Amalgam

DENTAL AMALGA

M

AMALGAMAmalgam - 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.

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

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 proportionMackert JR. Dental Amalgam and mercury. JADA 1991;122:54-71.

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.

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)

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

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


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.


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.

Property of Individual ComponentPROPERTY INGREDIENT

Silver Tin Copper ZincStrength 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 IncreasesCleanliness Increases

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

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

Tensile strength of phases of amalgam

Phases in Amalgam Alloys Tensile strength (Mpa) γ (Gamma) 170

γ1 30 γ2 20

Amalgam 60

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

CLASSIFICATIONBased on the particle shape

1. Lathe cut powder2. Spherical alloy powder3. Admixed alloy powder

Based on copper content4. Low copper alloys – less than 6%5. High copper alloys – 13 – 30 %

Based on zinc content6. Zinc containing alloys – 0.01%7. Non – zinc containing alloys – less than 0.01%

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

phasePhillips’ Science of dental materials, 11/e Anusavice.

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 15-35µmCraig,s Restorative Dental Materials, 12/e

Lathe cut Alloy Particles

Spherical Alloy Particles

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

Amalgamation Reaction – Low Copper Alloys

•During the reaction, the formation of body centered cubic form of Ag2Hg3 and hexagonal Sn7-8Hg occurs.

• 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

γ + Hg γ1 + γ2 + Unreacted alloy Particles

γ1 - Dominant phase – 54-56% Unreacted γ - 27- 35%γ2 - 11-13%

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%

• 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 Cu content of 12 %

INITIAL REACTION:γ + Ag-Cu Eutectic + Hg γ1 + γ2 + Unreacted γ +

Unreacted Ag-Cu

SECONDARY REACTION:γ2 + Ag-Cu Eutectic η (Cu6Sn5) + γ1 + Unreacted

Ag-Cu

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

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.

• γ + ε (Cu3Sn)+Hg γ1 + η + Unreacted γ and ε

• γ2 phase is eliminated in both admixed and spherical alloy

PROPERTIES

DIMEMSIONAL CHANGE

• Ideally an amalgam with no change in dimension and stable throughout is preferred.

• Expansion

• Contraction

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

• 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.

FACTORS FAVOURING CONTRACTION

• Less mercury content• Higher condensation pressure• Longer trituration time which hastens the

reaction• Smaller particle size.

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.

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

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.

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

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.

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.

CREEP

• Creep values(%)Low copper – 2.0Admixed – 0.4Spherical – 0.13

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

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.

FACTORS AFFECTING CREEP

• Trituration:Both over and under trituration increases the creepIncreased condensation pressure decreases creep

•Mercury content:High mercury content increases creep.Mercury content beyond 46% produces sudden increase in creep (mahler et al)

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.

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.

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)

Low copper amalgam γ2 phase the corrosive products are

Sn oxy Chloride+ SnO2 + SnCl + HgHg 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

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.

MERCURY

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

SourcesMercury 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

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

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.

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.

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.

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

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.

• Expressed in micrograms of mercury per gram of creatinine.

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

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.

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

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.

Hygiene – ADA RecommendationsRECOMMENDATIONS 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.


Hygiene – ADA RecommendationsRECOMMENDATIONS 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.


Hygiene – ADA RecommendationsMANAGEMENT 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 aroundA 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.


Recent Advances

• 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.

• 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.

• 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.

• 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.

Bonded Amalgam

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

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.

Bonded Amalgam - Materials

• Resin Cements ( Panavia) (MDP)• Adhesive Bonding Agents (4 Methacryloxyethyl

Trimellitate Anhydride - 4 META)-Initially designed for composites-OptiBond solo-Amalgambond-Scotchbond multipurpose

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

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

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.

Amalgam Failures

FAILURESReasons for replacement of amalgam restorations are

usually associated with• Tooth Fracture• Recurrent Caries• Gross amalgam fracture• Marginal breakdown

Richard Van Noort 3rd edition 2007

FAILURESTOOTH 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.


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.


FAILURESGROSS 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.


FAILURESMARGINAL 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.

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.

Amalgam Alternatives

When comparing how well a new restorative material can replace amalgam, the following factors should be considered• Biocompatibility• Prognosis• Technique sensitivity• Esthetics• cost

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 inexpensive.• Preferred – Composites and glass ionomers.

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 direct delievery but chairside is long and equipment is expensive. Abrasion resistant but abrades the opposing tooth.

• 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 sensitive, not esthetic and more expensive.

• 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 OnlayCore 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

• 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 – CompositeFull 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.

Frequently Asked Questions

• 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

• Zinc free alloys• High copper amalgam and low copper amalgam

reactions• Creep in amalgam Performance• Condensation of amalgam

THANK YOU

Amalgam

Science

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