Dental Materials: Metals and Metal Alloys Used in Dentistry

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ALLOYS USED IN METALALLOYS USED IN METAL
CERAMICSCERAMICS

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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

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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

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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 propertiesis responsible for many of the properties
of metals-electrical and thermal conductivity,of metals-electrical and thermal conductivity,
metallic luster, and (usually) high strengthmetallic luster, and (usually) high strength

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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

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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

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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

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Noble MetalNoble Metal
 Noble Metal is one whose compounds areNoble Metal is one whose compounds are
decomposable by heat alone at adecomposable by heat alone at a
temperature not exceeding that of redness.temperature not exceeding that of redness.
 They are corrosion and oxidation resistantThey are corrosion and oxidation resistant
because of inertness and chemicalbecause of inertness and chemical
resistance.resistance.
 8 Noble metals used in dentistry are Au,8 Noble metals used in dentistry are Au,
Pt, Pd, Ir, Os, Rh, Ru, Ag.Pt, Pd, Ir, Os, Rh, Ru, Ag.

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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

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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.

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Another Classification OfAnother Classification Of
MetalsMetals
 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.,High Ductile and Malleable metal – e.g.,
Au.Au.

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Microscopic Structure OfMicroscopic Structure Of
MetalsMetals
 Most metals have crystalline structure inMost metals have crystalline structure in
solid state which are held together bysolid state which are held together by
metallic bonds.metallic bonds.
 Metals also exist in liquid state eg, Hg, inMetals also exist in liquid state eg, Hg, in
which crystalline alignment is lost and thewhich crystalline alignment is lost and the
atoms move freely in mass of liquid metal.atoms move freely in mass of liquid metal.

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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 vaal’s bondsVander vaal’s bonds

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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.

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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.

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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.

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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.

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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.

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(contd.)(contd.)
 Such nucleus formations are calledSuch nucleus formations are called
DENDRITES.DENDRITES.
 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.

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(contd.)(contd.)

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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

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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.

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Crystal Space LatticeCrystal Space Lattice

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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.

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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.

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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.

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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.

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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.

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

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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

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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 to givepulling, pressing, hammering, etc in order to give
a certain shape to a metal.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.

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 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.

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 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

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

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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.

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

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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.

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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.

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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.

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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.

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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.

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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.

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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".

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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.

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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

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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.

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Solid SolutionSolid Solution

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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.

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 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.

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• ORDERED ARRANGEMENTORDERED ARRANGEMENT
 This produces an ordered space lattice.This produces an ordered space lattice.
 In this arrangement two types of metalIn this arrangement two types of metal
atoms occupy very specific or ordered (asatoms occupy very specific or ordered (as
if) positions within the crystal, resulting inif) positions within the crystal, resulting in
specific properties.specific properties.
 This produces a super lattice within theThis produces a super lattice within the
solid solution, which may distort thesolid solution, which may distort the
original lattice. This type of change occursoriginal lattice. This type of change occurs
with gold copper alloys during heatwith gold copper alloys during heat
treatments.treatments.

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 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.

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DISORDERED ARRANGEMENTDISORDERED ARRANGEMENT

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 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.

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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.

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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.

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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.

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Eutectic AlloysEutectic Alloys

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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

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 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

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

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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.

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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.

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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

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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.

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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.

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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.

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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

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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).

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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.

75
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.

76
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..

77
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.

78
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.

79
Different Metals Used In DentistryDifferent Metals Used In Dentistry
Gold (Au)Gold (Au)
 Gold provides a high level of corrosion and tarnish resistanceGold provides a high level of corrosion and tarnish resistance
 increases an alloy's melting range slightly.increases an alloy's melting range slightly.
 Gold improves workability, burnish ability, and raises theGold improves workability, burnish ability, and raises the
density .density .
 However, gold imparts a very pleasing yellow color to an alloy (ifHowever, gold imparts a very pleasing yellow color to an alloy (if
present in sufficient quantity).present in sufficient quantity).
 Unfortunately, that yellow color is readily offset by the additionUnfortunately, that yellow color is readily offset by the addition
of "white" metals, such as palladium and silver. Gold is a nobleof "white" metals, such as palladium and silver. Gold is a noble
metal.metal.

80
PalladiumPalladium
 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 will also elevate an alloy's melting range andPalladium will also elevate an alloy's melting range and
improve its sag resistance.improve its sag resistance.
 It has a very strong whitening effect, so an alloy with 90%It 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 but hasIt lowers the density of the gold-based alloys slightly but has
little similar effect on silver-based metals. Palladium, alittle similar effect on silver-based metals. Palladium, a
member of the platinum group, is a noble metalmember of the platinum group, is a noble metal

81
PlatinumPlatinum
 Platinum increases the strength, melting range,Platinum increases the strength, melting range,
and hardness of gold-based alloys whileand hardness of gold-based alloys while
improving their corrosion, tarnish, and sagimproving their corrosion, tarnish, and sag
resistance.resistance.
 It whitens an alloy and increases the density ofIt whitens an alloy and increases the density of
non gold-based metals because of its highnon gold-based metals because of its high
density.density.
 Platinum is a member of the platinum groupPlatinum is a member of the platinum group
and is a noble metaland is a noble metal

82
IridiumIridium
 serves as a grain refiner for gold- and palladium-serves as a grain refiner for gold- and palladium-
based alloys to improve the mechanicalbased alloys to improve the mechanical
properties as well as the tarnish resistance.properties as well as the tarnish resistance.
 Iridium is a member of the platinum group andIridium is a member of the platinum group and
is a noble metal.is a noble metal.

83
Ruthenium (Ru)Ruthenium (Ru)
 Ruthenium acts as a grain refiner for gold- andRuthenium acts as a grain refiner for gold- and
palladium- based alloys to improve theirpalladium- based alloys to improve their
mechanical properties and tarnish resistance (likemechanical properties and tarnish resistance (like
iridium).iridium).
 Ruthenium is a member of the palladium groupRuthenium is a member of the palladium group
and is a noble metal.and is a noble metal.

84
SilverSilver
 Silver lowers the melting range, improvesSilver lowers the melting range, improves
fluidity, and helps to control the coefficient offluidity, and helps to control the coefficient of
thermal expansion in gold- and palladium-basedthermal expansion in gold- and palladium-based
alloysalloys
 Silver-containing porcelain alloys have beenSilver-containing porcelain alloys have been
known to induce discoloration (yellow, brown,known to induce discoloration (yellow, brown,
or green) with some porcelains.or green) with some porcelains.

85
Silver (Contd)Silver (Contd)

Silver possesses a high affinity for oxygen absorption,Silver possesses a high affinity for oxygen absorption,
which can lead to casting porosity and/or gassing.which can lead to casting porosity and/or gassing.
 However, small amounts of zinc or indium added toHowever, small amounts of zinc or indium added to
gold- and silver-based alloys help to control silver'sgold- and silver-based alloys help to control silver's
absorption of oxygen.absorption of oxygen.
 Silver will also corrode and tarnish in the presence ofSilver will also corrode and tarnish in the presence of
sulfur. Although silver is a precious element, it is notsulfur. Although silver is a precious element, it is not
universally regarded as noble in the oral cavity .universally regarded as noble in the oral cavity .

86
AluminiumAluminium
 Aluminum is added to lower the melting rangeAluminum is added to lower the melting range
of nickel-based alloys.of 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 forWith the cobalt - chromium alloys used for
metal ceramic restorations, aluminum is one ofmetal ceramic restorations, aluminum is one of
the elements that is "etched" from the alloy'sthe elements that is "etched" from the alloy's
surface to create micromechanical retention forsurface to create micromechanical retention for
resin-bonded retainers (Maryland Bridges).resin-bonded retainers (Maryland Bridges).

87
BerylliumBeryllium
 Like aluminum, beryllium lowers the melting range ofLike aluminum, beryllium lowers the melting range of
nickel-based alloys, improves castability, improvesnickel-based alloys, improves castability, improves
polishability, is a hardener, and helps to control oxidepolishability, is a hardener, and helps to control oxide
formation.formation.
 The etching of nickel-chromium-beryllium alloysThe etching of nickel-chromium-beryllium alloys
removes a Ni-Be phase to create the micro retentionremoves a Ni-Be phase to create the micro retention
so important to the etched metal resin-bonded retainer.so important to the etched metal resin-bonded retainer.
 Questions have been raised as to potential health risksQuestions have been raised as to potential health risks
to both technicians and patients associated withto both technicians and patients associated with
beryllium-containing alloys .beryllium-containing alloys .

88
BoronBoron
 Boron is a deoxidizer.Boron is a deoxidizer.
 For nickel-based alloys, it is a hardening agentFor nickel-based alloys, it is a hardening agent
and an element that reduces the surface tensionand an element that reduces the surface tension
of the molten alloy to improve castability.of the 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 opposedcontain boron will pool on melting, as opposed
to the Ni-Cr-Be alloys that do not pool.to the Ni-Cr-Be alloys that do not pool.
 Boron also acts to reduce ductility and toBoron also acts to reduce ductility and to
increase hardness.increase hardness.

89
Chromium (Cr)Chromium (Cr)
 Chromium is a solid solution hardening agentChromium is a solid solution hardening agent
that contributes to corrosion resistance by itsthat contributes to corrosion resistance by its
passivating nature in nickel- and cobalt-basedpassivating nature in nickel- and cobalt-based
alloys.alloys.

90
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 a strengthenerthermal expansion and to act as a strengthener

91
Copper (Cu)Copper (Cu)
 Copper serves as a hardening and strengtheningCopper serves as a hardening and strengthening
agent, can lower the melting range of an alloy,agent, can lower the melting range of an alloy,
and interacts with platinum, palladium, silver,and interacts with platinum, palladium, silver,
and gold to provide a heat-treating capability inand gold to provide a heat-treating capability in
gold-, silver-, and palladium-based alloys.gold-, silver-, 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.

92
GalliumGallium (Ga)(Ga)
 Gallium is added to silver-free porcelain alloys toGallium is added to silver-free porcelain alloys to
compensate for the decreased coefficient ofcompensate for the decreased coefficient of
thermal expansion created by the removal ofthermal expansion created by the removal of
silver. (Concerns over silver's potential tosilver. (Concerns over silver's potential to
discolor dental porcelain have greatly limited itsdiscolor dental porcelain have greatly limited its
use in systems other than palladium-silver )use in systems other than palladium-silver )

93
IndiumIndium
 Indium serves many functions in gold-based metalIndium serves many functions in gold-based metal
ceramic alloys.ceramic alloys.
 It is a less volatile oxide-scavenging agent (to protectIt is a less volatile oxide-scavenging agent (to protect
molten alloy);molten alloy);
 lowers the alloy's melting range and density; improveslowers the alloy's melting range and density; improves
fluidity;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-silver)Alloys with a high silver content (eg, palladium-silver)
rely on indium to enhance tarnish resistance.rely on indium to enhance tarnish resistance.

94
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.

95
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.

96
Molybdenum (Mo)Molybdenum (Mo)
 Molybdenum improves corrosion resistance,Molybdenum improves corrosion resistance,
influences oxide production, and is helpful ininfluences oxide production, and is helpful in
adjusting the coefficient of thermal expansion ofadjusting the coefficient of thermal expansion of
nickel-based alloys.nickel-based alloys.

97
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 thermalalloys because its coefficient of thermal
expansion approximates that of gold and itexpansion approximates that of gold and it
provides resistance to corrosion.provides 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% andthe United States range from 9% to 31.9% and
from 0.8% to 20.7% among men .from 0.8% to 20.7% among men .

98
Tin (Sn)Tin (Sn)
 Tin is a hardening agent that acts to lower theTin is a hardening agent that acts to lower the
melting range of an alloy. It also assists in oxidemelting range of an alloy. It also assists in oxide
production for porcelain bonding in gold- andproduction for porcelain bonding in gold- and
palladium-based alloys. Tin is one of the keypalladium-based alloys. Tin is one of the key
trace elements for oxidation of the palladium-trace elements for oxidation of the palladium-
silver alloys.silver alloys.

99
Titanium (Ti)Titanium (Ti)
 Like aluminum and beryllium, titanium is addedLike aluminum and beryllium, titanium is added
to lower the melting range and improveto lower the melting range and improve
castability.castability.
 Titanium also acts as a hardener and influencesTitanium also acts as a hardener and influences
oxide formation at high temperatures.oxide formation at high temperatures.

100
Zinc (Zn)Zinc (Zn)
 Zinc helps lower the melting range of an alloyZinc helps lower the melting range of an alloy
and acts as a deoxidizer or scavenger to combineand acts as a deoxidizer or scavenger to combine
with other oxides.with other oxides.
 Zinc improves the castability of an alloy andZinc improves the castability of an alloy and
contributes to hardness when combined withcontributes to hardness when combined with
palladium.palladium.

101
Need For Dental casting alloysNeed For Dental casting alloys
 The Major factors areThe Major factors are
 Economy – The new materials perform the sameEconomy – The new materials perform the same
function as the old material but at the older costfunction as the old material but at the older cost
 Performance - The new materials perform better thanPerformance - The new materials perform better than
the old material in ease of processing improved handingthe old material in ease of processing improved handing
characters or increased fracture resistancecharacters or increased fracture resistance
 Esthetics – The new material provides more estheticEsthetics – The new material provides more esthetic
results such as increased translucencyresults such as increased translucency

102
Historical Perspective On DentalHistorical Perspective On Dental
Casting AlloysCasting Alloys
 This history of dental casting alloys has beenThis 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.

103
Casting Alloys (contd)Casting Alloys (contd)
 Taggarts presentation to the New York odontologicalTaggarts presentation to the New York odontological
group in 1907 on the fabrication of cast inlaygroup in 1907 on the fabrication of cast inlay
restorations often has been acknowledges as the firstrestorations often has been acknowledges as the first
reported application of the lost wax technique inreported application of the lost wax technique in
dentistry.dentistry.
 The inlay technique described by Taggarat was anThe inlay technique described by Taggarat was an
instant‘ success. It soon led to the casting of complexinstant‘ success. It soon led to the casting of complex
inlays such as on lays, crowns, fixed partial denturesinlays such as on lays, crowns, fixed partial dentures
and removable partial denture frame works.and removable partial denture frame works.
 Because pure gold did not have the physicalBecause pure gold did not have the physical
properties require of these dental restorations existingproperties require of these dental restorations existing
jewellery alloys were quickly adopted. These gold werejewellery alloys were quickly adopted. These gold were
further strengthened with Cu, Ag, or Ptfurther strengthened with Cu, Ag, or Pt

104
 1932, the dental materials group at the national1932, the dental materials group at the national
Bureau of standards surveyed the alloys beingBureau of standards surveyed the alloys being
used and roughly classified them as Type I, Typeused and roughly classified them as Type I, Type
II, Type III & Type IV.II, Type III & Type IV.
 At that time some tarnish tests indicated thatAt that time some tarnish tests indicated that
alloys with a gold content lower than 65% toalloys with a gold content lower than 65% to
75% furnished too readily for dental use75% furnished too readily for dental use

105
 By 1948, the composition of dental noble metalBy 1948, the composition of dental noble metal
alloys for east metal restorations has becomealloys for east metal restorations has become
rather diverse with these formulations, therather diverse with these formulations, the
furnishing tendency of the original alloysfurnishing tendency of the original alloys
apparently had disappeared.apparently had disappeared.

106
 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 rapidly thatIn 1978 the price of gold was climbing so rapidly that
attention focused on the noble metal alloys to reduceattention focused on the noble metal alloys to reduce
the precious metal content get retain the advantage ofthe precious metal content get retain the advantage of
noble metal for dental use.noble metal for dental use.

108
Desirable Properties Of CastingDesirable Properties Of Casting
Alloys: The metals must exhibitAlloys: The metals must exhibit
 1. Bio compatibility1. 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.

109
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

110
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)

111
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 no ble metal elementsno ble metal elements
Noble metalNoble metal >=25 wt% of no ble metal>=25 wt% of no ble metal
Predominantly base metalPredominantly base metal <25 wt% of the noble metal<25 wt% of the noble metal
elementselements

112
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% goldcolor, with greater than 60% gold
contentcontent
 White golds-White golds-
whitewhite color, but with more than 50%color, but with more than 50%
gold contentgold content

113
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 less thanusually yellow colored, with less than
60% gold (usually 42% to 55%)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 of goldmajor component; may contain small quantities of gold
(2%) and a limited amount of either copper or cobalt(2%) and a limited amount of either copper or cobalt

118
Metal Ceramic RestorationMetal Ceramic Restoration
 By Definition – Partial crown, full crown orBy Definition – Partial crown, full crown or
fixed partial denture made with a metal substratefixed partial denture made with a metal substrate
to which porcelain is bonded for estheticto which porcelain is bonded for esthetic
enhancement via an intermediate metal oxideenhancement via an intermediate metal oxide
layerlayer
 Also called as porcelain fused metal , porcelainAlso called as porcelain fused metal , porcelain
bonded to metal , porcelain to metal and ceramobonded to metal , porcelain to metal and ceramo
metalmetal

119
Need for metal ceramic alloysNeed for metal ceramic alloys
 The chief objection for the use of dental porcelain as restorativeThe chief objection for the use of dental porcelain as restorative
material is its low strength under tensile and shear, stressmaterial is its low strength under tensile and shear, stress
conditionsconditions
 A method by which this disadvantage can be minimized is toA method by which this disadvantage can be minimized is to
bond the porcelain directly to a cast alloy sub structure made tobond the porcelain directly to a cast alloy sub structure made to
fit the prepared toothfit 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 with thatPossess coefficient of thermal contraction compatible with that
of dental porcelainof dental porcelain
 Solidus temperature is sufficiently high to permit the aplicationSolidus temperature is sufficiently high to permit the aplication
of low fusing porcelainof low fusing porcelain

120
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 DuchateauDuchateau
 1774 -1774 - byby Duchateau,was introduced inDuchateau,was introduced in
England soon thereafterEngland soon thereafter byby de Chemant.de Chemant.

121
 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 in.the United States in
 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.

122
 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, who was the grandfatherLand, who was the grandfather ofof aviator Charlesaviator Charles
Lindbergh, described a technique for fabricatingLindbergh, 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.

123
 1962 - Weinstein et al , responsible for the patents of1962 - Weinstein et al , responsible for the patents of
long-standing superb aesthetic performance and clinicallong-standing superb aesthetic performance and clinical
survivability ,of metal-ceramic restaratians.survivability ,of metal-ceramic restaratians.
 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 allays that banded chemically ta andbe used to produce allays that banded chemically ta and
were thermally compatible with feldspathic porcelains.were thermally compatible with feldspathic porcelains.
 The first commercial porcelain was developed by VitaThe first commercial porcelain was developed by Vita
Zahnfabrik in about 1963Zahnfabrik in about 1963

124
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

125
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
restorationsrestorations

126
Noble Metal ContentNoble Metal Content
Indirectly denotes…..Indirectly denotes…..
 Corrosion resistance of the alloysCorrosion resistance of the alloys
 Inert properties of the alloysInert properties of the alloys

127
HardnessHardness
 Definition - Resistance of material to plasticDefinition - Resistance of material to plastic
deformationdeformation
 Important in relation to occlusal wear resistanceImportant in relation to occlusal wear resistance
and finishingand finishing
 affects polishing propertiesaffects polishing properties

128
Yield StrengthYield Strength
 The stress at which a test specimen exhibits aThe stress at which a test specimen exhibits a
specific amount of plastic strainspecific amount of plastic strain
 Necessary in determining Load Bearing abilityNecessary in determining Load Bearing ability
especially in FPD , since cross sectional area ofespecially in FPD , since cross sectional area of
metal used in PFM restoration are usuallymetal used in PFM restoration are usually
smaller than that of all metal restorationssmaller than that of all metal restorations

129
ElongationElongation
 Maximum amount of plastic strain a tensile testMaximum amount of plastic strain a tensile test
specimen can sustain it fracturesspecimen can sustain it fractures
 Related to Marginal finishing PropertiesRelated to Marginal finishing Properties
especially in Partial veneer crown and abutmentsespecially in Partial veneer crown and abutments

130
Fusion TemperatureFusion Temperature
 Temperature at which the metal solidifiesTemperature at which the metal solidifies
 Important in relation to SAG Resistance as it isImportant in relation to SAG Resistance as it is
necessary for the alloy to withstand temperaturesnecessary for the alloy to withstand temperatures
of the porcelain firing cycle.of the porcelain firing cycle.

131
Chemical PropertiesChemical Properties
 Tarnish ResistanceTarnish Resistance
 Corrosion ResistanceCorrosion Resistance

132
thermal propertiesthermal properties
 Critical for alloys used in PFM restorationsCritical for alloys used in PFM restorations
 Alloys must have sufficient elevated meltingAlloys must have sufficient elevated melting
Temperature range to provide dimensionalTemperature range to provide dimensional
stability during porcelain firing cyclestability during porcelain firing cycle
 Thermal creep results in distortions such as sagThermal creep results in distortions such as sag
in FPD frame work and margin opening duringin FPD frame work and margin opening during
porcelain firing cycleporcelain firing cycle

133
 Lab workability and Casting Accuracy – in orderLab workability and Casting Accuracy – in order
to provide clinically acceptable castingsto provide clinically acceptable castings

134
Bio CompatibilityBio Compatibility
Base metal alloys – Nickel (Ni) and BerylliumBase metal alloys – Nickel (Ni) and Beryllium
(Be)(Be)
 The occupational health and safetyThe occupational health and safety
administration (OSHA) specifies thatadministration (OSHA) specifies that
exposure to Beryllium dust in air should beexposure to Beryllium dust in air should be
limited to a concentration of 2 ug /meterlimited to a concentration of 2 ug /meter
cubecube

135
 The allowable maximumThe allowable maximum
concentration is 5 ug /meter cubeconcentration is 5 ug /meter cube
 Sensitivity – Contact dermatitisSensitivity – Contact dermatitis
with Nickel or Nickel containingwith Nickel or Nickel containing
alloysalloys

136
Porcelain Metal CompatibilityPorcelain Metal Compatibility
 Properties to consider when choosingProperties to consider when choosing
alloys for PFM restorationalloys for PFM restoration
 Thermal ExpansionThermal Expansion
 Bond strength of porcelain metalBond strength of porcelain metal
 CompositionComposition

137
Thermal ExpansionThermal Expansion
 Zero Residual Stress – desirable forZero Residual Stress – desirable for
porcelain fused to metal restorationsporcelain fused to metal restorations
and is achieved when total expansionand is achieved when total expansion
and contraction of porcelain and metaland contraction of porcelain and metal
are matched between porcelain firingare matched between porcelain firing
temperature and room temperaturetemperature and room temperature

138
Bond StrengthBond Strength
 Ensures retention of porcelain , bond to theEnsures retention of porcelain , bond to the
surface of metal through the formation ofsurface of metal through the formation of
surface oxide layer and in turn establishes thesurface oxide layer and in turn establishes the
longevity of the restorationslongevity of the restorations

139
CompositionComposition
 Key factor since components of alloy influencesKey factor since components of alloy influences
color of porcelaincolor of porcelain
 Can compromise esthetics of restorationsCan compromise esthetics of restorations
 Silver-color change causes greening of porcelainSilver-color change causes greening of porcelain
which occurs by exchange of silver from alloywhich occurs by exchange of silver from alloy
and sodium from porcelainand sodium from porcelain

141
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 Alloys thatFore Runner of improved High Gold Alloys that
remain as market today – Jelenko Oremain as market today – Jelenko O
 Composed principally of Gold and PlatinumComposed principally of Gold and Platinum
groupgroup

142
High gold alloysHigh gold alloys
 Gold content varies from 78% -87% by weight andGold content varies from 78% -87% by weight and
noble metal content is about 97%noble 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 tostrength and to promote a good porcelain bond to
metal oxidemetal oxide
 CostlyCostly
 Light yellow in color low tensile strength makes them aLight yellow in color low tensile strength makes them a
questionable choice for fixed partial denturesquestionable choice for fixed 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

143
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 for porcelainTrace elements like indium, iron, and tin for porcelain
bonding. (If the palladium content exceeds that ofbonding. (If the palladium content exceeds that of
platinum, then the alloys should be classified as Au-Pd-platinum, then the alloys should be classified as Au-Pd-
Pt.)Pt.)

144
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 color NotBiocompatible Some are yellow in color Not
"technique sensitive""technique sensitive"
 BurnishableBurnishable

145
Gold,Platinum,Palladium AlloysGold,Platinum,Palladium Alloys
(Contd)(Contd)
 Disadvantages;-Disadvantages;-
 High costHigh cost
 Poor sag resistance so not suited for long-spanPoor sag resistance so not suited for long-span
fixed partial denturesfixed partial dentures
 Low hardness (greaterLow hardness (greater wear)wear)
 High density (fewercastings per ounce)High density (fewercastings per ounce)

146
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%
Note :Note :
Like the Au-Pt-Pd alloys, trace amounts of oxidizableLike the Au-Pt-Pd alloys, trace amounts of oxidizable
elements are added for porcelain bondingelements are added for porcelain bonding..

147
(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

148
(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

149
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%
Note :Note :
Trace amounts of oxidizable elements forTrace amounts of oxidizable elements for
porcelein bondingporcelein bonding

150
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

151
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-silver group)discoloration (but less than high-silver group)

152
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%
Note :Note :
Iridium and tin are the oxidizable elements responsibleIridium and tin are the oxidizable elements responsible
for porcelain bondingfor porcelain bonding

153
 Excellent castabilityExcellent castability
 Good bond strengthGood bond strength
 Improved strength (sag resistance)Improved strength (sag resistance)
 Improved HardnessImproved Hardness
 Lower densityLower density

154
 Not thermally compatible with high expansionNot thermally compatible with high expansion
dental porcelainsdental porcelains

155
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)
Note :Note :
Trace elements of other oxidizable base elements areTrace elements of other oxidizable base elements are
also presentalso present

156
Palladium-Silver alloys (contd)Palladium-Silver alloys (contd)
 Good castability (whenGood castability (when
torch casting)torch casting)
 Good porcelain bondingGood porcelain bonding
 Excellent sag resistance)Excellent sag 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

157
Palladium-Silver alloys (contd)Palladium-Silver alloys (contd)
 High coefficient of thermalHigh coefficient of thermal
expansionexpansion
 Discoloration (yellow, brown,Discoloration (yellow, brown,
or green) may occur withor green) may occur with
some dental porcelainssome dental porcelains
 Some castability problemsSome castability problems
 Pd and Ag prone to absorbPd and Ag prone to absorb
gasesgases
 Require regular purgingRequire regular purging
of the porcelain furnaceof the 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

158
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% gold)(some high palladium-cobalt alloys may contain 2% gold)
Note:Note:
Trace amounts of oxidizable elements (such as galliumTrace amounts of oxidizable elements (such as gallium
and indium) are added for porcelain bonding.and indium) are added for porcelain bonding.

159
 Reportedly good sag resistanceReportedly good sag resistance
 Low density means moreLow density means more castings per ounce (thancastings per ounce (than
gold-based alloys) Some melt and cast easily Goodgold-based alloys) Some melt and cast easily Good
polishabilitypolishability
(supposed to be similar(supposed to be similar to Au-Pd alloys)to Au-Pd alloys)
 Reportedly easier to presolder than high Pd-Cu alloysReportedly easier to presolder than high Pd-Cu alloys

160
 More compatible with higher expansionMore compatible with higher expansion
porcelainsporcelains
 Some are more prone toSome are more prone to over-heating thanover-heating than
high Pd-Cu Produce a thick, dark oxidehigh Pd-Cu Produce a thick, dark oxide
Colored oxide layer may cause bluing ofColored oxide layer may cause bluing of
porcelainporcelain
 Prone to gas absorption Little information onProne to gas absorption Little information on
long-term clinical successlong-term clinical success

161
High Palladium-Silver-Gold alloysHigh Palladium-Silver-Gold alloys
 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)
Note :Note :
Trace amounts of oxidizabJe elements such asTrace amounts of oxidizabJe elements such as
indium and gallium.indium and gallium.

162
 AdvantagesAdvantages
 Improved sag resistance (better highImproved sag resistance (better high
temperature strength)temperature strength)
 Light-colored oxide layerLight-colored oxide layer

163
 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 prone toLike other palladium-based alloys are prone to
gaseous absorptiongaseous absorption
 Should not be cast in carbon cruciblesShould not be cast in carbon crucibles

164
High Palladium-Copper alloysHigh Palladium-Copper alloys
 Copper: 9%-15%Copper: 9%-15%
 Gold: 1 %-2% (if present)Gold: 1 %-2% (if present)
 Platinum: 1 % (if present)Platinum: 1 % (if present)
Note :Note :
 Some, but not all, high palladium-copper alloys containSome, but not all, high palladium-copper alloys contain
small quantities (1 %-3%) of gold and/or platinum.small quantities (1 %-3%) of gold and/or platinum.
 Trace amounts of the oxidizable elements gallium,Trace amounts of the oxidizable elements gallium,
indium, and tin are added for porcelain bonding.indium, and tin are added for porcelain bonding.

165
 Good castabilityGood castability
 Lower cost (thanLower cost (than gold-based alloys)gold-based alloys)
 Low density means more castings per ounceLow density means more castings per ounce
 Compatible with many dental porcelainsCompatible with many dental porcelains
 Some are available inSome are available in1-dwt ingots1-dwt ingots

166
 Produce dark, thick oxides May discolor (gray)Produce dark, thick oxides May discolor (gray)
some dental porcelainssome dental porcelains
 Must visually evaluate oxide color to determineMust visually evaluate oxide color to determine
if proper adherent oxide was formedif proper adherent oxide was formed
 Should not be cast in carbon crucibles (electricShould not be cast in carbon crucibles (electric
casting machines)casting machines)
 Prone to gaseousProne to gaseous absorptionabsorption

167
Disadvantages (Contd)Disadvantages (Contd)
 Subject to thermal creep (marginal opening)Subject to thermal creep (marginal opening)
 May not be suitable for long-span fixed partialMay not be suitable for long-span fixed partial
denturesdentures
 Little information onLittle information on long-term clinicallong-term clinical
successsuccess
 May be difficult to polishMay be difficult to polish
 Presoldering may be a problemPresoldering may be a problem
 High hardnessHigh hardness

168
Nickel-chromium-beryllium alloysNickel-chromium-beryllium alloys
 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 include, butNumerous minor alloying elements include, but
are not limited to: aluminum, carbon, gallium,are not limited to: aluminum, carbon, gallium,
iron, manganese, molybdenum, silicon, titanium,iron, manganese, molybdenum, silicon, titanium,
and/or vanadiumand/or vanadium

169
 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

170
 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 a learned skillProper melting and casting is a learned skill
 Bond failure more common in the oxide layerBond failure more common in the oxide layer
 High hardness (may wear opposing teeth) Difficult toHigh hardness (may wear opposing teeth) Difficult to
soldersolder
 Ingots do not poolIngots do not pool
 Difficult to cut through cemented castingsDifficult to cut through cemented castings

171
Nickel-chromium beryllium-freeNickel-chromium beryllium-free
alloysalloys
 Nickel: 62%-77%Nickel: 62%-77%
 Chromium: 11 %-22%Chromium: 11 %-22%
Boron (some), iron, molybdenum, niobium (orBoron (some), iron, molybdenum, niobium (or
colurr)ium), and/or tantalum.colurr)ium), and/or tantalum.

172
alloysalloys
 Do not contain berylliumDo not contain beryllium
 Low density means more castings per ounceLow density means more castings per ounce

173
alloysalloys
 Cannot use with nickel-sensitive patients CannotCannot use with nickel-sensitive patients Cannot
be etchedbe etched
 May not cast as well asMay not cast as well as Ni-Cr-Be alloysNi-Cr-Be alloys
 Produce more oxides thanProduce more oxides than Ni-Cr-Be alloysNi-Cr-Be alloys

174
Cobalt-chromium alloysCobalt-chromium alloys
 Cobalt: 53%-68%Cobalt: 53%-68%
 Chromium: 25%-34% / Trace elements includeChromium: 25%-34% / Trace elements include
molybdenum, ruthenium /(some) and/ormolybdenum, ruthenium /(some) and/or
wolfram.wolfram.

175
 Do not contain nickelDo not contain nickel
 Do not contain berylliumDo not contain beryllium
 Poor thermal conductorsPoor thermal conductors

176
 More difficult to process than nickel-base alloysMore difficult to process than nickel-base alloys
 High hardness (may wear the opposingHigh hardness (may wear the opposing
dentition)dentition)
 Oxidize more than bothOxidize more than both nickel-based alloysnickel-based alloys
 No information onNo information on long-term clinical studieslong-term clinical studies

177
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 grades of CPMaterials (ASTM), there are five unalloyed grades of CP
Ti (Grades 1-4, and Grade 7), based on the concentraTi (Grades 1-4, and Grade 7), based on the concentra
tion oftion 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 0.05 wtOther impurities include nitrogen (0.03 wt% to 0.05 wt
%),%),
 carbon (0.1 m%), and hydrogen (0.015 wt%).carbon (0.1 m%), and hydrogen (0.015 wt%).

178
 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 comparable toThe elastic modulus of CP Ti is comparable to
that of tooth enamel and noble alloys, but it isthat of tooth enamel and noble alloys, but it is
lower than that of other baselower than that of other base

179
 Casting of titanium alloys is difficult due to aCasting of titanium alloys is difficult due to a
high casting temperature – 2000 chigh casting temperature – 2000 c
 Rapid oxidation and reactions with investmentsRapid oxidation and reactions with investments
 Melting is done in specially designed furnacesMelting is done in specially designed furnaces
with an argon atmospherewith an argon atmosphere
 Ti-6Al-4v has been used for PFM restorationsTi-6Al-4v has been used for PFM restorations
 Used with low expansions porcelainsUsed with low expansions porcelains

180
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

181
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 --

182
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

192
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.

193
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.

194
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.

195
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).

196
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

197
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

198
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.

199
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.

200
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.

201
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

202
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.

Dental Materials: Metals and Metal Alloys Used in Dentistry

Dental Materials: Metals and Metal Alloys Used in Dentistry

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