dental amalgam - homestead schools

Dental AmalgamDental AmalgamCol 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

performanceClick here for briefing on dental amalgam (PDF)

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

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


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 compositeClick 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


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


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

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


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


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

SnSn

Conventional Low-Copper Alloys

Hg Hg

AgAg33Sn + HgSn + Hg AgAg33Sn + AgSn + Ag22HgHg33 + Sn + Sn88HgHg


1 2


• Gamma () = Ag3Sn– unreacted alloy– strongest phase and

corrodes the least– forms 30% of volume

of set amalgamAg-Sn Alloy

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

AgAgAg

Sn

SnSn

HgHg

Hg



1 2


• Gamma 1 (1) = Ag2Hg3

– matrix for unreacted alloyand 2nd strongest phase

– 10 micron grainsbinding gamma ()

– 60% of volume

1



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



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


AgAg33Sn + Ag-Cu + HgSn + Ag-Cu + Hg AgAg33Sn + Ag-Cu + AgSn + Ag-Cu + Ag22HgHg33 + Cu + Cu66SnSn55 1

Ag-Sn Alloy

Ag-Sn Alloy

Mercury

AgAgAg

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



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



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


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


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


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

• phases solidify– heat treat

• 400 ºC for 8 hours– grind, then mill to 25 - 50 microns– heat treat to release stresses of grinding


Manufacturing Process

• Spherical alloys– melt alloy– atomize

• spheres form as particles cool– sizes range from 5 - 40 microns

• variety improves condensability


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


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


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


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


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


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


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 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?

YesNo

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

Amalgam

Direct

Comp

Compo

mer

Comp I

nlays

Ceramic

Inlays

CAD/CAM

Cast G

old GI

Tunn

el ART

% 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

– [email protected]

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