3. CONTENTS
• INTRODUCTION-BASIC TERMINOLOGIES
• HISTORICAL PERSPECTIVE
• COMPOSITION AND CLASSIFICATION
• STRUCTURE
• PORCELAIN CONDENSATION
• SINTERING
• BONDING PORCELAIN TO METAL
• METHODS OF STRENGTHENING CERAMICS
• FINISHING AND POLISHING OF PORCELAINS
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4. • ALLOYS FOR METAL CERAMIC RESTORATIONS
• FACTORS AFFECTING COLOR
• PROPERTIES
• RECENT ADVANCES IN CERAMICS
• SUMMARY AND CONCLUSION
• BIBLIOGRAPHY
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18. Composition of dental ceramics
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Feldspar (60 -80 %)
is a naturally occurring mineral and composed of
two alkali aluminum silicates such as potassium
aluminum silicate (K2O-Al2O3-6SiO2); also called
as potash feldspar or ortho clase and soda
aluminum silicate (Na2O-Al2O3- 6SiO2); also
called as soda feldspar or albite .
It is the lowest melting compound and melts
first on firing.
Most of the currently available porcelains
contain potash feldspar as it imparts translucency
to the fired restoration.
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QUARTZ:or silica –12-25%
• It is a high fusing material forms the
framework around which the other
ingredients flow. Acts as REFRACTORY
MATERIAL. IT prevents the slumping of
the crown during the liquid phase.
20. • ALUMINA: Many European tooth
manufacturers use alumina in place of silica to
strengthen the teeth, especially around the
pins.
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KAOLIN:0-4%
• Kaolin is a type of clay material which is usually
obtained from igneous rock containing alumina.
Kaolin acts as a binder and increases the moldability
of the unfired porcelain.
• It also imparts opacity to the porcelain restoration so
dental porcelains are formulated with limited quantity
of kaolin.
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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.
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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
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OPACIFYING AGENT :
• translucency …..metal oxide ….refractive index .
…..melting point
FLUORESCENCE :
• The natural teeth possess a yellow white fluorescence,
Eg.the uranium salt, sodium di urinate.
This salt produces a strong greenish-yellow color.
Radiation hazards of including uranium.
So lanthanide oxide is used
26. CERAMIC MANUFACTURING--
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.
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27. • The oxides melt together to form a 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’.
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29. Ceramics can be classified by their Microstructure
(i.e., amount and type of crystalline phase and glass
composition).
They can also be classified by the Processing
technique (power-liquid, pressed or machined).
CLASSIFICATION
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30. MICROSTRUCTURAL CLASSIFICATION
At the microstructural level, There can be infinite
variability of the microstructures of materials, but they can be
broken down into four basic compositional categories, with a
few subgroups:
composition category 1 – glass-based systems (mainly
silica),
composition category 2 – glass-based systems (mainly
silica) with fillers, usually crystalline (typically leucite or, more
recently, lithium disilicate),
composition category 3 – crystalline- based systems with
glass fillers (mainly alumina) and
composition category 4 – polycrystalline solids (alumina
and zirconia).
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31. CLASSIFICATION
II.ACCORDING TO FIRING TEMPERATURE:
• High fusing : 1300 degree centigrade
• Medium fusing : 1101-1300 degree “
centigrade
• Low fusing : 850-1100 deg.centi
• Ultra low fusing :< 850 degree centigrade
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35. 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
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38. PORCELAIN CONDENSATION
Porcelain is supplied as a fine powder that is
designed to be mixed with DISTILLED water or
another vehicle and condensed to desired form.
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50. 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
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54. • 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:
• Porcelain shrinks 30-40 % during firing-
oversize the buildup.
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56. 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 .
The vacuum is then released and the furnace pressure
returns to 1 atm- Dense pore free porcelain.
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57. GLAZING
• After porcelain is cleaned required stains
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.
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59. 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
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60. 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.
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61. BONDING PORCELAIN TO
METAL
The primary requirement for ……
• The nature of bond can be divided into three main
components:
• Mechanical
• Compressive
• Chemical
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62. 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
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63. COMPRESSIVE BONDING
• Ceramo-metal systems are deliberately
designed with a very small degree of
mismatch in order to leave the porcelain
in a state of compression.
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64. • 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
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CHEMICAL BONDING:
65. Procedure of oxide forming : -- --Preheating
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.
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71. • Develop residual compressive stresses
• Minimize the number of firing cycles
• Minimize tensile stress through optimal
design of ceramic prosthesis
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72. Ion Exchange—small alkali ions to large
ions produce compressive force leading to
strengthening
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74. • 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
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76. 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.
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77. • 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.
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78. ALLOYS USED FOR METAL-CERAMIC
RESTORATIONS
1.HIGH NOBLE:
Gold-platinum-palladium
Gold palladium-silver
Gold-palladium
3.PREDOMINANTLY BASE
Nickel-chromium
Nickel-chromium-beryllium
Cobalt-chromium
2.NOBLE:
Palladium-silver
High palladium
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80. FACTORS AFFECTING THE COLOR
OF CERAMICS:
The three dimensions of color:
• Hue: dominant color of an object,
wavelength
• Chroma: saturation
• Value: lightness or darkness
….independent of hue
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81. • 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
• In the dental operatory or laboratory color matching
is usually performed by the use of shade guide.
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84. • 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
• “
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85. PROPERTIES
VARIOUS Restorative materials at our disposal:
1.Metals- have high tensile strength, toughness,
hardness, resistance to abrasion, fracture resistance,
elasticity, ductility, fatigue resistance poor
aesthetics
2.Polymers-inferior in most of these properties---
BRITTLE FRACTURE
3.Composites-BRITTLE FRACTURE -superb aesthetics
4.Ceramics-No ductility, high compressive strength,
low shear and tensile strengths excellent aesthetics
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86. MECHANICAL PROPERTIES
• COMPRESSIVE STRENGTH:
-- Maximal stress required to fracture a
structure under compression.
Enamel :37,800 psi
Dentin : 44,200 psi
Porcelain : 25,000 psi
• TENSILE STRENGTH:
• Maximal stress required to fracture a structure
under tension.
Porcelain: 5,000 psi
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87. HARDNESS (KHN):
Enamel: 343 (KHN)
Dentin: 068 “
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 MPa
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88. • FRACTURE TOUGHNESS: total energy per unit
volume to fracture the alloy
--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
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89. THERMAL PROPERTIES
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
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90. • 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
• “
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91. • MODULOUS OF ELASTICITY-- elastic deformation
before they rupture
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
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93. 1.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.
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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.
96. 2.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.
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99. • 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
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100. 3.PRESSABLE GLASS CERAMICS (IPS EMPRESS):
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.
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103. 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 cement
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104. 4.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
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108. 5.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.
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120. 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.
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121. 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.
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122. • 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
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123. •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.
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