Amalgam Seminar

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GOOD MORNING

AMALGAM

MATERIAL 2

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Introduction

• Dental amalgam has been used for over 150 years for the treatment of dental cavities and is still used, in particular in large cavities due to its excellent mechanical properties and durability.

• Dental amalgam is a combination of alloy particles and mercury.

• It contains about 50% of mercury in the elemental form.

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TerminologiesAmalgam: An alloy

of mercury with one or more metals.

Dental amalgam alloy: An alloy that contains solid metals of silver, tin, copper and sometimes zinc.

Dental amalgam: An alloy that results when mercury is combined with the previously mentioned alloys to form a plastic mass.

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History• 1833

– Crawcour brothers introduced amalgam to U.S.A

• powdered silver coins mixed with mercury

– expanded on setting

• 1895– G.V. Black developed

formula for modern amalgam alloy

• 67% silver, 27% tin, 5% copper, 1% zinc

– overcame expansion problems

• 1960’s– conventional low-copper lathe-cut

alloys• smaller particles

– first generation high-copper alloys• Dispersalloy (Caulk)

– admixture of spherical Ag-Cu– eutectic particles with

conventional lathe-cut– eliminated gamma-2 phase

• 1970’s– first single composition spherical alloys

• Tytin (Kerr)• Ternary system (silver/tin/copper)

• 1980’s– alloys similar to Dispersalloy and Tytin

• 1990’s– mercury-free alloys

Debut of Amalgam

• Introduced in 1800’s in France– alloy of bismuth, lead, tin

and mercury– plasticized at 100 °C– poured directly into cavity

• 1826 - Traveau– compounded a silver paste amalgam

• mixture of silver shavings from coins and mercury

– condensed into tooth at room temperature

Mackert JADA 1991 6

Amalgam War I

• 1833 - Crawcour brothers– heavily marketed their amalgam

of silver and mercury

• 1843 - American Society of Dental Surgeons– declared use of amalgam malpractice

• mercury is a poison

– threatened to expel users

• Amalgam use declined

Mackert JADA 1991 7

Amalgam War I

• 1895 - G.V. Black– developed effective amalgam

• improved handling and performance• similar to contemporary low-copper

amalgam

• Popularity of amalgam increased

Black Dent Cosmos 1896 8

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Amalgam War II

• 1924 - Alfred Stock– German professor of chemistry– became poisoned with mercury

• 25 years of laboratory research

– published papers on the dangers of mercury in dentistry

• Created considerable public concern

Stock Med Klin 1296

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Amalgam War II

• 1934 - German physicians– studied patients

• occupationally exposed to mercury– with and without amalgams

– published papers • no health risk from amalgams

• 1941 - Alfred Stock recanted his position

Mackert JADA 1991

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Amalgam War III

• 1970 - 1990– concern over occupational

exposure of mercury vapor to dentists

– excess levels in 10% of dental offices

• > threshold limit of 50 ug/mm3

– urinary mercury levels high• mild functional effects

found

– ADA institutes mercury hygiene campaign

– urinary mercury levels lowered 50 %

– a shift in concerns• from occupational risk to

dentists to patient risk– ability to measure mercury

release from amalgam restorations in expired air

• early tests grossly overestimated

Mandel JADA 1991

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Classification

According to the number of alloyed metals

Binary alloy

(silver, tin)

Ternary alloy

(silver, tin, copper)

Quaternary alloy

(silver, tin, copper,

and zinc)

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According to the shape of the powdered particles

Lath cutIrregular shaped powder particles ranging from spindles to shavings.

SphericalSmooth surface spheres

Advantages :Require less mercury.

Develop early strength.Require less

condensation force.Disadvantages:

More difficult to obtain inter-proximal contact and contours in class II

cavity.Have shorter working

time

SpheroidalFormulated by mixing

the lath cut and spherical particles

Increase the packing efficiency of the alloyReduce the amount of mercury required to

produce a workable mix.

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According to the particle diameter

1.Very fine particle size alloy

Advantages:Easily carved.

Produce excellent surface finish.

Disadvantages:Require more mercury.

Lower early compressive strength.

High rate of marginal breakdown.

2.Fine particle size alloy.

3.Medium particle size alloy

4.Coarse grained particle size alloy

Advantages:Require less mercury.

Produce amalgam with higher early strength.

Disadvantages:Difficult to carve.

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According to the zinc content of the

alloy

Zinc containing amalgam

(>0.01% zinc)

Zinc free amalgam

(<0.01% zinc)

According to the form supplied of the

powder

Powder

Tablets of condensed

powder particles

Capsules together with gauged amount

of mercury separated by a

diaphragm.

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According to the copper content of the alloy

.

Low copper alloys (Cu < 6%)

High copper alloys (Cu > 6%).

AdmixedUnicompositional

Based on size of alloy

Microcut/fine cut Macrocut/coarse cut

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According to generation

Class 1

•Silver and tin (8:1)

Class 2

•Silver, tin, copper (4%) and zinc

Class 3

•Silver eutectic alloy added to original alloy

Class 4

•Copper content increased to 29%

Class 5

•Indium added to mixture of silver, tin and copper

Class 6

•Noble metal such as palladium added

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Constituents in Amalgam

• Basic– Silver (Ag 40–70%)– Tin (Sn 12–30%)– Copper (Cu 12–24%)– Mercury

• Other– Zinc (Zn 0-1%)– Indium (0–4%)– Palladium ( 0.5%)

J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208.

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Basic Constituents

• Silver (Ag) Major element. Whitens alloy. Decreases creep. Increases strength. Increases expansion on setting. Increases tarnishing resistance.

• Tin (Sn) Controls the reaction between Ag & Hg. Reduces strength & hardness. Reduces resistance to tarnish & corrosion.

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• Copper (Cu)

Ties up tin reducing gamma-2 formation

Increases strength

Reduces tarnish and corrosion

Reduces creep Reduces marginal

deterioration

• Mercury (Hg)

Activates reaction Only pure metal that is

liquid at room temperature

Spherical alloys require less mercury smaller surface area

easier to wet 40 to 45% Hg Admixed alloys require more mercury Lathe-cut particles more difficult to wet 45 to 50% Hg

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Other Constituents

• Zinc (Zn) Small amount –not affect setting

reaction \ properties of amalgam. Act as a scavenger \ deoxidiser. Without Zn alloys are more brittle &

amalgam formed less plastic. Causes delayed expansion , if

contaminated with moisture during manipulation.

Beneficial effect on corrosion & marginal integration.

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• Indium (In) Decreases surface

tensionreduces amount of

mercury necessaryreduces emitted

mercury vapor Reduces creep and

marginal breakdown Increases strength Used in admixed

alloys Example:

INDISPERSE (indisperse distributing company)

• 5% INDIUM

PALLADIUM (PD) Reduced

corrosion Greater luster Example

VALIANT PHD (ivoclar vivadent)

• 0.5% PALLADIUM

Mahler J Dent Res 1990Powell J Dent Res 1989

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Effects of palladium addition on properties of dental amalgams

Palladium-containing amalgam alloys were developed utilizing the atomization method. Single-compositional type alloys were fabricated and palladium was substituted for silver in concentrations up to 5 w/o. Alloy powder with a particle size of less than 45 microns was collected and triturated with mercury. Creep, compressive strength and dimensional change tests were performed according to ADA Specification No. 1 along with controls of Tytin, Valiant and Valiant-Ph.D. Values for creep decreased and compressive strength increased markedly with additions of palladium. Current densities of the experimental amalgams containing palladium were determined to be an order of magnitude less than the original amalgams in the electrochemical test. A trend of positive relationships between properties and palladium additions was indicated.

Dent Mater. 1992 May;8(3):190-2

http://www.ncbi.nlm.nih.gov/pubmed/1521709

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PROPERTY INGREDIENT

Silver Tin Copper Zinc

Strength Increases

Durability Increases

Hardness Increases

Expansion Increases Decreases Increases

Flow Decreases Increases Decreases

Color Imparts

Setting time Decreases Increases Decreases

Workability Increases Increases

Cleanliness Increases

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ALLOY PRODUCTION

Alloy is produced predominantly as:

Irregularly shaped

Spherical shaped

Mixture of both types

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Irregular particlesGenerally “lathe-cut”. Annealed ingot of alloy placed in a milling machine or lathe.

Chips removed are needle-like, size reduced by ball-milling.

Homogenizing heat treatment performed for 8 hours at 400°C .

Treatment of the alloy particle with acid is performed.

Annealing at 100°C to reduce stress.

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Spherical particles

Produced by atomizing molten alloy in a chamber filled with an inert gas such as argon.

The molten metal falls through a distance of approximately 30 feet and cools as it does.

This results in spherical particle shapes(15 to 35 µm)

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COMPARISON OF LATHECUT WITH ATOMIZED SPHERICAL POWDER

AMALGAM FROM LATHECUT POWDER

AMALGAM FROM SPHERICAL POWDER

1. Resist condensation better 1. Very plastic-cannot rely on pressure of condensation to establish proximal contour.

2. Require > Hg 2. Require < Hg due to small surface area per volume .

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Metallurgical phases in dental amalgam

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Silver-Tin system

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AMALGAMATION AND RESULTING

MICROSTRUCTURE

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Low copper alloys

These are also known as ‘traditional’ or ‘conventional’ amalgam

Available as:1. Lathe cut alloys- coarse or fine grain2. Spherical alloys3. Blend of lathe cut and spherical alloys

Composition:• Silver ( Ag 67-74%).• Tin (Sn 25-28%).• Copper (Cu 0-6%).• Zinc (Zn 0-1%).

(L Williams, Wilkins: 2004)

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Setting ReactionMercury + Amalgam alloy

Mercury absorbed by the particles anddissolves the surface of the particles

Mercury becomes saturated with silver and tin

Gamma-1 (Ag-Hg) and Gamma-2 (Sn-Hg) phases begin to precipitate

Precipitation continues as long as 24hours when strength reaches a maximum

Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

Mercury (Hg)

AgAgAg

Sn

Sn

Sn

Hg Hg

Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg 1 2

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• Gamma () = Ag3Sn– unreacted alloy– strongest phase– corrodes the least– 30% of volume

of set amalgamAg-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

Ag

AgAg

Sn

Sn

Sn

HgHg

Hg


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• Gamma 1 (1) = Ag2Hg3

– matrix for unreacted alloy

– 2nd strongest phase

– 60% of volume

1


Ag-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

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• Gamma 2 (2) = Sn8Hg– weakest and softest

phase– corrodes fast, voids

form– 10% of volume– volume decreases

with time due to corrosion


2

Ag-Sn Alloy

Ag-Sn Alloy Ag-Sn

Alloy

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High copper alloys

• High-copper amalgam was developed in1962 by the addition of silver-copper eutectic particles to low-copper silver-tin lathecut particles.

• Compared to low-copper amalgam counterparts, high-copper alloys exhibit the following properties:

greater strength less tarnish and corrosion less creep less sensitive to handling variables and produce better long-term

clinical results.• High-copper amalgam restorations also have a much lower

incidence of marginal failure compared to low-copper amalgam.

(JF McCabe, AG Walls: 1998)

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• Two different types:1. Admixed alloy powder2. Single composition

alloy powder

Composition: Admixed alloy:

Silver – 40-70% Tin - 26-30% Copper- 9-20%

Zinc - 0-1%

Unicompositional alloy: Silver- 40-60% Tin - 22-30%

Copper-13-30%Zinc -0%

(JF McCabe, AG Walls: 1998)

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Admixed High-Copper Alloys

Amalgam is triturated

Mercury diffuses into the silver-tin particles

Silver and tin dissolve

Silver from the silver copper eutectic particles also enters mercury

Ag3Sn + Ag-Cu + Hg Þ Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

Ag

AgAg

SnSn

Ag-Cu Alloy

AgHgHg

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Admixed High-Copper Alloys

Copper combines with tin

Ring of Cu6Sn5 around the eutectic particles

Silver precipitates out as Gamma 1

Ag-Sn Alloy

Ag-Cu Alloy

Ag-Sn Alloy


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Admixed High-Copper AlloysFinal set amalgam

Gamma and silver-copper eutectic particles in a matrix

of gamma 1

Eutectic particles are surrounded by the eta phase

Ag-Sn Alloy

1

Ag-Cu Alloy

Ag-Sn Alloy


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Single Composition High-Copper Alloys

Amalgam is triturated

Mercury diffuses into the silver-tin-copper particles

Silver and Tin dissolve into Mercury

Silver precipitates out first as

silver-mercury (gamma 1)

Ag-Sn Alloy

Ag-Sn AlloyAg-Sn Alloy

Mercury (Hg)

Ag

SnAg

Sn

Ag3Sn + Cu3Sn + Hg Þ Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1

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Single Composition High-Copper Alloys

Copper + Tin

Cu6Sn5 on the surface of the particles and in the gamma-1

matrix

Set amalgam = core gamma particles in matrix of gamma 1

and Cu6Sn5

Ag-Sn Alloy

Ag-Sn AlloyAg-Sn Alloy

1

Ag3Sn + Cu3Sn + Hg Þ Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1

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Physical Properties of Dental Amalgam

Dimensional stability

Strength

Creep

Microleakage

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Dimensional stability

The net contraction or expansion of an amalgam is called its dimensional changeDimensional changes on setting:• CONTRACTION during alloy dissolution• EXPANSION during impingement of reaction product crystals • ANSI/ ADA specification No.1 requires dimensional change of no more than

20µm/cm at 37 °C between 5min and 24hrs after beginning of trituration.

Low-copper alloy have the greatest dimensional change ( 19.7m/cm).

High-copper unicompositional alloy have the least dimensional change (-1.9 m/cm).

Other alloys are ranging from (-8.8 to –14.8 m/cm)

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Dimensional change is affected by many factors:• Mercury/alloy ratio • Trituration • Condensation techniques

CONTRACTION:Result in microleakage & secondary caries.• Factors favouring contraction

Longer trituration time. Higher condensation pressure. Small particle size.High Hg alloy ratio.

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Delayed Expansion :

• Zn containing low cu \ high cu alloy contaminated during trituration or condensation , large expansion take place.

• Starts from 3-5 days and continue for months creating values more than 400um.

• H2O + Zn ZnO + H2O

Results in:– Protrusion of restoration out of cavity– Increase creep– Increase microleakage– Pitted surface of restoration– corrosion.

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Effect of Moisture Contamination on High-Copper Amalgam

Moisture contamination caused delayed excessive expansion and deterioration of the physical properties only with the non-high-copper lathe-cut alloy amalgam containing zinc, but not with the new high-copper amalgam and the non-high-copper spherical alloy amalgam containing zinc. It affected the compressive strength and creep but not the hardness. The setting dimensional change of all amalgams containing zinc was slightly affected by it.

JDR March 1981 vol. 60 no. 3 716-723

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STRENGTH

• The strength of an amalgam restoration must be high enough to resist the biting forces of occlusion.

• 1 hour 40% to 60% compressive strength (e.g., Tytin 45% and Dispersalloy 51%) • 24 hours 90% or more of their final strength

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Compressive Strength (psi) Tensile Strength (psi)15-min 1-hr 24-hr 15-min 1-hr 24-hr

LOW COPPER:Velvalloy 5,400 17,400 56,200 625 1,900 9,000Spheralloy 5,800 18,500 56,900 450 1,550 8,800

HIGH COPPER:Optalloy II 9,100 23,800 55,900 1,000 2,350 7,250Dispersalloy 6,200 22,400 59,900 575 1,750 6,990Indiloy 4,600 26,300 64,500 450 2,400 6,500Sybraloy 23,800 50,000 72,700 2,190 4,700 6,600Tytin 10,200 40,800 79,100 990 4,000 9,300

•The two types of strength are compressive strength and tensile strength.

•Tensile strength is 7 times less than compressive strength

•Since tensile and shear strengths are low, amalgam should be supported by tooth structures for clinical success

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• The rate at which an amalgam develops strength is an important clinical characteristic.

• If the amalgam restoration is subjected to chewing or other oral forces before sufficient strength develops, it is at risk for fracture.

• Spherical particle alloys and copper-enriched alloys develop strength more rapidly than conventional lathe-cut materials.

• Fine-grain, lathe-cut products develop strength more rapidly than coarse-grain products.

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Fracture

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Fracture toughness and critical strain energy release rate of dental amalgam

Fracture toughness, critical strain energy release rate and critical stress intensity factor were determined for lathe-cut, spherical, admixed, and two atomized high-copper dental amalgams. At a loading rate of 0.005cm min−1 for 24-hour samples, the spherical amalgam had the highest resistance to unstable crack propagation. At a loading rate of 0.05cm min−1 for both 24-hour and one-month samples, the lathe-cut amalgam had the highest resistance to unstable crack propagation. One of the atomized high copper amalgams showed the lowest resistance to crack propagation

Dental Materials Volume 8, Issue 3, May 1992, Pages 190–19

http://www.sciencedirect.com/science/journal/01095641

http://www.sciencedirect.com/science/journal/01095641/8/3

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CREEP• Creep is a slow change in shape caused by compression due to

intra-oral stresses. • Creep causes : Amalgam to flow unsupported amalgam protrudes from

the margin of the cavity. These unsupported edges may be further weakened by

corrosion. Fracture formation of a ‘ditch’ around the margins of the

amalgam restoration. Overhangs food trapping & secondary decay. • The gamma-2 phase of amalgam is primarily responsible for high

values of creep

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Material type Creep (%)

Conventional lathe-cut

2.5

Dispersion-modified, copper-enriched

0.2

Copper-enriched, containing 0.5% palladium

0.06

Values for static creep for amalgam

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Creep-fatigue as a Possible Cause of Dental Amalgam Margin Failure

Fracture of the margins is the most common cause of failure of dental amalgam restorations. Both corrosion and creep have been identified as possible contributors to this type of failure. The stresses that induce creep may arise from the continued setting expansion of the amalgam, the formation of corrosion products, mastication, or from the thermal expansion of the amalgam during ingestion of hot foods.

Biomaterials Volume 23, Issue 2, January 2002, Pages 597–608



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MICROLEAKAGE

Amalgam has got a self sealing property.

Corrosion products will fill the tooth restoration interface & prevent microleakage.

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Factors that promote microleakage:

• 2 to 20 micron-wide gap that always exists between the amalgam and tooth structure.

• Poor condensation techniques ,result in marginal voids.• Lack of corrosion by-products necessary to seal the

margins.• Coefficient of thermal expansion for amalgam which is

22 times greater than the coefficient for tooth structure.• Use of single-composition-spherical alloys which leak

more than lathe-cut or admixed alloys.

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Conventional and high-copper Class V amalgam restorations showed leakage after seven months' storage in artificial saliva and thermal-stressing. The rate of marginal microleakage was not significantly affected by the application of a Copal varnish after this period. At the 14-month storage and thermal-stressing period, all varnished and unvarnished high-copper restorations and the varnished conventional amalgam restorations showed significantly improved sealing properties in the occlusal wall compared with the seven-month period. The unvarnished conventional amalgam restorations appeared to have reached their peak sealing level by seven months under the conditions of this experiment. No significant improvement in the sealing properties of either the conventional or high-copper amalgam restorations was achieved after the 14-month period by the application of Copal varnish.

Long-term sealing properties of amalgam restorations: An in vitro study

Dental Materials Volume 5, Issue 3, May 1989, Pages 168–170



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CHEMICAL PROPERTIES

1. CHEMICAL CORROSION (TARNISH):

• Tarnishing involves the loss of luster from the surface of a metal or alloy due to formation of a surface coating.

• The integrity of the alloy is not affected, so no change in mechanical properties.

• Amalgam readily tarnishes due to the formation of a sulphide layer on the surface.

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2. ELECTROCHEMICAL CORROSION:

• Galvanic corrosion occurs when two dissimilar metals exist in a wet environment.

• Electrical current flows between the two metals, corrosion of one of the metals occurs.

• An acidic environment promotes galvanic corrosion.

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• Corrosion occurs both on the surface and in the interior of the restoration.

• Surface corrosion discolors an amalgam restoration, lead to pitting and also fills the tooth/amalgam interface with corrosion products, reducing microleakage.

• Internal corrosion will lead to marginal breakdown and fracture.

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Internal corrosion Corrosion at margins

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Low-copper amalgams High-copper amalgams

Corrosion products of Tin oxides and Tin chlorides

Tin oxides and tin Chloridesalong with copper chloride.

The most corrosion-prone phase is gamma-2 (Sn8Hg)

The most corrosion-prone phase is the eta phase (Cu6Sn5).

Corrode slower than low-copper amalgams (6 months to 2 years)

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Corrosion of dental amalgams: electrochemical study of Ag–Hg, Ag–Sn and Sn–Hg phases

Dental amalgams, formed by reaction of mercury with a powder alloy containing mainly Ag, Sn, Cu and Zn, have a complex metallurgical structure which can contain up to six phases. Their observed corrosion is thus a complex process, which involves contributions from each of the phases present as well as intergranular corrosion. It is thus of interest to investigate the corrosion of individual phases present in dental amalgams. In this work the corrosion behaviour in 0.9% NaCl solution of Ag–Hg, Ag–Sn and Sn–Hg phase components of dental amalgams was investigated by electrochemical methods. The corrosion resistance was found to decrease in the order γ1-Ag2Hg3, γ-Ag3Sn and γ2-Sn7Hg.

Journal of Oral Rehabilitation Volume 31, Issue 6, pages 595–599, June 2004

http://onlinelibrary.wiley.com/doi/10.1111/jor.2004.31.issue-6/issuetoc




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THERMAL PROPERTIES

1. Thermal diffusivity:• Amalgam has a relatively high value of thermal

diffusivity. Thus, in constructing an amalgam restoration, an insulating material, dentine is replaced by a good thermal conductor.

• In large cavities it is necessary to line the base of the cavity with an insulating, cavity lining material prior to condensing the amalgam.

• This reduces the harmful effects of thermal stimuli on the pulp.

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2. Coefficient of thermal expansion:• This value for amalgam is about three times

grater than that for dentine. • This coupled with the grater diffusivity of

amalgam, results in considerably more expansion and contraction in the restoration.

• Such a behavior may cause microleakage around the filling since there is no adhesion between amalgam and tooth substance.

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BIOLOGICAL PROPERTIES

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1.MERCURY TOXICITY:

• It is a concern in dentistry because mercury and its chemical compounds are toxic to the kidneys and the CNS.

• Mercury is toxic, but released in small amounts from set amalgam.

• Safety should be considered for: Patient Operator Environment• Proper handling and storage along with prompt

cleaning of all mercury spills will minimize risk of toxicity.

• OSHA: acceptable level of mercury exposure 0.005 mg/mm3

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How does mercury enter the human body?

Mercury vapour from surface of filling by chewing , tooth brushing or bruxism

Filling surface through wear or corrosion

Mercury particles embedded in gums or soft tissue of the mouth during the removal of old fillings.

Inhalation Dissolved in saliva and swallowed

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Mercury Dose from Amalgam

• Average daily dose from 8 – 10 amalgam surfaces 1-2 ug per day well below threshold levels

• Threshold urine mercury levels subtle, pre-clinical effects

30 ug per day considered dangerous

82 ug per day

Olsson J Dent 1995 Mackert Crit Rev Oral Biol Med1997 Berdouses J Dent Res1995

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Side effects of mercury

Allergy

Hypersensitivity

Systemic toxic effects

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Precautions

• The clinic should be well ventilated.• Proper storage of mercury in a

container with tight lid.• While using capsules, lids of the

capsules should be tight fitted and no spilling should occur.

• If by chance mercury is spilled on the floor, it should be wiped clean immediately.

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• If mercury comes in contacts with skin, one must wash with soap and water immediately.

• Proper waste disposal methods undertaken.

• Use of eye protection, disposable face masks, and gloves.

• Periodic monitoring of actual exposure levels in blood and urine.

• Avoid heating instruments to> 80°C

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Amalgam disposal

Contact amalgamNon-contact amalgam

Dental amalgam particles collected by any suction line .

Removed amalgam filling and teeth with filling

Excess dental amalgam generated during the placement of a filling

Broken and unused amalgam capsules

All amalgam waste must be released to an approved waste carrier for recycling or disposal in trenches

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Biocompatibility of dental amalgam

• Biocompatability of amalgam is thought to be determined largely by the corrossion products released.

• Corrosion depends on the type of amalgam.• In cell culture screening tests, free or non leaded mercury

from amalgam is toxic .With the addition of copper, amalgams becomes toxic to cells in culture but low copper amalgam that has set for 24hrs does not inhibit cell growth.

• Implantation tests show that low copper amalgams are well tolerated but the high copper amalgams can cause severe reactions when in direct contact with tissue.

BIOCOMPATIBILITY OF DENTAL MATERIALS

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• In usage tests, the response of the pulp to amalgam in shallow or in deep but lined cavities is minimal and amalgam rarely causes invisible damage to the pulp however, pain results from using amalgam is deep unlined cavity preparations( 0.5 mm or less)

• Margins of newly placed amalgam restorations show significant microleakage. Marginal leakage of corrosion and microbial products is probably enhanced by the natural daily thermal cycle in the oral cavity.

• Lichenoid reaction represent a long term effect in the oral mucous membrane adjacent to amalgam restoration. Buccal mucosa and lateral border of the tongue being the areas affected often.

BIOCOMPATIBILITY OF DENTAL MATERIALS

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“Accidental implantation of silver containing compounds into oral mucosal tissue”

Occur during:• Removal of old amalgam• Broken Pieces-socket-tooth

extraction• Particles entering surgical

wound• Amalgam dust in oral fluids-

abrasion areas• Seen as – Grayish black

pigmentation• Common Sites- Gingiva,

buccal mucosa, alveolar mucosa

2.AMALGAM TATTOO:

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Amalgam pigmentation (amalgam tattoo) of the oral mucosa: A clinico pathologic study

The most common location was the gingiva and alveolar mucosa, followed by the buccal mucosa. Histologically, the amalgam was present in the tissues as discrete, fine, dark granules and as irregular solid fragments. The dark granules were arranged mainly along collagen bundles and around blood vessels. They were also associated with the walls of blood vessels, nerve sheaths, elastic fibers, basement membranes of mucosal epithelium, striated muscle fibers, and acini of minor salivary glands. Dark granules were also present intracellularly within macrophages, multinucleated giant cells, endothelial cells, and fibroblasts. Although in 45 percent of the cases there was no tissue reaction to the amalgam, in 17 percent there was a macrophagic reaction and in 38 percent there was a chronic inflammatory response, usually in the form of a foreign body granuloma, with multinucleated giant cells of the foreign body and Langhans types.

JADA 1982, Vol. 40, No. 1 , Pages 9-16

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Indications• Amalgam should be considered for:

– class I, II. – the distal surface of the cuspids. – class V in posterior teeth.

• Material selection in such case will depend on:• The extent of the lesion.

Amalgam is preferable in the following situations:– Small and medium sized class I and II cavities– Cavities with four walls and floor to decrease the

tensile load– Under mined cusps will require cusp capping– In extensive lesions cast gold will serve better.

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• Caries incidence Amalgam may be favored if:– Repair or remake is likely to include extensions for

original cavities.– Patient with moderate to high caries incidence; as it is

• Less costly• Having good sealing ability

• Economics– Amalgam restorations cost far less than cast gold per se.

– If the restoration has to be replaced repeatedly this advantage becomes questionable.

– Core-build under full crown restorations.

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Contraindications

1. Amalgam will be objectionable for:– Esthetic conscious patient.– In conspicuous areas of the tooth– The posterior composite may be favored.

2. In cases of undermined cusps, where the tooth subjected to high load of tensile strength , where cast gold serve better .

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ADVANTAGES OF DENTAL AMALGAM

It is durable. Least technique sensitive Applicable to a broad

range of clinical situations. Newer formulations have grater long-term

resistance to surface corrosion.

It has good long-term clinical performance.

Ease of manipulation by dentist.

Corrosion products seal the tooth restoration interface and prevent bacterial leakage.

Minimal placement time

Long lasting if placed under ideal conditions.

Very economical. Self sealing Biocompatible

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DISADVANTAGES OF DENTAL AMALGAM

• Some destruction of sound tooth tissue.

• Poor esthetic qualities.• Long-term corrosion at

tooth-restoration interface may result in ‘ditching’ leading to replacement.

• Galvanic response potential exists.

• Local allergic potential.

• Marginal breakdown.• Bulk fracture• Secondary caries• Sometimes excess Hg within

the restoration may seep through the dentinal tubules, discolor dentin and result in blackish or grayish staining of teeth.

• Concern about possible mercury toxicity that affects the CNS, kidneys and stomach.

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Failures

• Bulk fractures

• Sensitivity or pain

• Corrosion

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• Secondary caries • Marginal fractures

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Signs of failures

1. Fracture Lines2. Marginal Ditching3. Proximal Overhangs4. Poor anatomic contours5. Marginal Ridge incompatibility6. Improper Proximal Contacts7. Recurrent Caries8. Poor occlusal Contacts9. Amalgam Blues

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Reasons For Failures

1. Improper Case Selection2. Improper Cavity Preparation3. Faulty Selection & manipulation of

Amalgam 4. Errors in Matricing Procedures 5. Post Operative Factors

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RECENT DEVELOPMENTs OF Dental AMALGAM

• Mercury free direct filling amalgam alloys• Gallium based alloys• Low mercury amalgams• Indium in mercury• Resin coated amalgam• Fluoridated amalgam• Bonded amalgam• Consolidated silver alloy system

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Mercury-free amalgam

• Gallium as a substitute for mercury• Similar handling characteristics to

traditional amalgam• Not a good alternative due to high

corrosion and lower strength• Not commonly used

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RESIN COATED AMALGAM

• To overcome the limitation of microleakage, a coating of unfilled resin over the restoration margins and the adjacent enamel, after etching the enamel.

• Resin may eventually wear away, it delays microleakage until corrosion products begin to fill the tooth restoration interface.

J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208

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• Mertz-fairhurst and others evaluated bonded and sealed composite restorations versus sealed conservative amalgam restorations and conventional unsealed amalgam restorations.

• Results indicate that both types of sealed restorations exhibited superior clinical performance and longevity compared with unsealed amalgam restorations over a period of 10 years.


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FLUORIDATED AMALGAM

• Fluoride, being cariostatic, has been included in amalgam to deal with the problem of recurrent caries.

• Disadvantage: fluoride is not delivered long enough to provide maximum benefit.

• Several studies investigated fluoride levels released from amalgam.

• These studies concluded that a fluoride containing amalgam may release fluoride for several weeks after insertion of the material in mouth. Fluoride release from this amalgam seems to be considerable during the first week.


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• An anticariogenic action of fluoride amalgam could be explained by its ability to deposit fluoride in the hard tissues around the fillings and to increase the fluoride content of plaque and saliva, subsequently affecting remineralization.

• In this way, fluoride from amalgam could have a favorable effect not only on caries around the filling but on any initial enamel demineralization.

• The fluoride amalgam thus serves as a “slow release device”


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BONDED AMALGAM

• Since amalgam does not bond to tooth structure, microleakage immediately after insertion is inevitable. So, to overcome these disadvantages, adhesive systems that reliably bond to enamel and dentin have been introduced.

• Amalgam bond is based on a dentinal bonding system developed in Japan by Nakabayashi and co-workers.

• The bond strengths recorded in studies have varied, approximately 12–15 Mpa.

• Using a spherical amalgam in one study of bonded amalgam, Summitt and colleagues reported mean bond strength of 27 MPa.

• Bond strengths achieved with admixed alloys tend to be slightly lower than those with spherical alloys.


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• Study compared post-insertion sensitivity of teeth with bonded amalgams to that of teeth with pin-retained amalgams. After 6 months, teeth with bonded amalgams were less sensitive than teeth with pin-retained amalgams.

• If bonding proves successful over the long term, method of mechanical retention can be eliminated, thus reducing the potential for further damage to tooth structure that occurs with pin placement or use of amalgam pins.


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CONSOLIDATED SILVER ALLOY SYSTEM

• One amalgam substitute being tested is a consolidated silver alloy system developed at the National Institute of Standards and Technology.

• It uses a fluoroboric acid solution to keep the surface of the silver alloy particles clean.

• The alloy, in a spherical form, is condensed into a prepared cavity in a manner similar to that for placing compacted gold.

• One problem associated with the insertion of this material is that the alloy strain hardens, so it is difficult to compact it adequately to eliminate internal voids and to achieve good adaptation to the cavity without using excessive force


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Gallium alloy

The current composition of gallium alloy comes as a powder and contain:• Silver 50%wt.• Tin 25.7%wt.• Copper 15%wt.• Palladium 9%wt.• Traces 0.3%wt.• Traces 0.5%wt.

It is also available as a liquid containing;

• Gallium 65%wt.• Indium 18.95%wt.• Tin 16%wt.


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Structure of gallium amalgam The structure of gallium amalgam has

been interpreted in terms of a reaction of CuGa2 and PdGa5, surrounding the unreacted alloy particles, which are held together by a matrix of Ag9In4 in which island of Ag9Ga3 and beta tin can be found.


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Clinical behavior of gallium alloy

• Changes in marginal integrity, surface texture, luster, and color were measured clinically over a period of up to 2 years.

• Significant change in luster and surface roughness occur within 4 months.

• Apparent corrosion behavior


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A comparison of the mechanical properties of a gallium-based alloy with a spherical high-

copper amalgam

• The mean hardness, 1 h compressive fracture strength, 24 h diametral tensile and 24 h flexural strengths of Galloy® were significantly lower (P<0.001) than Tytin®. No significant differences in modulus of elasticity, creep, dimensional change on setting, 24 and 168 h compressive fracture strength for the two alloys were identified.

• Significance: The significant reduction in the 1 h mean compressive fracture strength and hardness identified for Galloy® compared with Tytin® possibly indicate a slower setting reaction in the gallium-based alloy. Manual condensation of the gallium-based alloy produced specimens with inferior mechanical properties.P revious reports indicating poor corrosion resistance and moisture sensitivity of gallium-based alloys highlight the need for further research to investigate the effect of the oral environment on the gallium-based alloy.

Dental Materials Volume 17, Issue 2, March 2001, Pages 166–169



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The effect of water contamination on dimensional change and corrosion properties of a gallium alloy

The gallium-based alloy exhibited expansion if contaminated with water during the condensing and setting process. Post-setting exposure to water did not result in expansion of the gallium-based alloy. The alloy also exhibited a greater susceptibility to corrosion than the amalgam. Due to the possibility of delayed expansion, this material should be used cautiously, particularly in applications involving weakened tooth structure.

Dental Materials Volume 17, Issue 2, March 2001, Pages 142–148



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Conclusion

Historically, amalgam restorations have been among the most common of all dental restorations.

The use of high-copper amalgams has improved dramatically the clinical longevity of amalgam (5-10 years under ideal conditions).

Its major advantage has been the decline in the cases of microleakage.

The use of precapsulated amalgam has reduced significantly the risk of exposure of dental personnel to mercury vapor.

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Although small amounts of mercury release from amalgam is known to occur, it does not cause any major health problems.

Although there are other alternatives to amalgam they can not match amalgam’s longevity, ease of manipulation and versatility.

Hence dental amalgam will be a part of dentistry for a long time to come.

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References

• Phillips’ Science of Dental Materials – 11th Edition

• Craig’s Restorative Dental Materials – 12th Edition

• Sturdevant’s Art and Science of Operative Dentistry – 5th Edition

• Textbook of Operative Dentistry – Amit garg and Nisha garg

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• Dental Materials, clinical applications for dental assistants and dental hygienists

• Dental Amalgam: Update on Safety Concerns

JADA 1998; 129:494-501• Materiales dentales: Federico

Humberto Barceló Santana & Jorge Mario Palma Calero

http://www.ada.org/public/media/presskits/fillings/safety.pdf



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Amalgam Seminar