metals and alloys in prosthodontics

Materials Science & Engineering Dept.
Research Experience for Undergraduates
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing Dental EducationLeader in continuing Dental Education

INTRODUCTION
DEFINITION
METALLURGY -TYPES
GENERAL CHARACTERISTICS OF
METALS
STRUCTURE AND PROPERTIES OF
METALS
CONTENTS
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 CRYSTALLINE STRUCTURE
 NUCLEI
 DENDRITES
 GRAIN
 GRAIN BOUNDARIES
 EQUIAXED GRAIN STRUCTURE
 LATTICE TYPES
 DISLOCATIONS
 SLIP PLANES

 QUENCHING
 REFINED GRAIN STRUCTURE
 SEEDING
COLD WORKING
 DUCTILITY
 MALLEABILITY
 COLD WORKING
 FIBROUS STRUCTURE
 WORK HARDENING
 RECRYSTALLIZATION TEMPERATURE
 GRAIN GROWTH
ANNEALING
 STRESS RELIEF ANNEALINGwww.indiandentalacademy.com

STRUCTURE AND PROPERTIES
OF ALLOYS
ALLOY
ALLOY SYSTEM
METALLOID
AMALGAM
BINARY
TERNARY
QUATERNARY

SOLID SOLUTION – PHASE
 SUBSTITUTIONAL SOLID SOLUTION
 INTERSTITIAL SOLID SOLUTION
 SOLUTION HARDENING
 (COOLING CURVE) TIME-TEMPERATURE CURVE
 CORED STRUCTURE
 CORING
 PHASE DIAGRAM
 LIQUIDUS LINE
 SOLIDUS LINE
 HOMOGENISATION
INTERMETALLIC COMPOUND
EUTECTIC FORMATION
PERITECTIC ALLOYS

CLASSIFICATION OF METALS
AND ALLOY SYSTEMS
DENTAL CASTING ALLOYS -
DESIRABLE PROPERTIES
AND USES

 NICKEL-CHROMIUM ALLOYS
 COBALT-CHROMIUM ALOYS (STELLITES)
TITANIUM AND TITANIUM ALLOYS
ALLOYS FOR METAL CERAMIC
RESTORATIONS
PARTIAL DENTURE ALLOYS

 WROUGHT ALLOYS
AND
GOLD ALLOYS
CARBON STEELS
STAINLESS STEEL
COBALT-CHROMIUM (ELGILOY) NICKEL ALLOYS
NICKEL-TITANIUM ALLOYS (NITINOL)
β-TITANIUM ALLOYS
GOLD ALLOYS
SILVER-PALLADIUM ALLOYS
DENTAL IMPLANT MATERIALS

BIOCOMPATIBILITY
CONCLUSION
REFERENCES

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GPT 8 (GPT 8 (20052005) defines “) defines “METALMETAL” as any” as any
strongstrong relativelyrelatively ductileductile substance thatsubstance that
providesprovides electropositive ionselectropositive ions to ato a
corrosive environment and that can becorrosive environment and that can be
polished to a highpolished to a high lustrelustre. Characterized. Characterized
byby metallic atomic bondingmetallic atomic bonding..

The metals handbookThe metals handbook ((19921992) defines a “metal as) defines a “metal as
an opaque lustrous chemical substance that is aan opaque lustrous chemical substance that is a
goodgood conductor of heatconductor of heat and electricity and,and electricity and,
whenwhen polishedpolished, is a, is a good reflector of lightgood reflector of light””

In dentistry,In dentistry, metalsmetals representrepresent one of the fourone of the four
major classes of materials used for themajor classes of materials used for the
reconstruction of decayed, damaged orreconstruction of decayed, damaged or
missing teeth.missing teeth.

The science and art of theThe science and art of the extractionextraction of metalsof metals
from theirfrom their oresores together with the refinement oftogether with the refinement of
thesethese metalsmetals and their adaption to variousand their adaption to various usesuses..
METALLURGYMETALLURGY

TheThe extensive useextensive use of metals and theirof metals and their
combination during recent years has madecombination during recent years has made
specializationspecialization in this field. This specializationin this field. This specialization
has resulted in the development ofhas resulted in the development of severalseveral
branchesbranches of metallurgy , some of which areof metallurgy , some of which are
closely associated withclosely associated with chemistry, physicschemistry, physics andand
mechanics.mechanics.

Understanding of metallurgy and theUnderstanding of metallurgy and the
characteristiccharacteristic behaviorbehavior of various metals, orof various metals, or
combination of metals to formcombination of metals to form alloysalloys, is, is
highlyhighly desirabledesirable in the study ofin the study of restorativerestorative
materialsmaterials for several reasons like :for several reasons like :
There areThere are numerous metalsnumerous metals which are used inwhich are used in
various restorative operations.various restorative operations.

A knowledge of the characteristic behaviorA knowledge of the characteristic behavior
of metals is essential for anof metals is essential for an understanding ofunderstanding of
the qualitythe quality of the restoration fabricated fromof the restoration fabricated from
metals.metals.
The properties that the metal or alloy willThe properties that the metal or alloy will
display are quiet reproducible and serve asdisplay are quiet reproducible and serve as
guide in the studyguide in the study of the many related issuesof the many related issues
to the fabrication of dental restorations.to the fabrication of dental restorations.

METALLURGYMETALLURGY
 CHEMICALCHEMICAL
 PHYSICALPHYSICAL
 MECHANICALMECHANICAL

Chemical metallurgy deals principally withChemical metallurgy deals principally with
the production andthe production and refinementrefinement of metals.of metals.
Sometimes it is described as “Sometimes it is described as “processprocess””
metallurgy since it considers themetallurgy since it considers the processingprocessing
of oresof ores for thefor the productionproduction of metals.of metals.
CHEMICAL METALLURGYCHEMICAL METALLURGY

PHYSICAL METALLURGYPHYSICAL METALLURGY
Physical metallurgy isPhysical metallurgy is newer sciencenewer science andand
deals with thedeals with the structurestructure of possibleof possible
alteration in structure as well as thealteration in structure as well as the
characteristic physical propertiescharacteristic physical properties of metals.of metals.
In some respects physical metallurgy andIn some respects physical metallurgy and
metallographymetallography are closely related.are closely related.

MetallographyMetallography is primarily theis primarily the microscopicmicroscopic
examination of theexamination of the internal structureinternal structure ofof
metals. This metallographic examinationmetals. This metallographic examination
gives somegives some indicationindication of theof the physicalphysical
behaviorbehavior which the metal can be expected towhich the metal can be expected to
exhibit.exhibit.

MECHANICAL METALLURGYMECHANICAL METALLURGY
It includes various processes in theIt includes various processes in the fabricationfabrication
of a structureof a structure such as thesuch as the castingcasting,, rollingrolling oror
drawingdrawing operations.operations.
InIn restorative materialsrestorative materials,, physical metallurgyphysical metallurgy
combined withcombined with metallographymetallography and theand the
mechanicalmechanical phase of metallurgy are ofphase of metallurgy are of greatestgreatest
importance.importance.

FERROUS METALLURGYFERROUS METALLURGY
It is the metallurgy ofIt is the metallurgy of ironiron andand steelsteel..
InIn dentistrydentistry it is important in connection withit is important in connection with
the manufacture and use ofthe manufacture and use of steel instrumentssteel instruments
andand equipmentsequipments as well asas well as stainless steelstainless steel
appliancesappliances..
FURTHER SUBDIVISIONS

NON-FERROUS METALLURGYNON-FERROUS METALLURGY
It is the metallurgy ofIt is the metallurgy of all metalall metal andand alloysalloys
other thanother than iron and steeliron and steel ..
E.g.E.g. : Gold alloys, platinum alloys,: Gold alloys, platinum alloys, Cr - CoCr - Co oror
stellite alloysstellite alloys, as well as bronze, aluminum,, as well as bronze, aluminum,
and low fusing alloys etc.,and low fusing alloys etc.,

General characteristics of metalsGeneral characteristics of metals
A metal is any element thatA metal is any element that ionizes positivelyionizes positively inin
solution.solution.
Metals have certainMetals have certain typicaltypical andand characteristiccharacteristic
propertiesproperties that tend to identify and distinguishthat tend to identify and distinguish
them from the nonmetallic elements, such asthem from the nonmetallic elements, such as
lustrelustre,, opacityopacity,, densitydensity,, thermalthermal andand electricalelectrical
conductivityconductivity.. www.indiandentalacademy.comwww.indiandentalacademy.com

ExtremeExtreme ductilityductility andand malleabilitymalleability are oftenare often
desirable in metals used in dentistry anddesirable in metals used in dentistry and
these are found tothese are found to predominatepredominate inin purepure
metalsmetals rather than in alloys.rather than in alloys.

STRUCTURE AND PROPERTIES OF
METALS
Metals usually have crystalline structures in the solid
state.

In 1665,In 1665, Robert HookeRobert Hooke ((1635 - 17031635 - 1703) simulated) simulated
the characteristic shapes of crystals by stackingthe characteristic shapes of crystals by stacking
musket balls in piles.musket balls in piles.
AA SPACE LATTICESPACE LATTICE can be defined ascan be defined as
any arrangement of atoms in space such thatany arrangement of atoms in space such that
every atom isevery atom is situated similarlysituated similarly to every otherto every other
atom. It is also called aatom. It is also called a crystalcrystal..

There areThere are 1414 possible lattice types or forms, butpossible lattice types or forms, but
many of the metals used in dentistry belong to themany of the metals used in dentistry belong to the
cubic systemcubic system arrangement.arrangement.
 Simple cubic space latticeSimple cubic space lattice
 Single cells of cubic space latticeSingle cells of cubic space lattice
 Simple cubicSimple cubic
 Face-centered cubicFace-centered cubic
 Body-centered cubicBody-centered cubic
 ModelsModels

Other simple lattice types of dental interest.Other simple lattice types of dental interest.
A) RhombohedralA) Rhombohedral b) Orthorhombicb) Orthorhombic
c) Monoclinicc) Monoclinic d) Triclinic e) Tetragonald) Triclinic e) Tetragonal
f) Simple hexagonalf) Simple hexagonal
g) Close packed hexagonal h) rhombic.g) Close packed hexagonal h) rhombic.

When a molten metal or alloy is cooled, the
solidification process is one of crystallization
and is initiated at specific sites called nucleinuclei. The
nuclei are formed from impurities within the
molten mass of metal.

Crystals grow as dendrites, which can be
described as three-dimensional, branched
network structures emanating from the central
nucleus

Crystal growth continue until all the material has
solidified and all the dendritic crystals are in
contact.

Each crystal is known as a graingrain and the area
between two grains in contact is the graingrain
boundaryboundary

After crystallization, the grains, haveAfter crystallization, the grains, have
approximately theapproximately the same dimensionssame dimensions inin eacheach
direction, measureddirection, measured from thefrom the central nucleuscentral nucleus..
They areThey are notnot perfectly spherical or cubicperfectly spherical or cubic
however,however, nornor do theydo they conformconform to any otherto any other
geometric shapegeometric shape. They are said to have an. They are said to have an
equiaxed grain structure..

A change from anA change from an equiaxed structureequiaxed structure to one into one in
which the grains have a more elongated,which the grains have a more elongated, fibrousfibrous
structurestructure can cause importantcan cause important changes inchanges in
mechanical properties.mechanical properties.

The arrangement adopted by any oneThe arrangement adopted by any one
crystal depends on specific factors such ascrystal depends on specific factors such as
atomic radiusatomic radius andand charge distributionscharge distributions onon
the atoms. Although there is a tendencythe atoms. Although there is a tendency
towards a perfect crystal structure,towards a perfect crystal structure,
occasionaloccasional defectsdefects occur.occur.

Such defects are normally referred to asSuch defects are normally referred to as
dislocationsdislocations and their occurrence has anand their occurrence has an
effect on theeffect on the ductilityductility of the metal or alloy.of the metal or alloy.

When the material is placed under a sufficientlyWhen the material is placed under a sufficiently
high stress the dislocation is able to movehigh stress the dislocation is able to move
through the lattice until it reaches a grainthrough the lattice until it reaches a grain
boundary. Theboundary. The planeplane along which the dislocationalong which the dislocation
moves is called amoves is called a slip plane and the stressand the stress
required to initiate movement is therequired to initiate movement is the elastic limitelastic limit..

Grain boundariesGrain boundaries form aform a natural barriernatural barrier to theto the
movement ofmovement of dislocationsdislocations. The concentration of. The concentration of
grain boundaries increases as the grain sizegrain boundaries increases as the grain size
decreases.decreases. Metals with finer grain structure areMetals with finer grain structure are
generally harder and have higher values ofgenerally harder and have higher values of
elastic limit than those with coarser grainelastic limit than those with coarser grain
structure.structure. Hence it can be seen that materialHence it can be seen that material
properties can be controlled to some extent byproperties can be controlled to some extent by
controlling the grain sizecontrolling the grain size..

AA fine grain structurefine grain structure can be achieved bycan be achieved by rapidrapid
cooling of the molten metalcooling of the molten metal or alloy followingor alloy following
casting. This process, often referred to ascasting. This process, often referred to as
quenchingquenching, ensures that many nuclei of, ensures that many nuclei of
crystallization are formed, resulting in acrystallization are formed, resulting in a largelarge
numbernumber ofof relatively small grainsrelatively small grains..

Slow coolingSlow cooling causes relativelycauses relatively few nucleifew nuclei to beto be
formed which results in aformed which results in a larger grain sizelarger grain size..
Some metals and alloys are said to have aSome metals and alloys are said to have a refinedrefined
grain structure.grain structure. This is normally a fine grainThis is normally a fine grain
structure which is achieved bystructure which is achieved by seedingseeding thethe
molten metal with anmolten metal with an additive metaladditive metal which formswhich forms
nuclei crystallizationnuclei crystallization..

For an appliedFor an applied tensile forcetensile force thethe maximum degreemaximum degree
of extensionof extension is a measure theis a measure the ductilityductility of theof the
metal or alloy.metal or alloy.
For an appliedFor an applied compressive forcecompressive force thethe maximummaximum
degree of compressiondegree of compression is a measure ofis a measure of
malleabilitymalleability..
These changes occur when the stress is greaterThese changes occur when the stress is greater
than the elastic limit and atthan the elastic limit and at relatively lowrelatively low
temperaturestemperatures..
COLD WORKINGCOLD WORKING

Such cold working not only produces aSuch cold working not only produces a changechange
in microstructurein microstructure, with dislocations becoming, with dislocations becoming
concentrated at grain boundaries, but also aconcentrated at grain boundaries, but also a
change in grain shapechange in grain shape..
The grains areThe grains are no longer equiaxedno longer equiaxed but take up abut take up a
moremore fibrousfibrous..

Cold workingCold working is sometimes referred to asis sometimes referred to as workwork
hardeninghardening due to the effect on mechanicaldue to the effect on mechanical
properties. When mechanical work is carried outproperties. When mechanical work is carried out
on a metal or alloy at a moreon a metal or alloy at a more elevatedelevated
temperaturetemperature it is possible for the object to changeit is possible for the object to change
shapeshape withoutwithout any alteration in grain shape orany alteration in grain shape or
mechanical properties.mechanical properties.

The temperatureThe temperature belowbelow whichwhich work hardening iswork hardening is
possiblepossible is termed theis termed the recrystallizationrecrystallization
temperature.temperature.
If the material is maintained above theIf the material is maintained above the
recrystallization temperature for sufficient time,recrystallization temperature for sufficient time,
diffusion of atomsdiffusion of atoms across grain boundaries mayacross grain boundaries may
occur, leading tooccur, leading to grain growthgrain growth..
 It is clear that grain growth should beIt is clear that grain growth should be avoidedavoided ifif
the properties arethe properties are not to be adverselynot to be adversely affected.affected.

It is process ofIt is process of heatingheating a metal toa metal to reverse thereverse the
effectseffects associated with cold working such asassociated with cold working such as strainstrain
hardening, low ductilityhardening, low ductility andand distorted grains.distorted grains.
In general it hasIn general it has 33 stages.stages.
1)1) RRecoveryecovery
2)2) RRecrystallizationecrystallization
3)3) GGrain growth.rain growth.
AnnealingAnnealing

 RecoveryRecovery : is considered the stage at: is considered the stage at
which thewhich the coldwork properties begin tocoldwork properties begin to
disappeardisappear before any significant visiblebefore any significant visible
changes are observed under thechanges are observed under the
microscope.microscope.

 RecrystallizationRecrystallization ::
when a severely cold worked metal iswhen a severely cold worked metal is
annealed, recrystallization occurs after theannealed, recrystallization occurs after the
recovery stage. Therecovery stage. The old grains disappearold grains disappear
completely and arecompletely and are placed by a new set ofplaced by a new set of
strain free grainsstrain free grains..

 Grain growthGrain growth::
The crystallized structure has a certainThe crystallized structure has a certain
average grain sizeaverage grain size, depending on the, depending on the
number of nuclei .Thenumber of nuclei .The more severemore severe thethe
cold working, thecold working, the greater the numbergreater the number ofof
such nuclei. Thus, the grain size forsuch nuclei. Thus, the grain size for
completely recrystallized material cancompletely recrystallized material can
range from ratherrange from rather finefine toto fairly coarsefairly coarse..

 Cold working may cause the formation ofCold working may cause the formation of
internal stressesinternal stresses within a metal object. If thesewithin a metal object. If these
stresses are gradually relieved they may causestresses are gradually relieved they may cause
distortiondistortion which could lead towhich could lead to loss of fitloss of fit of, forof, for
exampleexample, an orthodontic appliance., an orthodontic appliance.
 For certain metals and alloys theFor certain metals and alloys the internal stressesinternal stresses
can becan be whollywholly oror partly eliminatedpartly eliminated by using aby using a
low temperature heat treatmentlow temperature heat treatment referred to asreferred to as
stress relief annealingstress relief annealing..

 This heat treatment is carried out wellThis heat treatment is carried out well belowbelow thethe
recrystallization temperaturerecrystallization temperature and hasand has nono
deleterious effectdeleterious effect onon mechanical propertiesmechanical properties sincesince
the original grain structure is maintained.the original grain structure is maintained.

STRUCTURE AND PROPERTIES OFSTRUCTURE AND PROPERTIES OF
ALLOYSALLOYS
 AnAn alloyalloy is a mixture ofis a mixture of two or more metalstwo or more metals..
Mixtures ofMixtures of twotwo metals are termedmetals are termed Binary alloysBinary alloys,,
mixtures ofmixtures of three metalsthree metals areare Ternary alloysTernary alloys
similarly mixture ofsimilarly mixture of four metalsfour metals is termed asis termed as
Quaternary alloysQuaternary alloys etc.etc.
 The termThe term alloy systemalloy system refers to all possiblerefers to all possible
compositions of an alloy. Forcompositions of an alloy. For exampleexample thethe silver-silver-
copper systemcopper system refers to all alloys withrefers to all alloys with
compositions ranging betweencompositions ranging between 100% silver100% silver andand
100% copper100% copper.. www.indiandentalacademy.comwww.indiandentalacademy.com

 In the molten state metals usually showIn the molten state metals usually show
mutual solubilitymutual solubility, one within another., one within another.
When the molten mixture isWhen the molten mixture is cooledcooled toto
below the melting pointbelow the melting point the followingthe following
things can occur.things can occur.
 The component metals mayThe component metals may remainremain
soluble in each othersoluble in each other forming aforming a solidsolid
solutionsolution.. www.indiandentalacademy.comwww.indiandentalacademy.com

 The solid solution may take one ofThe solid solution may take one of threethree
formsforms. It may be a. It may be a random solid solutionrandom solid solution
in which the component metal atomsin which the component metal atoms
occupyoccupy random sitesrandom sites in a common crystalin a common crystal
lattice.lattice.

Another possibility is the formation of anAnother possibility is the formation of an
ordered solid solutionordered solid solution in which component metalin which component metal
atoms occupyatoms occupy specific sitesspecific sites within a commonwithin a common
crystal lattice.crystal lattice.

The third type of solid solution is theThe third type of solid solution is the interstitialinterstitial
solid solutionsolid solution in which, for binary alloys, thein which, for binary alloys, the
primary lattice sites are occupied by one metalprimary lattice sites are occupied by one metal
atomatom and theand the atoms of the second component doatoms of the second component do
not occupy lattice sites but lie within thenot occupy lattice sites but lie within the
interstices of the latticeinterstices of the lattice. This is normally found. This is normally found
where thewhere the atomic radiusatomic radius of one component isof one component is
muchmuch smallersmaller than that of the other.than that of the other.

Solid solutions are generallySolid solutions are generally harder, strongerharder, stronger andand
havehave higher valueshigher values of elastic limit than the pureof elastic limit than the pure
metals from which they are derived. This explainsmetals from which they are derived. This explains
why pure metals are rarely usedwhy pure metals are rarely used..
The hardening effect, known asThe hardening effect, known as solutionsolution
hardeninghardening, is thought to be due to the fact that, is thought to be due to the fact that
atoms of different atomic radii within the sameatoms of different atomic radii within the same
lattice form a mechanical resistance to thelattice form a mechanical resistance to the
movement of dislocations along slip planes.movement of dislocations along slip planes.

Metals and alloys are sometimes characterizedMetals and alloys are sometimes characterized
usingusing cooling curvescooling curves. The material is heated till. The material is heated till
molten then allowed to cool and amolten then allowed to cool and a plot ofplot of
temperature against timetemperature against time is recorded.is recorded.
 Super coolingSuper cooling
 Heterogeneous NucleationHeterogeneous Nucleation

 Each alloy grain can be envisaged as having aEach alloy grain can be envisaged as having a
concentration of gradient metals; the higherconcentration of gradient metals; the higher
melting metal being concentrated close to themelting metal being concentrated close to the
nucleus and the lower melting metal close to thenucleus and the lower melting metal close to the
grain boundaries. The material is said to have agrain boundaries. The material is said to have a
cored structure..
 SuchSuch coring may influencemay influence corrosion resistancecorrosion resistance
sincesince electrolytic cellselectrolytic cells may be set up on themay be set up on the
surface of the alloy between areas of differentsurface of the alloy between areas of different
alloy composition.alloy composition.

Since coring may markedly reduce the corrosionSince coring may markedly reduce the corrosion
resistance of some alloys, aresistance of some alloys, a heat treatmentheat treatment isis
some times used to eliminate the cored structure.some times used to eliminate the cored structure.
Such a heat treatment is termed aSuch a heat treatment is termed a homogenizationhomogenization
heat treatmentheat treatment..
This involvesThis involves heating the alloyheating the alloy to a temperatureto a temperature
just below the solidus temperaturejust below the solidus temperature for a fewfor a few
minutes to allow diffusion of atoms and theminutes to allow diffusion of atoms and the
establishment of homogeneous structure. Theestablishment of homogeneous structure. The
alloy is then normallyalloy is then normally quenchedquenched in order toin order to
prevent grain growthprevent grain growth from occurring.from occurring.
E.g., Au-Ag system.E.g., Au-Ag system.

If the temperaturesIf the temperatures TT11 andand TT22 are obtained overare obtained over
a range of compositions for ana range of compositions for an alloy systemalloy system andand
their values plotted against percentagetheir values plotted against percentage
composition, acomposition, a useful graph emergesuseful graph emerges..

This is illustrated for aThis is illustrated for a hypothetical solid solutionhypothetical solid solution alloyalloy
ofof metals Ametals A andand BB. The melting points of the pure metals. The melting points of the pure metals
are indicated by the temperaturesare indicated by the temperatures TTmAmA andand TTmBmB. The. The
upper and lower temperature limits of the crystallizationupper and lower temperature limits of the crystallization
range,range, TT11 andand TT22 are shown for four alloys ranging inare shown for four alloys ranging in
composition fromcomposition from 80% A80% A –– 20% B20% B toto 20% A20% A -- 80% B80% B..

TheThe phase diagramphase diagram is completed byis completed by joiningjoining
together all thetogether all the T1 pointsT1 points and all theand all the T2 pointsT2 points,,
together with the melting points of the puretogether with the melting points of the pure
metals,metals, TTmAmA andand TTmBmB..
At temperatures in the region above the top line,At temperatures in the region above the top line,
known as theknown as the liquidus line, the alloy is, the alloy is totallytotally
liquidliquid. At temperatures in the region below the. At temperatures in the region below the
bottom line, known as thebottom line, known as the Solidus line,, the alloythe alloy
isis totally solidtotally solid..

At temperatures in the regionAt temperatures in the region betweenbetween the solidusthe solidus
and liquidus lines the alloy consists of aand liquidus lines the alloy consists of a mixturemixture
of solid and liquidof solid and liquid. The composition of the solid. The composition of the solid
and liquid phases at any temperature betweenand liquid phases at any temperature between TT11
andand TT22 can be predicted with the aid of thecan be predicted with the aid of the phasephase
diagram.diagram.

When two metals areWhen two metals are completely misciblecompletely miscible inin
liquid state, they are capable of forming anyliquid state, they are capable of forming any
alloy. When such a combination isalloy. When such a combination is cooledcooled, one, one
of the three possibilities may take place :of the three possibilities may take place :
a)a) SSolid solutionolid solution
b)b) IIntermetallic compoundntermetallic compound
c)c) EEutectic formationutectic formation

Intermetallic compoundsIntermetallic compounds
Chemicals withChemicals with chemical affinitychemical affinity for each otherfor each other
can form intermetallic compounds.can form intermetallic compounds.
E.g.,E.g., Ag3SnAg3Sn can be formed between silver andcan be formed between silver and
tin, which is antin, which is an essential constituentessential constituent ofof
DENTAL AMALGAM ALLOYSDENTAL AMALGAM ALLOYS..

Eutectic mixtureEutectic mixture
They occur when the metals areThey occur when the metals are miscible in themiscible in the
liquid stateliquid state but separate in the solid statebut separate in the solid state. The. The
two metals will be precipitated astwo metals will be precipitated as very finevery fine
layers of one metal over the other onelayers of one metal over the other one : such a: such a
combination as is called ancombination as is called an eutectic mixtureeutectic mixture..
E.g.,E.g.,72 %72 % silver,silver, 28 %28 % copper.copper.

Phase diagramPhase diagram for a Binary system where therefor a Binary system where there
Is complete solid insolubility.Is complete solid insolubility.
 CEF
 CDEGF
 ‘E’

A material of this composition is called aA material of this composition is called a
““Eutectic alloy””
 Important featuresImportant features ::
 HardHard andand BrittleBrittle
 Lowest meltingLowest melting alloy of the system -alloy of the system - solderssolders
 PoorPoor corrosion resistancecorrosion resistance
 Time-temperature curveTime-temperature curve for this alloy has afor this alloy has a
““Horizontal plateauHorizontal plateau” (like that of a” (like that of a pure metalpure metal))

Peritectic alloysPeritectic alloys
Limited solubilityLimited solubility of two metals can lead to aof two metals can lead to a
transformation referred as “transformation referred as “Peritectic transformationPeritectic transformation””
E.g.,E.g., Ag-SnAg-Sn
(Basis for the original Dental Amalgam alloy, is a(Basis for the original Dental Amalgam alloy, is a
Peritectic systemPeritectic system))
Invariant reactionInvariant reaction occurs at particularoccurs at particular temperaturetemperature andand
composition.composition.

CLASSIFICATIONCLASSIFICATION
OFOF
METALS AND ALLOY SYSTEMSMETALS AND ALLOY SYSTEMS

Metals can beMetals can be broadlybroadly classified according toclassified according to
composition ascomposition as
NOBLE METALSNOBLE METALS
The termThe term noblenoble identifies elements in terms of theiridentifies elements in terms of their
chemical stabilitychemical stability i.e., theyi.e., they resist oxidationresist oxidation and areand are
impervious to acidsimpervious to acids..
GGold,old, PPlatinum,latinum, PPalladium,alladium, RRhodium,hodium, RRuthenium,uthenium,
IIridium,ridium, OOsmium, andsmium, and SSilver are theilver are the eight nobleeight noble
metals.metals.
 In the oral cavityIn the oral cavity Silver is more reactiveSilver is more reactive andand
therefore istherefore is not considerednot considered as a noble metal.as a noble metal.

PRECIOUS METALSPRECIOUS METALS
The term “The term “preciousprecious” merely indicates whether a” merely indicates whether a
metal hasmetal has intrinsic valueintrinsic value, the noble metals (all eight), the noble metals (all eight)
are also precious metals and are defined as such byare also precious metals and are defined as such by
majormajor metallurgical societiesmetallurgical societies and theand the federalfederal
government agenciesgovernment agencies likelike National institute ofNational institute of
science and technology.science and technology.
 All noble metals are preciousAll noble metals are precious butbut all precious metalsall precious metals
are not nobleare not noble..
 SilverSilver is usually the major ingredient in most alloysis usually the major ingredient in most alloys
considered asconsidered as preciousprecious..

SEMIPRECIOUS METALSSEMIPRECIOUS METALS
There isThere is no accepted compositionno accepted composition that differentiatesthat differentiates
“precious from semiprecious” therefore, this“precious from semiprecious” therefore, this termterm isis
usuallyusually avoided.avoided.

BASE METALS
These areThese are IgnobleIgnoble elements. These remainelements. These remain
invaluable componentsinvaluable components ofof dental casting alloysdental casting alloys
because of their influence onbecause of their influence on physical propertiesphysical properties,,
control of the amountcontrol of the amount andand type of oxidationtype of oxidation, or, or
for theirfor their strengthening effectsstrengthening effects..
e.g., Chromium,e.g., Chromium, CCobalt,obalt, NNickel,ickel, IIron,ron, CCopperopper
etc.etc.

The bureau of standards establishedThe bureau of standards established gold casting alloysgold casting alloys
type i through type ivtype i through type iv according to function, withaccording to function, with
increasing hardnessincreasing hardness from type i to iv (from type i to iv (19271927))

InIn 19841984,, ADAADA proposed a simple classification forproposed a simple classification for
Dental casting alloysDental casting alloys

Alloy types by description

Removable partial denture alloysRemovable partial denture alloys
Although type IV noble metal alloys may beAlthough type IV noble metal alloys may be
used, majority of the removable partial frameused, majority of the removable partial frame
works are made from base metal alloys.works are made from base metal alloys.
E.g.,E.g., CCobalt-obalt-cchromium,hromium,
NNickel-ickel-cchromium.hromium.

DENTAL CASTING ALLOYS
The history of dental casting alloys has beenThe history of dental casting alloys has been
influenced byinfluenced by threethree major factors.major factors.
a)a) TThe technological changes of dental prosthesis.he technological changes of dental prosthesis.
b)b) MMetallurgic advancementsetallurgic advancements
c)c) PPrice changes of noble metals sincerice changes of noble metals since19681968..
InIn 19321932, the dental materials group at national, the dental materials group at national
bureau of standards surveyed thebureau of standards surveyed the alloysalloys being usedbeing used
and roughly classified themand roughly classified them typetype I-IVI-IV..

UsesUses
1)1) Fabrication of inlay, onlaysFabrication of inlay, onlays
2)2) Fabrication of crowns, conventional all metalFabrication of crowns, conventional all metal
bridges, metal-ceramic bridges, resin bondedbridges, metal-ceramic bridges, resin bonded
bridges.bridges.
3)3) Endodontic posts.Endodontic posts.
4)4) Removable partial denture frameworks.Removable partial denture frameworks.

Desirable propertiesDesirable properties
1) Biocompatibility.1) Biocompatibility.
2) Ease of melting.2) Ease of melting.
3) Ease of casting, brazing and polishing.3) Ease of casting, brazing and polishing.
4) Less solidification shrinkage.4) Less solidification shrinkage.
5) Minimal reactivity with the mould material.5) Minimal reactivity with the mould material.
6) Good wear resistance.6) Good wear resistance.
7) High strength and sag resistance.7) High strength and sag resistance.
8) Excellent tarnish and corrosion resistance.8) Excellent tarnish and corrosion resistance.www.indiandentalacademy.comwww.indiandentalacademy.com

Nickel-chromium and Cobalt-chromium
Alloys
Dental applications:Dental applications:
1)1) Partial denture framework:Partial denture framework: Co-CrCo-Cr,, Ni-CrNi-Cr
2)2) Porcelain - metal restorations:Porcelain - metal restorations: Co-CrCo-Cr,, Ni-CrNi-Cr
3)3) Crowns and bridges:Crowns and bridges: Ni-CrNi-Cr

During the years since theDuring the years since the Co-Cr casting alloysCo-Cr casting alloys
became available for cast removable partialbecame available for cast removable partial
denture constructions, they have continued todenture constructions, they have continued to
increase inincrease in popularitypopularity..

Function of various alloying elements:Function of various alloying elements:
• Chromium is responsible for theChromium is responsible for the tarnish resistancetarnish resistance
and stainless properties of these alloys.and stainless properties of these alloys.
• When chromium content of alloy is overWhen chromium content of alloy is over 30%30% , the, the
alloy isalloy is difficultdifficult to cast. With this percentage ofto cast. With this percentage of
chromium, the alloy also forms achromium, the alloy also forms a brittle phasebrittle phase, known, known
asas sigma phasesigma phase. Therefore cast base metal dental. Therefore cast base metal dental
alloys shouldalloys should notnot contain more thancontain more than 28-29%28-29% ofof
chromium.chromium.

• CobaltCobalt increases the elastic modulus, strength andincreases the elastic modulus, strength and
hardness of alloy more than does nickel.hardness of alloy more than does nickel.
• One of the effective ways of increasing their hardness isOne of the effective ways of increasing their hardness is
byby alteringaltering carbon content.carbon content.
0.2% increase0.2% increase changes the properties such thatchanges the properties such that
alloy would no longer be used in dentistry.alloy would no longer be used in dentistry.
[[Too brittleToo brittle]]
0.2% decrease0.2% decrease willwill reducereduce yield and ultimateyield and ultimate
tensile and yield strengths.tensile and yield strengths.

• AluminumAluminum in nickel containing alloysin nickel containing alloys increasesincreases thethe
ultimate tensile and yield strengths.ultimate tensile and yield strengths.
MicrostructureMicrostructure
Microstructure of any substance is the basicMicrostructure of any substance is the basic
parameter thatparameter that controls the propertiescontrols the properties. In other words,. In other words,
aa change in the physical propertieschange in the physical properties of material is aof material is a
strong indication that there must have been somestrong indication that there must have been some
alteration in its microstructure.alteration in its microstructure.

The microstructure of Co-Cr alloys in the castThe microstructure of Co-Cr alloys in the cast
condition is incondition is in homogeneoushomogeneous, consisting of an, consisting of an
austenitic matrixaustenitic matrix composed of a solid solution ofcomposed of a solid solution of
cobalt and chromium in a casedcobalt and chromium in a cased dendriticdendritic
structurestructure. The dendritic regions are. The dendritic regions are cobalt-richcobalt-rich,,
where as the interdendritic regions can be awhere as the interdendritic regions can be a
quaternary mixture.quaternary mixture.

ThreeThree mainmain disadvantagesdisadvantages in employing these alloysin employing these alloys
((Co-CrCo-Cr))
Clasps made of such alloysClasps made of such alloys break in servicebreak in service; some; some
break after relatively short time.break after relatively short time.
Due to relativelyDue to relatively high hardnesshigh hardness andand low elongationlow elongation
properties of these alloys someproperties of these alloys some minorminor but necessarybut necessary
adjustmentsadjustments needed at the time of delivery areneeded at the time of delivery are
difficult and also willdifficult and also will consumeconsume the chair time ofthe chair time of
dentist.dentist.
Due to theirDue to their high degree of hardnesshigh degree of hardness, the, the teethteeth
contacting the metal becomescontacting the metal becomes wornworn easily.easily.

MorrisMorris 19751975 stated thatstated that Co-Cr alloysCo-Cr alloys areare harderharder
than iron base alloys .than iron base alloys .
InIn 19791979, he stated that, he stated that heat treatmentheat treatment decreasesdecreases
strengthstrength of the alloy compared to Au-Pd alloys.of the alloy compared to Au-Pd alloys.
J.C. Wataha et.alJ.C. Wataha et.al,, 19921992 stated thatstated that preparativepreparative
proceduresprocedures such as steam sterilization,such as steam sterilization,
irradiation, plasma treatment and acid treatmentirradiation, plasma treatment and acid treatment
altered the surfacealtered the surface of alloys.of alloys.

InIn 19741974,, A C RoweA C Rowe stated that addingstated that adding TantalumTantalum
(13%)(13%) to a Co-Cr-Ni alloy the properties like ultimateto a Co-Cr-Ni alloy the properties like ultimate
tensile strength, yield strength are increased by 12-tensile strength, yield strength are increased by 12-
13%.13%. Tantalum reduces dislocationsTantalum reduces dislocations, a, a well orderedwell ordered
structurestructure is formed. Tantalum is ais formed. Tantalum is a stabilizerstabilizer. Example. Example
for stabilizers arefor stabilizers are carbon, molybdenum, tungsten.carbon, molybdenum, tungsten.
Hamid MohammadHamid Mohammad andand Kamal asgarKamal asgar 19731973, indicated, indicated
that a cobalt made from 40% Co, 30% Ni, 30% Crthat a cobalt made from 40% Co, 30% Ni, 30% Cr
strengthenedstrengthened by precipitation of coherent Intermetallicby precipitation of coherent Intermetallic
compounds of Tantalum.compounds of Tantalum.

They also haveThey also have criteriacriteria to select an additional elementto select an additional element
1)1) CCorrosion resistance.orrosion resistance.
2)2) RResistance to oxidation during alloying.esistance to oxidation during alloying.
3)3) EEfficiency as a nucleating agent during solidification.fficiency as a nucleating agent during solidification.
4)4) EEfficiency as a solid solution hardener.fficiency as a solid solution hardener.
5)5) FFineness of precipitate.ineness of precipitate.
6)6) CCoherency.oherency.

Titanium And Titanium Alloys:Titanium And Titanium Alloys:
Titanium’sTitanium’s resistance to electrochemicalresistance to electrochemical
degradationdegradation; the; the benign biological responsebenign biological response that itthat it
elicits; itselicits; its relatively low weightrelatively low weight; and its; and its lowlow
densitydensity,, low moduluslow modulus, and, and high strengthhigh strength makemake
titanium based materials attractive for use intitanium based materials attractive for use in
dentistry.dentistry.

Ti forms a veryTi forms a very stable oxidestable oxide layer with a thicknesslayer with a thickness
on the order of angstroms and iton the order of angstroms and it repassivatesrepassivates in ain a
time on the order of nanoseconds. This oxidetime on the order of nanoseconds. This oxide
formation is the basis for theformation is the basis for the corrosion resistancecorrosion resistance
andand biocompatibilitybiocompatibility of Ti.of Ti.
Commercially Pure TitaniumCommercially Pure Titanium ((CpTiCpTi) is used for) is used for
fabricatingfabricating dental implantsdental implants, and more recently, as, and more recently, as
crowns, partial and complete dentures,crowns, partial and complete dentures, andand
orthodontic wiresorthodontic wires..
Wrought alloys of Ti and V and of Ti and Mo areWrought alloys of Ti and V and of Ti and Mo are
used for orthodontic wires.used for orthodontic wires.

Commercially pure Ti is available inCommercially pure Ti is available in 4 grades4 grades whichwhich
vary according to thevary according to the OxygenOxygen (0.18-0.40 wt%) and(0.18-0.40 wt%) and ironiron
(0.2-0.5 wt%) contents.(0.2-0.5 wt%) contents.
At room temperature CpTi has aAt room temperature CpTi has a HCHCPP crystal latticecrystal lattice,,
which is denoted as thewhich is denoted as the alpha phasealpha phase. On beating, an. On beating, an
allotropic phase transformation occurs, at 883°c, aallotropic phase transformation occurs, at 883°c, a BCCBCC
phase, which is denoted as thephase, which is denoted as the beta(beta(β)β) phasephase forms.forms.
A component with aA component with a predominantly beta phasepredominantly beta phase isis
strongerstronger but morebut more brittlebrittle than a component with an alphathan a component with an alpha
phase microstructure,phase microstructure,

Titanium alloys
Pure titanium is of two types –Pure titanium is of two types –
 Grade IGrade I
 Grade II.Grade II.
Alloying elementsAlloying elements areare added to stabilizeadded to stabilize either theeither the
αα oror ββ phase by changingphase by changing ββ toto αα transportationtransportation
temperature.temperature.

ForFor exampleexample, in, in Ti 6 Al-4VTi 6 Al-4V,, aluminumaluminum is anis an αα
stabilizer, which expands thestabilizer, which expands the αα phase field byphase field by
increasing the (increasing the (αα ++ ββ) to) to ββ transformation temperature.transformation temperature.
VanadiumVanadium, as well as, as well as coppercopper andand palladiumpalladium areare ββ
stabilizers, which expand the ‘stabilizers, which expand the ‘β’β’ - phase field byphase field by
decreasing (decreasing (αα ++ ββ) transformation temperature.) transformation temperature.

Ti-6Al-4VTi-6Al-4V
 MostMost widelywidely used.used.
 At room temperature, Ti-6 Al-4V is a two phaseAt room temperature, Ti-6 Al-4V is a two phase αα ++ββ
alloy.alloy.
 At approximately 975 °C an allotropic phaseAt approximately 975 °C an allotropic phase
transformation takes place, transforming thetransformation takes place, transforming the
microstructure to a single phase BCCmicrostructure to a single phase BCC ββ alloy.alloy.
 Mostly used forMostly used for surgical implantssurgical implants..

Based on attributes, extensive knowledge, and clinicalBased on attributes, extensive knowledge, and clinical
success ofsuccess of wrought Ti implantswrought Ti implants, interest was developed, interest was developed
inin cast titanium for dental applications.cast titanium for dental applications.
TheThe twotwo most important factors in casting Titaniummost important factors in casting Titanium
based materials are thebased materials are the high melting pointhigh melting point andand
chemical reactivitychemical reactivity..
Cast Titanium:Cast Titanium:

Ti readilyTi readily reactsreacts with gaseous elements such aswith gaseous elements such as
hydrogen, oxygenhydrogen, oxygen andand nitrogennitrogen particularly atparticularly at highhigh
temperaturestemperatures. So any manipulation of Ti at. So any manipulation of Ti at elevatedelevated
temperaturestemperatures must be performed in amust be performed in a well-controlledwell-controlled
vaccumvaccum, Without a well controlled vaccum, Ti surfaces, Without a well controlled vaccum, Ti surfaces
will bewill be contaminatedcontaminated with anwith an oxygen enriched andoxygen enriched and
hardened surface layerhardened surface layer, which can be as thick as, which can be as thick as
100100 µmµm..
surface layers of this thicknesssurface layers of this thickness reduce strengthreduce strength andand
ductility andductility and promote crackingpromote cracking because ofbecause of embrittlingembrittling
effecteffect of oxygen.of oxygen.

Because of theBecause of the high affinityhigh affinity Titanium has forTitanium has for
hydrogen, oxygen and nitrogenhydrogen, oxygen and nitrogen,, standard crucibles andstandard crucibles and
investment materialsinvestment materials cannotcannot be used.be used.
Investment materialsInvestment materials must havemust have oxides that are moreoxides that are more
stable than the very stable Ti oxidestable than the very stable Ti oxide and must also beand must also be
able to withstand a temperature sufficient to meltable to withstand a temperature sufficient to melt
titanium. if this is not the case, thentitanium. if this is not the case, then diffusion ofdiffusion of
oxygenoxygen into the molten is likely to occur.into the molten is likely to occur.

Investment materials such as phosphate bondedInvestment materials such as phosphate bonded
silica and phosphate investment materials withsilica and phosphate investment materials with
added trace elementsadded trace elements achieve this goal. It hasachieve this goal. It has
been shown that withbeen shown that with magnesium oxide-basedmagnesium oxide-based
investments, internal porosity resultsinvestments, internal porosity results..

 Because of the low density of titanium, it is difficultBecause of the low density of titanium, it is difficult
to cast. In the last 10 to 15 yrs, advanced castingto cast. In the last 10 to 15 yrs, advanced casting
techniques, which combine centrifugation, vaccumtechniques, which combine centrifugation, vaccum
pressure and gravity casing, and new investmentpressure and gravity casing, and new investment
materials are used.materials are used.
 Properties of Alloyed TitaniumProperties of Alloyed Titanium
1)1) Lower melting points compared to pure Ti, but sameLower melting points compared to pure Ti, but same
as as Ni-Cr or Co-Cr alloys.as as Ni-Cr or Co-Cr alloys.
2)2) Mechanical properties of cast CPTi are similar toMechanical properties of cast CPTi are similar to
those of type III and IV gold alloys.those of type III and IV gold alloys.www.indiandentalacademy.comwww.indiandentalacademy.com

Other alloysOther alloys  Ti-15V, Ti-20Cu, Ti-30pd,Ti-15V, Ti-20Cu, Ti-30pd,
Ti-Co, Ti-Cu.Ti-Co, Ti-Cu.
DisadvantagesDisadvantages ((for dental purposefor dental purpose))
a)a) HHigh melting point.igh melting point.
b)b) HHigh reactivity.igh reactivity.
c)c) LLow casting efficiency.ow casting efficiency.
d)d) IInadequate expansion of investment.nadequate expansion of investment.
e)e) CCasting porosity.asting porosity.

f)f) DDifficulty in finishing this metal.ifficulty in finishing this metal.
g)g) DDifficult to weld, solder.ifficult to weld, solder.
h)h) EExpensive equipment.xpensive equipment.

Aluminum Bronze alloyAluminum Bronze alloy
Traditionally bronze isTraditionally bronze is copper-rich copper tincopper-rich copper tin..
CompositionComposition of ADA approved alloy of this group hasof ADA approved alloy of this group has
81-88% copper81-88% copper
7-11% wt aluminum7-11% wt aluminum
2-4% nickel2-4% nickel
1-4% iron.1-4% iron.
DisadvantageDisadvantage::
Copper reacts with sulfur to formCopper reacts with sulfur to form copper sulfidecopper sulfide,,
whichwhich tarnishestarnishes the surface of this alloy.the surface of this alloy.

METAL CERAMIC RESTORATIONS:METAL CERAMIC RESTORATIONS:
TheThe chief objectionchief objection to the use of dental porcelainto the use of dental porcelain
as a restorative material is itsas a restorative material is its low tensilelow tensile andand shearshear
strength. Thisstrength. This can be minimized by bondingcan be minimized by bonding
porcelain directly to aporcelain directly to a cast alloy substructurecast alloy substructure mademade
to fit the prepared tooth. If a strong bond isto fit the prepared tooth. If a strong bond is
attained between the porcelain veneers and theattained between the porcelain veneers and the
metal, the porcelain veneer is reinforced.metal, the porcelain veneer is reinforced.

The original metal ceramic alloys containedThe original metal ceramic alloys contained 88%88%
goldgold and were much too soft for stress-bearingand were much too soft for stress-bearing
restorations. As there wasrestorations. As there was no evidence of ano evidence of a
chemical bondchemical bond between these alloys and dentalbetween these alloys and dental
porcelain, thenporcelain, then mechanical retentionmechanical retention andand undercutsundercuts
were used to prevent detachment of the ceramicwere used to prevent detachment of the ceramic
veneer. By addingveneer. By adding lessless thanthan 1% of oxide elements1% of oxide elements
such as iron, indium and tin to this high-goldsuch as iron, indium and tin to this high-gold
content alloy, the porcelain metal bond strengthcontent alloy, the porcelain metal bond strength
was improved bywas improved by three foldsthree folds..

Classification of alloysClassification of alloys
used for metal ceramic restorations:used for metal ceramic restorations:
High nobleHigh noble
 Au-Pt-PdAu-Pt-Pd
 Au-Pd-AgAu-Pd-Ag
 Au-PdAu-Pd
NobleNoble
 Pd-AuPd-Au
 Pd-Au-AgPd-Au-Ag
 Pd-AgPd-Ag
Base metalBase metal
 Pure Ti, Ni-Cr-Mo-Be, Ti-Al-V, Ni-Cr-MoPure Ti, Ni-Cr-Mo-Be, Ti-Al-V, Ni-Cr-Mo

Inspite ofInspite of vastly different chemical compositionsvastly different chemical compositions,,
all alloys share at leastall alloys share at least threethree common features:common features:
 They have the potential to bond to dentalThey have the potential to bond to dental
porcelain.porcelain.
 They possess co-efficient of thermal contractionThey possess co-efficient of thermal contraction
compatible with those of dental porcelains.compatible with those of dental porcelains.
 Their solidus temperature is sufficiently high toTheir solidus temperature is sufficiently high to
permit the application of low-fusing porcelains.permit the application of low-fusing porcelains.

The following high noble alloys are usedThe following high noble alloys are used
Gold based metal ceramic alloysGold based metal ceramic alloys
These have aThese have a goldgold content ranging up tocontent ranging up to 88%88% withwith
varying amounts of Pd, Pt and small amounts ofvarying amounts of Pd, Pt and small amounts of
base metals. Alloys of this type are restricted tobase metals. Alloys of this type are restricted to
Three unit spansThree unit spans,, anterior cantileveranterior cantilever oror crownscrowns..

Gold-Palladium Silver alloysGold-Palladium Silver alloys
The gold based alloys contain between 39% and 77%The gold based alloys contain between 39% and 77%
goldgold up to 35%up to 35% palladiumpalladium, and, and silversilver levels as high aslevels as high as
22%.22%.
TheThe silversilver increasesincreases the thermal contraction co-efficientthe thermal contraction co-efficient
but it also has a tendency tobut it also has a tendency to discolordiscolor some porcelains.some porcelains.

Gold-Palladium alloysGold-Palladium alloys
They have 44-55% ofThey have 44-55% of goldgold and 35-45% ofand 35-45% of PdPd..
Used withUsed with porcelainsporcelains havinghaving low co-efficient oflow co-efficient of
thermal contractionthermal contraction toto avoidavoid the development ofthe development of
axial and circumferential tensile stressesaxial and circumferential tensile stresses inin
porcelain during the cooling part of the porcelainporcelain during the cooling part of the porcelain
firing cycle.firing cycle.
More economical than high gold alloys.More economical than high gold alloys.

NOBLE ALLOYSNOBLE ALLOYS
These areThese are Pd basedPd based alloys.alloys.
These alloys were introduced in lateThese alloys were introduced in late 197O197O’s’s
TheThe disadvantagedisadvantage was they had a tendency towas they had a tendency to
discolordiscolor the porcelain during firingthe porcelain during firing
This greenish-yellow discoloration, popularityThis greenish-yellow discoloration, popularity
termed an “termed an “GREENINGGREENING” is due to the” is due to the silversilver
vapour that escapes from the surface of thesevapour that escapes from the surface of these
alloys during firing of the porcelainalloys during firing of the porcelain..

The silver vapour diffuses asThe silver vapour diffuses as ionic silverionic silver into theinto the
porcelain, and is reduced formporcelain, and is reduced form colloidal metalliccolloidal metallic
silversilver in the surface of porcelain.in the surface of porcelain.
Some of the high palladium alloys develop a layer ofSome of the high palladium alloys develop a layer of
dark oxidedark oxide on their surface during cooling fromon their surface during cooling from
the degassing cycle, and this layer has proventhe degassing cycle, and this layer has proven
difficult to mask by the opaque porcelain.difficult to mask by the opaque porcelain.

CompositionComposition of Pd-Ag alloys fall within a narrowof Pd-Ag alloys fall within a narrow
range 53% to 61% palladium and 28% 40%range 53% to 61% palladium and 28% 40%
silver,silver, TinTin oror indiumindium or both are usually added toor both are usually added to
increase alloy hardnessincrease alloy hardness and toand to promote oxidepromote oxide
formationformation for adequate bonding of porcelain.for adequate bonding of porcelain.

Palladium-Copper alloysPalladium-Copper alloys
 Comparable inComparable in costcost to Pd-Ag alloys.to Pd-Ag alloys.
 Susceptible toSusceptible to creepcreep deformation at elevated firingdeformation at elevated firing
temperatures, sotemperatures, so attentionattention is given when these alloysis given when these alloys
are used for long span FPD’s with small connectors.are used for long span FPD’s with small connectors.
 Composition:Composition: 74-80% Palladium, 2-15% copper.74-80% Palladium, 2-15% copper.
 PorcelainPorcelain discolorationdiscoloration due to copper isdue to copper is notnot a majora major
problem.problem.
 These have 1145 Mpa ofThese have 1145 Mpa of yield strength and hardnessyield strength and hardness
valuesvalues equalequal toto base metal alloysbase metal alloys..
 These have aThese have a poor potential for burnishingpoor potential for burnishing when thewhen the
marginal areas are thinmarginal areas are thin

Palladium-Cobalt alloysPalladium-Cobalt alloys
 Comparable in cost to Pd-Ag alloys.Comparable in cost to Pd-Ag alloys.
 Often advertised as gold free, nickel free, berylliumOften advertised as gold free, nickel free, beryllium
free.free.
 These have a fine grain size to minimize hot tearingThese have a fine grain size to minimize hot tearing
during the solidification process.during the solidification process.
 It is the most sag-resistance of all noble alloys.It is the most sag-resistance of all noble alloys.
 Composition: 78-88% of Pd and 4-10% of Co.Composition: 78-88% of Pd and 4-10% of Co.

Palladium-Gallium-Silver and Pa-Gallium-SilverPalladium-Gallium-Silver and Pa-Gallium-Silver
Gold alloysGold alloys
 These areThese are most recentmost recent alloys.alloys.
 These have aThese have a slightly lighter coloredslightly lighter colored oxide thanoxide than
the Pd-Cu or Pd-Co alloys and they are thermallythe Pd-Cu or Pd-Co alloys and they are thermally
compatible with lower expansion porcelains.compatible with lower expansion porcelains.
 Silver content is lowSilver content is low (5%) and is inadequate to(5%) and is inadequate to
cause porcelain greening.cause porcelain greening.
 AreAre compatiblecompatible with lower expansion porcelainswith lower expansion porcelains
such as vita porcelain.such as vita porcelain.

Physical properties of high noble and noble alloysPhysical properties of high noble and noble alloys::
 Should have aShould have a high melting rangehigh melting range so that the metalso that the metal
is solid well above the porcelain sinteringis solid well above the porcelain sintering
temperature totemperature to minimize distortionminimize distortion of castingof casting
during porcelain application.during porcelain application.
 Must haveMust have considerably low fusing temperatureconsiderably low fusing temperature..
 GoodGood corrosion resistance.corrosion resistance.
 HighHigh modulus of elasticity.modulus of elasticity.

Base metal alloysBase metal alloys
Compared with ADA certifiedCompared with ADA certified type IVtype IV gold alloys.gold alloys.
Cobalt based alloys, Nickel based alloys, and PureCobalt based alloys, Nickel based alloys, and Pure
titanium have the followingtitanium have the following advantagesadvantages..
1)1) LLow costow cost
2)2) LLow densityow density
3)3) GGreater stiffnessreater stiffness
4)4) HHigher hardnessigher hardness
5)5) HHigh resistance to tarnish and corrosion.igh resistance to tarnish and corrosion.

CompositionComposition
Co-CrCo-Cr  53-67% of cobalt53-67% of cobalt
25-32% of chromium25-32% of chromium
02-06 wt % molybdenum.02-06 wt % molybdenum.
Ni-CrNi-Cr  61-81 wt % Nickel61-81 wt % Nickel
11-27% chromium11-27% chromium
02-05 wt of molybdenum.02-05 wt of molybdenum.
ChromiumChromium providesprovides passivationpassivation andand
corrosion resistancecorrosion resistance..www.indiandentalacademy.comwww.indiandentalacademy.com

Properties:Properties:
1)1) Higher hardness and stiffness.Higher hardness and stiffness.
2)2) More sag resistant at elevated temperatures.More sag resistant at elevated temperatures.
3)3) It is improbable than significant occlusal wear ofIt is improbable than significant occlusal wear of
these alloys occur. Therefore, particular attentionthese alloys occur. Therefore, particular attention
must be directed toward perfecting occlusalmust be directed toward perfecting occlusal
equilibration.equilibration.
4)4) It deforms only less thanIt deforms only less than 2525 µmµm when porcelain iswhen porcelain is
fired over it.fired over it.

Metals for partial denture alloyMetals for partial denture alloy
These are classified as:These are classified as:
High nobleHigh noble
Au-Ag-Cu-PdAu-Ag-Cu-Pd
NobleNoble
Ag-Pd-Au-CuAg-Pd-Au-Cu
Ag-PdAg-Pd
Base MetalBase Metal
Pure Ti, Ti-Al-V,Pure Ti, Ti-Al-V,
Ni-Cr-Mo-Be, Ni-Cr-Mo, Co-Cr-Mo.Ni-Cr-Mo-Be, Ni-Cr-Mo, Co-Cr-Mo.

Properties requiredProperties required
 HHigh tarnish - corrosion resistanceigh tarnish - corrosion resistance
 SShould be easily castablehould be easily castable
 GGood modulus of elasticity, which is a measure ofood modulus of elasticity, which is a measure of
stiffness and rigidity. It helps in determiningstiffness and rigidity. It helps in determining
thickness of various portions of framework.thickness of various portions of framework.
 SShould have high strength and hardness.hould have high strength and hardness.
 DDuctility should be higher which represents auctility should be higher which represents a
measure of amount of plastic deformation that ameasure of amount of plastic deformation that a
denture framework can withstand before itdenture framework can withstand before it
fractures.fractures.

WROUGHT BASE METAL AND GOLD ALLOYS:
 When a casting isWhen a casting is plastically deformedplastically deformed in anyin any
manner, it is calledmanner, it is called wrought metalwrought metal..
 Wrought base metal alloys are used in dentistry,Wrought base metal alloys are used in dentistry,
mainly asmainly as wireswires forfor orthodonticsorthodontics and asand as clasp armsclasp arms
forfor removable partial denturesremovable partial dentures..
The alloys include:The alloys include:
Stainless steel : iron-chromium-nickel alloyStainless steel : iron-chromium-nickel alloy
Co-Cr-NiCo-Cr-Ni
Ni-TiNi-Ti
ββ- Titanium alloys.- Titanium alloys.www.indiandentalacademy.comwww.indiandentalacademy.com

CARBON STEELS:
Steels areSteels are iron based alloysiron based alloys that usually containthat usually contain lessless
than 1.2% carbonthan 1.2% carbon..
The different classes of steels are based onThe different classes of steels are based on threethree
possible lattice arrangementspossible lattice arrangements of iron.of iron.

STAINLESSSTAINLESS STEELSTEEL
When 12-30% Cr is added to steel, the alloy is called asWhen 12-30% Cr is added to steel, the alloy is called as Stainless steelStainless steel

Ferritic stainless steel:Ferritic stainless steel:
 Often designated as American Iron and SteelOften designated as American Iron and Steel
institute (institute (AISIAISI) series 400 stainless steels.) series 400 stainless steels.
 GoodGood corrosion resistance.corrosion resistance.
 IsIs notnot hardenable by heat treatment.hardenable by heat treatment.
 LimitedLimited application in dentistry.application in dentistry.

Martensitic stainless steel:Martensitic stainless steel:
 Share theShare the AISI 400AISI 400 designation.designation.
 Have high strength and hardness, so used forHave high strength and hardness, so used for
surgicalsurgical andand cutting instruments.cutting instruments.
 PoorPoor corrosion resistance.corrosion resistance.

Austenitic stainless steel:Austenitic stainless steel:
 Most corrosion resistantMost corrosion resistant of all.of all.
 AISI 302AISI 302 is basic type, containing 18% or 8%is basic type, containing 18% or 8% NiNi
and 0.15%and 0.15% carboncarbon..
 Type 304Type 304 has 0.08% of carbon.has 0.08% of carbon.
 Both are designated asBoth are designated as 18-8 stainless steel18-8 stainless steel
 TypeType 316L316L (0.03% carbon) is ordinarily employed(0.03% carbon) is ordinarily employed
forfor implantsimplants..

Generally austenite stainless steel is preferable toGenerally austenite stainless steel is preferable to
ferritic because of the following characteristics.ferritic because of the following characteristics.
1)1) Greater ductilityGreater ductility andand ability to undergo cold workability to undergo cold work
without fracturing.without fracturing.
2)2) Substantial strengtheningSubstantial strengthening during cold working.during cold working.
3)3) Greater ease of weldingGreater ease of welding..
4)4) AbilityAbility to fairly readily overcome sensitization.to fairly readily overcome sensitization.
5)5) Less critical grain growthLess critical grain growth..
66) Comparative ease) Comparative ease in forming.in forming.

CORROSION RESISTANCE:CORROSION RESISTANCE:
 The 18-8 stainless steel mayThe 18-8 stainless steel may loselose itsits resistance toresistance to
corrosioncorrosion if it is heated betweenif it is heated between 400°C and 900°C400°C and 900°C..
 The reason for a decrease in corrosion is theThe reason for a decrease in corrosion is the
precipitation ofprecipitation of chromium carbidechromium carbide at the grainat the grain
boundaries at high temperature. The small, rapidlyboundaries at high temperature. The small, rapidly
diffusing carbon atoms migrate to graindiffusing carbon atoms migrate to grain
boundaries from all parts of the crystal to combineboundaries from all parts of the crystal to combine
with the large, slowly diffusing chromium atomswith the large, slowly diffusing chromium atoms
at the periphery of the grain, where energy isat the periphery of the grain, where energy is
highest.highest. www.indiandentalacademy.comwww.indiandentalacademy.com

WhenWhen chromium combines with the carbonchromium combines with the carbon in thisin this
manner, itsmanner, its passivating qualities are lostpassivating qualities are lost, and, as a, and, as a
consequence,consequence, corrosion resistancecorrosion resistance of the steel isof the steel is
reducedreduced..
Because that portion of grain adjacent to grainBecause that portion of grain adjacent to grain
boundary is generally depleted to produceboundary is generally depleted to produce
chromium carbide,chromium carbide, intergranular corrosionintergranular corrosion occurs,occurs,
and aand a partial disintegrationpartial disintegration of metal may resultof metal may result
withwith general weakening of structuregeneral weakening of structure..

STABILIZATION:STABILIZATION:
By addingBy adding TitaniumTitanium ((approximately 6 times ofapproximately 6 times of
carboncarbon)) precipitationprecipitation ofof chromium carbide can bechromium carbide can be
inhibitedinhibited for a short period at temperaturesfor a short period at temperatures
ordinarily encountered in soldering procedures.ordinarily encountered in soldering procedures.

Soldering for stainless steel:Soldering for stainless steel:
Silver soldersSilver solders are used as theirare used as their solderingsoldering
temperaturetemperature isis lowlow. These are alloys of. These are alloys of Ag, Cu,Ag, Cu,
andand ZnZn to whichto which SnSn,, InIn may be added tomay be added to lowerlower
fusion temperaturefusion temperature andand improve solderimprove solder abilityability..

COBALT-CHROMIUM-NICKEl ALLOYS:COBALT-CHROMIUM-NICKEl ALLOYS:
Co-Cr-Ni alloys are used successfully in orthodonticCo-Cr-Ni alloys are used successfully in orthodontic
appliances.appliances.
These alloys were originally developed for use asThese alloys were originally developed for use as
watch springs (Elgiloy).watch springs (Elgiloy).
COMPOSITION:COMPOSITION:
AA representative composition by massrepresentative composition by mass is Co-40%,is Co-40%,
Cr-20%, Ni-15%, Mo-70%, Mn-2%, C-0.16%,Cr-20%, Ni-15%, Mo-70%, Mn-2%, C-0.16%,
Be-0.04%, Fe-15. 8%.Be-0.04%, Fe-15. 8%.

PROPERTIES:PROPERTIES:
 Excellent resistanceExcellent resistance to tarnish & corrosion.to tarnish & corrosion.
 Yield strength, hardness, tensile strength areYield strength, hardness, tensile strength are
approximatelyapproximately equal to 18-8 stainless steelequal to 18-8 stainless steel..
 Ductility is greaterDuctility is greater than 18-8 stainless steel.than 18-8 stainless steel.
 More responsiveMore responsive to low temperature heatto low temperature heat
treatment.treatment.

NICKEL-TITANIUM ALLOYSNICKEL-TITANIUM ALLOYS
 Called asCalled as NITINOLNITINOL
 It has aIt has a large working range because of lowlarge working range because of low
stiffnessstiffness in combinationin combination with moderately highwith moderately high
strength.strength.

COMPOSITIONCOMPOSITION
 Ni-Ti alloysNi-Ti alloys used inused in dentistrydentistry containcontain
approximately 54% Ni, 44% Ti and 2% or lessapproximately 54% Ni, 44% Ti and 2% or less
cobalt.cobalt.
 This alloy can exist in variousThis alloy can exist in various crystallographiccrystallographic
formsforms. At. At high temperatureshigh temperatures, a BCC lattice, a BCC lattice
austentite phase occurs, onaustentite phase occurs, on coolingcooling a CHa CH
Martensitic phase occurs.Martensitic phase occurs.

These characteristics of the austentite toThese characteristics of the austentite to
martensite phase transition results inmartensite phase transition results in two uniquetwo unique
featuresfeatures ofof potential clinical relevancepotential clinical relevance ::
 Shape memoryShape memory andand Super elasticitySuper elasticity..
Memory effect is achieved by first establishing aMemory effect is achieved by first establishing a
shape at temperatures nearshape at temperatures near 482°C482°C..

 If the appliance such as an orthodontic arch wire, isIf the appliance such as an orthodontic arch wire, is
then cooled and formed into a second shape andthen cooled and formed into a second shape and
heated through a lower transition temperature, theheated through a lower transition temperature, the
wire will return into its original shape.wire will return into its original shape.
 Inducing the austentite to martensite transition byInducing the austentite to martensite transition by
stress can produce super elasticity, a phenomenonstress can produce super elasticity, a phenomenon
that is employed with some nickel-titaniumthat is employed with some nickel-titanium
orthodontic wires and some endodontic files.orthodontic wires and some endodontic files.

ββ-Titanium alloys-Titanium alloys
Like stainless steel and Nitinol,Like stainless steel and Nitinol, pure titanium haspure titanium has
different crystallographic formsdifferent crystallographic forms at high and lowat high and low
temperatures.temperatures.
AtAt temperatures lower than 885° Ctemperatures lower than 885° C, the hexagonal, the hexagonal
close-packed (HCP) or α-crystal lattice is stable,close-packed (HCP) or α-crystal lattice is stable,
where as atwhere as at higher temperaturehigher temperature, the metal re-, the metal re-
arranges into a BCC or β-crystal lattice.arranges into a BCC or β-crystal lattice.
An alloy with the composition ofAn alloy with the composition of TitaniumTitanium-11%,-11%,
molybdenum-6%, Zirconium-4%, tin is producedmolybdenum-6%, Zirconium-4%, tin is produced
inin wrought wire formwrought wire form forfor orthodontic applicationsorthodontic applications..www.indiandentalacademy.comwww.indiandentalacademy.com

1)1) Low elastic modulus.Low elastic modulus.
2)2) High ratio of yield strength to elastic modulusHigh ratio of yield strength to elastic modulus
produces orthodontic appliances that can sustainproduces orthodontic appliances that can sustain
large elastic activations.large elastic activations.
3)3) Highly cold worked.Highly cold worked.
4)4) Excellent corrosion resistance and environmentalExcellent corrosion resistance and environmental
stability.stability.

GOLD ALLOYS :GOLD ALLOYS :
Gold wires areGold wires are occasionally employedoccasionally employed in thein the
construction ofconstruction of removable partial denture claspsremovable partial denture clasps
butbut usedused inin fabricating orthodontic appliancesfabricating orthodontic appliances, and, and
asas retention pins for restorations.retention pins for restorations.

COMPOSITION:COMPOSITION:
 Many gold wires resemble the type IV gold castingMany gold wires resemble the type IV gold casting
alloys in composition, but typically they containalloys in composition, but typically they contain
less gold.less gold.
 Two types of gold wiresTwo types of gold wires are recognized in ADA.are recognized in ADA.
Specification No.7 (1984).Specification No.7 (1984).
Type IType I-High noble or noble metal alloys, they must-High noble or noble metal alloys, they must
contain atcontain at least 75%least 75% of gold and platinum groupof gold and platinum group
metals.metals.
Type IIType II-High noble or noble metal alloys, that must-High noble or noble metal alloys, that must
contain atcontain at least 65%least 65% of some noble metals.of some noble metals.

GENERAL EFFECTS OF THE CONSTITUENTS:GENERAL EFFECTS OF THE CONSTITUENTS:
Pt-PdPt-Pd ensureensure thatthat wire does not meltwire does not melt oror recrystallizerecrystallize
during soldering procedures.during soldering procedures.
EnsureEnsure aa fine grain structurefine grain structure..
CuCu -contributes to ability of alloy to age harden,-contributes to ability of alloy to age harden,
NiNi - strengthener, reduces ductility.- strengthener, reduces ductility.
ZnZn - scavenger.- scavenger.

MECHANICAL PROPERTIES OF NOBLE ALLOYMECHANICAL PROPERTIES OF NOBLE ALLOY
WIRESWIRES::
A wire of a given composition isA wire of a given composition is generally superiorgenerally superior
in mechanical properties to a casting of the samein mechanical properties to a casting of the same
composition.composition.

Because:Because:
 Casting containsCasting contains unavoidable porosityunavoidable porosity, which has, which has
a weakening effect.a weakening effect.
 When cast ingot is drawn into wire, the smallWhen cast ingot is drawn into wire, the small
pores and surface projections may be collapsed,pores and surface projections may be collapsed,
and welding may occur so that defects disappear.and welding may occur so that defects disappear.
Any defects of this type that areAny defects of this type that are not eliminatednot eliminated
willwill weakenweaken the wire.the wire.
 Because ofBecause of Fibrous microstructureFibrous microstructure..

Silver- palladium alloys:
 White in colorWhite in color
 Predominantly silver in composition but havePredominantly silver in composition but have
substantial mounts of palladium, that providesubstantial mounts of palladium, that provide
nobility and promote the silver resistance.nobility and promote the silver resistance.
 May or may not have copper and a small amount ofMay or may not have copper and a small amount of
gold.gold.
DisadvantagesDisadvantages
 Poor castabilityPoor castability
 Greater potential for tarnish and corrosion.Greater potential for tarnish and corrosion.

DENTAL IMPLANT MATERIALS:DENTAL IMPLANT MATERIALS:
Most commonly,Most commonly, metalsmetals andand alloysalloys are used.are used.
InitiallyInitially surgical grade stainless steelsurgical grade stainless steel andand Co-CrCo-Cr
alloysalloys were used because of theirwere used because of their acceptableacceptable
physical propertiesphysical properties and relativelyand relatively good corrosiongood corrosion
resistanceresistance andand biocompatibilitybiocompatibility..

STAINLESS STEEL: (S-S)STAINLESS STEEL: (S-S)
 Surgical stainless steel is an iron-carbon (0.05%)Surgical stainless steel is an iron-carbon (0.05%)
alloy with approximatelyalloy with approximately 18% chromium18% chromium to impartto impart
corrosion resistance andcorrosion resistance and 8% nickel8% nickel to stabilize theto stabilize the
austentite structure.austentite structure.
 The alloy is most frequentlyThe alloy is most frequently usedused in ain a wroughtwrought andand
heat-treated conditionheat-treated condition..
 It hasIt has increased strengthincreased strength andand ductilityductility; thus it is; thus it is
resistant to fractureresistant to fracture..www.indiandentalacademy.comwww.indiandentalacademy.com

Co-Cr-Mo alloyCo-Cr-Mo alloy
 These are most often used in aThese are most often used in a castcast oror cast andcast and
annealed conditionannealed condition..
 CompositionComposition 63% of Co, 30% of Cr, 5% Mo63% of Co, 30% of Cr, 5% Mo
and small concentrations of C, Mn, Ni.and small concentrations of C, Mn, Ni.
 MolybdenumMolybdenum serves toserves to stabilizestabilize the structure, andthe structure, and
carboncarbon asas hardenerhardener..
 These haveThese have outstanding resistance to corrosionoutstanding resistance to corrosion..
 These areThese are least ductileleast ductile..www.indiandentalacademy.comwww.indiandentalacademy.com

TITANIUMTITANIUM
ANDAND
Ti-Al-V ALLOYTi-Al-V ALLOY

Commercially pure Ti (CPTi) has become one ofCommercially pure Ti (CPTi) has become one of
thethe material of choicematerial of choice because of its predictablebecause of its predictable
interaction with the biological environment.interaction with the biological environment.
Titanium is aTitanium is a highly reactive materialhighly reactive material, it oxidizes, it oxidizes
on contact with air or normal tissue fluids. Thison contact with air or normal tissue fluids. This
reactivity is favourable for implant devicesreactivity is favourable for implant devices
because itbecause it minimizes biocorrosionminimizes biocorrosion..
AnAn oxide layeroxide layer 1010 A°A° thick forms on the cutthick forms on the cut
surface of pure Ti within a millisecond. Thus, anysurface of pure Ti within a millisecond. Thus, any
scratch or nick in the oxide coating is essentiallyscratch or nick in the oxide coating is essentially
self healingself healing..

Composition of alloyed TiComposition of alloyed Ti
TiTi - 90wt%- 90wt%
AlAl- 6wt%- 6wt%
VaVa- 4wt%- 4wt%

 HighHigh strength : weight ratio.strength : weight ratio.
 Modulus of elasticityModulus of elasticity approximatelyapproximately one halfone half ofof
that of stainless steel or Cr-Co alloys.that of stainless steel or Cr-Co alloys.
 Few titanium substructures areFew titanium substructures are plasma-sprayedplasma-sprayed oror
coatedcoated with awith a thin layer of calcium phosphatethin layer of calcium phosphate
ceramicceramic..

TheThe rationalerationale for coating the implant with tricalciumfor coating the implant with tricalcium
phosphate or hydroxyapatite, both rich in calciumphosphate or hydroxyapatite, both rich in calcium
and phosphorus isand phosphorus is to produce a bioactive surfaceto produce a bioactive surface
thatthat promotes bone growthpromotes bone growth andand induces a directinduces a direct
bond between the implant and hard tissuebond between the implant and hard tissue..
TheThe rationalerationale forfor plasma sprayedplasma sprayed surface is tosurface is to
provide a roughenedprovide a roughened,, biologically acceptablebiologically acceptable
surfacesurface forfor bone ingrowthbone ingrowth toto ensure anchorageensure anchorage inin
the jaw.the jaw.

OTHER METALS:OTHER METALS:
Gold, Palladium, Tantalum, Platinum and alloys ofGold, Palladium, Tantalum, Platinum and alloys of
these metals.these metals.
RecentlyRecently ZirconiumZirconium,, TungstenTungsten are used.are used.

BIOCOMPATABILITY OF METALS:BIOCOMPATABILITY OF METALS:
Laboratory techniques performed with metalsLaboratory techniques performed with metals
maymay exposeexpose us occasionally or routinely tous occasionally or routinely to
excessively high concentrations ofexcessively high concentrations of BerylliumBeryllium
andand Nickel dustNickel dust andand Beryllium vapour.Beryllium vapour.

BERYLLIUMBERYLLIUM
Although the beryllium concentration in dentalAlthough the beryllium concentration in dental
alloys rarely exceedsalloys rarely exceeds 2 wt %2 wt % the amount ofthe amount of
berylliumberyllium vaporvapor released in to the breathing spacereleased in to the breathing space
during melting of Ni-Cr-Be alloys may beduring melting of Ni-Cr-Be alloys may be
significantsignificant over an extended period.over an extended period.

The risk of Beryllium vapour exposure isThe risk of Beryllium vapour exposure is
greatest forgreatest for dental techniciansdental technicians during alloyduring alloy
melting especially in themelting especially in the absenceabsence of an adequateof an adequate
exhaustexhaust andand filtration system.filtration system.
High levels of Beryllium have been measuredHigh levels of Beryllium have been measured
duringduring finishingfinishing andand polishingpolishing when a localwhen a local
exhaust system was not used. They wereexhaust system was not used. They were reducedreduced
to levels considered safe whento levels considered safe when exhaust fanexhaust fan waswas
used.used.

Exposure of beryllium may result in acute andExposure of beryllium may result in acute and
chronic forms of Beryllium diseasechronic forms of Beryllium disease
BERYLLIOSIS.BERYLLIOSIS.
CLINICAL FEATURESCLINICAL FEATURES::
SymptomsSymptoms range from coughing, chest pain andrange from coughing, chest pain and
general weakness to pulmonary dysfunction.general weakness to pulmonary dysfunction.
Contact dermatitisContact dermatitis
Chemical pneumonitisChemical pneumonitis

NICKEL:NICKEL:
It is a great concern to dental patients with aIt is a great concern to dental patients with a
knownknown allergyallergy to this element.to this element.
The cloud ofThe cloud of controversycontroversy continues to hangcontinues to hang
over the use of nickel in Dentistry.over the use of nickel in Dentistry.
DermatitisDermatitis resulting from contact with nickelresulting from contact with nickel
solutions was described as early assolutions was described as early as 19891989..

Inhalation, ingestion and dermal contactInhalation, ingestion and dermal contact ofof
nickel or nickel containing alloys arenickel or nickel containing alloys are
common because nickel is found incommon because nickel is found in
environmental sourcesenvironmental sources such as air, soil andsuch as air, soil and
food as well as in synthetic objects such asfood as well as in synthetic objects such as
coins, kitchen utensils, and jewelry.coins, kitchen utensils, and jewelry.

Nickel allergy was determined byNickel allergy was determined by PATCH TESTPATCH TEST
((Luis-Blanco- Dalmau JPD 1982: 48; 99-101Luis-Blanco- Dalmau JPD 1982: 48; 99-101))
described a standard patch test consisting ofdescribed a standard patch test consisting of 5%5%
Nickel sulfate solution or 5% Nickel sulfateNickel sulfate solution or 5% Nickel sulfate
solution on a petrolatum basesolution on a petrolatum base, in centre portion, in centre portion
of a square Band-Aid of good quality.of a square Band-Aid of good quality.

Band-Aids in positionBand-Aids in position
One Band-Aid is removed. Observe for ++One Band-Aid is removed. Observe for ++
Both the Band-Aids are removed for comparisonBoth the Band-Aids are removed for comparison
Magnified erythema,papules,and vesicles,+++Magnified erythema,papules,and vesicles,+++

The patch is applied onThe patch is applied on medial aspect of upper armmedial aspect of upper arm,,
which was cleaned with awhich was cleaned with a alcohol swabalcohol swab, this is left, this is left
in place forin place for 48 hrs undisturbed48 hrs undisturbed. The patient is. The patient is
instructed not to moisten the arm or remove theinstructed not to moisten the arm or remove the
patch during this time. A Band-Aidpatch during this time. A Band-Aid without anywithout any
reagentreagent is placed adjacent to the first acts ais placed adjacent to the first acts a controlcontrol..
After 48 hrs, the control Band-aid is removed. TheAfter 48 hrs, the control Band-aid is removed. The
second Band-Aid is removed and the skin issecond Band-Aid is removed and the skin is
cleaned usingcleaned using alcoholalcohol oror acetoneacetone,, tests are readtests are read
after 20 min.after 20 min.

SSigns for recording degrees of patch test reactions are :igns for recording degrees of patch test reactions are :
00 No reaction.No reaction.
++ Erythema.Erythema.
++++  Erythema, papules.Erythema, papules.
++++++ Erythema, papules, vesicles.Erythema, papules, vesicles.
++++++++  Marked edema with vesicles.Marked edema with vesicles.

 DIMETHYL GLYOXINE TESTDIMETHYL GLYOXINE TEST::
 FEIGLFEIGL andand SHORESHORE stated that few drops ofstated that few drops of 1%1%
alcohol solution of dimethyl glyoxime, few dropsalcohol solution of dimethyl glyoxime, few drops
of ammonium hydroxideof ammonium hydroxide added to a metallicadded to a metallic
object, skin on solution will produce aobject, skin on solution will produce a strawberrystrawberry
red insoluble saltred insoluble salt in presence of nickel.in presence of nickel.

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