ceramic

DENTAL CERAMICS
DR. KUMARI KALPANA
PGT 1ST YEAR
DEPT. OF
PROSTHODONTICS,CROWN &
BRIDGE
1
1

CONTENTS Introduction
 Terminologies
 History
 Classification
 Composition
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 Methods of Strengthening Ceramics.
 Metal-Ceramic restorations
 All Ceramic restorations
Mechanical and thermal properties of dental ceramics.
Optical properties of dental ceramics.

5
 Porcelain Denture Teeth
 Factors affecting the Color of Ceramics.
 Recent advancements.
 Conclusion & References.

Introduction
Anusavice KJ. Phillip’s science of dental materials: Dental Ceramics. 11th ed. Philadelphia: Saunders; 2003. 655-719.
6

• Restorative and prosthetic materials used in dentistry can be grouped into 4
categories:
1. Metals
2. Polymers
3. Composites
4. Ceramics.
7

• The word ceramic is derived from the greek word keramos which
literally means ‘burnt stuff’ but which has come to mean more
specifically a material produced by burning or firing.
8

• According to phillip’s (12th ed.)
Dental ceramic is defined as “an inorganic compound with
non-metallic properties typically consisting of oxygen and one
or more metallic or semi metallic elements (al, ca, li, mg, k, si,
na, ti, zr) that is formulated to produce the whole or part of a
ceramic-based dental prosthesis.”
10

11
CERAMICS2
Compounds of one or more metals with a nonmetallic
element, usually oxygen. They are formed of chemical and
biochemical stable substances that are strong, hard, brittle,
and inert nonconductors of thermal and electrical energy
(GPT 9).

12
Metal-ceramic prosthesis: A partial crown, full crown, or
multiple-unit fixed dental prosthesis made from a metal
substrate and an adherent oxide to which dental porcelain is
bonded for esthetic enhancement and functional anatomy
(phillip’s).
CAD-CAM ceramic : A partially or fully sintered ceramic blank
that is used to produce a dental core or veneer structure using
a computer-aided design (CAD) and computer-aided
manufacturing or milling (CAM) process (phillip’s).

13
Zirconia : A partially stabilized zirconium oxide, usually in the
tetragonal phase, that is used primarily as a core (framework) for
dental prostheses. It has also been introduced as a monolithic
ceramic to be used without a veneering ceramic (phillip’s).

HISTORY1
14 14
Anusavice KJ. Phillip’s science of dental materials: Dental Ceramics. 11th ed. Philadelphia: Saunders; 2003. 655-719.

• Ceramics like tools have been used by humans since the end of the old
stone age around 10,000 BC to support the life styles and need of fisher-
hunter-gatherer civilizations.
• During the middle stone age ( 10,000 to 5500 BC) ceramics were important,
and they have retained their importance in human societies ever since.
15

 In 700 BC: Etruscan made teeth of ivory and bone that were held in
place by a gold framework.
 1774 : the introduction of porcelain in dentistry by Alexis Duchateau
is one of the most significant historic developments in dentistry.
16

 1789 : the first porcelain tooth material was patented by De
Chemant, a french dentist in collaboration with Duchateau.
 1808 : An italian dentist Fonzi invented a “ terrometallic”
porcelain tooth which was held into place by a platinum
pin which was subsequently improved by ash in 1837.
17

 1903 : The first porcelain crown was developed by Charles land.
 1962 : Weinstein and Weinstein et al. introduced most important
breakthroughs responsible for the long-standing superb esthetic
performance and clinical survival probabilities of metal-ceramic
restorations.
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 1965 : A significant improvement in the fracture resistance of all-
porcelain crowns was reported by Mclean and Hughes, when they
introduced a dental aluminous core ceramic consisting of a glass
matrix containing between 40% and 50% Al2O3 by weight.
 1984 : Improvement in all ceramic systems developed by controlled
crystallization of a glass (dicor) was demonstrated by Adair and
Grossman.
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 In earlier 1990: A pressable glass-ceramic (IPS empress),
containing approximately 34% volume of leucite, was introduced.
 In later 1990: IPS empress 2 was introduced containing 70 %
volume of lithium disilicate.
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• In 1992: DUCERAM LFC (low fusing ceramic) was developed
as less abrasive dental ceramic.
• These ceramics are considered as “self healing” due to 1
micron thick hydrothermal layer along the ceramic surface.
• These ceramics are now referred as “Low fusing ceramics”
have sintering temperature less than 850 degree celsius .
21

• Later, stronger/tougher ceramics were introduced. These
included:
PROCERA ALL- CERAM
IN CERAM ALUMINA
IN CERAM ZIRCONIA
LAVA
CERCON
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CLASSIFICATION
1. According to their use or indication:
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Anterior crowns
Posterior crowns
Veneers
Post and cores
FPDs
Stain and glaze ceramic

2. According to their composition:
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 Pure alumina
 Pure zirconia
 Silica glass
 Leucite – based glass ceramics
 Lithia based glass ceramics

3. According to their processing method:
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 Sintering
 Partial sintering and glass infiltration
 CAD-CAM and copy milling

• According to Anusavice1
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Firing temperature1,3,4,5:
1300 °C.
1101-1300 °C.
850 -1100 °C.
less than 850 °C

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• According to Craig3
1315 -1370 °C.
1090 -1260 °C.
870 – 1065 °C.

•
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According to rosenstiel4
1290 -1370 °C.
1090 -1260 °C.
870 – 1070 °C.

•
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According to shillingburg4
1290 -1370 °C.
1090 -1260 °C.
870 – 1065 °C.

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According to O’brien5
1288 -1371 °C.
1093 -1260 °C.
660 – 1066 °C.

5. According to microstructure: 32
6. According to translucency:
 Glass
 Crystalline
 Crystal containing glass.
 Opaque
 Translucent
 Transparent

7. According to fracture resistance
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 Low
 Medium
 High
Anusavice KJ. Phillip’s science of dental materials: Dental Ceramics. 12th ed. Philadelphia: Saunders; 2003.
8. According to substructure material:
cast-metal, swaged metal, glass-ceramic, CAD-CAM porcelain, or sintered
ceramic core.

The principal chemical components in dental porcelains
include crystalline minerals, such as feldspar, quartz,
alumina (aluminum oxide) and kaolin in a glass matrix ,
the exact proportions of each component vary with the
particular type of porcelain (high- medium and low
fusing) and specific brand.
35
Naylor, W. Patrick, James C. Kessler, and Arlo H. King. Introduction to Metal Ceramic Technology. Chicago: Quintessence Pub.
Co,Inc. 35

• The typical high-fusing porcelain is composed of feldspar (70%
to 90%), quartz (11% to18%), and kaolin (1% to 10%)
36

Feldspar is the ingredient primarily responsible for forming the glass matrix.
It has been used for a number of years because it blends itself so well to
the fritting and coloring processes. Naturally occurring feldspar does not
exist in a pure form, but is a mix of two substances: potassium aluminum
silicate (K20-Al203-6SiO2, also called as orthoclase or potash feldspar and
sodium aluminum silicate (Na2O-Al2O3-6SiO2), also called sodium feldspar.
Feldspar5 (albite)
37

The ratio of potash feldspar to sodium feldspar differs in a given batch
of material. This difference is important to porcelain manufacturers
because the two types of feldspar impart quite different handling
characteristics to porcelain.
38

Potash feldspar5
Potash feldspar is found in most present-day formulations because of the
translucent quality it adds to fired restorations. When melted between
1,250°C and 1,500°C (2,280°F to 2,730°F), potash fuses with quartz to
become a glass. The potash form of feldspar not only increases the viscosity,
or thickness, of the molten glass but also aids in controlling the porcelain’s
pyroplastic flow during sintering.
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Sodium feldspar
Sodium feldspar lowers the fusion temperature of porcelain,
causing it to be more susceptible to pyroplastic flow. Sodium
feldspar does not contribute to translucency, and it is also
considered as a less attractive substitute for potash feldspar.
40

Quartz5
Quartz (SiO2), also known as silica, has a high fusion
temperature and serves as the framework around which the
other ingredients can flow. By stabilizing the porcelain buildup at
high temperatures, quartz helps prevent the porcelain from
undergoing pyroplastic flow on the metal substructure during
sintering and strengthens the fired porcelain.
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Alumina5
The third component of dental porcelain, alumina (Al2O3), is
the hardest and strongest oxide. Naturally occurring alumina
has water molecules attached to it. Using a calcination process
similar to that used to refine gypsum products, “hydrated”
alumina is transformed to pure alumina.
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43
During the initial stages of calcination, the chemically bound
water in the alumina trihydrate is removed to yield “calcined”
alumina. A second calcination at 1,250°C converts the alumina to
its alpha form, which is then ground to a fine powder for use in
dentistry.

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Refined alumina is only slightly soluble in low-fusing
porcelain, but it is an important addition because it
increases the overall strength and viscosity of the melt. It
also has a low linear CTE (9 × 10-6/°C) compared to metal-
ceramic alloys (13.5 to 15.5 × 10-6/°C). So, manufacturers
add glass modifiers (e.g. oxides of potassium, sodium, and
calcium) to raise the CTE.

Kaolin5
kaolin (al2o3-2sio2-2h2o or hydrated aluminum silicate) It
has long since disappeared from the composition of metal-
ceramic porcelain, yet it continues to be mentioned in
dental materials textbooks.
45

46
Kaolin initially was added to act as a binder and to increase
the moldability of the unfired porcelain and enabled the
porcelain to be carved.
Because kaolin is also opaque, it was added in very small
quantities.

Glass Modifiers1
The sintering temperature of crystalline silica is too high for use in
veneering aesthetic layer which is bonded to metal substrates.
At such high temperatures, the alloys would melt.
Bonds between the silica tetrahedral can be broken by the addition of
alkali metal ions such as sodium, potassium, and calcium. These ions
are associated with the oxygen atoms at the corners of the tetrahedral
and interupt the oxygen-silicon bonds.
47

48
As a result, the three-dimensional silica network contains many
linear chains of silica tetrahedral that are able to move more
easily at lower temperatures than the atoms that are locked into
the three-dimensional structure of silica tetrahedral.

49
This ease of movement is responsible for the
Increased fluidity (decreased viscosity), lower
softening temperature, and increased thermal
expansion conferred by glass modifiers.

MANUFACTURE3
• Process is called “fritting”.
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the constituents are mixed
together and then fused to
form a frit
This is broken up, often by
dropping the hot material
into cold water
then ground into a fine
powder ready for use

Color Pigments / Coloring Agents1
 Pigmenting oxides are added to obtain the various shades needed
to simulate natural teeth.
 These colouring pigments are produced by fusing metallic oxides
together with fine glass and feldspar and then regrinding to a
powder.
 These powder are blended with the unpigmented powdered frit to
provide the proper hue and chroma.
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Ferric oxide, platinum Grey.
Chromium oxide, copper oxide Green
Cobalt salts Blue
Ferrous oxide, nickel oxide Brown
Titanium oxide Yellowish brown
Manganese oxide Lavender
Chromium tin, Chromium alum
ina
Pink
Indium Yellow, ivory
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Methods of Strengthening ceramics1
53
Anusavice KJ. Phillip’s science of dental materials: Dental Ceramics. 11th ed. Philadelphia: Saunders; 2003. 655-719
53

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Minimize the Effect of Stress Raisers
Stress raisers are discontinuities in ceramic and metal-ceramic structures
and in other brittle materials that cause a stress concentration in these areas.
The design of ceramic dental restorations should also avoid stress raisers in
the ceramic. Abrupt changes in shape or thickness in the ceramic contour
can act as stress raisers and make the restoration more prone to failure.
Thus the incisal line angles on an anterior tooth prepared for a ceramic crown
should be well rounded.

55
The fracture resistance of ceramic prostheses can be increased
through one or more of the following six options:
(1) select stronger and tougher ceramics;
(2) develop residual compressive stresses within the surface of the
material by thermal tempering,
(3) develop residual compressive stress within interfacial regions
of weaker, less tough ceramic layers by properly matching thermal
expansion coefficients,

56
(4) reduce the tensile stress in the ceramic by appropriate
selection of stiffer supporting materials,
(5) minimize the number of porcelain firing cycles,
(6) design the ceramic FPD prosthesis with greater bulk and
broader radii of curvature to minimize the magnitude of tensile
stresses and stress concentrations during function, and
(7) adhesively bond ceramic crowns to tooth structure.

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Develop Residual Compressive Stresses
One method of strengthening glasses and ceramics is the introduction of
residual compressive stresses within the veneering ceramic. The metal and
porcelain should be selected with a slight mismatch in their thermal contraction
coefficients (the metal thermal contraction coefficient being slightly larger) so
that the metal contracts slightly more than the porcelain on cooling from the
firing temperature to room temperature. This mismatch leaves the porcelain in
residual compression and provides additional strength for the prosthesis.

58
Minimize the Number of Firing Cycles
Changes in the leucite content caused by multiple firings can alter
the thermal contraction coefficient of the porcelain. Some
porcelains undergo an increase in leucite crystals after multiple
firings that will increase their thermal expansion coefficients. If the
expansion coefficient increases above the value for the metal, the
expansion mismatch between the porcelain and the metal can
produce stresses during cooling that are sufficient to cause
immediate or delayed crack formation in the porcelain.

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Minimize - Tensile Stress Through Optimal
Design of Ceramic Prostheses.
Of major concern are tensile stresses that are concentrated within the
inner surface of posterior ceramic crowns. Sharp line angles in the
preparation also will create areas of stress concentration in the
restoration, primarily where a tensile component of bending stress
develops. A small particle of ceramic along the internal porcelain
margin of a crown will also induce locally high tensile stresses. Thus
the ceramic surface that will be cemented to the prepared tooth or
foundation material should be examined carefully when it is delivered
from the laboratory.

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Ion Exchange.
The technique of ion exchange is one of the more sophisticated
and effective methods of introducing residual compressive
stresses into the surface of a ceramic. The ion-exchange process
is sometimes called (chemical tempering) and can involve the
sodium ion since sodium is a common constituent of a variety of
glasses and has a relatively small ionic diameter.

61
If a sodium-containing glass article 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 article and remain in place
after cooling. Since the potassium ion is about 35% larger than the
sodium ion, the diffusion of the potassium ion into the place formerly
occupied by the sodium ion creates residual compressive stresses in the
surface.

62
Thermal Tempering
Perhaps the most common method for strengthening glass is
by thermal tempering. Thermal tempering creates residual
surface compressive stresses by rapidly cooling (quenching)
the surface of the object while it is hot and in the softened
(molten) state. This rapid cooling produces a skin of rigid
glass surrounding a soft (molten) core.

63
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.

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Dispersion Strengthening
A further, yet fundamentally different, method of strengthening
glasses and ceramics is to reinforce them with a dispersed phase
of a different material that is capable of hindering a crack from
propagating through the material. This process is referred to as
dispersion strengthening. Almost all of the newer higher-strength
ceramics derive their improved fracture resistance from the crack-
blocking ability of the crystalline particles.

65
Dental ceramics containing primarily a glass phase can be strengthened
by increasing the crystal content of leucite (K2O ● Al2O3 ● 4SiO2), lithia
disilicate (Li2O ● 2SiO2), alumina (Al2O3), magnesia-alumina spinel
(MgO ● Al2O3), zirconia (ZrO2), and other types of crystals.
When a tough, crystalline material such as alumina (Al2O3) is added to a
glass, the glass is toughened and strengthened because the crack cannot
pass through the alumina particles as easily as it can pass through the
glass matrix.

66
Transformation Toughening
•Transformation of ZrO2 from a tetragonal crystal phase to a
monoclinic phase at the tips of cracks that are in regions of tensile
stress.
When pure ZrO2 is heated to a temperature between 1470˚ and
2010˚ C and it is cooled, its crystal structure begins to change
from a tetragonal to a monoclinic phase at approximately 1150˚
C.
During cooling to room temperature, a volume increase of
several percentage points occurs when it transforms from the
tetragonal to monoclinic crystal structure.
This polymorphic transformation can be prevented with certain
additives such as 3 mol% yttrium oxide (yttria or Y2O3).

67
Several types of crack shielding processes are possible, including
• microcracking,
• ductile zone formation, and
• transformation zone formation.
• By controlling the composition, particle size, and the temperature versus time cycle, zirconia
can be densified by sintering at a high temperature and the tetragonal structure can be
maintained as individual grains or precipitates as it is cooled to room temperature.
• The tetragonal phase is not stable at room temperature, and it can transform to the monoclinic
phase with a corresponding volume increase under certain conditions.

68
•When sufficient stress develops in the tetragonal structure and a crack in the
area begins to propagate, the metastable tetragonal crystals (grains) or
precipitates next to the crack tip can transform to the stable monoclinic form.
In this process a 3 vol% expansion of the ZrO2 crystals or precipitates occurs
that places the crack under a state of compressive stress and crack
progression is arrested.
For this crack to advance further, additional tensile stress would be required. Because
of this strengthening and toughening mechanism, the yttria-stabilized zirconia
ceramic is sometimes referred to as ceramic steel.

Metal ceramic restoration2
A tooth or/and implant retained fixed dental prosthesis that
uses a metal substructure upon which a ceramic veneer is
fused.(GPT 9)
70
65

Collarless metal ceramic restoration
A metal ceramic restoration whose cervical metal portion
has been eliminated. Porcelain is placed directly in contact
with the prepared finish line. (G.P.T-9)
71
66

Components of Metal Ceramic Restoration
72
67

Dental ceramics have a composite structure. Materials
for metal-ceramic restorations contain a vitreous phase,
also called glassy matrix, that represents 75 to 85% by
volume and are reinforced by various crystalline
phases.
Denry isabelle. Recent advances in ceramics for dentistry. Crit rev oral boil med 1996;7(2):134-143.
73

The match between refractive indices of the crystalline phase and
glassy matrix is a key factor for controlling the translucency of the
porcelain.
The match between the thermal expansion coefficients of the
crystalline phase and glassy matrix is critical in controlling
residual thermal stresses within the porcelain.
74

• Veneering ceramics for metal-ceramic restorations - feldspathic
porcelains
• Feldspathic dental porcelains usually contain between 15 and 25 vol %
leucite.
• Feldspar-derived glass has exhibits a low coefficient of thermal
expansion, i.e. around 8.6 × 10-6/°K
• Leucite (KAlSi2O6) is a potassium alumino-silicate mineral with a large
coefficient of thermal expansion (20 to 25 × 10-6/°K).
Denry isabelle, Holloway J.A. HJ. Ceramics for dental applications: a review. Materials 2010 jan;352-368.
75
70

• Leucite can be obtained by incongruent melting of naturally-occurring feldspar
at temperatures between 1150 and 1530 °C.
• It exhibits a tetragonal structure at room temperature. It undergoes a displacive
phase transformation from tetragonal to cubic at 625 °C, accompanied with a
volume expansion of 1.2%
• The addition of leucite to feldspar glass led to the production of veneering
ceramics with a coefficient of thermal expansion compatible with that of the
metal substructure.
76

REQUIREMENTS FOR A METAL-CERAMIC SYSTEM
3
1. High fusing temperature of the alloy.
2. Low fusing temperature of the ceramic.
3. The ceramic must wet the alloy readily .
4. A good bond between the ceramic and metal is
essential and is achieved by the interactions of the
ceramic with metal oxides and roughness of metal.
77
Craig GR, Powers MJ. Restorative dental materials. 13th ed. Elsevier: Missouri; 253-275.
72

5. Compatible coefficients of thermal expansion of the
ceramic and metal.
6. Adequate stiffness and strength of alloy core.
7. High sag resistance is essential.
8. An accurate casting metal coping is required.
9. Adequate design of restoration is critical.
78

79
CASTING ALLOYS FOR BONDING
TO DENTAL PORCELAIN5

High noble
Noble
Predominately base
80

High noble
• Gold-platinum-palladium
• Gold-palladium-silver
• Gold-palladium
• Pure gold (99.7 wt%)
81

Noble
• Palladium Gold
• Palladium Gold Silver
• Palladium Silver
• Palladium Copper Gallium
• Palladium Gallium Silver
82

Predominately base
• Nickel-chromium
• Nickel-chromium-beryllium
• Cobalt-chromium
83

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
veneer.
• The thickness of metal coping can vary, depending on the
type of casting alloy used and the amount of tooth
structure reduced by the dentist.
84
Naylor, W. Patrick, James C. Kessler, and Arlo H. King. Introduction to Metal Ceramic Technology. Chicago:
79

Primary functions
1. The casting provides fit of the restoration to the prepared tooth.
2. The metal forms oxides that bond chemically to the dental
porcelain.
3. The coping serve as a rigid foundation to which the brittle
porcelain can be attached for increased strength and support.
4. The substructure restores the tooth’s proper emergence profile.
85

Secondary functions
1. Metal occlusal and lingual articulating surfaces generally can be
less destructive to the enamel of opposing natural teeth.
2. Fabrication of a restoration with minimal occlusal clearance has
more potential for success with a metal substructure (and
occlusion in metal) than the all- ceramic materials.
86

3. The occluding surfaces can be easily adjusted and repolished
intraorally.
4. The metal axial walls can support the components of a removable
partial denture.
5. The axial surfaces can house attachments for fixed or removable
partial dentures.
87

• Areas of the metal substructure to be veneered with porcelain
must be at least 0.3 mm thick.
• With base metal alloys, the coping can be reduced to 0.2 mm or
less and still be strong enough to support the porcelain.
88
Thickness
83

Principles of substructure design
89

1. Are the occlusal contacts to be in
metal or porcelain???
90
85

 Occlusion in metal requires less tooth reduction
( 1 to 1.5 mm).
 Approx. 2 mm of occlusal reduction is necessary for posterior
teeth and 1.5 mm to 2mm for anterior teeth requiring
porcelain on occluding surfaces.
91

 Metal surfaces can be more easily adjusted and repolished at
chairside without adversely affecting the restoration. However,
on the other hand, removing the glaze of metal ceramic
restoration during intraoral adjustments weakens the porcelain
greatly.
92

2. Are the centric occlusal contacts 1.5 to
2mm from the porcelain-metal junction???
93

• Occlusal contacts when placed directly on or close
to the porcelain- metal junction, there is an
increased chances that the porcelain will chip or
fracture at that point of contact.
94

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.
95

3. Are the interproximal contacts to
be restored in metal or
porcelain???
96

• The inter proximal contact area 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.
97

• It is important to provide proper metal support to a porcelain
marginal ridge in the substructure design to prevent possible
fracture.
• However, the distal inter proximal contacts of posterior teeth
may be restored in either metal or porcelain because these
areas are not as critical aesthetically.
98

4. Are the cusp tips (or incisal edges)
adequately supported by the metal substructure
with no more than 2mm of unsupported
porcelain ?
99

• The ultimate goal of any substructure is to support an
even thickness ( 1mm min, 2mm max) of the porcelain
veneer.
• If this maximum thickness is exceeded, the ceramic layer
may no longer be properly supported.
100

Is the substructure thick enough to provide a rigid
foundation for porcelain veneer??
101

BONDING OF PORCELAIN TO METAL5
102

How does dental porcelain bond to metal??
1. Van der waals Forces (Lacy, 1977)
2. Mechanical Retention
3. Compression Bonding
4. Direct Chemical Bonding (Lacy,1977; mcLean, 1980)
103
98

Van der waals Forces (Lacy, 1977)
• The attraction between charged atoms that are in
intimate contact yet do not actually exchange
electrons is derived from van der waals forces.
• Van der waals forces are generally weak.
104

• The better the wetting of the metal surfaces, the greater the van
der waals forces.
• Van der waals forces are only minor contributors to the over all
attachment process.
105

Mechanical retention
• Air abrading the metal with aluminium oxide is believed to
enhance mechanical retention further by eliminating surface
irregularities (stress concentration)
• Mechanical retention’s contribution to bonding may be relatively
limited.
106

• Dental porcelain does not require a roughened area to bond to
metal but some surface roughness is effective in increasing
bonding forces.
107

Compression bonding
• Dental porcelain is strongest under
compression and weakest under tension;
hence, if the coefficient of thermal
expansion of metal substructure is
greater than that of porcelain placed over
it, the porcelain should be placed under
compression on cooling.
108

• The metal contracts faster than the porcelain but is resisted by the
porcelain’s coefficient of thermal expansion.
• This difference in contraction rate creates tensile forces on the
metal and corresponding compressive forces on porcelain.
109

Chemical Bonding
• It is the most significant mechanism of porcelain- metal
attachment is a chemical bond between dental porcelain and the
oxides on the surface of metal substructure.
110

Sandwich theory
 The oxide layer is permanently bonded to metal
substructure on one side while dental porcelain
remains on the other.
 The oxide layer itself is sandwiched in between the
metal substructure and the opaque porcelain.
 This theory is undesirable in that a thick oxide
layer might exist that would weaken the
attachment of metal to porcelain.
111

• The second 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 do metal
and porcelain share electrons.
112
Oxide dissolution theory

• The chemical “bonding” is generally accepted as a primary
mechanism in porcelain- metal attachment process.
113

The basic component of a traditional porcelain
kit include:
 Opaque porcelain
 Dentin porcelain
 Enamel porcelain
 Modifiers, stains & glazes.
 Newest products has high fusing shoulder
porcelain.
114

STEPS IN FABRICATION OF
METAL CERAMIC CROWN5
115

1.Elastomeric impression of prepared tooth
2.Fabrication of working cast and die
3.Wax pattern
4.Casting the metal substructure by lost-wax technique
5.Heating the coping to create an oxide rich layer on the surface
116

6. Building opaque porcelain layer and firing it
7. Condensing dentin porcelain and firing it
8. Condensing enamel porcelain and firing it
9. Final glazing and staining of the restoration
10.Slow cooling of the finished restoration.
117

• Should be removed ultrasonically with
airborne particle abrasion or with steam.
• Phosphate bonded investments are more
difficult to remove.
• Hydrofluoric acid can be used.
119

PREPARATION OF METAL
SUBSTRUCURE FOR PORCELAIN8,9
120

• To establish a chemical bond between metal and
porcelain, a controlled oxide layer must be created
on the metal surface.
• The oxide layer is obtained by placing the
substructure on a firing tray , inserting it into the
muffle of a porcelain furnace and raising the
temperature to a specified level that exceeds the
firing temperature of porcelain.
121

CONDENSATION
• The process of packing the powder particles
together and removing excess water is known
as condensation.
• During this step , the porcelain powder is
mixed with distilled water or any other liquid
binder and applied on the metal substrate in
subsequent layers.
122

Methods of condensation 4,9
• VIBRATION method
• SPATULATION method
• BRUSH method
• WHIPPING method
• ULTRASONIC method
• GRAVITATIONAL method
123

VIBRATION METHOD
• In this wet porcelain mix is
applied with a spatula and
vibrated gently till the
particles settle down.
• Excess water is then
removed with a tissue
paper.
• This is the most efficient
way to remove excess
water. 124

SPATULATION METHOD
• Here, the wet porcelain mix is smoothened with a
spatula to bring the excess water to the surface
which is absorbed with a tissue
Disadvantages:
Danger of dislodging the porcelain particles, may
cause invisible cracks.
The sandpaper like effect of porcelain on metal.
Discoloration of the final product. 125

BRUSH METHOD
• Capable of being transferred in small
increments
• Advantages of wet brush technique:
Maintains the moisture content in the porcelain.
The brush can be used to introduce enamel
colors, effect or stains without changing
instruments.
Greater control over small increments. 126

DRY BRUSH TECHNIQUE:
• Dry powder sprinkled over the wet porcelain
• Disadvantage:
It enhances the risk of porcelain drying out
Control of powder :difficult, time consuming.
127

WHIPPING
• This method may actually be nothing more than a variation of vibration
technique
• As the porcelain is build up, a brush is rapidly moved over the porcelain
surface with a whipping motion.
• The whipping action brings the liquid to outside surface for blotting.
128

ULTRASONIC METHOD
• The build up restoration are placed on vibrator and very
low amplitude (very little agitation) along with a very
high rate of vibrations per second, pulls the liquid to the
surface with almost no disturbance to the porcelain
contour.
• This is the final condensing procedure used only after
the porcelain has been well condensed and contoured.
129

OPAQUING THE METAL SUBSTRUCTURE
130

• At this stage, it is assumed that the metal has been
properly finished, cleaned and oxidized.
• The metal coping must not be touched and should be
protected from dust, oil from skin, any other forms of
contamination.
131

Function of opaque porcelain
1. It establishes the porcelain to metal bond.
2. It mask the colour of metal substructure.
3. It initiate the development of the selected shade.
132

THICKNESS
 The thickness range is-
 According to fowler and tamura, 1987; lacy, 1980;
naylor, 1986, it is 0.2 to 0.3 mm.
 According to dykema et al ,it is recommend 0.1 to 0.15
mm
133

Alternative method of applying porcelain
135

A properly fired opaque layer will have a sheen or egg
shell glisten.
136

Dentin and Enamel Porcelain
Application
137

• Proper moisture content is the key to building porcelain.
• Any excess moisture should be blotted away with tissue.
• A proper mix of body porcelain will have a thick creamy
and smooth consistency
138

Precautions during mixing
• During mixing do not fold to material itself and avoid excess
stirring.
• To remove air bubble, the mixing instrument can be vibrated by
pulling a serrated instrument across the handle.
• Rewetting of porcelain that has completely dried out on glass
slab.
139

Applying dentin porcelain
• The goal of dentin porcelain build up is to apply and condense
enough porcelain to create a restoration that is 10% to 15%
larger than normal.
• This overbuilding will accommodate the enamel veneer that will
be placed over dentin layer and help to compensate for shrinkage
of porcelain.
140

A properly fired porcelain body baked should have a slightly
rough, pebbly or “orange peel” appearance when fired
correctly.
141

• Firing is carried out for fusing (sintering) the porcelain.
• The compacted mass is placed on a fire clay tray and
inserted into the muffle of the ceramic or porcelain furnace.
PREHEATING
• It is first placed in front of the muffle of a preheated
furnace and later inserted into the furnace.
• If placed directly into the furnace, the rapid formation of
steam can break up the condensed mass.
143

Firing Methods
9800c
Temperature method: Temperature- Time method
144

Underfired porcelain
Porcelain that has not matured properly can be identified by a
lack of shine to the surface and a cloudy appearance, internally.
The resulting porcelain also will be weak and brittle, and
additional firings may not correct the problem.
145

Overfired porcelain
Overfired porcelain has a glazed appearance, others
problems that may be present with overfired porcelain are
excessive translucency, slumping or rounding and the
general loss of anatomic contours.
146

Firing procedure
Stages of firing (sintering)
1) Low bisque stage: As temperature rises, surface of
the particles begin to soften & these loose particles just
begin to join.
2) Medium bisque stage: On further heating, more
softening of particles takes place & they begin to melt.
Better cohesion.
Slight volume shrinkage.
147

3) High bisque stage : further heating causes melting of all
particles producing complete cohesion & maximum volume
shrinkage.
If heating is prolonged, liquid gradually flows under gravity i.e.
pyroplastic flow, & article looses sharp corners & its shape.
148

COOLING3
• If shrinkage is not uniform it causes cracking and loss of
strength.
• Too rapid cooling of outer layers may result surface crazing or
cracking; this is also called thermal shock.
• Slow cooling is preferred, and is accomplished by gradual
opening of the porcelain furnace.
150

PORCELAIN SURFACE
TREATMENT
GLAZING
151

TYPES OF GLAZE
1. Self glaze
2. Add on glaze
152

153
BEFORE
GLAZING
AFTER GLAZING

• The objective of this type of restoration is to improve esthetics.
• The thicker cast metal coping that is normally used is replaced by
thinner platinum foil, thus allowing more space for porcelain.
155

Metal reinforce system
1. Swaged gold alloy foil coping.
2. Electroformed
156

Swaged gold foil coping
• The most widely used product of this type has been captek which is an
acronym for “ capillary assisted technology”
 The product is designed to fabricate the metal coping of a metal ceramic
crown without the use of a metal- ceramic crown melting and casting
process.
 It is a laminated gold alloy foil sold as metal strip.
157

 Captek technology can produce thin metal copings
for single crowns or frameworks for metal ceramic
FPDs with a maximum span of 18 mm.
158

This system requires three pairs of material metal structure
1. Captek P and Captek G
Used to fabricate crown copings and fixed dental prosthesis
abutments.
2. Capcon and Capfil
Used to connect copings.
3.Captek repair paste and Capfil
Used to add material to captek structures.
159

 Strips of P (Au-Pt-Pd) metal is applied to die with a
swaging instrument and burnished with hand
instrument on die and fired at 1075 degree Celsius,
forming porous coping.
 During this firing cycle, pd and pt particles are
interconnected by sintering to form three-
dimensional network of capillary channels.
161

 Strip of G (97% Au, 2.5 %
Ag) metal is applied over the
captek p coping and refired.
• Capillary action draws the
gold into the porous gold-
platinum-palladium structure
to form the finished coping.
163

• The metal copings and Pd-Ag pontics are then coated with slurry of
Au, Pt, and Pd powder (capbond) and liquid , resulting in a thin
coating of gold to enhance areas of captek p that have been ground
during adjustment and to provide a gold color similar to that areas
that have not been ground.
• The completed metal coping or framework is a composite metal
sub-structure consisting of a gold matrix and small partcle of a Pt-Pd-
Au alloy with resulting grain size in the range of 15 to 20 µm.
164

 The outer surface of coping contain approx. 97% gold.
 The completed copings have a thickness of approximately
0.25 mm.
 Then the metal surfaces are veneered with two thin coats
of an opaque porcelain and additional layers of
translucent porcelains.
165

Advantages:
• Excellent esthetics and marginal adaptation.
• Provide thinner metal copings than those (0.50 mm)
typically produced by the cast-metal process. This
ensures minimal tooth reduction in comparison to
conventional metal ceramic crowns.
166

• The Helioform HF 600 system uses an electroforming technique to produce
a thin pure gold coping.
• The gold is deposited on polyurethane dies that are coated with a silver
spacer using computer-controlled plating equipment to control thickness.
• The coping is coated with a noble metal paste primer before porcelain
application.
• Electroforming enables very good marginal adaptation.
Electroformed
167

Bond failure classification: O’Brien4
Type I: Metal porcelain:
• When the metal surface is totally depleted of oxide prior to firing
porcelain, or
• When no oxides are available( Gold alloys).
• Also on contaminated porous surface.
Type II: Metal oxide- porcelain:
• Base metal alloy system.
• The porcelain fractures at the metal oxide surface leaving the oxide
firmly attached to the metal.
169

 Type III: Cohesive within porcelain:
Tensile fracture within the porcelain when the bond
strength exceeds the strength of the porcelain.
 Type IV: Metal- metal oxide:
Base metal alloys
Due to the overproduction of Ni and Cr oxides
The metal oxide is left attached to ceramic.
170

Type V: Metal oxide- Metal oxide
•Fracture occurs through the metal because of
the overproduction of oxide causing a sandwich
between porcelain and metal
Type VI :Cohesive within metal
•Unlikely in individual metal ceramic crowns.
•Connector area of bridges.
171

As opposed to metal-ceramics, all-ceramics contain a significantly greater amount of
crystalline phase, from about 35 to about 99 vol %.
This higher level of crystallinity is responsible for an improvement in mechanical
properties through various mechanisms, such as crystalline reinforcement or stress
induced transformation.
174
ALL-CERAMIC RESTORATIONS
Denry isabelle, Holloway J.A. HJ. Ceramics for dental applications: a review. Materials 2010 jan;352-368.

175
All
Ceramic
GLASS CERAMICS/
CASTABLE
SLIP CASTING CERAMICS/
GLASS INFILTRATED
HEAT/HOT PRESSED/
INJECTION MOLDED
SINTERED CERAMICS
MACHINED CERAMICS

176
Sintered All-Ceramic Materials3,4,6
Two main types of all-ceramic materials are available for the
sintering technique: alumina-based ceramic and leucite-reinforced
ceramic.

177
.
Alumina-Based Ceramic
The aluminous core ceramic used in the aluminous porcelain crown
developed by McLean in 1965
it is composed of aluminum oxide (alumina) crystals dispersed in a glassy
matrix.
Alumina has a high modulus of elasticity (350 GPa) and high fracture
toughness (3.5 to 4 MPa.m05).
Its dispersion in a glassy matrix of similar thermal expansion coefficient
leads to a significant strengthening effect.
.

178
excellent bond between the alumina and the glass phase is responsible for
this increase in strength compared with leucite-containing ceramics.
The first aluminous core porcelains contained 40 to 50% alumina by weight.

179
The technique used an opaque inner core containing 50% by
weight alumina for high strength. This core was veneered by a
combination of esthetic body and enamel porcelains with 15% and
5% crystalline alumina and matched thermal expansion. The
resulting restorations were approximately 40% stronger than those
using traditional feldspathic porcelain .

180
Platinum matrix
fabrication

182
The tinner's joint. A, Foil is trimmed so
one is exactly twice as long as the
other. B, The long end is carefully
folded over the short. C, Margin
discrepancy at the joint can be reduced
by removing a triangular section of foil.

185
GLASS-CERAMICS1
A glass-ceramic is a material that is formed into the desired shape
as a glass and then subjected to a heat treatment to induce partial
devitrification—that is, loss of glassy structure by crystallization of
the glass.
Crystalline particles, needles, or plates formed during this
ceramming process interrupts the propagation of cracks in the
material when an intraoral force is applied, thereby promoting
increased strength and toughness.

186
The use of glass-ceramics in dentistry was first proposed by
MacCulloch in 1968. He used a continuous glass-molding process
to produce denture teeth. He also suggested that it should be
possible to fabricate crowns and inlays by centrifugal casting of
molten glass.

187
Dicor was the first castable glass used
for dental prosthetic applications and
was developed by Corning Glass
Works and sold through Dentsply
International.
It is a glass ceramic that contained
55% by volume of tetrasilicic
fluormica.

188
Dicor is formed into an inlay, facial veneer, or full crown restoration
by lost wax casting process similar to that employed for metals.
after the glass casting core or coping is recovered, the glass is
sandblasted to remove residual casting investment and the sprues
are gently cut away.
The glass is then covered by a protective “ embedment” material
and subjected to a heat treatment that causes microscopic plate
like crystals of crystalline material (mica) to grow within the glass
matrix. This crystal nucleation and crystal growth process is called
creaming.

189
The ceramming process results in increased strength and
toughness, increased resistance to abrasion, thermal shock
resistance, chemical durability and decreased translucency.

190
Once the glass has been cerammed , it is fit on the prepared dies,
ground as necessary, and the coated with veneering porcelain to
match the shape and appearance of adjacent teeth .
Dicor glass ceramic is capable of producing surpurisingly good
asthetics perphaps because of the chameleon effect , where part of
the color of the restoration is picked up from the adjacent teeth as
well as from the tinted cements used for luting the restorations .

Increased strength and toughness
increased resistance to abrasion
Thermal shock resistance
chemical durability
Decreased translucency
191

Disadvantages
 Its limited use in low stress area .
 Its inability to be colored internally.
 Low tensile strength.
192

Dicor MGC(machinable glass ceramic)
 70% vol of tetrasilicic flouramica crystals which are 2 µm
in diameter
 Higher quality product that is crystallized by the
manufacturer and provided as cadcam blanks or ingots.
 Less translucent than Dicor.
193

i. Ease of fabrication
ii. Improved esthetics
iii. Relatively high flexural strength.
iv. Low thermal expansion.
194

195
Disadvantages
Limited use in low stress areas
Its inability to be colored internally

196
Heat-Pressed All-Ceramic Materials1,4,6
Heat pressed ceramics have been popular in restorative dentistry since the
early 1990s.
Heat-pressing relies on the application of external pressure at high
temperature to sinter and shape the ceramic. Heat pressing is also called
high temperature injection molding.
Heat-pressing is used in dentistry to produce all-ceramic crowns, inlays,
onlays, veneers, and more recently, fixed partial prostheses.

197
The restorations are waxed, invested, and pressed in a manner
somewhat similar to gold casting. Marginal adaptation seems to be
better with hot-pressing than with the high-strength alumina core
materials,

 The first generation of heat-pressed dental ceramics contains leucite as
a major crystalline phase, dispersed in a glassy matrix.
 The crystal size varies from 3 to 10 µm, and the leucite content varies
from about 35% to about 50%, by volume depending on the material.
 Leucite is used as a reinforcing phase due to the tangential stresses it
creates within the porcelain.
199
Glass ~ 65%
Ceramic Leucite ~
35%

200
 Ceramic ingots are pressed at high temperature (from 900° C to
1165° C [1650° F to 2130° F] depending on the material) into a
refractory mold made by the lost-wax technique with a dwell at
temperature of about 20 minutes.
 Among the currently available leucite-containing materials for
hot pressing are IPS Empress, Optimal Pressable Ceramic and
two lower fusing materials, Cerpress and Finesse.

Lack of metal
Translucent ceramic core
Moderately high flexural strength ( upto 125 MPa1)
Excellent fit
Excellent esthetics.( Translucence, fluroscence and opalescence)
Minimal shrinkage: that occurs is during cooling, that can be controlled
with an investment having an appropriate expansion.
201

Disadvantages
• Potential to fracture in the posterior areas.
• Low Fracture toughness (0.9 to 1.3 MPa.m1/2).1
• Need to use resin cement to bond the crown
micromechanically to the tooth structure.
• Expensive equipment.
202

Lithium Silicate based
 The glass ceramic is composed of 70% Li2O.SiO2 and 30% glass
by volume.
 Narrow range of sintering temperature.
 The material is pressed at 920° C (1690° F) and layered with a
glass containing some dispersed apatite crystals .
 They are applied for anterior three-unit fixed partial dentures.
203

204
Lithium Silicate based. IPS Empress and IPS Empress 2 are
typical products representative of several other lithia disilicate
reinforced glass ceramics respectively.

Properties of two pressable glass ceramics
Property IPS Empress IPS Empress 2
Flexural Strength (MPa) 112±10 400 ±40
Fracture toughness
(Mpam½)
1.3± 0.1 3.3 ±0.3
Thermal Expansion
Coefficient (ppm/ºC)
15.0± 0.25 10.6 ±0.25
Chemical durability (µg/
cm2 )
100-200 50
Pressing temperature
(º C)
1180 920
Veneering temperature
(º C)
910 800
Indications Veeners/inlay/onlay/
anterior crown
Veeners/inlay/onlay/
anterior and posterior crown
And anterior fpd
205

SLIP-CAST CERAMIC1,4
( glass infiltrated ceramics)
210

Slip casting _
 Is a process used to form “green” ceramic shapes by applying a
slurry of ceramic particles and water or a special liquid to form a
porous substrate( such as die material), thereby allowing capillary
action to remove water and densify the mass of deposited particles.
211

 The starting media in slip-casting is a slip that is an aqueous
suspension of fine alumina particles in water with dispersing
agents.
 The slip is applied onto a porous refractory die, which absorbs the
water from the slip and leads to the condensation of the slip on the
die.
 The piece is then fired at high temperature (1150° C).
212

 The fired porous core is later glass-infiltrated, a unique process in
which molten glass is drawn into the pores by capillary action at high
temperature.
 Materials processed by slip-casting tend to exhibit lower porosity and
less processing defects than traditionally sintered ceramic materials.

213

Three types of ceramics are available for slip-
casting: alumina-based (Al2O3), spinel-based
(MgAlO4), and zirconia-toughened alumina (12Ce-
TZP-Al2O3).
216
1. Anusavice; Phillips’ science of dental materials; 11TH edition; Page 655-718
2. Anusavice; Phillips’ Science of dental materials; 12th ed; Pg.418-69

Alumina-based
(Al2O3)
 Contains 85% of alumina by volume (approx).
 Grain size of 3 μm.
 At 1120°C, sintering takes place when the Al2O3 particles
diffuse at the surface to form a bond with their contact points .
 Chalky consistency and is easy to process.
 It is only after glass infiltration the high strength, typical tooth
colour and translucency of VITA In-Ceram ALUMINA are
obtained.
217

Indications
 Substructures for anterior and posterior single crowns
 and 3-unit anterior bridges.
 Contraindicated in the following cases:
 Insufficient hard tooth substance available.
 Inadequate preparation results.
 Bruxism.
218
Alumina-based
(Al2O3)

spinell-based
(MgAl2O4)
 Spinell (MgAl2O4) is a natural mineral found together in
limestone dolomite, granite and sand.
 It has the combination of high stability, good chemical
resistance and high translucency, but low flexure strength
(350 MPa).
 Since 1994 spinell is a component of the VITA In-Ceram slip
system.
219

zirconia-toughened
alumina (12Ce-TZP-
Al2O3).
220

 In Ceram Zirconia is considered a modification of In-
Ceram Alumina system with the addition of 35% of
partially stabilized zirconia oxide to the slip to increase
the strength of the ceramic.
221

 Advantages :
a. Optimum aesthetics and excellent biocompatibility, i.e.
i. No exposed metal margin
ii. Excellent marginal fit.
b. Withstands high functional stress. Flexural strength of 620 MPa.
c. No thermal irritations due to low thermometric conductivity
d. Possibility of non-adhesive integration
e. Excellent acceptance among the patients
222

Indications & Contraindications
223

Contraindications
 Insufficient hard tooth substance
 Insufficient preparation results
 Bruxism
225

226
Machined All-Ceramic Materials1,3,4,7
Computer Aided Design/Computer Aided Design
(CAD/CAM) technology was introduced indentistry by
Duret in the early 70’s. The evolution of CAD/CAM
systems for the production of machined inlays, onlays,
veneers, and crowns led to the development of a new
generation of ceramics that are machinable.

227
Cerec System. The Cerec system has been marketed for
several years with the improved Cerec 2 system introduced in
the mid-1990s and the cerec 3 in 2000.
The equipment consists of a computer integrated imaging and
milling system, with the restorations designed on the computer
screen. Several materials can be used with this system: Vita
Mark IIJ Dicor MGC, and ProCad.

228
Celay System. The Celay system uses a copy milling
technique to manufacture ceramic inlays or onlays. A resin pattern
is fabricated directly on the prepared tooth or on a master die, then
the pattern is used to mill a porcelain restoration. As with the Cerec
system, the starting material is a ceramic blank available in
different shades.

230
Procera AllCeram System. The Procera AllCeram
system involves an industrial CAD/ CAM process. The die is
mechanically scanned by the technician, and the data are sent
to a work station where an enlarged die is milled using a
computer-controlled milling machine. This enlargement is
necessary to compensate for the sintering shrinkage.

MECHANICAL AND THERMAL
PROPERTIES OF DENTAL CERAMICS3
Flexural strength : Feldspathic porcelains for metal-ceramic
restorations have a mean flexural strength between 60 and 80
mpa. Among the currently available all-ceramic materials, zirconia
ceramics exhibit the highest values (800-1300 mpa), followed by
slip-cast ceramics (378 to 630 mpa), and lithium disilicate–
reinforced ceramics (262 to 306 mpa). The flexural strength of
leucite-reinforced ceramics is around 100 mpa.
233

234
The shear strength of feldspathic porcelain is 110 MPa, and
the diametral tensile strength is lower at 34 MPa. The
compressive strength is about 172 MPa, and the Knoop
hardness is 460 kg/mm.

235
Fracture toughness is also an important property of ceramics; it
measures the resistance to brittle fracture when a crack is present.
The fracture toughness of conventional feldspathic porcelains is very
similar to that of soda lime glass (0.78 MPa ).
Leucite reinforced ceramics exhibit slightly higher fracture toughness
values (1.2 MPa ), followed by lithium disilicate–reinforced ceramics
(3.0 MPa). 3Y-TZP ceramics have the highest fracture toughness of
all-ceramic materials (greater than 5.0 MPa ).

236
The elastic constants of dental ceramics are needed in the
calculations of both flexural strength and fracture toughness.
Poisson’s ratio lies between 0.21 and 0.26 for dental ceramics.
The modulus of elasticity is about 70 gpa for feldspathic porcelain,
110 gpa for lithium disilicate heat-pressed ceramics, and 210 gpa for
3Y-TZP ceramics and reaches 350 gpa for alumina-based ceramics.

237
Shrinkage remains an issue for all-ceramic materials with the
exception of machined ceramics from fully sintered ceramic blocks
and heat-pressed ceramics. The large shrinkage of machined
zirconia restorations during the subsequent sintering at very high
temperature (about 25%) is compensated for at the design-stage
by computerized enlargement of the restorations.

238
The thermal properties of feldspathic porcelain include a
conductivity of 0.0030 cal/sec/cm2 (° C/cm), a diffusivity of 0.64
mm2/sec, and a linear coefficient of thermal expansion (CTE)
of about 12.0 × 10−6/° C between 25° and 500° C. The CTE is
about 10 × 10−6/° C for aluminous ceramics and lithium disilicate
ceramics, 10.5 × 10−6/° C for zirconia-based ceramics (3Y-TZP),
and 14 to 18 × 10−6/° C for leucite-reinforced ceramics.

OPTICAL PROPERTIES OF
DENTAL
CERAMICS 5
239
Quintessence Pub. Co, Inc.

Fluorescence5
The term fluorescence refers to the process by which an object
absorbs light at one wavelength and reflects it at another
wavelength. Not all fluorescent porcelains are equivalent. In fact, in
a dark setting illuminated with fluorescent lighting, some metal
ceramic restorations may appear dark compared to adjacent natural
teeth
240

241
Metamerism
The change in appearance of an object under varying
light sources is known as metamerism. When two
objects match in color under one light but differ in color
under another light, they may be referred to as a
metameric pair.

242
For example, when examined in daylight, a metal-
ceramic crown may match or blend well with the
adjacent natural teeth. when the light source change
from daylight to fluorescent lighting or even to UV
lighting, the artificial crown may reflect light differently
and no longer match the color of the surrounding natural
teeth.

243
Opalescence
While a dark environment and UV light are needed for
fluorescence to be detected, the opposite is true for opalescence.
In fact, for opalescence to be observed, there must be sufficient
daylight for light waves to be refracted in two ways.
Lower energy light is reflected back toward the viewer as blue or
blue-white wavelengths. At the same time, higher energy light
waves pass through translucent material and appear to the
observer as orange-yellow or orange-amber.
243

244
These opal effects have to do with the light-scattering
abilities of translucent porcelain, so opalescent
formulations are typically found in the enamel and
translucent powders of major porcelain brands. Opal
porcelains are available to reproduce the natural
opalescence of teeth. Enamel and translucent areas of
teeth are more likely to demonstrate greater
opalescence than dentin tooth structure.
244

Color coding dental porcelain
powders5
Several porcelain systems rely on organic dyes to color code the
porcelain powders. By convention, dentin powders are pink and
enamel powders are blue. The organic colorants burn off on
heating, so the porcelain literally turns white in color before the firing
cycle is finished. These dyes do not affect the shade of the fired
restoration in any way.
245
245

246
Once the porcelain mix is color coded, the technician establishes the
proper consistency by adding additional distilled water or a special
modeling liquid. Special liquids are useful because they do not dry out
as rapidly as distilled water. This is particularly helpful during the
buildup of multiple single units or for fixed partial dentures.
Tap water should never be used with dental porcelain because it
contains impurities that could contaminate the dental porcelain and
potentially discolor the fired restoration.

1. In-Ceram Spinell (VITA) had the highest amount of relative
translucency.
2. IPS Empress (Ivoclar Vivadent),
3. Procera (Nobel Biocare)
4. IPS Empress 2 (Ivoclar Vivadent),
5. In-Ceram Alumina (VITA),
6. In-Ceram Zirconia (VITA)
247
Heffernan MJ, Aquilino SA, Diaz-Arnold AM, Haselton DR, Stanford CM, Vargas MA. Relative translucency of six all-ceramic
systems. Part I: core materials. J Prosthet Dent 2002;88:4-9

 In statically loaded all-ceramic and metal-ceramic restoration
developed vertical cracks in the connector region before
failing, whereas the metal ceramic FPD developed cracks at
intaglio surface of pontic before failing.
 Exclusive mode of failure in all-ceramic restoration: Fracture
of connectors.
248
Raigrodski AJ. Contemporary all-ceramic fixed partial dentures: a review. Dent Clin North Am 2004;48:531-44.

 Most common mode of failure of all ceramic FPD is fracture of
connectors with 70% to 78% of cracks originating from
interface between core and ceramics.
249

PORCELAIN DENTURE TEETH 1
The manufacture of denture teeth constitutes virtually the sole current use
for high-fusing or medium-fusing dental porcelains. Their composition is
slightly higher in the alumina content. Denture teeth are made by packing
two or more porcelains of differing translucencies for each tooth into metal
molds. They are fired on large trays in high-temperature ovens. Porcelain
teeth are designed to be retained on the denture base by mechanical
interlocking.
250

251
The anterior teeth are made with projecting metal pins that become
surrounded with the denture base resin during processing, whereas
the posterior teeth are molded with diatoric spaces into which the
denture base resin may flow.
Porcelain teeth are generally considered to be more esthetically
satisfactory than acrylic teeth. They are also much more resistant
to wear, although the development of new polymers has improved
the wear resistance of acrylic teeth.

Factors affecting the Color of Ceramics1.
The principal reason for the choice of ceramics as restorative
materials is their esthetic qualities in matching the adjacent tooth
structure in translucency, color, and chroma. The structure of the tooth
influences its color. Dentin is more opaque than enamel and reflects
light very well. Enamel represents a predominantly crystalline layer
over the dentin and is composed of tiny prisms or rods cemented
together by an organic substance.
252

253
The indices of refraction of the rods and the cementing
substance are different. As a result, light rays are
dispersed by varying proportions of absorption,
transmission, scattering, and reflection to produce a
resulting translucent effect and a sensation of depth as the
scattered light ray reaches the eye. As the light ray strikes
the tooth surface, part of it is reflected, and the remainder
penetrates the enamel and is scattered.

254
Any light reaching the dentin is either absorbed or
partially reflected to the eye and partially scattered within
the enamel. If dentin is not present, as in the tip of an
incisor, some of the light ray may be transmitted into the
oral cavity. As a result, this area may appear to be more
translucent than that toward the gingival area.

Recent advances in
ceramics.
255

Evaluation of marginal and internal fit of ceramic
and metallic crown copings using x-ray
microtomography (micro-CT) technology
Prosthetic crown fit to the walls of the tooth preparation
may vary
depending on the material used for crown fabrication.
The purpose of this study was to compare the marginal
and internal fit of crown copings fabricated from 3 different
materials.
256
Pimenta MA. Frasca LC. Lopes R. Rivaldo E. Evaluation of marginal and internal fit of ceramic and metallic crown
copings using x-ray microtomography (micro-CT) technology. J Pros Dent.

257
The selected materials were zirconia (ZirkonZahn system, group
Y-TZP), lithium disilicate (IPS e.max Press system, group LSZ),
and nickel-chromium alloy (lost-wax casting, group NiCr). Five
specimens of each material were seated on standard dies. An x-
ray microtomography (micro-CT) device was used to obtain
volumetric reconstructions of each specimen. Points for fit
measurement were located in Adobe Photoshop, and
measurements were obtained in the CTAn SkyScan software
environment.

258
The results showed that The nickel-chromium alloy
exhibited the best marginal fit overall, comparable with
zirconia and significantly different from lithium disilicate.
Lithium disilicate exhibited the lowest mean values for
internal fit, similar to zirconia and significantly different
from the nickel-chrome alloy.

Effect of different dental ceramic
systems on the wear of human enamel:
An in vitro study
The purpose of this in vitro study was to compare the
wear of advanced ceramic systems against human
enamel antagonists.
.
259
Zandparsa R. Huni RM. Hirayama H. Johnson MI. Effect of different dental ceramic systems on the wear of human
enamel: An in vitro study. J Pros Dent

260
A, TA-317C multiple
sample vertical friction
wear device.
B, Mounted enamel
stylus specimens on
upper arm.
C, Mounted ceramic and
enamel disks specimens
on lower arm.

261
Results. After 125 000 bidirectional loading cycles, the mean loss
of opposing enamel volume for the enamel disks in the control
group was 37.08 mm3, the lowest mean value for IPS e.max
Press system was 39.75 mm3; 40.58 mm3 for IPS e.max CAD;
45.08 mm3 for Noritake Super Porcelain EX-3 system; and 48.66
mm3 for the Lava Plus Zirconia system. No statically significant
differences were found among the groups in opposing enamel
volume loss (P=.225) or opposing enamel height loss.

262
no differences were found in the linear and volumetric
reduction of enamel cusps abraded against enamel
disks and all other ceramic specimens. All ceramic
systems exhibited high durability and were wear-friendly
to opposing enamel.

Effect of digital impressions and production
protocols on the adaptation of zirconia copings
Purpose. The purpose of this in vitro study was to
compare the effects of digital impression protocols on
the marginal, axial, and occlusal adaptation of
zirconia copings.
The mean marginal discrepancy values were 85.6
mm for group Cn, 58.7 mm for group C, and 47.7 mm
for the Tr group. 263

265
It was concluded that the copings produced with the aid
of digital impression systems exhibited better marginal
and occlusal adaptation than those of the copings
produced with the aid of conventional impression.
Kocaagaoglu H. Kilinc HI. Albayrak H. Effect of digital impressions and production protocols on the adaptation of zirconia copings. J

268
1. Anusavice KJ. Phillip’s science of dental materials: Dental Ceramics. 11th ed.
Philadelphia: Saunders; 2003. 655-719.
2. Glossary of prosthodontics terms. J Prosthet Dent. 2005;94:10-85
3. Craig GR, Powers MJ. Restorative dental materials. 13th ed. Elsevier: Missouri;
253-275.
4. Rosenstiel, Contemporary Fixed Prosthodontics; Third Edition, Mosby Elsevier
India; page 740-804.
5. Naylor, W. Patrick, James C. Kessler, and Arlo H. King. Introduction to Metal
Ceramic Technology. Chicago: Quintessence Pub. Co, Inc.

269
6. Denry isabelle. Recent advances in ceramics for dentistry. Crit rev oral boil med
1996;7(2):134-143.
7. Denry isabelle, Holloway J.A. HJ. Ceramics for dental applications: a review.
Materials 2010 jan;352-368.
8. Captek video from https://www.youtube.com/watch?v=s2W-k2Z7bfw.
9. Heffernan MJ, Aquilino SA, Diaz-Arnold AM, Haselton DR, Stanford CM,
Vargas MA. Relative translucency of six all-ceramic systems. Part I: core materials.
J Prosthet Dent 2002;88:4-9

270
10. Raigrodski AJ. Contemporary materials and technologies for all-ceramic fixed
partial dentures: A review of the literature. J Pros Dent. 2004 Dec;92(6):557-62.
11. Pimenta MA. Frasca LC. Lopes R. Rivaldo E. Evaluation of marginal and internal
fit of ceramic and metallic crown copings using x-ray microtomography (micro-CT)
technology. J Pros Dent.
12. Zandparsa R. Huni RM. Hirayama H. Johnson MI. Effect of different dental
ceramic systems on the wear of human enamel: An in vitro study. J Pros Dent.
13. Kocaagaoglu H. Kilinc HI. Albayrak H. Effect of digital impressions and
production protocols on the adaptation of zirconia copings. J Pros Dent.

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