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Alloys used in metal ceramic/ cosmetic dentistry training Alloys used in metal ceramic/ cosmetic dentistry training Presentation Transcript

  • ALLOYS USED IN METALALLOYS USED IN METAL CERAMICSCERAMICS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  • ContentsContents  Basic Materials used in dentistryBasic Materials used in dentistry  Metals and their propertiesMetals and their properties  Alloys and their propertiesAlloys and their properties  Metal ceramic alloysMetal ceramic alloys www.indiandentalacademy.com
  • Basic Materials used in DentistryBasic Materials used in Dentistry  ClassificationClassification CERAMICS METALS POLYMER INORGANIC SALT CRYSTALLINE CERAMICS GLASSES ALLOYS INTERMETTALIC COMPOUNDS RIGID POLYMERS WAXES ELASTOMERS www.indiandentalacademy.com
  • MetalsMetals  A crystalline material that consists ofA crystalline material that consists of positively charged ions in an ordered, closelypositively charged ions in an ordered, closely packed arrangement and bonded with apacked arrangement and bonded with a cloud of b-ee electrons. This type of bond,cloud of b-ee electrons. This type of bond, called acalled a metallic bond,metallic bond, is responsible foris responsible for many of the properties of metals-electricalmany of the properties of metals-electrical and ther­mal conductivity, metallic luster,and ther­mal conductivity, metallic luster, and (usually) high strengthand (usually) high strength www.indiandentalacademy.com
  • AlloysAlloys  A material that exhibits metallic propertiesA material that exhibits metallic properties and is composed of one or more elements-atand is composed of one or more elements-at least one of which is a metal. For example,least one of which is a metal. For example, steel is an alloy of iron and carbon, brass issteel is an alloy of iron and carbon, brass is an alloy of copper and zinc, and bronze is anan alloy of copper and zinc, and bronze is an alloy of copper and tin.alloy of copper and tin. www.indiandentalacademy.com
  • Inter metallic CompoundsInter metallic Compounds  A chemical compound whose componentsA chemical compound whose components are metals. The gamma phase of amalgam,are metals. The gamma phase of amalgam, Ag3Sn, is an example of an inter metallicAg3Sn, is an example of an inter metallic compound.compound. www.indiandentalacademy.com
  • PolymersPolymers  A material that is made up of repeatingA material that is made up of repeating units, orunits, or mers.mers. Most polymers are based on aMost polymers are based on a carbon (-C-C-C-C-) backbone in thecarbon (-C-C-C-C-) backbone in the polymer chain, al­though a silicone (-O-Si-polymer chain, al­though a silicone (-O-Si- O-Si-O-) backbone is im­portant in manyO-Si-O-) backbone is im­portant in many polymerspolymers www.indiandentalacademy.com
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  • MetalsMetals  A crystalline material that consists of positivelyA crystalline material that consists of positively charged ions in an ordered, closely packedcharged ions in an ordered, closely packed arrange­ment and bonded with a cloud of b-eearrange­ment and bonded with a cloud of b-ee electrons. This type of bond, called aelectrons. This type of bond, called a metallicmetallic bond,bond, is responsible for many of the properties ofis responsible for many of the properties of metals-electrical and ther­mal conductivity,metals-electrical and ther­mal conductivity, metallic luster, and (usually) high strengthmetallic luster, and (usually) high strength www.indiandentalacademy.com
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  • Characteristic Properties Of MetalsCharacteristic Properties Of Metals  Metals are usuallyMetals are usually  HardHard  LustrousLustrous  DenseDense  Good conductors of heat and electricityGood conductors of heat and electricity  OpaqueOpaque  Malleable and ductileMalleable and ductile  They give electro positive ions in solutionThey give electro positive ions in solution www.indiandentalacademy.com
  • OccurrenceOccurrence  Metals occur either on pure elements or inMetals occur either on pure elements or in compounds with other elements .compounds with other elements . Example; Gold(Au)Example; Gold(Au) Silver(Ag)Silver(Ag) Copper Obtained as CuCopper Obtained as Cu22S, CuSS, CuS Iron Obtained as FeIron Obtained as Fe22OO33 Pure Elements Compounds www.indiandentalacademy.com
  • Classification Of MetalsClassification Of Metals  Pure Metal or Mixture of Metals – AlloysPure Metal or Mixture of Metals – Alloys  Base Metal or Noble MetalBase Metal or Noble Metal  Cast metal or wrought metalCast metal or wrought metal www.indiandentalacademy.com
  • Noble MetalNoble Metal  Noble Metal is one whose compounds areNoble Metal is one whose compounds are decomposable by heat alone at a temperaturedecomposable by heat alone at a temperature not exceeding that of redness.not exceeding that of redness.  They are corrosion and oxidation resistantThey are corrosion and oxidation resistant because of inertness and chemical resistance.because of inertness and chemical resistance.  8 Noble metals used in dentistry are Au, Pt, Pd,8 Noble metals used in dentistry are Au, Pt, Pd, Ir, Os, Rh, Ru, Ag.Ir, Os, Rh, Ru, Ag. www.indiandentalacademy.com
  • Base MetalsBase Metals  Base metal is one whose compounds withBase metal is one whose compounds with oxygen are not decomposed by heat alone,oxygen are not decomposed by heat alone, retaining oxygen at high temperature.retaining oxygen at high temperature.  A metal, which is easily oxidized when heated inA metal, which is easily oxidized when heated in air, is a base metal.air, is a base metal.  Examples: Ni, Cr, Co, Fe, Al, Sn, Pb, etcExamples: Ni, Cr, Co, Fe, Al, Sn, Pb, etc www.indiandentalacademy.com
  • Cast MetalCast Metal Cast metal is any metal that is melted andCast metal is any metal that is melted and poured into a mould.poured into a mould. www.indiandentalacademy.com
  • Wrought MetalWrought Metal Wrought metal is a cast metal, which has beenWrought metal is a cast metal, which has been worked upon, in cold condition – i.e, withoutworked upon, in cold condition – i.e, without heating.heating. www.indiandentalacademy.com
  • Another Classification Of MetalsAnother Classification Of Metals  Light Metal – e.g., Al.Light Metal – e.g., Al.  Heavy Metal – e.g., Fe.Heavy Metal – e.g., Fe.  High Melting Metal – e.g., Co, Cr.High Melting Metal – e.g., Co, Cr.  Low Melting Metal – e.g., Sn.Low Melting Metal – e.g., Sn.  High Ductile and Malleable metal – e.g., Au.High Ductile and Malleable metal – e.g., Au. www.indiandentalacademy.com
  • Microscopic Structure Of MetalsMicroscopic Structure Of Metals  Most metals have crystalline structure in solidMost metals have crystalline structure in solid state which are held together by metallic bonds.state which are held together by metallic bonds.  Metals also exist in liquid state eg, Hg, in whichMetals also exist in liquid state eg, Hg, in which crystalline alignment is lost and the atoms movecrystalline alignment is lost and the atoms move freely in mass of liquid metal.freely in mass of liquid metal. www.indiandentalacademy.com
  • Metallic BondMetallic Bond  Primary BondsPrimary Bonds 1.1. Ionic BondsIonic Bonds 2.2. Covalent BondsCovalent Bonds 3.3. Metallic BondsMetallic Bonds  Secondary BondsSecondary Bonds Vander walls bondsVander walls bonds www.indiandentalacademy.com
  • Fabrication (Shaping) Methods OfFabrication (Shaping) Methods Of MetalsMetals  Casting – is the best and popular method.Casting – is the best and popular method.  Working on the metal – either in cold or hotWorking on the metal – either in cold or hot condition (i.e, with or without heating). Thiscondition (i.e, with or without heating). This involves pressing, rolling or forging. The metalinvolves pressing, rolling or forging. The metal subjected to the above process are called assubjected to the above process are called as wrought metals.wrought metals. www.indiandentalacademy.com
  • Fabrication (Shaping) Methods OfFabrication (Shaping) Methods Of Metals (Contd.)Metals (Contd.)  Extrusion - The process in which the metal isExtrusion - The process in which the metal is forced through a die to form a metal tubing.forced through a die to form a metal tubing.  Powder Metallurgy – involves pressingPowder Metallurgy – involves pressing powdered metals into a mould of desired shapepowdered metals into a mould of desired shape and heating it to a high temperature to cause aand heating it to a high temperature to cause a solid mass.solid mass. www.indiandentalacademy.com
  • Solidification Of Pure MetalSolidification Of Pure Metal  Pure metal has a melting point-known as FusionPure metal has a melting point-known as Fusion Temperature, and has specific heat.Temperature, and has specific heat.  To melt a crystalline substance (metal) someTo melt a crystalline substance (metal) some what more heat energy is required to convert itwhat more heat energy is required to convert it from solid to liquid.from solid to liquid.  This extra heat is stored away within the atomsThis extra heat is stored away within the atoms in the form of latent heat of fusion.in the form of latent heat of fusion. www.indiandentalacademy.com
  • Solidification Of Pure Metal (Contd.)Solidification Of Pure Metal (Contd.)  MechanismMechanism When the solid metal changes into liquid, itsWhen the solid metal changes into liquid, its crystalline pattern disappears, and the atoms arecrystalline pattern disappears, and the atoms are randomly distributed in the mass of liquid andrandomly distributed in the mass of liquid and they have more energy and are therefore movethey have more energy and are therefore move about freely.about freely.  In the reverse process of changing into solid,In the reverse process of changing into solid, temperature of the melt goes gradually (cooling);temperature of the melt goes gradually (cooling); atoms make an attempt to reform the crystallineatoms make an attempt to reform the crystalline arrangement.arrangement. www.indiandentalacademy.com
  • Mechanism of CrystallizationMechanism of Crystallization  A pure metal may crystallize in a tree-branchA pure metal may crystallize in a tree-branch pattern to form what is called a NUCLEUSpattern to form what is called a NUCLEUS  The initial nuclei are small in size and few inThe initial nuclei are small in size and few in number known as EMBRYO, which do notnumber known as EMBRYO, which do not stabilize in the melt and soon disappear.stabilize in the melt and soon disappear.  As the temperature of the metal gradually goesAs the temperature of the metal gradually goes down, a stable NUCLEUS is formed.down, a stable NUCLEUS is formed. www.indiandentalacademy.com
  • Mechanism of CrystallizationMechanism of Crystallization (contd.)(contd.)  A pure metal crystallizes from nuclei in a patternA pure metal crystallizes from nuclei in a pattern that often resembles the branches of a treethat often resembles the branches of a tree yielding crystals that are called dendritesyielding crystals that are called dendrites  Dental base metal casting alloys solidify with aDental base metal casting alloys solidify with a dendritic microstructuredendritic microstructure  The inter dendritic regions serves as sites forThe inter dendritic regions serves as sites for crack propagationcrack propagation www.indiandentalacademy.com
  • Mechanism of CrystallizationMechanism of Crystallization (contd.)(contd.)  Most noble metal casting alloys solidify with anMost noble metal casting alloys solidify with an equiaxed polycrystalline microstructureequiaxed polycrystalline microstructure  The metal is therefore made of thousands ofThe metal is therefore made of thousands of tiny crystals, such a metal is called polycrystallinetiny crystals, such a metal is called polycrystalline and each crystal in the structure is called aand each crystal in the structure is called a GRAIN.GRAIN. www.indiandentalacademy.com
  • Mechanism of CrystallizationMechanism of Crystallization (contd.)(contd.) www.indiandentalacademy.com
  • Importance of grain boundaryImportance of grain boundary  During permanent deformation of ductile dentalDuring permanent deformation of ductile dental alloys the dislocations cannot cross from onealloys the dislocations cannot cross from one grain to an adjacent grain and they willgrain to an adjacent grain and they will subsequently pile up at the grain boundaries.subsequently pile up at the grain boundaries. Hence further deformation in these regionsHence further deformation in these regions require greater stress.require greater stress.  Low melting phases precipitates and porosity areLow melting phases precipitates and porosity are typically found at grain boundaries of dentaltypically found at grain boundaries of dental casting alloys.casting alloys. www.indiandentalacademy.com
  • Control Of Grain SizeControl Of Grain Size  More nuclei in a given area results in smallerMore nuclei in a given area results in smaller grain size.grain size.  Rate of Crystallization – is faster than the rate ofRate of Crystallization – is faster than the rate of nuclei formation there will be larger grains.nuclei formation there will be larger grains.  Rate of Cooling –Rate of Cooling – Rapid cooling – Smaller grain sizeRapid cooling – Smaller grain size Slow cooling – Larger grain sizeSlow cooling – Larger grain size www.indiandentalacademy.com
  • Importance of grain sizeImportance of grain size  For noble metal casting alloys the yield strengthFor noble metal casting alloys the yield strength vary inversely with the square root of grain sizevary inversely with the square root of grain size  Compositional uniformity and corrosionCompositional uniformity and corrosion resistance of a cast dental alloy will be superiorresistance of a cast dental alloy will be superior for a fine grain sizefor a fine grain size www.indiandentalacademy.com
  • Crystal Space LatticeCrystal Space Lattice  The formed crystals in a metal are arranged in aThe formed crystals in a metal are arranged in a orderly pattern – layer by layer in regular stacks.orderly pattern – layer by layer in regular stacks.  The crystals of a metal is in the form of a spaceThe crystals of a metal is in the form of a space lattice.lattice.  The type of space lattice varies from metal toThe type of space lattice varies from metal to metal.metal. www.indiandentalacademy.com
  • Crystal Space LatticeCrystal Space Lattice www.indiandentalacademy.com
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  • Lattice Imperfections Or DefectsLattice Imperfections Or Defects  During crystal growth they do not meet inDuring crystal growth they do not meet in regular fashion lattice by lattice plane, they growregular fashion lattice by lattice plane, they grow randomly and meet irregularly resulting inrandomly and meet irregularly resulting in imperfection or defects.imperfection or defects.  These defects may be POINT DEFECTS orThese defects may be POINT DEFECTS or LINE DEFECTS.LINE DEFECTS.  The line defects are also DISLOCATIONS.The line defects are also DISLOCATIONS. www.indiandentalacademy.com
  • Edge Dislocation Slip PlaneEdge Dislocation Slip Plane  The line defects in a lattice can be made to slipThe line defects in a lattice can be made to slip by stress until finally the dislocation reaches theby stress until finally the dislocation reaches the edge of the metal and disappears. This is knownedge of the metal and disappears. This is known as EDGE DISLOCATION.as EDGE DISLOCATION.  The plane along which the dislocation moves isThe plane along which the dislocation moves is the slip lane.the slip lane. www.indiandentalacademy.com
  • Edge Dislocation Slip PlaneEdge Dislocation Slip Plane www.indiandentalacademy.com
  • Edge Dislocation Slip PlaneEdge Dislocation Slip Plane www.indiandentalacademy.com
  • Edge Dislocation and Slip PlaneEdge Dislocation and Slip Plane (Contd.)(Contd.)  The strength and ductility of the metal dependsThe strength and ductility of the metal depends to a large extent on the ease with whichto a large extent on the ease with which dislocations are able to movedislocations are able to move  If the dislocation impedes each other’sIf the dislocation impedes each other’s movement and metal becomes harder suchmovement and metal becomes harder such hardening is called WORK HARDENING orhardening is called WORK HARDENING or STRAIN HARDENING.STRAIN HARDENING. www.indiandentalacademy.com
  • Edge Dislocation and Slip PlaneEdge Dislocation and Slip Plane (Contd.)(Contd.)  If this is done at room temperature withoutIf this is done at room temperature without heating the metal it is called COLD WORKINGheating the metal it is called COLD WORKING and the finished metal is called WROUGHTand the finished metal is called WROUGHT METAL.METAL. www.indiandentalacademy.com
  • Cooling Pattern of Liquid MetalCooling Pattern of Liquid Metal During SolidificationDuring Solidification  Liquidus temperature – the temperature atLiquidus temperature – the temperature at which a metal in liquid state undergoes firstwhich a metal in liquid state undergoes first solidification.solidification.  Solidus temperature – the temperature at whichSolidus temperature – the temperature at which the last liquid of the metal solidifies.the last liquid of the metal solidifies. www.indiandentalacademy.com
  • Cooling Pattern of Liquid MetalCooling Pattern of Liquid Metal During SolidificationDuring Solidification www.indiandentalacademy.com
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  • Working On MetalsWorking On Metals  Deformation of Metal – Cold WorkDeformation of Metal – Cold Work –– Hot WorkHot Work –– ElasticElastic – Permanent– Permanent • AnnealingAnnealing • Fracture of the metalFracture of the metal www.indiandentalacademy.com
  • Working On Metals (Contd.)Working On Metals (Contd.)  Cold Work – when a metal is worked uponCold Work – when a metal is worked upon without heating.without heating.  Hot Work – when a metal is worked uponHot Work – when a metal is worked upon without heating.without heating.  Working on metal involves rolling, bending,Working on metal involves rolling, bending, pulling, pressing, hammering, etc in order topulling, pressing, hammering, etc in order to give a certain shape to a metal.give a certain shape to a metal.  At the end of such a work the metal becomesAt the end of such a work the metal becomes wrought.wrought. www.indiandentalacademy.com
  • Working On Metals (Contd.)Working On Metals (Contd.)  Cold working results inCold working results in • Increased surface hardness, strength andIncreased surface hardness, strength and proportional limit.proportional limit. • Decreased ductility, resistance to corrosion andDecreased ductility, resistance to corrosion and distorted grain structure.distorted grain structure. www.indiandentalacademy.com
  • Working On Metals (Contd.)Working On Metals (Contd.)  Annealing – heat treatment of metal or glass toAnnealing – heat treatment of metal or glass to eliminate the undesirable effects of straineliminate the undesirable effects of strain hardening and return the metal to its originalhardening and return the metal to its original condition without changing its shape.condition without changing its shape.  It involves three steps,It involves three steps, 1.1. RecoveryRecovery 2.2. RecrystallizationRecrystallization 3.3. Grain growthGrain growth www.indiandentalacademy.com
  • RecoveryRecovery  During recovery, cold work properties begin toDuring recovery, cold work properties begin to disappear.disappear. www.indiandentalacademy.com
  • RecrystallizationRecrystallization  The temperature at which the Old grainsThe temperature at which the Old grains disappear completely and are replaced by newdisappear completely and are replaced by new set of strain free grains is called recrystallization .set of strain free grains is called recrystallization .  The metal gets back its original soft and ductileThe metal gets back its original soft and ductile nature.nature. www.indiandentalacademy.com
  • Grain GrowthGrain Growth  Grain growth stops when a coarse grainGrain growth stops when a coarse grain structure is reached.structure is reached. www.indiandentalacademy.com
  • AnnealingAnnealing www.indiandentalacademy.com
  • Fracture Of MetalFracture Of Metal  If cold work is continued then the metalIf cold work is continued then the metal eventually fractures.eventually fractures.  This may be ,This may be ,  Trans granular – through the crystals and occursTrans granular – through the crystals and occurs at room temperature.at room temperature.  Inter granular – in-between the crystals andInter granular – in-between the crystals and occurs at elevated temperatures.occurs at elevated temperatures. www.indiandentalacademy.com
  • ALLOYSALLOYS  Combination of two or more metals which areCombination of two or more metals which are generally mutually soluble in the liquidgenerally mutually soluble in the liquid condition.condition.  A metallic material formed by the intimateA metallic material formed by the intimate blending of 2 or more metals some times a non-blending of 2 or more metals some times a non- metal be added.metal be added.  A substance composed of 2or more elements atA substance composed of 2or more elements at least one of which is a metal.least one of which is a metal. www.indiandentalacademy.com
  • Methods of AlloyingMethods of Alloying  By melting together the base metal (main) andBy melting together the base metal (main) and the alloying element, mixing them thoroughly,the alloying element, mixing them thoroughly, and allowing the mixture to cool and solidify.and allowing the mixture to cool and solidify. This is a common method.This is a common method.  Sintering or by powder metallurgy. Metals areSintering or by powder metallurgy. Metals are powdered, mixed and pressed to the desiredpowdered, mixed and pressed to the desired shape and then heated but not melted till theshape and then heated but not melted till the powders unite to form a solid mass.powders unite to form a solid mass. www.indiandentalacademy.com
  • Objectives of AlloyingObjectives of Alloying 1.1. To increase hardness and strength.To increase hardness and strength. 2.2. To lower the melting point.To lower the melting point. 3.3. To increase fluidity of liquid metal.To increase fluidity of liquid metal. 4.4. To increase resistance to tarnish and corrosion.To increase resistance to tarnish and corrosion. www.indiandentalacademy.com
  • Objectives of Alloying (Contd.)Objectives of Alloying (Contd.) 5.5. To make casting or working on the metal easy.To make casting or working on the metal easy. 6.6. To change the microscopic structure of theTo change the microscopic structure of the metal.metal. 7.7. To change the color of the metal.To change the color of the metal. 8.8. To provide special electrical and magneticTo provide special electrical and magnetic properties.properties. www.indiandentalacademy.com
  • Types of AlloysTypes of Alloys  Ferrous alloys - in which iron is the base metalFerrous alloys - in which iron is the base metal and its alloy is stainless steel.and its alloy is stainless steel.  Gold and silver alloys - with added copper toGold and silver alloys - with added copper to increase hardness, e.g. jewellery gold.increase hardness, e.g. jewellery gold.  Fusible alloys - which have low meltingFusible alloys - which have low melting temperature. Lead is the main metal, e.g. solder,temperature. Lead is the main metal, e.g. solder, valves of pressure cooker.valves of pressure cooker. www.indiandentalacademy.com
  • Types of Alloys (Contd.)Types of Alloys (Contd.)  Die-casting alloys-zinc containing aluminum andDie-casting alloys-zinc containing aluminum and magnesium - e.g. car spare parts, door handles.magnesium - e.g. car spare parts, door handles.  Babbit metal (named after Mr. Isaac Babbit ofBabbit metal (named after Mr. Isaac Babbit of Boston)-tin or lead based alloys-e.g. bearings.Boston)-tin or lead based alloys-e.g. bearings.  Nickel alloys - to make coins "Monel".Nickel alloys - to make coins "Monel". www.indiandentalacademy.com
  • Classification Of AlloysClassification Of Alloys  On the basis of number of metalsOn the basis of number of metals present in anpresent in an alloy.alloy.  Binary - alloy of two constituents.Binary - alloy of two constituents.  Ternary - alloy of three constituents.Ternary - alloy of three constituents.  Quaternary - alloy of four constituents.Quaternary - alloy of four constituents.  Quinary - alloy of five constituents.Quinary - alloy of five constituents. www.indiandentalacademy.com
  • Classification Of Alloys (Contd.)Classification Of Alloys (Contd.)  On the basis of miscibility (solubility) of atomsOn the basis of miscibility (solubility) of atoms of the ingredient metals after solidification i.e, inof the ingredient metals after solidification i.e, in the solid state. The four possibilities are,the solid state. The four possibilities are, Solid solutionSolid solution Eutectic mixtureEutectic mixture Inter metallic compoundInter metallic compound Peritectic alloyPeritectic alloy www.indiandentalacademy.com
  • Solid SolutionSolid Solution  Complete solubility.Complete solubility.  These are the alloys in which the ingredient metals areThese are the alloys in which the ingredient metals are soluble in each other both in liquid state as well as insoluble in each other both in liquid state as well as in solid state, e.g. gold and copper alloy.solid state, e.g. gold and copper alloy.  These are the alloys in which alloying atoms areThese are the alloys in which alloying atoms are distributed throughout the crystals without causing adistributed throughout the crystals without causing a fundamental change in the shape of the parent spacefundamental change in the shape of the parent space lattice, and also the microscopic structure islattice, and also the microscopic structure is homogeneous and resembles that of pure metal.homogeneous and resembles that of pure metal. www.indiandentalacademy.com
  • Solid SolutionSolid Solution www.indiandentalacademy.com
  • Solid Solution (Contd.)Solid Solution (Contd.)  Some examples of Solid solutions are,Some examples of Solid solutions are,  Au-Ag alloyAu-Ag alloy  Au-Cu alloyAu-Cu alloy  Au-Pt alloyAu-Pt alloy  Au-Pa alloyAu-Pa alloy  Ag-Pd alloy, etc.Ag-Pd alloy, etc.  Solid solution alloys consist of single phase only and areSolid solution alloys consist of single phase only and are chemically homogenous.chemically homogenous. www.indiandentalacademy.com
  • Solid Solution (Contd.)Solid Solution (Contd.)  The solid-solution alloys may be;The solid-solution alloys may be; 1.1. SUBSTITUTIONAL SOLID SOLUTIONSUBSTITUTIONAL SOLID SOLUTION ALLOYALLOY - the- the atoms of one metal replaces theatoms of one metal replaces the atoms of parent metal in the space lattice andatoms of parent metal in the space lattice and occupies that place. Such a substitutional solidoccupies that place. Such a substitutional solid solution alloy can have TWO TYPES of latticesolution alloy can have TWO TYPES of lattice arrangement.arrangement. www.indiandentalacademy.com
  • Solid Solution (Contd.)Solid Solution (Contd.) a.a. ORDERED ARRANGEMENTORDERED ARRANGEMENT  This produces an ordered space lattice.This produces an ordered space lattice.  In this arrangement two types of metal atomsIn this arrangement two types of metal atoms occupy very specific or ordered (as if) positionsoccupy very specific or ordered (as if) positions within the crystal, resulting in specificwithin the crystal, resulting in specific properties.properties.  This produces a super lattice within the solidThis produces a super lattice within the solid solution, which may distort the original lattice.solution, which may distort the original lattice. This type of change occurs with gold copperThis type of change occurs with gold copper alloys during heat treatments.alloys during heat treatments. www.indiandentalacademy.com
  • Solid Solution (Contd.)Solid Solution (Contd.)  DISORDERED ARRANGEMENTDISORDERED ARRANGEMENT This produces disordered space lattice if theThis produces disordered space lattice if the atoms of both the metals are randomlyatoms of both the metals are randomly distributed in the space lattice.distributed in the space lattice. www.indiandentalacademy.com
  • DISORDERED ARRANGEMENTDISORDERED ARRANGEMENT www.indiandentalacademy.com
  • Solid Solution (Contd.)Solid Solution (Contd.)  INTERSTITIAL SOLID SOLUTION ALLOYINTERSTITIAL SOLID SOLUTION ALLOY The atoms of one metal do not replace theThe atoms of one metal do not replace the parent atom in a space lattice, insteadparent atom in a space lattice, instead occupy a space existing in between theoccupy a space existing in between the atoms of the parent metalatoms of the parent metal.. This can only happen if the atom of theThis can only happen if the atom of the alloying element is sufficiently small to fitalloying element is sufficiently small to fit into the spaces between the atoms of theinto the spaces between the atoms of the parent metal.parent metal. www.indiandentalacademy.com
  • Conditions Favoring Solid-SolubilityConditions Favoring Solid-Solubility  Atom size - if the atom sizes of the mixing metalAtom size - if the atom sizes of the mixing metal are same, it will produce solid solution type ofare same, it will produce solid solution type of alloy.alloy.  Valency - metals of the same valency willValency - metals of the same valency will produce solid-solution alloy.produce solid-solution alloy.  Space-lattice type - if same, preferably if faceSpace-lattice type - if same, preferably if face centered will favour solid solubility.centered will favour solid solubility.  Chemical affinity - must be less to produceChemical affinity - must be less to produce solid-solution alloy.solid-solution alloy. www.indiandentalacademy.com
  • Properties Of Solid-solution Type OfProperties Of Solid-solution Type Of AlloysAlloys  Strong and hard.Strong and hard.  High proportional limit.High proportional limit.  High tensile strength.High tensile strength.  More ductility and malleability.More ductility and malleability.  Have a melting range instead of point.Have a melting range instead of point.  Can be burnished and worked easily.Can be burnished and worked easily.  High resistance to tarnish and corrosion.High resistance to tarnish and corrosion. www.indiandentalacademy.com
  • Eutectic AlloysEutectic Alloys  Complete in-solubility in solid state.Complete in-solubility in solid state.  The ingredient metals are soluble in each otherThe ingredient metals are soluble in each other in liquid state, but separate out (precipitate) asin liquid state, but separate out (precipitate) as different layers in solid state.different layers in solid state.  Example, silver and copper alloy.Example, silver and copper alloy. www.indiandentalacademy.com
  • Eutectic AlloysEutectic Alloys www.indiandentalacademy.com
  • Eutectic Alloys (Contd.)Eutectic Alloys (Contd.)  In this type of alloy, there is one particularIn this type of alloy, there is one particular composition at which it behaves similar to purecomposition at which it behaves similar to pure metal-that is; it solidifies at a constantmetal-that is; it solidifies at a constant temperature (or a melting point) instead of atemperature (or a melting point) instead of a range.range.  Alloys with a composition less than that ofAlloys with a composition less than that of eutectic are hypoeutectic and alloys with aeutectic are hypoeutectic and alloys with a composition more than eutectic are calledcomposition more than eutectic are called hypereutectichypereutectic www.indiandentalacademy.com
  • Eutectic Alloys (Contd.)Eutectic Alloys (Contd.)  These alloys are called eutectic because theThese alloys are called eutectic because the temperature at which this occurs is lower thantemperature at which this occurs is lower than the fusion temperature of either constituentthe fusion temperature of either constituent metals.metals.  Example, Ag-72 per cent and Cu-28 per centExample, Ag-72 per cent and Cu-28 per cent www.indiandentalacademy.com
  • Eutectic Alloys (Contd.)Eutectic Alloys (Contd.)  Properties – BrittleProperties – Brittle Less strongLess strong Less resistance to corrosionLess resistance to corrosion www.indiandentalacademy.com
  • Inter metallic CompoundsInter metallic Compounds  Inter metallic compounds are those when theInter metallic compounds are those when the metals are soluble in the liquid state but unitemetals are soluble in the liquid state but unite and form a chemical compound on solidifying.and form a chemical compound on solidifying.  They are called inter metallic compoundsThey are called inter metallic compounds because the alloy is formed by a chemicalbecause the alloy is formed by a chemical reaction between a metal and metal.reaction between a metal and metal. www.indiandentalacademy.com
  • Inter metallic Compounds (Contd.)Inter metallic Compounds (Contd.)  Very hard and brittle.Very hard and brittle.  Properties do not resemble the properties ofProperties do not resemble the properties of their parent metals.their parent metals. www.indiandentalacademy.com
  • Peritectic AlloysPeritectic Alloys  E.g. Platinum-Silver in casting alloyE.g. Platinum-Silver in casting alloy  Limited solid solubility of 2 metals can result inLimited solid solubility of 2 metals can result in transformation referred as Peritectictransformation referred as Peritectic  More BrittleMore Brittle  Reduced corrosion resistanceReduced corrosion resistance www.indiandentalacademy.com
  • Heat TreatmentHeat Treatment  Heat treatment (not melting) of metals in theHeat treatment (not melting) of metals in the solid state is called SOLID STATEsolid state is called SOLID STATE REACTIONS.REACTIONS.  This is a method to cause diffusion of atoms ofThis is a method to cause diffusion of atoms of the alloy by heating a solid metal to a certainthe alloy by heating a solid metal to a certain temperature and for certain period of time.temperature and for certain period of time.  This will result in. the changes in theThis will result in. the changes in the microscopic structure and physical properties.microscopic structure and physical properties. www.indiandentalacademy.com
  • Heat Treatment (Contd.)Heat Treatment (Contd.)  Important criteria in this process are:Important criteria in this process are: 1.1. Composition of alloyComposition of alloy 2.2. Temperature to which it is heatedTemperature to which it is heated 3.3. Time of heatingTime of heating 4.4. Method of cooling - cooling slowly inMethod of cooling - cooling slowly in the air or quenching rapidly in coldthe air or quenching rapidly in cold water.water. www.indiandentalacademy.com
  • Purpose of Heat TreatmentPurpose of Heat Treatment  Shaping and working on the appliance in theShaping and working on the appliance in the laboratory is made easy when the alloy is soft.laboratory is made easy when the alloy is soft. This is the first stage and is called softening heatThis is the first stage and is called softening heat treatment.treatment.  To harden the alloy for oral use, so that it willTo harden the alloy for oral use, so that it will withstand oral stresses. The alloy is again heatedwithstand oral stresses. The alloy is again heated and this time it is called hardening heatand this time it is called hardening heat treatment.treatment. www.indiandentalacademy.com
  • Clinical significance of heatClinical significance of heat treatmenttreatment  Type I and II gold alloys usually do not hardenType I and II gold alloys usually do not harden or they harden to a lesser degree than do theor they harden to a lesser degree than do the types III and IV gold alloys.types III and IV gold alloys.  The mechanism of hardening is the result ofThe mechanism of hardening is the result of several different solid state transformationsseveral different solid state transformations  The type III and IV gold alloys that can beThe type III and IV gold alloys that can be hardened or strengthened from quenching, canhardened or strengthened from quenching, can also be softened by heat treatments.also be softened by heat treatments. www.indiandentalacademy.com
  • Types of Heat TreatmentTypes of Heat Treatment  Softening Heat treatmentSoftening Heat treatment  Hardening Heat treatmentHardening Heat treatment  Solution Heat treatmentSolution Heat treatment  Age HardeningAge Hardening www.indiandentalacademy.com
  • Softening heat treatment  Also known as ANNEALING. This is done forAlso known as ANNEALING. This is done for structures which are cold worked.structures which are cold worked.  TechniqueTechnique -- alloyalloy is placed in an electric furnaceis placed in an electric furnace at a temperature of 700°C for 10 minutes andat a temperature of 700°C for 10 minutes and then rapidly cooled (quenched).then rapidly cooled (quenched). www.indiandentalacademy.com
  • Softening heat treatment(Contd.)  Result of this is reduction in strength, hardnessResult of this is reduction in strength, hardness and pro­portional limit but increase in ductility.and pro­portional limit but increase in ductility. In other words the metal becomes soft. This isIn other words the metal becomes soft. This is also known as HOMOGENIZATIONalso known as HOMOGENIZATION TREATMENT.TREATMENT. www.indiandentalacademy.com
  • Hardening heat treatment  This is done for cast removable partialThis is done for cast removable partial dentures, saddles, bridges, but not fordentures, saddles, bridges, but not for Inlays.Inlays.  TechniqueTechnique -- The appliance (alloy) is heatThe appliance (alloy) is heat soaked at a temperature between 200-soaked at a temperature between 200- 450°C for 15-30 minutes and then rapidly450°C for 15-30 minutes and then rapidly cooled by quenching.cooled by quenching. www.indiandentalacademy.com
  • Hardening heat treatment(Contd.)  The result of this is increase in strength,The result of this is increase in strength, hardness and proportional limit but reduction inhardness and proportional limit but reduction in ductility.ductility.  Also known as ORDER HARDENINGAlso known as ORDER HARDENING oror PRECIPITATION HARDENINGPRECIPITATION HARDENING.. www.indiandentalacademy.com
  • Solution Heat Treatment Or Solution-Hardening  When the alloy is heat soaked, any precipitationsWhen the alloy is heat soaked, any precipitations formed during earlier heat treatment, will nowformed during earlier heat treatment, will now once again become soluble in the solvent metal.once again become soluble in the solvent metal.  Technique is same as softening heat treatment.Technique is same as softening heat treatment. www.indiandentalacademy.com
  • Age Hardening  After solution heat treatment, the alloy is onceAfter solution heat treatment, the alloy is once again heated to bring about further precipitationagain heated to bring about further precipitation and this time it shows in the metallography as aand this time it shows in the metallography as a fine dispersed phase.fine dispersed phase.  This also causes hardening of the alloy and isThis also causes hardening of the alloy and is known as age hardening because the alloy willknown as age hardening because the alloy will maintain its quality for many years.maintain its quality for many years. www.indiandentalacademy.com
  • Clinical significance of heatClinical significance of heat treatments in metal ceramic alloystreatments in metal ceramic alloys  Type I very high noble metal alloys with 96% toType I very high noble metal alloys with 96% to 98% noble alloys contains iron which is added as98% noble alloys contains iron which is added as a strengthening element.a strengthening element.  Iron reacts with platinum to form FePt3Iron reacts with platinum to form FePt3 precipitates, which strengthens the alloys.precipitates, which strengthens the alloys.  The optimum heat treatment is 30 minutes ;atThe optimum heat treatment is 30 minutes ;at 550o c which results in a 30% to 50% increase550o c which results in a 30% to 50% increase in the tensile strength.in the tensile strength. www.indiandentalacademy.com
  • Clinical significance of heatClinical significance of heat treatments in metal ceramic alloystreatments in metal ceramic alloys  In type III high noble metal alloys withIn type III high noble metal alloys with moderate silver alloys there is decrease in goldmoderate silver alloys there is decrease in gold which is made up by an increase in the palladiumwhich is made up by an increase in the palladium concentration to 26% to 31% plus an increase inconcentration to 26% to 31% plus an increase in the silver to 14% to 16%.the silver to 14% to 16%.  Neither of these alloys contain iron or platinumNeither of these alloys contain iron or platinum and both are strengthened mainly by a solidand both are strengthened mainly by a solid solution – hardening mechanism.solution – hardening mechanism. www.indiandentalacademy.com
  • Different Metals Used In DentistryDifferent Metals Used In Dentistry Gold (Au)Gold (Au)  noble metalnoble metal  provides a high level of corrosion and tarnish resistanceprovides a high level of corrosion and tarnish resistance  increases an alloy's melting range slightly.increases an alloy's melting range slightly.  improves workability, burnish ability, and raises the densityimproves workability, burnish ability, and raises the density  imparts a very pleasing yellow color to an alloy (if presentimparts a very pleasing yellow color to an alloy (if present in sufficient quantity).in sufficient quantity).  Unfortunately, that yellow color is readily offset by theUnfortunately, that yellow color is readily offset by the addition of "white" metals, such as palladium and silver.addition of "white" metals, such as palladium and silver. www.indiandentalacademy.com
  • PalladiumPalladium  Palladium, a member of the platinum group, is a noblePalladium, a member of the platinum group, is a noble metalmetal  Palladium is added to increase the strength, hardness (withPalladium is added to increase the strength, hardness (with copper), corrosion and tarnish resistance of gold-basedcopper), corrosion and tarnish resistance of gold-based alloys.alloys.  Palladium elevates an alloy's melting range and improvePalladium elevates an alloy's melting range and improve its sag resistance.its sag resistance.  Has a very strong whitening effect, so an alloy with 90%Has a very strong whitening effect, so an alloy with 90% gold and only 10% palladium will appear platinum-colored.gold and only 10% palladium will appear platinum-colored.  Palladium possesses a high affinity for hydrogen, oxygen,Palladium possesses a high affinity for hydrogen, oxygen, and carbon.and carbon.  It lowers the den­sity of the gold-based alloys slightly butIt lowers the den­sity of the gold-based alloys slightly but has little similar effect on silver-based metals.has little similar effect on silver-based metals. www.indiandentalacademy.com
  • PlatinumPlatinum  Platinum is a member of the platinum groupPlatinum is a member of the platinum group and is a noble metaland is a noble metal  Platinum increases the strength, meltingPlatinum increases the strength, melting range, and hardness of gold-based alloysrange, and hardness of gold-based alloys while improving their corrosion, tarnish, andwhile improving their corrosion, tarnish, and sag resistance.sag resistance.  It whitens an alloy and increases the densityIt whitens an alloy and increases the density of non gold-based metals because of its highof non gold-based metals because of its high density.density. www.indiandentalacademy.com
  • IridiumIridium  Iridium is a member of the platinum groupIridium is a member of the platinum group and is a noble metal.and is a noble metal.  serves as a grain refiner for gold- andserves as a grain refiner for gold- and palladium-based alloys to improve thepalladium-based alloys to improve the mechanical properties as well as the tarnishmechanical properties as well as the tarnish resistance.resistance. www.indiandentalacademy.com
  • Ruthenium (Ru)Ruthenium (Ru)  Ruthenium is a member of the palladiumRuthenium is a member of the palladium group and is a noble metal.group and is a noble metal.  Ruthenium acts as a grain refiner for gold-Ruthenium acts as a grain refiner for gold- and palladium- based alloys to improve theirand palladium- based alloys to improve their mechanical properties and tarnish resistancemechanical properties and tarnish resistance (like iridium).(like iridium). www.indiandentalacademy.com
  • SilverSilver  Although silver is a precious element, it is notAlthough silver is a precious element, it is not universally regarded as noble in the oral cavity .universally regarded as noble in the oral cavity .  Silver lowers the melting range, improves fluidity,Silver lowers the melting range, improves fluidity, and helps to control the coefficient of thermaland helps to control the coefficient of thermal expansion in gold- and palladium-based alloysexpansion in gold- and palladium-based alloys  Silver-containing porcelain alloys have beenSilver-containing porcelain alloys have been known to induce discolor­ation (yellow, brown, orknown to induce discolor­ation (yellow, brown, or green) with some porcelains.green) with some porcelains. www.indiandentalacademy.com
  • Silver (Contd)Silver (Contd)  Silver possesses a high affinity for oxygenSilver possesses a high affinity for oxygen absorption, which can lead to castingabsorption, which can lead to casting porosity and/or gassing.porosity and/or gassing.  However, small amounts of zinc or indiumHowever, small amounts of zinc or indium added to gold- and silver-based alloys helpadded to gold- and silver-based alloys help to control silver's absorption of oxygen.to control silver's absorption of oxygen.  Silver will also corrode and tarnish in theSilver will also corrode and tarnish in the presence of sulfur.presence of sulfur. www.indiandentalacademy.com
  • AluminiumAluminium  Aluminum is added to lower the melting range ofAluminum is added to lower the melting range of nickel-based alloys.nickel-based alloys.  Aluminum is a hardening agent and influencesAluminum is a hardening agent and influences oxide formation.oxide formation.  With the cobalt - chromium alloys used for metalWith the cobalt - chromium alloys used for metal ceramic restorations, aluminum is one of theceramic restorations, aluminum is one of the elements that is "etched" from the alloy's surfaceelements that is "etched" from the alloy's surface to create micromechanical reten­tion for resin-to create micromechanical reten­tion for resin- bonded retainers (Maryland Bridges).bonded retainers (Maryland Bridges). www.indiandentalacademy.com
  • BerylliumBeryllium  Like aluminum, beryllium lowers the meltingLike aluminum, beryllium lowers the melting range of nickel-based alloys, improves castability,range of nickel-based alloys, improves castability, improves polishability, is a hardener, and helps toimproves polishability, is a hardener, and helps to control oxide formation.control oxide formation.  The etching of nickel-chromium-beryllium alloysThe etching of nickel-chromium-beryllium alloys removes a Ni-Be phase to create the microremoves a Ni-Be phase to create the micro retention so important to the etched metal resin-retention so important to the etched metal resin- bonded retainer.bonded retainer.  potential health risks to both technicians andpotential health risks to both technicians and patients associ­ated with beryllium-containingpatients associ­ated with beryllium-containing alloys .alloys . www.indiandentalacademy.com
  • BoronBoron  Boron is a deoxidizer.Boron is a deoxidizer.  For nickel-based alloys, it is a hardening agent andFor nickel-based alloys, it is a hardening agent and an element that reduces the surface tension of thean element that reduces the surface tension of the molten alloy to improve castability.molten alloy to improve castability.  The nickel-chromium beryllium-free alloys thatThe nickel-chromium beryllium-free alloys that contain boron will pool on melting, as opposed tocontain boron will pool on melting, as opposed to the Ni-Cr-Be alloys that do not pool.the Ni-Cr-Be alloys that do not pool.  Boron also acts to reduce ductility and to increaseBoron also acts to reduce ductility and to increase hardness.hardness. www.indiandentalacademy.com
  • Chromium (Cr)Chromium (Cr)  Chromium is a solid solution hardeningChromium is a solid solution hardening agent that contributes to corrosionagent that contributes to corrosion resistance by its passivating nature in nickel-resistance by its passivating nature in nickel- and cobalt-based alloys.and cobalt-based alloys. www.indiandentalacademy.com
  • CobaltCobalt (Co)(Co)  Cobalt is an alternative to the nickel-basedCobalt is an alternative to the nickel-based alloys, but the cobalt-based metals are morealloys, but the cobalt-based metals are more difficult to process.difficult to process.  Cobalt is included in some high-palladiumCobalt is included in some high-palladium alloys to increase the alloy's coefficient ofalloys to increase the alloy's coefficient of thermal expansion and to act as athermal expansion and to act as a strengthener .strengthener . www.indiandentalacademy.com
  • Copper (Cu)Copper (Cu)  Copper serves as a hardening and strengtheningCopper serves as a hardening and strengthening agentagent  Lower the melting range of an alloy, and interactsLower the melting range of an alloy, and interacts with platinum, palladium, silver, and gold towith platinum, palladium, silver, and gold to provide a heat-treating capability in gold, silver,provide a heat-treating capability in gold, silver, and palladium-based alloys.and palladium-based alloys.  Copper helps to form an oxide for porcelainCopper helps to form an oxide for porcelain bonding, lowers the density slightly, and canbonding, lowers the density slightly, and can enhance passivity in the high palladium-copperenhance passivity in the high palladium-copper alloys.alloys. www.indiandentalacademy.com
  • GalliumGallium (Ga)(Ga)  Gallium is added to silver-free porcelainGallium is added to silver-free porcelain alloys to compensate for the decreasedalloys to compensate for the decreased coefficient of thermal expansion created bycoefficient of thermal expansion created by the removal of silver.the removal of silver.  Concerns over silver's potential to discolorConcerns over silver's potential to discolor dental porcelain have greatly limited its usedental porcelain have greatly limited its use in systems other than palladium-silverin systems other than palladium-silver www.indiandentalacademy.com
  • IndiumIndium  Serves many functions in gold-based metalServes many functions in gold-based metal ceramic alloys.ceramic alloys.  It is a less volatile oxide-scavenging agent (toIt is a less volatile oxide-scavenging agent (to protect molten alloy);protect molten alloy);  lowers the alloy's melting range and density;lowers the alloy's melting range and density; improves fluidity;improves fluidity;  Has a strengthening effect. Indium is added to nonHas a strengthening effect. Indium is added to non gold­based alloy systems to form an oxide layer forgold­based alloy systems to form an oxide layer for porce­lain bonding.porce­lain bonding.  Alloys with a high silver content (eg, palladium-Alloys with a high silver content (eg, palladium- silver) rely on indium to enhance tarnishsilver) rely on indium to enhance tarnish resistance.resistance. www.indiandentalacademy.com
  • Iron (Fe)Iron (Fe)  Iron is added to some gold-based porcelainIron is added to some gold-based porcelain systems for hardening and oxide production.systems for hardening and oxide production.  Iron is included in a few base metal alloys asIron is included in a few base metal alloys as well.well. www.indiandentalacademy.com
  • Manganese (Mn)Manganese (Mn)  Manganese is an oxide scavenger and aManganese is an oxide scavenger and a hardening agent in nickel- and cobalt-basedhardening agent in nickel- and cobalt-based alloys.alloys. www.indiandentalacademy.com
  • Molybdenum (Mo)Molybdenum (Mo)  Molybdenum improves corrosion resistance,Molybdenum improves corrosion resistance, influences oxide production, and is helpfulinfluences oxide production, and is helpful in adjusting the coefficient of thermalin adjusting the coefficient of thermal expansion of nickel-based alloys.expansion of nickel-based alloys. www.indiandentalacademy.com
  • Nickel (Ni)Nickel (Ni)  Nickel has been selected as a base for porcelainNickel has been selected as a base for porcelain alloys because its coefficient of thermal expansionalloys because its coefficient of thermal expansion approximates that of gold and it providesapproximates that of gold and it provides resistance to corrosion.resistance to corrosion.  Unfortunately, nickel is a sensitizer and a knownUnfortunately, nickel is a sensitizer and a known carcinogen.carcinogen.  Estimates of nickel sensitivity among women inEstimates of nickel sensitivity among women in the United States range from 9% to 31.9% and fromthe United States range from 9% to 31.9% and from 0.8% to 20.7% among men .0.8% to 20.7% among men . www.indiandentalacademy.com
  • Tin (Sn)Tin (Sn)  Tin is a hardening agent that acts to lowerTin is a hardening agent that acts to lower the melting range of an alloy.the melting range of an alloy.  It also assists in oxide production forIt also assists in oxide production for porcelain bonding in gold- and palladium-porcelain bonding in gold- and palladium- based alloys.based alloys.  Tin is one of the key trace elements forTin is one of the key trace elements for oxidation of the palladium-silver alloys.oxidation of the palladium-silver alloys. www.indiandentalacademy.com
  • Titanium (Ti)Titanium (Ti)  Like aluminum and beryllium, titanium isLike aluminum and beryllium, titanium is added to lower the melting range andadded to lower the melting range and improve castability.improve castability.  Titanium also acts as a hardener andTitanium also acts as a hardener and influences oxide formation at highinfluences oxide formation at high temperatures.temperatures. www.indiandentalacademy.com
  • Zinc (Zn)Zinc (Zn)  Zinc helps lower the melting range of anZinc helps lower the melting range of an alloy and acts as a deoxidizer or scavengeralloy and acts as a deoxidizer or scavenger to combine with other oxides.to combine with other oxides.  Zinc improves the castability of an alloy andZinc improves the castability of an alloy and contributes to hardness when combinedcontributes to hardness when combined with palladium.with palladium. www.indiandentalacademy.com
  • Need For Dental casting alloysNeed For Dental casting alloys  The Major factors areThe Major factors are  Economy – To perform the same functionEconomy – To perform the same function but at the lower costbut at the lower cost  Performance – To perform better in ease ofPerformance – To perform better in ease of processing, improved handing characters,processing, improved handing characters, and increased fracture resistanceand increased fracture resistance  Esthetics –To provide more esthetic resultsEsthetics –To provide more esthetic results such as increased translucencysuch as increased translucency www.indiandentalacademy.com
  • Historical Perspective On DentalHistorical Perspective On Dental Casting AlloysCasting Alloys  The history of dental casting alloys has beenThe history of dental casting alloys has been influenced by three major factors.influenced by three major factors.  1. The technological changes of dental1. The technological changes of dental prosthesisprosthesis  2. Metallurgical advancement2. Metallurgical advancement  3. Price changes of noble metals since 1968.3. Price changes of noble metals since 1968. www.indiandentalacademy.com
  • Historical Perspective On DentalHistorical Perspective On Dental Casting Alloys (contd)Casting Alloys (contd)  Taggarts presentation to the New YorkTaggarts presentation to the New York odontological group in 1907 on the fabrication ofodontological group in 1907 on the fabrication of cast inlay restorations often has beencast inlay restorations often has been acknowledged as the first reported application ofacknowledged as the first reported application of the lost wax technique in dentistry.the lost wax technique in dentistry.  The inlay technique described by Taggarat was anThe inlay technique described by Taggarat was an instant‘ success. It soon led to the casting ofinstant‘ success. It soon led to the casting of complex inlays such as on lays, crowns, fixedcomplex inlays such as on lays, crowns, fixed partial dentures and removable partial denturepartial dentures and removable partial denture frame works.frame works. www.indiandentalacademy.com
  • Historical Perspective On DentalHistorical Perspective On Dental Casting Alloys (contd)Casting Alloys (contd)  Because pure gold did not have the physicalBecause pure gold did not have the physical properties required for these dental restorationsproperties required for these dental restorations alloys were quickly adopted. These gold werealloys were quickly adopted. These gold were further strengthened with Cu, Ag, or Pt.further strengthened with Cu, Ag, or Pt.  1932, the dental materials group at the national1932, the dental materials group at the national Bureau of standards surveyed the alloys being usedBureau of standards surveyed the alloys being used and roughly classified them as Type I, Type II,and roughly classified them as Type I, Type II, Type III & Type IV.Type III & Type IV. www.indiandentalacademy.com
  • Historical Perspective On DentalHistorical Perspective On Dental Casting Alloys (contd)Casting Alloys (contd)  At that time some tarnish tests indicatedAt that time some tarnish tests indicated that alloys with a gold content lower thanthat alloys with a gold content lower than 65% to 75% tarnished too readily for dental65% to 75% tarnished too readily for dental useuse  By 1948, the composition of dental nobleBy 1948, the composition of dental noble metal alloys for cast metal restorations hasmetal alloys for cast metal restorations has become rather diverse with thesebecome rather diverse with these formulations, the tarnishing tendency of theformulations, the tarnishing tendency of the original alloys apparently had disappeared.original alloys apparently had disappeared. www.indiandentalacademy.com
  • Historical Perspective On DentalHistorical Perspective On Dental Casting Alloys (contd)Casting Alloys (contd)  The base metal removable partial denture wereThe base metal removable partial denture were introduced in1930's.introduced in1930's.  In late 1950's a breakthrough occurred in dentalIn late 1950's a breakthrough occurred in dental technology that was to influence significantly thetechnology that was to influence significantly the fabrication of dental restorations. This was thefabrication of dental restorations. This was the successful veneering of metal substrate with dentalsuccessful veneering of metal substrate with dental porcelain.porcelain.  In 1978 the price of gold was climbing so rapidlyIn 1978 the price of gold was climbing so rapidly that attention focused on the noble metal alloys tothat attention focused on the noble metal alloys to reduce the precious metal content get retain thereduce the precious metal content get retain the advantage of noble metal for dental use.advantage of noble metal for dental use. www.indiandentalacademy.com
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  • Desirable Properties Of CastingDesirable Properties Of Casting Alloys: The metals must exhibitAlloys: The metals must exhibit  11. Bio compatibility. Bio compatibility  2. Ease of melting & casting2. Ease of melting & casting  3. Ease of brazing and soldering & polishing3. Ease of brazing and soldering & polishing  4. Little solidification shrinkage.4. Little solidification shrinkage.  5. Minimal reactivity with mould material.5. Minimal reactivity with mould material.  6. Good wear resistance.6. Good wear resistance. www.indiandentalacademy.com
  • Desirable Properties Of CastingDesirable Properties Of Casting Alloys: The metals must exhibitAlloys: The metals must exhibit  7. High strength7. High strength  8. Sag resistance8. Sag resistance  9. Tarnish & corrosion resistance.9. Tarnish & corrosion resistance.  10.Alergenic components in casting alloys10.Alergenic components in casting alloys  11.Economic considerations11.Economic considerations  12. Lab cost12. Lab cost www.indiandentalacademy.com
  • Alloys type by function - 1932Alloys type by function - 1932 Type I gold alloysType I gold alloys Soft (VHN 50 TO 90)Soft (VHN 50 TO 90) Type II gold alloysType II gold alloys Medium (90 TO 120)Medium (90 TO 120) Type III gold alloysType III gold alloys Hard (120 TO 150)Hard (120 TO 150) Type IV gold alloysType IV gold alloys Extra Hard (more than 150)Extra Hard (more than 150) www.indiandentalacademy.com
  • Alloy type by functionAlloy type by function  Type I ;- small inlays easily burnished andType I ;- small inlays easily burnished and subject to very slight stresssubject to very slight stress  Type II;- inlays subject to moderate stressType II;- inlays subject to moderate stress thick three quarter crowns, abutmentsthick three quarter crowns, abutments pontics and full crownspontics and full crowns  Type III;- short span fixed partial denturesType III;- short span fixed partial dentures  Type IV;- long span fixed partial denturesType IV;- long span fixed partial dentures www.indiandentalacademy.com
  • Classification Of Alloys By ADA 1984Classification Of Alloys By ADA 1984 Alloy TypeAlloy Type Total Noble contentTotal Noble content High noble metalHigh noble metal >=40 wt% of Au and 60%>=40 wt% of Au and 60% wt ofwt of noble metalnoble metal elementselements Noble metalNoble metal >=25 wt% of noble metal>=25 wt% of noble metal Predominantly basePredominantly base metalmetal <25 wt% of the noble<25 wt% of the noble metal elementsmetal elements www.indiandentalacademy.com
  • Alloy classification based on color orAlloy classification based on color or compositioncomposition According to their color and principalAccording to their color and principal element or elements (Phillips, 1982).element or elements (Phillips, 1982).  Yellow golds-Yellow golds- yellowyellow color, with greater than 60%color, with greater than 60% gold contentgold content  White golds-White golds- whitewhite color, but with more thancolor, but with more than 50% gold content50% gold content www.indiandentalacademy.com
  • Alloy classification based on color orAlloy classification based on color or composition (Cond..)composition (Cond..)  Low (or economy) golds-Low (or economy) golds- usually yellow colored, with lessusually yellow colored, with less than 60% gold (usually 42% to 55%)than 60% gold (usually 42% to 55%)  High palladium –High palladium – white colored, with palladium thewhite colored, with palladium the major component; may contain small quantities ofmajor component; may contain small quantities of gold (2%) and a limited amount of either copper orgold (2%) and a limited amount of either copper or cobaltcobalt www.indiandentalacademy.com
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  • Metal Ceramic RestorationMetal Ceramic Restoration  By Definition – Partial crown, full crown orBy Definition – Partial crown, full crown or fixed partial denture made with a metalfixed partial denture made with a metal substrate to which porcelain is bonded forsubstrate to which porcelain is bonded for esthetic enhancement via an intermediateesthetic enhancement via an intermediate metal oxide layermetal oxide layer  Also called as porcelain fused metal ,Also called as porcelain fused metal , porcelain bonded to metal , porcelain toporcelain bonded to metal , porcelain to metal and ceramo metalmetal and ceramo metal www.indiandentalacademy.com
  • History of metal ceramic alloysHistory of metal ceramic alloys  1789 - The first porcelain tooth material was1789 - The first porcelain tooth material was patented inpatented in byby a French dentist (de Chemant) ina French dentist (de Chemant) in collaboration with a French pharmacistcollaboration with a French pharmacist (Duchateau). The product, was an improved(Duchateau). The product, was an improved versionversion ofof "mineral paste teeth“ that was"mineral paste teeth“ that was produced bproduced byy Duchateau in 1774 ,which wasDuchateau in 1774 ,which was introduced in England soon thereafterintroduced in England soon thereafter byby dede Chemant.Chemant. www.indiandentalacademy.com
  • History of metal ceramic alloysHistory of metal ceramic alloys  1808- Fonzi, an Italian dentist, invented a "terrometallic"1808- Fonzi, an Italian dentist, invented a "terrometallic" porcelain tooth that was held in placeporcelain tooth that was held in place byby a platinum pin or frame.a platinum pin or frame.  1817 - Planteau, a French dentist, introduced porcelain teeth to1817 - Planteau, a French dentist, introduced porcelain teeth to .the United States.the United States  1822 - Peale, an artist, developed a baking process in1822 - Peale, an artist, developed a baking process in Philadelphia for these teeth.Philadelphia for these teeth.  1825 -1825 - Commercial productionCommercial production ofof these teeth was started bythese teeth was started by Stockton.Stockton.  1837 - In England, Ash developed an improved version1837 - In England, Ash developed an improved version ofof thethe porcelain tooth.porcelain tooth.  1844, the nephew1844, the nephew ofof Stockton founded the S.S. White Company,Stockton founded the S.S. White Company, and this led to further refinementand this led to further refinement ofof the design and the massthe design and the mass productionproduction ofof porcelain denture teeth.porcelain denture teeth. www.indiandentalacademy.com
  • History of metal ceramic alloysHistory of metal ceramic alloys  1903 - Dr. Charles Land introduced one of the1903 - Dr. Charles Land introduced one of the first ceramic crowns to dentistry.first ceramic crowns to dentistry.  Land, described a technique for fabricatingLand, described a technique for fabricating ceramic crowns using a platinum foil matrix andceramic crowns using a platinum foil matrix and high-fusing felds­pathic porcelain.high-fusing felds­pathic porcelain.  These crowns exhibited excellent aesthetics; butThese crowns exhibited excellent aesthetics; but the low flexural strengththe low flexural strength ofof porcelain resulted inporcelain resulted in a high incidencea high incidence ofof failures.failures. www.indiandentalacademy.com
  • History of metal ceramic alloysHistory of metal ceramic alloys  1962 - Weinstein et al , responsible for the patents of1962 - Weinstein et al , responsible for the patents of long-standing aesthetic performance and clinicallong-standing aesthetic performance and clinical survivability of metal-ceramic restorations.survivability of metal-ceramic restorations.  One of these patents described the formulations ofOne of these patents described the formulations of feldspathic porcelain that allowed systematic control offeldspathic porcelain that allowed systematic control of the sintering temperature and thermal expansionthe sintering temperature and thermal expansion coefficient.coefficient.  The other patent described the components that couldThe other patent described the components that could be used to produce alloys that bonded chemically tobe used to produce alloys that bonded chemically to and were thermally compatible with feldspathicand were thermally compatible with feldspathic porcelains.porcelains.  The first commercial porcelain was developed by VitaThe first commercial porcelain was developed by Vita Zahnfabrik in about 1963Zahnfabrik in about 1963 www.indiandentalacademy.com
  • Requirements for metal ceramicRequirements for metal ceramic alloysalloys  The chief objection for the use of dental porcelain asThe chief objection for the use of dental porcelain as restorative material is its low strength under tensile andrestorative material is its low strength under tensile and shear, stress conditionsshear, stress conditions  A method by which this disadvantage can be minimized isA method by which this disadvantage can be minimized is to bond the porcelain directly to a cast alloy sub structureto bond the porcelain directly to a cast alloy sub structure made to fit the prepared toothmade to fit the prepared tooth  These alloys should have the potential to bond to the dentalThese alloys should have the potential to bond to the dental porcelainporcelain  Possess coefficient of thermal contraction compatible withPossess coefficient of thermal contraction compatible with that of dental porcelainthat of dental porcelain  Solidus temperature is sufficiently high to permit theSolidus temperature is sufficiently high to permit the aplication of low fusing porcelainaplication of low fusing porcelain www.indiandentalacademy.com
  • Metal – ceramic bondingMetal – ceramic bonding  Factors controlling metal ceramic adhesionFactors controlling metal ceramic adhesion areare  Formation of strong chemical bondingFormation of strong chemical bonding  Mechanical interlocking between twoMechanical interlocking between two materialsmaterials  Residual stressesResidual stresses www.indiandentalacademy.com
  • Chemical bondingChemical bonding  The original metal ceramic alloy containing 88%The original metal ceramic alloy containing 88% gold were too soft for stress bearing restorationsgold were too soft for stress bearing restorations since there was no chemical bond between alloysince there was no chemical bond between alloy and dental porcelain.and dental porcelain.  Mechanical retention and undercuts were used toMechanical retention and undercuts were used to prevent detachment of the ceramic veneer.prevent detachment of the ceramic veneer.  Since the bond strength of porcelain to this type ofSince the bond strength of porcelain to this type of alloy was less than the cohesive strength ofalloy was less than the cohesive strength of porcelain bond failures occurred at the metalporcelain bond failures occurred at the metal porcelain interface due to concentration of residualporcelain interface due to concentration of residual tensile stress at the metal ceramic interface .tensile stress at the metal ceramic interface . www.indiandentalacademy.com
  • Chemical bondingChemical bonding  The addition of 1% base metals to goldThe addition of 1% base metals to gold palladium and platinum alloys was sufficientpalladium and platinum alloys was sufficient to produce a slight oxide film on surface ofto produce a slight oxide film on surface of sub structure to achieve porcelain metalsub structure to achieve porcelain metal bond strength that surpassed the cohesivebond strength that surpassed the cohesive strength of porcelain. This new type of alloystrength of porcelain. This new type of alloy with small amounts of base metals addedwith small amounts of base metals added became the standards for metal ceramicbecame the standards for metal ceramic prostheses.prostheses. www.indiandentalacademy.com
  • Mechanical interlockingMechanical interlocking  Roughness or generally the topography ofRoughness or generally the topography of ceramic metal interface play a large part inceramic metal interface play a large part in adhesion. The ceramic penetrating into aadhesion. The ceramic penetrating into a rough metal surface can mechanically attachrough metal surface can mechanically attach to the metal, improving adhesion.to the metal, improving adhesion.  Roughness provides increased surface areaRoughness provides increased surface area for adhesion and more room for chemicalfor adhesion and more room for chemical bond to form.bond to form. www.indiandentalacademy.com
  • Mechanical interlockingMechanical interlocking  Roughness can reduce adhesion if ceramicRoughness can reduce adhesion if ceramic does not penetrate into the surface and voidsdoes not penetrate into the surface and voids are present at the interface; this may happenare present at the interface; this may happen with improperly fired porcelain or metalswith improperly fired porcelain or metals that are poorly wetted by the porcelain.that are poorly wetted by the porcelain.  Sandblasting is often used to roughen theSandblasting is often used to roughen the surface of the metal cooping to improve thesurface of the metal cooping to improve the bonding of the ceramic.bonding of the ceramic. www.indiandentalacademy.com
  • Thermal compatibilityThermal compatibility  Refers to the ability of a metal and its veneeringRefers to the ability of a metal and its veneering porcelain to contract at similar rates.porcelain to contract at similar rates.  The coefficient of thermal expansion by definitionThe coefficient of thermal expansion by definition is the change in length per unit of original lengthis the change in length per unit of original length of a material when its temperature is raised by 1o Kof a material when its temperature is raised by 1o K  When the co efficient of thermal expansion ofWhen the co efficient of thermal expansion of metal and porcelain are compatible the tensilemetal and porcelain are compatible the tensile stress that develop during cooling are insufficientstress that develop during cooling are insufficient to cause immediate cracking of porcelain orto cause immediate cracking of porcelain or delayed cracking after cooling at roomdelayed cracking after cooling at room temperature.temperature. www.indiandentalacademy.com
  • Thermal compatibilityThermal compatibility  If the porcelain has much larger coefficientIf the porcelain has much larger coefficient of contraction than that of metal, tensileof contraction than that of metal, tensile strength of porcelain may be exceeded sincestrength of porcelain may be exceeded since of large tensile stress causing crackof large tensile stress causing crack propagation in porcelain veneer.propagation in porcelain veneer.  If contraction coefficient of porcelain isIf contraction coefficient of porcelain is much lower than that of metal, failure levelmuch lower than that of metal, failure level stresses can occur at the metal porcelainstresses can occur at the metal porcelain interface.interface. www.indiandentalacademy.com
  • Thermal compatibilityThermal compatibility  Porcelains have coefficient of thermal expansionPorcelains have coefficient of thermal expansion between 13.0 and 14.0 X 10-6 and metal betweenbetween 13.0 and 14.0 X 10-6 and metal between 13.5 and 14.5 X 10-6.13.5 and 14.5 X 10-6.  The difference of 0.5 X10-6 in thermal expansionThe difference of 0.5 X10-6 in thermal expansion between metal and porcelain causes the metal tobetween metal and porcelain causes the metal to contract slightly more than does the ceramiccontract slightly more than does the ceramic during cooling after firing the porcelain.during cooling after firing the porcelain.  This puts the ceramic under slight residualThis puts the ceramic under slight residual compression which makes it less sensitive tocompression which makes it less sensitive to applied tensile forces.applied tensile forces. www.indiandentalacademy.com
  • Sag resistanceSag resistance  Coefficient of thermal expansion tends toCoefficient of thermal expansion tends to have a reciprocal relationship with thehave a reciprocal relationship with the melting point and range of alloysmelting point and range of alloys  Higher the melting temperature of metalHigher the melting temperature of metal lower its Coefficient of thermal expansionlower its Coefficient of thermal expansion  Metal ceramic alloys should have sufficientlyMetal ceramic alloys should have sufficiently high melting range to avoid sag deformationhigh melting range to avoid sag deformation or melting during sintering of porcelainor melting during sintering of porcelain veneer.veneer. www.indiandentalacademy.com
  • Selection of Metal Ceramic AlloysSelection of Metal Ceramic Alloys Physical properties includes..Physical properties includes.. ColorColor Noble Metal ContentNoble Metal Content HardnessHardness Yield StrengthYield Strength ElongationElongation Fusion TemperatureFusion Temperature www.indiandentalacademy.com
  • ColorColor  The most important obvious property of anThe most important obvious property of an alloy – Coloralloy – Color  Dentists prefer to have Gold color inDentists prefer to have Gold color in restorations which is compatible to the colorrestorations which is compatible to the color of porcelain than the dark color of baseof porcelain than the dark color of base metal alloys.metal alloys. www.indiandentalacademy.com
  • Noble Metal ContentNoble Metal Content Indirectly denotes…..Indirectly denotes…..  Corrosion resistance of the alloysCorrosion resistance of the alloys  Inert properties of the alloys which makes itInert properties of the alloys which makes it to tolerate oral fluids and not release anyto tolerate oral fluids and not release any harmful products into the oral environment.harmful products into the oral environment. www.indiandentalacademy.com
  • HardnessHardness  Definition - Resistance of material to plasticDefinition - Resistance of material to plastic deformationdeformation  Important in relation to occlusal wearImportant in relation to occlusal wear resistance and finishingresistance and finishing  affects polishing propertiesaffects polishing properties www.indiandentalacademy.com
  • Yield StrengthYield Strength  The stress at which a test specimen exhibitsThe stress at which a test specimen exhibits a specific amount of plastic straina specific amount of plastic strain  Necessary in determining Load BearingNecessary in determining Load Bearing ability especially in FPD , since crossability especially in FPD , since cross sectional area of metal used in PFMsectional area of metal used in PFM restoration are usually smaller than that ofrestoration are usually smaller than that of all metal restorationsall metal restorations www.indiandentalacademy.com
  • ElongationElongation  Maximum amount of plastic strain a tensileMaximum amount of plastic strain a tensile test specimen can sustain it fracturestest specimen can sustain it fractures  Related to Marginal finishing PropertiesRelated to Marginal finishing Properties especially in Partial veneer crown andespecially in Partial veneer crown and abutmentsabutments www.indiandentalacademy.com
  • Fusion TemperatureFusion Temperature  Temperature at which the metal solidifiesTemperature at which the metal solidifies  Important in relation to SAG Resistance as itImportant in relation to SAG Resistance as it is necessary for the alloy to withstandis necessary for the alloy to withstand temperatures of the porcelain firing cycle.temperatures of the porcelain firing cycle. www.indiandentalacademy.com
  • Chemical PropertiesChemical Properties  Tarnish and corrosion resistanceTarnish and corrosion resistance  Tarnish is a thin film of a surface deposit orTarnish is a thin film of a surface deposit or an interaction layer that is adherent to thean interaction layer that is adherent to the metal surface. E.g. these films are generallymetal surface. E.g. these films are generally found on gold alloys with relatively highfound on gold alloys with relatively high silver content or on silver alloys.silver content or on silver alloys. Selection of Metal Ceramic AlloysSelection of Metal Ceramic Alloys www.indiandentalacademy.com
  • Corrosion resistanceCorrosion resistance  Corrosion is the physical dissolution of a materialCorrosion is the physical dissolution of a material in an environment .in an environment .  corrosion resistance is derived from the materialcorrosion resistance is derived from the material components that being too noble to react in thecomponents that being too noble to react in the oral environment e.g. gold and palladium ororal environment e.g. gold and palladium or  By the ability of one or more of the metallicBy the ability of one or more of the metallic elements to form an adherent passivating surfaceelements to form an adherent passivating surface film, which inhibits any subsurface reactions Cr infilm, which inhibits any subsurface reactions Cr in Ni-Cr and Co-Cr alloys and titanium in Ti-6 Al- 4VNi-Cr and Co-Cr alloys and titanium in Ti-6 Al- 4V alloyalloy www.indiandentalacademy.com
  • Lab workability and Casting AccuracyLab workability and Casting Accuracy  To provide clinically acceptable castings byTo provide clinically acceptable castings by its ability to wet the investment moldits ability to wet the investment mold material and flow in to the most intricatematerial and flow in to the most intricate regions of the mold without any appreciableregions of the mold without any appreciable interaction with the investmentinteraction with the investment www.indiandentalacademy.com
  • Bio CompatibilityBio Compatibility Base metal alloys – Nickel (Ni) and Beryllium (Be)Base metal alloys – Nickel (Ni) and Beryllium (Be)  The occupational health and safety administrationThe occupational health and safety administration (OSHA) specifies that exposure to Beryllium dust(OSHA) specifies that exposure to Beryllium dust in air should be limited to a concentration of 2in air should be limited to a concentration of 2 ug /meter cubeug /meter cube  The allowable maximum concentration is 5 ugThe allowable maximum concentration is 5 ug /meter cube/meter cube  Sensitivity – Contact dermatitis with Nickel orSensitivity – Contact dermatitis with Nickel or Nickel containing alloysNickel containing alloys www.indiandentalacademy.com
  • CompositionComposition  Key factor since components of alloyKey factor since components of alloy influences color of porcelaininfluences color of porcelain  Can compromise esthetics of restorationsCan compromise esthetics of restorations  Silver-color change causes greening ofSilver-color change causes greening of porcelain which occurs by exchange of silverporcelain which occurs by exchange of silver from alloy and sodium from porcelainfrom alloy and sodium from porcelain  The color may vary from green, yellowThe color may vary from green, yellow green, yellow orange, orange and browngreen, yellow orange, orange and brown hueshues www.indiandentalacademy.com
  • Economic considerationsEconomic considerations  Cost of metals is major concern for the useCost of metals is major concern for the use of the alloys for metal ceramic restorations.of the alloys for metal ceramic restorations. www.indiandentalacademy.com
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  • High Gold AlloysHigh Gold Alloys  PFM introduced to dental profession withPFM introduced to dental profession with introduction of Caramco No : 1 alloy in 1958introduction of Caramco No : 1 alloy in 1958  Fore Runner of improved High Gold AlloysFore Runner of improved High Gold Alloys that remain as market today – Jelenko Othat remain as market today – Jelenko O  Composed principally of Gold and PlatinumComposed principally of Gold and Platinum groupgroup www.indiandentalacademy.com
  • High gold alloysHigh gold alloys  Gold content varies from 78% -87% by weight and nobleGold content varies from 78% -87% by weight and noble metal content is about 97%metal content is about 97%  Small amounts of tin, indium and iron are added forSmall amounts of tin, indium and iron are added for strength and to promote a good porcelain bond to the metalstrength and to promote a good porcelain bond to the metal oxideoxide  CostlyCostly  Light yellow in colorLight yellow in color  low tensile strength makes them a questionable choice forlow tensile strength makes them a questionable choice for fixed partial denturesfixed partial dentures  Hardness of alloys ideal for working characteristics andHardness of alloys ideal for working characteristics and ease of finishingease of finishing  Corrosion résistance is excellentCorrosion résistance is excellent www.indiandentalacademy.com
  • Gold,Platinum,Palladium AlloysGold,Platinum,Palladium Alloys  Composition ;-Composition ;-  Gold: 75%-88%Gold: 75%-88%  Platinum: up to 8%Platinum: up to 8%  Palladium: up to 11 %Palladium: up to 11 %  Silver: up to 5% (if present)Silver: up to 5% (if present)  Trace elements like indium, iron, and tin forTrace elements like indium, iron, and tin for porcelain bonding. (If the palladium contentporcelain bonding. (If the palladium content exceeds that of platinum, then the alloys should beexceeds that of platinum, then the alloys should be classified as Au-Pd-Pt.)classified as Au-Pd-Pt.) www.indiandentalacademy.com
  • Gold,Platinum,PalladiumGold,Platinum,Palladium Alloys(Contd)Alloys(Contd) AdvantagesAdvantages  Excellent castabilityExcellent castability  Excellent porcelain bondingExcellent porcelain bonding  Easy to adjust and finish High nobility levelEasy to adjust and finish High nobility level Excellent corrosion Advantages and tarnishExcellent corrosion Advantages and tarnish resistanceresistance  Biocompatible Some are yellow in colorBiocompatible Some are yellow in color  Not "technique sensitive"Not "technique sensitive"  BurnishableBurnishable www.indiandentalacademy.com
  • Gold,Platinum,Palladium AlloysGold,Platinum,Palladium Alloys (Contd)(Contd)  Disadvantages;-Disadvantages;-  High costHigh cost  Poor sag resistance so not suited for long-Poor sag resistance so not suited for long- span fixed partial denturesspan fixed partial dentures  Low hardness (greater wear)Low hardness (greater wear)  High density (fewer castings per ounce)High density (fewer castings per ounce) www.indiandentalacademy.com
  • Gold Palladium Silver AlloysGold Palladium Silver Alloys Introduced in 1970 as will ceram wIntroduced in 1970 as will ceram w composition -composition - Gold: 39%-53%Gold: 39%-53% Palladium:25%35%Palladium:25%35% Silver: 12%-22%Silver: 12%-22% Like the Au-Pt-Pd alloys, trace amounts ofLike the Au-Pt-Pd alloys, trace amounts of oxidizable elements are added for porcelainoxidizable elements are added for porcelain bondingbonding.. www.indiandentalacademy.com
  • Gold Palladium Silver AlloysGold Palladium Silver Alloys (Contd..)(Contd..) AdvantagesAdvantages  Less expensive than Au-Pt-Pd alloysLess expensive than Au-Pt-Pd alloys  Improved rigidity and sag resistanceImproved rigidity and sag resistance  High nobility levelHigh nobility level www.indiandentalacademy.com
  • Gold Palladium Silver AlloysGold Palladium Silver Alloys (Contd..)(Contd..) DisadvantagesDisadvantages  High silver content creates potential forHigh silver content creates potential for porcelain discolorationporcelain discoloration  High costHigh cost  High coefficient of thermal expansionHigh coefficient of thermal expansion  Tarnish and corrosion resistantTarnish and corrosion resistant www.indiandentalacademy.com
  • Gold-Palladium-Silver (low silverGold-Palladium-Silver (low silver group)group) CompositionComposition  Gold – 52% - 77%Gold – 52% - 77%  Palladium – 10% - 33%Palladium – 10% - 33%  Silver – 5% - 12%Silver – 5% - 12% Trace amounts of oxidizable elements forTrace amounts of oxidizable elements for porcelein bondingporcelein bonding www.indiandentalacademy.com
  • Gold-Palladium-Silver (low silverGold-Palladium-Silver (low silver group)group)  AdvantagesAdvantages  Less expensive than Au-Pt-Pd alloysLess expensive than Au-Pt-Pd alloys  Improved sag resistanceImproved sag resistance  High noble metal contentHigh noble metal content  Tarnish and corrosion resistantTarnish and corrosion resistant www.indiandentalacademy.com
  • Gold-Palladium-Silver (low silverGold-Palladium-Silver (low silver group)group)  DisadvantagesDisadvantages  High costHigh cost  High coefficient of thermal expansionHigh coefficient of thermal expansion  Silver creates potential for porcelainSilver creates potential for porcelain discoloration (but less than high-silverdiscoloration (but less than high-silver group)group) www.indiandentalacademy.com
  • Gold-Palladium alloysGold-Palladium alloys CompositionComposition  Gold – 44% -55%Gold – 44% -55%  Palladium – 35% - 45%Palladium – 35% - 45%  Gallium up to 5%Gallium up to 5%  Iridium and tin up to 8% - 12%Iridium and tin up to 8% - 12% Iridium and tin are the oxidizable elementsIridium and tin are the oxidizable elements responsible for porcelain bondingresponsible for porcelain bonding www.indiandentalacademy.com
  • Gold-Palladium alloysGold-Palladium alloys AdvantagesAdvantages  Excellent castabilityExcellent castability  Good bond strengthGood bond strength  Improved strength (sag resistance)Improved strength (sag resistance)  Improved HardnessImproved Hardness  Tarnish and corrosion resistantTarnish and corrosion resistant  Lower densityLower density www.indiandentalacademy.com
  • Gold-Palladium alloysGold-Palladium alloys DisadvantagesDisadvantages  High costHigh cost  Not thermally compatible with highNot thermally compatible with high expansion dental porcelainsexpansion dental porcelains www.indiandentalacademy.com
  • Palladium-Silver alloysPalladium-Silver alloys CompositionComposition  Palladium – 55% - 60%Palladium – 55% - 60%  Silver – 28% - 30%Silver – 28% - 30% Indium and tinIndium and tin  Palladium – 50% - 55%Palladium – 50% - 55%  Silver – 35% - 40%Silver – 35% - 40% Tin (little or no Indium)Tin (little or no Indium) Trace elements of other oxidizable base elementsTrace elements of other oxidizable base elements are also presentare also present www.indiandentalacademy.com
  • Palladium-Silver alloys (contd)Palladium-Silver alloys (contd) AdvantagesAdvantages  Good castability (whenGood castability (when torch casting)torch casting)  Good porcelainGood porcelain bondingbonding  Excellent sagExcellent sag resistance)resistance)  Low HardnessLow Hardness  BurnishabilityBurnishability  Good tarnish andGood tarnish and corrosion resistantcorrosion resistant  Low densityLow density  Low costLow cost  Moderate nobility levelModerate nobility level  Suitable for long-spanSuitable for long-span fixed partial denturesfixed partial dentures www.indiandentalacademy.com
  • Palladium-Silver alloys (contd)Palladium-Silver alloys (contd) DisadvantagesDisadvantages  High coefficient of thermalHigh coefficient of thermal expansionexpansion  Discoloration (yellow,Discoloration (yellow, brown, or green) maybrown, or green) may occur with some dentaloccur with some dental porcelainsporcelains  Some castability problemsSome castability problems  Pd and Ag prone to absorbPd and Ag prone to absorb gasesgases  Require regular purging ofRequire regular purging of the porcelain furnacethe porcelain furnace  May form internal oxidesMay form internal oxides  Should not be cast in aShould not be cast in a carbon cruciblecarbon crucible  Non carbon phosphateNon carbon phosphate bonded investmentsbonded investments recommendedrecommended www.indiandentalacademy.com
  • Palladium-cobalt alloysPalladium-cobalt alloys CompositionComposition  Palladium: 78%-88%Palladium: 78%-88%  Cobalt: 4%-10%Cobalt: 4%-10% (some high palladium-cobalt alloys may contain 2%(some high palladium-cobalt alloys may contain 2% gold)gold) Note:Note: Trace amounts of oxidizable elements (such asTrace amounts of oxidizable elements (such as gallium and indium) are added for porcelaingallium and indium) are added for porcelain bonding.bonding. www.indiandentalacademy.com
  • Palladium-cobalt alloysPalladium-cobalt alloys AdvantagesAdvantages  Low costLow cost  Reportedly good sag resistanceReportedly good sag resistance  Low density means moreLow density means more castings per ouncecastings per ounce (than gold-based alloys) Some melt and cast(than gold-based alloys) Some melt and cast easily Good polishabilityeasily Good polishability (supposed to be similar(supposed to be similar to Au-Pd alloys)to Au-Pd alloys)  Reportedly easier to presolder than high Pd-CuReportedly easier to presolder than high Pd-Cu alloysalloys www.indiandentalacademy.com
  • Palladium-cobalt alloysPalladium-cobalt alloys DisadvantagesDisadvantages  More compatible with higher expansionMore compatible with higher expansion porcelainsporcelains  Some are more prone toSome are more prone to over-heatingover-heating than high Pd-Cu Produce a thick, darkthan high Pd-Cu Produce a thick, dark oxide Colored oxide layer may causeoxide Colored oxide layer may cause bluing of porcelainbluing of porcelain  Prone to gas absorption Little informationProne to gas absorption Little information on long-term clinical successon long-term clinical success www.indiandentalacademy.com
  • High Palladium-Silver-Gold alloysHigh Palladium-Silver-Gold alloys CompositionComposition  Palladium: 75%-86%Palladium: 75%-86%  Silver: less than 1 %-7%Silver: less than 1 %-7%  Gold: 2%-6%Gold: 2%-6%  Platinum: less than 1.0% (if present)Platinum: less than 1.0% (if present) Trace amounts of oxidizabJe elements such asTrace amounts of oxidizabJe elements such as indium and gallium.indium and gallium. www.indiandentalacademy.com
  • High Palladium-Silver-Gold alloysHigh Palladium-Silver-Gold alloys  AdvantagesAdvantages  Low costLow cost  Low densityLow density  Improved sag resistance (better highImproved sag resistance (better high temperature strength)temperature strength)  Light-colored oxide layerLight-colored oxide layer www.indiandentalacademy.com
  • High Palladium-Silver-Gold alloysHigh Palladium-Silver-Gold alloys DisadvantagesDisadvantages  A relatively new alloy groupA relatively new alloy group  No data on long-term performanceNo data on long-term performance  Like other palladium-based alloys are proneLike other palladium-based alloys are prone to gaseous absorptionto gaseous absorption  Should not be cast in carbon cruciblesShould not be cast in carbon crucibles www.indiandentalacademy.com
  • High Palladium-Copper alloysHigh Palladium-Copper alloys CompositionComposition  Palladium: 70%-80%Palladium: 70%-80%  Copper: 9%-15%Copper: 9%-15%  Gold: 1 %-2% (if present)Gold: 1 %-2% (if present)  Platinum: 1 % (if present)Platinum: 1 % (if present)  Some, but not all, high palladium-copper alloysSome, but not all, high palladium-copper alloys contain small quantities (1 %-3%) of gold and/orcontain small quantities (1 %-3%) of gold and/or platinum.platinum.  Trace amounts of the oxidizable elements gallium,Trace amounts of the oxidizable elements gallium, indium, and tin are added for porcelainindium, and tin are added for porcelain bonding.bonding. www.indiandentalacademy.com
  • High Palladium-Copper alloysHigh Palladium-Copper alloys AdvantagesAdvantages  Good castabilityGood castability  Lower cost (than gold-based alloys)Lower cost (than gold-based alloys)  Low density means more castings per ounceLow density means more castings per ounce  Tarnish and corrosion resistantTarnish and corrosion resistant  Compatible with many dental porcelainsCompatible with many dental porcelains www.indiandentalacademy.com
  • High Palladium-Copper alloysHigh Palladium-Copper alloys DisadvantagesDisadvantages  Produce dark, thick oxides which mayProduce dark, thick oxides which may discolor (gray) some dental porcelainsdiscolor (gray) some dental porcelains  Should not be cast in carbon cruciblesShould not be cast in carbon crucibles (electric casting machines)(electric casting machines)  Prone to gaseous absorptionProne to gaseous absorption www.indiandentalacademy.com
  • High Palladium-Copper alloysHigh Palladium-Copper alloys Disadvantages (Contd)Disadvantages (Contd)  Subject to thermal creep (marginalSubject to thermal creep (marginal opening)opening)  May not be suitable for long-span fixedMay not be suitable for long-span fixed partialpartial denturesdentures  May be difficult to polishMay be difficult to polish  Presoldering may be a problemPresoldering may be a problem www.indiandentalacademy.com
  • Nickel-chromium-beryllium alloysNickel-chromium-beryllium alloys CompositionComposition  Nickel: 62%-82%Nickel: 62%-82%  Chromium: 11 %-20%Chromium: 11 %-20%  Beryllium: up to 2.0%Beryllium: up to 2.0% Numerous minor alloying elements includeNumerous minor alloying elements include aluminum, carbon, gallium, iron,aluminum, carbon, gallium, iron, manganese, molybdenum, silicon, titanium,manganese, molybdenum, silicon, titanium, and/or vanadiumand/or vanadium www.indiandentalacademy.com
  • Nickel-chromium-beryllium alloysNickel-chromium-beryllium alloys AdvantagesAdvantages  Low costLow cost  Low density permits more casting per ounceLow density permits more casting per ounce  High sag resistanceHigh sag resistance  Can produce thin castingsCan produce thin castings  Poor thermal conductorPoor thermal conductor  Can be etchedCan be etched www.indiandentalacademy.com
  • Nickel-chromium-beryllium alloysNickel-chromium-beryllium alloys DisadvantagesDisadvantages  Cannot use with nickel­ sensitive patientsCannot use with nickel­ sensitive patients  Beryllium exposure may be potentially harmful toBeryllium exposure may be potentially harmful to technicians and patientstechnicians and patients  Proper melting and casting is necessaryProper melting and casting is necessary  Bond failure more common in the oxide layerBond failure more common in the oxide layer  High hardness (may wear opposing teeth) DifficultHigh hardness (may wear opposing teeth) Difficult to solderto solder  Difficult to cut through cementedDifficult to cut through cemented castingscastings www.indiandentalacademy.com
  • Nickel-chromium beryllium-freeNickel-chromium beryllium-free alloysalloys CompositionComposition  Nickel: 62%-77%Nickel: 62%-77%  Chromium: 11 %-22%Chromium: 11 %-22% Boron, iron, molybdenum, niobium and/orBoron, iron, molybdenum, niobium and/or tantalum.tantalum. www.indiandentalacademy.com
  • Nickel-chromium beryllium-freeNickel-chromium beryllium-free alloysalloys AdvantagesAdvantages  Do not contain berylliumDo not contain beryllium  Low costLow cost  Low density means more castings per ounceLow density means more castings per ounce www.indiandentalacademy.com
  • Nickel-chromium beryllium-freeNickel-chromium beryllium-free alloysalloys DisadvantagesDisadvantages  Cannot use with nickel-sensitive patientsCannot use with nickel-sensitive patients Cannot be etchedCannot be etched  May not cast as well as Ni-Cr-Be alloysMay not cast as well as Ni-Cr-Be alloys  Produce more oxides than Ni-Cr-Be alloysProduce more oxides than Ni-Cr-Be alloys www.indiandentalacademy.com
  • Cobalt-chromium alloysCobalt-chromium alloys CompositionComposition  Cobalt: 53%-68%Cobalt: 53%-68%  Chromium: 25%-34% /Chromium: 25%-34% /  Trace elements include molybdenum,Trace elements include molybdenum, rutheniumruthenium www.indiandentalacademy.com
  • Cobalt-chromium alloysCobalt-chromium alloys AdvantagesAdvantages  Do not contain nickelDo not contain nickel  Do not contain berylliumDo not contain beryllium  Poor thermal conductorsPoor thermal conductors  Low densityLow density  Low costLow cost www.indiandentalacademy.com
  • Cobalt-chromium alloysCobalt-chromium alloys DisadvantagesDisadvantages  More difficult to process than nickel-baseMore difficult to process than nickel-base alloysalloys  High hardness (may wear the opposingHigh hardness (may wear the opposing dentition)dentition)  Oxidize more than nickel-based alloysOxidize more than nickel-based alloys www.indiandentalacademy.com
  • Titanium alloysTitanium alloys  High biocompatibilityHigh biocompatibility  According to the American Society for Testing andAccording to the American Society for Testing and Materials (ASTM), there are five unalloyed gradesMaterials (ASTM), there are five unalloyed grades of CP Ti (Grades 1-4, and Grade 7), based on theof CP Ti (Grades 1-4, and Grade 7), based on the concentra­tion ofconcentra­tion of  oxygen (0.18 wt% to 0.40 wt%) andoxygen (0.18 wt% to 0.40 wt%) and  iron (0.2 wt% to 0.5 wt%).iron (0.2 wt% to 0.5 wt%).  Other impurities include nitrogen (0.03 wt% to 0.05Other impurities include nitrogen (0.03 wt% to 0.05 wt%),wt%),  carbon (0.1 m%), and hydrogen (0.015 wt%).carbon (0.1 m%), and hydrogen (0.015 wt%). www.indiandentalacademy.com
  • Titanium alloysTitanium alloys  Grade 1 CP Ti is the purest and softest form.Grade 1 CP Ti is the purest and softest form.  It has a moderately high tensile strengthIt has a moderately high tensile strength  moderately high stiffness,moderately high stiffness,  low density,low density,  low thermal expansion coefficient.low thermal expansion coefficient.  The elastic modulus of CP Ti is compa­The elastic modulus of CP Ti is compa­ rable to that of tooth enamel and noblerable to that of tooth enamel and noble alloys, but it is lower than that of other basealloys, but it is lower than that of other base metal alloysmetal alloys www.indiandentalacademy.com
  • Titanium alloysTitanium alloys  Casting of titanium alloys is difficult due toCasting of titanium alloys is difficult due to a high casting temperature – 2000 ca high casting temperature – 2000 c  Rapid oxidation and reactions withRapid oxidation and reactions with investmentsinvestments  Melting is done in specially designedMelting is done in specially designed furnaces with an argon atmospherefurnaces with an argon atmosphere  Ti-6Al-4v has been used for PFMTi-6Al-4v has been used for PFM restorationsrestorations  Used with low expansions porcelainsUsed with low expansions porcelains www.indiandentalacademy.com
  • Noble Metal AlloysNoble Metal Alloys AuAu PdPd PtPt AgAg SnSn InIn Gold Platinum PalladiumGold Platinum Palladium SMG-2 (J.M.Ney Co)SMG-2 (J.M.Ney Co) 8787 55 77 -- <1<1 <1<1 Ultra Gold (J.F. Jelenko & Co)Ultra Gold (J.F. Jelenko & Co) 87.587.5 11 1010 -- ++ ++ Degudent H (Degussa Corp)Degudent H (Degussa Corp) 84.584.5 55 88 -- -- 2.52.5 Rx Y-Ceramic (Jeneric / Pentron,Rx Y-Ceramic (Jeneric / Pentron, Inc)Inc) 8484 66 77 11 0.70.7 0.50.5 700SL (Leach & Dillion)700SL (Leach & Dillion) 8484 66 77 1.51.5 -- 11 Will-Ceram Y2 (Williams DentalWill-Ceram Y2 (Williams Dental Co)Co) 8282 4.54.5 88 3.53.5 <1<1 <1<1 www.indiandentalacademy.com
  • AuAu PdPd PtPt AgAg SnSn InIn Gold Platinum PalladiumGold Platinum Palladium Jelenko O (J.F. Jelenko & Co)Jelenko O (J.F. Jelenko & Co) 87.587.5 66 4.54.5 11 0.40.4 0.30.3 Image (J.M. Ney Co)Image (J.M. Ney Co) 8585 55 55 44 <1<1 -- Gold PlatinumGold Platinum RhRh Rx-G (Jeneric / Pentron,Inc)Rx-G (Jeneric / Pentron,Inc) 8787 -- 1010 -- ++ ++ 1.51.5 Degudent G (Degussa Corp)Degudent G (Degussa Corp) 8686 -- 10.510.5 -- ++ <2<2 -- www.indiandentalacademy.com
  • AuAu PdPd PtPt AgAg SnSn InIn Gold Platinum SilverGold Platinum Silver Will Ceram WWill Ceram W (Williams Dental Co)(Williams Dental Co) 5454 26.526.5 -- 15.515.5 <5<5 <5<5 Cameo (J.F. Jelenko & Co)Cameo (J.F. Jelenko & Co) 52.552.5 2727 -- 1616 22 2.52.5 Rx WCG (Jeneric/Pentron,Inc)Rx WCG (Jeneric/Pentron,Inc) 5252 2828 -- 1414 11 33 Special White (Degussa Corp)Special White (Degussa Corp) 4545 4040 -- 16.516.5 33 44 www.indiandentalacademy.com
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  • Sub structure designSub structure design  majority of the porcelain-to-metal bond failuresmajority of the porcelain-to-metal bond failures occur as a direct result of improper substructureoccur as a direct result of improper substructure designdesign  Errors in the preparation of the metal ceramicErrors in the preparation of the metal ceramic sub­structure frequently go unnoticed until thesub­structure frequently go unnoticed until the brittle porcelain veneer fails in service.brittle porcelain veneer fails in service. www.indiandentalacademy.com
  • Sub structure design (contd)Sub structure design (contd)  Hence necessary to understand the essentials ofHence necessary to understand the essentials of proper substructure de­sign, since it will help toproper substructure de­sign, since it will help to ensure the longevity of the final prosthesis.ensure the longevity of the final prosthesis. www.indiandentalacademy.com
  • Primary functionPrimary function  1. The casting provides the fit of the restoration1. The casting provides the fit of the restoration to the prepared toothto the prepared tooth  2. The metal forms oxides that bond chemically2. The metal forms oxides that bond chemically toto dental porcelain.dental porcelain.  3. The coping serves as a rigid foundation to3. The coping serves as a rigid foundation to which the brittle porcelain can be attached forwhich the brittle porcelain can be attached for increased strength and support.increased strength and support.  4. The substructure restores the tooth's proper4. The substructure restores the tooth's proper emergence profile.emergence profile. www.indiandentalacademy.com
  • Fit of the restorationFit of the restoration  Fit should be evaluated in terms of bothFit should be evaluated in terms of both seatseat (incisal or occlusal(incisal or occlusal gap) andgap) and sealseal (marginal opening).(marginal opening).  A restoration that binds against tooth structure is apt to stressA restoration that binds against tooth structure is apt to stress the porcelain-metal bond and most likely will not seat or sealthe porcelain-metal bond and most likely will not seat or seal completely.completely.  Conversely, an over expanded metal substructure invariably willConversely, an over expanded metal substructure invariably will rely more heavily on the cement luting agent for its retentionrely more heavily on the cement luting agent for its retention than on good internal adaptation, and the latter resto­ration isthan on good internal adaptation, and the latter resto­ration is doomed to failure.doomed to failure.  A properly formed metal ceramic substructure should have whatA properly formed metal ceramic substructure should have what is called ais called a passivepassive fit and provide both internal adaptation (seat)fit and provide both internal adaptation (seat) and marginal integrity (seal).and marginal integrity (seal). www.indiandentalacademy.com
  • OxidationOxidation  A properly oxidized substrate can enhance theA properly oxidized substrate can enhance the attachment between porcelain and metalattachment between porcelain and metal  poorly contoured coping may permit stresspoorly contoured coping may permit stress concentrations to form as the fired porcelain cools toconcentrations to form as the fired porcelain cools to room temperature.room temperature.  In turn, these stresses in the porcelain may notIn turn, these stresses in the porcelain may not manifest themselves initially, but they can appear latermanifest themselves initially, but they can appear later and possibly lead to a bond failureand possibly lead to a bond failure www.indiandentalacademy.com
  • Rigidity of the copingRigidity of the coping  The metal should be as thick as possible for strengthThe metal should be as thick as possible for strength and rigidity yet as thin as possible so as not toand rigidity yet as thin as possible so as not to compromise esthetics by adding excess bulk to thecompromise esthetics by adding excess bulk to the restoration.restoration.  Generally, the minimum thickness of metal for theGenerally, the minimum thickness of metal for the porcelain-bearing areas for a single-unit metal copingporcelain-bearing areas for a single-unit metal coping will range between 0.3 mm and 0.5 mm, depending onwill range between 0.3 mm and 0.5 mm, depending on the type of alloy usedthe type of alloy used  Certain base metal alloys have suffi­ciently high yieldCertain base metal alloys have suffi­ciently high yield strengths to permit finishing below the recommendedstrengths to permit finishing below the recommended 0.3 mm level0.3 mm level www.indiandentalacademy.com
  • Proper emergence profileProper emergence profile  The substructure should be designed to restore theThe substructure should be designed to restore the properproper emergence profileemergence profile to the restorationto the restoration  The metal component of the metal ceramic systemThe metal component of the metal ceramic system restores tooth contour to its original form and function.restores tooth contour to its original form and function.  Certain substructure designs involve restoration ofCertain substructure designs involve restoration of most of the original tooth form in metal with onlymost of the original tooth form in metal with only esthetically critical areas receiving a veneer of porcelain.esthetically critical areas receiving a veneer of porcelain. www.indiandentalacademy.com
  • Secondary functionSecondary function  1.Metal occlusal and lingual articulating surfaces1.Metal occlusal and lingual articulating surfaces generally can be less destructive to the enamel ofgenerally can be less destructive to the enamel of opposing natural teeth (depending on the typeopposing natural teeth (depending on the type of casting alloy selected)of casting alloy selected)  2. Fabrication of a restoration with minimal2. Fabrication of a restoration with minimal occlusal clearance has more potential for successocclusal clearance has more potential for success with a metal substructure (and occlusion inwith a metal substructure (and occlusion in metal) than the all-ceramic materials.metal) than the all-ceramic materials. www.indiandentalacademy.com
  • Secondary function (contd)Secondary function (contd)  3. The occluding surfaces can be easily adjusted3. The occluding surfaces can be easily adjusted andand repolished intra orallyrepolished intra orally  4. The metal axial walls can support the4. The metal axial walls can support the componentscomponents of a removable partial denture.of a removable partial denture.  5. The axial surfaces can house attachments5. The axial surfaces can house attachments (precision or semi-precision) for fixed or(precision or semi-precision) for fixed or removable partial dentures.removable partial dentures. www.indiandentalacademy.com
  • Principles of substructure designPrinciples of substructure design  Occlusion in metal requires less tooth reduction (1 toOcclusion in metal requires less tooth reduction (1 to 1.5 mm).1.5 mm).  Approximately 2 mm of occlusal re­duction is necessaryApproximately 2 mm of occlusal re­duction is necessary for posterior teeth and 1 to 1.5 mm for anterior teethfor posterior teeth and 1 to 1.5 mm for anterior teeth requiring porcelain on occluding surfaces.requiring porcelain on occluding surfaces.  Metal surfaces can be more easily adjusted andMetal surfaces can be more easily adjusted and repolished at chair side without adversely affecting therepolished at chair side without adversely affecting the restoration.restoration.  On the other hand, removing the glaze of a metalOn the other hand, removing the glaze of a metal ceramic restoration during intraoral adjustmentsceramic restoration during intraoral adjustments weakens the porcelain greatlyweakens the porcelain greatly www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  occlusal contacts when placed directly on orocclusal contacts when placed directly on or close to the porcelain-metal junction, there is anclose to the porcelain-metal junction, there is an increased likelihood the porcelain will chip orincreased likelihood the porcelain will chip or fracture at that point of contact .fracture at that point of contact .  Porcelain is strongest under compression andPorcelain is strongest under compression and weakest under tension, so situations that induceweakest under tension, so situations that induce tensile stresses in the ceramic during functiontensile stresses in the ceramic during function are more apt to promote bond failures.are more apt to promote bond failures. www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  A substructure should be designed so theA substructure should be designed so the functional incisal or occlusal contacts are locatedfunctional incisal or occlusal contacts are located at least 1 .5 mm and perhaps as much as 2 mmat least 1 .5 mm and perhaps as much as 2 mm from the metal­porcelain junction.from the metal­porcelain junction. www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  The inter proximal contact areas of anteriorThe inter proximal contact areas of anterior teeth, and at least the mesial contacts ofteeth, and at least the mesial contacts of posterior teeth, are frequently restored inposterior teeth, are frequently restored in porcelainporcelain  with porcelain inter proximal contact areaswith porcelain inter proximal contact areas would be more esthetic, particularly withwould be more esthetic, particularly with anterior teeth.anterior teeth. www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  It is important to provide proper metal supportIt is important to provide proper metal support to a porcelain marginal ridge in the substructureto a porcelain marginal ridge in the substructure design to prevent possible fracturedesign to prevent possible fracture  However, the distal inter proximal contacts ofHowever, the distal inter proximal contacts of posterior teeth may be restored in either metalposterior teeth may be restored in either metal or porcelain because these areas are not asor porcelain because these areas are not as critical esthetically.critical esthetically. www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  The ultimate goal of any substructure is toThe ultimate goal of any substructure is to support an even thickness (1mm minimum, 2support an even thickness (1mm minimum, 2 mm maximum) of the porcelain veneer.mm maximum) of the porcelain veneer.  If this maximum thickness is exceeded, theIf this maximum thickness is exceeded, the ceramic layer may no longer be properlyceramic layer may no longer be properly supported, resulting in a catastrophic failure atsupported, resulting in a catastrophic failure at the cusp tip or incisal edgethe cusp tip or incisal edge www.indiandentalacademy.com
  • Principles of substructure design (contd)Principles of substructure design (contd)  Areas to be veneered with porcelain must be atAreas to be veneered with porcelain must be at least 0.3 mm thick.least 0.3 mm thick.  with base metal alloys, the coping can bewith base metal alloys, the coping can be reduced to 0.2 mm or less and still be strongreduced to 0.2 mm or less and still be strong enough to support the porcelainenough to support the porcelain www.indiandentalacademy.com
  • Casting procedureCasting procedure  Spruing techniquesSpruing techniques  A spruing system is intended to create a channel orA spruing system is intended to create a channel or series of channels in the set investment through whichseries of channels in the set investment through which molten alloy flows to reach the pattern areas.molten alloy flows to reach the pattern areas.  The general principles of spruingThe general principles of spruing, include ;-, include ;-  the spruing method (direct versus indirect),the spruing method (direct versus indirect),  sprue placement (or location),sprue placement (or location),  sprue gauge,sprue gauge, www.indiandentalacademy.com
  • The general principles of spruingThe general principles of spruing (contd)(contd)  reservoir location,reservoir location,  constricted spruing,constricted spruing,  sprue composition (wax versus plastic)sprue composition (wax versus plastic)  value of prefabricated wax sprues.value of prefabricated wax sprues. www.indiandentalacademy.com
  • Spuring method – direct spuringSpuring method – direct spuring  The flow of molten metal is straight (direct) from the casting crucible to the patternThe flow of molten metal is straight (direct) from the casting crucible to the pattern area in the ring.area in the ring.  Requires less time and effort.Requires less time and effort.  A straight sprue former is luted (attached) to the thickest part of the wax pattern atA straight sprue former is luted (attached) to the thickest part of the wax pattern at one end and secured to the crucible former at the other.one end and secured to the crucible former at the other.  The sprue former can be modified by placing a ball, or round reservoir, between theThe sprue former can be modified by placing a ball, or round reservoir, between the pattern and the button.pattern and the button.  Even with the ball reservoir, the spruing method is still direct.Even with the ball reservoir, the spruing method is still direct.  Direct spruing is used most frequently for single units and small, multiunit patternsDirect spruing is used most frequently for single units and small, multiunit patterns  . A basic weakness of direct spruing is the potential for suck-back porosity at the. A basic weakness of direct spruing is the potential for suck-back porosity at the junction of restoration and the spruejunction of restoration and the sprue www.indiandentalacademy.com
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  • Spuring method – Indirect spuringSpuring method – Indirect spuring  With indirect spruing, molten alloy does not flowWith indirect spruing, molten alloy does not flow directly from the casting crucible into the pattern areadirectly from the casting crucible into the pattern area in the heated moldin the heated mold  Instead, the casting alloy takes a circuitous (indirect)Instead, the casting alloy takes a circuitous (indirect) route before it reaches the pattern areas, thus the nameroute before it reaches the pattern areas, thus the name indirectindirect spruing.spruing.  The connector (or runner) bar is often 6- or 8-gaugeThe connector (or runner) bar is often 6- or 8-gauge round wax to which the wax pattern sprue formers areround wax to which the wax pattern sprue formers are attached on one side with two larger ingot sprueattached on one side with two larger ingot sprue formers on the other side,formers on the other side, www.indiandentalacademy.com
  • Indirect methodIndirect method www.indiandentalacademy.com
  • Spuring method – Indirect spuringSpuring method – Indirect spuring  The bar's large volume houses molten metal so theThe bar's large volume houses molten metal so the pattern areas fill with metal first and are able to drawpattern areas fill with metal first and are able to draw upon the reservoir if additional alloy is needed toupon the reservoir if additional alloy is needed to complete the solidification process .complete the solidification process .  The connector bar is often re­ferred to as a "reservoir"The connector bar is often re­ferred to as a "reservoir" bar.bar.  The composition of an alloy will influence the mannerThe composition of an alloy will influence the manner in which it fills the mold.in which it fills the mold.  For example, a palladium-silver alloy fills unidirectional,For example, a palladium-silver alloy fills unidirectional, whereas Type III gold fills in a random (scattered)whereas Type III gold fills in a random (scattered) fashionfashion www.indiandentalacademy.com
  • Spuring method – Indirect spuringSpuring method – Indirect spuring  indirect spruing offers advantages such asindirect spruing offers advantages such as  greater predictability and reliability in castinggreater predictability and reliability in casting  Enhanced control of solidification shrinkageEnhanced control of solidification shrinkage www.indiandentalacademy.com
  • Sprue former placementSprue former placement  The sprue former attached to the wax up should beThe sprue former attached to the wax up should be luted to the thickest part of the pattern to allow theluted to the thickest part of the pattern to allow the molten alloy to flow from regions of large volumemolten alloy to flow from regions of large volume (thick areas) to regions of lesser volume (thin sections).(thick areas) to regions of lesser volume (thin sections).  Placing the sprue former elsewhere might result in anPlacing the sprue former elsewhere might result in an incomplete casting if a thin section undergoesincomplete casting if a thin section undergoes solidification before the mold can fill completely.solidification before the mold can fill completely.  With thin anterior copings the most practical sprueWith thin anterior copings the most practical sprue location is the mid incisal arealocation is the mid incisal area www.indiandentalacademy.com
  • Sprue former gaugeSprue former gauge  A pattern sprue former of sufficient size should be selected to supply theA pattern sprue former of sufficient size should be selected to supply the volume of alloy required of the patterns to be cast.volume of alloy required of the patterns to be cast.  The roundThe round waxwax sprue formers are conveniently identified with a gaugesprue formers are conveniently identified with a gauge number (ie, 10, 8, 6).number (ie, 10, 8, 6).  The larger the number, the smaller the sprue formers diameter.The larger the number, the smaller the sprue formers diameter.  Alloy manufacturers invariably include size recommendations with their alloysAlloy manufacturers invariably include size recommendations with their alloys  With indirect spruing, the reservoir should be equal to or larger than theWith indirect spruing, the reservoir should be equal to or larger than the thickest cross-sectional area of the largest pattern.thickest cross-sectional area of the largest pattern.   This requirement is especially critical when metal pontics and large molarThis requirement is especially critical when metal pontics and large molar retainers are spruedretainers are sprued www.indiandentalacademy.com
  • Sprue former lengthSprue former length  With the direct spruing method, the sprue former should be longWith the direct spruing method, the sprue former should be long enough to position the wax patterns outside the heat center ofenough to position the wax patterns outside the heat center of the ring and into a cold zonethe ring and into a cold zone  The actual length of the sprue former will vary with the type andThe actual length of the sprue former will vary with the type and size of the crucible former and the casting ring used.size of the crucible former and the casting ring used. www.indiandentalacademy.com
  • Sprue former length (contd)Sprue former length (contd)  With indirect spruing pattern placement off the connector bar isWith indirect spruing pattern placement off the connector bar is recommended to ensure location of the patterns outside therecommended to ensure location of the patterns outside the thermal zone, or heat center, of the investment.thermal zone, or heat center, of the investment.  5-mm­long pattern sprue former is often sufficient to meet this5-mm­long pattern sprue former is often sufficient to meet this requirementrequirement   Incomplete castings may occur if the wax patterns are positionedIncomplete castings may occur if the wax patterns are positioned too far from the connector bar, because alloy may solidify in thetoo far from the connector bar, because alloy may solidify in the sprue channel before the pattern has filled completely.sprue channel before the pattern has filled completely. www.indiandentalacademy.com
  • Orientation of the wax patternOrientation of the wax pattern  The casting of an otherwise properly sprued pattern canThe casting of an otherwise properly sprued pattern can be jeopardized if the pattern is not correctly oriented inbe jeopardized if the pattern is not correctly oriented in the casting ring.the casting ring.  The sprue former is attached to the thickest portion ofThe sprue former is attached to the thickest portion of the wax pattern.the wax pattern.  Avoiding sharp 90-degree angles between the sprueAvoiding sharp 90-degree angles between the sprue former and the wax pattern or position the pattern soformer and the wax pattern or position the pattern so the alloy would have to flow back toward the ringthe alloy would have to flow back toward the ring entrance.entrance. www.indiandentalacademy.com
  • Orientation of the wax patternOrientation of the wax pattern www.indiandentalacademy.com
  • Orientation of the wax patternOrientation of the wax pattern  It is essential to take advantage of centrifugal andIt is essential to take advantage of centrifugal and gravitational forces by positioning the wax pattern suchgravitational forces by positioning the wax pattern such that the alloy is cast toward thinner sections, such as thethat the alloy is cast toward thinner sections, such as the margins.margins.  This is accomplished by positioning the margins of theThis is accomplished by positioning the margins of the patterns to the edge in the casting ring.patterns to the edge in the casting ring.  Before investing the patterns, a wax dot is placed on theBefore investing the patterns, a wax dot is placed on the crucible former to provide an orientation referencecrucible former to provide an orientation reference after the patterns have been invested .after the patterns have been invested . www.indiandentalacademy.com
  • Location of the reservoirLocation of the reservoir  The reservoir portion of a spruing system, be it a 6-, 3-,The reservoir portion of a spruing system, be it a 6-, 3-, or 1-gauge bar or round ball, should be positioned inor 1-gauge bar or round ball, should be positioned in thethe heat centerheat center of the ringof the ring  This permits the reservoir to remain molten longer andThis permits the reservoir to remain molten longer and enables it to furnish alloy to the patterns until theyenables it to furnish alloy to the patterns until they complete the solidification processcomplete the solidification process  Aside from being in the heat center, the reservoirAside from being in the heat center, the reservoir should have the largest mass of any part of the sprueshould have the largest mass of any part of the sprue system.system.  www.indiandentalacademy.com
  • Constricted spruingConstricted spruing  Tapering the sprue former at its attachment to the wax patternTapering the sprue former at its attachment to the wax pattern rather than flaring this area is referred to as "constricted spruing"rather than flaring this area is referred to as "constricted spruing"  The taper is to permit the sprue former to function like a trueThe taper is to permit the sprue former to function like a true reservoir, thereby decreasing the likelihood of suck-backreservoir, thereby decreasing the likelihood of suck-back porosity.porosity.  The constriction may be helpful in the mold-filling process forThe constriction may be helpful in the mold-filling process for lower density base metal alloys.lower density base metal alloys.  But, as the density of the metal increases, it is likely to interfereBut, as the density of the metal increases, it is likely to interfere with mold filling and lead to increased poros­itywith mold filling and lead to increased poros­ity  Therefore, it is recommended that the greater the alloy density,Therefore, it is recommended that the greater the alloy density, the greater the sprue -pattern access.the greater the sprue -pattern access. www.indiandentalacademy.com
  • Sprue former composition: wax versusSprue former composition: wax versus plasticplastic  Casting wax melts readily in the normal courseCasting wax melts readily in the normal course of the wax elimination (burnout) process,of the wax elimination (burnout) process, leaving little con­cern for carbon residues afterleaving little con­cern for carbon residues after heat-soaking at the recommended maximumheat-soaking at the recommended maximum temperature.temperature.  casting waxes that are certified by the Americancasting waxes that are certified by the American Dental Association will not leave a residue ofDental Association will not leave a residue of more than 0.1 % of the specimen's originalmore than 0.1 % of the specimen's original weight.weight. www.indiandentalacademy.com
  • Sprue former composition: wax versusSprue former composition: wax versus plasticplastic  plastic sprue formers do not burn out completely through the lowerplastic sprue formers do not burn out completely through the lower temperature rangetemperature range  There is a greater potential for carbon residue to remain in the mold.There is a greater potential for carbon residue to remain in the mold.  Plastic undergoes more expansion before softening than does wax, aPlastic undergoes more expansion before softening than does wax, a characteristic that may be responsible for investment cracking.characteristic that may be responsible for investment cracking.  More importantly, if the pathway for the escape of molten wax is blocked byMore importantly, if the pathway for the escape of molten wax is blocked by un melted plastic, the wax may overheat (boil), and erode the inner surface ofun melted plastic, the wax may overheat (boil), and erode the inner surface of the mold.the mold.  As a result, the castings may have a higher degree of surface roughness.As a result, the castings may have a higher degree of surface roughness.  To overcome this problem, manufacturers of plastic sprue formersTo overcome this problem, manufacturers of plastic sprue formers recommend applying a layer of wax over the entire surface of the plasticrecommend applying a layer of wax over the entire surface of the plastic sprue former to produce an escape mechanism for the melting wax patternssprue former to produce an escape mechanism for the melting wax patterns  .. www.indiandentalacademy.com
  • Sprue former composition: wax versusSprue former composition: wax versus plasticplastic  This procedure not only requires more time but canThis procedure not only requires more time but can increase the amount of irregularities in the investment ifincrease the amount of irregularities in the investment if the wax is not flowed evenly and smoothly over thethe wax is not flowed evenly and smoothly over the plastic components.plastic components.  Therefore, a two-stage burnout is recommended forTherefore, a two-stage burnout is recommended for plastic sprue formers with a 3D-minute heat soaking atplastic sprue formers with a 3D-minute heat soaking at 800°F for the first stage.800°F for the first stage.  When the oven reaches this temperature, burnout forWhen the oven reaches this temperature, burnout for 30 minutes (single ring), then reset the oven to the30 minutes (single ring), then reset the oven to the desired high temperature and continue wax eliminationdesired high temperature and continue wax elimination (burnout).(burnout). www.indiandentalacademy.com
  • Prefabricated sprue formersPrefabricated sprue formers  To meet the needs of individual cases.To meet the needs of individual cases.  To obtain a predictable and time­saving methodTo obtain a predictable and time­saving method of spruing.of spruing.  Examples of prefabricated wax sprue formersExamples of prefabricated wax sprue formers include Ready Sprues (Belle de St Claire) as partinclude Ready Sprues (Belle de St Claire) as part of the Casting Oval System and the Tri-Waxof the Casting Oval System and the Tri-Wax Sprues (Williams Dental Company)Sprues (Williams Dental Company) www.indiandentalacademy.com
  • Ready SpruesReady Sprues  The design of the Belle de St Claire Ready SpruesThe design of the Belle de St Claire Ready Sprues prefabricated indirect sprue formersprefabricated indirect sprue formers  Permits rapid placement of the pattern in thePermits rapid placement of the pattern in the accompanying sprue former and consistent location ofaccompanying sprue former and consistent location of the reservoir bar in the oval casting ring.the reservoir bar in the oval casting ring.  The bar is 6-gauge for both the large and the small waxThe bar is 6-gauge for both the large and the small wax Ready Sprue patterns. This size is most appropriate forReady Sprue patterns. This size is most appropriate for small- and medium-size wax patterns (anterior copingssmall- and medium-size wax patterns (anterior copings and small posterior metal ceramic substructures)and small posterior metal ceramic substructures)  The oval crucible former is indexed with a drop of waxThe oval crucible former is indexed with a drop of wax to orient the wax pattern's trailing edgeto orient the wax pattern's trailing edge www.indiandentalacademy.com
  • Tri-Wax systemTri-Wax system  The prefabricated Tri-Wax sprues from the Williams DentalThe prefabricated Tri-Wax sprues from the Williams Dental Company are available as direct and indirect sprues.Company are available as direct and indirect sprues.  The direct sprues are sold in three sizes: large, small, and mini,The direct sprues are sold in three sizes: large, small, and mini, with an 8-gauge, 10-gauge, and a 12-gauge ball, respectively.with an 8-gauge, 10-gauge, and a 12-gauge ball, respectively.  The indirect sprues have either a 4-gauge (large) or 6-gaugeThe indirect sprues have either a 4-gauge (large) or 6-gauge (small) runner bar.(small) runner bar.  The large indirect sprues are particularly useful for large ponticsThe large indirect sprues are particularly useful for large pontics or thick molar wax patternsor thick molar wax patterns  The cross-sectional area of a Tri-Wax reservoir bar is muchThe cross-sectional area of a Tri-Wax reservoir bar is much larger than that of a Ready Spruelarger than that of a Ready Sprue www.indiandentalacademy.com
  • Ready sprue and tri wax systemReady sprue and tri wax system www.indiandentalacademy.com
  • High-heat casting investmentsHigh-heat casting investments  The high melting ranges of metal ceramic alloysThe high melting ranges of metal ceramic alloys exceed the upper limits of the gypsum-bondedexceed the upper limits of the gypsum-bonded invest­mentsinvest­ments  Require the use of either phosphate ­bonded orRequire the use of either phosphate ­bonded or silica-bonded casting investments.silica-bonded casting investments.  The two phosphate varieties-carbon containingThe two phosphate varieties-carbon containing and non carbon containing-are more widely usedand non carbon containing-are more widely used than the silica-bonded materials.than the silica-bonded materials. www.indiandentalacademy.com
  • Carbon-containing phosphate-Carbon-containing phosphate- bonded investmentsbonded investments  These high-heat investments are gray-black because ofThese high-heat investments are gray-black because of the presence of carbon even after burnoutthe presence of carbon even after burnout  Divestment of the casting is supposedly made easier ifDivestment of the casting is supposedly made easier if carbon is added to an investment.carbon is added to an investment.  Many phosphate­ bonded investments require a specialMany phosphate­ bonded investments require a special liquid (colloidal silica), instead of distilled water.liquid (colloidal silica), instead of distilled water.  This liquid provides maximum investment expansion.This liquid provides maximum investment expansion.  Carbon-containing phosphate-bonded invest­ments areCarbon-containing phosphate-bonded invest­ments are generally recommended for gold-based metal ceramicgenerally recommended for gold-based metal ceramic alloys.alloys. www.indiandentalacademy.com
  • Non carbon-containing phosphate-Non carbon-containing phosphate- bonded investmentsbonded investments  The non carbon investments are easily identified by their whiteThe non carbon investments are easily identified by their white color, before and after mixing.color, before and after mixing.  They were developed out of concerns for the potentialThey were developed out of concerns for the potential interaction of carbon with the nickel- and cobalt-base castinginteraction of carbon with the nickel- and cobalt-base casting alloys, as well as the palladium-based noble metal alloysalloys, as well as the palladium-based noble metal alloys  These alloy systems are capable of dissolving available carbon toThese alloy systems are capable of dissolving available carbon to produce carbides and porosityproduce carbides and porosity  proponents of the non carbon investments use a carbonlessproponents of the non carbon investments use a carbonless system, especially since high temperature burnout (1,600°F) issystem, especially since high temperature burnout (1,600°F) is required to eliminate all the residual carbonrequired to eliminate all the residual carbon www.indiandentalacademy.com
  • Non carbon-containing phosphate-Non carbon-containing phosphate- bonded investments (contd)bonded investments (contd)  The non carbon investments generally have aThe non carbon investments generally have a grainy texture, like their carbon-containinggrainy texture, like their carbon-containing counter­parts.counter­parts.  Exceptions include the fine-particle invest­Exceptions include the fine-particle invest­ ments, Vestra-fine (3M/Unitek) or Cera-Finaments, Vestra-fine (3M/Unitek) or Cera-Fina (Whip Mix Corporation).(Whip Mix Corporation).  These particular materials mix to a smooth,These particular materials mix to a smooth, creamy consistency with ample working time.creamy consistency with ample working time. www.indiandentalacademy.com
  • Casting ring linersCasting ring liners  Asbestos had been the traditional material for lining casting ringsAsbestos had been the traditional material for lining casting rings  Evidently the asbestos fiber bundles were found to produceEvidently the asbestos fiber bundles were found to produce hazardous-size respirable particles capable of causing lunghazardous-size respirable particles capable of causing lung diseasedisease  Alternative non asbestos ring liner materials fall into threeAlternative non asbestos ring liner materials fall into three categories:categories:  ceramic (aluminum silicate),ceramic (aluminum silicate),  cellu­lose (paper), andcellu­lose (paper), and  a ceramic-cellulose combinationa ceramic-cellulose combination  The relative safety of the ceramic ring liners remains uncertain,The relative safety of the ceramic ring liners remains uncertain, because aluminum silicate also appears capable of producingbecause aluminum silicate also appears capable of producing hazardous-size respirable particleshazardous-size respirable particles www.indiandentalacademy.com
  • Asbestos liner and ceramic linerAsbestos liner and ceramic liner www.indiandentalacademy.com
  • Investing techniqueInvesting technique  Wax elimination (burnout) techniqueWax elimination (burnout) technique  The burnout technique will vary for alloys of differentThe burnout technique will vary for alloys of different compositions.compositions.  High temperature settings will range up to 1,600°F forHigh temperature settings will range up to 1,600°F for base metal alloysbase metal alloys  Between 1 ,400°F and 1 ,600°F for noble metal alloys.Between 1 ,400°F and 1 ,600°F for noble metal alloys.  Recommended temperature rate of rise for the burnoutRecommended temperature rate of rise for the burnout furnace ranges from 20°F/min to 50°F/min.furnace ranges from 20°F/min to 50°F/min. www.indiandentalacademy.com
  • Casting torch selectionCasting torch selection  There are two types of torch tips to choose from when selectingThere are two types of torch tips to choose from when selecting casting equipment:casting equipment:  multi orifice and single orificemulti orifice and single orifice  The tip most widely used for metal ceramic alloys is probably theThe tip most widely used for metal ceramic alloys is probably the multi ori­fice type.multi ori­fice type.  Advantage is the distribution of heat over a wide area for moreAdvantage is the distribution of heat over a wide area for more uniform heating of the alloy, which is particularly helpful inuniform heating of the alloy, which is particularly helpful in casting high-fusing base metal alloys.casting high-fusing base metal alloys.  The single-orifice tip may concentrate more heat in one area,The single-orifice tip may concentrate more heat in one area, but the area is smaller than that produced by the multi orifice tipbut the area is smaller than that produced by the multi orifice tip www.indiandentalacademy.com
  • Choice of fuelsChoice of fuels  The three fuel sources that merit specific mention are: acetylene, natural gas,The three fuel sources that merit specific mention are: acetylene, natural gas, and propaneand propane  1.1. Acetylene.Acetylene. This colorless gas has a distinctive garlic-like odor.This colorless gas has a distinctive garlic-like odor.  It will burn in air and can generate a flame approaching 3,OOO°F.It will burn in air and can generate a flame approaching 3,OOO°F. Unfortunately, acet­ylene is usually contaminated with carbon and otherUnfortunately, acet­ylene is usually contaminated with carbon and other elements, so it should not be used to melt metal ceramic alloys.elements, so it should not be used to melt metal ceramic alloys.  2.2. Natural gas.Natural gas. This fuel is the by-product of the "natural" decomposition ofThis fuel is the by-product of the "natural" decomposition of organic matter in the ground.organic matter in the ground.  When mixed with air, the natural gas flame approaches a temperature ofWhen mixed with air, the natural gas flame approaches a temperature of 2,200°F.2,200°F.  Replacing air with oxygen enables natural gas to attain tem­peratures requiredReplacing air with oxygen enables natural gas to attain tem­peratures required to melt the high-fusing noble and base metal alloys.to melt the high-fusing noble and base metal alloys. www.indiandentalacademy.com
  • Choice of fuels (contd)Choice of fuels (contd)  Natural gas is an accept­able fuel source, although it is not ideal.Natural gas is an accept­able fuel source, although it is not ideal.  Inadequate pressure in gas lines, fluctuations in pressure levels,Inadequate pressure in gas lines, fluctuations in pressure levels, water contamination, and variations in composition among gaswater contamination, and variations in composition among gas companies are some of the problems encountered by natural gascompanies are some of the problems encountered by natural gas users. Nonetheless, natural gas is a widely used fuel.users. Nonetheless, natural gas is a widely used fuel.  3.3. Propane.Propane. The problems with natural gas are avoided when usingThe problems with natural gas are avoided when using bottled propane gas.bottled propane gas.  The constant, regulated mixture of pure, uncontami­natedThe constant, regulated mixture of pure, uncontami­nated propane and oxygen provides a clean, consistent burn leading topropane and oxygen provides a clean, consistent burn leading to a more ideal melt.a more ideal melt. www.indiandentalacademy.com
  • Casting equipmentCasting equipment  Noble and base metal alloys can be cast withNoble and base metal alloys can be cast with either a torch in a centrifugal casting unit or ineither a torch in a centrifugal casting unit or in an induction casting machinean induction casting machine  Irrespective of the type of equip­ment selected,Irrespective of the type of equip­ment selected, the lower density alloys require an additionalthe lower density alloys require an additional wind of the casting arm to ensure adequatewind of the casting arm to ensure adequate casting pressurecasting pressure www.indiandentalacademy.com
  • Casting cruciblesCasting crucibles  Either zircon-alumina or quartz casting crucibles areEither zircon-alumina or quartz casting crucibles are recommended for noble and base metal ceramic alloys.recommended for noble and base metal ceramic alloys.  The clay-type crucibles will break down when exposed to theThe clay-type crucibles will break down when exposed to the high temperatures required to melt metal ceramic alloys, possiblyhigh temperatures required to melt metal ceramic alloys, possibly contaminating the meltcontaminating the melt  Carbon crucibles are well suited for gold-based alloys but are aCarbon crucibles are well suited for gold-based alloys but are a ready source of carbon contamination for palladium-, nickel-,ready source of carbon contamination for palladium-, nickel-, and cobalt based metals.and cobalt based metals.  The contamination in the form of carbide formation canThe contamination in the form of carbide formation can embrittle these alloys.embrittle these alloys.  Preheating the crucible prevents spalling (cracking) and prolongsPreheating the crucible prevents spalling (cracking) and prolongs the crucible's life.the crucible's life. www.indiandentalacademy.com
  • Casting cruciblesCasting crucibles www.indiandentalacademy.com
  • Electric casting machinesElectric casting machines  Electric casting machines with carbon cruciblesElectric casting machines with carbon crucibles are appropriate for gold-based alloys,are appropriate for gold-based alloys,  But they are generally not recommended forBut they are generally not recommended for palladium-, nickel-, and cobalt-based alloyspalladium-, nickel-, and cobalt-based alloys because of the potential for carbonbecause of the potential for carbon contamination.contamination.  As indicated previously, exposure to carbon canAs indicated previously, exposure to carbon can weaken the cast restorationweaken the cast restoration www.indiandentalacademy.com
  • Air-abrasive (blasting) compoundsAir-abrasive (blasting) compounds  Commercially availableCommercially available  abrasive compounds such as aluminum oxide (AI203),abrasive compounds such as aluminum oxide (AI203),  General purpose blasting compound, andGeneral purpose blasting compound, and  Glass beadsGlass beads  removes casting investment and surface oxides.removes casting investment and surface oxides.  A 50-fLm grit, non­recycled aluminum oxide abrasiveA 50-fLm grit, non­recycled aluminum oxide abrasive (white color) is commonly suggested for air-abrading(white color) is commonly suggested for air-abrading porcelain bearing surfaces and dental porcelainporcelain bearing surfaces and dental porcelain www.indiandentalacademy.com
  • Air-abrasive (blasting) compoundsAir-abrasive (blasting) compounds www.indiandentalacademy.com
  • The laws of castingThe laws of casting  17 separate recommendations for spruing,17 separate recommendations for spruing, investing, burnout, and melting and castinginvesting, burnout, and melting and casting procedures.procedures.  Collectively, these guidelines are referred to asCollectively, these guidelines are referred to as thethe laws of casting.laws of casting. www.indiandentalacademy.com
  • TheThe 11 st law of castingst law of casting  Attach the pattern sprue former to the thickest part of the wax patternAttach the pattern sprue former to the thickest part of the wax pattern..  As the molten alloy moves from the reservoir to the pattern margins it shouldAs the molten alloy moves from the reservoir to the pattern margins it should flow from areas of greater volume to areas of lesser volumeflow from areas of greater volume to areas of lesser volume  Molten metal flowing from a thin area to a thicker region (full waxup) mayMolten metal flowing from a thin area to a thicker region (full waxup) may solidify before the mold is completely filled.solidify before the mold is completely filled.  When using indirect spruing, be sure to select the appropriate-sizeWhen using indirect spruing, be sure to select the appropriate-size prefabricated sprue former.prefabricated sprue former.  TheThe penaltiespenalties for not obeying this law are: COLD SHUTS, SHORTfor not obeying this law are: COLD SHUTS, SHORT MARGINS, and INCOMPLETE CASTINGS.MARGINS, and INCOMPLETE CASTINGS. www.indiandentalacademy.com
  • TheThe 11 st law of castingst law of casting www.indiandentalacademy.com
  • The 2nd law of castingThe 2nd law of casting  Orient wax patterns so all the restoration marginsOrient wax patterns so all the restoration margins will face the trailing edge when the ring iswill face the trailing edge when the ring is positioned in the casting machine.positioned in the casting machine.  To identify that orientation, a wax dot is added to theTo identify that orientation, a wax dot is added to the crucible former it helps to place the ring in the castingcrucible former it helps to place the ring in the casting cradle correctly after the patterns have been investedcradle correctly after the patterns have been invested  TheThe penaltiespenalties for not obeying this law are: COLDfor not obeying this law are: COLD SHUTS and SHORT MARGINS.SHUTS and SHORT MARGINS. www.indiandentalacademy.com
  • The 3rd law of castingThe 3rd law of casting  Position the wax patterns in a "cold zone" of the investment mold and thePosition the wax patterns in a "cold zone" of the investment mold and the reservoir in the "heat center" of the casting ringreservoir in the "heat center" of the casting ring  ..  The coolest parts of the mold (cold zones) are at the end of the ring andThe coolest parts of the mold (cold zones) are at the end of the ring and along the ring periphery.along the ring periphery.  The hottest portion of the casting ring is located near the center of the ringThe hottest portion of the casting ring is located near the center of the ring (the "heat center")(the "heat center")  Adherence to this law increases the likelihood that casting porosity will occurAdherence to this law increases the likelihood that casting porosity will occur in the reservoir rather than in the restoration.in the reservoir rather than in the restoration.  TheThe penaltypenalty for not obeying this law is: SHRINK­AGE POROSITY in thefor not obeying this law is: SHRINK­AGE POROSITY in the restorations.restorations. www.indiandentalacademy.com
  • The 4th law of castingThe 4th law of casting  A reservoir must have sufficient molten alloy to accommodate the shrinkageA reservoir must have sufficient molten alloy to accommodate the shrinkage that occurs within the restorations.that occurs within the restorations.  Alloy that fills the restorations will solidify first.Alloy that fills the restorations will solidify first.   As that molten metal solidifies, it shrinks and creates a vacuum.As that molten metal solidifies, it shrinks and creates a vacuum.  For a complete casting, the vacuum must be able to draw additional metalFor a complete casting, the vacuum must be able to draw additional metal from an adjacent source- the reservoirfrom an adjacent source- the reservoir  A runner (connector) bar can be an effective reservoir if it is equal to orA runner (connector) bar can be an effective reservoir if it is equal to or greater than the thickest cross-sectional area of the wax patterngreater than the thickest cross-sectional area of the wax pattern  TheThe penaltiespenalties for not obeying this law are: SHRINK­AGE POROSITY and/orfor not obeying this law are: SHRINK­AGE POROSITY and/or SUCK-BACK POROSITYSUCK-BACK POROSITY www.indiandentalacademy.com
  • The 5th law of castingThe 5th law of casting  Do not cast a button if a connector (runner) bar, or otherDo not cast a button if a connector (runner) bar, or other internal reservoir, is usedinternal reservoir, is used  With indirect spruing, the largest mass of metal should be theWith indirect spruing, the largest mass of metal should be the reservoirreservoir  A button is counter productive because it can draw availableA button is counter productive because it can draw available molten alloy from the bar, shift the heat center and reduce themolten alloy from the bar, shift the heat center and reduce the feed of that metal to the restorationsfeed of that metal to the restorations  The wax patterns should not be larger than the connector bar, ifThe wax patterns should not be larger than the connector bar, if the bar is to act as a true reservoirthe bar is to act as a true reservoir  TheThe penaltiespenalties for not obeying this law are: SHRINKAGEfor not obeying this law are: SHRINKAGE POROSITY (and potential DISTORTION during porcelainPOROSITY (and potential DISTORTION during porcelain firing) and SUCK-BACK POROS1TYfiring) and SUCK-BACK POROS1TY www.indiandentalacademy.com
  • The 6th law of castingThe 6th law of casting  Turbulence must be minimized, if not totally elimi­natedTurbulence must be minimized, if not totally elimi­nated  Pathways for the flow of metal should be smooth, gradual, andPathways for the flow of metal should be smooth, gradual, and without impediments.without impediments.  Eliminate sharp turns, restrictions, points, or impingements thatEliminate sharp turns, restrictions, points, or impingements that might create turbulence and occlude air in the cast­ing.might create turbulence and occlude air in the cast­ing.  Restrictions, or constrictions, can accelerate the metal's rate ofRestrictions, or constrictions, can accelerate the metal's rate of flow and abrade the mold surface (mold wash)flow and abrade the mold surface (mold wash)  TheThe penaltiespenalties for not obeying this law are: VOIDS in the castingfor not obeying this law are: VOIDS in the casting and/or SURFACE PITTING.and/or SURFACE PITTING. www.indiandentalacademy.com
  • The 7th law of castingThe 7th law of casting  Select a casting ring of sufficient length and diameter toSelect a casting ring of sufficient length and diameter to accommodate the patterns to be in­vested.accommodate the patterns to be in­vested.  The casting ring should permit the patterns to be 1/4 in. apartThe casting ring should permit the patterns to be 1/4 in. apart and 1/4 in. from the top of the invest­ment with a minimum 3/8and 1/4 in. from the top of the invest­ment with a minimum 3/8 in. of investment between them and the ring linerin. of investment between them and the ring liner  If too little investment covers the wax patterns, the alloy is moreIf too little investment covers the wax patterns, the alloy is more likely to break through the mold.likely to break through the mold.  Too much investment over the wax ups may locate the waxToo much investment over the wax ups may locate the wax patterns too close to the heat center of the mold and impair thepatterns too close to the heat center of the mold and impair the escape of gasesescape of gases  .The.The penaltiespenalties for not obeying this law are: MOLD FRACTURE,for not obeying this law are: MOLD FRACTURE, CASTING FINS, and SHRINKAGE POROSITYCASTING FINS, and SHRINKAGE POROSITY www.indiandentalacademy.com
  • The 8th law of castingThe 8th law of casting  Increase the wet ability of the wax patterns.Increase the wet ability of the wax patterns.  A wetting agent should be brushed or sprayed on the patternsA wetting agent should be brushed or sprayed on the patterns and dried before investingand dried before investing  A clean wax surface better enables the casting invest­ment to wetA clean wax surface better enables the casting invest­ment to wet the patterns more completely.the patterns more completely.  Apply the liquid wax pattern cleaner sparingly and let it dryApply the liquid wax pattern cleaner sparingly and let it dry thoroughly before investing.thoroughly before investing.  Too much wetting agent can create a surface film that can diluteToo much wetting agent can create a surface film that can dilute and weaken the investment in that area and produce bubbles orand weaken the investment in that area and produce bubbles or fins on the castingfins on the casting  TheThe penaltypenalty for not obeying this law is: BUBBLES on the surfacefor not obeying this law is: BUBBLES on the surface of the casting as a result of the entrap­ment of air (too littleof the casting as a result of the entrap­ment of air (too little wetting agent) or excess liquid (too much wetting agent)wetting agent) or excess liquid (too much wetting agent) www.indiandentalacademy.com
  • The 9th law of castingThe 9th law of casting  Weigh any bulk investment and measure the in­vestment liquidWeigh any bulk investment and measure the in­vestment liquid for a precise powder-liquid ratio.for a precise powder-liquid ratio.  The correct proportions of powder to liquid and any dilution ofThe correct proportions of powder to liquid and any dilution of the (special) liquid with distilled water should be established forthe (special) liquid with distilled water should be established for each alloy.each alloy.  A thick mix of investment (reduced liquid) increases investmentA thick mix of investment (reduced liquid) increases investment expansion and produces loose-fitting castings.expansion and produces loose-fitting castings.  Too much liquid (special liquid and distilled water, if any) resultsToo much liquid (special liquid and distilled water, if any) results in a thinner mix and less expansion with tighter-fitting castingsin a thinner mix and less expansion with tighter-fitting castings  TheThe penaltypenalty for not obeying this law is: ILL-FITTINGfor not obeying this law is: ILL-FITTING CASTINGSCASTINGS www.indiandentalacademy.com
  • The 10th law of castingThe 10th law of casting  Eliminate the incorporation of air in the casting investment and remove theEliminate the incorporation of air in the casting investment and remove the ammonia gas by­product of phosphate-bonded investments by mixing underammonia gas by­product of phosphate-bonded investments by mixing under vacuum.vacuum.  Vacuum mixing removes more air and gas than hand spatulaion.Vacuum mixing removes more air and gas than hand spatulaion.  Areas of the mold that contain dense, bubble-free investment will expandAreas of the mold that contain dense, bubble-free investment will expand differently from sections that contain large voids (entrapped air).differently from sections that contain large voids (entrapped air).  The mixing time will depend on the type of investment used and the mixingThe mixing time will depend on the type of investment used and the mixing speed (slow-speed versus high­ speed mixing).speed (slow-speed versus high­ speed mixing).  TheThe penaltiespenalties for not obeying this law are: small NODULES on the casting, afor not obeying this law are: small NODULES on the casting, a WEAK MOLD, and DIS­TORTION of the castingWEAK MOLD, and DIS­TORTION of the casting www.indiandentalacademy.com
  • TheThe 1111 th law of castingth law of casting  Allow the casting investment to set completely beforeAllow the casting investment to set completely before initiating the burnout procedureinitiating the burnout procedure  If setting is not complete at the time a ring is placed inIf setting is not complete at the time a ring is placed in the oven, the mold may be weak and unable tothe oven, the mold may be weak and unable to withstand steam expansion during burnout.withstand steam expansion during burnout.  The investment could frac­ture as a consequence.The investment could frac­ture as a consequence.  For best results, burnout should be initiated only afterFor best results, burnout should be initiated only after the recommended set­ting time.the recommended set­ting time.  TheThe penaltiespenalties for not obeying this law are: MOLDfor not obeying this law are: MOLD CRACKING/BLOWOUT or FINS on the castingCRACKING/BLOWOUT or FINS on the casting www.indiandentalacademy.com
  • The 12th law of castingThe 12th law of casting  Use a wax elimination (burnout) technique that is specific for the type of patternsUse a wax elimination (burnout) technique that is specific for the type of patterns involved (wax versus plastic) and recommended for the particu­lar type of casting alloyinvolved (wax versus plastic) and recommended for the particu­lar type of casting alloy selectedselected  ..  Plastic sprues need to be heated slowly so they can soften gradually and not exertPlastic sprues need to be heated slowly so they can soften gradually and not exert pressure on the mold, so use a two­ stage burnoutpressure on the mold, so use a two­ stage burnout  Slow the rate of rise to permit the heat to move through the investment for uniformSlow the rate of rise to permit the heat to move through the investment for uniform expansion.expansion.  If burnout is incom­plete, the spruing system channels may be blocked by wax orIf burnout is incom­plete, the spruing system channels may be blocked by wax or plastic residue (carbon) and, on casting, air cannot escape completely when the metalplastic residue (carbon) and, on casting, air cannot escape completely when the metal enters the mold;enters the mold;  Therefore, use at least a 3D-minute heat-soaking at 800°F for the first burnout stage.Therefore, use at least a 3D-minute heat-soaking at 800°F for the first burnout stage.  TheThe penaltiespenalties for not obeying this law are: COLD SHUTS, SHORT MARGINS,for not obeying this law are: COLD SHUTS, SHORT MARGINS, COLD WELDS, MOLD CRACKS, and/or CASTING finsCOLD WELDS, MOLD CRACKS, and/or CASTING fins www.indiandentalacademy.com
  • The 13th law of castingThe 13th law of casting  Adequate heat must be available to properly melt and cast the alloyAdequate heat must be available to properly melt and cast the alloy  The selected heat source should be capable of melting the alloy to the pointThe selected heat source should be capable of melting the alloy to the point of sufficient fluidityof sufficient fluidity   Prolonged heating, caused by an improperly adjusted torch, can prevent theProlonged heating, caused by an improperly adjusted torch, can prevent the alloy from attaining the fluidity needed for complete mold filling andalloy from attaining the fluidity needed for complete mold filling and compensation for heat loss.compensation for heat loss.   Too much heat, or too high a temperature, can burn off minor alloyingToo much heat, or too high a temperature, can burn off minor alloying elements through vaporization and/or oxida­tion (burned metal).elements through vaporization and/or oxida­tion (burned metal).  TheThe penaltiespenalties for not obeying this law are: COLD SHUTS, SHORTfor not obeying this law are: COLD SHUTS, SHORT MARGINS, and COLD WELDS (too little heat), or ROUGH CASTINGSMARGINS, and COLD WELDS (too little heat), or ROUGH CASTINGS and INVEST­MENT BREAKDOWN (too much heat )and INVEST­MENT BREAKDOWN (too much heat ) www.indiandentalacademy.com
  • The 14th law of castingThe 14th law of casting  When torch casting, use the "reducing zone" of theWhen torch casting, use the "reducing zone" of the flame to melt the alloy and not the oxidizing zoneflame to melt the alloy and not the oxidizing zone  An improperly adjusted torch can add carbon orAn improperly adjusted torch can add carbon or oxygen to the alloy while heating.oxygen to the alloy while heating.  A melt achieved by the exclusive use of theA melt achieved by the exclusive use of the REDUCING ZONE minimizes the likelihood of metalREDUCING ZONE minimizes the likelihood of metal oxidation and gas absorption and ensures a properoxidation and gas absorption and ensures a proper melt.melt.  TheThe penaltiespenalties for not obeying this law are: GASfor not obeying this law are: GAS POROSITY and/or a change in the alloy's COEFFI­POROSITY and/or a change in the alloy's COEFFI­ CIENT OF THERMAL EXPANSION (due to alloyCIENT OF THERMAL EXPANSION (due to alloy contamination).contamination). www.indiandentalacademy.com
  • The 15th law of castingThe 15th law of casting  Provide enough force to cause the liquid alloy to flowProvide enough force to cause the liquid alloy to flow into the heated mold.into the heated mold.  Adjust the casting machine to the requirements of eachAdjust the casting machine to the requirements of each alloy.alloy.  Lower-density metals generally need four winds of aLower-density metals generally need four winds of a centrifugal casting arm as compared to higher-density,centrifugal casting arm as compared to higher-density, gold­ based alloys.gold­ based alloys.  penaltiespenalties for not obeying this law are: COLD SHUTS,for not obeying this law are: COLD SHUTS, SHORT MARGINS, COLD WELDS (insuffi­cientSHORT MARGINS, COLD WELDS (insuffi­cient force), or MOLD FRACTURE and FINS (too muchforce), or MOLD FRACTURE and FINS (too much forceforce www.indiandentalacademy.com
  • The 16th law of castingThe 16th law of casting  Cast toward the marginsCast toward the margins ofof the wax patternsthe wax patterns  Place the heated ring in the casting cradle using thePlace the heated ring in the casting cradle using the orientation dot so the pattern margins face the trailingorientation dot so the pattern margins face the trailing edge (the 2nd law).edge (the 2nd law).  In a centrifugal casting machine the metal will flowIn a centrifugal casting machine the metal will flow downward and to the right, taking advantage of thedownward and to the right, taking advantage of the centrifugal, rotational, and gravitational forces on thecentrifugal, rotational, and gravitational forces on the molten alloymolten alloy  TheThe penaltiespenalties for not obeying this law are: COLDfor not obeying this law are: COLD SHUTS, SHORT MARGINS, and otherwise INCOM­SHUTS, SHORT MARGINS, and otherwise INCOM­ PLETE CASTINGS.PLETE CASTINGS. www.indiandentalacademy.com
  • The 17th law of castingThe 17th law of casting  Do not quench the ring immediately after casting.Do not quench the ring immediately after casting.  Allow the alloy and the investment to cool to roomAllow the alloy and the investment to cool to room temperature.temperature.  Uneven cooling and shrinkage between alloy andUneven cooling and shrinkage between alloy and investment can apply tensile forces to the castinginvestment can apply tensile forces to the casting  After casting, the alloy may not possess sufficientAfter casting, the alloy may not possess sufficient strength to resist these forces and the restoration couldstrength to resist these forces and the restoration could tear, if quenched.tear, if quenched.  TheThe penaltypenalty for not obeying this law is: HOT TEARS infor not obeying this law is: HOT TEARS in the restoration.the restoration. www.indiandentalacademy.com
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