Dental Amalgam

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DENTAL AMALGAM Structure and Properties
Dental Materials Lecture BDS II Year
Dr. Raghuwar D Singh Associate Professor
Prosthodontic Department King Georges Medical
University UP, Lucknow
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• Amalgam is an alloy of mercury with one or more
  other metals.
• Dental amalgam alloy is an alloy that contains
  solid metals of silver, tin, copper and some
  times zinc.
• Dental amalgam is the alloy that results when
  mercury is combined with the previously mentioned
  alloys to form a plastic mass.

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Advantages

• Inexpensive
• Ease of use
• Proven track record
• gt100 years
• Familiarity
• Resin-free
• less allergies than composite

4
History

• 1833
• Crawcour brothers introduceamalgam to US
• powdered silver coins mixed with mercury
• expanded on setting
• 1895
• G.V. Black develops formula for modern amalgam
  alloy
• 67 silver, 27 tin, 5 copper, 1 zinc
• overcame expansion problems

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History

• 1960s
• conventional low-copper lathe-cut alloys
• smaller particles
• first generation high-copper alloys
• Dispersalloy (Caulk)
• admixture of spherical Ag-Cueutectic particles
  with conventional lathe-cut
• eliminated gamma-2 phase

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History

• 1970s
• first single composition spherical
• Tytin (Kerr)
• ternary system (silver/tin/copper)
• 1980s
• alloys similar to Dispersalloy and Tytin
• 1990s
• mercury-free alloys

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USES OF AMALGAM

• ANTERIOR TEETH
• Class III distal surfaces
  of Canine .
• POSTERIOR TEETH
• Class I Class II
• OTHER USES
• Retrograde root canal
  filling ,
• Post Core preparation .

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Amalgam Capsules

• Contain (in separate compartments)
• powdered amalgam alloy
• liquid mercury
• Some are manually activated, others
  self-activated
• Pestle usually included

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Amalgamator (Triturator)

• Speeds vary upward from 3000 rpm
• Times vary from 520 seconds
• Mix powder and liquid components to achieve a
  pliable mass
• Reaction begins after components are mixed

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Constituents in Amalgam

• Basic
• Silver
• Tin
• Copper
• Mercury
• Other
• Zinc
• Indium
• Palladium

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Alloy Powder Composition
Type 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 unicomp- ositional spherical 40-60 22-30 13-30 0 0-5 In, 0-1 Pd
compositions in weight percent compositions in weight percent compositions in weight percent compositions in weight percent compositions in weight percent compositions in weight percent
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Basic Constituents

• Silver (Ag)
• increases strength
• increases expansion
• Tin (Sn)
• decreases expansion
• decreased strength
• increases setting time

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Basic Constituents.

• Copper (Cu)
• ties up tin
• reducing gamma-2 formation
• increases strength
• reduces tarnish and corrosion
• reduces creep
• reduces marginal deterioration

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Basic Constituents.

• Mercury (Hg)
• activates reaction
• only pure metal that is liquid at room
  temperature
• spherical alloys
• require less mercury
• smaller surface area easier to wet
• 40 to 45 Hg
• admixed alloys
• require more mercury
• lathe-cut particles more difficult to wet
• 45 to 50 Hg

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Basic Constituents.

• Zinc (Zn)
• used in manufacturing
• decreases oxidation of other elements
• sacrificial anode
• provides better clinical performance
• less marginal breakdown
• Osborne JW Am J Dent 1992
• causes delayed expansion with low Cu alloys
• if contaminated with moisture during condensation
• Phillips RW JADA 1954

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Other Constituents

• Indium (In)
• decreases surface tension
• reduces amount of mercury necessary
• reduces emitted mercury vapor
• reduces creep and marginal breakdown
• increases strength
• must be used in admixed alloys
• example
• Indisperse (Indisperse Distributing Company)
• 5 indium

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Other Constituents

• Palladium (Pd)
• reduced corrosion
• greater luster
• example
• Valiant PhD (Ivoclar Vivadent)
• 0.5 palladium

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Basic Setting Reactions

• Conventional low-copper alloys
• Admixed high-copper alloys
• Single composition high-copper alloys

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Conventional Low-Copper Alloys

• Dissolution and precipitation
• Hg dissolves Ag and Snfrom alloy
• Intermetallic compoundsformed

Ag-Sn Alloy
Hg
Hg
Ag
Ag
Sn
Ag
Sn
Sn
Ag-Sn Alloy
Ag-Sn Alloy
Mercury (Hg)
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Conventional Low-Copper Alloys

• Gamma (?) Ag3Sn
• unreacted alloy
• strongest phase and corrodes the least
• forms 30 of volume of set amalgam

Hg
Ag-Sn Alloy
Hg
Hg
Ag
Ag
Sn
Ag
Sn
Sn
Ag-Sn Alloy
Ag-Sn Alloy
Mercury
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Conventional Low-Copper Alloys

• Gamma 1 (?1) Ag2Hg3
• matrix for unreacted alloyand 2nd strongest
  phase
• 10 micron grainsbinding gamma (?)
• 60 of volume

Ag-Sn Alloy
?1
Ag-Sn Alloy
Ag-Sn Alloy
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Conventional Low-Copper Alloys

• Gamma 2 (?2) Sn8Hg
• weakest and softest phase
• corrodes fast, voids form
• corrosion yields Hg which reacts with more gamma
  (?)
• 10 of volume
• volume decreases with time due to corrosion

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Admixed High-Copper Alloys

• Ag enters Hg from Ag-Cu spherical eutectic
  particles
• eutectic
• an alloy in which the elements are completely
  soluble in liquid solution but separate into
  distinct areas upon solidification
• Both Ag and Sn enter Hg from Ag3Sn particles

Ag3Sn Ag-Cu Hg Þ Ag3Sn Ag-Cu Ag2Hg3
Cu6Sn5
?
?
?1
?
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Admixed High-Copper Alloys

• Sn diffuses to surface of Ag-Cu particles
• reacts with Cu to form (eta) Cu6Sn5 (?)
• around unconsumedAg-Cu particles

Ag3Sn Ag-Cu Hg Þ Ag3Sn Ag-Cu Ag2Hg3
Cu6Sn5
?
?
?1
?
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Admixed High-Copper Alloys

• Gamma 1 (?1) (Ag2Hg3) surrounds (?) eta phase
  (Cu6Sn5) and gamma (?) alloy particles (Ag3Sn)

?
Ag-Cu Alloy
Ag-Sn Alloy
Ag-Sn Alloy
?1
Ag3Sn Ag-Cu Hg Þ Ag3Sn Ag-Cu Ag2Hg3
Cu6Sn5
?
?
?1
?
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Single Composition High-Copper Alloys

• Gamma sphere (?) (Ag3Sn) with epsilon coating
  (?) (Cu3Sn)
• Ag and Sn dissolve in Hg

?
Ag
Sn
Sn
Ag
Mercury (Hg)
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Single Composition High-Copper Alloys

• Gamma 1 (?1) (Ag2Hg3) crystalsgrow binding
  together partially-dissolved gamma (?)
  alloyparticles (Ag3Sn)
• Epsilon (?) (Cu3Sn) develops crystals on surface
  of gamma particle (Ag3Sn) in the form of eta
  (?) (Cu6Sn5)
• reduces creep
• prevents gamma-2 formation

?
?1
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Classification of dental amalgam alloys
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Copper Content

• Low-copper alloys
• 4 to 6 Cu
• High-copper alloys
• thought that 6 Cu was maximum amount
• due to fear of excessive corrosion and expansion
• Now contain 9 to 30 Cu
• at expense of Ag

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Particle Shape

• Lathe cut
• low Cu
• New TrueDentalloy
• high Cu
• ANA 2000
• Admixture
• high Cu
• Dispersalloy, Valiant PhD

• Spherical
• low Cu
• Cavex SF
• high Cu
• Tytin, Valiant

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Method of Adding Copper

• Single Composition Lathe-Cut (SCL)
• Single Composition Spherical (SCS)
• Admixture Lathe-cut Spherical Eutectic (ALE)
• Admixture Lathe-cut Single Composition
  Spherical (ALSCS)

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Single Composition Lathe-Cut

• More Hg needed than spherical alloys
• High condensation force needed due to lathe cut
• 20 Cu
• Example
• ANA 2000 (Nordiska Dental)

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Single Composition Spherical

• Spherical particles wet easier with Hg
• less Hg needed (42)
• Less condensation force, larger condenser
• Gamma particles as 20 micron spheres
• with epsilon layer on surface
• Examples
• Tytin (Kerr)
• Valiant (Ivoclar Vivadent)

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Admixture Lathe-cut Spherical Eutectic

• Composition
• 2/3 conventional lathe cut (3 Cu)
• 1/3 high Cu spherical eutectic (28 Cu)
• overall 12 Cu, 1 Zn
• Initial reaction produces gamma 2
• no gamma 2 within two years
• Example
• Dispersalloy (Caulk)

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AdmixtureLathe-cut Single Composition
Spherical

• High Cu in both lathe-cut and spherical
  components
• 19 Cu
• Epsilon layer forms on both components
• 0.5 palladium added
• reinforce grain boundaries on gamma 1
• Example
• Valiant PhD (Ivoclar Vivadent)

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Manufacturing Process

• Lathe-cut alloys
• Ag Sn melted together
• alloy cooled
• phases solidify
• heat treat
• 400 ºC for 8 hours
• grind, then mill to 25 - 50 microns
• heat treat to release stresses of grinding

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Manufacturing Process

• Spherical alloys
• melt alloy
• atomize
• spheres form as particles cool
• sizes range from 5 - 40 microns
• variety improves condensability

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Alloy Selection

• Handling characteristics
• Mechanical and physicalproperties
• Clinical performance

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Handling Characteristics

• Spherical
• advantages
• easier to condense
• around pins
• hardens rapidly
• smoother polish
• disadvantages
• difficult to achieve tight contacts
• higher tendency for overhangs

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Handling Characteristics

• Admixed
• advantages
• easy to achieve tight contacts
• good polish
• disadvantages
• hardens slowly
• lower early strength

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Amalgam Properties
1Fine Cut, Caulk 2 Dispersalloy, Caulk
3Tytin, Kerr
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Material-Related Variables

• Dimensional change
• Strength
• Corrosion
• Creep

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Dimensional Change

• Most high-copper amalgams undergo a net
  contraction
• Contraction leaves marginal gap
• initial leakage
• post-operative sensitivity
• reduced with corrosion over time

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Dimensional Change

• Net contraction
• type of alloy
• spherical alloys have more contraction
• less mercury
• condensation technique
• greater condensation higher contraction
• trituration time
• overtrituration causes higher contraction

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Strength

• Develops slowly
• 1 hr 40 to 60 of maximum
• 24 hrs 90 of maximum
• Spherical alloys strengthen faster
• require less mercury
• Higher compressive vs. tensile strength
• Weak in thin sections
• unsupported edges fracture

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Properties of Dental Amalgam

• Compressive strength
• -Amalgam is strongest in compression and much
  weaker in tension and shear.
• -HCU materials have the highest compressive
  strength.

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Properties of Dental Amalgam

• Tensile Strength
• -Amalgam is strongest in compression and much
  weaker in tension and shear.
• -HCU materials have the highest early tensile
  strength.

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Properties of Dental Amalgam

• Strength of various phases
• Unreacted Ag3Sn (?) phase. (strongest)
• Ag2Hg3(?1)phase.
• Sn8Hg (?2)phase.(weakest)

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Properties of Dental Amalgam

• Elastic Modulus
• -High- copper alloys are stiffer than low-copper
  alloys.
• -Amalgam are viscoelastic.

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Corrosion

• Reduces strength
• Seals margins
• low copper
• 6 months
• SnO2, SnCl
• gamma-2 phase
• high copper
• 6 - 24 months
• SnO2 , SnCl, CuCl
• eta-phase (Cu6Sn5)

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Creep

• Slow deformation of amalgam placed under a
  constant load
• 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

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Creep

• High-copper amalgams have creep resistance
• prevention of gamma-2 phase
• requires gt12 Cu total
• single composition spherical
• eta (Cu6Sn5) embedded in gamma-1 grains
• interlock
• admixture
• eta (Cu6Sn5) around Ag-Cu particles
• improves bonding to gamma 1

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MCQs

• 1. Dental situation in which Silver amalgam is
  most commonly used
• Anterior Class 4
• Posterior Class 1
• Root canal feeling
• Pit and fissure

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• 2. Zn containing Amalgam contains
• a) .001 Zn
• b) .01 Zn
• c) More than .o1 Zn
• d) More than .001 Zn

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• 3. Epsilon phase in dental amalgam is
• Ag-Sn
• Cu3Sn
• Ag3Sn
• Cu6Sn

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• 4. Beta phase in dental amalgam is
• Ag-Sn
• Cu3Sn
• Ag3Sn
• Cu6Sn5

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• 5. The weakest phase in amalgam is
• Gamma- 1
• Beta
• Beta- 1
• Gamma

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• 6. Gamma -2 phase in dental amalgam is
• Cu6Sn5
• Sn7Hg
• Ag-Cu
• Ag3Sn

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• 7. Pain, after delayed expansion of amalgam is
  produced by
• Presence of Zn
• Hydrogen gas
• Presence of H2O
• Improper cavity preparation

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• 8. Which phase of amalgam promotes tarnish and
  corrosion
• Gamma
• Gamma- 1
• Gamma- 2
• Eta

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• 9. Low copper dental amalgam alloy contains
  maximum amount of copper upto
• 3
• 11
• 6
• 19

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• 10. All of the following are feathers of the high
  Cu alloys, except
• Low dimensional changes
• Low compressive strength
• Lower creep values
• Less susceptible to corrosion