1) Alloy is a mixture of two or more metals while amalgam is an alloy that contains mercury as one of its components. 2) Amalgam has advantages such as being inexpensive, durable, and resistant to wear but has disadvantages like its metallic color and potential toxicity from mercury. 3) The basic components of dental amalgam include silver, tin, copper, and mercury while other components like zinc and indium can be added to improve properties.

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ALLOY Versus AMALGAM
• Alloy is a mixture of 2 or more metals
Amalgam • AMALGAMMATION / TRITURATION – reaction
when a silver based alloy is mixed with
mercury, a liquid metal.
• Dental Amalgam - Is an alloy that contains
mercury as one of its component
Why Amalgam?
• Inexpensive ADVANTAGES DISADVANTAGES
• Ease of use • Less technique sensitive • Esthetics, metallic color
• Proven track record • More durable • No bonding to tooth surface
– >100 years • Less costly • Extensive tooth preparation
• Excellent abrasion and wear
• Familiarity resistance
• Life expectancy – 15 yrs • Tends to seal itself against
• Resin-free leakage
• Bacteria do not adhere to it
– less allergies than composite
as strongly as n composite
Composition of Dental Amalgam
Indications ( I,II,III, V,VI) Contraindications • Basic
• Moderate to large • Esthetically prominent areas – Silver
restoration of teeth – Tin
• Restorations that are not in – Copper
highly esthetic areas of
mouth. – Mercury
• Restorations that have • Other
heavy occlusal contacts. – Zinc
• Restorations that can’t be – Indium
well isolated – Palladium
• Pin retained
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Basic Constituents Basic Constituents
• Silver (Ag)
– increases strength • Copper (Cu)
– increases expansion – increases strength
– Decrease setting time
– reduces tarnish and corrosion
• Tin (Sn)
– decreased strength
– reduces creep
– decreases expansion • reduces marginal deterioration
– increases setting time
– Improves physical properties
when compounded with Ag
Phillip’s Science of Dental Materials 2003
Phillip’s Science of Dental Materials 2003
Dental Materials - Saunders
Tarnish Corrosion
• Oxidation that attacks the surface of the Am and • Oxidation from interaction of 2 dissimilar
extends slightly below the surface. metals in the presence of a solution
• Contact with oxygen, chlorides, and sulfides in containing electrolytes
the mouth. • Galvanism
• Dark dull appearance but not destructive to Am • Oxidation of one of the metals
• Palladium and Polishing may help reduce tarnish
• The rougher the surface, the more it tends to
tarnish
Creep Basic Constituents
• Mercury (Hg)
• Refers to the gradual change in shape of the – activates reaction
restoration from compression by the opposing – only pure metal that is liquid
at room temperature
dentition. – 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 2003
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Other Constituents
• Zinc (Zn) • Indium (In)
• decreases oxidation of other elements
– decreases surface tension
– provides better clinical performance • reduces amount of mercury necessary
• less marginal breakdown
• reduces emitted mercury vapor
– reduces creep and marginal breakdown
– causes delayed expansion
• if contaminated with moisture during condensation – increases strength
Powell J Dent Res 1989
Phillip’s Science of Dental Materials 2003
Other Constituents
Component High copper Alloy % Low copper alloy %
• Palladium (Pd) Silver 40 -70 68 – 72
– reduced corrosion
Tin 12 – 30 28 – 36
– greater luster
Copper 10 – 30 4–6
Zinc 0-1 0-2
Mahler J Dent Res 1990
Classifications Copper Content
• Based on copper content • Low-copper alloys
• Based on particle shape – 4 to 6% Cu
• High-copper alloys
– thought that 6% Cu was maximum amount
• due to fear of excessive corrosion and expansion
– Now contain 10 to 30% Cu
• at expense of Ag
Phillip’s Science of Dental Materials 2003
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4. 3/5/2012
Setting Reaction of Low Copper
Low Copper Amalgam
Amalgam
• “traditional” “conventional”
(β+γ ) + Hg γ1 + γ2 + unconsumed alloy particles (β+γ )
• COMPOSITION: ( Black’s)
γ – greek letter gamma
• 65% SILVER - used to designate the AgSn alloy or gamma phase
• 25% Tin γ1 – AgHg
• < 6% copper γ2 – SnHg
• 1% zinc
Low Copper Amalgam High Copper Am
• Compared with low copper alloys, this have
become a material of choice.
• Improved mechanical properties
• Corrosion resistance
• Better marginal integrity
• Imroved performance in clinical trials
High Copper Am Admixed
• 2 types • “Blended” , “admix”, or “dispersion”
• These are called admixed alloys
• Admixed
as they contain atleast 2 kinds
• Single composition of particles
• Am made from these powders is stronger than
am made from lathe cut low copper powder, bec
• Both types contain more than 6 wt % copper of inc in residual alloy particles and resultant dec
in matrix
• Silver-copper particles as well as the AgSn
paricles probably act as strong fillers in Am.
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Spherical High Copper Amalgams Particle Shape
• Unlike admixed, each particle of these alloy • Lathe cut alloy
powders have the same chemical composition  Formed by shaving particles
from a block of the alloy by a
• Thus , single composition alloys lathe
• Single composition, high copper, spherical • Spherical  Formed by spraying molten
dental amalgams alloy into an inert gas
• Admixed  Mixture of the two .
• Have only 1 shape
 Alloy maybe made from
• The particles are a combination of silver 60 wt different particle shapes to
% , tin 27 wt %, copper 13 wt % and other increase packing efficiency and
elements reduce amount of Hg needed
to obtain a workable mix.
Setting Transformation
• Alloy + liquid Hg = chemical reaction
• Mixture – putty like consistency
• Gradually becomes firmer
• Working time – the Am can be carved
• Initial set – it can’t be carved any more
• Once fully set , they are hard , strong
and durable
Properties of Amalgam Dimensional Change
• Dimensional change • Severe contraction leaves marginal gap
– initial leakage
• Strength • post-operative sensitivity
– reduced with corrosion over time
• Corrosion
 Expansion leads to post operative sensitivity due to pressure
• Creep on pulp
ADA specification No.1 requires amalgam neither contract or
expand more than 20 um/cm
Measured at 37 deg between 5 mins and 24 hours after
beginning of trituration.
Phillip’s Science of Dental Materials 2003
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Dimensional Change Effect of Moisture contamination
• Net contraction • If a zinc containing low copper, or high copper
– type of alloy
amalgam is contaminated by moisture during
• spherical alloys have more
trituration or condensation, a large expansion
contraction can take place.
– less mercury
• after 3-5 days
– condensation technique
• greater condensation = higher contraction
• may continue for months reaching values <
400 um.
– trituration time
• overtrituration causes higher contraction • DELAYED EXPANSION or SECONDARY
EXPANSION
Phillip’s Science of Dental Materials 2003
Strength Strength
• Develops slowly • High compressive strength
– 1 hr: 40 to 60% of maximum • Low tensile and shear strength
– 24 hrs: 90% of maximum • Therefore
• Spherical alloys strengthen faster • Am MUST be supported by tooth structure
– require less mercury
• Am needs sufficient bulk ( 1.5 or more)
• Weak in thin sections
– unsupported edges fracture
Phillip’s Science of Dental Materials 2003
Corrosion Creep
• Reduces strength • Slow deformation of amalgam placed under a
constant load
• Seals margins
– load less than that necessary to produce fracture
• Gamma 2 dramatically affects creep rate
– slow strain rates produces plastic deformation
• allows gamma-1 grains to slide
• Correlates with marginal breakdown
Sutow J Dent Res 1991
Phillip’s Science of Dental Materials 2003
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Clinical performance of Am
Creep Restoration
• Slow change in shape • Small amt of leakage under amalgam is unique
• caused by compression
• Properly inserted – leakage decreases as
restoration ages
• High-copper amalgams have
• Corrosion products form along the interface
creep resistance between the tooth and the resto
– prevention of gamma-2 phase
Minimal Mercury Technique
Mercury/alloy ratio
Eames Technique
• Historically, the only way to achieve smooth and • Most obvious method for reducing mercury
plastic mixes was to use mercury considerably in content is to reduce the original mercury/ alloy
excess of that desirable in final restoration. ratio.
• For convenional mercury –added systems, 2 • Sufficient mercury must be present in the original
techniques were employed to remove excess mix to provide a coherent and plastic mass after
mercury trituration
1. Removal of excess mercury was accomplished by • But low enough so that the mercury content is at
squeezing or wringing themixed amalgam in a an acceptable level without the need to remove
squeeze cloth an appreciable amt during condensation
2. Additional excess mercury was worked to top • Mercury content of finished should be about 50%
during condensation of each increment wt% with lesser amt for spherical alloy
Proportioning Proportioning
• Recommended mercury / alloy ratio for most • Mercury / alloy dispensers
modern lathe cut alloy is approx 1:1 or 50% • Preweighed pellets or tablets
mercury • Liquid mercury dispenser
spherical alloys its closer to 42% mercury
• Proper proportioning = proper mix
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Proportioning Trituration
• Disposable amalgam capsules
• Preportioned mercury
Trituration
• OBJECTIVEs : • Sphrerical or irregular low copper alloy – low speed
• To provide a proper amalgamation of mercury and • High copper – high speed
alloy
• Achieve a workable mass at a minimum time • AMALGAMATOR Speed:
• Reduce particle size leading to faster and more • Low – 3200-3400 cycles/min
complete amalgamation • Medium – 3700-3800 cycles/min
• High – 4000-4400 cycles/min
• Capsules serves as mortar • INCREASED TRITURATION TIME = DECREASED
• a cylindrical metal or plastic piston serves as the pestle WORKING AND SETTING TIME
Dentist-Controlled Variables
• Manipulation
– trituration
– condensation
– burnishing
– polishing
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Trituration Mercury content
• Mixing time • Sufficient mercury should be mixed with the
– refer to manufacturer alloy to coat the alloy particles and to allow a
recommendations
thorough amalgamation.
• Overtrituration
– “hot” mix • Each particle of the alloy must be wet by the
• sticks to capsule mercury; otherwise a dry , granular mix results
– decreases working / setting time
– slight increase in setting contraction • Any excess of mercury left in the restoration
• Undertrituration can produce a marked reduction in strength
– grainy, crumbly mix
 Properly triturated – warm, smoth- max
strength , smooth Phillip’s Science of Dental Materials 2003
Condensation Hand Condensation
• GOAL: • Never touch with bare hands
• To compact the alloy into the prepared cavity • Gloves
so that greatest possibitlity of density is
attained • Immediatley condensed once inserted in the
cavity
• Mercury rich layer is brought to the surface of
the restoration, so that successiv elayers bond • With sufficient pressure
to each other • Ave force applied: 13.3-17.8 N or (3-4 lb)
• A fresh amalgam mix should be condensed
within 3-4 mins
Condensation Carving and Finishing
• All amalgams except spherical alloys are • Reproduce proper tooth anatomy
condensed by small condensers to reduce voids • Immediately after condensation
• After carving = SMOOTHED by.. BURNISHING
• Spherical alloys: large increments and
condensers to fill entire cavity. • Burnish the surface and margins
• After , it will still be rough at a microscopic
level
• FINAL POLISHING – after 24 hours
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Side Effects of mercury Allergy
• Am restoration is possible bec of mercury. • Antibody – antigen reaction
• Itching,
• The use of mercury has raised concerns as
• Rashes
well as alleged side effects that may be • Sneezing
sustained by patients who received amalgam • Difficulty in breathing
restorations • Swelling
• Contact Dermatitis or Coombs’Type IV
hypersensitivity
• But these are experienced by less tha 1% of
treated population.
Toxicity Toxicity
• It is still thought that mercury toxocity from • The most significant contribution to mercury
dental restoration is cause of certain undiagnosed assimilation from dental amalgamis
illnesses • VAPOR PHASE
• Encounter is brief
• And a real hazard may exist for dentists and
• Mercury vapor amt – NO EFFECT level
dental assistants when mercury vapor is inhaled • The threshold value for mercury industry workers-
during mixing and placement of amalgam. • 350 -500 ug per dya ( 40 hr /wk)
• Improvements in encapsulation technology, scrap • Patients get far below the values by US federal got
storage, elimination of carpets and other mercury • Max level occupational exposure (safe) 50 um per
retention sites cubic meter of air per day
Potential hazards form mercury can be
reduced by:
• Mercury in blood • Well ventilated Operatory
• Patients w/ Am – 0.7 ng/ml
• Patients w/o Am- 0.3 ng/ml • Well sealed containers ( Am scraps, capsules)
• 1 saltwater meal per wk raised mercury level in blood :
• Proper disposals
• From 2.3 to 5.1 ng/ml • Spilled mercury- cleaned up as soon as
posiible
• Daily normal intake of Hg:
• 15 um – food • Mercury suppressant powders
• 1 ug – air • If comes in contact with skin – wash with soap
• 0.4 ug - water
and H2O
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