Dental casting alloys/ oral surgery courses

DENTAL CASTINGDENTAL CASTING
ALLOYSALLOYS
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing Dental EducationLeader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
Because pure metals are apt to be soft and many tend to corrode rapidly andBecause pure metals are apt to be soft and many tend to corrode rapidly and
also because of high cost their use is quite limited in dentistry. To optimizealso because of high cost their use is quite limited in dentistry. To optimize
properties, most metals commonly used in dentistry are mixtures of two orproperties, most metals commonly used in dentistry are mixtures of two or
more metallic elements or one or more metal and/or non metals (THEmore metallic elements or one or more metal and/or non metals (THE
ALLOY).ALLOY).
CASTING is one of the most widely used methods for fabrication of metalCASTING is one of the most widely used methods for fabrication of metal
restorations out of the mouth. A pattern of lost tooth structure or the dentalrestorations out of the mouth. A pattern of lost tooth structure or the dental
prosthesis to be reproduced in metal is constructed in wax. The wax isprosthesis to be reproduced in metal is constructed in wax. The wax is
surrounded by an investment. After the investment has hardened the wax issurrounded by an investment. After the investment has hardened the wax is
removed and the molten metal is forced into the mold space.removed and the molten metal is forced into the mold space.
My seminar deals with these dental casting alloys.My seminar deals with these dental casting alloys.

Contents
 EvolutionEvolution
 Desirable propertiesDesirable properties
 ClassificationClassification
 Microstructure of alloysMicrostructure of alloys
 Alloys for all metal and resin veneered restorations.Alloys for all metal and resin veneered restorations.
 High noble and noble alloys for metal ceramic prosthesis.High noble and noble alloys for metal ceramic prosthesis.
 Base metal alloys for cast metal and metal ceramic prosthesisBase metal alloys for cast metal and metal ceramic prosthesis
 Partial denture alloysPartial denture alloys
 Review of literatureReview of literature
 Alternatives to cast metal technologyAlternatives to cast metal technology
 TroubleshootingTroubleshooting
 Summary and conclusionSummary and conclusion
 ReferencesReferences www.indiandentalacademy.comwww.indiandentalacademy.com

““What we will be tomorrow is because of what we areWhat we will be tomorrow is because of what we are
today, and what we are today is because of what wetoday, and what we are today is because of what we
were yesterday.”were yesterday.”

EVOLUTION OF DENTAL CASTING ALLOYSEVOLUTION OF DENTAL CASTING ALLOYS
The history of dental casting alloys has been influenced by three majorThe history of dental casting alloys has been influenced by three major
factorsfactors
The technological changes of dental prostheses.The technological changes of dental prostheses.
Metallurgic advancements.Metallurgic advancements.
Price changes of noble metals since 1968Price changes of noble metals since 1968

Taggart’s presentation to the New York OdontologicalTaggart’s presentation to the New York Odontological
Group in 1907 on the fabrication of cast inlay restorations oftenGroup in 1907 on the fabrication of cast inlay restorations often
has been acknowledged as the first reported application of losthas been acknowledged as the first reported application of lost
wax technique in dentistry.wax technique in dentistry.
The inlay technique described by Taggart was an instantThe inlay technique described by Taggart was an instant
success and it soon lead to the casting of complex restorationssuccess and it soon lead to the casting of complex restorations
such as inlays, onlays, crowns, fixed partial dentures andsuch as inlays, onlays, crowns, fixed partial dentures and
removable partial denture frameworks.removable partial denture frameworks.

Because pure gold did not have physical properties requiredBecause pure gold did not have physical properties required
for those dental restorations existing jewelry alloys were quicklyfor those dental restorations existing jewelry alloys were quickly
adopted. These gold alloys were further strengthened with copper,adopted. These gold alloys were further strengthened with copper,
silver or platinum.silver or platinum.
In 1932 the dental materials Group at the National Bureau ofIn 1932 the dental materials Group at the National Bureau of
Standards surveyed the alloys being used and roughly classifiedStandards surveyed the alloys being used and roughly classified
them as a Type I, II, III and IV.them as a Type I, II, III and IV.
In the following years several patents were issued for alloysIn the following years several patents were issued for alloys
containing Palladium, as a substitute for Platinum.containing Palladium, as a substitute for Platinum.

By 1948 the composition of dental noble metal alloys forBy 1948 the composition of dental noble metal alloys for
lost metal restorations had become rather diverse, withlost metal restorations had become rather diverse, with
these formulations, the tarnishing tendency of thethese formulations, the tarnishing tendency of the
original alloys apparently had disappeared. It is noworiginal alloys apparently had disappeared. It is now
known that in gold alloys Palladium is added toknown that in gold alloys Palladium is added to
counteract the tarnishing potential of silver.counteract the tarnishing potential of silver.

The base metal removable partial denture alloys wereThe base metal removable partial denture alloys were
introduced in the 1930s. Since that time, both Ni-Cr and Co-introduced in the 1930s. Since that time, both Ni-Cr and Co-
Cr formulati0ons have become increasingly popularCr formulati0ons have become increasingly popular
compared with conventional type IV gold alloys, whichcompared with conventional type IV gold alloys, which
previously were the predominant metals used for suchpreviously were the predominant metals used for such
prostheses.prostheses.
Likewise by 1978, the price of gold was climbing soLikewise by 1978, the price of gold was climbing so
rapidly attention focused on the noble metal alloys. Torapidly attention focused on the noble metal alloys. To
reduce the precious noble metal content and yet retain thereduce the precious noble metal content and yet retain the
advantages of noble metals for dental use.advantages of noble metals for dental use.

DESIRABLE PROPERTIES OF DENTALDESIRABLE PROPERTIES OF DENTAL
CASTING ALLOYSCASTING ALLOYS
BIOCOMPATIBILITYBIOCOMPATIBILITY
CORROSION RESISTANCECORROSION RESISTANCE
ALLERGENIC COMPONENTS IN CASTING ALLOYSALLERGENIC COMPONENTS IN CASTING ALLOYS
ESTHETICSESTHETICS
THERMAL PROPERTIESTHERMAL PROPERTIES
MELTING RANGEMELTING RANGE
COMPENSATION FOR SOLIDIFICATIONCOMPENSATION FOR SOLIDIFICATION
STRENGTH REQUIREMENTSSTRENGTH REQUIREMENTS
CASTABILITYCASTABILITY
FINISHING OF CAST METALSFINISHING OF CAST METALS
PORCELAIN BONDINGPORCELAIN BONDING
ECONOMIC CONSIDERATIONSECONOMIC CONSIDERATIONS

““Even the proverbial needle in the haystackEven the proverbial needle in the haystack
can be found if there is a system and methodcan be found if there is a system and method
to the searchto the search””

CLASSIFICATION OF DENTAL CASTING ALLOYSCLASSIFICATION OF DENTAL CASTING ALLOYS
““Cast dental alloys can be classified according to the followingCast dental alloys can be classified according to the following
five categories:five categories:
1. USE (All metal inlays, crowns and bridges, metal and1. USE (All metal inlays, crowns and bridges, metal and
ceramic prostheses,ceramic prostheses, posts and cores, removable partialposts and cores, removable partial
dentures, implants).dentures, implants).
2. MAJOR ELEMENTS :( Gold based, palladium based, silver2. MAJOR ELEMENTS :( Gold based, palladium based, silver
based, nickel based, cobalt based and titanium based)based, nickel based, cobalt based and titanium based)
3. NOBILITY: High noble, noble, predominantly base metal.3. NOBILITY: High noble, noble, predominantly base metal.
4. PRINCIPAL THREE ELEMENTS: E.g.: Au-Pd-Ag, Pd-4. PRINCIPAL THREE ELEMENTS: E.g.: Au-Pd-Ag, Pd-
Ag- Ni-Cr-BeAg- Ni-Cr-Be
Co-Cr-Mo etcCo-Cr-Mo etc
DOMINANT PHASE SYSTEM: Solid solution(substitutionalDOMINANT PHASE SYSTEM: Solid solution(substitutional
type and inter metallic type),Coring, Eutectic, Peritectic, andtype and inter metallic type),Coring, Eutectic, Peritectic, and
Intermetallic.Intermetallic. www.indiandentalacademy.comwww.indiandentalacademy.com

cc
CCLASSIFICATION OF DENTAL CASTING GOLD
ALLOYS: ISO DRAFT (2002)
TYPE I: LOW STRENGTH: For castings subjected to very light
stress ( inlays) the minimum yield strength is 80 MPa and the
minimum % elongation is 18%
TYPE II : MEDIUM STRENGTH : For castings subjected to high
stress ( inlays, onlays and thin crowns ) the minimum yield strength
is 180 MPa and % elongation is 10%
TYPE III: HIGH STRENGTH : For castings subjected to high
stress (onlays, thin copings, pontics, crowns, saddles) the minimum
yield strength is 270 MPa and the minimum % elongation is 5%
TYPE IV : EXTRA HIGH STRENGTH :For castings subjected to
very high stress ( saddles, bars, clasps, single units and partial
denture frameworks) the minimum yield strength is 360 MPa and the
minimum % elongation is 3%www.indiandentalacademy.comwww.indiandentalacademy.com

MICROSTRUCTURE OF ALLOYSMICROSTRUCTURE OF ALLOYS
METALMETAL: An element whose atomic structure rapidly loses electron to: An element whose atomic structure rapidly loses electron to
form positively charged ions, and which exhibits metallic bonding,form positively charged ions, and which exhibits metallic bonding,
opacity good light reflectance from a polished surface, and highopacity good light reflectance from a polished surface, and high
electrical ands thermal conductivity.electrical ands thermal conductivity.
Of the 103 elements listed in the periodic table 80 are classed as metalsOf the 103 elements listed in the periodic table 80 are classed as metals
and they exhibit the following properties:and they exhibit the following properties:
Metallic luster and metallic ringMetallic luster and metallic ring
Opaque, harder, stronger and denser than other elementsOpaque, harder, stronger and denser than other elements
Solids at room temperatureSolids at room temperature
Good conductors of heat and electricity.Good conductors of heat and electricity.
Ductile and malleableDuctile and malleable
ElectropositiveElectropositive

ALLOYALLOY: A crystalline substance with metallic properties that is: A crystalline substance with metallic properties that is
composed of two or more chemical elements, at least one of which is acomposed of two or more chemical elements, at least one of which is a
metal.metal.
ALLOY SYSTEMALLOY SYSTEM is an aggregate of two or more metals in allis an aggregate of two or more metals in all
combinations.combinations.
In order to specify a particular alloy it is necessary to list theIn order to specify a particular alloy it is necessary to list the
metals or elements present in the alloy and the amount of each elementmetals or elements present in the alloy and the amount of each element
present. Two methods are available:present. Two methods are available:
The weight percentage of each element.The weight percentage of each element.
The atomic fraction or percentage.The atomic fraction or percentage.
The properties of an alloy relate more to the atomic percentage.The properties of an alloy relate more to the atomic percentage.

PHASE DIAGRAMS(CONSTITUTION DIAGRAMPHASE DIAGRAMS(CONSTITUTION DIAGRAM).).
A graph of the phase field limits as a function of temperature andA graph of the phase field limits as a function of temperature and
composition. Phase diagrams usually represent equilibrium conditions.composition. Phase diagrams usually represent equilibrium conditions.
USES: They show the phases that are present in an alloy system forUSES: They show the phases that are present in an alloy system for
different compositions and temperatures.different compositions and temperatures.

PROPERTIES OF DIFFERENT ALLOYINGPROPERTIES OF DIFFERENT ALLOYING
ELEMENTS:ELEMENTS:
GOLDGOLD
1. Pure gold is soft, malleable, ductile metal that does not oxidize under1. Pure gold is soft, malleable, ductile metal that does not oxidize under
atmospheric conditions and is attacked by only a few of the mostatmospheric conditions and is attacked by only a few of the most
powerful oxidizing agents.powerful oxidizing agents.
2. It has a rich yellow color with a strong metallic luster.2. It has a rich yellow color with a strong metallic luster.
3. Although it is the most malleable and ductile metal, it ranks much3. Although it is the most malleable and ductile metal, it ranks much
lower in strength.lower in strength.
4. The pure metal fuses at 1060 degree Celsius4. The pure metal fuses at 1060 degree Celsius
5. Small amounts of impurities have a pronounced effect on mechanical5. Small amounts of impurities have a pronounced effect on mechanical
properties of gold and its alloysproperties of gold and its alloys

6. The specific gravity of pure gold is between19.30 and 19.33 making6. The specific gravity of pure gold is between19.30 and 19.33 making
it one of the heavy metalsit one of the heavy metals
7. Air or water at any temperature doesn’t tarnish gold.7. Air or water at any temperature doesn’t tarnish gold.
8.BHN of 258.BHN of 25
9. Boiling point of 2970 degree Celsius9. Boiling point of 2970 degree Celsius
10.Linear coefficient of thermal expansion 0.14210.Linear coefficient of thermal expansion 0.142
PURITY OF GOLDPURITY OF GOLD
The purity of gold is expressed in karat or finenessThe purity of gold is expressed in karat or fineness
Karat refers to parts of pure gold in 24 parts of gold alloyKarat refers to parts of pure gold in 24 parts of gold alloy
Fineness refers to parts of pure gold in 1000 parts of gold alloy.Fineness refers to parts of pure gold in 1000 parts of gold alloy.

PALLADIUMPALLADIUM::
1. Palladium is not used in pure state in dentistry but it is used in many1. Palladium is not used in pure state in dentistry but it is used in many
dental alloys combined with either gold or silver.dental alloys combined with either gold or silver.
2. It is cheaper than platinum and since it imparts many of the properties2. It is cheaper than platinum and since it imparts many of the properties
of platinum to dental alloys it is often used as a replacement forof platinum to dental alloys it is often used as a replacement for
platinum.platinum.
3. Palladium is a white metal some what darker than platinum.3. Palladium is a white metal some what darker than platinum.
4. Its specific gravity is 11.4 i.e., about half that of platinum and a little4. Its specific gravity is 11.4 i.e., about half that of platinum and a little
more than half of gold.more than half of gold.
5. It is a malleable and ductile metal with a melting point of1555 degree5. It is a malleable and ductile metal with a melting point of1555 degree
Celsius which is the lowestCelsius which is the lowest of the platinum group of metals.of the platinum group of metals.
6. It hardens the alloy, imparts it whiter color and compensates the6. It hardens the alloy, imparts it whiter color and compensates the
reddening effect of copper. Increase the melting point of the alloy andreddening effect of copper. Increase the melting point of the alloy and
renders silver tarnish resistant.renders silver tarnish resistant.

SILVERSILVER::
Silver is malleable, ductile, white in color and best known for itsSilver is malleable, ductile, white in color and best known for its
conduction of heat and electricity. It is stronger and harder than gold butconduction of heat and electricity. It is stronger and harder than gold but
softer than copper.softer than copper.
Melting point of 960.5 degree CelsiusMelting point of 960.5 degree Celsius
It combines with sulfur, chlorine and phosphorus or their vaporsIt combines with sulfur, chlorine and phosphorus or their vapors
Pure silver is seldom employed in dental restorations because of thePure silver is seldom employed in dental restorations because of the
black sulfide formation on the metal in the mouth although it is used asblack sulfide formation on the metal in the mouth although it is used as
small additions to many gold alloys.small additions to many gold alloys.
Addition of palladium to silver containing alloys prevents the rapidAddition of palladium to silver containing alloys prevents the rapid
corrosion of such alloys in the oral environment.corrosion of such alloys in the oral environment.
Silver increases the hardness slightly, whitens the alloy to over comeSilver increases the hardness slightly, whitens the alloy to over come
the reddening effect of copper. Molten silver can dissolve oxygen andthe reddening effect of copper. Molten silver can dissolve oxygen and
cause porosity in the casting and silver can encourage corrosion.cause porosity in the casting and silver can encourage corrosion.www.indiandentalacademy.comwww.indiandentalacademy.com

COPPERCOPPER
1.Hardens the alloy.1.Hardens the alloy.
2.Reduces the melting point of alloy.2.Reduces the melting point of alloy.
3. Reduces the density of the alloy3. Reduces the density of the alloy
4. Excessive copper renders the alloy more susceptible to tarnish4. Excessive copper renders the alloy more susceptible to tarnish
and corrosion and reddens the alloy.and corrosion and reddens the alloy.
ZINCZINC::
It is an oxide scavenger during melting of the alloy for castingIt is an oxide scavenger during melting of the alloy for casting
procedure.procedure.
in the absence of zinc silver absorbs oxygen at high temperaturein the absence of zinc silver absorbs oxygen at high temperature
from the atmosphere. This oxygen is rejected during solidificationfrom the atmosphere. This oxygen is rejected during solidification
tending to produce porosity in the castingtending to produce porosity in the casting

IRIDIUM, RUTHENIUM AND RHODIUMIRIDIUM, RUTHENIUM AND RHODIUM::
Iridium is a hard metal that is quite brittle white with a high specificIridium is a hard metal that is quite brittle white with a high specific
gravity of 22.42 and an exceptionally high melting point of 2440gravity of 22.42 and an exceptionally high melting point of 2440
degree Celsius.degree Celsius.
1.As little as 0.005% of Iridium is effective in refining the grain size1.As little as 0.005% of Iridium is effective in refining the grain size
of cast gold alloys.of cast gold alloys.
2. Ruthenium produces a similar effect.2. Ruthenium produces a similar effect.
GALLIUM:GALLIUM:
Used mainly in silver free alloys to compensate for the decreasedUsed mainly in silver free alloys to compensate for the decreased
thermal expansion seen in silver free alloys. (Silver is avoided inthermal expansion seen in silver free alloys. (Silver is avoided in
metal ceramics as it has as greening effect)metal ceramics as it has as greening effect)
IRON,TINIRON,TIN::
Increases the hardness. Also provides an oxide coat which improvesIncreases the hardness. Also provides an oxide coat which improves
bonding of porcelain to alloy.bonding of porcelain to alloy.www.indiandentalacademy.comwww.indiandentalacademy.com

HEAT TREATMENT OF HIGH NOBLE ANDHEAT TREATMENT OF HIGH NOBLE AND
NOBLE METAL ALLOYS:NOBLE METAL ALLOYS:
HOMOGENIZATION:HOMOGENIZATION:
The cast alloy is held at a temperature near its solidus to achieve theThe cast alloy is held at a temperature near its solidus to achieve the
maximum amount of diffusion without melting (up to a period of 6maximum amount of diffusion without melting (up to a period of 6
hours in some instances)hours in some instances)
This treatment allows atomic diffusion to occur which eliminates as-This treatment allows atomic diffusion to occur which eliminates as-
cast compositionalcast compositional nonuniformity. This treatment results in:nonuniformity. This treatment results in:
Increase in tarnish and corrosion resistance.Increase in tarnish and corrosion resistance.
Increase in the ductility of the alloy.Increase in the ductility of the alloy.

SOLUTION HEAT TREATMENTSOLUTION HEAT TREATMENT::
It involves heating the casting to a temperature below the solidusIt involves heating the casting to a temperature below the solidus
(usually 700 degree Celsius) , holding for a short period of time(usually 700 degree Celsius) , holding for a short period of time
(typically 10 min) so that the alloy returns to random substitutional(typically 10 min) so that the alloy returns to random substitutional
solid solution , and then quenching to retain this atomic arrangementsolid solution , and then quenching to retain this atomic arrangement
at room temperature.at room temperature.
The tensile strength, hardness and proportional limit areThe tensile strength, hardness and proportional limit are
reduced by such a treatment but the ductility is increased. Thisreduced by such a treatment but the ductility is increased. This
treatment is indicated for structures that are to to be ground, shapedtreatment is indicated for structures that are to to be ground, shaped
or otherwise cold worked, either in or out of the mouth.or otherwise cold worked, either in or out of the mouth.

HARDENING HEAT TREATMENTHARDENING HEAT TREATMENT::
The age hardening of the dental alloys can be accomplished inThe age hardening of the dental alloys can be accomplished in
several ways. One of the most practical hardening treatments is byseveral ways. One of the most practical hardening treatments is by
SOAKING or AGEING the casting at a specific temperature for aSOAKING or AGEING the casting at a specific temperature for a
definite time, usually 15 to 30 minutes, before it is water quenched.definite time, usually 15 to 30 minutes, before it is water quenched.
The ageing temperature depends on the alloy composition but isThe ageing temperature depends on the alloy composition but is
generally between 200 and 450 degree Celsius.generally between 200 and 450 degree Celsius.
This treatment is indicated for metallic partial dentures,This treatment is indicated for metallic partial dentures,
bridges and other similar structuresbridges and other similar structures..

CASTING SHRINKAGECASTING SHRINKAGE::
All metals and alloys of practical dental interest shrinkAll metals and alloys of practical dental interest shrink
when they change from liquid to solid state. This occurs inwhen they change from liquid to solid state. This occurs in
three stages:three stages:
The thermal contraction of the liquid metal between theThe thermal contraction of the liquid metal between the
temperature to which it is heated and the liquidus.temperature to which it is heated and the liquidus.
The contraction of the metal inherent in its change fromThe contraction of the metal inherent in its change from
the liquid to the solid state.the liquid to the solid state.
The thermal contraction of the solid metal that occurs onThe thermal contraction of the solid metal that occurs on
further cooling to room temperature.further cooling to room temperature.

SILVER PALLADIUM ALLOYSSILVER PALLADIUM ALLOYS::
These alloys are white and predominantly silver in composition butThese alloys are white and predominantly silver in composition but
have substantial amounts of palladium at least 25%)have substantial amounts of palladium at least 25%)
that provides nobility and promote tarnish resistance. They may orthat provides nobility and promote tarnish resistance. They may or
may not have copper and a small amount of gold.may not have copper and a small amount of gold.
ADVANTAGES:ADVANTAGES:
Adequate strength properties.Adequate strength properties.
Acceptable castabilityAcceptable castability
Low costLow cost
LIMITATION:LIMITATION:
Great potential for tarnish and corrosion.Great potential for tarnish and corrosion.

HIGH NOBLE AND NOBLE ALLOYS FOR METAL-HIGH NOBLE AND NOBLE ALLOYS FOR METAL-
CERAMIC PROSTHESISCERAMIC PROSTHESIS
In spite of vastly different chemical compositions all suchIn spite of vastly different chemical compositions all such
alloys must share at least three common features:alloys must share at least three common features:
They must have the potential to bond to dental porcelain.They must have the potential to bond to dental porcelain.
They posses coefficients of thermal contraction compatible withThey posses coefficients of thermal contraction compatible with
those ofthose of dental porcelains.dental porcelains.
Their solidus temperature is sufficiently high to permit applicationTheir solidus temperature is sufficiently high to permit application
of low fusing porcelains.of low fusing porcelains.
The coefficients of thermal expansion tend to be reciprocal toThe coefficients of thermal expansion tend to be reciprocal to
melting point of the alloys.melting point of the alloys.
high sag resistance.high sag resistance.

GOLD PALLADIUM SILVER ALLOYS (LOW SILVER CONTENT)GOLD PALLADIUM SILVER ALLOYS (LOW SILVER CONTENT)
ADVANTAGESADVANTAGES::
EconomicalEconomical
Excellent resistance to tarnish and corrosionExcellent resistance to tarnish and corrosion
Relative freedom from technique sensitivityRelative freedom from technique sensitivity
DISADVANTAGE:DISADVANTAGE:
The potential for porcelain discoloration when silver vapor is released.The potential for porcelain discoloration when silver vapor is released.
GOLD- PALLADIUM-SILVER ALLOYS (HIGH SILVER CONTENT)GOLD- PALLADIUM-SILVER ALLOYS (HIGH SILVER CONTENT)
Gold alloys that contain 12% Ag or more account for approximatelyGold alloys that contain 12% Ag or more account for approximately
20% of the current alloy market.20% of the current alloy market.
Lower costLower cost
Favorable physical propertiesFavorable physical properties
DISADVANTAGE:DISADVANTAGE:
Potential for porcelain discoloration.Potential for porcelain discoloration.www.indiandentalacademy.comwww.indiandentalacademy.com

GOLD PALLADIUM ALLOYS:GOLD PALLADIUM ALLOYS:
The first alloy of this type was introduced in 1977 by J.F.Jelenko andThe first alloy of this type was introduced in 1977 by J.F.Jelenko and
Co. This alloy was designed to overcome the porcelain discolorationCo. This alloy was designed to overcome the porcelain discoloration
effect (because it is silver free) and also to provide an alloy with a lowereffect (because it is silver free) and also to provide an alloy with a lower
thermal contraction coefficient than that of either Au-Pd-Ag or Pd-Agthermal contraction coefficient than that of either Au-Pd-Ag or Pd-Ag
alloys. Their gold content varies from 45 to 52% and palladium contentalloys. Their gold content varies from 45 to 52% and palladium content
varies between 37-45%.varies between 37-45%.

ADVANTAGESADVANTAGES::
These alloys are considered nearly ideal because:These alloys are considered nearly ideal because:
Contain no silverContain no silver
Their surface oxide layer is virtually indiscernibleTheir surface oxide layer is virtually indiscernible
Their sag resistance is better than that of Au-Pt-Pd alloysTheir sag resistance is better than that of Au-Pt-Pd alloys
Their castability, corrosion resistance and adherence to porcelain areTheir castability, corrosion resistance and adherence to porcelain are
excellentexcellent
Cost effectiveCost effective
PROPERTIESPROPERTIES::
HV of about 200HV of about 200
Yield strength of 570 MPaYield strength of 570 MPa
Elongation of 20%Elongation of 20%

PALLADIUM GOLD ALLOYSPALLADIUM GOLD ALLOYS::
Relatively few alloys are available in the market due to the priceRelatively few alloys are available in the market due to the price
volatility of palladium and their laboratory and clinical performance hasvolatility of palladium and their laboratory and clinical performance has
not been adequately documented.not been adequately documented.
PALLADIUM-GOLD-SILVER ALLOYSPALLADIUM-GOLD-SILVER ALLOYS::
These have a potential for porcelain discoloration. Gold content is fromThese have a potential for porcelain discoloration. Gold content is from
5-32% and silver content from 6.5-14%.5-32% and silver content from 6.5-14%.
These alloys have a range of thermal contraction coefficients thatThese alloys have a range of thermal contraction coefficients that
increase with an increase in silver contentincrease with an increase in silver content

PALLADIUM-SILVER ALLOYSPALLADIUM-SILVER ALLOYS::
This alloy type was introduced in the market in 1974 as the first goldThis alloy type was introduced in the market in 1974 as the first gold
free noble alloy available for metal ceramic restorationsfree noble alloy available for metal ceramic restorations
The Pd content is 53-61% and 28-40% Ag in addition to tin and/orThe Pd content is 53-61% and 28-40% Ag in addition to tin and/or
indium.indium.
The low specific gravity and their low cost make them attractiveThe low specific gravity and their low cost make them attractive
economic alternatives to gold based alloys.economic alternatives to gold based alloys.
Adequate physical propertiesAdequate physical properties
Alloys of this type are easy to polish and burnishAlloys of this type are easy to polish and burnish
Adherence to porcelain is acceptable although a predominantlyAdherence to porcelain is acceptable although a predominantly
mechanical type of bonding has been suggested for this alloy.mechanical type of bonding has been suggested for this alloy.
DISADVANTAGESDISADVANTAGES::
Silver discoloration effect is most severe for these alloys. Gold metalSilver discoloration effect is most severe for these alloys. Gold metal
conditioners or ceramic coating agents may minimize this effect. Inconditioners or ceramic coating agents may minimize this effect. In
addition many of today’s porcelains are formulated to minimize thisaddition many of today’s porcelains are formulated to minimize this
problemproblem www.indiandentalacademy.comwww.indiandentalacademy.com

PALLADIUM-COPPER-GALLIUM ALLOYSPALLADIUM-COPPER-GALLIUM ALLOYS::
First introduced in 1983, these alloys were very popular in 1990s.First introduced in 1983, these alloys were very popular in 1990s.
However the price volatility of palladium required dentists to useHowever the price volatility of palladium required dentists to use otherother
alloys. A brown or black oxide layer is formed during oxidation andalloys. A brown or black oxide layer is formed during oxidation and
subsequent porcelain firing cycles. Because of all these factors thesesubsequent porcelain firing cycles. Because of all these factors these
alloys have not been well accepted in the dental practice.alloys have not been well accepted in the dental practice.
PALLADIUM-GALLIUM-SILVER ALLOYSPALLADIUM-GALLIUM-SILVER ALLOYS::
These alloys have a slightly lighter oxide layer than Pd-Cu alloys andThese alloys have a slightly lighter oxide layer than Pd-Cu alloys and
they are thermally compatible with lower expansion porcelains. Inthey are thermally compatible with lower expansion porcelains. In
addition they have a comparatively low hardness which allows the alloyaddition they have a comparatively low hardness which allows the alloy
to be adjusted in the dental lab or the chair side.to be adjusted in the dental lab or the chair side.

•DISCOLORATION OF PORCELAIN BYDISCOLORATION OF PORCELAIN BY SILVERSILVER::
The colloidal dispersion of silver atoms entering the body and incisalThe colloidal dispersion of silver atoms entering the body and incisal
porcelain or the glazed surface from vapor transport or surface diffusionporcelain or the glazed surface from vapor transport or surface diffusion
may cause color changes including green, yellow-green, yellow-orange,may cause color changes including green, yellow-green, yellow-orange,
orange and brown hues. This phenomenon is termed GREENING.orange and brown hues. This phenomenon is termed GREENING.
Porcelains with higher sodium content are believed to exhibit morePorcelains with higher sodium content are believed to exhibit more
intense discoloration because of more rapid silver diffusion in sodiumintense discoloration because of more rapid silver diffusion in sodium
containing glass.containing glass.
The intensity of discoloration increases for higher silver content alloys,The intensity of discoloration increases for higher silver content alloys,
is more in the cervical region, lighter shades, multiple firing proceduresis more in the cervical region, lighter shades, multiple firing procedures
and certain brands of porcelain and also in silver free alloys due toand certain brands of porcelain and also in silver free alloys due to
vaporization of silver from the walls of contaminated furnaces.vaporization of silver from the walls of contaminated furnaces.

PREVENTION OF DISCOLORATIONPREVENTION OF DISCOLORATION::
Use of ultra low fusing porcelain or non greening porcelainUse of ultra low fusing porcelain or non greening porcelain
A pure gold film can be fired on a metal substrate to reduce the surfaceA pure gold film can be fired on a metal substrate to reduce the surface
silver concentration.silver concentration.
A ceramic conditioner can be fired as a barrier between the alloy andA ceramic conditioner can be fired as a barrier between the alloy and
the porcelain.the porcelain.
Use of a graphite block routinely to maintain a reducing atmosphere.Use of a graphite block routinely to maintain a reducing atmosphere.

THERMAL COMPATIBILITY ANDTHERMAL COMPATIBILITY AND
INCOMPATIBILITY OF METAL-CERAMICINCOMPATIBILITY OF METAL-CERAMIC
SYSTEMSSYSTEMS
Thermal compatibility refers to the ability of the metal and itsThermal compatibility refers to the ability of the metal and its
veneering porcelain to contract at similar ratesveneering porcelain to contract at similar rates
(thermal co efficient of expansion of metal is comparable in(thermal co efficient of expansion of metal is comparable in
magnitude with the co efficient of thermal expansion of porcelainmagnitude with the co efficient of thermal expansion of porcelain.).)

PHYSICAL PROPERTIES OF HIGH NOBLE AND
NOBLE ALLOYS
BASE METAL ALLOYS FOR CAST METAL AND METAL
CERAMIC PROSTHESIS
The no of dental laboratories using base metal alloys steadily increased
through 70s and 80s. Although the increased acceptance of these alloys
during this period was greatly influenced by the price fluctuation of the
noble metals, the trend continued through 90s even when the prices of
noble metals had come down. The Ni-Cr-Be alloys have retained their
popularity despite the potential toxicity of beryllium and the allergenic
potential of nickel.

There are several reasons for the use of nickel chromium and/or cobalt
chromium alloys in dentistry
Nickel is combined with Chromium to form a highly corrosion resistant
alloy
Cost effectiveness
Alloys such as Ticonium 100 have been used in re4movable partial
denture frameworks for many years with few reports of allergic
reactions.
Although Beryllium is a toxic metal, dentists and patients should not be
affected because the main risk occurs mainly in the vapor form which is
a concern for the technician.
Nickel alloys have excellent mechanical properties such as high elastic
modulus, high hardness, high sag resistance and a reasonably high
elongation (ductility)
Lower density

On the other hand it is also important the realize the limitations of theseOn the other hand it is also important the realize the limitations of these
alloys, particularly Vis-a –Vis metal ceramic restorations:alloys, particularly Vis-a –Vis metal ceramic restorations:
These alloys are more difficult to cast and presolderThese alloys are more difficult to cast and presolder
The ability to obtain acceptable fitting castings may require specialThe ability to obtain acceptable fitting castings may require special
procedures to adequately compensate for the higher solidificationprocedures to adequately compensate for the higher solidification
shrinkageshrinkage
Potential for porcelain delamination as a result of separation of poorlyPotential for porcelain delamination as a result of separation of poorly
adherent oxide layer from the metal substrate.adherent oxide layer from the metal substrate.
Finishing and polishing require special procedures and is not easy eitherFinishing and polishing require special procedures and is not easy either
in the lab or at chair side.in the lab or at chair side.
Removal of defective restorationsRemoval of defective restorations may take time.may take time.
Repair of crowns with fractured porcelain veneers which may be simplyRepair of crowns with fractured porcelain veneers which may be simply
performed on noble metal substrates using pin-retained facings or metalperformed on noble metal substrates using pin-retained facings or metal
ceramic onlays, is more difficult to accomplish in base metalceramic onlays, is more difficult to accomplish in base metal
frameworksframeworks www.indiandentalacademy.comwww.indiandentalacademy.com

COMPOSITION AND PROPERTIES OF BASE METALCOMPOSITION AND PROPERTIES OF BASE METAL
ALLOYS:ALLOYS:

PARTIAL DENTURE ALLOYS AND GUIDELINESPARTIAL DENTURE ALLOYS AND GUIDELINES
FOR SELECTIONFOR SELECTION
EFFECT OF EACH ALLOY CONSTITUENT:EFFECT OF EACH ALLOY CONSTITUENT:
CHROMIUM:CHROMIUM:
Chromium content is responsible for the tarnish resistance and stainlessChromium content is responsible for the tarnish resistance and stainless
properties of these alloys. When the chromium of an alloy is over 30%properties of these alloys. When the chromium of an alloy is over 30%
the alloy is more difficult to cast. It also forms a brittle phase known asthe alloy is more difficult to cast. It also forms a brittle phase known as
the zigma phase. Therefore dental alloys of these types should notthe zigma phase. Therefore dental alloys of these types should not
contain more than 28-29% chromium.contain more than 28-29% chromium.
COBALT AND NICKEL:COBALT AND NICKEL:
They are somewhat interchangeable to a certain extent. Cobalt increasesThey are somewhat interchangeable to a certain extent. Cobalt increases
the elastic modulus, strength and harness of the alloy more than nickelthe elastic modulus, strength and harness of the alloy more than nickel
does. Nickel may increase ductility.does. Nickel may increase ductility.www.indiandentalacademy.comwww.indiandentalacademy.com

CARBON CONTENT:CARBON CONTENT:
The hardness of cobalt based alloys is increased by the increasedThe hardness of cobalt based alloys is increased by the increased
content of carbon. A change in the carbon content in the order of 0.2 %content of carbon. A change in the carbon content in the order of 0.2 %
in these alloys changes their properties to csuch an extent that the alloyin these alloys changes their properties to csuch an extent that the alloy
would no longer be usable in dentistry.would no longer be usable in dentistry.
ALUMINIUM:ALUMINIUM:
Al in Ni containing alloys forms a compound of Nickel and AluminiumAl in Ni containing alloys forms a compound of Nickel and Aluminium
(Ni3-Al).This compound increases the ultimate tenmsile and yield(Ni3-Al).This compound increases the ultimate tenmsile and yield
strength.strength.
BERYLLIUM:BERYLLIUM:
1 % of this element to Nickel based alloys reduces the fusion range of1 % of this element to Nickel based alloys reduces the fusion range of
the alloy by about 100 degree Celsius. It also aids in solid solutionthe alloy by about 100 degree Celsius. It also aids in solid solution
hardening. It improves the casting characteristics which possibly aid inhardening. It improves the casting characteristics which possibly aid in
porcelain bondingporcelain bonding..

MOLYBDENUM:MOLYBDENUM:
The presence of 3-6% molybdenum contributes to the strength of theThe presence of 3-6% molybdenum contributes to the strength of the
alloy.alloy.
SILICON AND MANGANESESILICON AND MANGANESE::
These are added to increase the castability of these alloys. They areThese are added to increase the castability of these alloys. They are
present primarily on oxide to prevent oxidation of other elements duringpresent primarily on oxide to prevent oxidation of other elements during
melting. . When the nitrogen content of the final alloy is more than 0.1melting. . When the nitrogen content of the final alloy is more than 0.1
% the castings loose some of their ductility since the minor ingredients% the castings loose some of their ductility since the minor ingredients
of carbon, nitrogen and oxygen effectively increase the properties of theof carbon, nitrogen and oxygen effectively increase the properties of the
final formulated and designed in such a way as to maximize the rigidityfinal formulated and designed in such a way as to maximize the rigidity
of the prosthesis.of the prosthesis.

BIOLOGICAL HAZARDS AND PRECAUTIONSBIOLOGICAL HAZARDS AND PRECAUTIONS
Lab technicians may be exposed occasionally or routinely toLab technicians may be exposed occasionally or routinely to
excessively high concentrations of beryllium and nickel dustexcessively high concentrations of beryllium and nickel dust
and beryllium vapor. Although the amount of berylliumand beryllium vapor. Although the amount of beryllium
rarely exceeds 2% by weight, the atomic concentration ofrarely exceeds 2% by weight, the atomic concentration of
beryllium is around 10.7%.beryllium is around 10.7%.
The Occupational Health and Safety AdministrationThe Occupational Health and Safety Administration
(OSHA) specifies that the exposure to beryllium dust in air(OSHA) specifies that the exposure to beryllium dust in air
should be limited to a particulate beryllium concentration ofshould be limited to a particulate beryllium concentration of
2micrograms/m3 of air ( both respirable and nonrespirable2micrograms/m3 of air ( both respirable and nonrespirable
particles) determined from an 8 hr time weighted average.particles) determined from an 8 hr time weighted average.

The allowable maximum concentration is 5microgram/m3(not to beThe allowable maximum concentration is 5microgram/m3(not to be
exceeded for a 15 min period). The National Institute for Occupationexceeded for a 15 min period). The National Institute for Occupation
Safety and Health (NIOSH) recommends a limit of 0.5 micrograms /m3Safety and Health (NIOSH) recommends a limit of 0.5 micrograms /m3
based on a 130 min sample. Moffa et al reported that when a localbased on a 130 min sample. Moffa et al reported that when a local
exhaust system was used the concentration of beryllium was reduced toexhaust system was used the concentration of beryllium was reduced to
safe levels.safe levels.
Physiologic responses to beryllium vary from contact dermatitis toPhysiologic responses to beryllium vary from contact dermatitis to
severe chemical pneumonitis which can be fatal. Symptoms may rangesevere chemical pneumonitis which can be fatal. Symptoms may range
from coughing, chest pain and general weakness to pulmonaryfrom coughing, chest pain and general weakness to pulmonary
dysfunction.dysfunction.

ALLERGY POTENTIAL OF NICKELALLERGY POTENTIAL OF NICKEL::
Of greater concern to dental patient is intra oral exposure toOf greater concern to dental patient is intra oral exposure to
nickel, especially for patient with a known allergy to thisnickel, especially for patient with a known allergy to this
element.element.
Nickel allergy is determined by patch test using 5% NickelNickel allergy is determined by patch test using 5% Nickel
sulfate. The effects of nickel exposure to humans havesulfate. The effects of nickel exposure to humans have
included dermatitis, cancer of nasal sinus and larynx,included dermatitis, cancer of nasal sinus and larynx,
irritation and perforation of nasal septum, loss of smell,irritation and perforation of nasal septum, loss of smell,
asthmatic lung disease, pulmonary pneumoconiosis, lungasthmatic lung disease, pulmonary pneumoconiosis, lung
dysfunction and death.dysfunction and death.
OSHA standard: 8 hr time weighted average concentrationOSHA standard: 8 hr time weighted average concentration
limit of 1000 microgram/m3 of nickel and nickel compoundslimit of 1000 microgram/m3 of nickel and nickel compoundswww.indiandentalacademy.comwww.indiandentalacademy.com

TITANIUM FOR CASTING APPLICATIONSTITANIUM FOR CASTING APPLICATIONS
Titanium was first isolated then named 200 years ago but the metal weTitanium was first isolated then named 200 years ago but the metal we
know is less than 40 years old. It is the fourth most abundant metal inknow is less than 40 years old. It is the fourth most abundant metal in
the earth's crust. It is a reactive metal and hence difficult to extract. Dr.the earth's crust. It is a reactive metal and hence difficult to extract. Dr.
Wilhelm Kroll invented useful metallurgical processes for theWilhelm Kroll invented useful metallurgical processes for the
commercial production of titanium metal and hence he is called thecommercial production of titanium metal and hence he is called the
father of titanium industry.father of titanium industry.
PROPERTIES OF TITANIUMPROPERTIES OF TITANIUM
The physical and mechanical properties of titanium and its alloys varyThe physical and mechanical properties of titanium and its alloys vary
greatly with the addition of traces of other elements such as oxygen,greatly with the addition of traces of other elements such as oxygen,
iron and nitrogen. Commercially pure Ti is available in four gradesiron and nitrogen. Commercially pure Ti is available in four grades
(Grade I to Grade IV) based on the incorporation of small amounts of(Grade I to Grade IV) based on the incorporation of small amounts of
oxygen, nitrogen, hydrogen, iron and carbon during purificationoxygen, nitrogen, hydrogen, iron and carbon during purification
procedures.procedures.
The most commonly used and important Ti alloy is Ti-6Al-4V alloyThe most commonly used and important Ti alloy is Ti-6Al-4V alloy
because of its desirable proportion and predictable producibility.because of its desirable proportion and predictable producibility.

PROPERTIES OF TITANIUM AND ITS ALLOY (Ti-PROPERTIES OF TITANIUM AND ITS ALLOY (Ti-
6Al-4V)6Al-4V)
Ti is the most biocompatible metal used for dental prostheses.Ti is the most biocompatible metal used for dental prostheses.
High melting point of 1668 degree Celsius.High melting point of 1668 degree Celsius.
It is highly resistant to tarnish and corrosion due to the formation of aIt is highly resistant to tarnish and corrosion due to the formation of a
coat of titanium oxide on the surface.coat of titanium oxide on the surface.
But as the oxidation rate of Ti increases rapidly above a temperature ofBut as the oxidation rate of Ti increases rapidly above a temperature of
850 degree Celsius, it is desirable to use ultra low fusing porcelains for850 degree Celsius, it is desirable to use ultra low fusing porcelains for
Ticeramic prostheses.Ticeramic prostheses.
A density of 4.51, VHN of 130210, % elongation of 1524A density of 4.51, VHN of 130210, % elongation of 1524
yield strength of 241548 MPayield strength of 241548 MPa
Melting point of 3035Melting point of 3035

A special casting machine with arc melting capability and argonA special casting machine with arc melting capability and argon
atmosphere is used along with a compatible investment are used toatmosphere is used along with a compatible investment are used to
ensure acceptable castability.ensure acceptable castability.
The most widely used Ti alloy used in dentistry is Ti6Al4VThe most widely used Ti alloy used in dentistry is Ti6Al4V
which is a alphabeta alloy. Although it is stronger than CP Ti, it is notwhich is a alphabeta alloy. Although it is stronger than CP Ti, it is not
as attractive from a biocompatibility point of view due to slow releaseas attractive from a biocompatibility point of view due to slow release
of Al and V atoms in vivo.of Al and V atoms in vivo.

REVIEW OF LITERATUREREVIEW OF LITERATURE
P.J Brockhurst and R.W.S Canon in 1981 examined the requirements ofP.J Brockhurst and R.W.S Canon in 1981 examined the requirements of
alloys for metalceramic crowns and bridgework and discussed thealloys for metalceramic crowns and bridgework and discussed the
functional requirements and manipulative behavior of as well as cost offunctional requirements and manipulative behavior of as well as cost of
alternatives to high gold alloys.alternatives to high gold alloys.
They concluded that base metal alloys functioned satisfactorily asThey concluded that base metal alloys functioned satisfactorily as
compared to highcompared to high noble alloys provided proper dental lab proceduresnoble alloys provided proper dental lab procedures
were employed. Nickel and beryllium did not appear to be healthwere employed. Nickel and beryllium did not appear to be health
hazards for themhazards for them

J. Robert Kelly and Thomas C.Rose in 1983 discussed the variousJ. Robert Kelly and Thomas C.Rose in 1983 discussed the various
physical properties, biocompatibility, porcelain bonding and corrosionphysical properties, biocompatibility, porcelain bonding and corrosion
resistance of various non precious alloys and concluded that though theresistance of various non precious alloys and concluded that though the
manipulation of non precious alloys is technique sensitive and exacting,manipulation of non precious alloys is technique sensitive and exacting,
their better physical properties and clinical performance meritedtheir better physical properties and clinical performance merited
consideration. They were of the opinion that beryllium was not a healthconsideration. They were of the opinion that beryllium was not a health
hazard provided proper exhaust and ventilation was used in the dentalhazard provided proper exhaust and ventilation was used in the dental
lab and that the allergenic potential of nickel needed further research.lab and that the allergenic potential of nickel needed further research.
Russel R. Wang and Aaron Fenton in 1996 reviewed the literature onRussel R. Wang and Aaron Fenton in 1996 reviewed the literature on
Titanium for prosthodontic applications. They described theTitanium for prosthodontic applications. They described the
development and properties of titanium for the purpose of evaluating thedevelopment and properties of titanium for the purpose of evaluating the
present status and future trends in its use.present status and future trends in its use.

Selcuk Oruc and Ybrahim Tulunoglu in 2000 evaluated theSelcuk Oruc and Ybrahim Tulunoglu in 2000 evaluated the
marginal and inner fit of metal –cramic restorations andmarginal and inner fit of metal –cramic restorations and
frameworks made with a NickelChromium alloy (Remaniumframeworks made with a NickelChromium alloy (Remanium
CS) and a commercially pure TitaniumCS) and a commercially pure Titanium (Rematitan). They(Rematitan). They
concluded that the fit of base metal alloy metal ceramicconcluded that the fit of base metal alloy metal ceramic
crowns was better than the commercially pure Titanium metalcrowns was better than the commercially pure Titanium metal
ceramic crowns. However both the artificial crowns wereceramic crowns. However both the artificial crowns were
clinically acceptable.clinically acceptable.

A study was conducted in the dept. of prosthodontics ,under the able
guidance of DR.N.P.Patil, to evaluate the
effects of recasting on the mechanical properties like yield strength and
percentage elongation of High Palladium alloys. It was concluded that:
Both the high palladium alloys tested for mechanical properties like
yield strength and percentage of elongation
showed lesser values for the cast test samples as compared to the values
given by the manufacturer.
The test cast specimen made with new alloy and mixed alloy to50:50
proportion had almost same yield strength and percentage of elongation
values for both alloys tested.

Another study was conducted under the able guidance of
Dr.N.P.Patil, in 1997, to evaluate the effect of heat cycles on the
release of nickel and chromium from nickelchromium base metal
alloys. It was concluded that :
There is a definite release of metal ions from the alloys used for
restoration in the oral cavity.
The release rate of metal ions was found to be maximum after 1
day and diminished over time.
There was a significant difference in release of nickel ion from
alloy A to alloy B and it was related to difference in chromium
content.
The amount of metal ions (nickel and chromium) released from
these alloys may not cause systemic toxicity ,but the local effects on

ALTERNATIVES TO CAST METALALTERNATIVES TO CAST METAL
TECHNOLOGYTECHNOLOGY
To avoid the challenges and cost associated with metal casting process,To avoid the challenges and cost associated with metal casting process,
four technologies are availablefour technologies are available
SINTERING OF BURNISHED FOIL:SINTERING OF BURNISHED FOIL:
The Captek system consists of three pairs of materials:The Captek system consists of three pairs of materials:
CaptekP layer which is adapted first to the die and fired at a temperatureCaptekP layer which is adapted first to the die and fired at a temperature
of 1075 degree Celsiusof 1075 degree Celsius
Captek G which is applied over the Captek P coping and the former isCaptek G which is applied over the Captek P coping and the former is
drawn by capillary action into the network structure of the Captek Pdrawn by capillary action into the network structure of the Captek P
coping vacated by the adhesive binder.coping vacated by the adhesive binder.
Captek Repair paste and Capfil which are used to add material to CaptekCaptek Repair paste and Capfil which are used to add material to Captek
structures.structures.
The main ADVANTAGE of Captek structures is the very low thicknessThe main ADVANTAGE of Captek structures is the very low thickness
of metal that can be achieved which ensures minimal tooth preparationof metal that can be achieved which ensures minimal tooth preparationwww.indiandentalacademy.comwww.indiandentalacademy.com

CAD-CAM PROCESSINGCAD-CAM PROCESSING
A CADCAM System electronically or digitally records surface coA CADCAM System electronically or digitally records surface co
ordinates of the prepared tooth and stores these retrieved data in theordinates of the prepared tooth and stores these retrieved data in the
memory of a computer. The image data can then be retrievedmemory of a computer. The image data can then be retrieved
immediately to mill or grind a metal, ceramic or composite prosthesis byimmediately to mill or grind a metal, ceramic or composite prosthesis by
computer control from a solid block of the chosen material. Withincomputer control from a solid block of the chosen material. Within
minutes the prosthesis can be fabricated and placed in a prepared toothminutes the prosthesis can be fabricated and placed in a prepared tooth
and bonded or cemented in the mouth of a patient.and bonded or cemented in the mouth of a patient.
The optical scanning procedure eliminates the need forThe optical scanning procedure eliminates the need for anan
impression. An advantage of ceramics is that homogeneous, high qualityimpression. An advantage of ceramics is that homogeneous, high quality
materials with minimal porosity and other typical defects are designedmaterials with minimal porosity and other typical defects are designed
for CADCAMfor CADCAM applications.applications.

COPY MILLINGCOPY MILLING
This process is based on the principle of tracing the surface of a patternThis process is based on the principle of tracing the surface of a pattern
that is then replicated from a blank of ceramic, composite, or metal thatthat is then replicated from a blank of ceramic, composite, or metal that
is ground, cut or milled by a rotating wheel whose motionis controlledis ground, cut or milled by a rotating wheel whose motionis controlled
by a link through the tracing device. Eg : The Celay : Mikronaby a link through the tracing device. Eg : The Celay : Mikrona
Technologies, Spreintenbach, Switzerland)Technologies, Spreintenbach, Switzerland)

ELECTROFORMINELECTROFORMINGG
A master cast of the prepared tooth is prepared and coated with a specialA master cast of the prepared tooth is prepared and coated with a special
die spacer to facilitate separation of the duplicating material. Afterdie spacer to facilitate separation of the duplicating material. After
applying a conductive silver layer to the duplicated surface (Gypsumapplying a conductive silver layer to the duplicated surface (Gypsum
product) , the dieproduct) , the die is connected to a plating head and connected to ais connected to a plating head and connected to a
power source and then placed in a plating solution. After a sufficientlypower source and then placed in a plating solution. After a sufficiently
thick layer of gold or other material is deposited, the gypsum is removedthick layer of gold or other material is deposited, the gypsum is removed
and the coping is sandblasted. Subsequent ceramic layers are condensedand the coping is sandblasted. Subsequent ceramic layers are condensed
and sintered in a conventional way.and sintered in a conventional way.

TROUBLESHOOTING:
When combinations of dissimilar metals are in direct physical contact,
GALVANIC CORROSION OR GALVANISM is produced. This may
occur either due to two adjacent dissimilar crowns or two dissimilar
opposing crowns. Hence care should be taken when two or more teeth
are being restored.
When the surface of crown is heterogeneous as regards to its
composition and surface topography corrosion ensues. Especially
solder joints. In case of surface irregularity such as roughness
concentration cell corrosion is seen. These can be avoided by proper
selection of alloy, proper heat treatment and immaculate finishing.
The correct mass of alloy required for a casting a particular wax
pattern is given by the formula:

Mm = Dm x Mw
Dw
Where:
Mm is mass of metal alloy
Dm is density of the metal alloy
Mw is mass of the wax pattern
Dw is density of the wax pattern
Because of difference in hardness, percentage elongation and ultimate
tensile strength, different trimming and polishing techniques are
employed for different alloys:
Gold alloy: Carbide burs, Al oxide, rubber wheels, Tripoli or rouge
Metal ceramic alloys: Carbide burs are preferred as Al oxide may
contaminate with residual abrasive and interfere with bonding.
Base alloys: Sand blasting or Carbide burs are used followed by
electrolytic polishing. www.indiandentalacademy.comwww.indiandentalacademy.com

Summary and conclusionSummary and conclusion
 ""INDIVIDUAL COMMITMENT TO A GROUPINDIVIDUAL COMMITMENT TO A GROUP
EFFORT-THAT IS WHAT MAKES A TEAMEFFORT-THAT IS WHAT MAKES A TEAM
WORK, A COMPANY WORK, A SOCIETYWORK, A COMPANY WORK, A SOCIETY
WORK, A CIVILIZATION WORK."WORK, A CIVILIZATION WORK."

References
 Phillips’science of dental materials – Kenneth J.Anusavice,11Phillips’science of dental materials – Kenneth J.Anusavice,11thth
Edition.Edition.
 Removable partial prosthodontics McCracken,9Removable partial prosthodontics McCracken,9thth
Edition.Edition.
 Dental laboratory procedures – Fixed partial dentures RobertDental laboratory procedures – Fixed partial dentures Robert
M. Murrow, Kenneth D. Rudd, John E. Rhoads.M. Murrow, Kenneth D. Rudd, John E. Rhoads.
 Notes on Dental materials – E.C.Combe,6Notes on Dental materials – E.C.Combe,6thth
Edition.Edition.
 Contemporary Fixed Prosthodontics – Stephen F. Rosenstiel,Contemporary Fixed Prosthodontics – Stephen F. Rosenstiel,
Martin F. Land, Junhei Fujimoto,3Martin F. Land, Junhei Fujimoto,3rdrd
Edition.Edition.
 Restorative dental materials – Robert G.Craig, John M.Restorative dental materials – Robert G.Craig, John M.
Powers.Powers.

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