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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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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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