Amalgam past,present& future-I
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Transcript of 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
• 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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Esthetics
Small (even moderate) defects in
posterior teeth
Requirement for reinforcement of
tooth
CONTRAINDICATIONS OF AMALGAM
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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” :
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
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
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
In the 18th century, John Hill, an Englishman, described mercury as, “It
penetrates the substance of all metals, and dissolves, and makes them brittle.”
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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’.
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
• Traveau described a “silver paste” filing material in 1826. He produced amalgam by mixing the silver coins with mercury.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
1833
-- Crawcours brothers introduced their “Royal Mineral Succedaneum” to America
--mixed shaved French silver coins and mercury.
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
Gayler ML. Dental amalgams. J Inst Metals. 1937;60:407–19
Greener EH. Amalgam-yesterday, today and tomorrow. Oper Dent. 1979;4:24–35.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
J Conserv Dent. 2010 Oct;13(4):204-8.Dental amalgam: An update
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
1970’s• first single composition
spherical• Tytin (Kerr)• ternary system
(silver/tin/copper)
1980’s- mercury free alloys introduced
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
AMALGAM WARS-the controversy
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
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.”
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
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
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
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.
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• During this Second Amalgam War, the American Dental Association vigorously defended silver amalgam and its widespread use was continued
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
3rd amalgam war in 1980s
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.
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
3rd amalgam war in 1980s
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
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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”
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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.
The amalgam controversy-an evidence based analysis ; JADA,Vol.132,march 2001
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
American Dental Association (ADA) Council on ScientificAffairs, “Statement on dental amalgam,” 2011, http://www.ada.org/1741.aspx
“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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
American Dental Association (ADA) Council on ScientificAffairs, “Statement on dental amalgam,” 2011, http://www.ada.org/1741.aspx
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
American Dental Association (ADA) Council on ScientificAffairs, “Statement on dental amalgam,” 2011, http://www.ada.org/1741.aspx
Classification of AmalgamA) According to Alloyed Metals
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Sturdevant’s Art & Science of Operative Dentistry; 5th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Lathecut spherical
Admixed
C) According to copper content
Sturdevant’s Art & Science of Operative Dentistry; 5th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Low copper amalgam(<0-6%)
High copper amalgam(>6-
13%)
D)According to zinc content
Sturdevant’s Art & Science of Operative Dentistry; 5th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Zinc containing alloy
(>0.01-2%)
Non zinc containing alloy
(<0-0.01%)
1st generation
2nd generation
3rd generation
3Ag + Sn
Cu Zn
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Phillip’s Science of Dental Materials;11th ed
Silver(Ag)
Decreases creep & setting time
Decreases corrosion
Increases hardness & edge strength
Increase tarnishing
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Phillip’s Science of Dental Materials;11th ed
Tin(Sn)
Low strength
Larger contraction
Decreases expansion
Increased corrosion
Increased plasticity
Increased setting time
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Copper(Cu)
Decreases plasticity
Increases hardness strength of alloy
Reduce creep
Reduce tarnish & corrosion
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Zinc(Zn)
Decreases brittleness
Acts as a deoxidizer
Less marginal breakdown
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Phillip’s Science of Dental Materials;11th ed
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*
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Alloy Powder: Dispersalloy®
Silver69%
Tin18%
Copper12%
Zinc1%
Mixing proportions: 50% alloy, 50% mercury
Sturdevant’s Art & Science of Operative Dentistry;5th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Alloy Powder: Tytin®
Mixing proportions: 57.5% alloy, 42.5% mercury
Silver59%
Tin13%
Copper28%
Zinc0%
Sturdevant’s Art & Science of Operative Dentistry;5th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Phillip’s Science of Dental Materials;11th ed
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
γ2 phase is extremely weak & soft, deforming readily & the strength of amalgam is limited by its presence
Contributes to static creep of amalgam
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Scanning electron microscopic view of SnHg (γ2) crystals, that occurs in the matrix of set low copper amalgam
Sturdevant’s Art & Science of Operative Dentistry;5th ed
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Improves strength of the resulting amalgam
But if in excess, leads to expansion on setting
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
In the long term the conversion of γ1 to β1 may occur in the presence of unreacted γ phase alloy…
γ + γ1 → β1
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
High copper admixed alloy
2. Sn8Hg + AgCu Cu6Sn5 + Ag2Hg3 + Ag3Sn (2) ( ) (1 ) ( )
1. Ag3Sn + AgCu + Hg Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu ( ) (1 ) (2 ) ( )
CRAIG’s Restorative Dental Materials;12th ed
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High copper unicompositional alloy
Ag3Sn + Cu3Sn + Hg Cu6Sn5 + Ag2Hg3 ( ) ( ) ( ) (1 )
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Microstructure of Set Low Copper Amalgam.
(Ag3Sn)
2(Sn8Hg)
Voids
1(Ag2Hg3)
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Microstructure of Set High-Copper Admixed Amalgam.
1(Ag2Hg3)
(Ag3Sn)
Eutectic(Ag3Cu2)
(Cu6Sn5)
IntroductionHistory Amalgam wars ClassificationComponentsSetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Manufacture of alloy powderLathe cut alloy powder
Materials science for dentistry;9th ed B.W.Darvell
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Spherical alloy powder
Materials science for dentistry;9th ed B.W.Darvell
A. Lathecut alloyB. Spherical alloyC. Admixed alloy
Phillip’s Science of Dental Materials;11th ed
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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.
Phillip’s Science of Dental Materials;11th ed
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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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Phillip’s Science of Dental Materials;11th ed
• 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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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)
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.̊
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
20µm 20µm 20µm 20µm
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
High-Cu, admixed
High-Cu, single comp.
Low-Cu
If amalgam expanded during hardening, leakage around the margins of restorations would be eliminated.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Evidently the detrimental effect of shrinkage occurs only when the amalgam mass shrinks > 50 µm.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Delayed expansion
Materials science for dentistry;9th ed B.W.Darvell
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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)
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
-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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
-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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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)
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• Creep is related to marginal breakdown of low copper amalgams
• Higher the creep, the greater is the degree of marginal deterioration(ditching)
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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%
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
Phillip’s Science of Dental Materials;11th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
The degree of tarnish depends on :
i. The oral environment
ii. The type of alloy used
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
GAP
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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)
CRAIG’s Restorative Dental Materials;12th ed
• The p/o small amounts of tin, silver & copper that may dissolve in various amalgam phases has a great influence on their corrosion resistance
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• 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 :
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
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 )
CRAIG’s Restorative Dental Materials;12th ed
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.
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
• 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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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:
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
Sturdevant’s Art & Science of Operative Dentistry;5th ed
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
CRAIG’s Restorative Dental Materials;12th ed
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
• Smoothening & polishing the restoration
• Correct mercury/alloy ratio & proper manipulation
• Avoid dissimilar metals including mixing of high & low copper amalgams
IntroductionHistory Amalgam wars ClassificationComponentssetting reactionManufacturePropertiesManipulationRecent advances Sideeffects of mercuryDurabilityFuture Conclusion
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.