Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy
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Transcripts - Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy
PORCELAINS USED IN METAL
INDIAN DENTAL ACADEMY
Leader in continuing dental education
Metal ceramic restorations
combine the strength and
accuracy of cast metal with the
esthetics of porcelain.
Metal ceramic restoration:
• "a fixed restoration that
employs a metal substructure
on which a ceramic veneer is
fused" (Glossary of
Prosthodontic Terms, 1987).
A 13- unit metal-ceramic
• HISTORY/ DEVELOPMENT OF
• PROPERTIES OF FUSED
• CHEMISTRY & COMPOSITION
• CLASSIFICATION OF DENTAL
Metal ceramic technology.
• METAL CERAMIC SUBSTRUCTURE
• BONDING BETWEEN THE METAL
DESIGN & PORCELAIN
• PORCELAIN APPLICATION
• FIRING PROCEDURES
• FINISHING & ADJUSTMENTS
• The word Ceramics is derived
from Greek word “keramos”
which means ‘pottery’ or ‘burnt
Porcelain in English means
Compounds of one or more metals
with a non metallic element,
usually oxygen. They are formed
of chemical and biochemical
stable substances that are strong,
hard , brittle, and inert non
conductors of thermal and
Porcelain is defined as
A ceramic material formed of
infusible elements joined by lower
fusing materials. Most dental
porcelain are glasses and are
used in the fabrication of teeth for
dentures, pontics and facings,
metal ceramic restorations,
crowns, inlays, onlays, and other
Other designations of metal
• Porcelain-fused to metal.
• Ceramo-metal crown.
• Porcelain veneer crown.
• Porcelain bonded to metal
Structure of ceramics
•Dental porcelain are glassy materials
Glasses may be regarded as a super
cooled liquids or as non crystalline solids
• Their atomic structure and resultant
properties depend, not only on
composition, but also on thermal history.
• CHINESE ARE CREDITED WITH
THE DEVELOPMENT OF
PORCELAIN AS EARLY AS 1000
• D’ENTRECOLLES, INGRATIED
HIMSELF WITH CHINESE
POTTERS AROUND 1717 IN
ORDER TO LEARN THE COVETED
• IN 1760 FAUCHARD AND OTHERS
HAD REPORTED USING ‘BAKED
• IN 1774 ALEXIS DUCHATEAU &
DENTURES FROM A MATERIAL
THEY REFERRED TO AS “MINERAL
• IN 1808 GIUSSEPPANGELO FONZI
DEVISED A METHOD TO MASS
PORCELAIN DENTURE TEETH
• 1850 Samuel Stockton was the first to
mass produce these teeth first in
• Claudius Ash created a artificial tooth
that could be placed over a post on
either a complete denture of FPD. It
was known as “tube” tooth.
• 1889 Dr Charles H. Land gave the
idea of fusing porcelain to a thin
platinum foil. – he developed low
fusing porcelain in 1898. 1903 he
introduced the porcelain jacket crown
• 1907 Stockton developed dental
• 1962 –M. Weinstein, S.Katz, and
A.B.Weinstein patented a method to
fabricate the first metal ceramic
• Two of the most important breakthroughs
responsible for the long-standing superb
aesthetic performance and clinical
survivability of metal-ceramic restorations
are the patents of Weinstein and
Weinstein (1962) and Weinstein et al
• One of these patents described the
formulations of feldspathic porcelain that
allowed systematic control of the sintering
temperature and thermal expansion
• The other patent described the
components that could be
used to produce alloys that
bonded chemically to and
were thermally compatible with
What are ceramics?
– Dental ceramics may consist
primarily of glasses ,porcelains,
– The properties of ceramics are
customized for dental application
by precise control of the type &
amount of the components used
in their production.
• Ceramics are more resistant to
corrosion. Ceramics generally do
not react with most liquids, gases,
alkalies & acids. And they remain
stable over long time.
• Dental ceramics exhibit far to
excellent flexure strength & fracture
• Although ceramics are strong,
temperature-resistant & resilient
these materials are brittle and may
fracture when quickly heated and
• Dental ceramics are non-metallic
containing components of oxygen
with one or more metallic or semi
Properties of ceramics.
• Most ceramics are
characterized by their refractory
nature, high hardness,
(relatively low tensile strength
and essentially zero percent
elongation), and chemical
• For dental applications a
hardness of a ceramic less than
that of enamel and an easily
polishable surface are desirable
to minimize the wear damage that
can be produced on enamel by
the ceramic surface.
• 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.
a) Flexure strength:
• It is a combination of compressive,
tensile, as well as shear strength.
• Glazed porcelain is stronger than
• Ground-75.8 Mpa (11,000 psi)
• Glazed-141.1 Mpa (20,465 psi)
b) Compressive strength:
• Porcelains have good compressive
• 331 Mpa (48,000psi)
c) Tensile strength:
• Is low
• 34 MPa (5000psi).
d) Shear strength:
• It is low and is due to the ductility
caused by the complex structure of
• 110 Mpa (16000psi).
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.
2) Modulus of elasticity:
• Porcelain as high modulus of
• 69 GPa .
3) Surface hardness:
• Porcelain is much harder than natural
• 460 KHN
4) Wear resistance:
• Porcelain is more resistant to wear
than natural teeth. Thus, it should not
be placed opposite to natural teeth.
5) Specific gravity:
• Is 2.242.
• The specific gravity of fired porcelain
is usually less, because of the
presence of air voids. It varies from
2.2 to 2.3.
6) Dimensional stability:
• Porcelain is dimensionally stable after
7) Chemical stability:
• It is insoluble and impermeable to oral
fluids. Also it is resistant to most
solvents. However, contact with
hydrofluoric acid causes etching of
the porcelain surface.
8) Esthetic properties:
• Are excellent. It is able to match
adjacent tooth structure in
translucence, color and intensity.
• It is compatible with the oral tissue.
10) Thermal compatibility
• Refers to the ability of a metal
and its veneering porcelain to
contract at similar rates.
• The coefficient of thermal
expansion by definition is the
change in length per unit of
original length of a material when
its temperature is raised by 1o K
Thermal compatibility (contd.)
• When the co efficient of thermal
expansion of metal and porcelain
are compatible the tensile stress
that develop during cooling are
insufficient to cause immediate
cracking of porcelain or delayed
cracking after cooling at room
• Porcelains have coefficient of thermal
expansion between 13.0 and 14.0 X
10-6 and metal between 13.5 and
14.5 X 10-6.
• The difference of 0.5 X10-6 in thermal
expansion between metal and
porcelain causes the metal to contract
slightly more than does the ceramic
during cooling after firing the
• This puts the ceramic under
slight residual compression
which makes it less sensitive
to applied tensile forces.
Methods of strengthening ceramics
• Strengthening occurs through two
• 1) development of residual
• 2) interruption of crack propagation.
• Development of residual compressive
• 1) Ion exchange: (chemical
• 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.
• Thermal tempering.
• By rapidly cooling the surface of the
object while it is hot and in the molten
state. 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
• THERMAL EXPANSION COEFFICIENT
• Ceramic in combination with metal are
heated 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.
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
• 2) By change of crystal structure under
stress to absorb energy from the crack.
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 alumina
particles as easily as it can propagate in
the glass. Thus the aluminous porcelains
were developed for Porcelain Jacket
• A crystalline material is incorporated that
is capable of undergoing a change in
crystal structure when placed under
stress. The crystalline material used is
termed as partially stabilized zirconia
(PSZ).The refractive index of PSZ is
higher than glass matrix. Thus the PSZ
scatters the light producing an opacifying
Porcelain-fused-to-metal (PFM): a
popular alternative designation
for the metal ceramic restoration.
• Porcelain bonding: a term used to
explain the mechanisms by which
dental porcelain fuses or adheres to a
• Coping: the word coping can be used to
identify the metal substructure of singleunit crowns designed for bonding to
dental porcelain. Copings are made on
a single tooth preparation, which may
be a single unit or attached to pontics
for a fixed partial denture.
• Framework: this term is often applied
to fixed partial dentures and identifies
a one-piece substructure composed
on either several copings attached to
a pontic or multiple single units that
are joined together as a single
• Degassing: the process of heat-treating
a cast metal substructure in a porcelain
furnace as one of the preparatory steps
to applying an opaque porcelain.
Subjecting the finished metal to
elevated temperatures (980° to
1,050°C) in a reduced atmosphere
(vacuum) or in air reportedly burns off
organic surface impurities and
eliminates entrapped gaseous
contaminants. A newer and perhaps
more appropriate term—oxidizing—has
emerged in the literature to describe
• Oxidation (or oxidizing): the
process by which a metal
substructure is heated in a
porcelain furnace to produce an
oxide layer for porcelain bonding
as well as to cleanse the
porcelain-bearing surfaces of
ADVANTAGES OF DENTAL
• Dental ceramics are attractive
because of their biocompatibility,
long-term color stability, wear
resistance, and their ability to be
formed into precise shapes.
• They require costly processing
equipment and specialized
• Susceptibility to brittle fracture
at relatively low stresses
The chemical components of dental
• Feldspar (K2O –Al 2O3-6SiO2 & Na2o –
• Quartz (SiO2)
• Alumina (Al2O3)
• Kaolin (Al2O3 -2SiO2 2H2O)
• Found as a mix of two substances .
• It does not occur in pure form in
• Mineral is crystalline and opaque
• Color is indefinite and between gray
Potassiu (K2O.Al orthocla
O3.6Si se or
aluminiu O )
fluidity of the molten
2.helps to maintain
the form of the
qualities to fired
temperature of the
• On heating it becomes glassy and
fuses at 1290 C, on overheating it
may loose its shape .
• Impurities : Mica
Iron –it is important to
remove it as its oxides act as strong
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
• Primarily responsible for forming
• 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 porcelains
coefficient of thermal expansion by
breaking up oxygen crosslinking.
Silica (Quartz or Flint) SiO2
• Primarily responsible for
forming glass matrix
• Has a fusion temperature
• Silica contributes stability to the
mass of porcelain during heating
by providing a framework for the
• Also acts to strengthen the
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 for dental porcelain.
Preparation of clay
• Repeated washing until all foreign
materials are separated.
• Allowed to settle.
• Dried and screened.
• Nearly white powder is obtained.
Properties of clay
Its gives OPAQUENESS to porcelain
MOULDABLE :On mixing with water it
becomes sticky and aids in forming a
workable mass of the porcelain during
III. Clay-water suspension maintains its
shape during firing in a furnace.
IV. On subjecting to high heat it adheres to
the framework of Quartz particles and
• Little or no kaolin is found is
modern day low fusing
• Kaolin is not used in enamel
powder as it will decrease its
• The hardest and perhaps the
• Its CTE is similar to the low fusing
• It also strengthens the porcelain.
Manufacturing of ceramics
• The process of blending, melting and
quenching the glass components is
• All the raw mineral powders are mixed
together in a refractory crucible and
heated till a molten mass is formed.
• It is then quenched in water.
• It immediately breaks into fragments and
this is termed the “frit”.
• Frits are ground to the specific particle
size established by individual
manufacturers for their particular brand of
• TOOTH PREPARATION FOR
THE METAL CERAMIC
• Make at least
cuts in the
of the facial
• Next align the
flat end tapered
portion of the
• Sink the side of
the diamond into
center of the
to the gingival
surface of the
• Make two incisal
that are 2mm
should be parallel to
the incisal edge
done with the
flat end tapered
• If there sound
• Begin the lingual
reduction with the
1.4mm. Sink this
the lingual tooth
structure up to
• Lingual axial reduction
torpedo diamond and carbide
done with the
• 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 incisal
notches with no.171
Components of the metal
• Two major components:
• a metal substructure and a porcelain
• The surface oxide layer that lies
between the metal and the porcelain
veneer could be considered a
separate component, but it is an
integral part of the casting alloy
The basic components of a traditional
porcelain kit include
Modifiers, stains & glazes.
Newest products has high fusing
The metal substructure
• Conventional low-fusing dental
porcelain lacks the strength
required of an all-porcelain
restoration, so a metal substructure
is added to support the porcelain
• The thickness of the metal coping
can vary, depending on the type of
casting alloy used and the amount
of tooth structure reduced by the
The oxide layer
• Most metal ceramic alloys are
oxidized after the porcelainbearing area of the restoration has
been properly finished and
• The metal oxides that form on the
alloy's surface during this heattreatment procedure play a key role
in bonding the dental porcelain to
the underlying metal substructure.
• Because noble elements do not
oxidize, an alloy's base metal
constituents are principally
responsible for forming this oxide
• Differences in alloy composition
require that oxidation techniques be
• Ideally this oxidation should be no
more than a discrete, monomolecular
film on the alloy's surface for all metal
ceramic alloys, irrespective of
Opaque porcelain layer
• These porcelains are made opaque by the
addition of insoluble oxides, such as
• tin oxide (SnO2),
• titanium oxide (TiO2),
• zirconium oxide (ZrO2),
• cerium oxide (CeO2),
Opaque porcelain layer contd.
barium zinc oxide.
Such oxides have high refractive
indices, so they scatter light.
Composition on chemical
• Between 8% and 15% of an opaque
powder is composed of metallic
oxides, and some particles may be
less than 5 um in size.
• Even small differences in particle size
distribution are thought to influence
the ability of opaques to mask the
color of a metal substructure.
• The opaque porcelains three major
• (1) to establish the porcelain-metal
• (2) to mask the dark color of the
metal substructure, and
• (3) to initiate the development of
the selected shade of porcelain.
• A uniform thickness of 0.2 to 0.3
mm generally is regarded as ideal.
• That masking power is influenced
by the amount and the color of the
oxidized (degassed) metal casting
• A casting alloy of a different
composition might generate a thick,
dark oxide layer (Naylor, 1986) and
require 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
• 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, and
• 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
• 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 custom
shading is desired.
• They differ in appearance in the fired
state because of variations in the
amount and type of metallic oxide
pigments each contains.
The dentin porcelain veneer
• The major color contribution is derived
from the pigmented metal oxides in the
dentin body porcelain
• It is this initial layer of dental porcelain
that imparts the dentin shade
associated with, but not confined to, the
gingival two thirds of a tooth.
• The dentinal layer is overbuilt slightly,
cut back, and overlaid with enamel
porcelain in those sections of the
restoration where greater translucency
• For more accurate shade
duplication, estimates of the
combined thickness of fired dentin
and enamel porcelains range from
a minimum of 0.5 to 1.0 mm to a
maximum thickness of 1.5 to 2.0
• For uniformity of shade and maximum
strength, it is desirable to have an even
thickness of porcelain covering the
• The minimum total thickness of
porcelain may be between 1.2 to 1.3
mm at the middle one third of the
restoration and 1.5 to 1.6 mm at the
incisal edge (Yamamoto, 1985).
ENAMEL PORCELAIN VENEER
• Enamel porcelains are more
translucent than dentin porcelains.
• The enamel porcelains are usually in
the violet to grayish range & impart a
combination of true translucency &
the illusion of the translucency by
virtue of their grayish or some times
• When fired, enamel porcelains are
more translucent than dentin porcelains
• They also have a more restricted range
of shades. A typical porcelain system
may provide only four or five bottles of
enamel powders to cover the entire
range of shades in the kit.
• Translucent porcelains are not
transparent, they do not allow the
transmission of all light.
• They are applied as a veneer over nearly
the entire surface of a typical porcelain
• This veneer imparts depth and a natural
enamel-like translucency without
substantially altering the body shade that
• These porcelains are more color concentrated &
were designed to aid in the achieving internal
• 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 the
• Stain powders contain less silica or
alumina & more sodium & potassium
• They contain high concentration of
• They are created by mixing the
metallic oxides with lower fusion point
• Glazes are generally colorless, low fusing
• They possess considerable fluidity at high
• They fill small surface porosities &
irregularities. when fired helps to recreate
the external glazy appearance of the
• A glazed ceramic surface is
generally considered beneficial by
increasing the fracture resistance
and reducing the potential
abrasiveness of ceramic surfaces
• By convention dentin powders are pink
and enamel powders are blue.
• These organic colors burn off during firing
procedure and do not affect the shade of
the fired restoration in any way.
• Some manufacturers color code the
distilled water instead of the powder.e.g.
CLASSIFICATION OF DENTAL
• Different types of dental ceramics are
available 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
• These products can be
classified in several possible
ways according to their: (1) use
or indications (anterior,
posterior, crowns, veneers, post
and cores, FPDs, stain ceramic,
and glaze ceramic);
• (2) composition (pure alumina,
pure zirconia, silica glass, leucitebased glass-ceramic, and lithiabased glass-ceramic
• (3) processing method (sintering,
partial sintering and glass
infiltration ,CAD-CAM, and copymilling);
• Microstructure (glass, crystalline,
and crystal-containing glass);
• Translucency (opaque,
translucent, and transparent);
Fracture resistance; or
Based on the method of fabrication
1. Condensation porcelains using
condensation and sintering
2. Castable ceramics –Dicor-Dentsply
3. Pressable ceramics
4. Machinable ceramics
5. Infiltrated ceramics
6. Injection molded ceramics –Cerestore
1) Regular feldspathic porcelain
2) Aluminous porcelain
3) Metal bonding porcelain.
Based on their fusion temperature (Phillips,1982)
1288 to 1371
denture teeth .
1093 to 1260
for all ceramic
871 to 1066 C
ceramic and all
METAL SUB STRUCTURE
• Majority of the porcelain-to-metal bond
failures occur as a direct result of improper
• Errors in the preparation of the metal
ceramic sub-structure frequently go
unnoticed until the brittle porcelain veneer
fails in service.
METAL SUB STRUCTURE
Types of metal ceramic system.
• 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 in
• a) Bonded platinum foil coping.
• b) Swaged gold alloy foil coping.
a) Bonded platinum foil coping:
• Another method of bonding porcelain to
metal is the use of tin oxide coatings on
• The method consists of bonding
aluminous porcelain to platinum foil
• Attachment of the porcelain is secured by
electroplating the foil with a thin layer of tin
and then oxidizing it in a furnace.
• The objective of this type of
restoration 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.
b) Swaged Gold Alloy Foil Coping:
• A laminated gold alloy supplied in fluted
shape is also used as an alternative to the
cast metal coping.
• The foil is swaged onto the die and flame
sintered to form a coping.
• An “interfacial alloy” powder is applied
and fired and the coping is then veneered
Primary functions:• The casting provides fit of the
restoration to the prepared tooth.
• The metal forms oxides that bond
chemically to the dental porcelain.
• The coping serves as a rigid
foundation to which the brittle
porcelain can be attached for
increased strength & support.
• The sub structure restores the
tooth's proper emergence profile.
• Metal occlusal & lingual articulating
surfaces generally less destructive to
the enamel of the opposing natural
• Fabrication of the restoration with
minimal occlusal clearance has more
potential for the success with metal
substructure than all ceramic alloys.
• Occlusal surfaces can be easily
adjusted & repolished intraorally.
• The metal axial walls can support
the removable partial denture.
Metal sub structure design
• Majority of the porcelain-to-metal
bond failures occur as a direct result
of improper substructure design
• Errors in the preparation of the metal
ceramic sub-structure frequently go
unnoticed until the brittle porcelain
veneer fails in service.
Sub structure design (contd)
• Hence necessary to understand
the essentials of proper
substructure design, since it will
help to ensure the longevity of the
Principles of substructure
• Are the occlusal contacts to be
in metal or porcelain?
• Occlusion in metal requires less tooth
reduction (1 to 1.5 mm).
• Approximately 2 mm of occlusal
reduction is necessary for posterior
teeth and 1 to 1.5 mm for anterior
teeth requiring porcelain on occluding
• Metal surfaces can be more easily
adjusted and repolished at chair side
without adversely affecting the
• On the other hand, removing the
glaze of a metal ceramic restoration
during intraoral adjustments weakens
the porcelain greatly
• 2. Are the centric occlusal
contacts 1.5 to 2mm from the
• occlusal contacts when placed
directly on or close to the porcelainmetal junction, there is an increased
likelihood the porcelain will chip or
fracture at that point of contact .
• Porcelain is strongest under
compression and weakest under
tension, so situations that induce
tensile stresses in the ceramic during
function are more apt to promote
• A substructure should be designed so
the functional incisal or occlusal
contacts are located at least 1 .5 mm
and perhaps as much as 2 mm from
the metal-porcelain junction.
• When the
contact in the
incisal region,it is
to consider a
lingual surface in
porcelain to avoid
functioning on or
• Do not design
occurs at the
• When the anterior
teeth occlude in the
gingival half of the
maxillary teeth or
when the lingual
tooth reduction is
less than 1mm it is
best to design the
sub structure with
occlusion in the
• 3.Are the interproximal contacts
to be restored in metal or
• The inter proximal contact areas of
anterior teeth, and at least the mesial
contacts of posterior teeth, are
frequently restored in porcelain
• with porcelain inter proximal contact
areas would be more esthetic,
particularly with anterior teeth.
• It is important to provide proper metal
support to a porcelain marginal ridge
in the substructure design to prevent
• However, the distal inter proximal
contacts of posterior teeth may be
restored in either metal or porcelain
because these areas are not as
• 4.Are the cusp tips (or incisal
edges )adequately supported by
the metal substructure with no
more than 2mm of unsupported
• The ultimate goal of any substructure
is to support an even thickness (1mm
minimum, 2 mm maximum) of the
• If this maximum thickness is
exceeded, the ceramic layer may no
longer be properly supported,
resulting in a catastrophic failure at
the cusp tip or incisal edge
• 5. Is the substructure thick
enough to provide a rigid
foundation for the porcelain
• Areas to be veneered with
porcelain must be at least 0.3 mm
• with base metal alloys, the
coping can be reduced to 0.2 mm
or less and still be strong enough
to support the porcelain
How does dental porcelain bond to
(1) van der Waals forces (Lacy, 1977),
• (2) mechanical retention,
• (3) compression bonding, and
• (4) direct chemical bonding (Lacy,
1977; McLean, 1980;
van der Waals forces
• The attraction between charged
atoms that are in intimate contact yet
do not actually exchange electrons is
derived from van der Waals forces.
• These secondary forces are
generated more by a physical
attraction between charged particles
• Van der Waalsforces are generally
• The better the wetting of the
metal surface, the greater the van
der Waals forces.
• porcelain's adhesion to metal can
be diminished or enhanced by
alterations in the surface
character (texture) of the
porcelain-bearing surface on the
• van der Waals forces are only
minor contributors to the overall
• The porcelain-bearing area of a metal
casting contains many microscopic
irregularities 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
contribution to bonding may be
• Dental porcelain does not require
a roughened area to bond to
metal but some surface
roughness is effective in
increasing bonding forces
• Dental porcelain is strongest under
compression and weakest under
tension; hence, if the coefficient of
thermal expansion of the metal
substrate is greater than that of the
porcelain placed over it, the porcelain
should be placed under compression
• the metal contracts faster than the
porcelain but is resisted by the
porcelain's lower coefficient of
• This difference in contraction
rates creates tensile forces on the
metal and corresponding
compressive forces on the
• The single most significant
mechanism of porcelain-metal
attachment is a chemical bond
between dental porcelain and the
oxides on the surface of the metal
• The two hypothesis that explains
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
• The oxide layer itself is
sandwiched in between the metal
substructure and the opaque
porcelain. This "sandwich" theory
is undesirable in that a thick oxide
layer might exist that would
weaken the attachment of metal
• The second, and more likely, theory
suggests that the surface oxides
dissolve, or are dissolved by, the
opaque layer. The porcelain is then
brought into atomic contact with the
metal surface for enhanced wetting
and direct chemical bonding so metal
and porcelain share electrons.
(McLean, 1980; Yamamoto, 1985)
• Chemical "bonding" is generally
accepted as the primary
mechanism in the porcelain-metal
The oxidation (degassing) process
• After the cast metal ceramic
castings have been properly
carbide burs or ceramic abrasives
the castings are heat-treated in a
porcelain furnace (in air or a
temperature for a specified period
of time (Naylor, 1986).
allows specific oxides to form on
the metal surface. These oxides
are responsible for the chemical
porcelain- metal "bond."
• A high-gold-content alloy contains
oxidizable trace elements such as tin,
indium, and iron to produce an
adherent 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
permit the non noble trace elements
to form the oxide layer
• The base metal alloys readily
oxidize, but trace elements are
still added in an effort to form a
particular type of oxide for a
stable bond .
• The oxidation procedure may be
carried out in a vacuum to
minimize the amount of oxidation,
and the hold time is often reduced
• Allowing certain base metal alloys
to oxidize in air, or to remain at
temperature, could lead to over
oxidation. An excessively thick
and non-adherent oxide layer is
often responsible for porcelain
• A properly oxidized casting often
has a distinctive appearance in
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 the
• Some manufacturers do not
degassing step; instead, they
advocate minimizing the number
of firings to which the casting is
Removing the oxide layer
• Two principal methods for
removing oxides are
– Acid treatment (chemical method)
– Nonacid treatment (mechanical
• Different types of acids are used to reduce
or eliminate surface oxides, including
hydrofluoric, hydrochloric, and dilute
• 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
• A rubber-tipped instrument should be
used to place oxidized castings into
the acid appropriate for the alloy.
• Place the covered container in an
• Remove the casting and thoroughly
rinse it under tap water. For the final
cleaning step, put the coping in a
container of distilled water and clean
it ultrasonically for 10 to 15 minutes.
• Castings can be air-abraded with pure, 50um aluminum oxide (Al2o3) that is nonrecycled.
• Steam clean or ultrasonically clean the
casting in distilled water for 10 to 15
minutes before applying the opaque
Porcelain-metal bond failures
• Metal ceramic alloys, whether noble
or base metals, all oxidize differently
because of variations in their
• If the oxidation process is not
performed properly, the subsequent
porcelain-metal bond may be weak
and may lead to bond failure.
• With base metal alloys, the
separation of the porcelain veneer
from the metal substrate can be
more a loss of the "attachment" of
the oxide layer that is either too
thick or is poorly adherent to the
Porcelain delamination contd
• Overoxidation has been a particular
problem with the heavily oxidizing
base metal alloys and has been
linked to their increased tendency for
bond failures .
• Bond failures are not caused by a loss
of the chemical bond between the
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 that
the bond is lost through it .
• This particular problem is caused by
the formation of a thick and poorly
adherent oxide layer.
Classification of bond failures in
(Given by O’ Brien (1977).
• 1) Metal – Porcelain:
Fracture leaves a clean surface of
metal. Seen when metal surface is devoid
of oxides. May also be due to
contaminated or porous metal surface.
Usually occurs in high gold alloys.
• 2) Metal oxide – Porcelain:
Porcelain fractures at metal oxide
surface, leaving oxide firmly attached to
metal .Seen more often in base metal
• 3) Metal – Metal Oxide:
Metal oxide breaks away from the
metal and is left attached to the porcelain.
Seen commonly in base metal alloy
systems due to over production of
chromium and nickel oxides.
• 4) Metal Oxide –Metal Oxide:
Fracture occurs through the metal
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
• 6) Cohesive within Porcelain:
Tensile failure within porcelain. Bond
strength exceeds strength of porcelain.
Seen in high gold content alloys.
oxides by the
porcelain can lower
alter the final
shade (cause a
graying or bluing),
or do both (Naylor,
• Changes in the
shade of the
not be noticeable
particularly if a
masks the dark
• Further more, bond failures are not always
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 the
veneering porcelain and the metal ceramic
alloy may be slight yet sufficient to be
responsible for cracking of the ceramic
veneer or substantial enough to result in
• The oxidation procedure varies for alloys
of different compositions.
• Careful processing followed by an
appearance of each casting will ensure
that the procedure was accomplished
• Castings that are either overoxidized or
underoxidized should be reprocessed
accordingly until a uniform oxide of the
desired color and thickness recommended
for the alloy involved has formed.
– castings that demonstrate some form
of contamination may not have to be
remade but by simply refinishing a
surface may be all that is necessary
when surface debonding becomes
evident. Uncontaminated finishing
materials are used to prevent this.
the surface and
and resulted in
Applying Porcelain to the Metal
• The application of dental porcelain to
the metal substructure is the single
most demanding procedure in the
fabrication of a metal ceramic
• As a rule, the skills needed for this
particular process require the most
effort to perfect.
Instruments and equipment
• A variety of brush sizes and styles are
available in porcelain instrument kits, the
most important of which are the brushes
used for building or stacking porcelain.
. The size range varies from a no. 4 to a no. 8.
Sable brushes are the standard because
they permit easy manipulation of the
• Another frequently used instrument is a
large no.10 brush, often referred to as a
• A basic instrument kit should also include
flat brushes with relatively stiff bristles.
These large- and small-sized brushes
should be kept dry because they are used
exclusively to remove porcelain particles
from non porcelain-bearing areas and from
inside the substructure prior to firing.
• Very small no. 0 to no. 000 sable
brushes are required for the
placement of stains or small
increments of porcelain. These
brushes are useful anywhere
maximum control is necessary
• Porcelain carving instruments, designed for
shaping and carving porcelain buildups.
• Carving instruments serve two principal
• 1.Those with a serrated handle can be
used to condense wet porcelain.
• 2.Instruments with blades, as well as the
small discoid carver, can be used to build
(stack) porcelain, shape the buildup, and
carve the porcelain.
• Small, flexible, metal spatula is used
to dispense and mix porcelain.
• Any small metal fragments generated
during mixing can then be introduced
• This metal debris can dramatically discolor
the mix as well as the fired porcelain
restoration. With careful use, however, the
metal mixing spatula need not be
• But for added safety, a glass mixing rod is
often substituted for the metal spatula to
avoid this problem altogether.
• Another necessity in the basic set of
some type of razor knife,
equipped with a thin, flexible blade for
carving the porcelain buildup.
• A small, straight or curved hemostat is
needed to hold the work during the
opaquing process and during porcelain
additions and condensation.
• Hemostats can be modified to hold the
damaging the metal margins. However, an
18-gauge handle added to the lingual collar
provides a convenient, safe, yet secure grip
for removing the restoration from the
working cast and holding it during
Glass or ceramic mixing slab
• Finally, either a glass slab, ceramic tile, or
ceramic 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).
• As modifiers are added and more
complex buildups are attempted,a larger
working surface will be required to
accommodate all the different porcelain
• Condensing dental porcelain actually
refers 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.
• Any liquid or air that remains trapped in
the unfired porcelain will form voids in the
• The presence of porosity in fired porcelain
weakens the restoration and impairs its
• In well-condensed porcelain there is
reduction in the amount of firing
• Methods of porcelain condensation.
• 1) capillary action.
• 2) vibration
• 3) spatulation
• 4) whipping
• 5) dry powder addition.
• The technique of blotting a wet
built up with absorbent paper
uses surface tension.
• Is created by passing a serrated
instrument over the neck of a
hemostat in which the restoration is
• Vibration is a means to mechanically
draw additional moisture to the
surface where it can then be removed
by blotting paper.
• A spatula is used to apply ,
then rub the porcelain built up
to force the liquid to the
• A no. 10 sable brush is rapidly
moved over the porcelain surface
with a whipping motion. The
whipping motion brings the liquid
to the outer surface for blotting.
Dry powder addition.
• Requires dry porcelain powder be
sprinkled on an area of wet
porcelain, using the existing liquid
to moisten the powder addition.
Opaquing the metal
• The areas of the substructure that will
be veneered with porcelain must not
be touched and should be protected
from dust, oils from the skin, and any
other forms of contamination
Applying opaque porcelain—
glass rod technique
• First wet the oxidized metal substructure
to be veneered with distilled water and
gently vibrate the casting to thoroughly
wet the 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 metal
Glass rod technique.
• 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 the
porcelain-metal junction from one
interproximal area to the other and
cover the incisal edge.
• Then move the opaque over the incisal
edge 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
• If, during the opaque application,
areas of opaque appear rough and
irregular, lightly tap the hemostat
handle or move the serrations on a
carver across the hemostat in a
• The vibrations created by either of
these procedures will act to
condense the wet porcelain into a
more uniform layer.
• Excess moisture should be removed
before the opaque is applied to the metal.
Gently blend the opaque at the porcelainmetal junction.
• Lightly tap the hemostat and dry the
opaque by placing it in front of an open
porcelain furnace muffle.
• Dry the opaque layer
by exposing it to the
heat radiating from
the porcelain muffle.
• A properly fired
should have a
• If a second application of opaque
porcelain is required, lightly wet the
opaqued surface with opaque liquid.
• Apply the second opaque porcelain
layer in the same manner as the first.
• Keep this second layer as thin and
uniform as possible.
Applying opaque porcelain—
• Simply mix the
.Use the tip of
porcelain brush to lift
a portion of the mixed
• Apply the porcelain on the most
convex part of the oxidized coping.
Repeat the process several times
until the porcelain-bearing area is
completely covered with porcelain.
Mixing dentin porcelains
– 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.
Mix the body
and enamel) with
liquid (Vita VMK
68 porcelain and
modeling liquid )
• When properly
• If too much liquid is
added to the mix,
use a tissue or
blotting paper to
liquid until the
Appling dentin porcelain.
• The dentin porcelain buildup
procedure is to apply and condense
enough porcelain to create a
restoration that is 10% to 15% large
• This overbuilding will accommodate
the enamel veneer that will be placed
over the dentin layer and help to
compensate for shrinkage of the
porcelain. A high quality sable brush
is preferred to create the porcelain
The dentin built up technique.
• Return the
to the master
• To minimize the
entrapment of air in
move the tip of the
through the mixed
and remove the
brush with the
captured on the
• Apply the
porcelain to the
area) on the
• Coax the porcelain
incisal areas. Add
more porcelain to
the facial surface
and use a light
tapping motion to
move the porcelain
• Move the porcelain
down to the incisal
edge and lightly blot
the buildup to
porcelain on the
the additional dentin
porcelain in the incisal
region and move it
interproximal area to
• Control the flow of
the material and
the wet porcelain
with the tissue. use
light gingival-toincisal strokes on
the facial surface
to create the
• Add additional
porcelain to the
incisal aspect of
the incisal edge.
• Add additional
mesial and distal
Cutting back the dentin buildup
• With the buildup complete, dentin
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 enamel
placement is referred to as the "dentin
If dentin porcelain is overbuilt(A), the amount of
dentin remaining after the cutback may also be
When the restoration has the correct
anatomical contours and is slightly
overbuilt(A) by 10% to 15%, the dentin
cutback will also be correct.
Dentin cut back technique
• With a razor
knife cut back
the incisal edge
from between 1
to 1.5 mm.
• Remove dentin
porcelain at the
angle. Extend the
cut to the junction
of the middle and
gingival one thirds
• Cut across the
middle one third.
Stop the cut
back at the distal
• At the distal
angle, make a cut
from the incisal edge
toward the gingival
one third as far as
required for the
esthetics .Then cut
back the middle one
third of the facial
surface as necessary.
• Examine the
an incisal view
and adequacy of
• Smooth the
so the transitions
from dentin to
• For younger
depressions on the
facial surface with
from incisal to
Mixing the enamel
• Glass rod is used
to mix the powder
and liquid .The
enamel mix is
slightly wetter than
the dentin mix to
addition to a
• The mixed enamel
porcelain should have
a consistency that
permits it to be readily
picked up by a
• With a pointed
to one corner of
• Add more enamel
move it across the
facial surface in the
incisal one third.
Push the wet mix
toward the middle
one third of the
crown and work it
into the opposite
• Blend the enamel
porcelain at the
junction of the
middle and gingival
one thirds and
begin to establish
the incisal edge
and condense the
• With additional
incisal edge length
and the mesialincisal line angle.
Work your way
along the incisal
edge to create
more of a distalincisal line angle.
• Blend the enamel
porcelain into the
gingival one third
on the facial
contours and line
• Shape the mesialincisal corner as
required for each
case. Examine the
builtup from an
incisal view and
Make certain the
slightly over built.
• Condense the built
• Use your thin razor
knife to cut and
shape the mesial
porcelain below the
• Carefully remove
the crown from the
master cast. Add
to the small
dimples in each
• Remove excess
porcelain from the
junction and clean the
facial metal collar of
any porcelain with a
small brush or your
• The large bulk need more time to dry and
• Adhere to manufacturers recommended
• A properly fired porcelain body bake
should have a pebbly or “orange peel
Adjusting and finishing the metal
• Applying and firing the porcelain veneer to
a metal substructure only approximates
the shape, contour, occlusion, and surface
• The porcelain application process requires
slight overbuild of the ceramic, this results
in a bulky restoration.
• Consequently, the fired porcelain requires
additional adjustments to reduce any
overcontouring and recreate a lifelike
ceramic surface finish before the
characterizing (staining) and glazing
• Adjusting , contouring, and finishing
procedures for metal ceramic restorations
play a critical role in achieving both proper
function and optimal esthetics.
• 1. Equipment – Handpiece with speeds of
50,000 rpm or below.
• 2. Instruments – Iwanson metal caliper.
• 3. Materials – Diamond abrasives,
Prepolish wheels, diamond disks.
• The iwanson
can be used for
of metal or metal
• Diamond abrasive
• Diamond disks
• For adjusting
Procedures in adjusting and
finishing the metal ceramic
• 1. To ensure the
on the die.
2.Adjusting the interproximal contacts.
• a) Mark the
thin double –
• b) Marking
• Adjustments in
the contact area
• The thickness of
the restoration is
ensure that it is
• The desired
is marked and
Staining and glazing.
• After a restoration has been adjusted and
finished, it is necessary to make color
corrections or additions and create a
lifelike surface luster.
• Surface stains
applied with a
• Stain is placed
in area where
Blend or dilute
the effect of the
• The glaze is
picked up with
applied to the
• Dry the
restoration in the
• The restoration is
fired according to the
• Mechanical polishing of the
restoration after glazing gives the
restoration a natural life like
A diamond polishing
polishing. A life
like luster is
created in the
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