SnO
• In amalgam, concentration cell corrosion takes place
at the inter phase
• Self sealing restoration
51. Mercuroscopic Expansion
• During electrochemical corrosion, Hg from γ2 phase
re-reacts with silver tin particles and produces
expansion during the new reaction.
• This mechanism is called mercuroscopic expansion
proposed by Jorgensen.
53. Forms
• Three forms
• Organic – Methyl and ethyl mercury (most
Toxic)
• Inorganic - mercuric chloride, mercurous
chloride, mercuric sulfide and mercuric selenide
(least toxic)
• Elemental mercury
• Elemental Hg – converted to soluble inorganic
forms - methylated in water by microorganisms
– enters food chain - accumulated in tissues of
large predatory fishes
54.
55. Sources
Mercury is distributed ubiquitously in the
environment and therefore taken up by general
population.
• Ingestion of Food and water – mainly sea food
(Bluefin Tuna)
• Methyl mercury mainly from fishes
• Inhalation - Exposure to mercury through dental
and medical treatment
• Elemental mercury from amalgam
• Occupational exposure
• Inhalation from ambient air
56. Properties
• Symbol – Hg
• Only metal that is liquid at room temp
• Retains globular form due to high surface
tension
• Contaminated easily by sulfur gases forming
sulfides
• Purification- Repeated distillation – Triple
distilled Hg
• Impurities decrease the rate of reaction
• Has very high vapor pressure
57. Mercury Release
• Has very high vapor pressure (1.20x10-3 Torr at
20ºC) where as that for amalgam surface ranges
10-6 to 10-10 Torr. This implies release of mercury
vapor from set amalgam will be lower than that
from liquid mercury.(Wielickzka et al 1996)
• Hg vapor released - minute quantities during all
procedures including amalgam mixing, setting,
polishing and removal. Also during mastication and
drinking hot beverages – release correlated with
quantity of Hg used during trituration
• Covered by saliva – reduces the vapor pressure of
Hg
• Addition of Indium (8-14%) – decreases vapor
pressure.
58. Concentrations
• OSHA – Threshhold limit value – 0.05mg/m3
(50µg/m3 ) in a 8hr work over a 40 hr work week.
• Mercury in urine – Body cannot retain metallic
Hg – excretes in urine – peak levels are twice as
great when amalgam is removed (4µg/L) rather
than during insertion (2.5µg/L) that returns to 0
after 7 days.
• Neurological changes not detected until urine
level exceeds 500µg/L nearly 170 times the
peak level found in amalgam insertion.
59. Concentrations
• Dental personnel – been reported have more exposure
to Hg , urine Hg level has 3-22µg/L compared to the
non occupational group which can be 1-5µg/L
• Mercury in blood – max allowable is (3µg/L)
• Blood Hg – easily influenced by other factors and
cannot be explicitly related to amalgam.
• Mercury is normally present in amniotic fluid and
increases with fish intake and number of amalgam
fillings however no adverse effects were observed
throughout pregnancy and to the new born.
Safety of dental amalgam and alternative dental restoration materials for
patients and users. SCHENIHR 2008 European Commirssion.
60. Toxicokinetics
• Elemental and inorganic Hg poorly absorbed from
GI (0.01%) and actively absorbed from lungs (80%)
– Due to high lipid solubility of Hg, penetrates
alveolar membranes and easily distributed to all
tissues of the body.
• Oxidation of elemental mercury may also occur in
the CNS and results in the accumulation of Hg2+ in
the CNS since Hg2+ is unable to cross the blood
brain barrier and diffuse out of the brain. Hg2+ is
tightly bound to sulfhydryl groups in proteins which
represents the principle mode of action for its
toxicity and is responsible for the slow elimination.
• Half life of Hg is 20-90 days and kidney contains the
highest conc of Hg following exposure to elemental
mercury
61. Toxicity
• Inhalation of elemental mercury in excess of 10
mg/m3 – Bronchitis and pneumonia in addition to
CNS symptoms
• Major manifestations of long term Hg poisoning
are tremors, increased excitability, muscle tremors
in fingers, eye lids and lips that progress to chronic
spasm of extremities.
• Early phase of toxicity is less specific and referred
to as micromercurialism. Clinical findings includes
tremors, enlargement of the thyroid with increase
iodine intake by thyroid, tachycardia, gingivitis and
hematological changes. For diagnosis of early
elemental mercury intoxication, at least 3 of the
above findings along with increased Hg conc in
blood or urine should be present.
Safety of dental amalgam and alternative dental restoration materials for
patients and users. SCHENIHR 2008 European Commirssion.
62. • Expressed in micrograms of mercury per gram
of creatinine.
63. Systemic Reactions
• Minamata’s disease - methyl mercury poisoning that
occurred due to disposal into the nearby bay. Symptoms
include ataxic gait, convulsions, numbnesss in mouth and
limbs, constriction in visual field and difficulty speaking
which is particularly unique to mercury poisoning.
• Alzheimer’s disease – Inorganic mercury is neurotoxin at
high doses and is therefore suspected to play a role in the
pathogenesis of neurodegenerative diseases like
alzhemer’s
• Multiple sclerosis – evidences of association of amalgam
and multiple sclerosis is not conclusive.
• Parkinson’s disease – very difficult to establish a link with
dental amlagam
• Paresthesia
• Autism
64. Localized mucosal Reactions
• Type IV delayed reactions – Tissue damage seen as
contact mucositis i.e., intraoral diffuse, red zones,
blisters or ulcerations with pain and burning
sensation. The inflammation is not confined to
exposure site. Contact dermatitis may be observed
in the face or more distant locations as urtricarial
or eczematous reactions.
• Type I immediate reactions – Urtricaria, asthmatic
seizures, swelling of the mucosa of the throat and
eyes and even result in anaphylaxis.
65. Monitoring Hg levels
• Mercury vapor may be determined by using a
mercury detection meter such as Hg sniffer.
• Paper discs impregnated with palladium chloride
can be used but the major disadv is, it lacks
reaction specificity.
• Dosimeter - Badge system may be used in which
mercury is adsorbed on gold foil. Worn by the
personnel in dental office.
• Mercury in vapor and dust may be determined by
passing known volume of air through absorbing
system and then quantifying the absorbed mercury
66. Hygiene – ADA
RecommendationsGENERAL RECOMMENDATIONS
• Train all personnel involved in the handling of mercury
and dental amalgam regarding the potential hazards
• Remove professional clothing before leaving the
workplace.
OFFICE ENGINEERING
• - Work in well-ventilated work areas, with fresh air. The
air-conditioning filters should
• be replaced periodically.
• - Floor coverings should be nonabsorbent, seamless and
easy to clean. Do not use Carpets
• - Periodically check the dental operatory for mercury
vapor.
Dental mercury hygiene recommendation. J am Dent Assoc 2003;134:1498.
67. Hygiene – ADA
Recommendations
RECOMMENDATIONS DURING PREPARATION
• Use only capsulated amalgam alloys.
• Use amalgammator with hood
• Use care when handling amalgam. Avoid skin contact
with mercury or freshly mixed amalgam.
• Use high-volume evacuation systems (fitted with traps
or filters) when finishing or removing amalgam.
• Salvage and store scrap amalgam in tightly closed
container under radiographic fixer solution.
Dental mercury hygiene recommendation. J am Dent Assoc 2003;134:1498.
68. Hygiene – ADA
Recommendations
RECOMMENDATIONS DURING PREPARATION
• When feasible recycle amalgam waste or dispose
amalgam scrap or waste in accordance with the
applicable law.
• Dispose mercury contained items in sealed bags.
• Do not polish amalgam without adequate cooling
water as has a very low melting point (127º C) similarly
during amalgam removal the surface temperature can
increase several times when not used with adequate
cooling water. So rubber dam, high vloume evacuation
and water cooling can control this situation.
Dental mercury hygiene recommendation. J am Dent Assoc 2003;134:1498.
69. Hygiene – ADA Recommendations
MANAGEMENT OF MERCURY SPILLS
• In case of an accidental mercury spill (regardless of size),
• Never use a vacuum cleaner to clean up the mercury.
• Never use household cleaning products to clean up the
spill, particularly those containing ammonia or chlorine.
• Never allow mercury to go down the drain.
• Never use a broom or a paintbrush to clean up the
mercury.
• Never allow people whose shoes may be contaminated
with mercury to walk around
A spill is considered small if there are less than 10 grams of
mercury present. Small spills can be cleaned safely using
commercially available mercury cleanup Kits. Cleanup of
large mercury spills requires experienced environmental
personnel.
Dental mercury hygiene recommendation. J am Dent Assoc 2003;134:1498.
71. • Resin coated amalgam – To overcome the limitations
of microleakage, a coating of unfilled resin over the
restoration margins and the adjacent enamel, after
etching the enamel. Although resin may wear away, it
delays microleakage until corrosion products begin to
fill the tooth restoration interface.
• Fluoridated amalgam – Fluoride being anticariogenic,
is included in amalgam to deal with the problem of
recurrent caries. Anticariogenic effect can be explained
by its ability to deposit fluoride in the hard tissue
around the filling.
72. • Bonded amalgam – Conventional amalgam does not
restore the fracture resistance of the tooth that was
lost during cavity preparations. To overcome this
adhesive systems that reliably bond to enamel and
dentin have been introduced.
• Consolidated Silver alloy system – Uses Cold welding
of pre alloyed silver coated particles. Fluoroboric acid
is used to keep the surface of silver alloy particles
clean. The alloy in a spherical form, is condensed into
the prepared cavity similar to that of placing
compacted gold. Alloy strain hardens and is difficult to
compact adequately to eliminate voids.
73. • Gallium Alloys (Gallium alloy GP, Galloy) – 1956
Smith and Caul claimed that gallium based alloys
could serve as a alternative to amalgam. They
found that mixing gallium with either nickel copper
and mercury and tin produced a pliable mass that
could be condensed into the prepared cavity which
after setting had properties suitable for a restorative
material. Gallium melts at 28ºC and can be used to
produce liquid alloys at room temperature by
addition of small amount of other elements like
indium.
74. • Indium Alloys – Powell et al 1989 formulated
indium alloys by repeated addition of pure indium
powder in conc of 8% to high copper amalgam
alloy to decrease the mercury vaporisation. Lead to
total reduction of amount of mercury present.
Addition of 5-10% of indium to the alloy resulted
in the improved resistance to creep and corrosion,
reduced the dimensional change and improvements
in compressive strength (Johnson1985). Mueller
and Narea (1985) demonstrated lower mercury to
alloy ratio with the addition of indium content.
76. Bonded Amalgam - History
• Baldwin’s technique (1897) - Painting the cavity walls
with thin coal of zinc phosphate cement and
condensing the amalgam immediately on the wet
surface that improved the retention and seal of
amalgam.
• Zardiackas technique (1976) – Developed selective
interfacial amalgam liner by combining components of
polycarboxylate cement with amalgam alloy particles.
• Development of amalgam bonding came with the
development of metal adhesive resins which were
used for fixing Maryland bridges (Superbond based on
4-META with TBB and Panavia based on MDP
monomer). Hence they were initially better than
amalgam and achieved increased bond strength and
reduced micro leakage
77. Bonded Amalgam - Technique
• Method involves Etching the tooth surface and
primer application followed by adhesive resin
liner. The adhesive resin liner is chemically
activated.
• Amalgam is condensed on the unset adhesive
resin liner that leads to mechanical interlocking.
• Adhesive resin adheres to amalgam roughness
micromechanically forming a rigid physical
bond. While with dentin it forms a hybrid layer.
Setcos JC, Staninec and Wilson NHF. British Dental Journal 1999;186:328-332.
Moore DS, Johnson WW, Kaplan I.Int J Prosth 1995;461-465.
79. Bonded Amalgam - Adv
• Conserve more tooth structure by reducing the
need to remove sound tooth tissue for
mechanical retention.
• Increased Amalgam retention.
• Reduce marginal leakage
• Reduce the need for dentine pins.
• Potentially reduce sensitivity
• Improve fracture resistance
80. Bonded Amalgam - Indications
• Not recommended for routine amalgam cavities
with sufficient mechanical retention and
undercuts.
• Useful for large multi surface amalgams to avoid
use of pins
• Useful for amalgam repairs
81. Bonded Amalgam - Limitations
• Technique sensitive
• Adhesion may breakdown over time. Studies
have shown increased microleakage after one
year (Moore et al)
• Increased cost of restoration
Moore DS, Johnson WW, Kaplan I. Int J Prosth 1995;461-465.
83. FAILURES
Reasons for replacement of amalgam restorations are
usually associated with
• Tooth Fracture
• Recurrent Caries
• Gross amalgam fracture
• Marginal breakdown
Richard Van Noort 3rd edition 2007
84. FAILURES
TOOTH FRACTURE
• Weakened Tooth structure – Amalgam does not
strengthen tooth structure. Hence minimum removal
of tooth structure should be employed. Also by cutting
enamel parallel to prism direction. (90 cavosurface
angle)
• Undermined enamel – Flat walls and floors to a cavity
walls may produce unsupported enamel that breaks to
produces a gap.
Richard Van Noort 3rd edition 2007
85.
86. FAILURES
• Residual Caries – They undermine the cusp causing
fracture
RECURRENT CARIES
• Contamination – Causes poor adaptation of restoration
to cavity walls
• Poor Matrix Techniques – Causes proximal overhangs
and poor contact points with adjacent teeth that
accumulates plaque and causes recurrent caries.
• Poor Condensation – causes porosity of amalgam and
presence of excess mercury which reduces the
strength of amalgam and poor marginal adaptation.
Richard Van Noort 3rd edition 2007
87. FAILURES
GROSS AMALGAM FRACTURE
• Shallow Preparations – Leads to thin sections of
amalgam placement causing bending forces to fracture
• Non-Retentive Proximal Boxes – Very common fracture
of amalgam due to its low tensile strength. Sharp
internal line angles may lead to fracture of proximal
boxes and proximal box dislodged. Overcome by self
retentive proximal box by placing retentive grooves.
• Sharp internal Line angles – Concentrates stress that
increases the risk of fracture of both tooth and the
filling. Avoided by roundening the line angles.
Richard Van Noort 3rd edition 2007
88.
89. FAILURES
MARGINAL BREAKDOWN (Ditching)
• Incorrect cavosurface Angle – Primary cause is
incorrect cavosurface angle leading to marginal
fracture of enamel or amalgam. Occurs more readily
when amalgam has acute margin angle.
90. FAILURES
• Delayed Expansion – The expansion can cause
extension of amalgam beyond the surface causing
marginal breakdown
• Overfilling, underfilling and Overcarving – causes acute
amalgam margins leading to marginal breakdown
• Creep and corrosion of amalgam – may lead to
marginal breakdown.
92. When comparing how well a new restorative
material can replace amalgam, the following
factors should be considered
• Biocompatibility
• Prognosis
• Technique sensitivity
• Esthetics
• cost
93. Non occlusal functions – Primary sites are enamel caries
below the height of contour, cervical abrasions and root
caries. Alternative restorative materials includes
• Direct gold foil – good prognosis, resist tarnish and
corrosion, excellent biocompatibility but yet allows
microleakage and has no positive esthetic value
• Bonded composite – esthetic alternative. Has short term
high retention rates. It is technique sensitive. To protect
against caries, used in combination with glass
ionomers.
• Glass ionomer – ideal alternative to class V amalgam.
Releases fluorides and retards recurrent caries. Has
some esthetic value. Surface should be dry and
restoration should be protected. If these are mastered,
technique is short and simple. It is biocompatible and
94. Small Occlusal Restorations– For small Class I and
Class II
• Direct Composite- Posterior composites may last as
well as amalgam for 5 years. The smaller the
restoration the better the material. May restore some
degree of intercuspal strength but leads to more pulpal
responses. Lacks resistance to abrasion and has some
amount of microleakage.
• Composite Inlays – Polymerisation shrinkage takes
place outside and initially resists leakage. Has mild
improvement in abrasion resistance. It is more time,
technique and equipment sensitive and hence more
expensive than direct technique.
• Porcelain Inlays – Resin bonding has the same adv and
disadv of composite bonding. CAD CAM offers a
95. • Goil Inlays – Have been taught as excellent alternative
but still it rely on cement bonding. Has shorter clinical
prognosis than amalgam and is expensive.
• Electroformed Inlay – indirect restoration by gold
electroplating. It is a combination of pure gold and
porcelain. Porcelain is veneered over the electroformed
gold. Has good esthetic value and excellent marginal
adaptation.(Behrend 1997, Wirz Jaeger 2003)
• Preferred technique – Electroformed inlays,
Composite inlays and direct composite with periodic
resurfacing.
Large Occlusally Functioning Restorations – Cast
procedures are legitimate alternatives for restoration
requiring cuspal replacement and protection
• Gold Onlay – Offers cuspal protection, resists wear and
does not abrade opposing tooth. But is technique
96. • Porcelein Onlay – Distinct adv of being esthetic, resists
abrasion but abrades the opposing tooth. Technique
sensitive
• Composite Onlay – Though esthetic, has no abrasion
resistance and is technique sensitive
• Electroformed Onlay – similar to electroformed inlay
• Preferred Technique – Gold, Electroformed or
Ceramic Onlay
Core build ups – Glass ionomers (Cermet) and
Composite resins.
• Glass ionomers – May be used for partial buildups
when two or more walls exists. For full buildups, they
may be inefficient
97. • Composites – Used abundantly as they are quick and
easy to place. Dentine is still water permeable and
water can undermine the properties. Has no resistance
to caries and causes recurrent caries
• Cast post and cores – Placement procedure can be
tedious and time consuming
• Preferred technique – Composite
Full Veneer restorations are not considered as amalgam
alternatives as they require significant reduction of
tooth structure and may also require a buildup for
appropriate retention
No one material or technique fits all the needs amalgam
has fullfilled but some can begin to compete.
Newman SM. Amalgam Alternatives. What can compete. JADA 1991;122:67-71.
99. • Substitutes for amalgam (amalgam alternatives)
• Mercury free amalgam
• Gallium and Indium alloys
• Current status of amalgam as a restorative
material
• Recent advances in amalgam
• Mercury Toxicity
• Mercury Hygiene
• Manufacture of amalgam alloys
• Phases of amalgam
100. • Zinc free alloys
• High copper amalgam and low copper amalgam
reactions
• Creep in amalgam Performance
• Condensation of amalgam
