Dental Amalgam dr shabeel pn

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Click here for briefing on dental amalgam (PDF) Overview History Basic composition Basic setting reactions Classifications Manufacturing Variables in amalgam performance Click here for briefing on dental amalgam (PDF)

History 1833 1895 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 1980’s 1990’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.

Click here for Talking Paper on Amalgam Safety (PDF) 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

Phillip’s Science of Dental Materials 2003 Basic Constituents Silver (Ag) increases strength increases expansion Tin (Sn) decreases expansion decreased strength increases setting time Phillip’s Science of Dental Materials 2003

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

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 Þ 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

Phillip’s Science of Dental Materials 2003 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 Sn Ag Ag Sn Sn Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg) Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg 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 Hg Ag-Sn Alloy Hg Hg Ag Sn Ag Ag Sn Sn Ag-Sn Alloy Ag-Sn Alloy Mercury Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg Phillip’s Science of Dental Materials 2003  1 2

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 Þ Ag3Sn + Ag2Hg3 + Sn8Hg Phillip’s Science of Dental Materials 2003  1 2

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 2 Ag-Sn Alloy Ag3Sn + Hg Þ Ag3Sn + Ag2Hg3 + Sn8Hg Phillip’s Science of Dental Materials 2003  1 2

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 Ag-Sn Alloy Mercury Ag Sn Ag-Cu Alloy Hg Ag3Sn + Ag-Cu + Hg Þ Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5   1  Phillip’s Science of Dental Materials 2003

Admixed High-Copper Alloys Ag-Sn Alloy Ag-Cu Alloy  Sn diffuses to surface of Ag-Cu particles reacts with Cu to form (eta) Cu6Sn5 () around unconsumed Ag-Cu particles Ag3Sn + Ag-Cu + Hg Þ 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 Ag-Sn Alloy 1 Ag3Sn + Ag-Cu + Hg Þ Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5   1  Phillip’s Science of Dental Materials 2003

Single Composition High-Copper Alloys Ag-Sn Alloy Gamma sphere () (Ag3Sn) with epsilon coating () (Cu3Sn) Ag and Sn dissolve in Hg  Ag-Sn Alloy Ag Ag-Sn Alloy Sn Sn Ag Mercury (Hg) Ag3Sn + Cu3Sn + Hg Þ Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 Phillip’s Science of Dental Materials 2003  1  

Single Composition High-Copper Alloys Ag-Sn Alloy Gamma 1 (1) (Ag2Hg3) crystals grow binding together partially- dissolved gamma () alloy particles (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 Alloy 1 Ag3Sn + Cu3Sn + Hg Þ Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 Phillip’s Science of Dental Materials 2003  1  

Classifications Based on copper content Based on particle shape Based on method of adding copper

Phillip’s Science of Dental Materials 2003 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 Admixture Spherical low Cu high Cu low Cu New True Dentalloy high Cu ANA 2000 Admixture 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

Phillip’s Science of Dental Materials 2003 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

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

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 high copper                                                       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

Phillip’s Science of Dental Materials 2003 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

Click here for table of creep values 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

Phillip’s Science of Dental Materials 2003 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 spherical alloys admixture 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 Post-carve Combined 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

Click here for more details 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   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 Phillip’s Science of Dental Materials 2003

Survey of Practice Types Civilian General Dentists Amalgam Free Amalgam Users Haj-Ali Gen Dent 2005

Frequency of Posterior Materials by Practice Type Amalgam Users Amalgam Free Haj-Ali Gen Dent 2005

Profile of Amalgam Users Civilian Practitioners Do you use amalgam in your practice? Do you place fewer amalgams than 5 years ago? No No Yes Yes DPR 2005

Review of Clinical Studies (Failure Rates in Posterior Permanent Teeth) % Annual Failure Hickel J Adhes Dent 2001

Review of Clinical Studies (Failure Rates in Posterior Permanent Teeth) % Annual Failure Standard Deviation Longitudinal and Cross-Sectional Data Manhart Oper Dent 2004 Click here for abstract

Acknowledgements Questions/Comments Dr. David Charlton Dr. Charles Hermesch Col Salvador Flores Questions/Comments Col Kraig Vandewalle DSN 792-7670 ksvandewalle@nidbr.med.navy.mil