amalgam past,present& future-i

POSTGRADUATE DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS

SEMINAR TOPIC:-

DENTAL AMALGAM-PAST, PRESENT & FUTURE-I

(EVOLUTION & PROPERTIES)

Presented by-Ashish Choudhary Pg student

UNDER GUIDANCE OF :-

Prof. Dr Riyaz Farooq (HOD) Dr Aamir Rashid (lecturer) Dr Fayaz Ahmed (lecturer)

Contents IntroductionHistory of amalgamAmalgam wars Classification Components of amalgam Basic setting reactionManufacture of alloy powder Properties of amalgamManipulation of amalgam Recent advances in amalgam Side effects of mercuryDurability of amalgam Future of amalgam Conclusion

INTRODUCTIONDental amalgam is one of the most

versatile restorative materials used in

dentistry. It constitutes approximately 75% of all restorative

materials used by dentists. It has served as a dental

restoration for more than 165 years. J Conserv Dent. 2010 Oct;13(4):204-8.

Dental amalgam: An update

IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion

http://www.ncbi.nlm.nih.gov/pubmed/21217947



• There is still no adequate economic alternative for dental amalgam. The combination of reliable long-term performance in load bearing situations and low cost is unmatched by other dental restorative material. It has a myriad of uses: rather low technique sensitivity, self-sealing property and its longevity


J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update




AMALGAM POPULARITY

Cost effective and long

life

Acceptable biocompatib

ility

Less technique sensitive






Over the last few years improvements in composition have led to -

Reduced marginal

failure due to decreased creep and corrosion

Early seal between the

tooth and restoration

But development of alternatives based on ceramics and composites , and questions on its safety have led to its decline.







Cavity design & prepation

Selection of alloy & its

manipulation with mercury

Contouring & finishing

procedures

Age of the restoration &

its environment

The variables for amalgam’s appearance

Amalgam: past,present & futureJADA,Vol.86,April 1973

What is amalgam????

a·mal·gam: any alloy of mercury with any another metal [silver amalgam is used as a dental filling]

word amalgam is derived from greek name ‘emolient’ which means paste.


Source: Webster’s New World Dictionary of the American Language, Guralnik DB, Ed., New York: World Publishing Co., 1972

Dental amalgam is an alloy made by mixing mercury with a silver tin

amalgam alloy (Ag-Sn)

Amalgam alloy is a silver tin alloy to which varying amounts of copper(Cu) and small amounts of zinc(Zn) have

been added


Sturdevant’s Art & Science of Operative dentistry..5th ed; 152

INDICATIONS OF AMALGAM

Moderate to large Class I and Class II

restorations

Class V restorations in unaesthetic

areas

Foundations


Esthetics

Small (even moderate) defects in

posterior teeth

Requirement for reinforcement of

tooth

CONTRAINDICATIONS OF AMALGAM


ADVANTAGES OF AMALGAM• Cost effective

• Time effective• Ease of placement • Wear

resistance• Prevent marginal leakage after a period of time

• Adequate resistance to fracture

• Maintains anatomical form

• Not overly technique sensitive

• Favourable long term clinical research results


• Aesthetics• Toxicity

• Corrosion and galvanic action

• Difficult tooth preparation

• Initial marginal leakage

• Technique sensitive if bonded

• Brittle

• Marginal breakdown

• Do not help retain weakened tooth structure

Disadvantages IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion

• Less microleakage, interfacial staining.

• Slightly increase strength of remaining tooth structure.

• Minimal postoperative sensitivity.

• Some retention benefit.

• Esthetic benefit of sealing by not permitting the Amalgam to discolor the adjacent tooth structure.

Bonded Amalgams have “Bonding benefits” :


HISTORY OF AMALGAM

A Chinese medical text(Material medica) mentions using a “silver paste”, a type of amalgam, to fill teeth in the 7th century-by Su Kung in 659 AD






In Europe, Johannes Stokers, a municipal physician in Ulm, Germany, recommended amalgam as a filling material in 1528.

Later, Li Shihchen (1578) chronicled a dental mixture of 100 parts mercury with 45 parts silver and 900 parts tin






In the 18th century, John Hill, an Englishman, described mercury as, “It

penetrates the substance of all metals, and dissolves, and makes them brittle.”


• In 1818, Louis Nicolas Regnart, a Parisian physician invented amalgam by the addition of one-tenth by weight of mercury to another metal or metals.

Dental silver amalgam was probably introduced in England by Joseph Bell, a British chemist, in 1819, and was known as ‘Bell’s putty’.





• Traveau described a “silver paste” filing material in 1826. He produced amalgam by mixing the silver coins with mercury.


1833

-- Crawcours brothers introduced their “Royal Mineral Succedaneum” to America

--mixed shaved French silver coins and mercury.






In 1877, Foster Flagg published the results of

his laboratory tests and 5-year clinical observation of new alloys with 60% of silver and 40% of tin as major constituents in

1881 and thus predated by some 15 years the

work of G.V. BlackJ Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update





The universal acceptance of amalgam as a restorative

material resulted from investigations of G V Black in

1895, 1896, 1908

By combining the principles of cavity design, extension of the cavity into

“immune” areas and the development of an alloy with the composition of

68.5% silver, 25.5% tin, 5% gold, 1% zinc, Black advanced amalgams into

modern times






Traditional or conventional amalgam alloys were produced by early dental manufactures

(S S White) & predominated from 1900 untill 1970.the basic

composition was 65%Ag, 30%Sn, 5%Cu,& less than 1%zinc



ADA specification No 1 was adapted for amalgam in 1929.




Extensive studies of the setting reaction of dental amalgams was performed by Gayler in 1937 & found that in the coarse filling alloys

of that time, copper contents greater than 6% produced excessive expansion

This was later challenged by Greener in 1970’s


Gayler ML. Dental amalgams. J Inst Metals. 1937;60:407–19

Greener EH. Amalgam-yesterday, today and tomorrow. Oper Dent. 1979;4:24–35.





• In 1959, Dr. Wilmer Eames recommended a 1:1 ratio of mercury to alloy, thus lowering the 8:5 ratio of mercury to alloy that others had recommended. Eames WB. Preparation and condensation of amalgam with low mercury alloy ratio. J Am Dent Assoc. 1959;58:78–83






In 1962, a spherical particle dental alloy was introduced by Innes & Youdelis

This was followed in 1963 by a high copper dispersion alloy system that proved to be superior to its low copper predecessors

Example; Dispersalloy (Caulk)






1970’s• first single composition

spherical• Tytin (Kerr)• ternary system

(silver/tin/copper)

1980’s- mercury free alloys introduced


AMALGAM WARS-the controversy


• In 1841, the American Society of Dental Surgeons declared that

“the use of amalgam constitutes malpractice”

AMALGAM USE DECLINED

Dr. Christopher S. Brewster (1846) - condemned the use of amalgam in all cases merely because its use was abused by some “unprincipled quacks” was unwise.

The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001

1842 – a belief prevailed that amalgam exerted “a vitiating influence upon the fluids of the mouth and gives rise to an unhealthy action in the gums.”

1844 - the society’s members were warned that they were to sign a pledge “NEVER TO USE amalgam” or they would risk being expelled from the membership.



Townsend - gave his personal directions for preparing the amalgam, known as “Townsend’s Amalgam”.

In 1858, Townsend reversed his stance on amalgam and recommended removal of teeth that could not be saved by gold.In 1867, the St. Louis Odontological Society unanimously adopted a resolution to the effect that amalgam was “injurious and detrimental to health” AMALGAM


Dr. J. Payne in 1874, claimed that the dental profession was poisoning “thousands of people all over the world from corrosive sublimate generated in the mouth from amalgam plugs in the teeth.” IN 1883, DR. ALTON H. THOMPSON COMMENTED

• The presence of amalgam with us is a tremendous fact which we must accept



1924 - Alfred Stock became poisoned with mercury & published papers on the dangers of mercury in dentistry

1934 - German physicians - no health risk from amalgams

In December 2003, Dr. Frederick Eichmiller, - Amalgam is a SAFE, AFFORDABLE, AND DURABLE MATERIAL.”



the first one……

• In 1845, American Society of Dental Surgeons condemned the use of all filling material other than gold as toxic, thereby igniting "first amalgam war'.

AMALGAM WARSIntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion


What ended the amalgam war??

• Professional and consumer demand.

• In 1859, the leaders of the profession regrouped to form the American Dental Association.

• Between 1860 and 1890, many experiments were done to improve amalgam filling materials.

• it was the classical work of GV Black in 1895that a systemic study was done on properties & appropriate manipulation of amalgam.



Then came the second amalgam war….

• Controversy over amalgam use surfaced again in 1926 and into the 1930's when a German physician, Dr. Alfred Stock, showed that mercury escaped from fillings in the form of a dangerous vapor that could cause significant medical damage.



• During this Second Amalgam War, the American Dental Association vigorously defended silver amalgam and its widespread use was continued



Remarkably, the Food and Drug Administration (FDA) has separately approved the mercury and the alloy

powder for dental use; but the amalgam mixture has never been

approved as a dental device

Unfortunately now came the second world war over Europe &" the second amalgam war" fell in

forgetfulness



3rd amalgam war in 1980s

It was the Neurobiologist Mats Hanson, Assosiate professor in physiology at Lund University in Sweden, who in 1981 started the fight against the authorities




but began primarily through seminars ,writings,& videotapes of Dr HA Higgins, a dentist from Colarado Springs in the same year

Pressure from mounting clinical evidence forced the ADA to finally publicly concede that mercury vapor does escape from the amalgam filling into the patients mouth.




But the ADA remained adamant that mercury in patients' mouths is safe, and

in 1986 it changed its code of ethics, making it unethical for a dentist to

recommend the removal of amalgam because of mercury

but problem flared in 1990’s by the telecast of television program ‘60

minutes’ in CBC television



Current status on the amalgam war

The amalgam war continues to rage on today. some states have already appointed holistic/biological dentists to dental boards, effectively ending the ADA monopoly on state dental boards.



Current status on the amalgam war

• The problem is so serious that American Council on Health & Science, has determined that allegations against amalgam constitute one of the greatest “unfounded health scares of recent times”



• There is presently a congressional bill in The United States House of Representatives (H.R. 4163) introduced by Rep. Diane Watson (D-CA) and Rep. Dan Burton (R-IN) to ban the continued use dental amalgam fillings.



STATEMENT ON AMALGAM-ADA"No controlled studies have been published

demonstrating systemic adverse effects from amalgam restorations-FDI & WHO;1997

“based on available scientific information, amalgam continues to be a safe and effective restorative

material.“-ADA;1998

"There currently appears to be no justification for discontinuing the use of dental amalgam.“-ADA;1998


American Dental Association (ADA) Council on ScientificAffairs, “Statement on dental amalgam,” 2011, http://www.ada.org/1741.aspx

“The current data are insufficient to support an association between mercury release from dental amalgam and the various complaints that have been attributed to this restoration

material”-LSRO &FDA;2004



“there were no statistically significant differences in adverse neuropsychological or renal effects observed over the 5-year period in children whose caries are restored using dental amalgam or composite materials- Journal of the American Medical Association (JAMA) and Environmental Health Perspectives;2006



amalgam is a valuable, viable and safe choice for dental patients-ADA;2009

material is a safe and effective restorative option for patients-FDA;2009



Classification of AmalgamA) According to Alloyed Metals


Sturdevant’s Art & Science of Operative Dentistry; 5th ed

Number of

alloyed metal

Binary alloy (Ag-

Sn)

Tertiary alloy

(Ag-Sn-Cu)

Quarternary alloy (Ag-Sn-Cu-

Zn)

B) According to shape of powdered particle



Lathecut spherical

Admixed

C) According to copper content



Low copper amalgam(<0-6%)

High copper amalgam(>6-

13%)

D)According to zinc content



Zinc containing alloy

(>0.01-2%)

Non zinc containing alloy

(<0-0.01%)

1st generation

2nd generation

3rd generation

3Ag + Sn

Cu Zn


Ag3Cu

3Ag + Sn

3Ag + Sn

4th generation Ag Sn Cu upto 29%

5th generation Ag Sn Cu In

6th generation

E)Generations based on the improvement in composition

Ag Cu Pd

Ternary alloy

Quaternary alloy

Eutectic alloy 1st, 2nd, 3rd generation+

Components of dental amalgam

OtherZinc IndiumPalladium

Silver Tin

Copper Mercury

Basic


Phillip’s Science of Dental Materials;11th ed

Silver(Ag)

Decreases creep & setting time

Decreases corrosion

Increases hardness & edge strength

Increase tarnishing



Tin(Sn)

Low strength

Larger contraction

Decreases expansion

Increased corrosion

Increased plasticity

Increased setting time



Copper(Cu)

Decreases plasticity

Increases hardness strength of alloy

Reduce creep

Reduce tarnish & corrosion



Zinc(Zn)

Decreases brittleness

Acts as a deoxidizer

Less marginal breakdown



Indium(In)decreases surface tension• reduces amount of mercury

necessary• reduces emitted mercury vapor

reduces creep and marginal breakdown

increases strength

example• Indisperse (Indisperse Distributing

Company)• 5% indium*


operative dentistry journal1992 Sep-Oct;17(5):196-202

`

• Palladium (Pd)– reduced corrosion– greater luster– example

• Valiant PhD (Ivoclar Vivadent)– 0.5% palladium

Mahler J Dent Res 1990


Palladium pellets placed in an amalgam restoration were effective in reducing the amount of mercury vapor released in the 7 days following placement.

Dental Materials Volume 15, Issue 6, November 1999, Pages 382-389

The optimal palladium content in γ1 seems to be in the range between 0.50 and 0.75 wt%.

Biomaterials, Volume 18, Issue 13, July 1997, Pages 939-946


http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VP3-3XMGS4W-2&_user=5010750&_coverDate=11/30/1999&_alid=1175495605&_rdoc=31&_fmt=high&_orig=search&_cdi=6195&_sort=r&_docanchor=&view=c&_ct=22049&_acct=C000066081&_version=1&_urlVersion=0&_userid=5010750&md5=a3dc9e65ea898a1775ca0fab58f3917a

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VP3-3XMGS4W-2&_user=5010750&_coverDate=11/30/1999&_alid=1175495605&_rdoc=31&_fmt=high&_orig=search&_cdi=6195&_sort=r&_docanchor=&view=c&_ct=22049&_acct=C000066081&_version=1&_urlVersion=0&_userid=5010750&md5=a3dc9e65ea898a1775ca0fab58f3917a

Mercury (Hg) - only pure metal that is liquid at room temperature

Activates reaction

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



Alloy Powder CompositionType Ag Sn Cu Zn Other

Low copper 63-72 26-28 2-7 0-2 —

High-Cu admixed lathe-cut 40-70 26-30 12-30 0-2 —

High-Cu admixed spherical 40-65 0-30 20-40 0 0-1 Pd

High-Cu single spherical

40-60 22-30 13-30 0 0-5 In, 0-1 Pd

compositions in weight percent

Sturdevant’s Art & Science of Operative Dentistry;5th ed


Alloy Powder: Dispersalloy®

Silver69%

Tin18%

Copper12%

Zinc1%

Mixing proportions: 50% alloy, 50% mercury



Alloy Powder: Tytin®

Mixing proportions: 57.5% alloy, 42.5% mercury

Silver59%

Tin13%

Copper28%

Zinc0%



Phases in Amalgam Alloys and Set Dental

Amalgams

Formula

g Ag3Sn

g1 Ag2Hg3

g2 Sn7-8Hg

b Ag4Sn (silver-rich)

e Cu3Sn

h Cu6Sn5

Silver-copper eutectic

Ag-Cu



BASIC COMPOSITION

MatrixAg2Hg3 called gamma 1 - cement Sn7Hg called gamma 2 - voids

Filler (bricks)Ag3Sn called gamma can be in various shapes irregular (lathe-cut), spherical or a combination of both.

A silver-mercury matrix containing filler particles of silver-tin.

Ag3Sn

Ag2Hg3Sn7Hg8


Basic setting reactionsAg-Hg

Ag

Hg

Ag4Hg5 (ƴ1 phase)Initial product

Ag

Hg

Ag5Hg4 (β1 phase)In p/o excess Ag

IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion

Materials science for dentistry;9th ed B.W.Darvell

Silver-Tin (Ag - Sn) System

Most commercial alloys fall within the limited composition range of B to C i.e (β + γ) and γ

If Sn > 26.8 wt% γ + Sn-rich phase is formed.


• Dissolution and precipitation • Hg dissolves Ag and Sn

from alloy• Intermetallic compounds

formedAg

Sn

Conventional Low-Copper Alloys

Hg

Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg 1 2

CRAIG’s Restorative Dental Materials;12th ed


• Gamma () = Ag3Sn– unreacted alloy– strongest phase and

corrodes the least– forms 30% of volume

of set amalgam

• Gamma 1 (1) = Ag2Hg3

– matrix for unreacted alloyand 2nd strongest phase

– 60% of volume



IMPORTANCE OF γ2 PHASE:-

• Sn8Hg in a set amalgam may be reduced in quantity or even eliminated by the presence of ε–phase (Cu3Sn)

• Potentially valuable rxn for several reasons:-

tin act as a most electropositive element present in absence of Zn, so with high activity in the γ2 phase, it makes the most electropositive phase, hence the most easily corroded Materials science for dentistry;9th ed

B.W.Darvell


γ2 phase is extremely weak & soft, deforming readily & the strength of amalgam is limited by its presence

Contributes to static creep of amalgam



Scanning electron microscopic view of SnHg (γ2) crystals, that occurs in the matrix of set low copper amalgam



Improves strength of the resulting amalgam

But if in excess, leads to expansion on setting



COPPER

Depending on its quantity & amt of Sn in the alloy, it may present as:-

1.Cu3Sn (ε-phase) 2.Cu6Sn (ή-phase)

As solubility of Cu in γ and γ1 phase is low, thus Cu-Sn phase formed during setting process will probably be ή phase



The reaction rate of β or γ phase Ag-Sn

with Hg is sufficiently fast that the γ2 phase is always formed initially, but Cu3Sn (ε phase) & γ2 phase cannot exist together for long & relatively slow reaction must occur.

ε + γ2 → ή + (Hg)



SLOW REACTIONS

This is at relatively low rate because it is a solid state reaction

Also the 2 phases will be distributed as small grains throughout the amalgam without necessarily touching , & all diffusion of metal atoms must be through other phases or grain boundaries



In the long term the conversion of γ1 to β1 may occur in the presence of unreacted γ phase alloy…

γ + γ1 → β1



In the presence of excess Hg ( in terms of reaction with Ag-Sn phases),namely the decomposition of Cu-Sn phases to give the phase Cu7Hg6 (β2 phase) occurs….

ε , ή (IN P/O EXCESS Hg) → β2 + γ2



Added Cu

As >6% Cu may not be included in the ‘conventionally’ formulated alloy because of excessive expansion

However, if the extra Cu in incorporated in the form of second alloy powder, mixed with the first(admixed alloy),the difficulty may be avoided



One such second alloy is eutectic of Ag-Cu system;this corresponds to composition 3Ag.2Cu

α + α1 + γ2 ή + γ1

The elimination of γ2 phase results in improved properties, particularly in the compressive strength.



High copper admixed alloy

2. Sn8Hg + AgCu Cu6Sn5 + Ag2Hg3 + Ag3Sn (2) ( ) (1 ) ( )

1. Ag3Sn + AgCu + Hg Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu ( ) (1 ) (2 ) ( )



High copper unicompositional alloy

Ag3Sn + Cu3Sn + Hg Cu6Sn5 + Ag2Hg3 ( ) ( ) ( ) (1 )



Microstructure of Set Low Copper Amalgam.

(Ag3Sn)

2(Sn8Hg)

Voids

1(Ag2Hg3)


Microstructure of Set High-Copper Admixed Amalgam.

1(Ag2Hg3)

(Ag3Sn)

Eutectic(Ag3Cu2)

(Cu6Sn5)


Produced by cooling molten 72% Ag and 28% Sn and forming an ingot (The ingot may be 3-4 cm in diameter and 20 -30 cm in length)

Alloy is heated for 8 hours at 400°C for homogeneous distribution of silver and tin

Ingot is lathe-cut to produce the particles, ball-milled to reduce their size

The particles are 60-120µm in length, 10-70µm in width & 10-35µm in thickness(Irregular in shape)


Manufacture of alloy powderLathe cut alloy powder


Produced by atomizing the molten alloy in a chamber filled with an inert gas- argon

Molten metal falls through a distance of approximately 30 feet and cools

Results in characteristic spherical particle shapes.

If particles are allowed to cool before they contact the surface of chamber, they are spherical in shape. If they are allowed to cool on contact with the surface they are flake shaped.

Particle size ranges form 5 to 40 microns


Spherical alloy powder


A. Lathecut alloyB. Spherical alloyC. Admixed alloy



Homogenizing anneal

1. to overcome the coring & segregation in the solid ingot

2. to reestablish the equilibrium phase relationship

the ingot is placed in an oven & heated at temp. below solidus for a sufficient time to allow diffusion of the atoms to occur.



Temperature

for Ag-Sn: 480 degree

Celsius

if Cu present: 465 degree

celsius

if Zn present: lower it further

The time of heat treatment may vary depending on the temp. used & size of ingot, but 24 hr at the selected temp.(350 to 450 iC) is usual.



• At the end of heat treatment:-

If rapid quenching done

• The phase distribution remains unchanged

• e.g. in an Ag-Sn alloy results in the formation of βphase in max. amount

If allowed to cool slowly

• The proportion of phases continue to adjust towards room temperature equilibrium ratio

• e.g. formation of γ phase



Particle(surface) treatment

Freshly cut alloys amalgamate & set more promptly than aged particles, but some aging of alloy is desirable to improve the shelf life of product

Amalgams made from acid washed powders tends to be more reactive than those ,made from unwashed powders



• The aging is related to relief of stress in the particles during the cutting of the ingot

(Phillip’s Science of Dental Materials;11th ed )

• The alloy particles are aged by subjecting them to a controlled temperature of 60-100 degree celsius for 1-6 hrs

(Craig’s restorative dental materials,12th ed)


PARTICLE SIZE

• Greater amount of mercury to form an acceptable amalgam

Tiny particles

• More rapid hardening and a greater early strength

Small-to-average

particle size

• A rough surface • Corrosion

Larger particles


Properties of amalgam

• ANSI/ADA specification No.1 for amalgam alloy contains certain requirements:-

1. Maximum creep value of 3%

2. Minimum Compressive strength of 80 MPa at 1 hr when a cylindrical specimen is compressed at a rate of 0.25mm/minute

3. Dimensional change between 5 min & 24 hrs after trituration, should fall within a range of ±20µm/cm at 3 7̊ 7WC.̊



DIMENSIONAL CHANGES

Amalgam can expand or contract depending on manipulation

Severe contraction leads to plaque accumulation & secondary caries

Expansion leads to postoperative pain & splitting of tooth



Immediately after packing a rapid contraction may be observed, followed by a slower expansion, and then a slight & slower contraction(amalgam setting

dimensional change curve)



20µm 20µm 20µm 20µm


High-Cu, admixed

High-Cu, single comp.

Low-Cu

If amalgam expanded during hardening, leakage around the margins of restorations would be eliminated.


Shrinkage• when alloy & mercury are

mixed ,contraction results as particles begin to dissolve & ƴ1 crystals grow

• 8Ag3Sn + 31Hg (823.5ml/mol)=6Ag4Hg5 + Sn8Hg

(774.9ml/mol)

• Thereby a decrease of 5.9% by volume, or 2.0% by length (effect of solidification of mercury)



Evidently the detrimental effect of shrinkage occurs only when the amalgam mass shrinks > 50 µm.


LOSS OF GLOSS• Shrinkage due to reaction will initially

cause a decrease in the bulk volume, but once contacts between alloy particles or new crystals interfere with this, there is no choice but for the Hg to be withdrawn into the mass, leaving behind outline of the alloy particles.



The failure of any amalgam to provide a marginal seal is due to the shrinkage of the liquid mercury on reaction & surface tension(a,b)



• The crinkly surface thus produced clearly cannot be in direct contact with the cavity wall & a leakage path exists which survives even if there is subsequent expansion



• The effect infact lead to loss of gloss, a freshly mixed pellet of amalgam is very smooth & shiny-metallically wet looking, but as setting proceeds it acquires a frosted or sand blasted appearance.

• Leakage path can also occur because of the surface tension of mercury



EXPANSION

• The impingement of growing crystals one on another will cause outward forces which will result in some expansion (crystal growth pressure)

• If sufficient Hg is present to produce a plastic matrix, expansion occurs as a result of growth of ƴ1 crystals & viceversa



DELAYED EXPANSION

Zinc containing low/high copper amalgam is contaminated by moisture during trituration or condensation, a

large expansion can take place

This expansion usually starts after 24 hrs, reach at peak within 3-5 days & may continue for months reaching

values >400µm.Materials science for dentistry;9th ed B.W.Darvell


• Hydrogen is produced by electrolytic action involving zinc & water

• H2 doesnt combine with the amalgam rather it collects within amalgam, increasing internal pressure of amalgam leading to expansion



Delayed expansion



STRENGTHA) Compressive strength

Because amalgam is strongest in compression & much weaker in tension & shear, the prepared cavity design should take benefit of that

When subject to a rapid application of stress either in tension or compression a dental amalgam does not exhibit significant deformation or elongation & as a result function as a brittle material



• High copper single composition materials have the highest early compressive strength of more than 250 Mpa at 1 hr

• While it is lowest for the low copper lathe cut alloy(45 Mpa)



• High values for early compressive strength are advantage for an amalgam, because they reduce the possibility of fracture by application of prematurely high occlusal forces by the patient before the final strength is reached

• The compressive strength at 7 days is again highest for the high copper single composition alloys, with only modest differences in the other alloys



B) Tensile strength• Amalgam cannot withstand high tensile or

bending stresses

• The design of the restoration should include supporting structures whenever there is danger that it will be bent or pulled in tension

• Both low & high copper amalgams have tensile strength that range between 48-70 MPa



Factors affecting strength

-depends on the type of amalgam alloy, the trituration time & the speed of amalgamator

-either under or overtrituration decreases the strength in both traditional & high copper amalgams



1) Effect of trituration

2) Effect of mercury content

dry granular mixrough & pitted surfacecorrosion

high mercury contentmore γ2

phase

low mercury contentmore

unreacted AgSn particlesimparts

strength to restoration

sufficient mercury should be mixed with the alloy to wet each particle of the alloy


-good condensation techniques express mercury & results in smaller volume fraction of matrix phases

-in lathe cut alloys, higher condensation pressure results in higher compressive strength, particularly the early strength(at 1 hr)

-on the other hand spherical amalgams condensed with lighter pressures produce adequate strength



3) Effect of condensation

-voids & porosities reduces strength-porosity is caused by:-

a. decreased plasticity of the mix (due to low Hg/alloy ratio, delayed condensation, undertrituration)

b. inadequate condensation pressure(results in inappropriate adaptation at the margins & increase number of voids)



4) Effect of porosity

c. irregularly shaped particles of alloy powder

d. insertion of too large increments

-fortunately, voids are not the problem with spherical alloys



-amalgams do not gain strength as rapidly as might be desired

-at the end of 20min,compressive strength may be only 6% of 1 wk strength

-ADA stipulates a min of 80MPa at 1 hr



5) Effect of rate of hardening

-the 1 hr compressive strength of high Cu single composition amalgams is relatively high compared with admixed high Cu amalgams

-patients should be cautioned not to subject the restoration to high bitting stresses for atleast 8 hrs after placement ,by that time a typical amalgam has reached at least 70% of its strength



even after 6 months ,some amalgams may still be increasing in

strength, suggesting that the reactions between matrix phases & the alloy particles may continue

indefinitely



Strength of various phases• By studying the initiation & propagation of

crack in a set amalgam, the strength of various phases can be observed

• Possible to view under a conventional metallographical microscope

• The propagation of the crack can be halted & the specimen etched to identify the various phases



• Results of such studies have led to the following ranking of different phases of a set low copper amalgam from strongest to weaker:

Ag3Sn(γ),silver-Hg phase(γ1),tin-Hg phase(γ2) and the voids

• In high copper amalgams, there is preferential crack propagation through the γ1 phase & copper containing particle



CREEP• Defined as time dependent strain or

deformation produced by stress(as in Phillips)

• Creep of dental amalgam is a slow progressive permanent deformation of set amalgam which occurs under constant stress(static creep) or intermittent stress(dynamic creep)



• Creep is related to marginal breakdown of low copper amalgams

• Higher the creep, the greater is the degree of marginal deterioration(ditching)



• According to ADA sp. No.1 creep should be below 3%

• creep values:--low copper amalgam:0.8-8%-high copper amalgam:0.1-1%



Creep rate has been found to correlate with marginal breakdown of conventional low-copper amalgams.

ADA spec. #1: creep rate < 3%IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion

Microstructure Vs. Creep

Low-Cu Larger g1 volume fraction

Presence of g2

Larger g1 grain sizes

Single compositionspherical

h(Cu6Sn5) around Ag-Cu particles improves bonding to 1g

h (Cu6Sn5) embedded ing1 grains and interlock

High-copper amalgams have creep resistance:- lack of gamma-2 phase.

Admixture


Factors influencing creep:

Large 1 volume fraction

Larger 1 grain sizes

smaller 1 grain sizes

2 associated with high creep rates.

phase which act as barrier to

deformation of 1 phase.

Phases of amalgam

restorations

High CREEP Low CREEP

Materials science for dentistry;9th ed B.W.Darvell0

For increased strength & low creep values:-

Mercury alloy ratio should be minimum

Condensation pressure should be maximum for lathe cut or admixed alloys

Careful attention should be given towards timing of trituration & condensation



Effect of manipulative variables

Compressive Strength (MPa)

% Creep Tensile Strength(24 hrs) (MPa)

Amalgam Type 1 hr 7 days

Low Copper1 145 343 2.0 60

Admixture2 137 431 0.4 48

Single Composition3 262 510 0.13 64

Phillip’s Science of Dental Materials 2003

1Fine Cut, Caulk 2

Dispersalloy, Caulk 3Tytin, Kerr

MICROLEAKAGE OF AMALGAM

The 2 to 20micron-wide

gap

Poor condensation techniques -

marginal voids

Lack of corrosion by-products

Coefficient of thermal

expansion

Single-composition-spherical alloys which leak more - do not adapt as

well to the margins


• Penetration of fluids & debris around the margins may cause secondary caries

• If the amalgam restoration is inserted properly, leakage decreases as the restoration ages in mouth due to the corrosion products that forms in the tooth-restoration interface

• Thus amalgam is the self sealing restoration



• Both low & high copper amalgams are capable of sealing against microleakage but the accumulation of corrosion products is slower with the high copper alloys*

*Corrosion sealing of amalgam restorations -in vitro study Oper Dent. 2009 May-Jun;34(3):312-20.


• The sealing ability of different types of dental amalgams when used as retrograde fillings with and without a cavity varnish was studied.

• Of the materials tested, a copper-containing spherical amalgam gave the best results.

• Regardless of material used, the apical seal was significantly improved when a varnish was applied to the cavity prior to the placement of the retrograde amalgam filling

Journal of EndodonticsVolume 9, Issue 12 , Pages 551-553, December 1983


http://www.jendodon.com/issues?issue_key=S0099-2399(83)X8045-9

THERMAL EXPANSION AND CONDUCTIVITY

Amalgam 22-28 9.4

Composite resin 20-60 0.25

GIC 10-11 0.15-0.35

Tooth 11.4 0.18-0.47

Thermal expansion coefficient E 10-6 / C

Thermal conductivity K 10-

6 / C(mm2/s)

E = volume expansion for unit rise in temperatureK = quantity of heat passing per s through a block of unit thickness and cross sectional area for a temp. difference of 1C



CHEMICAL PROPERTIES

Dental amalgam restorations undergo both chemical and electrochemical corrosion.

TARNISH AND CORROSION

Tarnish : is a surface discolouration on a metal or even a slight loss or alteration of the surface finish or luster.

Corrosion : is an actual deterioration of a metal by reaction with its environment.



The degree of tarnish depends on :

i. The oral environment

ii. The type of alloy used



In dental practice , a limited amount of corrosion around the margins of amalgam restorations may

be beneficial, since the corrosion products tends to seal the marginal gap & inhibit the ingress of fluids

& bacteria

But excessive corrosion can lead to increased porosity, reduced marginal integrity, loss of strength

& the release of metallic products into the oral environment



GAP



Liberation of corrosion products

Electrochemical measurements on pure phases

Ag2Hg3(γ1) (highest corrosion

resistance)Ag3Sn(γ) Ag3Cu2

Cu3Sn(ε),Cu6Sn5(ή)Sn7-8Hg(γ2)

(least corrosion resistance)


• The p/o small amounts of tin, silver & copper that may dissolve in various amalgam phases has a great influence on their corrosion resistance



• The higher content of tin , less the corrosion resistance

• The tin content of the γ1 phase is higher for low copper alloys than for high copper alloys



• The p/o a relatively high %age of tin in low copper alloys reduces the corrosion resistance of their γ1 phase so its lower than their γ phase

• This is not true for high copper alloys



• Occurs most notably on the occlusal surface and produces a black amalgam silver tarnish film

• Corrosion products are mainly oxides and chlorides of tin.

Chemical Corrosion :



Electrochemical corrosion

Chemically different sites act as anode or cathode.

Electrolyte (saliva)

The anode corrodes, producing soluble and insoluble reaction products.

Ag2Hg3 phase has the highest corrosion resistance, followed by Ag3Sn, Ag-Cu, Cu3Sn, Cu6Sn5 and Sn7-8Hg.



LOW COPPER ALLOYS – low corrosion resistance

The average depth of corrosion for most amalgam alloys is 100-500 m.

Most corrodible phase is tin-mercury or 2 phase

Even though, a relatively small portion (1- 13%) of the amalgam mass consists of the 2 phase, in an oral environment, the structure of such an amalgam will contain a higher percentage of corroded phase



The corrosion results in the formation of tin oxychloride, from the tin in 2 and also liberates Hg.

Sn7-8Hg + 1/202 + H2O + Cl- Sn4 (OH) 6 Cl2 + Tin oxychloride

Additional l and 2 result in porosity and lower strength.

Unreacted g

Hg

g 1 and g 2

( Mercuroscopic Expansion )


THE HIGH COPPER ADMIXED AND UNICOMPOSITION ALLOY

• No 2 phase in the final set mass.

• The η phase formed with high copper alloys is not an interconnected phase such as the 2 phase, and it has better corrosion resistance.

• η phase is the least corrosion resistant phase in high copper amalgam - corrosion product CuCl2.3Cu (OH)2

Cu6Sn5 + 1/202 +H2O + Cl- CuCl2.3Cu (OH)2 + SnO.



• Surface tarnish of low copper amalgams is more associated with γ than γ1 phase, whereas in high copper amalgams surface tarnish is related to the copper rich phases,ή & silver-copper eutectic



Galvanic corrosion

If dental amalgam is in direct contact with an adjacent metallic restoration such as gold crown, the dental amalgam is the anode in the circuit.

Between titanium and direct filling alloys• Small

galvanic interaction

High copper dental amalgams when in contact with Ti• little

galvanic corrosion

Gallium direct filling alloys• galvanic

interaction more detrimental

Dental Materials, Volume 15, Issue 5, September 1999, Pages 318-322


Local electrochemical cells may arise whenever a portion of amalgam is covered by plaque on soft tissue. It behaves anodically and corrodes. If these occur in cracks or crevice, it is called crevice corrosion.

• Regions that are under stress display a greater probability for corrosion, thus resulting in stress corrosion.• For occlusal dental amalgam greatest combination of stress and corrosion occurs along the margins.

Crevice Corrosion:

Stress Corrosion:



Factors related to excess tarnish & corrosion

High residual mercury

Surface texture-small scratches &

exposed voids

Contact of dissimilar metals,

eg. gold & amalgam

Moisture contamination

during condensation

Type of alloy-low cu alloy>high cu alloy



• Smoothening & polishing the restoration

• Correct mercury/alloy ratio & proper manipulation

• Avoid dissimilar metals including mixing of high & low copper amalgams


Corrosion of amalgam can be reduced by:-

END OF PART-I

REFERENCES • PHILLIPS’ Science of Dental Materials;11th ed Kenneth J. Anusavice• CRAIG’s Restorative Dental Materials;12th ed John M. Powers, Ronald L. Sakaguchi• Materials science for dentistry;9th ed B.W.Darvell• Sturdevant’s Art & Science of Operative Dentistry; 5 th ed;

Roberson, Heymann, Swift• fundamentals of operative dentistry, a contemporary approach;

3rd ed Summitt, Robbins, Hilton, Schwartz• Essentials of operative dentistry; I Anand Sherwood

• Dental amalgam: An update J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208• The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001• Effect of admixed indium on the clinical success of amalgam restorations. operative dentistry journal1992 Sep-Oct;17(5):196-202

• American Dental Association (ADA) Council on Scientific Affairs, “Statement on dental amalgam,” 2011,

• Dental Materials Volume 15, Issue 6, November 1999, Pages 382-389

• Biomaterials, Volume 18, Issue 13, July 1997, Pages 939-946• Journal of Endodontics

Volume 9, Issue 12 , Pages 551-553, December 1983• Corrosion sealing of amalgam restorations -in vitro study Oper Dent. 2009 May-Jun;34(3):312-20.

http://www.jendodon.com/issues?issue_key=S0099-2399(83)X8045-9

amalgam past,present& future-i

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