Dental ceramics /certified fixed orthodontic courses by Indian dental academy

DENTAL CERAMICS

 INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com


CONTENTS
Introduction
Historical aspects
Classification
Composition
Condensation and firing
Aesthetic properties
Mechanical properties
Methods of strengthening ceramics


What are ceramics?

• “Ceramic” derived from Greek words
“Keramikos” = Earthen
“Keramos” = Burnt stuff
• Described as man made solid objects formed by baking
raw materials (minerals) at high temperatures.
• Defined as:
An inorganic compound with non metallic properties
typically composed of oxygen and metallic or semi metallic
elements.
(Aluminum,Calcium,Lithium,Magnesium,Potassium,Silicon,So
dium, Tin,Titanium,Zirconium)


• Dental Ceramics contain a glassy matrix reinforced
by various dispersed phases consisting of crystalline
structures such as Lucite, alumina & mica.

• Porcelain is a specific type of ceramic characterized
by it being white & transparent

• The term ‘glass ceramic’ has been introduced to
classify ceramics where one or more crystalline
phases have been precipitated from a glassy phase.


HISTORICAL PERSPECTIVE

• Dates back to 10 000 years

POTTERY IN EUROPE UPTO
1700AD:

• Making usable pottery was a great
challenge
The raw material was clay and it
presented two major problems:
1) Consistency
2)Shrinkage on firing


solutions found were:
• To beat the clay prior to molding
to remove entrapped air.

• Another development was the
technique of raising temperature very
gradually during firing process


• The most serious obstacle during this phase in the
development of ceramic technology was the
temperature at which the pottery could be fired.
• The conversion of clay from a mass of individual
particles loosely held by a water binder to a
coherent solid relies on the process called Sintering
In this process the point at which the individual
particles are in contact fuse at sufficiently high
temperatures.


• The need for high uniform temperatures led to invention of
Kilns, that is, the oven specially designed for pottery

• Initial kiln temperatures were 9000 C

• Invention of Glaze to overcome surface porosities


Chinese Porcelain:

• The Chinese had produced stoneware in 100 BC itself and
by the 10th century AD they were able to produce ceramics.

• Remained a secret for European countries till 18th century

• The basic components of Chinese porcelain were identified
as kaolin, silica and feldspar

• Once the secret of Chinese porcelain was out, soon it was
possible to make it in any shade or tint and the
translucency gave such a depth of color that it was not long
before its dental potential was recognized.


•1789 First porcelain tooth material patented in collaboration
with a French pharmacist Duchateau
An Italian dentist Gussipangelo Fonzi launched the first single
porcelain teeth “terro metallic” tooth in 1808


•1808 An Italian dentist invented a “terrometallic” porcelain tooth that
was held in place by platinum pin or frame


• 1817 Planteau, a French dentist, introduced porcelain teeth to
the US

• 1822 Peacle ,an artist, developed baking process for these
teeth in Philadelphia

• 1825 Commercial production of these teeth began

• 1837 In England, Ash developed an improved version of the
porcelain tooth.


•1844 The S.S.White Company was founded which further modified the
design & began mass production of the denture teeth.


• 1903 Dr. Charles Land introduced one of the first ceramic crowns to
dentistry using a platinum foil matrix and high fusing feldspathic
porcelain.


In 1962 Weinstein use the gold alloys for porcelain

Alumina reinforce crowns was developed in 1963 by Mc Lean
and Hughes

1n 1976 Mc Lean develop the stronger platinum bonded
alumina crown


•1967 Restriction of uranium to 1% by wt.

•1968 first use of glass ceramic by Mc Cullouch

•1970 development of porcelain fused base metal alloys

•1974 porcelain fused to noble metal alloys

•1983 development of high expansion core material by O’Brien

•1985 organic liquid binder instead of water by SANDERSON
•In 1985 Logan fused porcelain to platinum post

•Dr Swann Felcher did work on reinforcing the porcelain


1991
REPAIR OF PORCELAIN BY Ralph by using hydrofluoric acid
etching silane

1993 Monsenego Burdaicon studied the effect of florescence
in ceramics


Indications
• Esthetic alternative for discolor teeth
• Traumatic fractures of incisal angles
or buccal cusps
• Congenital abnormalities
• Veneers
• Inlays and onlays
• Crowns
• Denture tooth material


CLASSIFICATION OF
CERAMIC MATERIALS


CLASSIFICATION OF DENTAL CERAMICS
According to Skinner:
1. According to their use or indications:
Anterior
Posterior
Crowns
Veneers
Post & Cores
FPDs
Stain ceramic
Glaze ceramic
Denture teeth


2. According to composition:

• Pure alumina
• Pure zirconium
• Feldspathic porcelain
• Lucite based glass ceramic &
• Lithia based glass ceramic


III. According to processing method:

Sintering
Partial sintering & glass infiltration
Casting
CAD-CAM
Copy milling
Machinable
Pressable


IV. According to firing temperature:

Ultra low fusing < 8500 C. Used for crown &
bridge
Low fusing 8500-11000 C.

Medium fusing 11010-13000 C.
High fusing 13000 C. Used for production of
denture teeth


V. According to microstructure:
Glass
Crystalline
Crystal containing glass

VI. According to translucency:
Opaque
Translucent
Transparent

VII. According to resistance

VIII. According to abrasiveness


Based on crystalline nature
• Crystalline ceramics ex: feldspathic
porcelain containing Lucite [crystal
phase]

• Non crystalline ceramics eg:Glass


Based On Application

• Core porcelain :
• shows good mechanical properties, and provide strong
base for the restoration

• Opaque porcelain

Body porcelain

• Enamel porcelain


According to substrate material

•Cast metal
•Sintered metal
•Swaged metal
•Glass ionomer
•CAD/CAM.


According to Type

•Feldspathic porcelain
•Aluminous porcelain
•Glass infiltrated aluminous
•Glass infiltrated spinell
•Glass ceramics
According to Firing Technique

•Air fired (at atmospheric pressure)
•Vacuum fired (at reduced pressure)
•Diffusible gas firing


According to Application

For porcelain teeth

For Ceramo-metal restorations (Metal-
Ceramic Systems)

For All-ceramic restorations (All-Ceramic
System)


ALL CERAMIC SYSTEMS

1) Conventional Powder – Slurry Ceramics : using
condensing & sintering.

(a)Alumina reinforced Porcelain e.g.. : Hi-Ceram

(b) Magnesia reinforced Porcelaine.g.: Magnesia cores

(c) Leucite reinforced (High strength porcelain)
e.g.. : Optec HSP
(d) Zirconia whisker – fiber reinforced e.g..:MirageII
(Myron Int)
(e) Low fusing ceramics (LFC): (i) Hydrothermal LFC
e.g..: Duceram LFC

(ii)Finesse(Ceramco Inc)

Castable Ceramics :

Using casting & ceramming

1) Flouromicas e.g..: Dicor
2) Apatite based Glass-Ceramics e.g.. Cera Pearl
3) Other Glass-Ceramics
e.g..: Lithia based, Calcium phosphate based


Machinable Ceramics : Milling machining by mechanical
digital control

A) Analogous Systems
(Pantograph systems – copying methods)

1) Copy milling / grinding techniques
a) Mechanical e.g.. : Celay
b) Automatic e.g: Ceramatic II. DCP

2) Erosive techniques :

a)Sono-erosion e.g..: DFE, Erosonic
b) Spark-erosion e.g..: DFE, Procera

B) Digital systems (CAD / CAM):
1) Direct e.g..: Cerec 1 & Cerec 2

2) Indirect e.g. : Cicero, Denti CAD, Automill, DCS-President

Pressable Ceramics :

By pressure molding & sintering

1) Shrink-Free Alumina Reinforced Ceramic
(Injection Molded)
E.g. : Cerestore / Alceram
2) Leucite Reinforced Ceramic (Heat – Transfer
Molded)
E.g.: IPS Empress, IPS Empress 2, Optec OPC

Infiltrated Ceramics

by slip-casting, sintering & glass infiltration

1) Alumina based e.g.: In-Ceram Alumina
2) Spinel based e.g.: In-Ceram Spinel
3) Zirconia based e.g..: In-Ceram Zirconia


COMPOSITION OF DENTAL PORCELAINS
• The quality of any porcelain depends on the choice of
ingredients, the correct proportioning of each and the
control of the firing procedure.

• Ceramics are composed of essentially the same material
as porcelain, the principal difference being in the
proportioning of the primary ingredients & the firing
procedure.


The various ingredients used in different formulations of ceramics
are:

1. Silica (Quartz or Flint) – Filler
2. Kaolin (China clay) – Binder
3. Feldspar – Basic glass former
4. Water – Important glass modifier
5. Fluxes – Glass modifiers
6. Colour pigments
7. Opacifying agents
8. Stains and colour modifiers
9. Fluorescent agents
10. Glazes and Add-on porcelain
11. Alternative Additives to Porcelain


Feldspar 60% -80%
Silica 10%
Kaolin 3% -4%
Fluorspar 1%
Boric oxide 2%
Calcium oxide 5-10%
Metallic pigments >1%


• Other compounds such as potash, soda or lime are often
added to give special properties.

• Glass:
is a fusible combination of silica & potash, therefore it is
transparent.

• Porcelain:
Contains infusible elements held together by lower
fusing materials and hence is less transparent.


2D Diagram of Oxide M2O3 2D Diagram of Oxide M2O3
In the crystalline form In the glass form


a) Feldspar:
• Natural feldspar is a mixture of albite (Na2 Al2 Si6 O16)
and orthoclase or microline (K2Al2Si6O16) with free
crystalline quartz.
• In its mineral state, feldspar is crystalline and opaque
with an indefinite color between grey and pink.
• Chemically it is designated as potassium-aluminum
silicate, with a composition of K2O, Al2 O3 6SiO2.
• On heating, it fuses at about 12900C, becomes glossy
and unless overheated, retains its form without rounding.


Potassium and sodium Feldspar are normally occurring
materials composed of potash (K2O), Soda (Na2O),
Alumina (Al2O3), and Silica (SiO2).
Commonly potassium feldspar is used
It is used in the preparation of many dental porcelains
designed for metal ceramic crowns and many other
dental glasses and ceramics.
When potassium feldspar is mixed with various metal
oxides and fired to high temperatures, it can form
leucite and a glass phase that will soften and flow
slightly.


The softening of this glass phase during porcelain firing,
allows the porcelain powder particles to coalesce
together.
For dental porcelains, the process by which the particles
coalesce is called “Liquid - Phase Sintering”, a process
controlled by diffusion between particles at a temperature
sufficiently high to forma dense solid.

b) Silica:
• Pure quartz crystals (SiO2) are used in dental porcelains.
• Silica remains unchanged at temperature normally used
in firing porcelain and this contributes stability to the
mass during heating by providing a framework for other
ingredients.


It can exist in four different forms.
• Crystalline quartz
• Crystalline cristobalite
• Crystalline tridymite
• Non-crystalline fused silica

0 0
 
 0  Si  0  Si  0
 
0 0


C) Kaolin:

• It is produced in nature by weathering of feldspar during
which the soluble potassium silicate is washed out by
acid waters. In this process the residue is deposited and
at the bottom of the streams in the form of clay.
• Kaolin gives porcelain its properties of opaqueness.

• It gives Consistency to mix and form a workable mass during
molding

• When subjected to a high temperature it binds the particle and
maintains the framework


 Color Frits:
• They are coloring pigments added to the porcelain
mixture.
• Added in small quantities to obtain the delicate shades
necessary to imitate natural teeth.
• They are prepared by grinding together, metallic
oxides with fine glass and feldspar, fusing the mixture
in a furnace and regrinding to a powder.


• Metallic pigments:

Titanium oxide – yellow brown shade
Manganese oxide – lavender
Iron oxide – Brown
Nickel oxide – Brown
Cobalt oxide – Blue (particularly useful for producing
enamel shades)
Copper or chromium oxide – Green
Chromium – tin or chrome – alumina – Pink
Iron oxide or platinum – Grey


 Opacifying Agents:
• Generally consists of metal oxide (between 8% to
15%) growned to a very fine particle size (<5 µm) to
prevent a speckled appearance in porcelain.

• Commonest oxides are:
Cerium oxide
Zirconium oxide
Titanium oxide
Tin oxide
Zircon oxide


Typical oxide composition of a dental Porcelain

Material wt%

Silica 63
Alumina 17
Boric oxide 7
Potash (K2O) 7
Soda (Na2O) 4
Other oxides 2


• The opaque layer serves 3 primary functions:-

a) It wets the metal surface and establishes a metal
porcelain bond
b) It masks the color of the metal substructure
c) It initiates development of the selected shade
 Stains:
• A stain is more concentrated than the color modifier
• They can be supplied as pure metal oxides but are
sometimes made from lower fusion point glasses so that
they can be applied at temperatures below the maturing
temperature of the enamel and dentin porcelains.


Generally used as a surface colorant or to provide enamel check
lines, decalcification spots etc. in the body of a porcelain jacket
crown.

These stain products are also called as surface colorants or
characterization porcelain

Internal Staining

permanent staining by using them internally.

can produce a very life-like result, when built into
porcelain rather than when it is merely applied to the
surface.


 Glazes and add-on porcelain:

• One purpose of an industrial glaze is to seal the open
pores in the surface of a fire porcelain.
• Dental glazes consists of low fusing porcelains which
can be applied to the surface of a fired crown to
produce a glossy surface.
• It should mature at a temperature below that of the
restoration and the thermal expansion of the glaze
should be fractionally lower than the ceramic body to
which it is applied.


Glass modifiers ∀
0 0
 
 0  Si  0  Si  0 + Na2O
∀
0 0
 
∀
0 0
 
 0  Si  • •  Si  0 + 2Na+
∀
0 0
 
Diagram showing interruption of silica tetrahedral by sodium oxide.


• Acts as fluxes and help in reducing the
softening temperature

• Decreasing the amount of cross-linking
between the oxygen and the glass forming
elements like silica i.e., they disrupt the
continuity of the SiO4 network.

• Should not be too high, because if too many
tetrahedra are disrupted, there may occur
crystallization during the porcelain firing
operations.


The most commonly used are
potassium,
sodium
calcium oxides
. Introduced as carbonates that revert to oxides on
heating.

Other oxides
Lithium oxide,
Magnesium oxide,
Phosphorous pentoxide etc.


Body Porcelain:
• This term collectively describes four principal types of porcelain powders
used to create the body of a restoration i.e.
1) Dentin (body or gingival)
2) Enamel
3) Translucent
4) Modifier or color frits


Dentin:
• They correspond in color to the dentin of natural teeth.
2) Enamel Porcelains:
• When fired, enamel porcelains are more translucent than
dentin porcelain.
• Restricted range of shades – usually in the violet to grey
range.

3) Translucent Porcelain:
• They are applied as veneer over nearly the entire surface
of a typical porcelain buildup. This veneer imparts depth
and a natural enamel like translucency without
substantially altering the body shade.

4) Body Modifiers:
• These porcelains are more color concentrated and were
designed to aid in achieving internal color modifications.
• Modifiers are color intense,
Dentin porcelains are color predominant,
Enamel and translucent porcelains are color reduced


Other Additions to Dental Porcelains:
 Boric oxide (B2O3) can behave as a glass modifier
• It decreases viscosity,
lowers the softening temperature, and
forms its own glass network.
 Alumina (Al2O3)
• Its role in glass formation is complicated
• It takes part in the glass network to alter the softening
point and viscosity


 Lithium Oxide:
• Added as an additional fluxing agent
 Magnesium Oxide:
• May also be present but in minute quantities
• It can replace calcium oxide


 Phosphorus Pent oxide:
• Is sometimes added to induce opalescence and is also a
glass forming oxide.

Color Coding Dental Porcelain:
• Organic dies are used to color code the porcelain
powders


Condensation of Dental Porcelain

Condensation:
The process of packing the particles together and
removing the liquid binder is known as condensation.
• Distilled water the most common and most useful liquid
binder.
• Other binders: Glycerine, propylene glycol or alcohol.
• “Brush Application Method”
• Not recommended because the control of the powder is
difficult and time consuming.


• “Wet Brush Technique”
• is the most logical approach because:
a) Wet brush maintains the moisture content in the porcelain.
Metal spatula cause more rapid drying out.
b) The brush can be used to introduce enamel colors, effect
masses or stains without changing instruments.
c) Greater control over applying small increments of
porcelain.
d) Blending of enamel veneers can be achieved with greater
delicacy


Condensing Techniques:
a) Vibration
b) Spatulation
c) Whipping
d) Mechanical
e) Ultrasonic vibration


Volume Porosity of Powders:
• The volume porosity of regular air or vacuum firing powders is
in the region of 40-49%.
• Vacuum firing powders generally have less shrinkage than the
coarser air fire powders.
• Size and shape of particles
• Gap and grading system


Air-Firing Porcelain:
• In air firing methods a very slow maturation period is ideal for
which to aim, in order to allow the maximum amount of
entrapped air bubbles to escape.
• Heating the porcelain 30o-50oC below the maximum firing
temperature is recommended.

Vacuum Firing Procedures:

• Vacuum firing porcelains were introduced primarily to give
improved aesthetics in the enamel porcelains.

• Vines et al. (1958) have explained the densification of porcelain
by vacuum firing.


Translucency:
• The particle size distribution of a
dental porcelain has a marked
influence on the translucency of the
final product.
• The translucency is affected by the
number and size of the entrapped
air bubbles.
• Larger particles – larger interstitial
voids – fewer bubbles – improved
translucency.
• Small particles – smaller interstitial
voids – more fine air bubbles –
reduced translucency

To avoid porosities:-
a) Porcelain powder must be dried slowly to eliminate all
water vapor and vacuum must be applied before the
porcelain enters the hot zone of the furnace. In this way,
the internal pores are reduced before the surface skin
seals off the interior too rapidly.
b) Vacuum firing should not be prolonged, once the surface
skin is sealed as it can cause surface blistering since
residual air bubbles will try to rise to the surface through
the molten porcelain.


The vacuum should be broken whilst the work is still in the hot
zone of the furnace. This allows the dense surface skin of
porcelain to hydrauically compress the low pressure internal air
bubbles.

Vacuum firing also has its limitations. If large bubbles are
trapped in the porcelain by poor condensation techniques,
these bubbles cannot be reduced in size to any significant
degree.


Diffusible gas firing

Helium hydrogen or steam is substituted
for the ordinary furnace atmosphere

Gases diffuse or dissolve in porcelein


Classification of Stages of Maturity:

Low Bisque Medium Bisque High Bisque
Surface very porous Less porous Completely sealed and
smooth
Grains start to soften Entrapped air becomes A slight shine appears on
and “lense” sphere shaped the surface
Shrinkage is minimal Definite shrinkage
Body extremely weak Body is strong
and friable

Thermal Shock:
• It is caused by uneven heating or cooling.
• A crown’s surface may expand on contract more quickly than the interior and
due to the differential thermal expansion, stresses will be set up.


PROPERTIES


AESTHETICS


Aesthetics of Dental Porcelain

Color is a complex science that was described by Munsell in
the Munsell color ordered system as having three
dimensions: Hue, value, chroma (Munsell 1936; Preston
and Bergen 1980).

Munsell’s Color Wheel

The color that is seen by an observer in making a tooth
shade will depend upon:
• The spectral energy distribution of the light source e.g..
daylight or artificial light.
• The spectral characteristic of tooth, in respect to
absorption, reflection and transmission.
• The sensitivity of the eye.
• The conditions under which the color of the tooth is being
viewed, e.g.. oral background, wet or dry conditions,
angle and intensity of illumination.


 Optical Properties:
1) Translucent objects will both reflect and
transmit some light.
a) Reflections
a) Specular and

b) Diffused

b) Refractive index and dispersion
2) Fluorescence


Areas of light reflection and transmission through the natural human tooth

Four Dimensions of tooth color system:
a) Hue: Basic color of an object.
b) Chroma: Degree of saturation of a particular hue.
c) Value: Defined as brightness.
• Ranging from white to black:
• white being highest in value black the lowest
d) Maverick: Colors seen through dentin without
organization


The Zone System
• The color of teeth is determined by the hue of the dentin and the thickness
and hue of the overlying enamel.
• A tooth may have more than one dentin hue present.

Body or Dentin Porcelain Layer:
• Gives more opportunity to make use of diffused light than the opaque layer
as it has twice the latter thickness, thus permitting more light to enter.

Incisal or Enamel Porcelain Layer:
• It should cover the entire surface
• Should be translucent and bulkiest at the incisal or cusp region and taper to
a feather edge at the gingival margin
• It permits the light to enter the crown, travel to its depth, and reflect color in
all directions.


Absorption:
• There is always a degree of absorption when light rays encounter any
surface. Dark objects absorb more light than light objects.
• An object is perceived as red because it is absorbing the blue and green
rays of the incident light and reflecting red rays.


Light Scattering:
• Dental porcelain can be regarded as optically heterogeneous, i.e. it is a
transparent medium containing small particles such as metallic oxides
(opacifiers), crystals or glassy grains of dissimilar refractive indices.
• When a beam of light enters such a system, a portion of a beam is scattered
and the intensity of the beam is reduced.
• In any ceramic system, the greatest light scattering effect is obtained with an
increasing difference in refractive index between the particles and the main
bulk of porcelain phase.

Opacity:
• The important optical characteristic seen when a beam of light enters a
typical dental porcelain is:
a) A fraction of light is reflected (specular reflection) and this determines the
degree of glaze or gloss on the surface.
b) Of the remaining light, a fraction is diffusely reflected, and the remainder
directly and diffusely transmitted.


• In opaque materials, the degree of diffuse reflection is related to the surface
roughness.

• It is therefore undesirable to apply dentin and enamel porcelains onto highly
glazed opaque's since a mirror surface is created and bright spots may
appear particularly at the incisal third of the preparation.
• A rougher surface can be produced by lightly blasting the surface of the
opaque with 30 µm aluminum oxide grit.

Translucency:
• Diffuse reflection of light produced by internal scattering must not be too
great in dental porcelain, otherwise anterior crowns look very artificial.
• We require minimal light absorption but maximum light scattering to give an
effect similar to enamel prisms.
Surface Gloss:
• The glaze or gloss on the surface of a ceramic crown is intimately related to
the relative amount of specular and diffuse reflection.
• These factors are primarily determined by the index of reflection and by the
surface smoothness.


Role of Opaque Porcelains in Obtaining Aesthetics:

• It has been said that opaque porcelains are not required
in dental ceramics and that the original air-fired crown
could provide the best system.
• However, if a porcelain crown is to simulate natural teeth,
greater degree of light transmission in the enamel and
dentin porcelain, consequently, may be required.
• The use of opaque porcelain in the metal ceramic crown
was dictated by the metal background and unfortunately,
the aesthetic benefits of vacuum-firing have been
partially lost.


 Shade Matching Guidelines:
• Shade matching may be divided into two areas:
Artistic
- Scientific.
 Artistic:
• Requires many years of intense study and practice
 Scientific:
• Modern color measuring equipment can substantially
reduce trial and error


Some common guidelines:
• The patient should be viewed so that his head is at the
operator’s eye level.
• Use of maximum amount of day-light
• For precise color matching, the clinician should use a
small angular field. In addition, he must be careful not to
become influenced by apparent changes in color due to
“successive contrast” effects.
• It is not advisable, to view colors for long periods.
• The natural dentition should always be kept dry and teeth
viewed from several different angles.


• It is better to concentrate on the middle
third of the tooth since the body shade is
the most important basic color in the tooth.
• A shade slightly lower in value (darker) than
the tooth being matched should be
selected. A slightly darker shade is less
conspicuous than a lighter shade.
• Select the basic hue of the tooth by
matching the shade of the patient’s canine,
which is the most chromatic tooth in the
mouth.


Tooth Shade Guide:
 The primary requirements for a tooth color guide
should include:-
a) Should be made from same material from which
the restoration will be made.
b) Backed by metal
c) Has the same thickness as the restoration will
have.


d) Employs the same overlaying techniques used to make the restorations.
e) A logical arrangement in color space.
f) An adequate distribution in color space.

Two basic types:
1) Customized shade guide
2) Commercial shade guide
a) Vita shade guide – the most logical of all


b) Vita 3D master – 3 dimensional shade guide

lighter darker
paler

richer

reddish
yellowish


c) Digital shade guide:

Accessories Software


Aesthetics of Metal Ceramic Crown:
a) Reduction in the thickness of the metal coping
b) Reduction in the light reflectivity from the metal opaque porcelain
• When the thickness of the current high fusing gold alloy copings is reduced
much below 0.5 mm, there is a risk of metal creep occurring during the
sintering of the porcelain veneer which results in unacceptable clinical fit.
• Alternatively, when a base metal alloy of higher melting point is used to
overcome the problem of metal creep, the effectiveness of the bond between
porcelain and metal remains in doubt. In addition, base metals are difficult to
cast in thin section and obtain a good fit and they tend to induce grey color
effect in the porcelain.
• For these reasons, preformed copings or foil in various thickness were used
with aluminous porcelain for bonding.


PROPERTIES
Compressive strength
50,000 psi
Tensile strength
5,000 psi
Shear strength -
16,000 psi
Elastic modulus
10X106 psi


Linear coefficient of thermal expansion -
12X10-6 / °C
Specific gravity 2.2 to 2.3
Linear shrinkage -
High fusing - 11.5
Low fusing - 14.0%
Refractive index- 1.52 to 1.54


•Blebs are internal voids tend to reduce the specific gravity
of porcelain.

•Porcelains extremely hard materials and because of this
property offer considerable resistance to abrasion. This
could be a disadvantage in that it causes excessive wear of
the opposing natural tooth structure or the restorative
material.


•The brittleness → 0.1% deformation is
sufficient to fracture porcelain before fracture
•.
•Uranium oxide / cerium oxide is added to match
the fluorescence of porcelain to that of the natural
tooth.


1. Relatively inert.
2. Chemically stable.
3. Corrosion resistant.
4. Highly biocompatible.
5. Conducive to gingival health – as it prevents plaque
addition.
6. Solubility is less.


 TWO FACTORS AFFECTING THE PROPERTIES
• Manner and degree of condensation /
compaction of power.
 Degree of firing and procedure followed to fuse mass.


Methods of Strengthening
Ceramics

• Predictable strength of a substance is based on the
strength of the individual bonds between the atoms
in the material.
• However, the measured strengths of most
materials are more than 100 times lower than this
theoretical value.


 Reasons for low strength
 Minute scratches and other defects present
on all the material, behave as sharp notches
whose tips ma be as narrow as the spacing
between atoms.
 - A phenomenon known as “Stress
concentration” at the tips of these minute
scratches or flaws causes the localized
stress to increase to the theoretical strength
of the material at a relatively low average
stress throughout the structure.


•The compressive strength is quite high
compare to tensile or shear strength.
•The tensile strength is low because of the
unavoidable surface defects.
•The shear strength is low because of lack of
ductility in the material.
•Voids and blebs greatly reduce the strength of
porcelain.


 Methods to Overcome the Deficiencies of
Ceramics fall into 2 categories:
a) Methods of strengthening brittle materials
i) Development of residual compressive stresses
within the surface of the material.
ii) Interruption of crack propagation through the
material.
b) Methods of designing components to minimize
stress concentrations and tensile stresses.


i) Development of residual compressive
stresses within the surface of the
material.
• One of the widely used methods of
strengthening glasses and ceramics
• Strengthening is gained by virtue of the
fact that these residual stresses must
first be negated by developing tensile
stresses
• Net tensile stress develops


• Three methods of introducing these residual
compressive stresses are:
a) Ion exchange or chemical tempering is a
process involving the exchange of larger
potassium ions (K) for the smaller sodium ions
(Na), a common constituent of a variety of glasses.
b) Thermal tempering is a common method. It
creates residual surface compressive stresses by
rapidly cooling (quenching) the surface of the
object while it is hot and in the softened (molten)
core.
c) Thermal compatibility

 ii) Interruption of crack propagation through
the material:
 Two different methods:-
a) One type relies on the toughness of the
particle to absorb energy from the crack and
deplete its driving force for propagation.
b) The other relies on crystal structural change
under stress to absorb energy from the
crack.


a) Dispersion of a crystalline phase:

Alumina Particles Acting as SEM of Alumina Reinforced
Crack Stoppers Core showing the alumina particles
embedded in a glassy matrix composed of
feldspar
• Dicor glass-ceramic: The cast glass crown is subjected to a heat treatment
that causes micron-sized mica crystals to grow in the glass.

 b) Transformation Toughening:
• This technique involves the incorporation of a
crystalline material that is capable of undergoing a
change in crystal structure when placed under
stress.
• The crystal material usually used is termed
partially stabilized zirconia (PSZ).


 Reducing Stress Raisers:
• Stress raisers are discontinuities in ceramic
structures and in other brittle materials that causes
stress concentrations. Abrupt change in shape or
thickness in the ceramic contour can act as stress
raiser and make the restoration more prone to
failure.


• In porcelain jacket crowns, many conditions
can cause stress concentration:
a) Creases or folds of the platinum foil substrate
that become embedded in the porcelain,
leaves notches that act as stress raisers.
b) Sharp line angles in the preparation also
create areas of stress concentration.
c) Large changes in porcelain thickness, a
factor also determined by the tooth
preparation, can create areas of stress
concentration.


 d) Large changes in porcelain thickness, a factor
also determined by the tooth preparation, can
create areas of stress concentration.
 e) A small particle of porcelain along the internal
porcelain margin of a crown also induces locally
high tensile stresses.
 f) If the occlusion is not adjusted properly on a
porcelain surface, contact points rather than
contact areas will greatly increase the localized
stresses in the porcelain surface as well as within
the internal surface of the crown.


 In case of a porcelain veneer crown this can be
achieved in three ways:
1. Reinforcement of the inner surface by a higher
strength ceramic.
2. Reinforcement of the inner surface by a metal
casting or foil bonded to the porcelain.
3. Surface treatment of the porcelain by chemical
toughening.


Metal Ceramic Alloys/ Technology


• The six basic principle features which distinguish a metal
ceramic alloy from both crown and bridge and removable
partial denture alloys are:
• MCA be able to produce surface oxides for chemical
bonding with dental porcelains.
• coefficient of thermal expansion is slightly greater than
that of the porcelain veneer to maintain the metal-
porcelain attachment.
• melting range considerably higher than the fusing of the
dental porcelain fired on it. This temperature separation
is needed so the porcelain build-up can be sintered to a
proper level of maturity without the fear of distortion of
the metal substructure.

• Ability to withstand, exposure to high
temperatures, without undergoing
dimensional change -- high temperature
strength or sag resistance.
• Processing should not be too technically
demanding
• A casting alloy should be bio-compatible.


 Classification for Metal Ceramic Alloys: by Naylor,
1986
• Based on composition
• All alloys are first separated into one of two major types:
 Noble (precious)
 Base metal (non-noble or non-precious).


System Group
Noble metal alloys:
i) Gold-platinum-palladium High silver
ii) Gold-palladium-silver Lower silver
iii) Gold-palladium
iv) Palladium – silver Cobalt
v) High palladium Copper
Silver-gold

Base Metal Alloys:
i) Nickel-Chromium Beryllium
ii) Cobalt-Chromium Beryllium-free
iii) Other systems


Levels of Content:
The designation “low”, ‘medium’ and ‘high’ are given
with the following values in order to describe the level of
the principle constituent on which an alloy is based
(Naylor, 1986).
Low - 0% to 33%
Medium - 34% to 66%
High - 67% to 100%


NOBLE METAL ALLOYS

Typical Formulations:
a) Gold – platinum – palladium alloys:
Gold – 84%
Platinum – 7.9%
Palladium – 4.6%
Silver – 1.3%
Indium & tin addition approx. – 2%
b) Gold – platinum – tantalum alloys:
Same as above but palladium replaced by
tantalum


 c) Gold – palladium – silver alloys:
 Gold – 50%
 Palladium–30%
Silver 12%
 Indium & tin – 8%

 d) Palladium-silver alloys:
Palladium 60%
 Silver-40%
 Addition of indium and tin to increase hardness


Base-metal Alloys:

a) Ni-Cr without Beryllium
Chromium – 12-25%
Molybdenum 0% - 10%
Minor amounts of Al, Fe, Si, Ga, etc.

b) Ni-Cr with Beryllium

Chromium – 12-20%
Molybdenum 0% - 10%
with aluminium, silicone, manganese and typically
1.5 to 2.0 wt% beryllium


 Co-Cr
 Chromium 20-30%
 Molybdenum 0% - 7%
Si, Mn, Al, Tungsten, Gallium, Tantalium, Ruthenium


Alloy Advantages Disadvantages
Gold - Excellent bonding to - Low sag or creep
Platinum porcelain resistance, can distort at
- Good castability fine margins or warp on
Palladium
- Easily finished and long span bridges
polished - High cost
- Corrosion resistant and
non-toxic
- Excellent for producing
occlusal surfaces

Gold - High melting range giving - Silver content may cause
Palladium better creep resistance greening of porcelain
Silver - Yield strength can be - White color may show
higher than some Au-Pt Pd through grey in the mouth
alloys - High palladium content
- Good castability can increase risk of H2
- Easily finished and gas absorption during
polished casting
- Non-toxic - Bonding to porcelain not
yet proven clinically or
- Low cost
experimentally

Alloy Advantages Disadvantages
Palladium - High yield strength and - Difficult to cast
Silver modulus of elasticity - Does not reproduce fine
Alloys - Suitable for long span margins like the high gold alloys
bridges - High silver content can
-Non-toxic interfere with bonding and
-Low cost cause discoloration of porcelain
- High palladium content
increases gas absorption
- Poor color

Nickel - High modulus of elasticity - Very difficult to cast accurately
Chromium and yield strength allows - Margins may be short or rough
alloys use in thinner section - Permanence of bond yet to be
- Low cost established
- Can be toxic in nickel sensitive
patients
- Very difficult to remove from
teeth in event of repair


Role of Constituent Elements:
a) Aluminium (Al):
• It lowers the melting range of Nickel (Ni)-based alloys.
• It is a hardening agent and influences oxide formation.
b) Beryllium (Be):
• Lowers the melting range, improves castability,
improves polishability and helps to control oxide
formation.
c) Boron (B):
• Is a deoxidizer.


 d) Chromium (Cr):
• Is a solid solution hardening agent that contributes
to corrosion resistance by its passivating nature in
Ni and Co (Cobalt) based alloys.
 e) Copper (Cu):
• Serves as a hardening and strengthening agent,
can lower the melting range of an alloy.


f) Gallium (Ga):
• Added to silver-free porcelain alloys to compensate for
the decreased coefficient of thermal expansion created
by removal of silver.
g) Gold (Au):
• Provides a high level of corrosion and tarnish
resistance and increases an alloy’s melting range
slightly.
• It improves workability, burnishability and raises the
density and the cost of an alloy.


 h) Indium (In):
• Is a less volatile oxide-scavenging agent, lowers the
alloys melting range and density, improves fluidity and
has a strengthening effect.
 i) Nickel (Ni):
• Its coefficient of thermal expansion approximates that of
gold and it provides resistance to corrosion.
• Unfortunately, nickel is a sensitizer and
 a known carcinogen.


Functions of Metal Ceramic Substructure:
Two types:
a) Primary
b) Secondary
Primary Functions:
i) The casting provides the fit of the restoration to the
prepared tooth.
ii) The metal forms oxides that bond chemically to dental
porcelain.
iii) The coping serves as a rigid foundation to which the
brittle porcelain can be attached for increased strength
and support.
iv) The substructure restores the tooth’s proper
emergencewww.indiandentalacademy.com
profile.

 Secondary functions :
a) Metal occlusal and lingual articulating surfaces
generally can be less destructive to the enamel of
opposing natural teeth.
b) The occluding surfaces can be easily adjusted and
repolished intra orally.
c) Fabrication of a restoration with minimal occlusal
clearance has more potential for success with a
metal substructure than the all-ceramic materials.


Metal Ceramic Bond:
• Four theories have been proposed to explain the
processes that leads to porcelain to metal bond:
i) Van der Waals forces
ii) Mechanical retention
iii) Compression bonding
iv) Direct chemical bonding

Chemical form of attachment is the predominant and
most important mechanism

Vander Waals Forces:
• These secondary forces are generated more by a
physical attraction between charged particles than by
an actual sharing or exchange of electron in primary
(chemical) bonding.

• These forces are generally weak. Only minimal
attraction exists between the electron and nuclei of
atoms in one molecule and the nuclei and electron of
atoms in the adjacent molecule.


• The better the wetting of the metal surface, the
greater the Van der Waals forces.
• Van der Waals forces are only minor contributors to
the overall attachment process.


Mechanical Retention:
• The porcelain bearing area of a metal casting contains
many microscopic irregularities into which opaque
porcelain may flow when fired.
• Air abrading the metal with aluminium oxide is
believed to enhance mechanical retention further by
eliminating surface irregularities while increasing the
overall surface area available for bonding.
• Despite its presence, mechanical retentions contribute
to bonding are relatively limited.


Compression Bonding:
• Dental porcelain is strongest under compression and
weakest under tension, hence, if the coefficient of thermal
expansion of the metal substrate is greater than that of the
porcelain placed over it, the porcelain should be placed
under compression on cooling.
Chemical Bonding:
• Two mechanisms may exist with the chemical bonding
theory. According to one hypothesis, the oxide layer is
permanently bonded to the metal substructure on one side
while the dental porcelain remains on the other.
• The oxide layer itself is sandwiched in between the metal
substructure and the opaque porcelain.


• The second, and more likely, theory suggests that the
surface oxides dissolves, or are dissolved by the opaque
layer.
• The porcelain is then brought into atomic contact with
the metal surface for enhanced wetting and direct
chemical bonding so that metal and porcelain share
electron.
• Both covalent and ionic bonds are thought to form but
only a monomolecular layer of oxide is believed to be
required for chemical bonding to occur.
• Chemical bonding is generally accepted as the primary
mechanism in the porcelain metal attachment process.


Porcelain Failure:
• Fracture in porcelain on a metal ceramic restoration may take place
1) During fabrication
2) During placement
3) During service

1) Fabrication fracture may be caused by:
i) Thermal expansion/ contraction mismatch.
ii) Improper restoration design-sharp angles, insufficient metal, or
excessive unsupported porcelain and small radii.
iii) Improper firing practice resulting in altered thermal expansion/
contraction of the porcelain.


2) Insertion fracture: are usually associated with elastic or plastic
deformation of the metal substrate. The deformation stresses are
generally imposed by
a) Questionable path of insertion
b) The presence of undercuts
c) Insufficient tooth reduction
d) Difficulty of cement escape

The stresses encountered in metal ceramic restoration are
generally longitudinal (along the length), tangential (along the
circumference), and radial (along the radius). Each of these
stresses may assume the form of compression or tension,
depending on whether the alloy contracts more or less than the
porcelain.


Types of Metal-Porcelain
Bond Failure:
• Classification of ceramo-metal
failures by O’Brien (1977)

1) Metal-porcelain: Generally seen 3
when the metal surface is totally
depleted of oxide prior to baking
the porcelain or when no oxides
are available.
• It may also be due to
contaminated or porous
metal surfaces.
5
2) Metal oxide porcelain: Common
type of failure in the base metal
alloy system.
3) Metal-metal oxide: When there is
over production of chromium and
nickel oxide at the interface.


4) Metal oxide – Metal oxide: Occurs due to over
production of oxide causing a sandwich effect between
metal and porcelain.
5) Cohesive within metal: It is most unlikely type of fracture
for the individual metal ceramic crown. Occurs in cases
where the joint area in bridges break.
6) Cohesive within porcelain: This is most common type of
fracture in the high gold alloys.


 Advantages of Metal Ceramics:
a) Very high strength values due to prevention of
crack propagation from the internal surfaces of
crowns by the metal reinforcement.
b) Improved fit on individual crowns provided by cast
gold collar.
c) The only porcelain material that can be used in
fixed bridge work and for splinting teeth.


Disadvantages of Metal Ceramics:
a) Increased opacity and light reflectivity, particularly in
tungsten filament light.
b) More difficulty to create depth of translucency in the
crown due to the ‘mirror’ effect of the dense opaque
masking porcelain.
c) The fit of long span bridges or splints may be affected by
the creep of the metal during successive bakes of
porcelain.
d) More difficult to obtain good aesthetics than regular or
aluminous porcelain.
e) Porcelains used in the metal-ceramic techniques are
more liable to devitrification which can produce
cloudiness. www.indiandentalacademy.com

Indications of Metal Ceramics:
a) In case of parafunctional mandibular activity where an
aesthetic restoration is essential.
b) Teeth requiring fixed splinting or being used as bridge
abutments.
c) In all posterior teeth where full coverage is necessary for
aesthetic reasons.
d) Where lingual clearance of less than 0.8 mm is present.


 Contraindications:
a) Adolescent teeth where minimal tooth preparation
is essential.
b) Teeth where enamel wear is high and there is
insufficient bulk of tooth structure to allow room for
metal and porcelain.
c) Anterior teeth where esthetics is of prime
importance e.g. high shades of very translucent
teeth.


ALL CERAMIC SYSTEMS


Characteristic Features of All-Ceramic Crowns
Ø Excellent esthetic result.
Ø Moderate strength for single - unit anterior tooth
restorations when bonded with resin cement.
Ø Lack of gray/ brown metal show through since a metal
substructure is absent.
Ø Inability to cover the color of a darkened tooth
preparation or post / core, since the crowns are translucent.
Ø Laboratory costs higher than those for typical PFM
crowns.


The advantages of All-ceramic restorations
include:

Increased translucency
Improved fluorescence
Greater contribution of colour from the underlying tooth
structure
Inertness
Bio-compatibility
Resistance to corrosion
Low temperature / electrical conductivity


Newer types of all-ceramic restorations developed may
prove to have a lower incidence of clinical fracture for 3
important reasons :

stronger materials and involve better fabricating
techniques
can be etched and bonded to the underyling tooth
structure with the new dentin adhesives
greater tooth reduction -enough room to create thicker and
stronger restorations.


Disadvantages
Wear of opposing occluding enamel or dentin if the
pressed all-ceramic crowns are a part of heavy incisal
guidance or canine rise.
Ø Difficulty in removing the crown and cementing
medium when replacement is necessary (Bonded pressed
ceramic crowns are much more difficult to remove than
standard PFM crowns)


Currently available all-ceramics can be broadly
categorized according to their method of fabrication :

Ø CONVENTIONAL (POWDER – SLURRY)
CERAMICS

Ø CASTABLE CERAMICS

Ø MACHINABLE CERAMICS

Ø PRESSABLE CERAMICS

Ø INFILTRATED CERAMICS


CONVENTIONAL POWDER/ SLURRY
CERAMICS


TYPES :
Alumina – Reinforced porcelain (Aluminous Porcelain

Magnesia – Reinforced porcelain (magnesia core
ceramics)

Leucite Reinforced (Non-pressed)

Low fusing ceramics

Zirconia whisker- fibre reinforced,


ALUMINA – REINFORCED PORCELAIN

(ALUMINOUS PORCELAINS )

Alumina glass composites used in dental ceramic work
have been termed “Aluminous Porcelain” (McLean &
Hughes, 1965).


Porcelains used in an all aluminous porcelain
crown consists of :
Aluminous core porcelain :
40-50 % by wt fused alumina crystals fritted in a low-
fusing glass.
The alumina (α - alumina ) particles have very high
tensile strength.
They are stronger and more effective in interrupting
crack propagation
strengthening by two to three folds with the proportion of
the crystalline phase. ·


Dull/ opaque porcelain with lack of translucency.
used as core material (0.5 -1mm) over platinum foil
veneered with feldspathic porcelain.
strength still insufficient to bear high stresses.
Eg:
Vitadur – N(Vident)
Hi – Cream (Vident)


Advantages

Ø Low coefficient of thermal expansion in the range of
8*10-6/0C.

Disadvantages
Ø Requires specially formulated and compatible enamel
and dentin porcelains for veneering.
Improvement in strength is insufficient to bear high stresses.


MAGNESIA – REINFORCED PORCELAIN

Magnesia Core Ceramics are high expansion ceramics
described by O’Brien in 1984

used as core material for metal ceramic veneer porcelain.
dispersion strengthened core ceramics made by fine
dispersion of crystalline magnesia (40-60%)

The magnesia crystals strengthen the glass matrix by both
dispersion strengthening and crystallization within the

Advantages:

Increased coefficient of thermal expansion (CTE14.5x10-
6/0C) I
improves its compatibility with conventional feldspathic metal
veneering porcelains . (CTE: 12 to 15x 10-6/0C).

Improved strength and a high expansion property compared
suitable for use as a core material ,

substituting for a metallic core as substructure.


LEUCITE – REINFORCED PORCELAINS

Feldspathic porcelains, dispersion strengthened by
crystallization of leucite crystals in the glass - matrix .


Optec HSP (Optec high Strength porcelain )
(Jeneric/Pentron)
leucite reinforced feldspathic porcelain - condensed and
sintered like aluminous and traditional feldspathic porcelain
on a refractory die instead of a platinum foil .
Its moderate strength is derived from the nucleation and
growth of fine dispersion of a higher volume fraction of
leucite crystals.
.Despite the increase in crystallization ,the material retains its
translucency apparently because of the closeness of the
refractive index of leucite with that of the glass matrix . The
flexure strengthwww.indiandentalacademy.com
is approximately 140 Mpa..

Composition :

It is a glass ceramic with a leucite content of 50.6 weight %
dispersed in a glassy matrix .

uses :
Inlays ,
onlays,
crowns and veneers.


Advantages

Ø Despite lack of metal or opaque substructure, it has high
strength by leucite reinforcement, hence can be used as a
core material.
Ø Good translucency
Ø Moderate flexural strength
Ø No special laboratory equipment needed.


Disadvantages

Ø Potential marginal inaccuracy caused by porcelain
sintering shrinkage.

Ø Potential to fracture in posterior teeth.
Increased leucite content may contribute to high
abrasive effect on opposing teeth.


Hydrothermal ceramics
new dental ceramics developed from industrial ceramics by
introducing hydroxyl groups into the ceramic structure under
heat and steam from which the tem ‘hyrdothermal’ ceramic is
derived.
The term ‘hydrothermal manufacturing processes’ introduced
by Ryabov et al, Bartholomew, Bertschtein and Stepanov
& Scholze in the 1970’s and 1980s


The hydrothermal ceramic systems- low fusing porcelains
containing hydroxyl groups in the glass matrix.

Although the melting, softening and sintering temperatures
had reduced, these materials exhibited an increase in
thermal expansion and mechanical strength without a
compromise in their chemical solubility.


Hydrothermal ceramics can be formulated as two types :

Ø A single phase porcelain
Eg: Duceram LFC® (Degussa Dental, South Plainfield, NJ)

Ø A leucite containing two phase material
Eg.: Duceragod® (Degussa Dental, South Plainfield, NJ)


Advantage of hydrothermal ceramics over
conventional porcelains:

Ø Lower fusion temperature (680-7000 C)

Ø Increased coefficient of thermal expansion

Ø Minimal abrasion of opposing dentition

Ø Greater toughness and durability

Ø Stronger bond to the deep gold coloured Degunorm
alloy(Degussa Dental, S. Plainfield, NJ).


Duceram LFC:
low fusing hydrothermal ceramic composed of an amorphous
glass containing hydroxyl (-OH) ions
.
It was developed in mid 1980’s based on the ideas and studies
on industrial porcelain ceramic from the early 1960’s and was
first introduced to the market in 1989 for use in all ceramic
prostheses, ceramic / metal-ceramic inlay and partial crowns.


Advantages over feldspathic porcelain:
Ø Greater density
Ø Higher flexural strength attributed to OH ion
exchange and sealing of surface microcracks
Ø Greater fracture resistance
Ø Lower abrasion than feldspathic porcelain (wear rate
equal to that of natural teeth)
Ø Surface resistant to chemical attack by fluoride
containing agents.
Ø Highly polishable, not requiring re-glazing during
adjustment.


Disadvantages :
Cannot be directly sintered on the metallic substructure
because of the low coefficient of expansion.
Thus, an inner lining of conventional high-fusing ceramic is
required on the metal substructure because of the low
coefficient of expansion.


CASTABLE CERAMICS


Glass-ceramics are polycrystalline materials developed
for application by casting procedures using the lost wax
technique, hence referred to as “castable ceramic”.

Glass ceramics in general are partially crystallized glass
and show properties of both crystalline and amorphous
(glassy) materials.

They are fabricated in the vitreous (Glass or non-
crystalline/amorphous) state and converted to a ceramic
(crystalline state) by controlled crystallization using
nucleating agents during heat treatment.


Castable dental Glass-Ceramics

Fluoromicas OtherGlass-Ceramics
(SiOK2MgOA12O3ZrO2) Based on
a) Lithia
E.g Dicor b)Calciumphosphate

Apatite Glass-Ceramic
(CaOMgOPO5SiO2 system
E.g: Cera Pearl (Kyocera Bioceram)


Dicor:
Dicor, the first commercially available castable glass-ceramic
material for dental use was developed by The Corning Glass
Works (Corning N.Y.) and marketed by Dentsply International
(Yord, PA, U.S.A).
The term “DICOR” is a combination of the manufacturer’s
names: Dentsply International & Corning glass.
Dicor is a castable polycrystalline fluorine containing tetrasilicic
mica glass-ceramic material, initially cast as a glass by a lost-
wax technique and subsequently heat - treated resulting in a
controlled crystallization to produce a glass - ceramic material.

Major Ingredients

SiO2 45-70%,
K2O upto 20%;
MgO 13-30%

MgF2 (nucleating agent & flux 4 to 9%)

Minor Ingredients

A12O3 upto 2% (durability & hardness)

ZrO2 upto 7%; Fluorescing agents (esthetics)

BaO 1 to 4% (radiopacity)


Advantages of Dicor

Ø Chemical and physical uniformity

Ø Excellent marginal adaptation (fit)

Ø Compatibility with lost-wax casting process

Ø Uncomplicated fabrication from wax-up to casting,
ceramming and colouring

Ø Ease of adjustment


Ø Excellent esthetics resulting from natural translucency, light
absorption, light refraction and natural colour for the
restoration.

Ø Relatively high strength (reported flexural strength of 152
MPa), surface hardness (abrasion resistance) and occlusal
wear similar to enamel.

Ø Inherent resistance to bacterial plaque and biocompatible
with surrounding tissues.

Ø Low thermal conductivity.
Radiographic density is similar to that of enamel.


Disadvantages

Ø Requires special and expensive equipments such as
Dicor casting machine, ceramming oven. (High investment
cost for the lab)
Ø Although short term clinical studies, verified the
efficacy of the Dicor system in laboratory studies for use
as veneers and inlays, failure rates as high as 8% (# of
the restoration) were reported, especially in the posterior
region. In addition, failure rates as high as 35% have been
reported with full coverage
Dicor crowns not bonded to tooth (The poor strength is
thought to be caused by porosity, especially in the
outermost "ceram layer").

Dicor must be shaded/ stained with low fusing feldspathic
shading porcelain to achieve acceptable esthetics,
however the entire stain/ colors maybe lost during
occlusal adjustment (use of abrasives), during routine
dental prophylaxis or through the use of acidulated
fluoride gels.


Two ceramic products were introduced to overcome the
above problem:

Ø Dicor plus (Dentsply, Trubyte division) : Consists of
a cast cerammed core (Dicor substrate) and shaded
feldspathic porcelain veneer.
However, as Dicor plus is a feldspathic porcelain that
contains leucite, the abrasiveness is expected to be similar
to other feldspathic porcelains.

Willis Glass : Consists of a Dicor cast cerammed core
and a Vitadur-N porcelain veneer similar in nature to that
used for Dicor Plus.


CASTABLE APATITE GLASS CERAMIC

Castable apatite ceramic is classified as CaO-P2O5-MgO-
SiO glass ceramic.

1985 -Sumiya Hobo & Iwata developed a castable apatite
glass-ceramic which was commercially available as Cera
Pearl (Kyocera Bioceram, Japan).


CERA PEARL (Kyocera San Diego, CA): contains a
glass powder distributed in a vitreous or non-crystalline
state.

Composition: Approximately (By weight)

Ø Calcium oxide (CaO) -45%
Ø Phosphorus Pentoxide (P2O5) -15% Aids in glass
formation
Ø Magnesium oxide (MgO) -5% Decreases the viscosity
(antiflux)
Ø Silicon dioxide (SiO2) -35% Forms the glass
matrix.
Ø Other -Trace elements Nucleating agents(during
ceramming).


Desirable characteristics of Apatite Ceramics

Ø Cerapearl is similar to natural enamel in composition,
density, refractive index, thermal conductivity, coefficient of
thermal expansion and hardness.
Similarity in hardness prevents wear of opposing enamel.


Bonding to tooth structure –
Glass ionomer cements adhere to tooth structure (dentin
and enamel) primarily bonding to the apatite component,
and thus should also bond to the apatite phase within the
glass-ceramic.
To enhance this possibility, Cerapearl surface is activated
by air abrading (to provide mechanical interlocking effect)
or treatment with activator solution (etching of with 2N HCI
preferentially removes the glassy phase from the surface,
thus exposing the apatite phase).
The glass ionomer can then bond to this apatite phase
both chemically (ion-exchange) and mechanically
(interlocking effect).

Lithia Based Glass-Ceramic

Developed by Uryu; and commercially available as
-Olympus Castable Ceramic (OCC)

Composition:

It contains mica crystals of NaMg3 (Si3AlO10) F2 and
Beta Spodumene crystals of LiO.AI2O3.4SiO2 after heat
treatment.


Calcium Phosphate Glass-Ceramic

Reported by Kihara and others, for fabrication of all-
ceramic crowns by the lost wax technique.
It is a combination of calcium phosphate and
phosphorus pentoxide plus trace elements.
The glass ceramic is cast at 1050°C in gypsum
investment mold.
The clear cast crown is converted to a crystalline
ceramic by heat treating at 645°C for 12 hours.
Reported Flexural strength (116 Mpa);
Hardness close to tooth structure.

Disadvantages
Weaker than other castable ceramics;

Opacity reduces the indication for use in anterior
teeth.


Advantages of castable glass ceramics

Ø High strength because of controlled particle size
reinforcement.
Ø Excellent esthetics resulting from light transmission
similar to that of natural teeth .and convenient procedures
for imparting the required colour.
Ø Accurate form for occlusion, proximal contacts, and
marginal adaptation.
Ø Uniformity and purity of the material.
Ø Favorable soft tissue response.
Ø X-ray density allowing examination by radiograph


Colour control, optical effects allow predictable and
esthetic results.
Cast glass ceramics are thermal resistant.

Bacterial plaque adherence on the surface is inhibited,
thus maintaining the tissues surrounding the restoration.
Radiolucency allows for a dimension of depth in the
observation of marginal integrity.

Wear rate values are similar to that of human enamel.


MACHINABLE
CERAMICS


CAD/CAM is an acronym for Computer Aided Design /
Computer Aided Manufacturing (or Milling).

French system
Swiss system
Minnesota system


Triad of fabrication:
Fabrication of a restoration whether with traditional lost-wax
casting technique or a highly sophisticated- technology such
as a CAD/CAM system has three functional components:

Data acquisition
Restoration design
Restoration fabrication


Machinable Ceramic system (MCS) for dental
restorations:
Ø Digital Systems (CAD/CAM):

Direct
Indirect

Three steps :
§ 3-dimensional surface scanning

§ CAD -Modelling of the restoration

§ Fabrication of restoration.


Ø Analogous systems (Copying methods)
Copy Milling / Copy Grinding or Pantography Systems

Two steps :

§ Fabrication of prototype for scanning;

§ Copying and reproducing by milling


DIGITAL SYSTEMS
Computer aided design and computer aided manufacturing
(CAD/ CAM) technologies have been integrated into systems
to automate the fabrication of the equivalent of cast
restorations.

CAD/CAM milling
uses digital information about the tooth preparation or a
pattern of the restoration to provide a computer-aided design
(CAD) on the video monitor for inspection and modification.
The image is the reference for designing a restoration on the
video monitor. Once the 3-D image for the restoration design
is accepted, the computer translates the image into a set of
instructions to guide a milling tool (computer-assisted
manufacturing [CAM]) in cutting the restoration from a block of
material.


Stages of fabrication
Although numerous approaches to CAD/CAM for
restorative dentistry have evolved, all systems ideally
involve 5 basic stages:

Ø Computerized surface digitization

Ø Computer - aided design

Ø Computer - assisted manufacturing

Ø Computer - aided esthetics

Ø Computer - aided finishing


CEREC SYSTEM

The CEREC (Ceramic Reconstruction) system
( Siemen/sirna corp)

originally developed by Brains AG in Switzerland and
first demonstrated in 1986, but had been repeatedly
described since 1980.
Identified as CEREC CAD/CAM system, it was
manufactured in West Germany and marketed by the
Siemens group.


Cerec System consists of :

Ø A 3-D video camera (scan head)

Ø An electronic image processor (video processor) with
memory unit (contour memory)

Ø A digital processor (computer) connected to
,
Ø A miniature milling machine (3-axis machine)


Machinable ceramics ( Ceramics used in machining
systems)
are pre-fired blocks of feldspathic or glass - ceramics.

Composition :
Modified feldspathic porcelain or special fluoro-alumino-
silicate composition are used for machining restorations.

Properties

Ø Excellent fracture and wear resistance
Ø Pore-free
Ø Possess both crystalline and non-crystalline phase (a
2-phase composition permits differential etching of the
internal surface for bonding).


Ceramic CAD/ CAM restorations are bonded to tooth
structure by :

Ø Etching for a bond to enamel
Ø Conditioning, priming and bonding (when appropriate)
Ø Etching (by HF acid) and priming (silanating)
Ø Cementing with luting resin.


Machinable Ceramics
The industrially prefabricated ceramic ingots/ blank used
are practically pore-free which do not require high
temperature processing and glazing, hence have a
consistently high quality.
The blanks measure approximately 9 x 9 x 13 mm and are
industrially fabricated using conventional dental porcelain
techniques. Eg: Vitadur 353N (Vita Zahnfabrik, Bad
Sackingen, West Germany) frit powder is mixed with
distilled water, condensed into a 10 x 10 x l5 mm steel die
and fired under vacuum (the temperature is increased at a
rate of 60OC/min to 950oC and held for one minute).

Two classes

Fine-scale feldspathic porcelain

Glass-ceramics


Cerec Vitabloc Mark I :
This feldspathic porcelain was the first composition used
with the Cerec system (Siemens) with a large particle size
(10 - 50µm). It is similar in composition, strength, and wear
properties to feldspathic porcelain used for metal-ceramic
restorations.

Cerec Vitabloc Mark II : This is also a feldspathic
porcelain reinforced with aluminum oxide (20-30%) for
increased strength and has a finer grain size (4µm) than
the Mark I composition to reduce abrasive wear of

Dicor MGC (Dentsply, L.D. Caulk Division) :
This is a machinable glass-ceramic composed of
fluorosilica mica crystals in a glass matrix.
The micaplates are smaller (average diameter 2 um) than
in conventional Dicor (available as Dicor MGC - light and
Dicor MGC - dark).
Greater textural strength than castable Dicor and the
Cerec compositions.
Softer than conventional feldspathic porcelain. Less
abrasive to opposing tooth than Cerec Mark I, and more
than Cerec Mark II (invitro study results).


Other machinable ceramics being developed include:

Ø Bioglass (Alldent Corp., Rugell, Liechtenstein)

Ø DFE -Keramik/Krupp Medizintechnir GmbH, Essen,
Germany; Bioverit / Mikrodenta Corp

Ø Empress / Vivadent –lvoclar Corp, Schaan,
Liectenstein.


The clinical advantages of the Cerec system:

Ø The restorations made from prefabricated and
optimized, quality-controlled ceramic porcelain can be
placed in one visit.
Ø Transluency and color of porcelain very closely
approximate the natural hard dental tissues.
Ø Further, the quality of the ceramic porcelain is not
changed by the variations that may occur during
processing in dental laboratories.
Ø The prefabricated ceramic is wear resistant.


CICERO System

Computer Integrated Crown Reconstruction (Elephant
industries).
This Dutch system was marketed with the Duret (French)
system, Sopha Bioconcept and the Minnesota system
(Denti CAD) as the only three systems capable of
producing complete crowns and FPD's.
The Cicero CAD/CAM system developed for the
production of ceramic-fused-to-metal restorations, makes
use of :
Ø Optical scanning
Ø Nearly net -shaped metal and ceramic sintering
Ø Computer-aided crown fabrication techniques. Alloy
sintering eliminates casting and therewith many processing
steps in the fabrication of metal-ceramic restorations.


COMET System

(Coordinate M Easuri ng Technique, Steinbichler Optotechnik,
GmbH, Neubeurn, Germany)
This system allows the generation of a 3-dimensional data
record for each superstructure with or without the use of a
wax-pattern.
For imaging, 2 - dimensional line grids are projected onto an
object, which allows mathematical reproduction of the tooth
surfaces.
It uses a pattern digitization and surface feedback technique,
which accelerates and simplifies the 3-dimensional
representation of tooth shapes while allowing, individual
customization and correction in the visualized monitor image.

Advantage of CAD/CAM (Cerec system)over other
systems

Ø Eliminates impression model making and fabrication
of temporary prosthesis.
Ø Dentist controls the manufacturing of the restoration
entirely without laboratory assistance.
Ø Single visit restoration and good patient acceptance.
Ø Alternative materials can be used, since milling is
not limited to castable materials.
Ø The use of CAD/ CAM system has helped provide
void free porcelain restorations, without firing shrinkage
and with better adaptation.


Ø CAD - CAM device can fabricate a ceramic
restoration such as inlay/ onlay at the chair-side.
Ø Eliminates the asepsis link between the patient, the
dentist, operational field and ceramist.
The shapes created in the CAD unit are well defined,
and thus a factor such as correct dimensions can be
evaluated and corrections/modifications can be carried out
on the display screen itself .


Glazing is not required and Cerec inlay onlays can
easily be polished.

Minimal abrasion of opposing tooth structure
because of homogeneity of the material (abrasion
does not exceed that of conventional and hybrid
posterior composite resins).

The mobile character of the entire system enables
easy transport from one dental laboratory to another.


Disadvantages:

Ø Limitations in the fabrication of multiple units.
Ø Inability to characterize shades and translucency.
Ø Inability to image in a wet environment (incapable of
obtaining an accurate image in the presence of excessive
saliva, water ore blood).
Ø Incompatibility with other imaging system.
Ø Extremely expensive and limited availability.
Ø Still in early introductory stage with few long-term
studies on the durability of the restorations.


 Lack of computer-controlled processing support
for occlusal adjustment.
 Technique sensitive nature of surface imaging
that is required for the prepared teeth.
 Time and cost must be invested for mastering
the technique and the fabrication of several
restorations, to develop proficiency in the operator.


PROCERA System :

The Procera System (Nobel Biocare, Gioteborg, Sweden)
embraces the concept of CAD/CAM to fabricate dental
restorations.
It was developed by Andersson .M & Oden .A in 1993,
through a co-operative effort between Nobel Biocare AB
(Sweden) and Sandvik Hard Materials AB (Stockholm,
Sweden).

It consists of a computer controlled design station in the
dental laboratory that is joined through a modern
communication link to Procera Sandvik AB in Stockholm,
Sweden, where the coping is manufactured with advanced
powder technology and CAD/CAM technique.


Procedure requires 3 steps for fabrication:

Scanning : At the design station, a computer controlled
optical scanning device maps the surface of the master die
and is sent via modem to the Procera production facility.

Machining : At the production facility, an enlarged die is
fabricated that compensates for the 15-20% sintering
shrinkage of the alumina core material.
High-purity alumina powder is pressed onto the die under
very high pressure, milled to required shape, and fired at a
high temperature (1550°C) to form a Procera coping.


 veneering :

The sintered alumina coping is returned to the dental
laboratory for veneering thermally compatible low fusing
porcelains (All Ceram veneering porcelain) to create the
appropriate anatomic form and esthetic qualities.

All Ceram veneering porcelain (Ducera) has a coefficient of
thermal expansion adjusted to match that of aluminium oxide
(7x10-6 /°C).


It also has the fluorescent properties similar to that of
natural teeth and the veneering procedures require no
special considerations.
The reported flexural strength of the Procera All Ceram
crown (687 Mpa) is relatively the highest amongst all the
all-ceramic restorations used in dentistry (attributed to the
99.9% alumina content).


This system can be used to fabricate two types of dental
restorations :

A Porcelain-fused-to-metal restoration made of
titanium substructure with a compatible veneering
porcelain using a combination of machine duplication and
spark-erosion (The Procera Method, Noble Biocare).

An all-ceramic restoration using a densely sintered
high-purity (99.9%) alumina coping combined with a
compatible veneering porcelain.


PRESSABLE
CERAMICS


PRESSABLE CERAMICS

Shrink-free Ceramics Leucite-reinforced
Glass-ceramics
Cerestore IPSEmpress

Al-Ceram Optec
Pressable Ceramic (OPC)


SHRINK FREE ALUMINA CERAMICS
The shortcomings of the traditional ceramic material and
techniques; like failures related to poor functional strength
and firing shrinkage limited the use of "all-ceramic" jacket
crowns.
The development of non-shrinking ceramics such as the
Cere.store systen'l was directed towards providing an
alternate treatment

Shrink-free ceramics were marketed as two generation of
materials under the commercial names :
Ø Cerestore (Johnson & Johnson. NJ, USA)
Al-Ceram (Innotek Dental Corp, USA)

CERESTORE Non-Shrink Alumina Ceramic (Coors
Biomedical Co., Lakewood, Colo.)
shrink-free ceramic with crystallized magnesium alumina
spinel fabricated by the injection molded technique to form a
dispersion strengthened core.

Composition Of Shrink Free Ceramic
Fired Composition (Core)

A12O3 (Corundum) 60%
MgA12O4 (Spinel) 22%
BaMg2A13(Barium Osomilite) 10%


Unfired Composition

A12O3 (small particles) 43%
A12O3 (large particle) 17%
MgO 9%
Glass frit 13%
Kaolin Clay 4%
Silicon resin (Binder) 12%
Calcium Stearate 1%
Sterylamide 1%


Advantages :

Ø Innovative feature is the dimensional stability of the
core material in the molded (unfired) and fired states. Hence,
failures related to firing shrinkage are eliminated.

Ø Better accuracy of fit and marginal integrity.

Ø Esthetics enhanced due to depth of colour due to the
lack of metal coping.

Ø Biocompatible (inert) and resistant to plaque formation
(glazed surface).


Ø Radiodensity similar to that of enamel (presence of
Barium osumilite phase in the fired core allows
radiographic examination of marginal adaptation and
visualization under the crown).

Ø Low thermal conductivity; thus reduced thermal
sensitivity.

Low coefficient of thermal expansion and high modulus
of elasticity results in protection of cement seal.


Disadvantages :

Ø Complexity of the fabrication process.
Ø Need for specialized laboratory equipment
(Transfer molding process) and high cost.
Ø Inadequate flexural strength (89MPa) compared to
the metal-ceramic restorations.
Ø Poor abrasion resistance, hence not recommended
in patients with heavy bruxism or inadequate clearance.


Limitations and high clinical failure rates of the Cerestore
led to the withdrawal of this product from the market. The
material underwent further improvement and developed
into a product with a 70 to 90% higher flexural strength.
This was marketed under the commercial name Al Ceram
(Innotek Dental, Lakewood, Colo.).


LEUCITE REINFORCED PORCELAINS ( Transfer-
molded )
Leucite reinforced porcelains can be broadly divided into
two groups:

Ø Pressed –
· IPS Empress & IPS Empress 2 (Ivoclar)
· Optec Pressable Ceramic / OPC (Jeneric/Pentron)

Ø Non-Pressed
· Optec HSP & Optec VP (Jeneric / Pentron)
· Fortress (Mirage)


Pressed Ceramic / Injection Molded Glass Ceramic are
leucite-reinforced, vacuum-pressed glass-ceramic, also
referred to as Heat transfer-molded glass ceramics.
Eg: IPS Empress (Ivoclar Williams); Optec (Jeneric Pentron)

IPS EMPRESS (Ivoclar Williams)
pre-cerammed, pre-coloured leucite reinforced glass-ceramic
formed from the leucite system (SiO2-AI2O3-K20) by
controlled surface crystallization, subsequent process stages
and heat treatment.


This technique was first described by Wohlwend & Scharer;
and marketed by Ivoclar (Vivadent Schaan, Liechtensein).
The glass contains latent nucleating agents and controlled
crystallization is used to produce leucite crystals measuring a
few microns in the glass matrix.
The partially pre-cerammed product of leucite-reinforced
ceramic powder available in different shades is pressed into
ingots and sintered.
The ingots are heated in the pressing furnace until molten
and then injected into the investment mold.


Uses :
Ø Laminate veneers and full crowns for anterior teeth
Ø Inlays, Onlays and partial coverage crowns
Ø Complete crowns on posterior teeth.


Advantages :
Ø Lack of metal or an opaque ceramic core
Ø Moderate flexural strength (120-180MPa range)
Ø Excellent fit (low-shrinkage ceramic)
Ø Improved esthetics (translucent, fluorescence)
Ø Etchable
Ø Less susceptible to fatigue and stress failure
Ø Less abrasive to opposing tooth
Ø Biocompatible material


Disadvantages :

Ø Potential to fracture in posterior areas.
Ø Need for special laboratory equipment such as
pressing oven and die material (expensive)
Ø Inability to cover the colour of a darkened tooth
preparation or post and core, since the crowns are
relatively translucent.
Ø Difficulty in removing the crown and cementing
medium during replacement.
Compressive strength and flexural strength lesser
than metal-ceramic or glass-infiltrated (In-Ceram)
crowns.


OPTEC (Optimal Pressable Ceramic/OPC):
Optec stands for Optimal Technology.
It is a type of feldspathic porcelain with increased Ieucite
content designed to press restorations using leucite-
reinforced ceramic in a press furnace that doubles as a
conventional porcelain furnace.
The manufacturer claims that the crystalline leucite particle
size has been reduced with a more homogenous
distribution without reducing the crystalline content and this
leucite content increase has resulted in an overall increase
in flexural strength of OPC (over 23,000 psi and
compressive strength upto 187,320 psi).

However, because of its high leucite content, it can be
expected that its abrasion against natural teeth will be
higher than that of conventional feldspathic porcelain.
Fabrication is similar to IPS Empress


Dental ceramics /certified fixed orthodontic courses by Indian dental academy

Dental ceramics /certified fixed orthodontic courses by Indian dental academy

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Dental ceramics /certified fixed orthodontic courses by Indian dental academy

Ähnlich wie Dental ceramics /certified fixed orthodontic courses by Indian dental academy (20)

Mehr von Indian dental academy

Mehr von Indian dental academy (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Dental ceramics /certified fixed orthodontic courses by Indian dental academy