Dental ceramics/prosthodontic courses

DENTAL CERAMICS
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

INTRODUCTION

CONTENTS
• HISTORICAL PERSPECTIVE
• CLASSIFICATION AND COMPOSITION
• STRUCTURE
• PORCELAIN CONDENSATION
• SINTERING
• BONDING PORCELAIN TO METAL

• METHODS OF STRENGTHENING CERAMICS
• ABRASIVENESS OF DENTAL CERAMICS
• FINISHING AND POLISHING OF PORCELAINS
• ALLOYS FOR METAL CERAMIC RESTORATIONS
• FACTORS AFFECTING COLOR
• PROPERTIES
• REVIEW OF LITERATURE
• RECENT ADVANCES IN CERAMICS
• SUMMARY AND CONCLUSION
• BIBLIOGRAPHY

HISTORICAL PERSPECTIVE
• Stone age more than 10,000 years ago ….
flaking
• In 700 B.C., the Etruscans made ivory teeth and
bone teeth
• Porcelain was obtained in China by fluxing
white china clay with “ chine stone” to produce
a white translucent stone ware in about 1000
A.D

• The first known case of industrial espionage… a
Jesuit father named D’entrecolles in 1717…
• In 1774 a French apothecary named Alexis
Duchateau
• Nicholas Dubious de chemant of Paris in
collaboration with Alexis Duchateau considerably
improved the method of fabricating dentures.
• In 1838 Elias Wildman
• Italian dentist Fonzi … terrometallic teeth
• patents of Weinstein and Weinstein(1962) and
Weinstein et al (1962) which described the
formulations of feldspathic porcelain

• The first commercial porcelain was developed in
1965 by Vita Zahnfabrik.
• A significant improvement in fracture resistance was
reported by Hughes in 1965 with the introduction of
aluminous core porcelain.

CLASSIFICATION
ACCORDING TO HISTORY
• Earthenware:
• Fired at low temperature and is relatively
porous.
• Stoneware:
• Appeared in china in about 100 B.C
• Porcelain:
• Obtained by fluxing white China with “Chine
stone” to produce a white translucent
stoneware.

CLASSIFICATION
ACCORDING TO FIRING TEMPERATURE:
• High fusing : 1300 degree centigrade
• Medium fusing : 1101-1300 degree
centigrade
• Low fusing : 850-1100 degree
centigrade
• Ultra low fusing :< 850 degree
centigrade

CLASSIFICATION
ACCORDING TO USE:
Anterior
Posterior
Crowns
Veneers
Post and cores
FPD
Stain ceramic
Glaze ceramic

CLASSIFICATION
ACCORDING TO COMPOSITION:
Pure alumina
Pure Zirconia
Silica glass
Leucite based glass ceramic
Lithia based glass ceramic

CLASSIFICATION
ACCORDING TO PROCESSING METHOD:
 Sintering
 Partial sintering
 Glass infiltration
 CAD-CAM
 Copy milling
• ACCORDING TO TRANSLUCENCY
 Opaque
 Translucent
 Transparent

COMPOSITION
•CERAMIC
•GLASS
•SINTERING
•VITRIFICATION
•FRITTING

FELDSPAR :
They are mixtures of potassium aluminum silicate
K2O.Al2O3.6SiO2, and albite Na2O.Al2O3.6SiO2.
when feldspar is melted at approximately 1250-
1500 degree Celsius, it fuses to become a glass
with a free crystalline silica phase..
When feldspar is heated at temperatures between
1150 and 1530 degree centigrade it undergoes
INCONGRUENT MELTING to form crystals of
leucite which is a K-Al-Silicate mineral with a
large coefficient of thermal expansion.

KAOLIN:
• Is hydrated aluminum silicate
(Al2O3.2SiO2.2H2O) that acts as a binder to
increase the moldability of the unfired porcelain .
Because of its opaqueness it is present in only
very small quantities if at all.
QUARTZ:
• It is a high fusing material forms the framework
around which the other ingredients flow. It
prevents the slumping of the crown during the
liquid phase.
ALUMINA: Many European tooth manufacturers
use alumina in place of silica to strengthen the
teeth, especially around the pins.www.indiandentalacademy.com

FLUXES:
• Potassium, lithium, sodium and calcium oxide and
boric acid are used as fluxes by interrupting the
integrity of the SiO4 network, and lower the
softening temperature of a glass by reducing the
amount of cross linking between silica and oxygen
The O: Si ratio in a glass is of greatest importance
and increasing this ratio will cause reduced
viscosity, lowered fusion temperature and
increased thermal expansion.www.indiandentalacademy.com

COLORING AGENTS:
The coloring pigments added to porcelain are
known as color frit. These are prepared by fritting
metallic oxides into the basic glass used in
porcelain. Some of the common colors used are:
• Pink : Tin chromium or chroma alumina
• Yellow : Indium or praesmodyium
• Blue : Cobalt salt
• Green : Chromium oxide
• Grey : Iron oxide or platinum

OPACIFYING AGENT :
• translucency …..metal oxide ….refractive index .
…..melting point
FLUORESCENCE :
• The natural teeth possess a yellow white
fluorescence,
• the uranium salt, sodium di urinate.
• T his salt produces a strong greenish-yellow color.
• radiation hazards of including uranium.

STRUCTURE
• Dental porcelains
contain a crystal
phase and glass
phase based on the
silica structure. This
structure is
characterized by the
Si-O tetrahedron in
which a Si 4+ cation
is positioned at the
center of a
tetrahedron with O-
anions at each four
corners

• Potassium, sodium and calcium oxides are
used as glass modifiers
• Boric oxide can act as a flux and also as a glass
former.
• Oxides like alumina may react either way,
depending on other factors such as
composition. Such oxides are called
intermediates.

PORCELAIN CONDENSATION
• Porcelain is supplied as a fine powder that is
designed to be mixed with water or another vehicle
and condensed to desired form. The particles are of
a particular size distribution to produce the most
densely packed porcelain when packed. This
provides two benefits:
Lower firing shrinkage
Less porosity.
The methods of condensation are:
• Vibration technique
• Spatulation technique
• Brush technique www.indiandentalacademy.com

SINTERING OF PORCELAIN
The purpose of firing is simply to fuse the particles
together, a process called sintering.
The condensed porcelain mass is placed …..
Preheating for 5 min …. rapid production of steam
White
areas are
powder
particles
and the
area
between
are voids

STAGES IN FIRING
• LOW BISQUE:
The glass grains have softened and have started to
flow. The fired article exhibits rigidity but it is very
porous. The powder particles lack complete
cohesion. A negligible amount of firing shrinkage
occurs.
• MEDIUM BISQUE:
The glass grains have flowed to the extent that the
powder particles exhibit complete cohesion. The
article is still porous and at this stage there is
definite shrinkage.
• HIGH BISQUE:
After the high bisque stage, the shrinkage is complete
and the mass exhibits a smoother surface but the
body does not appear glazed. The work can be
removed from the furnace and cooled at any of these
stages, so that additions can be made.

• The fewer the firing cycles to which the
restoration is exposed, the higher will be the
strength and better the esthetics.
• Minimum of three firings are needed for
fabrication of ceramometal restoration:
• Opaque
• Dentin and enamel
• Stain and glaze
• Porcelain shrinks 30-40 % during firing-
oversize the buildup.

Porcelain for PFM are fired under vacuum thus as the
furnace door closes the pressure is lowered to 0.1
atmosphere and the temp is raise until firing tempo
is reached . th e vacuum is then released and the
furnace pressure returns to 1 atm- Dense pore free
porcelain.
GLAZING
• After porcelain is cleaned stains required are applied
and porcelain returned to furnace for final glaze
firing. When the glazing temp is reaches a thin
glassy film( glaze) is formed by viscous flow on the
porcelain surface. Glazed porcelain is stronger than
unglazed.
• Glaze is effective in reducing crack propagation. If
glaze is removed by grinding transverse strength is
reduced to half.

Two types of glazes :
• Over glaze
• Self glaze.
• Porcelains may be characterized with stains and
glazes to provide a more life like appearance.
• One method of ensuring that the stains remain
permanently is by incorporating the stains internally

COOLING:
• Must be carried out gradually and uniformly.
• Too rapid – surface cracking and loss of strength
• Too slow- might induce formation of additional
leucite. Increased the overall coefficient of thermal
expansion cracking, crazing.
• Less is the no of firing higher is the strength and
better the esthetics. Too many firing cycles – lifeless
over translucent porcelain.

BONDING PORCELAIN TO
METAL
The primary requirement for ……
• The nature of bond can be divided into three main
components:
• Mechanical
• Compressive
• Chemical

Mechanical:
• It is dependent upon good wetting of the metal or
metal oxide surface by porcelain. It is improved by a
textured surface. A rough surface may enhance the
bond resistance against induced shear stresses,
especially for base metal alloys. E.g.: air abrasion.
Advantages:
• Enhances wettability
• Additive bond strength
• Increased surface area
Compressive:
• Ceramo-metal systems are deliberately designed
with a very small degree of mismatch in order to
leave the porcelain in a state of compression.www.indiandentalacademy.com

Chemical bonding:
• When dental porcelain is fired onto metal with a
definite oxide (indium, tin or zinc oxide) layer, the
oxygen surface of the molten glass diffuses within
the oxygen surface on the metal to reduce then no.
of bridging oxygen and thus improves the
screening of cations at the interface

Procedure:
The metal is degassed by heating at 1000
degrees in vacuum for around 10 min and then
slowly air cooled in normal atmosphere. This
procedure will:
Degas the casting.
Induce age hardening of the alloy.
Base metal atoms will diffuse onto the surface
to form an oxide film.
Shear strengths of enamel porcelain bonds:www.indiandentalacademy.com

METHODS OF
STRENGTHENING CERAMICS
• Minimize the effect of stress raisers
• Develop redidual compressive stresses
• Minimize the number of firing cycles
• Minimize tensile stress through optimal design of ceramic
prosthesis
• Ion Exchange
• Thermal tempering
• Dispersion strengthening This is reinforcement with a
dispersed phase of a different material that is capable of
hindering a crack from propagating through the material
• Transformation tougheningwww.indiandentalacademy.com

ABRASIVENESS OF DENTAL
CERAMICS• Abrasive wear mechanisms for ceramics and tooth
enamel are predominantly due to micro fracture
which results from gouging, asperities, impact, and
contact stresses that cause cracks or localized
fracture.
• Steps to minimize wear:
 Ensure cuspid guided disclusion
 Eliminate occlusal prematurities
 Use metal in functional bruxing areas
 If occlusion in ceramic, use ultralow fusing ceramics
 Polish functional ceramic surfaces
 Repolish ceramic surfaces periodically
 Readjust occlusion periodically if needed.www.indiandentalacademy.com

• 1. Contour with flexible diamond disks,
diamond burs, heatless stones or green
stones (Silicone carbide)
• 2. Finish with white stones or abrasive
impregnated rubber disks, cups or points.
• 3. Polish with fine impregnated rubber
cups, and points or diamond paste applied
with a brush
• 4. Apply an over glaze layer.

ALLOYS USED FOR METAL-
CERAMIC RESTORATIONS
• HIGH NOBLE:
• Gold-platinum-
palladium
• Gold palladium-silver
• Gold-palladium
• NOBLE:
• Palladium-silver
• High palladium
PREDOMINANTLY
BASE:
Nickel-chromium
Nickel-chromium-
beryllium
Cobalt-chromium

FACTORS AFFECTING THE
COLOR OF CERAMICS:
• “A dark red that is yellower and less
strong than cranberry, paler and slightly
yellower than average garnet, bluer, less
strong, and slightly lighter than
pomegranate, and bluer and paler than
average wine”

The three dimensions of color:
• Hue: dominant color of an object, wavelength
• Chroma: saturation
• Value: lightness or darkness ….independent of hue
• Metamerism: objects that appear to be color matched
under one type of light appear different under
another light source
• Fluorescence: the property of an object to emit light
of different wavelength than the one incident upon
it
• Eincident=Escattered+Ereflected+Eabsorbed+Etrans
mitteed+Efluoresced
• In the dental operatory or laboratory color matching
is usually performed by the use of shade guide.

• Dentin is more opaque than enamel and will
reflect light.. pale yellow in color
• Enamel……crystalline……. different refractory
indices at the incisal region ….bluish white
(thick) at cervical margin-yellow (thin. reflects
color of underlying dentin)
• …..Translucence……DEPTH
• “Northern light from a blue sky during the
middle portion of day that is slightly
overcast”

PROPERTIES
• Discussion of mechanical properties… IN
VACUUM……HOLISTIC
Restorative materials at our disposal:
• Metals-high tensile strength, toughness, hardness,
resistance to abrasion, fracture resistance, elasticity,
ductility fatigue resistance
• Polymers-inferior in most of these
properties….BRITTLE FRACTURE
• Composites-BRITTLE FRACTURE superb aesthetics
• Ceramics-No ductility, high compressive strength,
low shear and tensile strengths excellent aesthetics

• COMPRESSIVE STRENGTH:
• Maximal stress required to fracture a
structure under compression.
• Enamel:37,800 psi
• Dentin: 44,200 psi
• Porcelain : 25,000 psi
• Metalceramic alloys : yield strength of 65-
80,000 psi
• TENSILE STRENGTH:
• Maximal stress required to fracture a
structure under tension.
• Porcelain: 5,000 psiwww.indiandentalacademy.com

• HARDNESS (KHN):
• Enamel: 343
• Dentin: 68
• Porcelain: 460
• FLEXURAL STRENGTH (BENDING STRENGTH
OR MODULOUS OF RUPTURE):
• Force per unit area at the point of fracture of a test
specimen subjected to flexural loading.
• Feldspathic porcelain: 141 MPa
• Aluminous porcelain: 139 MPa
• IPS Empress2: 400 MPa
• Gold alloy: 350-600 MPawww.indiandentalacademy.com

• FRACTURE TOUGHNESS:
• Feldspathic porcelain: 0.9-1.5 MPa.m1/2
• Aluminous porcelain: 2-2.9
• Yttria stabilized zirconia: 9
• Gold alloy: 20
• Enamel: 0.7
• IPS Empress2: 3.3
• THERMAL COEFFICIENT OF EXPANSION:
( mm/mm.K)*10-6
• Change in unit length per unit rise in temperature
• Tooth : 11.4
• Low fusing ceramic: 12.2-15.8
• IPS Empress 2: 10.6
• Ceramometal: ? www.indiandentalacademy.com

• THERMAL CONDUCTIVITY (cal.cm/cm2.sec.C):
• Ability of a body to transfer energy
• Enamel: 0.0022
• Dentin: 0.0015
• Porcelain: 0.0030
• THERMAL DIFFUSIVITY (cm2/sec):
• Enamel: 0.0042
• Dentin: 0.0026
• Porcelain: 0.64
• “Effectiveness of a material in preventing
heat transfer is directly dependent on its
thickness and inversely dependent on itswww.indiandentalacademy.com

• MODULOUS OF ELASTICITY
Porcelain: 69GPa
Type IV gold alloy: 99.3 GPa
Composite: 16.6Gpa
• Because of their moderately high m of elasticity
and relatively low tensile strength porcelains can
undergo very little elastic deformation (0.1%)
before they rupture i.e., they are not flexible

RECENT ADVANCES IN
DENTAL CERAMICS

• METAL CERAMIC CROWNS BASED ON
BURNISHED FOIL COPINGS: THE
CAPTEK SYSTEM
• Malleable Captek metal strips are burnished on a
refractory die to fabricate the metal coping of a metal
ceramic crown without the use of a melting and casting
process.
• The finished metal coping may be described as a
composite material consisting of a gold matrix reinforced
with small particles of a Pt-Pd-Au alloy.
• The units are then veneered with two thin layers of opaque
porcelain and other veneering porcelains.
• The Captek coping has a thickness of 0.25 mm which is
half of the traditional cast metals thus providing
additional space for vennering porcelain.

•Indications: crowns
and FPDs

• CASTABLE GLASS CERAMICS : DICOR
Dicor is a castable glass (55% tetraflurosilicic mica crystals)
that is formed into an inlay, facial veneer or full crown
restoration by a lost wax casting process……..
, it is covered by a protective embedment material and
subjected to heat treatment that causes mica to grow within
the glass matrix. This process is called CERAMMING.
Then it is fit on dies, ground as necessary and coated with
veneering porcelain.

• ADV:
Ease of fabrication
Improved esthetics-chameleon effect
Minimal shrinkage
Good marginal fit
High flexural strength
Low thermal expansion
Minimal abrasiveness of enamel
• DISADV:
Limited use in low stress areas (Low tensile
strength)
Inability to be colored internally

• PRESSABLE GLASS CERAMICS (IPS
EMPRESS):
• It is provided as core ingots that are heated and pressed
until the ingot flows into a mold. It contains a higher
proportion of leucite crystals that increase resistance to
crack propagation. The hot pressing process occurs over a
45 min period at high temperature to produce the ceramic
substructure. The crown form can be either stained and
glazed or built up using a conventional layering technique.
• ADV:
• Lack of metal
• Translucent ceramic core
• High flexural strength
• Excellent fit
• Excellent esthetics
• DISADV:
• Potential to fracture in posterior areas
• Need to use resin cementwww.indiandentalacademy.com

• INFILTRATED CERAMICS (INCERAM):
– Available as two component system:
– Powder: alumina/spinell/zirconia
• - Low viscosity glass
 A slurry of the powder is slip cast on a refractory die and heated in
a furnace at 1120 degree centigrade for 10 hrs and then it is
infiltrated with the low viscosity glass at 1100 degree centigrade for
4 hrs to eliminate porosity and to strengthen the slip cast core.
• ADV:
– Lack of metal substructure
– High flexural strength
– Excellent fit
• DISADV:
 Opacity
 Special die material and high temperature oven is required
 Have abrasive properties

• CAD –CAM CERAMICS (PROCERA, CEREC,
CELAY, DICOR MGC):
• It stands for Computer aided design/Computer aided
manufacturing.
• It is supplied as ceramic ingots available in various
shades. These are placed in a machinable apparatus to
produce the desired contours. This machined
restoration is checked for fit on the tooth. Occlusal
adjustment is done followed by polishing, etching and
bonding the restoration to the prepared tooth.

• ADV:
• Negligible porosity levels
• Freedom from making an impression
• Need for a single patient appointment (with
CEREC system)
• Good patient acceptance
• DISADV:
• Need for costly equipment
• Lack of computer controlled processing
support for occlusal adjustment
• Technique sensitive nature of surface imaging.

REVIEW OF LITERATURE
Francois Duret, Jean Louis Blouin and Bernard Duret
in 1988 discussed the role of CAD-CAM in dentistry.
They explained the equipment needed in the dental
office, the design of the clinical crown the build up
required and the milling process. They concluded
that CAD CAM had exciting possibilities in the
coming years.

J.Robert Kelly, Ichiro Nishimura and Stephen D.
Campbell in 1996 presented a brief history of dental
ceramics and offerd perspectives on recent research
aimed at the future development of ceramics for
clinical use . They concluded that sound scientific
and collaborative foundations exist for the continued
understanding and improvement of dental ceramic
systems.
Frankie Sulaiman, John Chai, Lee M. Jameson and
Wayne T. Wozniak in 1997 compared the marginal
fit of In-Ceram, IPS Empress and Procera Crowns.
They found In-Ceram to have the greatst marginal fit
discrepancy followed by Procera and IPS Empress.
The facial and lingual margins exhibited significantly
larger marginal discrepancies than the proximal
margins.

John Chai, Yukuta Takahashi, Frankie Suleiman, Kok-
heng Chong and Eugene P.Lautenschlager in 2000
compared the probability of fracture of 4 systems of
all ceramic crowns i.e.,Inceram, CEREC 2, IPS
Empress and Procera.
. Ten crowns of each system were fabricated and
compressed at 45 degree . The data obtained was
subjeced to statistical analysis. They found no
significant difference in the probability of fracture
among the 4 systems.

A study conducted in our department under the able
guidance of Dr. N.P. Patil sir evaluated the shear
bond strength of three porcelain repair systems with
various surface treatments in response to thermal
stress. This study was conducted on intentionally
fractured 30 porcelain-fused-to-metal samples. 3M
Scotchbond system, Clearfil Porcelain Bond and
Ceramic Repair Materials were used to restore the
fractured porcelain surface. The findings of the
study suggests that Clearfil Porcelain Bond
undergoes least changes in the bond strength of
composite resin to porcelain or metal surface after
thermocycling treatment.

Another study conducted in our department under
the able guidance of Dr. N.P.Patil sir examined the
effect of recasting of base metals on bond strength
of porcelain. It was observed that the addition of
one third new metal to the alloy once cast, restores
the bonding characteristics of PFM and also that
Ni-Cr had superior bonding properties with
porcelain than Co-Cr alloys.

SUMMARY & CONCLUSION
•Considerable advances in the field of dental ceramics
has brought forth novel processing technologies which
have enhanced the properties and clinical acceptability
of these materials.
•Yet, these have yet again highlighted our inability to
comprehend its greatest deficiencies, i.e., inadequate
tensile strength and brittleness.
•It is this challenge to the upcoming prosthodontists that
ceramics beckons, and to which we all should rise.www.indiandentalacademy.com

BIBLIOGRAPHY
• Restorative dental materials – Robert G.Craig, John
M. Powers,8th
Edition.
• Phillips’science of dental materials – Kenneth
J.Anusavice,11th
Edition.
• Notes on Dental materials – E.C.Combe,6th
Edition.
• Ralph W.Philips- Skinner’s Science of Dental
Materials.

• Dental Materials Properties and Manipulation – Robert
G.Craig,O’Brien,Powers.
• Clinical Handling of Dental Materials-
Smith,Wright,Brown.
• Clinical aspects of Dental Materials – Philips – 8th
Edition.
• Theory and Practice for Ceramo Metal Restorations –
Masahiro Kuwata
• The Science and Art of Dental Ceramics,Vol II : Bridge
Design and Laboratory Proceedures In Dental Ceramics –
John W.Mclean www.indiandentalacademy.com

•Evaluation and comparison of shear bond strength of
three porcelain repair systems with various surface
treatments in response to thermal stress – an in vitro
study - Dr. Meenakshi T.
•Kelly J.R.et al .Ceramics in Dentistry: Historical roots
and Current Perspective.J Prosthet Dent 1996;75:18-32.
•Duret F,Jean-louis Blouin,Duret Bernard. CAD-CAM in
Dentistry.JADA 1988;117:715-720.
•Sulaiman F,Chai J, Jameson LM, A Comparison of the
Marginal Fit of In-Ceram,Ips Empress,and Procera
Crowns. Int J Prosthodont 1997;10:478-484.
•Chai J et al, Probability of Fracture of All-Ceramic
Crowns. Int J Prosthodont 2000;13:420-424.www.indiandentalacademy.com

Thank Youwww.indiandentalacademy.com

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