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Transcript of Amalgam
Dental AmalgamDental Amalgam
Col Kraig S. VandewalleUSAF Dental Evaluation & Consultation Service
Official Disclaimer
• The opinions expressed in this presentation are those of the author and do not necessarily reflect the official position of the US Air Force or the Department of Defense (DOD)
• Devices or materials appearing in this presentation are used as examples of currently available products/technologies and do not imply an endorsement by the author and/or the USAF/DOD
Overview• History
• Basic composition
• Basic setting reactions
• Classifications
• Manufacturing
• Variables in amalgam performance
Click here for briefing on dental amalgam (PDF)
History
• 1833– Crawcour brothers introduce
amalgam 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
History• 1960’s
– 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
Mahler J Dent Res 1997
History• 1970’s
– first single composition spherical• Tytin (Kerr)• ternary system (silver/tin/copper)
• 1980’s– alloys similar to Dispersalloy and Tytin
• 1990’s– mercury-free alloys
Mahler J Dent Res 1997
Amalgam
• An alloy of mercury with another metal.
Why Amalgam?
• Inexpensive
• Ease of use
• Proven track record– >100 years
• Familiarity
• Resin-free– less allergies than composite
Click here for Talking Paper on Amalgam Safety (PDF)
Constituents in Amalgam• Basic
– Silver– Tin– Copper– Mercury
• Other– Zinc– Indium– Palladium
Basic Constituents
• Silver (Ag)– increases strength– increases expansion
• Tin (Sn)– decreases expansion– decreased strength– increases setting time
Phillip’s Science of Dental Materials 2003
Basic Constituents
• Copper (Cu)– ties up tin
• reducing gamma-2 formation
– increases strength– reduces tarnish and corrosion– reduces creep
• reduces marginal deterioration
Phillip’s Science of Dental Materials 2003
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
Click here for ADA Mercury Hygiene Recommendations
Phillip’s Science of Dental Materials 2003
Other 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
Phillip’s Science of Dental Materials 2003
H2O + Zn ZnO + H2
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
Powell J Dent Res 1989
Other Constituents
• Palladium (Pd)– reduced corrosion– greater luster– example
• Valiant PhD (Ivoclar Vivadent)– 0.5% palladium
Mahler J Dent Res 1990
Basic Composition• A silver-mercury matrix containing filler particles of
silver-tin• Filler (bricks)
– Ag3Sn called gamma• can be in various shapes
– irregular (lathe-cut), spherical,or a combination
• Matrix– Ag2Hg3 called gamma 1
• cement
– Sn8Hg called gamma 2 • voids
Phillip’s Science of Dental Materials 2003
Basic Setting Reactions
• Conventional low-copper alloys
• Admixed high-copper alloys
• Single composition high-copper alloys
• Dissolution and precipitation • Hg dissolves Ag and Sn
from alloy• Intermetallic compounds
formed Ag-Sn Alloy
Ag-Sn Alloy
Ag-Sn Alloy
Mercury (Hg)
AgAgAg
Sn
Sn
Sn
Conventional Low-Copper Alloys
Hg Hg
AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg
Phillip’s Science of Dental Materials 2003
1 2
Conventional Low-Copper Alloys
• Gamma () = Ag3Sn– unreacted alloy– strongest phase and
corrodes the least– forms 30% of volume
of set amalgam
Ag-Sn Alloy
Ag-Sn Alloy
Ag-Sn Alloy
Mercury
Ag
AgAg
Sn
Sn
Sn
HgHg
Hg
AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg
Phillip’s Science of Dental Materials 2003
1 2
Conventional Low-Copper Alloys
• Gamma 1 (1) = Ag2Hg3
– matrix for unreacted alloyand 2nd strongest phase
– 10 micron grainsbinding gamma ()
– 60% of volume
1
AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg
Phillip’s Science of Dental Materials 2003
1 2
Ag-Sn Alloy
Ag-Sn Alloy
Ag-Sn Alloy
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
AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg
Phillip’s Science of Dental Materials 2003
1 2
2
Ag-Sn Alloy
Ag-Sn Alloy
Ag-Sn Alloy
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
Phillip’s Science of Dental Materials 2003
AgAg33Sn + Ag-Cu + HgSn + Ag-Cu + Hg AgAg33Sn + Ag-Cu + AgSn + Ag-Cu + Ag22HgHg33 + Cu + Cu66SnSn55 1
Ag-Sn Alloy
Ag-Sn Alloy
Mercury
Ag
AgAg
SnSn
Ag-Cu Alloy
AgHgHg
Admixed High-Copper Alloys
• Sn diffuses to surface of Ag-Cu particles – reacts with Cu to form
(eta) Cu6Sn5 ()• around unconsumed
Ag-Cu particles
Ag-Sn Alloy
Ag-Cu Alloy
Ag-Sn Alloy
Phillip’s Science of Dental Materials 2003
AgAg33Sn + Ag-Cu + HgSn + Ag-Cu + Hg AgAg33Sn + Ag-Cu + AgSn + Ag-Cu + Ag22HgHg33 + Cu + Cu66SnSn55 1
Admixed High-Copper Alloys
• Gamma 1 (1) (Ag2Hg3)
surrounds () eta phase (Cu6Sn5) and gamma ()
alloy particles (Ag3Sn) Ag-Sn Alloy
1
Ag-Cu Alloy
Ag-Sn Alloy
Phillip’s Science of Dental Materials 2003
AgAg33Sn + Ag-Cu + HgSn + Ag-Cu + Hg AgAg33Sn + Ag-Cu + AgSn + Ag-Cu + Ag22HgHg33 + Cu + Cu66SnSn55 1
Single Composition High-Copper Alloys
• Gamma sphere () (Ag3Sn) with epsilon coating () (Cu3Sn)
• Ag and Sn dissolve in Hg
Ag-Sn Alloy
Ag-Sn AlloyAg-Sn Alloy
Mercury (Hg)
Ag
SnAg
Sn
AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu + Cu66SnSn55
Phillip’s Science of Dental Materials 2003
1
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
Ag-Sn Alloy
Ag-Sn AlloyAg-Sn Alloy
1
AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu + Cu66SnSn55
Phillip’s Science of Dental Materials 2003
1
Classifications• Based on copper content
• Based on particle shape
• Based on method of adding copper
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
Phillip’s Science of Dental Materials 2003
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
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)
Single Composition Lathe-Cut (SCL)
• More Hg needed than spherical alloys
• High condensation force needed due to lathe cut
• 20% Cu
• Example– ANA 2000 (Nordiska Dental)
Single Composition Spherical (SCS)
• 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)
Admixture: Lathe-cut + Spherical Eutectic
(ALE)• 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)
Admixture: Lathe-cut + Single Composition
Spherical (ALSCS)• 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)
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
Phillip’s Science of Dental Materials 2003
Manufacturing Process
• Spherical alloys– melt alloy– atomize
• spheres form as particles cool
– sizes range from 5 - 40 microns• variety improves condensability
Phillip’s Science of Dental Materials 2003
Material-Related Variables
• Dimensional change
• Strength
• Corrosion
• Creep
Dimensional Change• Most high-copper amalgams undergo a
net contraction
• Contraction leaves marginal gap– initial leakage
• post-operative sensitivity
– reduced with corrosion over time
Phillip’s Science of Dental Materials 2003
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
Phillip’s Science of Dental Materials 2003
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
Phillip’s Science of Dental Materials 2003
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)
Sutow J Dent Res 1991
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
Phillip’s Science of Dental Materials 2003
Creep• High-copper amalgams have creep
resistance– prevention of gamma-2 phase
• requires >12% 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
Click here for table of creep values
Dentist-Controlled Variables
• Manipulation– trituration– condensation– burnishing– polishing
Trituration• Mixing time
– refer to manufacturerrecommendations
• Click here for details
• Overtrituration– “hot” mix
• sticks to capsule
– decreases working / setting time– slight increase in setting contraction
• Undertrituration– grainy, crumbly mix
Phillip’s Science of Dental Materials 2003
Condensation• Forces
– lathe-cut alloys• small condensers • high force
– spherical alloys• large condensers • less sensitive to amount of force• vertical / lateral with vibratory motion
– admixture alloys• intermediate handling between lathe-cut and spherical
Burnishing
• Pre-carve– removes excess mercury– improves margin adaptation
• Post-carve– improves smoothness
• Combined– less leakage
Ben-Amar Dent Mater 1987
Early Finishing
• After initial set– prophy cup with pumice– provides initial smoothness to restorations– recommended for spherical amalgams
Polishing
• Increased smoothness
• Decreased plaque retention
• Decreased corrosion
• Clinically effective?– no improvement in marginal integrity
• Mayhew Oper Dent 1986• Collins J Dent 1992
– Click here for abstract
Alloy Selection
• Handling characteristics
• Mechanical and physicalproperties
• Clinical performance
Click here for more details
Handling Characteristics
• Spherical– advantages
• easier to condense– around pins
• hardens rapidly• smoother polish
– disadvantages• difficult to achieve tight contacts• higher tendency for overhangs
Phillip’s Science of Dental Materials 2003
Handling Characteristics
• Admixed– advantages
• easy to achieve tight contacts• good polish
– disadvantages• hardens slowly
– lower early strength
Amalgam Properties
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
Survey of Practice TypesCivilian General Dentists
68%
32%
Amalgam Users
Amalgam Free
Haj-Ali Gen Dent 2005
Frequency of Posterior Materialsby Practice Type
39%
51%
3% 7%
Amalgam Direct Composite Indirect Composite Other
3%
77%
8%
12%
Amalgam Users
Amalgam Free
Haj-Ali Gen Dent 2005
Profile of Amalgam UsersCivilian Practitioners
78%
22%
Do you use amalgam in your practice?
Yes
No
DPR 2005
88%
12%
Do you place fewer amalgams than 5 years ago?
Yes
No
Review of Clinical Studies(Failure Rates in Posterior Permanent Teeth)
0
2
4
6
8
Amalgam DirectComp
CompInlays
CeramicInlays
CAD/CAMInlays
GoldInlays &Onlays
GI
Longitudinal Cross-Sectional
Hickel J Adhes Dent 2001
% Annual Failure
0
5
10
15
Amalg
am
Direct
Com
p
Compo
mer
Comp
Inlay
s
Ceram
ic In
lays
CAD/CAM
Cast G
old GI
Tunn
elART
% Annual Failure
Manhart Oper Dent 2004 Click here for abstract
Standard Deviation
Longitudinal and Cross-Sectional Data
Review of Clinical Studies(Failure Rates in Posterior Permanent Teeth)
Acknowledgements• Dr. David Charlton
• Dr. Charles Hermesch
• Col Salvador Flores
Questions/CommentsCol Kraig Vandewalle
– DSN 792-7670