dental ceramics. / academy of fixed orthodontics

POTTERY IN EUROPE
CLAY
SAND
GROUND SEASHELLS
VOIDS---CLAY---FIRING
BEATING ( WEDGING )
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SINTERING
The conversion of clay from a mass of individual particles
loosely held together by a water binder to a coherent solid
relies on a process known as SINTERING.
In this process, the points at which the individual particles are in
Contact fuse at sufficiently high temperatures.

KILN
UP-DRAUGHT KILN
EARLY KILNS---900 ۫C---pottery fired at this
temperature is known as EARTHENWARE---
higher kiln temperatures---impervious
pottery---STONEWARE.

CHINESE PORCELAIN
10 Century AD
Ceramic technology in China was so advanced to such a
stage that they were able to produce:
‘A ceramic so white that it was comparable only to snow, so
strong that vessels needed walls only 2-3 mm thick and
consequently light could shine through it. So continuous was
the internal structure that a dish ,if lightly struck would ring
like a bell’

The dental application of porcelain dates from 1774,when a
French apothecary named Alexis Duchateau considered the
possibility of replacing his ivory dentures with porcelain

MILE STONES AND PIONEERSMILE STONES AND PIONEERS
 700 BC: ETRUSCANS
 1774 DUCHATEAU.
 1789 DE CHEMANT
 1808 FRONZI
 1817 PLANTEAU
 1825 STOCKTON
 1903 Dr.CHARLES LAND
 1962 WEINSTEIN and
WEINSTEIN
 1962 WEINSTEIN et al
 1963 VITA ZAHNFABRIK
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 1965 MCLEAN and HUGHES
 1980 CEREC 1,2 and 3
 1984 ADAIR and GROSSMAN
 1990 PRESSABLE GLASS CERAMIC
 1992 DUCERAM LFC…….

The term ceramics is derived from the Greek word
‘keramos’ meaning ‘potter’s clay’/ burnt stuff.

CERAMIC: defined as inorganic compound with
nonmetallic properties consisting of metallic or semi
metallic elements.
PORCELAIN: refers to a family of ceramic materials
composed essentially of kaolin ,quartz, feldspar also
fired at high temperature.

 PREDOMINANTLY
GLASSY MATERIAL.
 Amorphous.
 Derived from feldspar.
 Resistant to
devitrification long
firing range.
 Biocompatible
 3D network.

CLASSIFICATION OF DENTAL
CERAMICS
 USE
 COMPOSITION
 PROCESSING METHOD
 FIRING TEMPERATURE
 MICROSTRUCTURE
 TRANSLUCENCY

FABRICATION CRYSTALLINE
PHASE
ALL
CERAMIC
MACHINED Al, feldspar, mica
SLIP CAST Al, spinel
HEAT PRESSED Leucite ,lithium
disilicate
SINTERED Al, Leucite
CERAMIC
METAL
SINTERED Leucite
DENTURE
TEETH
MANUFACTURED feldspar

CLASSIFICATION OF CERAMICS
By content:
Regular feldspathic porcelain
Aluminous porcelain
Leucite reinforced porcelain.
Glass infiltrated alumina
Glass infiltered spinel
All ceramic

By use:
 Denture teeth
 Metal ceramic
 Veneers, inlays, crowns, anterior bridges
By processing method:
Sintering
Casting
Machining

By their firing temperature
High fusing -1300°C
Medium fusing ---1100 - 1300° C
Low fusing--850 - 1100°
Ultralow fusing < 850 °C
Air fired i.e. at atmospheric pressure
Vacuum fired i.e. at reduced pressure.

By their area of application:
Opaque porcelain
Body dentine porcelain
Gingival dentin porcelain
Overlay enamel
Incisal enamel

Basic composition
 Feldspar: Mixture of potassium and aluminium silicates
Two important properties
-retains its form
-incongruent melting
 Kaolin (china clay) : hydrated aluminium silicate
 Silica (in the form of quartz, and remains as a fine
dispersion after firing)
 Aluminum oxide

COMPOSITION
In dentistry porcelain were initially used for the fabrication of
the denture teeth.
Denture teeth porcelain: Mix of powders of feldspar, clay and quartz.
This is also referred to as high temperature porcelain.
Feldspathic porcelains: These have been in use for more than 50 years.
The feldspathic porcelains are too weak to use as all ceramic restorations
and hence are supported with a metal coping.

Conventional dental porcelain is a ceramic based on a
network of silica (Si) and potash feldspar or Soda feldspar
or both. Pigments opacifiers and glasses are added to
control the fusion temperature, sintering temperature,
thermal contraction coefficient and solubility.

Silica
It is a polymorphic material and can exist in 4 different
forms.
 Crystalline quartz
 Crystalline cristobalite
 Crystalline tridymite
 Non crystalline fused silica

Fused silica is a high melting material its high meltingFused silica is a high melting material its high melting
temperature is attributed to the 3 dimensional network oftemperature is attributed to the 3 dimensional network of
covalent bonds between the silica tetrahedra which is thecovalent bonds between the silica tetrahedra which is the
basic structure for the glass network.basic structure for the glass network.

The vitreous matrix is made of silicate glass.
Silica which is a prototype of glass forming
oxides ion is small and highly charged and fills
the space between oxygen atoms. The tetrahedra
must permit sharing of oxygen atoms to permit
the formation of silica groups thus resulting in
polymerization and a three dimensional network.

Alumina silicate glass
The aluminum can replace the silicone ions and this results in
the formation of Aluminosilicate glass. Because of the sharing
of the oxygen ions the glass containing silicatetrahedra and
aluminium tetrahedra polymerises.

Fluxes
Potassium, sodium and calcium oxides are used as glass
modifiers and act as fluxes by interrupting the integrity of
the silicone network. The purpose of a flux is principally to
lower the softening temperature of a glass by reducing the
amount of cross linking between the oxygen and glass
forming elements when soda is introduced instead as
bridging the atoms together, it contributes a oxygen atom
which acts a non bridging oxygen and as a result a gap is
produced in the silicone network.

So the silica tetrahedra thus obtained are able to move
more easily at lower temperature than the earlier
network.

Intermediate oxides
The addition of glass modifiers and fluxes not only
lowers the softening point but also decreases the
viscosity. Dental porcelains requires a high viscosity as
well as low firing temperature. This is done by using
intermediate, oxides like Al2O3 can replace the Sio4
tetrahedra.

Each aluminum has a charge of +3 as compared with a
charge of +4 of silicon ion, hence an additional unit
positive charge must be present to neutralize the
negatively charged aluminum ions. So the Na+ ions get
attracted to the Al. Boric oxides can also be used in a
similar way as aluminum oxide.

Other additions of dental porcelain
Pigmented oxides are added to obtain various shades
needed. These coloring pigments are produced by fusing
metallic oxide together with fine glass and feldspar.
These powders are then blended with the unpigmented
powders frit to provide the proper hue and chroma for
eg. Iron / nickel oxides (brown), copper oxide (green),
titanium oxide (yellowish brown), cobalt oxide (blue).

Devitrification and thermal expansion
vitrification refers to the development of a liquid phase by
reaction / melting which on cooling provides a glassy phase.
This structure is termed /vitreous/ when too many silicone
tetrahedra are disrupted the glass may crystallize / devitrify.

This is usually associated with high expansion glasses
where more amounts of alkalis, like soda (Na are seen. By
contrast less devitrifica is observed in aluminous porcelain
as they contain much less soda devitrification may be seen
when cloudiness develop in the porcelain which can be
accentuated by repeated firings.

Coloring and opacifying dental porcelain
The addition of concentrated color frits to dental
porcelain is insufficient to produce life like tooth effect
since the translucency of porcelain is too high. An
opacifying agent generally consists of a metal oxide
ceramic to a very fine particle size.

Common oxides used are:
1. Cerium oxide
2. Titanium oxide
3. Zirconium oxide (the most popular opalcyfying agent
used) Potassium and sodium feldspar is naturally occurring
minerals composed of potash soda, alumina, and silica. It is
used in the preparation of dental porcelains designed for
metal ceramic crowns.

When feldspar is heated at temperatures between 1530 and
1560 degree centigrade, it undergoes incongruent melting
to form crystals as leucite in a liquid phase. Incongruent
melting is the process by which one material melts to
forms a liquid plus a different crystalline material. This
crystalline phase formed is lecture, which is potassium
aluminum silicate with a large coefficient of thermal
expansion.

Fritting:
The term frit is used to describe the final glass product. The
raw mineral powders are mixed together in a refractory
crucible and heated to a temperature well above their
ultimate maturing temperature. The oxides melt together to
forma molten glass, gases are allowed to escape and the melt
is then quenched in water. The red hot glass striking the cold
water immediately breaks up into fragments and this is
termed as ‘frit’.

GENERAL PROPERTIES OF CERAMICS
Biological properties:
These are inert materials with excellent biocompatibility.
Chemical properties:
The greatest advantage of this material is the extreme resistance
offered to attach by chemicals. Chemicals such as hydrofluoric acid
are required to dissolve ceramics. As ceramics are inert obtaining
adhesion to them is difficult, ceramic restorations are roughened by
etching with hydrofluoric acid / by sand blasting to improve the
retention of a cement to the internal surface of the restorations.

Mechanical properties:
Hardness of ceramics for dental application should be
similar to enamel, as it is desirable to minimize the wear
of the ceramics restorations and simultaneously to reduce
the wear damage of enamel by the ceramic restorations.
- Low tensile strength
- Exhibits little amount of plastic deformation
-Impact resistance is low
-They have a good compressive strength. The
susceptibility to brittle fracture is a drawback particularly
when flow and tensile stress co exist in the same region
of the restoration.

Thermal properties:
These are insulating materials as a result though when the
metal is electrically / thermally stimulated the outermost
electrons are transferred to the ceramic thus stabilizing it.

Optical properties:
Excellent optical properties dental porcelains are translucent
because there are no free electrons and can be colored by
pigments such as metallic oxides to match the shade of teeth.
Presence of crystalline inclusions have a marked opacifying
effect.

STRENGTH OF PORCELAINS :
These materials usually fall to show the strength of 2 Gpa
which they are supposed to show theoretically, as the minute
scratches and other defects that are present on the surface of
nearly all the materials behave as sharp pitches whose tips
may be as narrow as the spacing between atoms in the
materials.

A phenomenon known as stress concentration at the
tips of these minute scratches/ flames causes the
localized stress to increase to the theoretical strength of
the material at a relatively low average stress
throughout the structure. When the theoretical it of the
material is exceeded at the tip the bonds at the notch tip
break and initiate the crack formation.

As the crack propagates through the material the stress
concentration is maintained at the crack tip until the
crack moves completely through the material/ meets
another. Crack a pore or a crystalline particle.
Thus phenomenon of stress cone explains how materials
can fail at stresses for lower than the theoretical strength.

Static fatigue:
Exposure to water reduces the strength the porcelain
causing delayed failure. Delayed failure in glasses had been
attributed to a stress enhanced chemical reaction between
glass and water this is likely to occur primarily at the tips
of the surface cracks.

Water reacts with glass destroying the Si - o network and hydroxyl
ions attach the siloxane bonds of the network.
OH+ R—Si-O-Si-R R—SioH + R-Sio
The silonate groups formed are strongly basic and can be
hydrolyzed by water to form silonol groups and hydroxyl ions.
R- Sio+H2O R-SioH +OH
Thus in the presence of water the amount of energy
required to rupture the silicone oxygen bond is diminished
by about 20 times. Thus providing a surface coating for
the flames reduces this.

METHODS OF STRENGTHENING PORCELAIN
The principal deficiencies faced by ceramics are -
brittleness, low fracture toughness and low tensile
strength.
Methods used to overcome the deficiencies fall into 2
general categories:
1. Method of strengthening brittle materials.
2. Method of designing components to minimize the stress
concentrations and tensile stresses.

Method of strengthening materials: In the oral
environment tensile stresses are usually created by
bending forces, and the maximum tensile stresses occur at
the surface of the restoration. It is for this reason removal
of the surface flaws can result in the increased strength of
the material. Smoothing and reducing flaws is one o the
reason for glazing of dental porcelain.
Now strengthening of the brittle materials can be done in
a 2 ways.

1.Development of residual compressive stresses within
the surface of the material.
2. Interruption of crack propagation through the
material.
Development of residual compressive stresses within
the surface of the material:
One widely used method of strengthening ceramics is
the introduction of residual compressive stresses.

Strength is gained by virtue of the fact that the residual
stresses developed must first be negated by the
developing tensile stresses before a net tensile stress
develops in the material.
THREE of the methods used in achieving this objective
are:

a. ion exchange mechanism:
This technique is called as chemical tempering and is
the most sophisticated and effective way of
introducing residual compressive stresses. In this
procedure a sodium containing glass is placed in a
bath of molten potassium nitrate, potassium ions in the
bath exchange places with some of the sodium ions in
the surface of the glass particle. The potassium ion is
about 35% larger than the sodium ion.

The squeezing of the potassium ion into place
formerly occupied by sodium ion creates large
residual compressive stresses in the surface of the
glass. These residual stresses produce a strengthening
effect. This process is best used on the internal surface
of the crown, veneer/inlay as the surface is protected
from grinding and exposure to acids.

The technique is as follows:
Characterize the finished crown and adjust the
occlusion.
Place the crown into a mould of analytically pure
potassium nitrate powder. Hold in a small
porcelain crucible/ stainless steel container. The
internal parts as the crown should be packed with
the powder to ensure that it sinks in to the
melting salt and does not float on the surface.

Place the container in a cool furnace and raise the
temperature slowly to 500°C
Hold the temperature at 500 C for 6 hours.
Remove the crown from the solution and allow it to
drain in the furnace

Remove the crown from the furnace and cool to room
temperature. *Further more it was observed that
grinding this crown by only 100 μm of the external
surface reduces the strength of the materials.

Furthermore contact with acidulated phosphate fluoride
for over 3 hours removes most of the ion exchange layer
and not all ceramics are amenable for ion exchange
especially those highly enriched with potash feldspar.

b. Thermal tempering:
This is the most common method of strengthening
glass. This creates residual surface compressive stresses
by rapidly cooling (quenching) the surface of the object
while it is hot and in the softened state. This rapid
cooling produces a skin of rigid glass surrounding a
soft molten core. As the molten core solidifies, it tends
to shrink, but the outer skin remains rigid.

The pull of the solidifying molten core as it shrinks,
creates residual tensile stresses in the core and residual
compressive stresses within the outer surface. For
dental applications it is more effective to quench the
glass phase ceramics in silicone oil. Or other special
liquids than using air as it may not uniformly cool the
surface.

While doing porcelain fused to metal restorations the
metal should be selected such that it contracts slightly
more (higher coefficient of thermal contraction) than
porcelain on cooling from the firing temperature to
room temperature. This mismatch leaves the porcelain
in residual compression.

Disruption of crack propagation
This can be categorized into 3 types:
1. Crack tip interactions
2. Crack tip shielding
3. Crack bridging

Crack tip interactions:
These occur when obstacles in the microstructure
act to improve crack motion.
These obstacles are generally second phase
particles and act to deflect the crack out of the crack
plane. It has been theorized that the reorientation of
the crack plane leads to the reduction of the force
being exerted of the crack in the area of deflection.

When the crack is deflected out of plane the crack is no
longer subjected to pure tensile stresses and will
involve some shear displacement; thus increasing the
difficulty of crack propagation.

Crack tip shielding:
This results when events are triggered by high stresses in the
crack tip region that acts to reduce these high stresses.
a. Transformation toughening
b. Microcrack toughening
are the 2 mechanisms that lead to crack tip shielding.
This is most often associated with the presence of zirconia. Under
unrestrained conditions zirconia undergoes a high to low
temperature phase transformation which involves a 3% to 5°/a
volume increase.

In toughened ceramic the high temperature phase of
zirconia is constrained at room temperature. Applied
tensile stress work to advance the crack plane.
In the area directly behind the crack tip, the matrix
constraints of zirconia are released, allowing the low
temperature transformation to take place, the
transformed phase occupies a greater volume in the bulk
material resulting in compressive forces that tends to
counteract / shield any advancing crack tip stresses.

Microcrack toughening:
It has been theorized that the high coefficient of
thermal contraction and volume reduction associated
with the high to low temperature phase transformation
of the leucite crystals create a condition which causes
the leucite crystals to contract significantly more than
the glass matrix.

Compressive forces are created in the glass matrix
surrounding the particles leading to microcracking in
the leucite phase. The residual compressive stresses in
the glass phase around to particles can act to counter
tensile stresses, which drive the crack forward.

Crack tip bridging:
This it the third strengthening mechanism that has
been proposed. It occurs when a second phase acts as
a ligament to make it more difficult for the crack
faces to open. This is better understood by bonded
fiber composites.

The fibers act as ligaments which make it more difficult
to open the crack at an applied stress.
Methods of designing components to minimize stress
concentrations and tensile stresses
The design should avoid exposure of ceramics to high
tensile stresses. It should also avoid stress concentration
at sharp angles or marked changes in thickness.

Minimizing tensile stresses:
When porcelain is fired onto a rigid material the shape
of the metal will influence the stresses set up in the
porcelain. If it is a full coverage crown the metal being
of higher thermal expansion will contract faster than
the porcelain as a result the metal is placed in tension
and the porcelain in compression.

For partial metal coverage the junction between the
metal coverage the junction between the metal and
porcelain is therefore a potential site for high stress
as the area with only metal will have no balancing
compressive forces.

Reducing stress raisers;
Stress raisers are discontinuities in ceramic structures
in brittle materials that cause stress concentration. The
design of ceramic dental restoration should also avoid
stress raisers. Abrupt changes in shape/ thickness in
the ceramic contour can act as stress raisers and make
the restoration more prone to failure.

Notches caused in the porcelain due to the folds of the
underlying platinum foil substrate. Sharp line angle in
the preparation, large changes in the thickness of
porcelain are factors creating areas of stress cone.
Usually contact points should be avoided and contact
areas should be preferred to avoid localized stress
areas.

TECHNIQUE INVOLVED IN FABRICATING
PORCELAIN FUSED TO METAL
There are 2 basic methods of fabricating porcelain
fused to metal.
1.Involves the swaging of a platinum matrix on a
model of the tooth and building the porcelain.
2. Supporting the porcelain to metal foundation.

Platinum foil technique:
This technique involves fabrication on either a single
platinum foil or a double platinum foil.
Fabrication on single platinum foil: A pure platinum foil
is swaged directly to the model then the porcelain is
built up. Later after the completion as the firing cycles
the platinum is peeled off. The fit of the crown is
secured leaving enough space for the cement.

Fabrication using a double foil matrix technique: Here
a second layer of platinum foil is swaged on the first
and cut back by at least 0.5 mm from the gingival
shoulder. The second layer is sand basted and cleaned
with caustic soda and citric acid to improve impurities
this is followed by electroplating, oxidization and
finally build up of the porcelain. Later after the
procedure is accomplished the inner layer is removed
allowing space for the placement of the cement.

Swaged gold alloy foil capping:
A laminated gold foil 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, then the coping is veneered with
porcelain.

Supporting the porcelain of a metal foundation
The various alloys that can be used are
High noble.
- Gold platinum palladium
- Gold palladium silver
- Gold palladium
Have noble metal content greater than 60% with at
least 40% gold.

Noble:
- Palladium silver
-High palladium
They have less than 25% noble metal content

Predominantly base metals:
- Nickel chromium
- Nickel chromium
- Cobalt beryllium

BONDING MECHANISMS
Four mechanism have been described to explain
the bond between the ceramic veneer and the metal
substructure.
1. Mechanical entrapment
2. Compressive forces
3. Van der waals forces
4. Chemical bonding

Mechanical entrapment:
This creates attachment by interlocking the ceramic
into the microabrasions on the surface of the metal
coping which are created by finishing the metal with
non contaminating stones / discs and are abrasives.
Air abrasion appears to enhance the wettability,
provide mechanical interlocking
The use of a bonding agent having platinum spheres
3-6 μm in diameter can also increase the bond
significantly.

Compressive forces:
These are developed by a properly designed
coping and a slightly higher coefficient of thermal
expansion than the porcelain veneered over it. This
slight difference will cause the porcelain to draw
towards the metal coping when the restoration
cools after firing.

Vander waals forces
It is an affinity based on a mutual attraction of
charged molecules. They are minor force for
bonding.
Chemical bonding
It is indicated by the formation of an oxide layer
on the metal. The trace elements like tin, indium,
gallium/iron form oxides and bond to similar
oxides in the opaque layer of the porcelain.

Bonding of porcelain to metal using electrodeposition:
A layer of pure gold is deposited onto the cast metal,
followed by a short flashing deposition of tin. This
method has been successfully used for metals and
alloys such as cobalt, chromium, stainless steel,
palladium silver, high and low gold content alloys and
titanium.

The advantages of this methods are:
1. Bonding is improved because of improved
wetting the metal by the porcelain and reduced
porosity at the porcelain metal interface
2. The electrodeposited layer acts as barrier
between the metal casting and porcelain to inhibit
ion penetration by the metal within normal limits
of porcelain maturation

3. The gold color of the oxide film improves the vitality
and esthetics of porcelain, when compared to the normal
dark oxides which require thick opaque layers of
porcelain to mark it.
4. The deposited layer acts as a buffer zone to absorb
stresses.

Classification of bond failures in metal ceramics:

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 surfaces.
Metal oxide porcelain: Porcelain fractures at metal
oxide surface, leaving oxide firmly attached to the
metal seen often in base metal alloys.

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 overproduction of Ch /Ni
oxides
Metal oxide - metal oxide: Fracture through the
metal oxides results from over production of oxide.

Alloy surface treatment:
Once the coping in made proper finishing with
aluminium oxide strips is done to remove any
surface irregularity and small particles as
investment that may have been embedded in the
surface of the casting.

Heat treatment:
The coping is placed in a furnace at relatively low
temperature and is then raised slowly to about
1000°C in vacuum and slowly air cooled in
normal atmosphere. This process of degassing
allows any contaminants/ gas inclusion to burn
off. At the same time base metal atoms will
diffuse to the surface of the metal and form on
oxide film, tin.

 ThicknessThickness::
 Cleaning :Cleaning :

OxidizingOxidizing
Controlled oxide layerControlled oxide layer
should be created .should be created .
OPAQUE LAYEROPAQUE LAYER
APPLICATION.APPLICATION.

Methods of condensation:
The Porcelain is mixed and applied.
Vibration:
Mild vibrations are used to densely pack the wet powder
upon the underlying matrix. The excess water comes to
the surface and is blotted with a tissue paper.

Spatulation:
A small spatula is used, to apply and smoothen the wet
porcelain. This action brings excess water to the surface.
Brush technique:
Dry powder is placed by a brush. Water is drawn towards
the dry powder and the wet particles are pulled together.
Ultrasonic:
Mild vibrations are transmitted electrically.

METHODS OF BUILDING AND CONDENSING
PORCELAIN
The porcelain is usually built to shape using a liquid
binder to hold the particles together. This process of
packing the particles and removing the liquid is known
as condensation. The main objective in building
porcelain powder is to achieve maximum packing density
of the powder i.e. minimum amount of air space is left in
the green or inferred porcelain after driving off the liquid
binder by heating.

Types of binders:
Distilled water: Is the most popular binder used in
dentin and enamel porcelain.
Propylene glycol: Used in alumina core build up.
Alcohol or formaldehyde based liquid for opaque / core
build up.

Building porcelain:
1 The powder is mixed on a glass slab.
2. The mix should not be overstored to avoid the
incorporation of large air bubbles.
3. High room temperature and dry atmosphere is to be
avoided as the powder can dry out rapidly due to which all
spaces are created in the powder bed.
Crowns which are built from such a build up will inevitably
be subjected to the entrapment of large air bubbles and areas
which are opaque may appear.

Firing dental porcelain:
After the condensation and building of a crown it is fired
to high density and correct form. Initially the infected/
green porcelains placed on a sager and introduced into
either a drying chamber/ the entrance of a furnace muffle.
The liquid binder is driven off and the porcelain become
brittle and chalky.

At this stage the green porcelain is introduced into
the hot zone of the furnace and the firing starts, the
glass particles soften at their contact areas and fuse
together. This is often referred to as sintering. Before
firing the temperature is raised gradually to the
manufacturers recommended temperature.

This allows the air/gas bubbles to escape via the grain
boundaries. Sealing the surface by quick firing arrests
the process and can cause bloating / blustering.
The powder will shrink and become denser. In air fired
porcelain a pint is reached where flow of glass grains
around the air spaces trips the remaining air in the
porcelain and on cooling spheroid bubbles are left in
the porcelain. However, then porcelain is fired in
vacuum, the air/atmosphere is removed from the
interstitial spaces before sealing of the surface occurs.

Do not prolong vacuum firing as by then the surface
skin is sealed and further application of vacuum can
cause surface blistering since residual air bubbles will
try to rise to the surface through the molten porcelain.

Classification of the stages in Maturity:
Low Bisque:
The surface of the porcelain is very porous and will
easily absorb a water soluble die. At this stage the
grains of porcelain will have started to soften.
Shrinkage will be minimal and the fired body is
extremely weak and friable. Lack translucency and
glaze.

Medium bisque:
The surface will still be slightly porous but the flow
of the glass grains will have increased. A definite
shrinkage will have taken place. Lacks translucency
and high glaze.
High bisque:
The surface of the porcelain would be completely
sealed and presents a much smoother surface with a
slight shine. shrinkage is complete. Appears glazed.

Cooling
Must be carried out slowly and uniformly. If
shrinkage is not uniform it causes cracking and loss of
strength.
Glazing
Porcelains are glazed to give a smooth and glossy
surface, enhance, esthetics and promote hygiene.

The glazing should be done only on a slightly
roughened surface and never should be applied on
glazed surfaces.
1. Overglaze
2. Self glaze

Over glaze:
These are ceramic powders containing more
amount of glass modifiers thus lowering fusion
temperature. It may be applied to porcelain and
then fired.
Self glaze:
All the constituents on the surface are melted to
form a molten mass about 25 μm thick. Thus the
porcelain is said to be self glazed.

Add on porcelains
The add on porcelains are made from similar
materials to glaze porcelain except for the addition
of opacifiers and coloring pigments. The add on
porcelain is made from the same grit as used to
manufacture regular porcelain.
These are sparingly used for simplest corrections
like correcting of tooth contour / contact points.

Repair of fracture ceramic restoration
Roughen the fracture ceramic surface using an
intraoral sand blaster generally using 30-50 μm
aluminium grit.
Silane is applied.
Dentine bonding agent containing 4 META applied
to the porcelain surface.
The defect is restored with composite restorative
material.

Aluminous porcelain:
There were developed by Mc Lean in 1965. Its
composition is similar to that of conventional
porcelain except for the increased alumina
content (40-50%). The dispersed alumina crystal
strengthens by interruption of crack propagation.
The crack cannot penetrate the alumina crystals
as easily as it can penetrate through the glass.

These are used to construct the core layer for
PJC. These are considered to provide crowns
more esthetics than metal ceramic crowns. Their
strength is almost twice that of conventional
porcelains and is sufficient for use on anterior
teeth. However, for posterior teeth it is
inadequate.

These are moreover less expensive than metal
ceramic crowns. But the disadvantage of this
material is the addition of alumina which makes it
opaque.
Aluminous porcelain shrink during the baking
procedure, the fit of the finished aluminous crowns
is generally poorer than that of ceramometal crowns.

Since the introduction of the first successful
porcelain fused to metal in the early 1960’s there
has been an increasing demand for ceramic
materials. This popularity is a result of the range of
shades that can help achieve life like results.
However, because of their relatively low tensile
strength and brittleness it has been fused to a metal
substrate.

However, this meta substrate can affect the
esthetics of porcelain by decreasing the light
transmission and by creating metal ion
discoloration, in addition some patients are
allergic / sensitive to certain metals. All these
drawbacks led to the development of the new call
ceramic systems.

The evolution of ceramic materials has been a battle for
the ideal strength, aesthetic combination.
The first all ceramic crowns introduced by Land in 1903
were relatively weak materials with limited clinical use.
In 1965 McLean and Hughes formulated aluminous
porcelain compositions.

These materials are composed of feldspathic
porcelain to which approximately 50% aluminium
oxide is added to increase the strength and baking
temperature.40 -80 % alumina crystals and rest is
formed as feldspar, quartz and Kaolin. The
fabrication is similar to feldspathic porcelain
except that the sintering should be slow to allow
the porosities to escape. The porcelain should not
reach the maturing temperature in less than 5
minutes.

Classification of all ceramic systems:
i. Conventional powder and slurry ceramics
ii. Castable ceramics
iii. Machinable ceramics
iv. Infiltrated ceramics

ALUMINOUS CORE CERAMICSALUMINOUS CORE CERAMICS
 Mclean and Hughes 1965.Mclean and Hughes 1965.
 Alumina content 40-55%.Alumina content 40-55%.
 Aluminous oxide crystals dispersed in a glassy matrixAluminous oxide crystals dispersed in a glassy matrix
 Method consisting of bonding aluminous porcelain toMethod consisting of bonding aluminous porcelain to
platinum foil copingplatinum foil coping
 Foil provides inner skin –decreases subsurface porosity andFoil provides inner skin –decreases subsurface porosity and
formation of micro cracks and increases strengthformation of micro cracks and increases strength

Strength twice that of conventional porcelain sufficient to
use in anterior teeth but is considered inadequate to use in
posterior teeth.
flexural strength-100 MPa. particle size 10-25 microns.
Example- vitadur N
Used as core.

CASTABLE GLASS CERAMICSCASTABLE GLASS CERAMICS
 DICORDICOR: By Corning glass works and marketed by: By Corning glass works and marketed by
DentsplyDentsply
 Lost wax technique.Lost wax technique.
 After the core is recovered it is then covered byAfter the core is recovered it is then covered by
protective embedment material and subjected to heatprotective embedment material and subjected to heat
treatment that causes the microscopic plate liketreatment that causes the microscopic plate like
crystals to grow --- CERAMMING.crystals to grow --- CERAMMING.

 Good esthetics --- chameleon effectGood esthetics --- chameleon effect
 55% tetrasilicic fluoromica crystals.55% tetrasilicic fluoromica crystals.

Ceramming increases strength, toughness, increasesCeramming increases strength, toughness, increases
resistance to abrasion, chemical durability and decreasesresistance to abrasion, chemical durability and decreases
translucency.translucency.
Particle size 5-7 microns, volume 50%

 DICOR MGCDICOR MGC
 70% TETRASILICIC FLUROMICA CRYSTAL.70% TETRASILICIC FLUROMICA CRYSTAL.
 Particle size 1-5 microns, volume 65 %.Particle size 1-5 microns, volume 65 %.
 Provided as CAD/CAM blanksProvided as CAD/CAM blanks
 No longer soldNo longer sold
 DisadvantagesDisadvantages
Limited use in low stress bearing areasLimited use in low stress bearing areas
Unable to color internallyUnable to color internally

 Dicor plus : pigmented feldspathic porcelainDicor plus : pigmented feldspathic porcelain
veneer.veneer.
 Willis glass : veneer of aluminous porcelain.Willis glass : veneer of aluminous porcelain.

PRESSABLE GLASS CERAMICPRESSABLE GLASS CERAMIC
 MacCulloch in 1968MacCulloch in 1968
 Type of Feldspathic porcelainType of Feldspathic porcelain
 IPS Empress 1--- Leucite 35%IPS Empress 1--- Leucite 35%
adv : translucent, increased flexural strength,adv : translucent, increased flexural strength,
Excellent fit and estheticsExcellent fit and esthetics
IPS Empress 2 ---- Lithia disilicate 70%IPS Empress 2 ---- Lithia disilicate 70%
Scattering similar to tooth enamelScattering similar to tooth enamel

SLIP CAST CERAMICSSLIP CAST CERAMICS
 SLURRY OF MATERIAL IS SLIP CAST ON THE DIE ANDSLURRY OF MATERIAL IS SLIP CAST ON THE DIE AND
HEATED IN THE FURNACE TO PRODUCE A PARTIALLYHEATED IN THE FURNACE TO PRODUCE A PARTIALLY
SINTERED COPING.SINTERED COPING.
 THIS COPING IS INFILTRATED WITH GLAS AT 1100THIS COPING IS INFILTRATED WITH GLAS AT 1100
FOR 4 HRS TO STRENGTHEN COREFOR 4 HRS TO STRENGTHEN CORE
 EX: ICS, ICA, ICZEX: ICS, ICA, ICZ

ceramicceramic CeramicCeramic
typetype
CeramicCeramic
veneerveneer
IndicationsIndications FlexuralFlexural
strengthstrength
(Mpa)(Mpa)
ICSICS Mgo-Mgo-
alal22oo33
aluminousaluminous
porcelainporcelain
Anterior crownAnterior crown 350350
ICAICA AlAl22oo33
aluminousaluminous
porcelainporcelain
Anterior crownAnterior crown
and posteriorand posterior
crown andcrown and
anterior FPDanterior FPD
500500
ICZICZ AlAl22oo33--
zrozro
aluminousaluminous
porcelainporcelain
Posterior crownPosterior crown
and posterior FPDand posterior FPD
700700

Fabrication stepsFabrication steps

REFERENCES
1. Science of dental materials- K J Anusavice
2. Restorative dental materials - R G Craig
3. Dental biomaterials- E C Coombe
4. Applied dental Materials - John F McCabe
5. Introduction to Dental Materials- Richard Van Noort

Evolution of dental ceramics in twentieth century-J W McLean, J Prosthet Dent
2001,85(1),61-66.
Future ceramic systems -J F Roulet and R Landa, Operative Dentistry 2001,6,211-
218.
Recent advances in ceramics for dentistry-I L Denry, Crit Rev Oral Biol Med
1996,7(2),134-143.
Dental Ceramics an update-V Piddock and J E Qualtrough, J Dent 1990,18,227-235.
Recent developments in restorative dental ceramics-K J Anusavice,JADA,124,1993
A review of All-Ceramic Restorations- M A Rosenblum and A
Schulman,JADA,128,1997297-307.

Thank you
For more details please visit

dental ceramics. / academy of fixed orthodontics

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