Alloys used in metal ceramic/ cosmetic dentistry training

ALLOYS USED IN METALALLOYS USED IN METAL
CERAMICSCERAMICS
INDIAN DENTAL ACADEMY
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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

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

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

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.

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.

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

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

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

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

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

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.

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

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

(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

(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.

(contd.)(contd.)

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.

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

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

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.

Crystal Space LatticeCrystal Space Lattice

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.

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.

Edge Dislocation Slip PlaneEdge Dislocation Slip Plane

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.

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.

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.

Cooling Pattern of Liquid MetalCooling Pattern of Liquid Metal
During SolidificationDuring Solidification

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

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.

 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.

 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

RecoveryRecovery
 During recovery, cold work properties begin toDuring recovery, cold work properties begin to
disappear.disappear.

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.

Grain GrowthGrain Growth
 Grain growth stops when a coarse grainGrain growth stops when a coarse grain
structure is reached.structure is reached.

AnnealingAnnealing

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.

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.

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.

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.

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.

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.

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".

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.

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

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.

Solid SolutionSolid Solution

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.

 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.

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.

 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.

DISORDERED ARRANGEMENTDISORDERED ARRANGEMENT

 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.

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.

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.

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.

Eutectic AlloysEutectic Alloys

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

 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

 Properties – BrittleProperties – Brittle
Less strongLess strong
Less resistance to corrosionLess resistance to corrosion

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.

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.

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

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.

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.

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.

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.

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

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).

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.

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.

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..

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

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).

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 .

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.

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.

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 .

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.

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

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.

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.

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.

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 .

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.

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.

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.

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

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.

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.

 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.

 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.

 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.

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.

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

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)

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

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

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

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

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

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.

 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.

 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.

 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

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

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

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 .

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.

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.

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.

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.

 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.

 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.

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.

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

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.

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.

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

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

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

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.

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

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

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

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

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

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.

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

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

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.)

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

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)

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..

(Contd..)(Contd..)
 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

(Contd..)(Contd..)
DisadvantagesDisadvantages
 High silver content creates potential forHigh silver content creates potential for
porcelain discolorationporcelain discoloration
 High coefficient of thermal expansionHigh coefficient of thermal expansion
 Tarnish and corrosion resistantTarnish and corrosion resistant

Gold-Palladium-Silver (low silverGold-Palladium-Silver (low silver
group)group)
 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

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

group)group)
 DisadvantagesDisadvantages
 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)

Gold-Palladium alloysGold-Palladium alloys
 Gold – 44% -55%Gold – 44% -55%
 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

 Excellent castabilityExcellent castability
 Good bond strengthGood bond strength
 Improved strength (sag resistance)Improved strength (sag resistance)
 Improved HardnessImproved Hardness
 Lower densityLower density

 Not thermally compatible with highNot thermally compatible with high
expansion dental porcelainsexpansion dental porcelains

Palladium-Silver alloysPalladium-Silver alloys
 Silver – 28% - 30%Silver – 28% - 30%
Indium and tinIndium and tin
 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

Palladium-Silver alloys (contd)Palladium-Silver alloys (contd)
 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

Palladium-Silver alloys (contd)Palladium-Silver alloys (contd)
 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

Palladium-cobalt alloysPalladium-cobalt alloys
 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.

 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

 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

High Palladium-Silver-Gold alloysHigh Palladium-Silver-Gold alloys
 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.

 AdvantagesAdvantages
 Low densityLow density
 Improved sag resistance (better highImproved sag resistance (better high
temperature strength)temperature strength)
 Light-colored oxide layerLight-colored oxide layer

 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

Alloys used in metal ceramic/ cosmetic dentistry training

Alloys used in metal ceramic/ cosmetic dentistry training

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