Dental Amalgam
Col Kraig S. Vandewalle
USAF 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-Cu
eutectic 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
Click here for ADA Mercury
Hygiene Recommendations
• 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
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
H2O + Zn  ZnO + H2
Phillip’s Science of Dental Materials 2003
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
Conventional Low-Copper Alloys
• Dissolution and precipitation
• Hg dissolves Ag and Sn
from alloy
• Intermetallic compounds
formed
Ag-Sn Alloy
Hg
Hg
Ag Ag
Ag
Sn
Sn
Ag-Sn
Ag-Sn
Alloy
Alloy
Mercury
(Hg)
Sn
Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg


1
2
Phillip’s Science of Dental Materials 2003
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
Alloy
Sn
Sn
Ag
Ag
Sn
Ag-Sn
Alloy
Mercury
Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg


1
2
Phillip’s Science of Dental Materials 2003
Conventional Low-Copper Alloys
• Gamma 1 (1) = Ag2Hg3
–
–
–
matrix for unreacted alloy
and 2nd strongest phase
10 micron grains
binding gamma ()
60% of volume
Ag-Sn Alloy
1
Ag-Sn
Alloy
Ag-Sn
Alloy
Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg


1
2
Phillip’s Science of Dental Materials 2003
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
Ag-Sn Alloy
Ag-Sn
Alloy
2
Ag-Sn
Alloy
Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg


1
2
Phillip’s Science of Dental Materials 2003
Admixed High-Copper Alloys
• Ag enters Hg from Ag-Cu
spherical eutectic particles
–
Ag-Cu Alloy
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
Hg
Ag Ag
Ag
Ag-Sn
Alloy
Sn
Hg
Ag
Sn
Ag-Sn
Alloy
Mercury
Ag3Sn + Ag-Cu + Hg  Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5


1

Phillip’s Science of Dental Materials 2003
Admixed High-Copper Alloys
• Sn diffuses to surface of
Ag-Cu particles
–

Ag-Cu Alloy
reacts with Cu to form
(eta) Cu6Sn5 ()
•
around unconsumed
Ag-Cu particles
Ag-Sn
Alloy
Ag-Sn
Alloy
Ag3Sn + Ag-Cu + Hg  Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5


1

Phillip’s Science of Dental Materials 2003
Admixed High-Copper Alloys
• Gamma 1 (1) (Ag2Hg3)
surrounds () eta phase
(Cu6Sn5) and gamma ()
alloy particles (Ag3Sn)

Ag-Cu Alloy
Ag-Sn
Alloy
1
Ag-Sn
Alloy
Ag3Sn + Ag-Cu + Hg  Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5


1

Phillip’s Science of Dental Materials 2003
Single Composition
High-Copper Alloys
• Gamma sphere () (Ag3Sn)
Ag-Sn Alloy

with epsilon coating ()
Ag
(Cu3Sn)
Sn
Sn
Ag
Ag-Sn Alloy
• Ag and Sn dissolve in Hg
Ag-Sn Alloy
Mercury (Hg)
Ag3Sn + Cu3Sn + Hg  Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5




1

Phillip’s Science of Dental Materials 2003
Single Composition
High-Copper Alloys
• Gamma 1 (1) (Ag2Hg3) crystals
grow binding together partiallydissolved gamma () alloy
particles (Ag3Sn)

• Epsilon () (Cu3Sn) develops
crystals on surface of
gamma particle (Ag3Sn)
in the form of eta () (Cu6Sn5)
–
–
Ag-Sn Alloy
Ag-Sn Alloy
Ag-Sn Alloy
1
reduces creep
prevents gamma-2 formation
Ag3Sn + Cu3Sn + Hg  Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5




1

Phillip’s Science of Dental Materials 2003
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 True
Dentalloy
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
•
–
heat treat
•
–
–
phases solidify
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 manufacturer
recommendations
• 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 physical
properties
• 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
1Fine
Cut, Caulk
Caulk
3Tytin, Kerr
2 Dispersalloy,
Phillip’s Science of Dental Materials 2003
Survey of Practice Types
Civilian General Dentists
32%
Amalgam
Free
Amalgam
Users
68%
Haj-Ali Gen Dent 2005
Frequency of Posterior Materials
by Practice Type
3%
7%
39%
Amalgam Users
51%
Amalgam
Direct Composite
12%
Indirect Composite
3%
8%
Amalgam Free
Haj-Ali Gen Dent 2005
77%
Other
Profile of Amalgam Users
Civilian Practitioners
Do you use amalgam in
your practice?
Do you place fewer amalgams
than 5 years ago?
12%
22%
No
No
Yes
Yes
78%
88%
DPR 2005
Review of Clinical Studies
(Failure Rates in Posterior Permanent Teeth)
% Annual Failure
8
6
4
2
0
Amalgam
Direct
Comp
Comp
Inlays
Longitudinal
Ceramic CAD/CAM
Inlays
Inlays
Gold
Inlays &
Onlays
GI
Cross-Sectional
Hickel J Adhes Dent 2001
Review of Clinical Studies
(Failure Rates in Posterior Permanent Teeth)
% Annual Failure
15
Standard Deviation
10
Longitudinal and Cross-Sectional Data
5
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Manhart Oper Dent 2004
Click here for abstract
Acknowledgements
• Dr. David Charlton
• Dr. Charles Hermesch
• Col Salvador Flores
Questions/Comments
Col Kraig Vandewalle
– DSN 792-7670
– ksvandewalle@nidbr.med.navy.mil