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Dental_Amalgam-Structure___Properties-16-12-14.ppt
- 1. Dr. Raghuwar D Singh Associate Professor Prosthodontic Department King George’s Medical University UP, Lucknow Dental Materials Lecture BDS II Year
- 2. 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.
- 3. Advantages • Inexpensive • Ease of use • Proven track record – >100 years • Familiarity • Resin-free – less allergies than composite
- 4. 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
- 5. 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
- 6. 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
- 7. 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 .
- 8. Amalgam Capsules • Contain (in separate compartments): – powdered amalgam alloy – liquid mercury • Some are manually activated, others self-activated • Pestle usually included
- 9. Amalgamator (Triturator) • Speeds vary upward from 3000 rpm • Times vary from 5–20 seconds • Mix powder and liquid components to achieve a pliable mass • Reaction begins after components are mixed
- 10. Constituents in Amalgam • Basic – Silver – Tin – Copper – Mercury • Other – Zinc – Indium – Palladium
- 11. 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
- 12. Basic Constituents • Silver (Ag) – increases strength – increases expansion • Tin (Sn) – decreases expansion – decreased strength – increases setting time
- 13. Basic Constituents…. • Copper (Cu) – ties up tin • reducing gamma-2 formation – increases strength – reduces tarnish and corrosion – reduces creep • reduces marginal deterioration
- 14. • 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 Basic Constituents….
- 15. • 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 Basic Constituents….
- 16. 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
- 17. Other Constituents… • Palladium (Pd) – reduced corrosion – greater luster – example • Valiant PhD (Ivoclar Vivadent) – 0.5% palladium
- 18. Basic Setting Reactions • Conventional low-copper alloys • Admixed high-copper alloys • Single composition high-copper alloys
- 19. • Dissolution and precipitation • Hg dissolves Ag and Sn from alloy • Intermetallic compounds formed Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg) Ag Ag Ag Sn Sn Sn Conventional Low-Copper Alloys Hg Hg Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2
- 20. 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 Ag Ag Sn Sn Sn Hg Hg Hg Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2
- 21. Conventional Low-Copper Alloys • Gamma 1 (1) = Ag2Hg3 – matrix for unreacted alloy and 2nd strongest phase – 10 micron grains binding gamma () – 60% of volume 1 Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy
- 22. 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 Ag3Sn + Hg Ag3Sn + Ag2Hg3 + Sn8Hg 1 2 2 Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy
- 23. 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 Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1 Ag-Sn Alloy Ag-Sn Alloy Mercury Ag Ag Ag Sn Sn Ag-Cu Alloy Ag Hg Hg
- 24. 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 Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1
- 25. 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 Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag-Cu + Ag2Hg3 + Cu6Sn5 1
- 26. Single Composition High-Copper Alloys • Gamma sphere () (Ag3Sn) with epsilon coating () (Cu3Sn) • Ag and Sn dissolve in Hg Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg) Ag Sn Ag Sn Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1
- 27. Single Composition High-Copper Alloys • 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 Ag-Sn Alloy 1 Ag3Sn + Cu3Sn + Hg Ag3Sn + Cu3Sn + Ag2Hg3 + Cu6Sn5 1
- 28. Classification of dental amalgam alloys BASED ON Cu CONTENT HIGH Cu ALLOYS LOW Cu ALLOYS > 6% Cu < 6% Cu ADMIXED SINGLE COMPOSITION REGULAR UNICOMPOSITION
- 29. BASED ON Zn CONTENT Zn CONTAINING Zn FREE ALLOY > 1% Zn < 1% Zn
- 30. BASED ON SHAPE OF ALLOY LATHECUT SPHERICAL ADMIXED
- 31. BASED ON NUMBER OF ALLOY METAL BINARY TERTIARY QUATERNARY Ag,Sn Ag,Sn,Cu Ag,Sn,Cu,Zn
- 32. BASED ON SIZE OF ALLOY MICROCUT FINE CUT MACROCUT COURSE CUT
- 33. 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
- 34. 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
- 35. 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)
- 36. 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)
- 37. 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)
- 38. 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)
- 39. Admixture: Lathe-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)
- 40. 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
- 41. Manufacturing Process • Spherical alloys – melt alloy – atomize • spheres form as particles cool – sizes range from 5 - 40 microns • variety improves condensability
- 42. Alloy Selection • Handling characteristics • Mechanical and physical properties • Clinical performance
- 43. Handling Characteristics • Spherical – advantages • easier to condense – around pins • hardens rapidly • smoother polish – disadvantages • difficult to achieve tight contacts • higher tendency for overhangs
- 44. Handling Characteristics • Admixed – advantages • easy to achieve tight contacts • good polish – disadvantages • hardens slowly – lower early strength
- 45. 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
- 46. Material-Related Variables • Dimensional change • Strength • Corrosion • Creep
- 47. Dimensional Change • Most high-copper amalgams undergo a net contraction • Contraction leaves marginal gap – initial leakage • post-operative sensitivity – reduced with corrosion over time
- 48. 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
- 49. 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
- 50. VI. Properties of Dental Amalgam 1. Compressive strength -Amalgam is strongest in compression and much weaker in tension and shear. -HCU materials have the highest compressive strength.
- 51. Properties of Dental Amalgam 2. Tensile Strength: -Amalgam is strongest in compression and much weaker in tension and shear. -HCU materials have the highest early tensile strength.
- 52. Properties of Dental Amalgam • Strength of various phases: 1. Unreacted Ag3Sn () phase. (strongest) 2. Ag2Hg3(1)phase. 3. Sn8Hg (2)phase.(weakest)
- 53. Properties of Dental Amalgam 3. Elastic Modulus: -High- copper alloys are stiffer than low-copper alloys. -Amalgam are viscoelastic.
- 54. 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)
- 55. 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
- 56. 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
- 57. MCQs 1. Dental situation in which Silver amalgam is most commonly used: a) Anterior Class 4 b) Posterior Class 1 c) Root canal feeling d) Pit and fissure
- 58. 2. Zn containing Amalgam contains: a) .001% Zn b) .01% Zn c) More than .o1% Zn d) More than .001% Zn
- 59. 3. Epsilon phase in dental amalgam is: a) Ag-Sn b) Cu3Sn c) Ag3Sn d) Cu6Sn
- 60. 4. Beta phase in dental amalgam is: a) Ag-Sn b) Cu3Sn c) Ag3Sn d) Cu6Sn5
- 61. 5. The weakest phase in amalgam is: a) Gamma- 1 b) Beta c) Beta- 1 d) Gamma
- 62. 6. Gamma -2 phase in dental amalgam is: a) Cu6Sn5 b) Sn7Hg c) Ag-Cu d) Ag3Sn
- 63. 7. Pain, after delayed expansion of amalgam is produced by: a) Presence of Zn b) Hydrogen gas c) Presence of H2O d) Improper cavity preparation
- 64. 8. Which phase of amalgam promotes tarnish and corrosion: a) Gamma b) Gamma- 1 c) Gamma- 2 d) Eta
- 65. 9. Low copper dental amalgam alloy contains maximum amount of copper upto: a) 3% b) 11% c) 6% d) 19%
- 66. 10. All of the following are feathers of the high Cu alloys, except: a) Low dimensional changes b) Low compressive strength c) Lower creep values d) Less susceptible to corrosion