Presentation on theme: "Dr. Raghuwar D Singh Associate Professor Prosthodontic Department King George’s Medical University UP, Lucknow Dental Materials Lecture BDS II Year."— Presentation transcript:
Dr. Raghuwar D Singh Associate Professor Prosthodontic Department King George’s Medical University UP, Lucknow Dental Materials Lecture BDS II Year
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.
Advantages Inexpensive Ease of use Proven track record –>100 years Familiarity Resin-free –less allergies than composite
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
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
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.
Amalgam Capsules Contain (in separate compartments): –powdered amalgam alloy –liquid mercury Some are manually activated, others self-activated Pestle usually included
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
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
Basic Constituents…. Copper (Cu) –ties up tin reducing gamma-2 formation –increases strength –reduces tarnish and corrosion –reduces creep reduces marginal deterioration
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….
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 H 2 O + Zn ZnO + H 2 Basic Constituents….
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
Dissolution and precipitation Hg dissolves Ag and Sn from alloy Intermetallic compounds formed Ag-Sn Alloy Mercury (Hg) Ag Sn Conventional Low-Copper Alloys Hg Ag 3 Sn + Hg Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 11 22
Conventional Low-Copper Alloys Gamma ( ) = Ag 3 Sn – unreacted alloy – strongest phase and corrodes the least – forms 30% of volume of set amalgam Ag-Sn Alloy Mercury Ag Sn Hg Ag 3 Sn + Hg Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 11 22
Conventional Low-Copper Alloys Gamma 1 ( 1 ) = Ag 2 Hg 3 – matrix for unreacted alloy and 2nd strongest phase – 10 micron grains binding gamma ( ) – 60% of volume 11 Ag 3 Sn + Hg Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 11 22 Ag-Sn Alloy
Conventional Low-Copper Alloys Gamma 2 ( 2 ) = Sn 8 Hg – 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 3 Sn + Hg Ag 3 Sn + Ag 2 Hg 3 + Sn 8 Hg 11 22 22 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 Ag 3 Sn particles Ag 3 Sn + Ag-Cu + Hg Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 11 Ag-Sn Alloy Mercury Ag Sn Ag-Cu Alloy Ag Hg
Admixed High-Copper Alloys Sn diffuses to surface of Ag-Cu particles – reacts with Cu to form (eta) Cu 6 Sn 5 ( ) around unconsumed Ag-Cu particles Ag-Sn Alloy Ag-Cu Alloy Ag-Sn Alloy Ag 3 Sn + Ag-Cu + Hg Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 11
Admixed High-Copper Alloys Gamma 1 ( 1 ) (Ag 2 Hg 3 ) surrounds ( ) eta phase (Cu 6 Sn 5 ) and gamma ( ) alloy particles (Ag 3 Sn) Ag-Sn Alloy 11 Ag-Cu Alloy Ag-Sn Alloy Ag 3 Sn + Ag-Cu + Hg Ag 3 Sn + Ag-Cu + Ag 2 Hg 3 + Cu 6 Sn 5 11
Single Composition High-Copper Alloys Gamma sphere ( ) (Ag 3 Sn) with epsilon coating ( ) (Cu 3 Sn) Ag and Sn dissolve in Hg Ag-Sn Alloy Mercury (Hg) Ag Sn Ag Sn Ag 3 Sn + Cu 3 Sn + Hg Ag 3 Sn + Cu 3 Sn + Ag 2 Hg 3 + Cu 6 Sn 5 11
Single Composition High-Copper Alloys Gamma 1 ( 1 ) (Ag 2 Hg 3 ) crystals grow binding together partially- dissolved gamma ( ) alloy particles (Ag 3 Sn) Epsilon ( ) (Cu 3 Sn) develops crystals on surface of gamma particle (Ag 3 Sn) in the form of eta ( ) (Cu 6 Sn 5 ) – reduces creep – prevents gamma-2 formation Ag-Sn Alloy 11 Ag 3 Sn + Cu 3 Sn + Hg Ag 3 Sn + Cu 3 Sn + Ag 2 Hg 3 + Cu 6 Sn 5 11
Classification of dental amalgam alloys BASED ON Cu CONTENT HIGH Cu ALLOYS > 6% Cu SINGLE COMPOSITION ADMIXED REGULARUNICOMPOSITION LOW Cu ALLOYS < 6% Cu
BASED ON Zn CONTENT Zn CONTAINING > 1% Zn Zn FREE ALLOY < 1% Zn
BASED ON SHAPE OF ALLOY LATHECUTSPHERICALADMIXED
BASED ON NUMBER OF ALLOY METAL BINARY Ag,Sn TERTIARY Ag,Sn,Cu QUATERNARY Ag,Sn,Cu,Zn
BASED ON SIZE OF ALLOY MICROCUT \FINE CUT MACROCUT \COURSE CUT
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 More Hg needed than spherical alloys High condensation force needed due to lathe cut 20% Cu Example – ANA 2000 (Nordiska Dental)
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)
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)
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)
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
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
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.
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.
Properties of Dental Amalgam Strength of various phases: 1.Unreacted Ag 3 Sn ( ) phase. (strongest) 2.Ag 2 Hg 3 ( 1 )phase. 3.Sn 8 Hg ( 2 )phase.(weakest)
Properties of Dental Amalgam 3.Elastic Modulus: -High- copper alloys are stiffer than low-copper alloys. -Amalgam are viscoelastic.
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 (Cu 6 Sn 5 ) embedded in gamma-1 grains – interlock –admixture eta (Cu 6 Sn 5 ) around Ag-Cu particles – improves bonding to gamma 1
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
2. Zn containing Amalgam contains: a).001% Zn b).01% Zn c) More than.o1% Zn d) More than.001% Zn
3. Epsilon phase in dental amalgam is: a)Ag-Sn b)Cu 3 Sn c)Ag 3 Sn d)Cu 6 Sn
4. Beta phase in dental amalgam is: a)Ag-Sn b)Cu3Sn c)Ag3Sn d)Cu6Sn5
5. The weakest phase in amalgam is: a)Gamma- 1 b)Beta c)Beta- 1 d)Gamma
6. Gamma -2 phase in dental amalgam is: a)Cu 6 Sn 5 b)Sn 7 Hg c)Ag-Cu d)Ag 3 Sn
7. Pain, after delayed expansion of amalgam is produced by: a)Presence of Zn b)Hydrogen gas c)Presence of H 2 O d)Improper cavity preparation
8. Which phase of amalgam promotes tarnish and corrosion: a)Gamma b)Gamma- 1 c)Gamma- 2 d)Eta
9. Low copper dental amalgam alloy contains maximum amount of copper upto: a)3% b)11% c)6% d)19%
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