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Transcript of Porcelains Used in Metal Ceramics / orthodontic courses by Indian dental academy
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PORCELAINS USED IN METALCERAMICS.
INDIAN DENTAL ACADEMY
Leader in continuing dental education
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INTRODUCTION
Metal ceramic restorations
combine the strength and
accuracy of cast metal with the
esthetics of porcelain.
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Metal ceramic restoration:
• "a fixed restoration that
employs a metal substructure
on which a ceramic veneer isfused" (Glossary of
Prosthodontic Terms, 1987).
• Indian dental academy
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A 13- unit metal-ceramic
restoration.
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• HISTORY/ DEVELOPMENT OF
CERAMICS.
• PROPERTIES OF FUSEDPORCELAIN.
• TERMINOLOGY• CHEMISTRY & COMPOSITION
• CLASSIFICATION OF DENTAL
CERAMICS.
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• METAL CERAMIC SUBSTRUCTURE
• BONDING BETWEEN THE METAL
DESIGN & PORCELAIN• PORCELAIN APPLICATION
METHOD
• FIRING PROCEDURES• FINISHING & ADJUSTMENTS
Metal ceramic technology.
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• The word Ceramics is derived
from Greek word ―keramos‖
which means ‗pottery‘ or ‗burntstuff‘.
Porcelain in English means
―china‖.
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Ceramics
Compounds of one or more metalswith a non metallic element,
usually oxygen. They are formedof chemical and biochemicalstable substances that are strong,
hard , brittle, and inert nonconductors of thermal andelectrical energy(GPT-7).
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Porcelain is defined as
A ceramic material formed ofinfusible elements joined by lowerfusing materials. Most dentalporcelain are glasses and areused in the fabrication of teeth fordentures, pontics and facings,
metal ceramic restorations,crowns, inlays, onlays, and otherrestorations.
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er es gna ons o me aceramics
• Porcelain-fused to metal.
• Ceramo-metal crown.
• Porcelain veneer crown.
• Porcelain bonded to metal
crown.
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Structure of ceramics
• Their atomic structure and resultant
properties depend, not only on
composition, but also on thermal history.
•Dental porcelain are glassy materials
Glasses may be regarded as a super cooled
liquids or as non crystalline solids
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History
• CHINESE ARE CREDITED WITHTHE DEVELOPMENT OF
PORCELAIN AS EARLY AS 1000
AD.• D‘ENTRECOLLES, INGRATIED
HIMSELF WITH CHINESE
POTTERS AROUND 1717 INORDER TO LEARN THE COVETED
PORCELAIN MANUFACTURING
PROCESS www.indiandentalacademy.com
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• IN 1760 FAUCHARD AND OTHERS
HAD REPORTED USING ‗BAKEDENAMEL.
• IN 1774 ALEXIS DUCHATEAU &
NICOLAS DUBOIUS
CONSTRUCTED COMPLETE
DENTURES FROM A MATERIAL
THEY REFERRED TO AS ―MINERAL
PASTE‖.
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• IN 1808 GIUSSEPPANGELO FONZI
DEVISED A METHOD TO MASS
PRODUCE INDIVIDUALPORCELAIN DENTURE TEETH
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• 1850 Samuel Stockton was the first to
mass produce these teeth first in America
• Claudius Ash created a artificial tooth
that could be placed over a post on
either a complete denture of FPD. Itwas known as ―tube‖ tooth.
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• 1889 Dr Charles H. Land gave the
idea of fusing porcelain to a thin
platinum foil. – he developed lowfusing porcelain in 1898. 1903 he
introduced the porcelain jacket crown
to dentistry
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• 1907 Stockton developed dental
porcelain.
• 1962 –M. Weinstein, S.Katz, and
A.B.Weinstein patented a method tofabricate the first metal ceramic
crown.
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• Two of the most important breakthroughs
responsible for the long-standing superbaesthetic performance and clinical
survivability of metal-ceramic restorations
are the patents of Weinstein and
Weinstein (1962) and Weinstein et al
(1962).
• One of these patents described the
formulations of feldspathic porcelain that
allowed systematic control of the sintering
temperature and thermal expansion
coefficient. www.indiandentalacademy.com
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• The other patent described the
components that could be
used to produce alloys thatbonded chemically to and
were thermally compatible withfeldspathic porcelains
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What are ceramics?
–Dental ceramics may consistprimarily of glasses ,porcelains,
glass-ceramics.
–The properties of ceramics arecustomized for dental application
by precise control of the type &
amount of the components usedin their production.
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• Ceramics are more resistant to
corrosion. Ceramics generally donot react with most liquids, gases,
alkalies & acids. And they remain
stable over long time.• Dental ceramics exhibit far to
excellent flexure strength & fracture
toughness.
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• Although ceramics are strong,
temperature-resistant & resilient
these materials are brittle and mayfracture when quickly heated and
cooled.
• Dental ceramics are non-metallic
inorganic structures,primarily
containing components of oxygen
with one or more metallic or semi
metallic elements.
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• Most ceramics arecharacterized by their refractory
nature, high hardness,(relatively low tensile strengthand essentially zero percent
elongation), and chemicalinertness.
Properties of ceramics.
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• For dental applications a
hardness of a ceramic less thanthat of enamel and an easily
polishable surface are desirableto minimize the wear damage that
can be produced on enamel by
the ceramic surface.
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1) Strength.
• Porcelain is a material having good
strength. However, it is brittle and
tends to fracture.• The strength of porcelain is usually
measured in terms of its flexure
strength or modulus of rupture.
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a) Flexure strength:
• It is a combination of compressive,
tensile, as well as shear strength.
• Glazed porcelain is stronger thanground porcelain.
• Ground-75.8 Mpa (11,000 psi)
• Glazed-141.1 Mpa (20,465 psi)
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b) Compressive strength:
• Porcelains have good compressive
strength.
• 331 Mpa (48,000psi)
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c) Tensile strength:
• Is low
• 34 MPa (5000psi).
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d) Shear strength:
• It is low and is due to the ductility
caused by the complex structure of
dental porcelain.• 110 Mpa (16000psi).
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Factors affecting strength.
• 1) Composition.
• 2) Surface integrity: Surface imperfections
like microscopic cracks and porosities
reduce the strength.
• 3) Firing procedure: Inadequate firing
weakens the structure as vitrification is not
complete. Overfiring also decrease
strength as more of the core gets
dissolved in the fluxes, thereby weakening
the core network.www.indiandentalacademy.com
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2) Modulus of elasticity:
• Porcelain as high modulus of
elasticity.
• 69 GPa .
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3) Surface hardness:
• Porcelain is much harder than natural
teeth.
• 460 KHN
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4) Wear resistance:
• Porcelain is more resistant to wear
than natural teeth. Thus, it should not
be placed opposite to natural teeth.
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5) Specific gravity:
• Is 2.242.
• The specific gravity of fired porcelain
is usually less, because of thepresence of air voids. It varies from
2.2 to 2.3.
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6) Dimensional stability:
• Porcelain is dimensionally stable after
firing.
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7) Chemical stability:
• It is insoluble and impermeable to oral
fluids. Also it is resistant to most
solvents. However, contact withhydrofluoric acid causes etching of
the porcelain surface.
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8) Esthetic properties:
• Are excellent. It is able to match
adjacent tooth structure in
translucence, color and intensity.
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9) Biocompatibility.
• It is compatible with the oral tissue.
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10) Th l tibilit
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• Refers to the ability of a metal
and its veneering porcelain tocontract at similar rates.
• The coefficient of thermalexpansion by definition is thechange in length per unit of
original length of a material whenits temperature is raised by 1o K
• .
10) Thermal compatibility
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Thermal compatibility (contd.)
• When the co efficient of thermalexpansion of metal and porcelainare compatible the tensile stressthat develop during cooling areinsufficient to cause immediate
cracking of porcelain or delayedcracking after cooling at roomtemperature.
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• Porcelains have coefficient of thermal
expansion between 13.0 and 14.0 X
10-6 and metal between 13.5 and14.5 X 10-6.
• The difference of 0.5 X10-6 in thermal
expansion between metal andporcelain causes the metal to contract
slightly more than does the ceramic
during cooling after firing the
porcelain.
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• This puts the ceramic under
slight residual compression
which makes it less sensitiveto applied tensile forces.
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Methods of strengthening ceramics
• Strengthening occurs through two
mechanism,
• 1) development of residualcompressive stresses.
• 2) interruption of crack propagation.
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• Development of residual compressive
stresses.
• 1) Ion exchange: (chemicaltempering)
• exchange of potassium ions (which is
35% larger) for sodium ions. thus
there is squeezing of the potassium
ion into smaller spaces. This creates
a residual compressive stresses on
the surface of the glass.
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• Thermal tempering.
• By rapidly cooling the surface of the
object while it is hot and in the moltenstate. This rapid cooling produces a
layer of rigid glass surrounding a soft
core. As the molten core solidifies ,it
tends to shrink, creates a residual
tensile stress in the core thus leaving
the outer layer in residual
compressive stress.
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S O CO C
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• THERMAL EXPANSION COEFFICIENT
MISMATCH:
• Ceramic in combination with metal areheated together .The metal which is
veneered with ceramic has a higher
coefficient of thermal expansion than the
ceramic. Hence on cooling, the metal
contracts more than the ceramics thus
leaving the outer layer, of ceramic in
residual compressive stress.
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Interr ption of crack propagation
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Interruption of crack propagation.
• Two different types of dispersions used to
interrupt crack propagation are:
• 1) By absorption of energy by the
dispersed tough particle from the crack
and thus depleting its driving force for
propagation.
• 2) By change of crystal structure under
stress to absorb energy from the crack.
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1) Di i f t lli
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1) Dispersion of a crystalline
phase.
• A tough crystalline material like alumina is
added in particulate form. The glass is
toughened and strengthened because the
crack cannot penetrate the aluminaparticles as easily as it can propagate in
the glass. Thus the aluminous porcelains
were developed for Porcelain JacketCrown. (PJC)
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Transformation toughening.
• A crystalline material is incorporated that
is capable of undergoing a change in
crystal structure when placed under
stress. The crystalline material used istermed as partially stabilized zirconia
(PSZ).The refractive index of PSZ is
higher than glass matrix. Thus the PSZscatters the light producing an opacifying
effect.
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Terminology.
Porcelain-fused-to-metal (PFM): a
popular alternative designation
for the metal ceramic restoration.
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• Porcelain bonding: a term used toexplain the mechanisms by which
dental porcelain fuses or adheres to ametal substructure
• Coping: the word coping can be used toidentify the metal substructure of single-unit crowns designed for bonding todental porcelain. Copings are made ona single tooth preparation, which may
be a single unit or attached to ponticsfor a fixed partial denture.
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• Framework: this term is often applied
to fixed partial dentures and identifiesa one-piece substructure composed
on either several copings attached to
a pontic or multiple single units thatare joined together as a single
structure.
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• Degassing: the process of heat-treatinga cast metal substructure in a porcelain
furnace as one of the preparatory stepsto applying an opaque porcelain.Subjecting the finished metal toelevated temperatures (980° to
1,050°C) in a reduced atmosphere(vacuum) or in air reportedly burns offorganic surface impurities andeliminates entrapped gaseous
contaminants. A newer and perhapsmore appropriate term—oxidizing—hasemerged in the literature to describe this
procedure. www.indiandentalacademy.com
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• Oxidation (or oxidizing): the
process by which a metalsubstructure is heated in a
porcelain furnace to produce an
oxide layer for porcelain bondingas well as to cleanse the
porcelain-bearing surfaces of
contaminants
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ADVANTAGES OF DENTAL
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ADVANTAGES OF DENTAL
PORCELAIN
• Dental ceramics are attractive
because of their biocompatibility,
long-term color stability, wear
resistance, and their ability to be
formed into precise shapes.
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Disadvantages.
• They require costly processing
equipment and specialized
training.• Susceptibility to brittle fracture
at relatively low stresses
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The chemical components of dental
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The chemical components of dental
porcelain.
• Feldspar (K2O – Al 2O3-6SiO2 & Na2o –
Al2o3-6SiO2)
• Quartz (SiO2)
• Alumina (Al2O3)
• Kaolin (Al2O3 -2SiO2 2H2O)
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Feldspar
• Found as a mix of two substances .• It does not occur in pure form in
nature
• Mineral is crystalline and opaque
• Color is indefinite and between gray
and pink.
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Type of Chemical Other Properties uses
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Type of
feldspar
Chemical
formula
Other
names
Properties uses
Potassiu
m
aluminiu
m
silicate.
(K2O.Al
2O
3.6Si
O2 )
orthocla
se or
potashfeldspar
1.Reduces the
fluidity of the molten
materials
2.helps to maintain
the form of the
porcelain buildup
3.adds translucent
qualities to fired
restorations.
Found in
majority
of the
porcelain
systems
Sodium
aluminu
m
silicate
(Na2O.
Al2O3.
6SiO2)
albite or
sodiumfeldspar
.
1.Lowers fusion
temperature of the
porcelain.
Less
preferred
Lime
feldspar
CaO.2
Al2O3.2www.indiandentalacademy.com
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• On heating it becomes glassy and
fuses at 1290 C, on overheating itmay loose its shape .
• Impurities : Mica
Iron –it is important to
remove it as its oxides act as strong
coloring agents.
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Removal of impurities
Iron-
• manually only light colored pieces of
feldspar are selected• Feldspar is grounded into fine powder
and vibrated down inclined planes
surrounded by induction magnets
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• Primarily responsible for forming
glass matrix
Functions
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• Glass modifiers such as the oxides of
potassium, sodium, and calcium acts
as fluxes to increase a porcelains
coefficient of thermal expansion.
• The fluxes increase the porcelainscoefficient of thermal expansion by
breaking up oxygen crosslinking.
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• Primarily responsible for
forming glass matrix
• Has a fusion temperature
Silica (Quartz or Flint) SiO2
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SiO2
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• Silica contributes stability to the
mass of porcelain during heating
by providing a framework for theother ingredients.
• Also acts to strengthen the
porcelain.
Functions
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KAOLIN (Al2 o3-2sio22H2o)
• It is deposited along the banks and at the
bottom of streams in the form of clay.•
Only purest form of clay are used fordental porcelain.
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Preparation of clay
• Repeated washing until all foreign
materials are separated.
• Allowed to settle.• Dried and screened.
• Nearly white powder is obtained.
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Properties of clay
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Properties of clay
I. Its gives OPAQUENESS to porcelain
II. MOULDABLE :On mixing with water itbecomes sticky and aids in forming a
workable mass of the porcelain duringmolding.
III. Clay-water suspension maintains itsshape during firing in a furnace.
IV. On subjecting to high heat it adheres tothe framework of Quartz particles andshrinks considerably.
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• Little or no kaolin is found is
modern day low fusing
porcelain.
• Kaolin is not used in enamelpowder as it will decrease its
translucency.
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Alumina (Al o )
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Alumina.(Al2o3)
• The hardest and perhaps the
strongest oxide.
• Its CTE is similar to the low fusingporcelains.
• It also strengthens the porcelain.
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Manufacturing of ceramics
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Manufacturing of ceramics
powder
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Fritting.
• The process of blending, melting andquenching the glass components istermed ―fritting‖.
• All the raw mineral powders are mixedtogether in a refractory crucible andheated till a molten mass is formed.
• It is then quenched in water.
• It immediately breaks into fragments andthis is termed the ―frit‖.
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• Frits are ground to the specific particle
size established by individual
manufacturers for their particular brand of
porcelain.
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• TOOTH PREPARATION FOR
THE METAL CERAMIC
RESTORATION
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• Depth
orientation
grooves flatend tapered
diamond.
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• Make at least
two verticalcuts in the
incisal portionof the facial
surface.
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• Sink the side of
the diamond intothe mesiodistal
center of the
facial
surface,maintain
the instrument
alignment parallel
to the gingivalsurface of the
facial segment.
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• Make two incisal
orientation grooves
that are 2mm
deep.The diamondshould be parallel to
the incisal edge
faciolingally.
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• Incisal
reduction is
done with the
flat end tapered
diamond.
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• Facialreduction;
incisal half,flat
end tapereddiamond.
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• If there soundtooth structure
inter proximally,
wingpreparation is
done.
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• Begin the lingual
reduction with thesmall round
diamond with
diameter of
1.4mm. Sink this
instrument into
the lingual tooth
structure up to0.7mm.
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• Lingual axial reduction
torpedo diamond and carbidefinishing bur.
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• Lingual
reduction is
done with thesmall wheel
diamond.
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• Smooth the entire
facial surface with
no.171 bur .Round
over the any sharp
angles on the incisal
angle or along the
edges of the incisalnotches with no.171
bur.
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Components of the metal
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Components of the metal
ceramic restoration
• Two major components:
• a metal substructure and a porcelain
veneer.• The surface oxide layer that lies
between the metal and the porcelain
veneer could be considered aseparate component, but it is anintegral part of the casting alloy
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The basic components of a traditional
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The basic components of a traditional
porcelain kit include
1.opaque porcelain.
2.dentin porcelains
3.enamel porcelainsModifiers, stains & glazes.
Newest products has high fusing
shoulder porcelains.
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The metal substructure
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• Conventional low-fusing dental
porcelain lacks the strengthrequired of an all-porcelainrestoration, so a metal substructureis added to support the porcelainveneer.
• The thickness of the metal copingcan vary, depending on the type ofcasting alloy used and the amountof tooth structure reduced by thedentist.
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The oxide layer
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y
• Most metal ceramic alloys are
oxidized after the porcelain-
bearing area of the restoration hasbeen properly finished and
cleaned.
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• The metal oxides that form on the
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The metal oxides that form on thealloy's surface during this heat-
treatment procedure play a key rolein bonding the dental porcelain tothe underlying metal substructure.
• Because noble elements do notoxidize, an alloy's base metalconstituents are principally
responsible for forming this oxidelayer.
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• Differences in alloy composition
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Differences in alloy composition
require that oxidation techniques be
alloy specific
• Ideally this oxidation should be no
more than a discrete, monomolecular
film on the alloy's surface for all metal
ceramic alloys, irrespective ofcompositional differences.
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Opaque porcelain layer
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Opaque porcelain layer
• These porcelains are made opaque by theaddition of insoluble oxides, such as
• tin oxide (SnO2),
• titanium oxide (TiO2),
• zirconium oxide (ZrO2),
• cerium oxide (CeO2),
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Opaque porcelain layer contd
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Opaque porcelain layer contd.
• oxide, and
• rubidium oxide,
• barium zinc oxide.• Such oxides have high refractive
indices, so they scatter light.
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Composition on chemical
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analysis
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• Between 8% and 15% of an opaque
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• Between 8% and 15% of an opaque
powder is composed of metallic
oxides, and some particles may beless than 5 um in size.
• Even small differences in particle sizedistribution are thought to influence
the ability of opaques to mask the
color of a metal substructure.
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Th l i th j
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• The opaque porcelains three major
functions:
• (1) to establish the porcelain-metal
bond,
• (2) to mask the dark color of themetal substructure, and
• (3) to initiate the development of
the selected shade of porcelain.
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• A uniform thickness of 0.2 to 0.3
mm generally is regarded as ideal.
• That masking power is influencedby the amount and the color of the
oxidized (degassed) metal casting
(Naylor, 1986)
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• A casting alloy of a different
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A casting alloy of a different
composition might generate a thick,
dark oxide layer (Naylor, 1986) andrequire a thicker opaque covering.
• The thickness of the opaque layer
needed to veneer the metal and
mask the surface oxides differs
among brands of porcelain and
even varies for different shades
within the same porcelain system
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Body porcelains
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y p
• Body porcelain collectively describes
four principal types of porcelain
powders used to recreate the "body" of
a restoration: dentin (body or gingival),
enamel (or incisal), translucent, andmodifier.
• These body porcelains are mixed with
either distilled water or a special liquid(provided with the porcelain kit) that
helps to prevent the buildup from drying
out rapidly www.indiandentalacademy.com
• They are applied directly over the fired
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• They are applied directly over the fired
opaque layer .
• The dentin, enamel, translucent, and
modifier powders all have the same
chemical and physical properties, they
may be intermixed freely if customshading is desired.
• They differ in appearance in the fired
state because of variations in theamount and type of metallic oxide
pigments each contains.
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The dentin porcelain veneer
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• The major color contribution is derivedfrom the pigmented metal oxides in thedentin body porcelain
• It is this initial layer of dental porcelainthat imparts the dentin shade
associated with, but not confined to, thegingival two thirds of a tooth.
• The dentinal layer is overbuilt slightly,cut back, and overlaid with enamelporcelain in those sections of therestoration where greater translucencyis desired.
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F t h d
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• For more accurate shade
duplication, estimates of thecombined thickness of fired dentin
and enamel porcelains range from
a minimum of 0.5 to 1.0 mm to amaximum thickness of 1.5 to 2.0
mm
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• For uniformity of shade and maximum
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y
strength, it is desirable to have an even
thickness of porcelain covering themetal substructure.
• The minimum total thickness of
porcelain may be between 1.2 to 1.3mm at the middle one third of the
restoration and 1.5 to 1.6 mm at the
incisal edge (Yamamoto, 1985).
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ENAMEL PORCELAIN VENEER
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ENAMEL PORCELAIN VENEER
• Enamel porcelains are moretranslucent than dentin porcelains.
• The enamel porcelains are usually in
the violet to grayish range & impart acombination of true translucency &
the illusion of the translucency by
virtue of their grayish or some timesbluish appearance.
• www.indiandentalacademy.com
• When fired, enamel porcelains are more
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When fired, enamel porcelains are more
translucent than dentin porcelains
(McLean, 1979).• They also have a more restricted range
of shades. A typical porcelain system
may provide only four or five bottles ofenamel powders to cover the entire
range of shades in the kit.
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Translucent porcelains
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Translucent porcelains
• Translucent porcelains are nottransparent, they do not allow the
transmission of all light.
• They are applied as a veneer over nearlythe entire surface of a typical porcelain
buildup.
• This veneer imparts depth and a naturalenamel-like translucency without
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BODY MODIFIERS
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• These porcelains are more color concentrated &were designed to aid in the achieving internal
color modifications.
• They are used to distinguish the dentin, enamel
& translucent porcelains, because they have the
same basic physical & chemical properties.
• All these powders are basically same materials,
they do differ in the appearance because of themodifiers.
BODY MODIFIERS
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STAINS
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• Stain powders contain less silica oralumina & more sodium & potassium
oxides.
• They contain high concentration of
metallic oxides.
• They are created by mixing themetallic oxides with lower fusion point
glasses
STAINS
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GLAZES
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GLAZES
• Glazes are generally colorless, low fusingporcelains.
• They possess considerable fluidity at high
temperatures.• They fill small surface porosities &
irregularities. when fired helps to recreate
the external glazy appearance of thenatural tooth
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GLAZE (Contd.)
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GLAZE (Contd.)
• A glazed ceramic surface isgenerally considered beneficial by
increasing the fracture resistanceand reducing the potential
abrasiveness of ceramic surfaces
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Color coding
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Color coding
• By convention dentin powders are pinkand enamel powders are blue.
• These organic colors burn off during firing
procedure and do not affect the shade ofthe fired restoration in any way.
• Some manufacturers color code the
distilled water instead of the powder.e.g.pencraft porcelain
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CLASSIFICATION OF DENTAL
CERAMICS
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CERAMICS
• Different types of dental ceramics areavailable These include core ceramic,
liner ceramic, margin ceramic,
opaque dentin (also, body or gingival)ceramic, dentin ceramic, enamel
(incisal) ceramic, stain ceramic, glaze
ceramic, and addition ceramic
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• These products can be
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classified in several possible
ways according to their: (1) useor indications (anterior,posterior, crowns, veneers, post
and cores, FPDs, stain ceramic,and glaze ceramic);
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• (2) composition (pure alumina
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• (2) composition (pure alumina,
pure zirconia, silica glass, leucite-based glass-ceramic, and lithia-
based glass-ceramic
• (3) processing method (sintering,partial sintering and glass infiltration
,CAD-CAM, and copy-milling);
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• Microstructure (glass, crystalline,and crystal-containing glass);
• Translucency (opaque,translucent, and transparent);
Fracture resistance; or
Abrasiveness
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Based on the method of fabrication
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1. Condensation porcelains usingcondensation and sintering
2. Castable ceramics –Dicor-Dentsply
3. Pressable ceramics
4. Machinable ceramics
5. Infiltrated ceramics
6. Injection molded ceramics –Cerestore
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Classification (Mclean)
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1) Regular feldspathic porcelain
2) Aluminous porcelain
3) Metal bonding porcelain.
( )
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Based on their fusion temperature (Phillips,1982)type Fusing
temperature
uses
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temperature
range
High fusingporcelains-
1288 to 1371C
1200-1400
used formanufacturing
denture teeth .
Both aresimilar in
composition
and
microstructure.
Medium fusing
Porcelains-
1093 to 1260
C
1050-1200
for all ceramic
restorations
and
prefabricatedpontics.
Low fusing
porcelains-
871 to 1066 C
800-1050
for metal
ceramic and all
ceramic.www.indiandentalacademy.com
METAL SUB STRUCTURE
DESIGN
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DESIGN.
• Majority of the porcelain-to-metal bondfailures occur as a direct result of improper
substructure design
• Errors in the preparation of the metalceramic substructure frequently go
unnoticed until the brittle porcelain veneer
fails in service.
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METAL SUB STRUCTURE
DESIGN
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• TYPES
• FUNCTIONS.
• DESIGN.
DESIGN.
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Types of metal ceramic system.A C l i ll
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• A. Cast metal ceramic alloys:
• 1.Noble-metal alloy systems:• High gold - a) Gold platinum palladium.
• Low gold - b) Gold palladium silver.
• Gold free - c) Palladium silver.• 2.Base metal alloys systems:
• Nickel chromium alloy.
• Cobalt chromium alloys ( rarely used inceramic bonding).
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• B. Foil copings:
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g
•
• a) Bonded platinum foil coping.
• b) Swaged gold alloy foil coping.
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a) Bonded platinum foil coping:
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) p p g
• Another method of bonding porcelain tometal is the use of tin oxide coatings onplatinum foil.
• The method consists of bondingaluminous porcelain to platinum foilcopings.
• Attachment of the porcelain is secured by
electroplating the foil with a thin layer of tinand then oxidizing it in a furnace.
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• The objective of this type ofrestoration is to improve esthetics.
• The thicker cast metal coping that is
normally used is replaced by a thinner
platinum foil, thus allowing more
space for the porcelain.
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b) Swaged Gold Alloy Foil Coping:
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• A laminated gold alloy supplied in flutedshape is also used as an alternative to the
cast metal coping.
• The foil is swaged onto the die and flamesintered to form a coping.
• An ―interfacial alloy‖ powder is applied
and fired and the coping is then veneeredwith porcelain.
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Primary functions:-
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• The casting provides fit of the
restoration to the prepared tooth.
• The metal forms oxides that bondchemically to the dental porcelain.
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• The coping serves as a rigid
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• The coping serves as a rigid
foundation to which the brittleporcelain can be attached for
increased strength & support.
• The sub structure restores the
tooth's proper emergence profile.
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Secondary functions.
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• Metal occlusal & lingual articulatingsurfaces generally less destructive to
the enamel of the opposing natural
tooth.
• Fabrication of the restoration with
minimal occlusal clearance has more
potential for the success with metal
substructure than all ceramic alloys.
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Metal sub structure design
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• Majority of the porcelain-to-metalbond failures occur as a direct result
of improper substructure design
• Errors in the preparation of the metal
ceramic substructure frequently go
unnoticed until the brittle porcelain
veneer fails in service.
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Sub structure design (contd)
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• Hence necessary to understandthe essentials of proper
substructure design, since it will
help to ensure the longevity of the
final prosthesis.
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Principles of substructure
design
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design.
• Are the occlusal contacts to bein metal or porcelain?
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• Occlusion in metal requires less tooth
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q
reduction (1 to 1.5 mm).
• Approximately 2 mm of occlusal
reduction is necessary for posterior
teeth and 1 to 1.5 mm for anteriorteeth requiring porcelain on occluding
surfaces.
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• Metal surfaces can be more easily
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y
adjusted and repolished at chair side
without adversely affecting the
restoration.
• On the other hand, removing theglaze of a metal ceramic restoration
during intraoral adjustments weakens
the porcelain greatly
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• 2. Are the centric occlusalcontacts 1.5 to 2mm from the
porcelain-metal junction?
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• occlusal contacts when placed
directly on or close to the porcelain-
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directly on or close to the porcelain-
metal junction, there is an increasedlikelihood the porcelain will chip or
fracture at that point of contact .
• Porcelain is strongest undercompression and weakest under
tension, so situations that induce
tensile stresses in the ceramic duringfunction are more apt to promote
bond failureswww.indiandentalacademy.com
• A substructure should be designed so
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g
the functional incisal or occlusal
contacts are located at least 1 .5 mm
and perhaps as much as 2 mm from
the metalporcelain junction.
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• Do not
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design the
sub structure
so contact
occurs at theporcelain
metal
junction.
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• When the anteriorteeth occlude in thei i l h lf f th
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gingival half of the
maxillary teeth orwhen the lingualtooth reduction isless than 1mm it is
best to design thesub structure withocclusion in themetal.
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• 3.Are the interproximal contactsto be restored in metal or
porcelain?
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• The inter proximal contact areas of
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anterior teeth, and at least the mesial
contacts of posterior teeth, are
frequently restored in porcelain
• with porcelain inter proximal contactareas would be more esthetic,
particularly with anterior teeth.
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• It is important to provide proper metal
t t l i i l id
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support to a porcelain marginal ridge
in the substructure design to preventpossible fracture
• However, the distal inter proximal
contacts of posterior teeth may be
restored in either metal or porcelain
because these areas are not as
critical esthetically.
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• The ultimate goal of any substructure
is to support an even thickness (1mm
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pp (
minimum, 2 mm maximum) of theporcelain veneer.
• If this maximum thickness is
exceeded, the ceramic layer may nolonger be properly supported,
resulting in a catastrophic failure at
the cusp tip or incisal edge
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• 5. Is the substructure thickenough to provide a rigid
foundation for the porcelain
veneer?
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• Areas to be veneered with
l i t b t l t 0 3
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porcelain must be at least 0.3 mm
thick.
• with base metal alloys, the
coping can be reduced to 0.2 mmor less and still be strong enough
to support the porcelain
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How does dental porcelain bond to
metal?
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metal?
(1) van der Waals forces (Lacy, 1977),• (2) mechanical retention,
• (3) compression bonding, and
• (4) direct chemical bonding (Lacy,
1977; McLean, 1980;
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van der Waals forces
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• The attraction between chargedatoms that are in intimate contact yetdo not actually exchange electrons isderived from van der Waals forces.
• These secondary forces aregenerated more by a physicalattraction between charged particles
• Van der Waalsforces are generallyweak.
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• The better the wetting of the
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The better the wetting of the
metal surface, the greater the vander Waals forces.
• porcelain's adhesion to metal can
be diminished or enhanced by
alterations in the surface
character (texture) of theporcelain-bearing surface on the
substructurewww.indiandentalacademy.com
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• van der Waals forces are onlyminor contributors to the overall
attachment process.
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Th l i b i f t l
Mechanical retention
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• The porcelain-bearing area of a metal
casting contains many microscopicirregularities into which opaque
porcelain may flow when fired.
• Air abrading the metal with aluminum
oxide is believed to enhance
mechanical retention further by
eliminating surface irregularities
(stress concentrations)www.indiandentalacademy.com
• Mechanical retention's
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Mechanical retention s
contribution to bonding may berelatively limited.
• Dental porcelain does not require
a roughened area to bond to
metal but some surface
roughness is effective inincreasing bonding forces
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Compression bonding
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• Dental porcelain is strongest undercompression and weakest under
tension; hence, if the coefficient of
thermal expansion of the metalsubstrate is greater than that of the
porcelain placed over it, the porcelain
should be placed under compressionon cooling
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• the metal contracts faster than the
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porcelain but is resisted by theporcelain's lower coefficient of
thermal expansion.
• This difference in contraction
rates creates tensile forces on the
metal and correspondingcompressive forces on the
porcelain.www.indiandentalacademy.com
Chemical bonding
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• The single most significantmechanism of porcelain-metal
attachment is a chemical bondbetween dental porcelain and the
oxides on the surface of the metal
substructure
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• The two hypothesis that explains
chemical bonding are
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chemical bonding are
• 1, The sandwich theory
the oxide layer is permanently
bonded to the metal substructure on
one side while the dental porcelain
remains on the other
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• The oxide layer itself is
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The oxide layer itself is
sandwiched in between the metalsubstructure and the opaque
porcelain. This "sandwich" theory
is undesirable in that a thick oxidelayer might exist that would
weaken the attachment of metalto porcelain
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• Chemical "bonding" is generallyaccepted as the primary
mechanism in the porcelain-metal
attachment process
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The oxidation (degassing) process
Aft th t t l i
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• After the cast metal ceramiccastings have been properlyfinished with uncontaminatedcarbide burs or ceramic abrasivesthe castings are heat-treated in aporcelain furnace (in air or a
vacuum) to a designatedtemperature for a specified periodof time (Naylor, 1986).
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• The heat-treatment process
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allows specific oxides to form onthe metal surface. These oxides
are responsible for the chemical
porcelain- metal "bond."
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• A high-gold-content alloy contains
oxidizable trace elements such as tin
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oxidizable trace elements such as tin,
indium, and iron to produce anadherent oxide layer. Because
elements like gold and the other noble
metals do not oxidize, it is often
necessary to hold these castings at
temperature for several minutes to
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• The base metal alloys readilyoxidize, but trace elements are
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still added in an effort to form aparticular type of oxide for astable bond .
• The oxidation procedure may becarried out in a vacuum tominimize the amount of oxidation,
and the hold time is often reducedor omitted.
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• A properly oxidized casting often
has a distinctive appearance in
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terms of color and character(texture, thickness, etc).
• That appearance of a properly
oxidized metal substructure differs
among alloy systems and may
also differ among alloys within thesame system.
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• Some manufacturers do notrecommend an oxidation/
degassing step; instead, they
advocate minimizing the number
of firings to which the casting is
subjected.
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Removing the oxide layer
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• Two principal methods for
removing oxides are
– Acid treatment (chemical method)
–Nonacid treatment (mechanical
method).www.indiandentalacademy.com
Acid treatment(chemical method)
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• Different types of acids are used to reduceor eliminate surface oxides, including
hydrofluoric, hydrochloric, and dilute
sulfuric acid.
• The potential hazards of these acids
require that they be stored and used in
clearly marked, resealable plastics bottles.
• It is advisable to wear protective rubber
gloves and eye protection during all
handling procedures.www.indiandentalacademy.com
• A rubber-tipped instrument should beused to place oxidized castings into
the acid appropriate for the alloy.
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the acid appropriate for the alloy.
• Place the covered container in anultrasonic unit for the time
recommended by the alloy
manufacturer.
• Remove the casting and thoroughly
rinse it under tap water. For the finalcleaning step, put the coping in a
container of distilled water and clean
it lt i ll f 10 t 15 i twww.indiandentalacademy.com
Nonacid treatment(Mechanical method)
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• Castings can be air-abraded with pure, 50-um aluminum oxide (Al2o3) that is non-
recycled.
• Steam clean or ultrasonically clean thecasting in distilled water for 10 to 15
minutes before applying the opaque
porcelain.
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Porcelain-metal bond failures
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• Metal ceramic alloys, whether nobleor base metals, all oxidize differently
because of variations in their
composition.• If the oxidation process is not
performed properly, the subsequent
porcelain-metal bond may be weakand may lead to bond failure.
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Porcelain delamination
With b t l ll th
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• With base metal alloys, the
separation of the porcelain veneer
from the metal substrate can be
more a loss of the "attachment" ofthe oxide layer that is either too
thick or is poorly adherent to the
metal substructure.
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Porcelain delamination contd
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• Overoxidation has been a particularproblem with the heavily oxidizing
base metal alloys and has been
linked to their increased tendency forbond failures .
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• Bond failures are not caused by a lossof the chemical bond between the
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ceramic and the oxide layer• on the contrary, the porcelain might
remain visibly attached to the oxides
but the oxide layer may be so thick thatthe bond is lost through it .
• This particular problem is caused by
the formation of a thick and poorlyadherent oxide layer.
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Classification of bond failures inmetal-ceramics.
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• (Given by O‘ Brien (1977). • 1) Metal – Porcelain:
• Fracture leaves a clean surface of
metal. Seen when metal surface is devoidof oxides. May also be due to
contaminated or porous metal surface.
Usually occurs in high gold alloys.
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• 2) Metal oxide – Porcelain:
• Porcelain fractures at metal oxide
surface leaving oxide firmly attached to
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surface, leaving oxide firmly attached to
metal .Seen more often in base metal alloysystems.
• 3) Metal – Metal Oxide:
• Metal oxide breaks away from themetal and is left attached to the porcelain.
Seen commonly in base metal alloy
systems due to over production ofchromium and nickel oxides.
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• 4) Metal Oxide –Metal Oxide:
• Fracture occurs through the metal
oxide Results from overproduction of
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oxide. Results from overproduction of
oxide causing sandwich effect between
metal and porcelain. Occurs during the
usage of nickel-chromium alloys.
• 5) Cohesive within Metal:
• More common in bridges where the
joint area breaks. Rarely seen in single
crowns.
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• 6) Cohesive within Porcelain:
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6) Cohesive within Porcelain:
• Tensile failure within porcelain. Bond
strength exceeds strength of porcelain.
Seen in high gold content alloys.
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• Excessive
absorption of
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oxides by theporcelain can lower
the porcelain's
coefficient of
thermal expansion,
alter the final
shade (cause a
graying or bluing),or do both (Naylor,
1986www.indiandentalacademy.com
• Changes in theshade of the
porcelain may
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not be noticeablewith posterior
restorations,
particularly if agreater thickness
of porcelain
masks the darkoxides
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Incompatible materials• Further more, bond failures are not always
attributable to improper oxidation but may
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attributable to improper oxidation but may
actually be caused by a physical
incompatibility between the porcelain and
the metal substructure. The difference in
the coefficient of thermal expansion of theveneering porcelain and the metal ceramic
alloy may be slight yet sufficient to be
responsible for cracking of the ceramicveneer or substantial enough to result in
porcelain debonding.www.indiandentalacademy.com
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Overoxidation/underoxidation
• The oxidation procedure varies for alloys
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p y
of different compositions.• Careful processing followed by an
assessment of the postoxidation
appearance of each casting will ensurethat the procedure was accomplishedcorrectly.
• Castings that are either overoxidized or
underoxidized should be reprocessedaccordingly until a uniform oxide of thedesired color and thickness recommendedfor the alloy involved has formed.www.indiandentalacademy.com
• Contamination
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–castings that demonstrate some formof contamination may not have to beremade but by simply refinishing a
substructure's porcelain-bearingsurface may be all that is necessarywhen surface debonding becomesevident. Uncontaminated finishingmaterials are used to prevent this.
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• Simply
refinishing this
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casting removedthe surface and
subsurface
contaminationand resulted in
an appropriate
porcelain-metalbond.
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Applying Porcelain to the MetalSubstructure
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• The application of dental porcelain to
the metal substructure is the single
most demanding procedure in the
fabrication of a metal ceramic
restoration.
• As a rule, the skills needed for thisparticular process require the most
effort to perfect.www.indiandentalacademy.com
Instruments and equipment
• Brushes
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• A variety of brush sizes and styles areavailable in porcelain instrument kits, themost important of which are the brushesused for building or stacking porcelain.
. The size range varies from a no. 4 to a no. 8.Sable brushes are the standard becausethey permit easy manipulation of the
porcelain.
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• Another frequently used instrument is a
large no.10 brush, often referred to as a
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g ,
whipping brush
• A basic instrument kit should also include
flat brushes with relatively stiff bristles.
These large- and small-sized brushesshould be kept dry because they are used
exclusively to remove porcelain particles
from non porcelain-bearing areas and frominside the substructure prior to firing.
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• Very small no. 0 to no. 000 sable
brushes are required for the
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brushes are required for the
placement of stains or small
increments of porcelain. These
brushes are useful anywhere
maximum control is necessary
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Carving Instruments• Porcelain carving instruments, designed for
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shaping and carving porcelain buildups.• Carving instruments serve two principalfunctions.
• 1.Those with a serrated handle can beused to condense wet porcelain.
• 2.Instruments with blades, as well as thesmall discoid carver, can be used to build
(stack) porcelain, shape the buildup, andcarve the porcelain.
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Spatula
• Small, flexible, metal spatula is used
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p
to dispense and mix porcelain.• Any small metal fragments generated
during mixing can then be introduced
into the wet porcelain ascontaminants.
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• This metal debris can dramatically discolorthe mix as well as the fired porcelain
restoration. With careful use, however, the
metal mixing spatula need not be abraded.
• But for added safety, a glass mixing rod is
often substituted for the metal spatula to
avoid this problem altogether.
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Razor knives
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• Another necessity in the basic set of
instruments is some type of razor knife,
equipped with a thin, flexible blade for
carving the porcelain buildup.
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Hemostat• A small, straight or curved hemostat is
needed to hold the work during the
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needed to hold the work during theopaquing process and during porcelainadditions and condensation.
• Hemostats can be modified to hold the
metal substructure securely withoutdamaging the metal margins. However, an18-gauge handle added to the lingual collarprovides a convenient, safe, yet secure gripfor removing the restoration from theworking cast and holding it duringcondensation
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Glass or ceramic mixing slab
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• Finally, either a glass slab, ceramic tile, orceramic tray can serve as a plate for
mixing and storing the porcelain during the
buildup procedure. Initially, a small mixing
slab will suffice (Fig 8-9a).
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• As modifiers are added and morecomplex buildups are attempted,a larger
working surface will be required to
accommodate all the different porcelain
mixtures
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PORCELAIN CONDENSATION.
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• Condensing dental porcelain actuallyrefers to any procedure that results in the
unfired porcelain particles being tightly
packed on to themselves.
• As the particles moves closer together, the
air and moisture previously occupying the
space between the individual particles
move to the surface of the buildup.
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• Any liquid or air that remains trapped inthe unfired porcelain will form voids in the
unfired ceramic.
• The presence of porosity in fired porcelainweakens the restoration and impairs its
esthetic qualities.
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Capillary action.
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• The technique of blotting a wetbuilt up with absorbent paper
uses surface tension.
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Vibration.
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• Is created by passing a serratedinstrument over the neck of a
hemostat in which the restoration is
held.• Vibration is a means to mechanically
draw additional moisture to the
surface where it can then be removedby blotting paper.
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Spatulation.
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• A spatula is used to apply ,then rub the porcelain built up
to force the liquid to the
surface.
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Whipping.
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• A no. 10 sable brush is rapidlymoved over the porcelain surface
with a whipping motion. The
whipping motion brings the liquidto the outer surface for blotting.
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Dry powder addition.
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• Requires dry porcelain powder besprinkled on an area of wet
porcelain, using the existing liquid
to moisten the powder addition.
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Opaquing the metalsubstructure
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• The areas of the substructure that willbe veneered with porcelain must notbe touched and should be protected
from dust, oils from the skin, and anyother forms of contamination
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Applying opaque porcelain—
glass rod technique
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• First wet the oxidized metal substructure
to be veneered with distilled water and
gently vibrate the casting to thoroughly wetthe surface.
• A wet surface makes porcelain application
easier and reduces the possibility of
trapping air between the porcelain and the
metal. The thin film of water also will draw
the opaque particles onto the metalwww.indiandentalacademy.com
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Glass rod technique.
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• Use the pointed end of the glass rod to
apply the opaque porcelain. Begin by
opaquing the most convex portion of the
coping Move the opaque toward theporcelain-metal junction from one
interproximal area to the other and
cover the incisal edge.
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• Then move the opaque over the incisaledge to cover the porcelain-bearing
surface on the lingual aspect. Once the
porcelain-bearing areas are completely
covered, lightly tap the hemostat and the
porcelain will settle into any concavities
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• If, during the opaque application,areas of opaque appear rough andirregular, lightly tap the hemostat
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handle or move the serrations on acarver across the hemostat in asawing motion.
• The vibrations created by either ofthese procedures will act tocondense the wet porcelain into a
more uniform layer.•
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• Excess moisture should be removedbefore the opaque is applied to the metal.
Gently blend the opaque at the porcelain-
metal junction.
• Lightly tap the hemostat and dry the
opaque by placing it in front of an open
porcelain furnace muffle.
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• Dry the opaque layer
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y p q y
by exposing it to the
heat radiating from
the porcelain muffle.
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• A properly fired(sintered)
opaque layer
should have asheen or
eggshell glisten.
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• If a second application of opaque
porcelain is required, lightly wet the
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opaqued surface with opaque liquid.• Apply the second opaque porcelain
layer in the same manner as the first.
• Keep this second layer as thin anduniform as possible.
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Applying opaque porcelain—brush technique
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• Simply mix theopaque porcelain
.Use the tip of
porcelain brush to lift
a portion of the mixed
opaque
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• Apply the porcelain on the most
convex part of the oxidized coping.
R h l i
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Repeat the process several timesuntil the porcelain-bearing area is
completely covered with porcelain.
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Mixing dentin porcelains
f
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–The technique for mixing body
porcelains is same as that used
to mix opaque porcelains in that a
glass rod is preferred to a metal
spatula and the liquid is carefully
added to the powder to prevent
the entrapment of air.
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• Mix the body
powders (dentin
d l) ith
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and enamel) with
the
recommended
liquid (Vita VMK
68 porcelain and
modeling liquid )
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Wh l
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• When properlymixed, dentin
porcelain should
have asmooth,cream
consistency.
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If t h li id i
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• If too much liquid isadded to the mix,
use a tissue or
blotting paper to
remove excessliquid until the
proper consistency
is achieved.
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Appling dentin porcelain.
Th d ti l i b ild
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• The dentin porcelain buildupprocedure is to apply and condense
enough porcelain to create a
restoration that is 10% to 15% largethan normal.
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• This overbuilding will accommodate
the enamel veneer that will be placed
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over the dentin layer and help to
compensate for shrinkage of the
porcelain. A high quality sable brush
is preferred to create the porcelain
buildup
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The dentin built up technique.
R t th
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• Return thecleaned,
opaqued coping
to the mastercast.
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• To minimize theentrapment of air in
the porcelain,
th ti f th
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move the tip of thepointed brush
through the mixed
dentin porcelainand remove the
brush with the
dentin porcelain
captured on the
brush
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• Apply the
porcelain to the
t
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most convexsurface (midfacial
area) on the
restoration.
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• Coax the porcelain
toward the
interproximal and
incisal areas Add
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incisal areas. Addmore porcelain to
the facial surface
and use a lighttapping motion to
move the porcelain
along theporcelain-metal
junction.www.indiandentalacademy.com
• Move the porcelaindown to the incisal
edge and lightly blot
the buildup to
condense the
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condense theporcelain on the
substructure. place
the additional dentin
porcelain in the incisal
region and move it
from one
interproximal area tothe other.
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• Control the flow ofthe material and
condense the
buildup by
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buildup byperiodically blotting
the wet porcelain
with the tissue. use
light gingival-to-
incisal strokes on
the facial surface
to create thedesired facial
contour.www.indiandentalacademy.com
Add additional
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• Add additionalporcelain to the
incisal aspect of
the incisal edge.
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Add additional
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• Add additionalporcelain to
complete the
mesial and distalcorners.
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Cutting back the dentin buildup
• With the buildup complete, dentin
l i t b d f th
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porcelain as to be removed from those
areas of the crown where you would like to
have enamel porcelain. The procedure of
removing dentin porcelain for enamelplacement is referred to as the "dentin
cutback."
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If dentin porcelain is overbuilt(A), the amount ofdentin remaining after the cutback may also be
incorrect.
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When the restoration has the correctanatomical contours and is slightly
overbuilt(A) by 10% to 15%, the dentin
cutback will also be correct
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cutback will also be correct.
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• Remove dentin
l i t th
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porcelain at the
mesial
interproximal line
angle. Extend thecut to the junction
of the middle and
gingival one thirdsfor younger
patients.www.indiandentalacademy.com
• Cut across the
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• Cut across themiddle one third.
Stop the cut
back at the distalinterproximal
area.
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• At the distal
interproximal line
angle, make a cut
from the incisal edge
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from the incisal edgetoward the gingival
one third as far as
required for the
esthetics .Then cutback the middle one
third of the facial
surface as necessary.
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• Examine thei f
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• Examine therestoration from
an incisal view
for symmetryand adequacy of
the cutback.
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• Smooth thetb k
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• Smooth thecutback areas
with the
porcelain brushso the transitions
from dentin to
enamel porcelainare gradual.
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• For younger
patients develop
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patients ,developmamelons.With a
pointed brush
,create twodepressions on the
facial surface with
vertical strokes
from incisal to
gingival.www.indiandentalacademy.com
Mixing the enamel
porcelain
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porcelain.
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• Glass rod is used
to mix the powder
and liquid .The
enamel mix is
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enamel mix isslightly wetter than
the dentin mix to
facilitate itsaddition to a
previously applied
and condenseddentin layer.
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• The mixed enamel
porcelain should have
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porcelain should have
a consistency that
permits it to be readily
picked up by aproperly pointed
porcelain brush.
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• With a pointedb h l
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• With a pointedbrush, apply
enamel porcelain
to one corner ofthe cutback.
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• Add more enamelporcelain andmove it across the
facial surface in thei i l thi d
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facial surface in theincisal one third.Push the wet mixtoward the middle
one third of thecrown and work itinto the oppositeinterproximal lineangle.
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• Blend the enamelporcelain at the
junction of the
middle and gingival
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middle and gingivalone thirds and
begin to establish
the incisal edgeand condense the
porcelain by
blotting
periodically.
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• With additional
enamel porcelain,
complete theincisal edge length
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complete theincisal edge length
and the mesial-
incisal line angle.
Work your wayalong the incisal
edge to create
more of a distal-incisal line angle.
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• Blend the enamel
porcelain into the
gingival one third
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gingival one thirdon the facial
surface. Re-create
the interproximalcontours and line
angles.
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• Shape the mesial-incisal corner as
required for each
case Examine the
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case. Examine thebuiltup from an
incisal view and
evaluate theoverall shape.
Make certain the
restoration is
slightly over built.
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• Condense the built
up
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up.
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• Use your thin razorknife to cut and
shape the mesial
and distalinterproximal
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and distalinterproximal
areas. This
procedure also
removes any
unwanted
porcelain below the
interproximalcontact areas.
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• Carefully remove
the crown from the
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the crown from the
master cast. Add
enamel porcelain
to the smalldimples in each
interproximal
contact area.
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• Remove excess
porcelain from the
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pporcelain-metal
junction and clean the
facial metal collar of
any porcelain with a
small brush or your
pointed porcelain
buildup brush.
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Firing procedure.
• The large bulk need more time to dry and
pre-heat
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pre heat.
• Adhere to manufacturers recommended
drying time.
• A properly fired porcelain body bake
should have a pebbly or ―orange peel
appearance‖.
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Adjusting and finishing the metalceramic restoration.
• Applying and firing the porcelain veneer to
a metal substructure only approximates
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a metal substructure only approximates
the shape, contour, occlusion, and surface
finish restoration.
• The porcelain application process requires
slight overbuild of the ceramic, this results
in a bulky restoration.
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• Consequently, the fired porcelain requires
additional adjustments to reduce any
overcontouring and recreate a lifelike
ceramic surface finish before the
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ceramic surface finish before thecharacterizing (staining) and glazing
stages.
• Adjusting , contouring, and finishingprocedures for metal ceramic restorations
play a critical role in achieving both proper
function and optimal esthetics.
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Armamentarium.
• 1. Equipment – Handpiece with speeds of
50 000 rpm or below
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50,000 rpm or below.
• 2. Instruments – Iwanson metal caliper.
• 3. Materials – Diamond abrasives,
Prepolish wheels, diamond disks.
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• The iwansonmetal calipers
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The iwansonmetal calipers
can be used for
thicknessmeasurements
of metal or metal
and porcelain.
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• Diamond abrasive
instruments
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instruments.
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• Porcelain
prepolish wheel
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prepolish wheel
.Designed for
smoothening andpolishing
ceramic
surfaces.
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• Diamond disks
For adj sting
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• For adjusting
and contouring
interproximalareas.
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Procedures in adjusting and
finishing the metal ceramic
restoration.
• 1. To ensure the
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1. To ensure the
casting
completely seats
on the die.
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2.Adjusting the interproximal contacts.
• a) Mark the
mesial
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mesial
interproximal
contact usingthin double –
sided marking
film.
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• b) Marking
identifies the
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identifies the
location and
intensity ofcontact.
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• Adjustments in
the contact area
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the contact area
with pre-polish
wheel.
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• The thickness of
the restoration is
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the restoration is
periodically
checked toensure that it is
not over
contoured.
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• The desired
characterization
is marked andwith an
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with an
abrasive the
appropriateshape is
created with
desired effect.
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Staining and glazing.
• After a restoration has been adjusted and
finished, it is necessary to make color
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, y
corrections or additions and create a
lifelike surface luster.
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• Stain is placedin area where
the
characterizationis intended.
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is intended.
Blend or dilute
the effect of the
stain
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• The glaze ispicked up with
a staining
brush and
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applied to the
ceramic
surface wheredesired.
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• Dry the
restoration in the
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restoration in the
porcelain
furnace.
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• The restoration is
fired according to thel i
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porcelain
manufacturers
direction.
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• Typicallyglazed
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yp yglazed
restoration.
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Mechanical polishing.
• Mechanical polishing of thet ti ft l i i th
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p grestoration after glazing gives the
restoration a natural life like
appearance.
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A diamond polishingpaste.
Pumice flour
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• Aftermechanical
polishing. A
life like luster
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is created in
the ceramic
yet the surfacecharacterizatio
n remains.
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