Castable Ceramics: A Guide to Dicor Glass-Ceramics

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

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.

History of evolution of glass ceramics:
1837 – Murphy was probably the first dentist to melt glass
onto a platinum sheet that had been fit in the cavity
preparation.
1891 – Herbst made glass restoration out of pulverized
coloured glass particles with a gas flame directly on the
plaster model.
1930 – Frederick Carder, the founder of Steuben division
of the Corning Glass Works perfected fabricating 3-
dimensional glass articles for decorative purposes using the
lost wax technique. Although delicate objects were cast
accurately, the mechanical properties of glass restricted its
use to artistic application.

1957 – S.D. Stookey from the Corning Glass Works observed
how an industrial impure glass changed into ceramic with
organic crystalline form and coined the term “Glass-ceramic”.
Thus ‘Pyroceram’ an industrial glass ceramic which had the
properties of both glass and ceramics was developed.
1968 W.T. MacCulloch realised the usefulness of glass
ceramics and proposed its use for dental restorative purposes
(denture teeth; crowns; inlays). He used a continous glass
molding process to produce denture teeth, and suggested
fabrication of crowns/ inlays by centrifugal casting of molten
glass.
1973- Dr. David Grossman developed and patented the
MaCor (Machninable Corning), a predecessor of Dicor
(Grossman D.G.).

Since 1978 – Peter Adair of Biocor Inc, in association with
the Corning Glass Works and Dentsply international,
researched and developed the clinical application of glass-
ceramics.
1984 – Peter Adair patented Dicor, the commercial glass
ceramic material.
1985 – Sumiyo Hobo & Iwata developed a castable apatite
glass ceramic Cerapearl.
1986 – The world wide patent for the castable glass-ceramic
material and its entire processing system was given to the
manufacturing company De Trey/ Corning ware.
1988 – Tamura reported on fabrication of hydroxyapatite
crowns.

Glass-ceramic systems for dental application:
Li2
O ZnO – SiO2
Li2
O - Si2
O
Li2
O – CaO - Al2
O3
– SiO2
-
Na2
O– K2
O– Cao – Mgo - Al2
O3
- P2
O5
- SiO3
– F
CaO P2
O5
CaO – MgO - P2
O5
– SiO2
R2
O – Mg - SiO2
– F

Most glass ceramics are opaque or cloudy and are not
suitable for dental use. The first glass ceramic employed in
dentistry was introduced by MacCulloch (1968) for the
construction of denture teeth, and was based on the Li O2
-
ZnO - SiO2
- systems. At that time, the use of acrylic denture
teeth was becoming popular and the idea of glass ceramics
was not exploited further. The exploration of glass-ceramic
for dental use was taken up by other researchers and has
resulted in at least two major commercially available
products

Castable dental Glass-Ceramics
Fluoromicas Apatite Glass-Ceramic OtherGlass-Ceramics
(SiO2
K2
MgOA12
O3
ZrO2
(CaOMgOP2
O5
SiO2
system) Based on a) Lithia
E.g Dicor E.g: Cera Pearl (Kyocera Bioceram) b)Calcium
phosphate

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.

Composition of Dicor is based on the SiO2
K2
OmgOA12
O3
ZrO2
system. Its composition (w/w) according to different statements.
Supplied as : Dicor castable ceramic cartridges- special DICOR
casting crucibles each containing a 4.1 gm DICOR ingot and the
Dicor shading porcelain kit.
Equipment
 DICOR Casting Machine
 DICOR Ceramming Furnace with Ceramming Trays
Major Ingredients Minor Ingredients
SiO2
45-70%, K2
O upto 20%; MgO 13-
30%
MgF2
(nucleating agent & flux 4 to 9%)
A12
O3
upto 2% (durability &
hardness)
ZrO2
upto 7%; Fluorescing
agents (esthetics)
BaO 1 to 4% (radiopacity)

Fabrication of castable ceramics restoration consists of
mainly 2 steps:
 Casting: The glass liquefies at 1370°C to such a degree
that it can be cast into a mold using lost-wax and centrifugal
casting techniques.
• The wax pattern of the proposed restoration made on the
model/ die is invested in Castable Ceramic Investment (a
carbon-free, phosphate-based investment, specially formulated
to match DICOR castable ceramic) in a double-line casting ring
and burned out in a conventional burnout at 900°C for 30 mins.
• Glass ingots of castable ceramic material is placed in a
special zirconia crucible (melted at 1360°C / 2600°F) and
centrifugally cast .in the electronically-controlled DICOR
Casting Machine (Dentsply Int), maintaining the spin pressure
for upto 4 minutes and 30 seconds.www.indiandentalacademy.com

• The transparent glass casting obtained is amorphous and
fragile. After cooling, it is divested, sandblasted (25um Al2O3
particles at 40 psi) and carefully separated from the sprue.
 Ceramming: The cast glass material is subject to a
single-step heat treatment called as 'Ceramming' to produce
controlled crystallization by internal nucleation and crystal
growth of microscopic plate like mica crystals within the glass
matrix. This procedure gives glass-ceramic the special
physical and mechanical properties of DICOR.
Method: The transparent fragile casting is embedded in
castable ceramic embedment material (Gypsum-based) and
placed in a Ceramming tray in the DICOR Ceramming
Furnace. www.indiandentalacademy.com

Ceramming cycle:
650-1075 °C for 1 1/2hours and sustained upto 6 hours.
The cerammed glass-ceramic casting is achromatic and
appears as a whitish opaque semi-crystalline material; hence
external colourants are required to develop the required
shade (by veneering self - glazing, pre-mixed DICOR shading
porcelain provided by the manufacturer).

The computer controlled ceramic process is adjusted so that
the cast glass ceramic is composed of:
 Tetrasilic flouromica crystals (crystalline) - 55% by
volume.
 Glass matrix (non-crystalline) - 45% by volume.
The microstructure after ceramming consists of
multiple interlocking small plate-like crystals of tetrasilicic
flouromica (K2
Mg5
-Si4
O10
F2
) approximately 1 µm thick and 5-
6mm in diameter. On the surface of the cerammed glass are
‘Enstatite crystals’ at a thickness of 15-50µ m, which occur
through fluorine depletion (that occurs through interactions
with the embedment material used for the ceramming process.
The enstatite crystals are in an orthongnal direction to the
surface and are whitish and opaque in color.www.indiandentalacademy.com

The crystals function in following ways:
 Improved strength: Interlocking of randomly oriented small
plate-like mica crystals increases the resistance to fracture. The
mica crystals readily cleave along its long axis, causing cracks to
deflect, branch or blunt; thus disrupting crack propagation. Strength
also depends upon crystal diameter and crystal-glass expansion
mismatches.
 Improved esthetics - The varying crystal sizes and the
difference in the refractive indices of the glass and crystalline phase
makes the glass appear transparent. The refractive index of the mica
crystals is matched to that of the surrounding glass phase thus
reducing light scatter (as in aluminious porcelains) and results in
transparency close to that of enamel.
Reduced abrasive property - Since mica crystals replace the more
abrasive leucite crystals found in traditional feldspathic porcelain.www.indiandentalacademy.com

Following the ceramming process a “Ceram layer” or
‘skin’ of 25-100µm thickness is formed on the surface of the
DICOR restoration. Contained within that ‘ceram layer’ is what
has been described as crystal ‘whiskers’ oriented perpendicular
to the external surface. According to the manufacturer’s
laboratory manual, the ‘rod-like crystals that form on the
surface of the casting during ceramming increase its opacity ’.
Therefore, the outer ‘skin’ may or may not be removed
following the ceramming process, depending on the level of
translucency desired in the final restoration.

Therefore, a shaded Dicor restoration should be
viewed as a non - homogenous material composed largely of
the internal (parent) castable glass-ceramic veneered with a
thick, hard cerammed “skin” covered with multiple layers of
shading porcelain.
DICOR components KHN KHN
The Ceram layer 505 Dental
porcelain
After adding shading
porcelain
447 460
Internal/parent Dicor glass-
ceramic material located below
the cerammed skin
369 Dental enamel 343

Chameleon effect of Dicor
The transparent crystals scatter the incoming light. The light and
also its color, is disbursed as if the light is bouncing off a large
number of small mirrors that reflect the light and spread it over
the entire glass-ceramic. This property is called the ‘chameleon
effect’. This means Dicor glass – ceramics change color according
to their surroundings, which enhances its esthetic properties.
Dicor restoration surfaces were reported to have an appreciable
decrease in plaque accumulation compared to that of natural teeth.
Probable theories suggest the ability of Dicor surface to interfere
with the bacterial adhesion to different proteins (plaque) normally
found on natural teeth due to the following reasons :
 It has a smooth non-porous surface
 Presence of an electrical charge inhibiting plaque formation
or fluoride in the chemical structure.www.indiandentalacademy.com

Advantages of Dicor
 Chemical and physical uniformity
 Excellent marginal adaptation (fit)
 Compatibility with lost-wax casting process
 Uncomplicated fabrication from wax-up to casting,
ceramming and colouring
 Ease of adjustment

 Excellent esthetics resulting from natural translucency,
light absorption, light refraction and natural colour for the
restoration.
 Relatively high strength (reported flexural strength of 152
MPa), surface hardness (abrasion resistance) and occlusal
wear similar to enamel.
 Inherent resistance to bacterial plaque and biocompatible
with surrounding tissues.
 Low thermal conductivity.
 Radiographic density is similar to that of enamel.

Disadvantages
 Requires special and expensive equipments such as Dicor
casting machine, ceramming oven. (High investment cost for the
lab)
 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:
 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-P2
O5
-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)
 Calcium oxide (CaO) -45%
 Phosphorus Pentoxide (P2
O5
) -15% Aids in glass formation
 Magnesium oxide (MgO) -5% Decreases the viscosity
(antiflux)
 Silicon dioxide (SiO2
) -35% Forms the glass matrix.
 Other -Trace elements Nucleating agents(during
ceramming).
Chemistry: Apatite glass-ceramic melts (1460°C) and flows like
molten glass and when cast (1510°C) it has an amorphous
microstructure.

Apatite Glass-Ceramic Molten glass CaPO4
(CaO-P2O5 -MgO-SiO2) (Amorphous)
The amorphous CaPO4
formed after melting and casting changes
into a crystalline oxyapatite on heat treatment (ceramming) at
870°C for 1 hour. The chemically unstable oxyapatite when
exposed to moisture (water) further converts to crystalline
hydroxyapatite (HA crystals).
CaPO4 Oxyapatite Hydroxyapatite
(Amorphous) (Crystalline) (Crystalline)
Ca10
(PO4
)8
20H
Strength is dependent on these crystals and the bond between the
1460°C
melting
1510o
C
casting
1460°C
Ceramming
Exposure
to moisture

Natural Enamel Cerapearl
Composition of HA crystals Similar
Arrangement of H.A. crystals Regular Irregular
Light Refractive Index (Xo) 1.655 1.63
PH of solute in water 8.0 7.9
Density (g/cm3
) 2.97 2.9
Thermal conductivity (Cal. Cm/cm2
Sec. °C) 0.0022 0.0023
Compressive strength (Mpa / psi) 384/0.05 x 106
590 / 0.08 x 106
Young’s Modulus of Elasticity (Gpa / Psi) 84.1 / 12.2 x 106
103 / 15.0 x 106
Tensile strength (Mpa) 103 150
Knoop Hardness Number (KHN) 343 350
Comparison of Physical Properties of Natural Enamel and
Cerapearl

Other Physical Properties:
 Coefficient of thermal expansion : 11.0 x 10-6
/°C
 Young's Modulus : 103Gpa
 Casting Shrinkage : 0.53%
 Flexural strength similar to Dicor
Biologic properties : Dense material, Chemically stable, pH
similar to natural enamel, Non toxic/ biocompatible

Fabrication
 Casting: The wax pattern of the proposed restoration is
invested in phosphate-bonded high heat investment developed
exclusively for this system (CTE to match Cera Pearl's casting
shrinkage of 0.53%). Following burnout, the investment is
transferred to an automatic casting machine designed
especially for this system. The Cera Pearl crystals (8-10gms)
are placed in the ceramic crucible, melted under vacuum (at
1460o
C) and cast (at 1510o
C) into the mold. Annealing is done
one hour after the casting in an automatic furnace to release
the inner stresses of the cast structure. The investment
material around the cast structure is removed by sandblasting
(25-30um Al2
O3
beads) and ultrasonically cleaned. The
annealed casting is reinvested (CP crystal mold, Kyocera
Corp.) for ceramming.www.indiandentalacademy.com

 Ceramming: The ceramming oven is preheated at
750°C for 15 minutes. After the cast glass ceramic is place in
the oven the temperature is raised at the rate 50o
C/min until it
reaches 870°C and held for 1 hour. After crystallization, the
casting is dis-invested, and cleaned by sandblasting (201µm
Al2
O3
powder). It appears white in comparison with natural
enamel and requires the application of an external stain. Eg,
Cerastain (Bioceram), which consists of B2
O3
-SiO2
-Al2
03
-K2
O
glass, traces of various metal oxides.

Desirable characteristics of Apatite Ceramics
 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).www.indiandentalacademy.com

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.www.indiandentalacademy.com

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

 Hardness and wear properties closely matched to those
of natural enamel
 Similar thermal conductivity and thermal expansion
to natural enamel
 Dimensional stability regardless of any porcelain
corrective procedure and subsequent firings

Advantage of cast glass-ceramics over metal-ceramics
 The component chemical compounds are standardized,
eliminating any inaccuracies, The forming procedures can be
quality controlled.
 Superior compressive strength because of its semi-
crystalline form and is also a machinable material, Crack
propagation's are interrupted by the crystalline structure.
 Utilized conventional lost-wax technique similar to casting
alloys. Hence, casting and finishing can be easily done.
 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.www.indiandentalacademy.com

 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

Regardless of the advanced state of the 300-year old
technique of casting, each of its steps could induce error in the
final casting. Until 1988, indirect ceramic dental restorations
were fabricated by conventional methods (sintering, casting
and pressing) and neither were pore-free. Pore-free
restorations can be alternately produced by machining blocks
of pore-free industrial quality ceramic. The tremendous
advances in computers and robotics could also be applied to
revolutionize dentistry and provide both precision and reduce
time consumption. With the combination of optoelectronics,
computer techniques and sinter-technology, the morphologic
shape of crowns can be sculpted in an automated way.
Registration of the mandibular jaw movements or of the
functionally generated path in the mouth provides the
necessary data for an interference-free escape of cusps from
their fossae. www.indiandentalacademy.com

CAD/CAM is an acronym for Computer Aided Design / Computer
Aided Manufacturing (or Milling).
History of machining systems:
1971 - CAD/CAM technologies were introduced to the dental
profession.
1979 - Heitlinger and Rodder followed by,
1980 -Moermann &Brandestini began to share this approach.
1983 -First dental CAD/CAM prototype was presented at the
Garanciere conference in France.
1985 -The first CAD/CAM crown was publicly milled and installed
in a mouth without any laboratory involvement.
1986 -The first generation Cerec 1 (Siemens Corp) was introduced.
1994 -The second generation Cerec 2 (Siemens Corp) was presented.www.indiandentalacademy.com

Application of CAD/CAM techniques was actively pursued
by three groups of researches :
 Group supported by Henson International of France.
 Combined group effort between the University of Zurich
and Brains, Brandestini Instruments of Switzerland.
 University of Minnesota, supported by the U.S.
National Institute of Dental Research.

Although each group had a slightly different philosophy and
approach, they worked towards a common goal of integrating
engineering applications of automation in the creation of
dental restorations.
 French system: Optical impression -Laser scanner,
Data processed by : Shape recognition software. It has a
library (memory) describing theoretical teeth. The system
uses
• 3-D probe system based on electro-optical method
• Surface modelling and screen display
 Automatic milling by a numerically controlled 4-axis
machine

 Swiss system: Optical impression - Optical topographic
scanning using a 3-D oral camera; Data processed by an
interactive CAD unit. The system uses:
• A desk top model computer
• Display monitor permitting visual verification of quality of
data being acquired
• Electronically controlled 3-axis N/C milling machine
 Minnesota system: Optical impression -Photographic
based system using a 35-mm camera with magnifying lens. Data
obtained in the dental office is sent to another location for
processing and machining. 3-D Reconstruction uses :
• Direct line transformation and an alternative technique
proposed by Grimson
 Milling with a 5-axis N/C machine.

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
SUBTRACTIVE METHODS
Grinding of porcelain restorations out of a preformed block
either by means of CAD/CAM or by using a copy milling
unit can be done by the so-called subtractive methods.

Machinable Ceramic system (MCS) for dental restorations:
      Digital Systems (CAD/CAM):
•Direct
•Indirect

Three steps :
         3-dimensional surface scanning
         CAD -Modelling of the restoration
         Fabrication of restoration.

      Analogous systems (Copying methods)
•Copy Milling / Copy Grinding or Pantography Systems
Two steps :
         Fabrication of prototype for scanning;
         Copying and reproducing by milling
•Erosive techniques
        Sono Erosion
        Spark Erosion

MACHINING SYSTEMS
CAD/CAM (Digital) COPYING SYSTEMS (Analogous)
Direct Indirect Copy Milling Erosion
Cerec 1
&
Cerec 2
Automill,
DCS-
President,
Cicero,
Denta,
Denti CAD,
Sopha –
Bioconcept
Manual Automatic Sono-
erosion
Spark
–
erosion
Celay Ceramatic
II DCP
DFE
Eroson
ic
DFE
Procer
a

Traditional technique High technology
Data acquisition or
information by impressions
and translated into
articulated stone casts
Data acquisition or
information is captured
electronically, either by a
specialized camera, laser
system, or a miniature
contact digitizer.
Restoration design is the
process of creating the wax
pattern
Restoration design is done by
the computer – either with
interactive help from the user
or automatically.
Restoration fabrication
includes all the procedures
from dewaxing upto the final
casting (lost wax technique)
Restoration fabrication
includes machining with
computer controlled milling
machines, electrical discharge
machining and sintering

IMPRESSION
CAMERA LASER
CONTACT
DIGITIZER
CASTS & DIE
COMPUTERIZED
DESIGN
WAX
PATTERN
INVEST
CAST
MACHINE ELECTRICAL
DISCHARGE
MACHINE
SINTER
Data
acquisition
Restoration
Design
Restoration
fabrication

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:
      Computerized surface digitization
      Computer - aided design
      Computer - assisted manufacturing
      Computer - aided esthetics
      Computer - aided finishing
(The last two stages are more complex and are still being
developed for including in commercial systems).

Computerized surface digitization: 3D-surface digitizing
or scanning methods are separated into :
•     Direct (at the tooth)
• Indirect methods(via impression making & model
fabrication or via pro-inlay)
•     Mechanical
•     Optical sensors

Types of computerized surface digitization techniques:
      Photogrammetry
      Moire
      Laser scanning
      Computerized tomography (CT) scanning
      Magnetic resonance imaging (MRl)
      Ultrasound
      Contact profilometry

Mechanical scannings conducted by a profilometer or
pinpoint sensor are very precise, but have several
shortcomings. Among the various methods of optical
surface scanning, the active (laser) triangulation has been
proven the most suitable, however it requires non-
reflective surfaces for scanning (contact powder coating).
Laser technique and contact digitization are the most
promising approaches from the point of view of cost and
accuracy.

FLOW CHART SHOWING SEQUENTIAL EVENTS OCCURING DURING CAD –
CAM TECHNIQE OF FABRICATING A CERAMIC RESTORATION :
The cavity preparation is scanned stereo-photogrammetrically, using a three-
dimensional miniature video camera
The small microprocessor unit stores the three dimensional pattern depicted
on the screen
The video display serves as a format for the necessary manual construction via
an electric signal
The microprocessor develops the final three-dimensional restoration from the two
dimensional construction
The processing unit automatically deletes data beyond the margins of
the preparation
The electronic information is transferred numerically to the miniature three-axis
milling device
Driven by a water turbine unit, the milling device generates a precision fitting
restoration from a standard ceramic block

CEREC SYSTEM
The CEREC (Ceramic Reconstruction) system ( Siemen/sirna
corp) was 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 :
      A 3-D video camera (scan head)
   An electronic image processor (video processor) with
memory unit (contour memory)
      A digital processor (computer) connected to,
      A miniature milling machine (3-axis machine)www.indiandentalacademy.com

The Optical impression: A small hand held video camera
with a 1-cm wide lens (scanner) when placed over the
occlusal surface of the prepared tooth, emits infrared light
which passes through an internal grid containing a series of
parallel lines. The pattern of light and dark stripes which
falls on the prepared tooth surface is reflected back to the
scanning head and onto a photoreceptor, where its intensity
is recorded as a measure of voltage and transmitted as digital
data to the CAD unit.

Procedure:
•        The prepared and surrounding tooth surfaces are coated
with CEREC powder (L.D. caulk -Ti02 and talc) to eliminate
light reflections and to obtain an opaque reflective surface
(few µm thick only).
•        The hand - held camera is positioned over the prepared
tooth, and an image of the preparation is then simultaneously
projected onto the screen.
•         The camera is adjusted until the image is clear and
properly angulated for all aspects of the prepared tooth to be
visible in complete focus.

• The video search mode enables assessment whether
the camera viewing axis is compatible with the inlay/ onlay
path of insertion. If viewing is acceptable the three
dimensional scanning is triggered by release of the foot
pedal.
• The operator now checks the preparation and its
three-dimensional representation for corrections or
modifications to be made, if necessary. Once the
appropriate optical orientation is generated, the operator can
'freeze-frame' the preparation into a static image.

Designing the Restoration: The proposed restoration is
designed by tracing frame lines on the optical impression
(fixed image) which is projected onto the screen. A cursor
controlled by reverse 'mouse' located on top of the unit is
used to define the limits/boundaries, starting from the
gingival margin and moved along the internal line angles at
intermediate positions commands the computer which draws
a continuos line, through all placed points and displays it on
the screen. The operator can carefully examine, edit and if
necessary, even modify the pattern at any moment in the
procedure. After the margins, walls, proximal contour and
contact as well as the location of marginal ridges are
established, the electronically designed proposed restoration
can be viewed as a 3-dimensional model on the monitor, and
stored automatically on the program disk (floppy).

Milling of the Ceramic restoration: The restoration is
milled (4 – 7minutes) with a diamond wheel from a pre-
manufactured and standardized ceramic block in the milling
chamber of the CAM unit. Factory standardized, preformed
dental porcelain blocks are homogenous and almost pore-
free (Vita Cerec blocks; Dicor-Cerec blocks).

The CAM unit:
A pump system with an attached water reservoir located at
the base of the mobile cart maintains the water pressure
required for the hydraulic driven water turbine in the milling
chamber. During milling about 5 litres of water is cycled
internally which eliminates the need for external water
supply and drainage. The water reservoir system also
contains a microporous filter that traps any of the loosened
diamond particles separated from the wheel for future
retrieval.

Procedure:
       The appropriate ceramic block is selected from a series
consisting of different sizes and shades.
       The ceramic block is mounted on a metal stub (retainer),
inserted into the milling unit and grinding operation is initiated.
       Grinding of the ceramic restoration is done by a diamond-
coated disk/ wheel in conjunction with a high velocity water-spray,
which simultaneously cools and cleans the milling disk. The
restoration is milled from the mesial to the distal proximal surfaces
with the block rotating along its central axis and being steadily
advanced forward during the milling process. In addition, the
diamond wheel not only rotates but also translates up and down over
the porcelain block being milled. A series of steps (200-400) or cuts
are required for milling a ceramic restoration.
    At the end of the milling operation, the completed restoration
falls to the bottom of the chamber from where it can be readily www.indiandentalacademy.com

The computer program associated with the milling process
has additional interesting features such as:
 Before the milling process, the screen displays the
dimensions of the restoration from one proximal surface to
the other in 1/900th
of a mm.
 During the milling operation, the screen continuously
informs the operator of the percentage of the completion.
A continuous readout is displayed concerning the cutting
efficiency of the diamond wheel, thereby indicating the
probable need for replacement.

Clinical shortcoming of Cerec 1 system:
           Although the CEREC system generated all internal
and external aspects of the restoration, the occlusal anatomy
had to be developed by the clinician using a flame-shaped,
fine-particle diamond instrument and conventional porcelain
polishing procedures were required to finalize the restoration.
             Inaccuracy of fit or large interfacial gaps.
    Clinical fracture related to insufficient depth of
preparation.
            Relatively poor esthetics due to the uniform colour
and lack of characterization in the materials used.

Cerec 2 system
The Cerec 2 unit (Siemen/Sirona), based on the process
developed by Morman & Brandestini was introduced in
September 1994, and is the result of constant further development
via different generations of Cerec units to eliminate the previous
limitations.
The maior changes include :
         Enlargement of the grinding unit from 3 axis to 6 axis.
   Upgrading of the software with more sophisticated technology
which allows machining of the occlusal surfaces for the occlusion
and the complex machining of the floor parts.
Other technical innovations of Cerec 2 compared to Cerec 1:
      The improved Cerec 2 camera : new design, easy to handle,
a detachable cover (asepsis/sterilization), reduction in the pixel
size/picture element to improve accuracy and reduce errors.

      Data representation in the image memory and processing
increased by 8 times, while the computing capacity is 6 times
more efficient.
       Magnification factor increased from x8 to x12 for
improved accuracy during measurements.
      Monitor can be swiveled and tilted, thus facilitating visual
control of the video image. Other changes include modification
of foot control, keys and their positions on the keyboard.
      Simultaneous grinding using cylindrical diamonds (2mm
diameter, particle #64um, 77,000rpm and cutting speed 8m/s)
and radial infeed grinding of the grinding disk (6um particle #,
18000rpm and cutting speed 38m/s).

       Extended matching options facilitate grounding of
complex floor shapes in inlays/ onlays. Provides three
different programs for Extrapolation, Correlation and
Veneer.
       Cerec 2 software (cos 4.20) permits custom veneer
preparation and class IV preparations with incisal edge
coverage.
       Improved in rigidity and grinding precision by 24
times.
         Improved accuracy of fit (reduction in inter-facial
gap from 84+38um/ Cerec 1 to 56+27um/ Cerec 2).

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

Ceramic CAD/ CAM restorations are bonded to tooth
structure by :
      Etching for a bond to enamel
      Conditioning, priming and bonding (when appropriate)
      Etching (by HF acid) and priming (silanating)
      Cementing with luting resin.

CAD/CAM restorations (inlay/onlays) are fabricated
primarily from ceramic materials, while subtractive
fabrication of metal alloys or titanium have only been
investigated for crowns, copings and bridges.

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
60O
C/min to 950o
C and held for one minute).
Two classes of machinable ceramics available are:
 Fine-scale feldspathic porcelain
 Glass-ceramics www.indiandentalacademy.com

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.
Cerac 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 opposing tooth.
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).

MGC -F (Corning Inc.) : Machinable glass ceramic developed to
overcome the deficiencies of the Vita Mark II and Dicor MGC. It is
a tetrasilicic mica glass - ceramic with minor compositional and
microstructural changes from Dicor MGC to enhance its
fluorescence and machinability.
Pro CAD (Ivoclar AG, Liechtenstein) : The Pro CAD line
(Professional Computer Assisted Design) is a product package
suitable for all Cerec 2 applications. It is a high-strength optimized,
leucite-reinforced glass ceramic material, available as blocks in
different sizes and in the chromascop shades.
Celay : This material can be used in both copy milling and
CAD/CAM techniques. According to the manufacturer, it is a fine-
grained feldspathic porcelain used to reduce abrasiveness with a
composition identical to that of Cerec Vitablocs Mark II. In
addition, both In-Ceram and Spinell (Vita) are available for
processing in the green state in conjunction with Celay. www.indiandentalacademy.com

Other machinable ceramics being developed include:
      Bioglass (Alldent Corp., Rugell, Liechtenstein)
       DFE -Keramik/Krupp Medizintechnir GmbH, Essen,
Germany; Bioverit / Mikrodenta Corp
      Empress / Vivadent –lvoclar Corp, Schaan, Liectenstein.

Clinical procedures for Cerec CAD/CAM:
Tooth preparation & Optical registration : Simple, box shaped
preparations suffice for the Cerec three-dimensional scanning and
fabrication process. The procedure is not dependent on any cavity
preparation size. Simple and complex proximal preparations for both
inlays and onlays are readily and correctly milled. Undercuts in cavity
walls do not affect the optical scanning and are tilled in with composite
resin during the cementation. Straight walls with right angles are
recommended The 4 to 6 degree divergence required for cast inlays is not
necessary using Cerec system; parallel walls suffice, thereby ensuring
maximal preservation of hard dental tissues. The occlusal and proximal
cavity margins are not beveled. Instead, the cavity walls and enamel edges
are finished using diamond coated finishing stones. The gingival floor is
horizontal or declines between 5 and 15 degrees towards the gingival
margin. The optical scanning is facilitated by having clearly defined walls
and cavity margins and by the use of rubber dam during the optical
scanning and cementation stages. Gingival margins of the preparation
must be made clearly visible by placement of retraction cord, or by use of
electrosurgery incision surgery. www.indiandentalacademy.com

The optical scanning is facilitated by having clearly defined
walls and cavity margins and by the use of rubber dam
during the optical scanning and cementation stages.
Gingival margins of the preparation must be made clearly
visible by placement of retraction cord, or by use of
electrosurgery incision surgery.
Cementation: The small quantities of composite resin
cement required for cementation ensures a thin layer
between the ceramic and the enamel. This thin layer,
together with the microretentive bond within the ceramic
and enamel apparently minimizes the negative aspects of
the polymerization shrinkage and the high thermal
expansion of the cement. Composite resin cements blend
esthetically with porcelain and enamel.

The clinical advantages of the Cerec system:
      The restorations made from prefabricated and optimized,
quality-controlled ceramic porcelain can be placed in one visit.
       Transluency and color of porcelain very closely
approximate the natural hard dental tissues.
       Further, the quality of the ceramic porcelain is not
changed by the variations that may occur during processing in
dental laboratories.
       The prefabricated ceramic is wear resistant. The
optimized structure of the ceramic enables optimal polishability
of the material and low abrasion of the cusp enamel of
thCICERO System


• Porcelain ceramic etching (HF 5% for 60 seconds):
microrentive adhesive bond between porcelain/ceramic and
the bonding agent/composite resin cement.
 Enamel-etching technique (H3PO4 35% for 30
seconds): microretentive adhesive bond between composite
resin cement/bonding agent and enamel.

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 :
      Optical scanning
      Nearly net -shaped metal and ceramic sintering
  Computer-aided crown fabrication techniques. Alloy
sintering eliminates casting and therewith many processing
steps in the fabrication of metal-ceramic restorations.www.indiandentalacademy.com

The unique feature of the Cicero system is that it
produces Crowns, FPD's and inlays with different layers
such as metal and dentin and incisal porcelains, for
maximum strength and esthetics.

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.

Other Digital Systems:

The Duret System (Hanson International):
The Duret CAD-CAM system was developed by Francois
Duret and produced by Sopha (Lyon, France). It was made
of 3 discrete units :
 A camera module
 A CAD module
The milling module.

Optical impression was made using Electro-optical method (a
laser scanner) combining Holography and Moire. The
digitized data from the CAD unit is combined with data
relating to the dynamic movements of jaw which is provided
by a proprietary articulator. called the Access Articulator
linked to the CAD unit. This original Duret system using
highly sophisticated and complex imaging/ designing
procedure was designed primarily to fabricate full crowns.
However, since its introduction, both the original system and
the derivative version The SOPHA system have had limited
commercial success.

The SOPHA System (Sopha Bioconcept, Inc Los Angeles,
CA) was commercially introduced in 1990/91 in France, but
is apparently no longer available.

The REKOW Svstem (Digital Dental System) was
developed by Dr. Diane Rekow at the University of
Minnesota. This system initially used a photogrammetric
method for intraoral surface digitization of the preparation
using a pen digitizer, but later used mechanical - manual
scanning and was marketed for dental laboratory use in
Europe by Bego (Bremen, Germany).

The Denti CAD svstem: Used a miniature mechanical
linkage designed by Foster Miller Inc (Wallham, Mass
USA) (unique robotic arm digitizer) which can be used
both intraoral1y or an traditional models and dies for
tracing the image. The Denti CAD system is capable of
producing restorations from alloys, composites and
ceramics. It uses a unique robotic arm digitizer (a
miniature mechanical linkage), designed by Foster Miller
Inc (Waltham, Mass, U.S.A.) that can be used both
intraorally or traditional models and dies for tracing the
image.

The DUX s stem/The Titan System (DCS groups Dental,
Allschwill, Switzerland) was introduced in 1991 by
DCS/GIM -Alldent. It consists of ;
A miniature contact digitizer (pantograph)
A central computer
A milling unit.
The digitizer consists of a table that shifts a die or model
beneath ~ contact stylus. This system is currently distributed
under the brand name DCS -President (DCS/ Girrbach).

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

       It can construct various types of ceramic restorations.
Hence, can be used as an alternative to metallic restorations
allowing placement of esthetic inlays/onlays in stress bearing
areas of posterior teeth (because of its high resistance to
abrasion, good marginal adaptation and also as an alternative to
complete or full coverage crowns that require extensive tooth
reduction). Half and three-quarter crowns and Cerec veneer
laminates can also be directly placed as easily.
       CAD - CAM device can fabricate a ceramic restoration
such as inlay/ onlay at the chair-side.
      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 .

      Using industrially prefabricated ceramic blanks compared
to that fabricated by the dental technician is the maintenance of
consistently optimally high quality of the material under
industrial conditions controlled by the manufacturer.
      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:
      Limitations in the fabrication of multiple units.
      Inability to characterize shades and translucency.
      Inability to image in a wet environment (incapable of
obtaining an accurate image in the presence of excessive
saliva, water ore blood).
      Incompatibility with other imaging system.
      Extremely expensive and limited availability.
      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.

ANALOGOUS SYSTEMS (COPYING /
PANTOGRAPHY METHODS )
Copy milling
It is the mechanical shaping of an industrially prefabricated
ceramic material, which is consistent in quality and its
mechanical properties (an improvement over conventional
ceramics). Copy milling includes fabrication of a prototype
(pro-inlay or crown) usually via impression making and model
preparation. Based on the model, a replica of inlay / crown is
made and fixed in the copying device and transferred 1: 1 into
the chosen material such as ceramic.

Materials used -The choice of material depends in mostly on
the type of margin required for the restoration. Virtually any
geometry and size can be copy milled as long as there is
direct access of the finger guide and cutting tool to the
surfaces involved. Because titanium has a very high melting
temperature, it is difficult to conveniently cast; however it
can be copy milled easily and inexpensively. Composite and
ceramic materials are most commonly used for copy milling
dental restorations.

Sono erosion -is based on ultrasonic methods. First, metallic
negative moulds (so-called sonotrodes) are produced of the
desired restoration, both from the occlusal as well as from
the basal direction. Both sonotrodes fitting exactly together
in the equational plane of the intended restoration are guided
onto a ceramic blank after connecting to an ultrasonic
generator, under slight pressure. The ceramic blank is
surrounded by an abrasive suspension of hard particles, such
as boron carbide, which are accelerated by ultrasonics, and
thus erode the restoration out of the ceramic blank.

Spark Erosion refers to 'Electrical Discharge Machining'
(EDM) which was used by the tool and die industry during
the 1940's and was adapted into dentistry in 1982. It may
be defined as a metal removal process using a series of
sparks to erode material from a workpiece in a liquid
medium under carefully controlled conditions. The liquid
medium usually, is a light oil called the dielectric fluid. It
functions as an insulator, a conductor and a coolant and
flushes away the particles of metal generated by the
sparks.

Advantages of EDM desirable for dental applications:
•EDM is not affected by metal-hardness because it is a thermal
process.
•Adhesive characteristics of the workpiece do not affect EDM
because it is a non-contact method of removing metal.
•EDM provides a smooth bur-free surface.
•EDM can be used to machine thin objects without distortion
because there are virtually no mechanical forces created.
•EDM can be used to make long, small diameter cuts because
there is little, if any, torque on the electrode to cause breakage.
•EDM is accurate to within 0.0001 inch.
The major disadvantage is the cost of the equipment.

Spark Erosion (SAE) unit (Dental Arts Laboratories, Inc,
Illinois).
A graphite or copper electrode acts as a tool that invades the
piece of base metal and erodes a negative form in the shape of
the electrode. The process is accomplished by lightning like
sparks generated between the electrode and the restoration. The
sparks melt the alloy by heating it to between 3000°C and
5000°C. These sparks remove small amounts of the metal
substrate within microseconds. The entire process takes place
in a dielectric liquid bath that prevents the alloy from burning.
Stress characteristics can be eliminated through the application
of spark erosion before or after the ceramic or acrylic resin
surface is added. The spark erosion method can be applied to
any type of conductible metal/ alloy such as gold, base metal
and titanium. This method of erosion has been named as SAE
Secotec. www.indiandentalacademy.com

CELAY System
The Celay System (Mikrona AG, Spreintenbach, Switzerland)
became first commercially available in 1992. It is a high
precision, manually operated copy milling machine and the
fabrication principle is the same as for 'Key' duplication. This
system was originally. designed and intended for use in the
dental laboratory; however., it may also be used at the
chairside.
Method:
 An impression (silicone) of the prepared tooth is made
and poured in die stone.
 A prototype resin coping of the restoration (prototype)
called 'pro-inlay' (a provisional inlay) is fabricated on the die
using a blue light-cured resin (Celay-Tech, Mikrona
Technologies, AG, Switzerland).

      The cured resin prototype is removed from the die and
fixed on the left side of the relay unit using a special retaining
device (rod shaped).
       A prefabricated ceramic blank (eg-aluminous core
ceramic'In- Ceram') is fixed in the carving chamber on the right
side of the relay unit.
      The reference disk (tracing tool) mechanically traces or
scans the surface of the prototype (pro-inlay).

 Duplicating the movements of the reference disk, the
rough milling disk (a coarse diamond instrument with a grit
size of 126 µm) and a high speed turbine driven by air
pressure, machines the rough contour of the ceramic
restoration by synchronized grinding over 8-axes for
effective bulk reduction. For milling a coping, the lumen of
the coping is scanned and milled with coarse ball and round
tipped diamonds. Both sides of the relay unit are connected
by a geometric transfer mechanism to link the three-
dimensional movement of the tracing device with the
milling device. During the milling process, the milling
chamber is protected with a clear cover and a cooling liquid
(Celcool, Mikrona AG) is sprayed on the blank and on the
instrument.

       Since the rough milling disk is slightly smaller than the
scanning disk, it produces a slightly oversized restoration. The final
contour of the restoration is developed with 64µm grit finishing
diamond instruments.
       To ensure a complete and accurate tracing, the pattern is
coated with contact or indicating powder (Celtouch, Mikrona AG).
This powder is removed on contact with the tracing instruments so
that areas already scanned can be differentiated from un scanned
areas.
      The external surfaces are finished with -disks and the internal
surfaces with round-tipped and sharp/ fine-tipped diamond stones.
       Final fit of the machined inlay/ coping is examined, and
internal discrepancies marked and reworked with repeated scanning
      The internal surface is either acid etched or air-abraded before
silanization and cementation. www.indiandentalacademy.com

By combining the Celay system, with elements of In-Ceram
technology, copy milled glass-infiltrated aluminous core
restorations can be fabricated. In-Ceram or In-Ceram Spinell
materials are machined by Celay and then infiltrated with a
sodium-lanthanum glass in a manner similar to that of
conventional In-Ceram restorations, and finally veneered with
Vitadur Alpha porcelain. The fabrication of copy-milled In-
Ceram crown substructures with the Celay system combines
the positive mechanical properties of glass-infiltrated
aluminous core materials with the advantages of industrially
prefabricated ceramics.

Advantages over conventional In-Ceram technology:
       The processing time is considerably shorter because
die duplication and 10 hour sintering are not necessary.
      Glass infiltration can be performed in a conventional
ceramic furnace in 40 minutes, because of the higher
capillary effect of the industrially sintered alumina blank
(homogenous structure, even particle distribution).
         The industrially prefabricated material also has a
higher flexural strength than the conventional In-Ceram
material.

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.

Porcelain-fused-to-metal restoration : The Procera
System was initially used to fabricate veneered crowns and
fixed partial dentures by combining a titanium substructure
with compatible low-fusing veneering porcelain such as Ti-
Ceram.

Components used: Rods of pre-fabricated cold-worked bars
or solid cylindrical blanks of Commercially pure Titanium
(CpTi) and a low fusing veneering porcelain Ti-Ceram fired
at 750°C.

Procedure: The working time required to fabricate the titanium
coping is about 35 minutes. It requires two procedures :
•Mechanical milling process -external surface of titanium
coping is milled from the cylindrical titanium blank in 5-6
minutes.
•Spark erosion process -The internal configuration of the
titanium coping is developed in about 8 to 10 minutes. The
internal surface of the titanium coping is air abraded (120µm
particles of Al2
O3
) to remove the surface oxide layer
accumulated during the spark erosion process. The external
surface is also air abraded and then veneered with a low-fusing
veneering porcelain compatible with titanium such as Ti-Ceram
in the conventional manner and fired at 750°C.
•This method can also be used for milling implant system
restorations.

Advantages (mainly related to use of titanium) :
•Biocompatibility of titanium - suitable for use mainly in
metal sensitive patients.
•Low-cost of titanium relative to noble metal alternatives.
•Standardization of procedure for fabricating titanium
coping with consistent results.
•Accuracy of fit
•Ti-Ceram is less abrasive than conventional porcelain.

All-ceramic restoration: The Procera system has also been used to
produce an all-ceramic crown known as Procera All Ceram Crown
which is composed of a densely sintered, high-purity (99.9%)
alumina coping combined with a compatible veneering low fusing
porcelain such as All Ceram Porcelain (Ducera).

Other copying systems
 Ceramatic II Svstem (Askim Corp. Sweden): In this system
scanning is performed automatically, and this applies to the DCP
system as well.
 The DFE -system and Erosonic (ESPE Dental Medizin
Corp., Seefeld Germany) both make use of ultrasonic erosion for
the machining of ceramic. For this purpose sonotrodes must be made
in advance as negative forms of the inner and outer contours of the
restoration. www.indiandentalacademy.com

Advantage of milling methods :
•Reducing the labour time needed.
•Single appointment restorations (in a period of 3 to 13
minutes).
•Can be used for both direct and indirect fabrications.

Advantages of Celay system over the Cerec system :
•Celay could recreate all surfaces of a restoration whereas
Cerec I could not make the occlusal surface.
•Celay has the potential to fabricate crowns and short-span
bridges with In-Ceram system (Vita, Germany).

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.
Brief History :
1983 - Sozio & Riley described the use of shrink-free ceramic
coping.
1987 - Hullah & Williams described the formulation of shrink free
ceramics
Shrink-free ceramics were marketed as two generation of materials
under the commercial names :
 Cerestore (Johnson & Johnson. NJ, USA)
 Al-Ceram (Innotek Dental Corp, USA)

CERESTORE Non-Shrink Alumina Ceramic (Coors
Biomedical Co., Lakewood, Colo.) is a 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
Unfired Composition Fired Composition (Core)
A12
O3
(small particles) 43%
A12
O3
(large particle) 17%
MgO 9%
Glass frit 13%
Kaolin Clay 4%
Silicon resin (Binder) 12%
Calcium Stearate 1%
Sterylamide 1%
A12
O3
(Corundum) 60%
MgA12
O4
(Spinel) 22%
BaMg2
A13
(Barium
Osomilite) 10%

Chemistry: The shrink-free ceramic material essentially
consists of Al2
O3
and MgO mixed with a Barium glass frits.
On firing a combination of chemical and crystalline
transformation produces Magnesium aluminate spinel, which
occupies a greater volume than the original mixed oxides
(raw ingredients), and thus compensates for the conventional
firing shrinkage of ceramic.
 Chemical transformation: During firing from 160 °C to
800°C, the silicone resin (binder) converts from SiO to SiO2
which in turn combines with alumina to form
aluminosilicate.
 Crystalline transformation: The primary inorganic
reaction involves MgO, Al2
O3
and the glass frit. The
aluminosilicate formed reacts with the incorporated
magnesia to form spinel, which is also one of the strongest
ceramic oxides.

Alumina (AI2
O3
) + Magnesia (MgO)  Magnesium
Aluminate
Spinel (MgAl2
O4
)
         Al2
O3
  +   MgO                  MgAI2
O4
Density (g/cm3
)         3.9   +    3.58                      3.60
Mol wt(g)        101.96  +  40.31                   142.27
Volume cm3
         25.72  +  11.26 (36.98)        39.52
(Net Volume Increase - 2.54 cm3
)
Net % volume expansion - 6.87%
Net % linear expansion - 2.35%

During firing from 900 to 1300°C, the glass frit takes MgO &
Al2
O3
into solution and subsequently precipitates the spinel
phase which in conjunction with the coarser alumina particles
acts as strengthener in the fired core. The final microstructure
of the core material consists of a multiphased mixed oxide
system of aluminates. Flexural strength is similar to that of the
traditional alumina core.
Fabrication: By Transfer Molding process which is identical to
injection moulding of acrylic resin denture bases. Copings are
formed by transfer-molding the ceramic directly onto non-
shrinking heat stable epoxy master dies
 The wax pattern on the epoxy die is sprued, invested and
burned out. www.indiandentalacademy.com

       The flask is placed on a heating element (oven) and
removed after it reaches the molding temperature.
      Shrink-free ceramic material supplied as dense pellets is
heated until the silicone resin binder is flowable (160°C) and
then transferred by pressure (under a plunger) directly on the
master die. The silicone resin binder is thermoplastic and
thermosetting, hence after injection into the mold and around
the master die, it automatically sets.
      The flask is quenched and the ceramic coping is fired in a
micro-processor controlled furnace (1300°C) to achieve zero-
shrinkage.
      The sintered coping is replaced on the die and veneered
with conventional aluminous porcelain.

Physical properties of First Generation Cerestore Core
Material :
Compressive Strength : 10.48 MN/m2
;
Flexural Strength : 120 MN/m2
Modulus of elasticity : 1.23 x 105MN/m2
Density : 2.9 gm/cm3
Linear coefficient thermal expansion : 5.6xl0-6
/°C
Poison's ratio : 0.23

Advantages :
       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.
      Better accuracy of fit and marginal integrity.
      Esthetics enhanced due to depth of colour due to the lack of
metal coping.
       Biocompatible (inert) and resistant to plaque formation
(glazed surface).
       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).
      Low thermal conductivity; thus reduced thermal sensitivity.
      Low coefficient of thermal expansion and high modulus of
elasticity results in protection of cement seal.

Disadvantages :
      Complexity of the fabrication process.
       Need for specialized laboratory equipment (Transfer
molding process) and high cost.
      Inadequate flexural strength (89MPa) compared to the
metal-ceramic restorations.
       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.). www.indiandentalacademy.com

Advantage second generation Cerestore Core Materials :
      Recrystallization of residual glass - Flexural strength >
22.5 MN/m2
(32,000psi)
       High polycrystalline content - static fatigue potential
comparable to high glass content systems.
      Same relative thermal conductivity of core and veneer
porcelain - Interfacial stress comparable to ceramometal
systems.
      Low coefficient of thermal expansion - Thermal shock
resistance, Interfacial stress.
         High modulus of elasticity - Low stress on cement.

LEUCITE REINFORCED PORCELAINS ( Transfer-molded )
Leucite reinforced porcelains can be broadly divided into two
groups:
      Pressed –
•        IPS Empress & IPS Empress 2 (Ivoclar)
•        Optec Pressable Ceramic / OPC (Jeneric/Pentron)
      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) is a pre-cerammed, pre-
coloured leucite reinforced glass-ceramic formed from the leucite
system (SiO2
-AI2
O3
-K2
0) 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. www.indiandentalacademy.com

Composition : (wt %)
      SiO2
-63%
      Al2
O3
-17.7%
      K2
O -11.2%
      Na2
O -4.6%
      B2
O3
-0.6%
      CeO2
-0.4%
      CaO -1.6%
      BaO -1.6%
      TiO2
-0.2%

It is a type of feldspathic porcelain containing a higher
concentration of leucite crystals, which increases the
resistance to crack propagation.
A special furnace Empress EP500 designed for this system is
capable of high temperatures. The pressing furnace contains
an enlarged heat dome, a pneumatic pressure system, a
reducing valve, and a monometer to control the pressure.
Leucite content
Conventional
Porcelain
Dicor Glass-
ceramic
IPS Empress
Pressable
ceramic
30-35% 50-60% 80-85%

Brief history of the evolution of pressable ceramics :
1936 - A patented heat-press technique was first described for
the construction of ceramic complete dentures.
1969 - Droge described a ceramic press technique based on
the hot-press resin technique. McPhee improved Droge's
technique to produce complete coverage metal-ceramic
restorations that accurately duplicated occlusal surfaces.
1983 - To overcome the disadvantage of additional ceramic
shrinkage during ceramming of castable glass-ceramic, a heat-
pressed technique (Empress) was researched and developed by
Arnold Wohlwend of the Dept. of Fixed and Removable
Prosthodontics and Dental Materials at the University of
Zurich, Zurich, Switzerland. Since 1986, the development has
proceeded in conjunction with a dental company Ivoclar
(Schaan Liechtensein). www.indiandentalacademy.com

Fabrication:
 Lost-wax technique: The wax pattern of the proposed
restoration is invested in a special flask (specially designed
cylindrical crucible former) using IPS Empress special investment
material (phosphate bonded).
 Pressing Procedure : Following burnout (at 850°C) the
crucible former is placed into the base of a specialized automated
furnace (EP 500 Press furnace) that has an alumina plunger. The
ceramic ingot of the selected dentinal shade is placed under the
plunger and the entire assembly is preheated to 1,1000
C (at which
temperature the ceramic plasticizes). When the temperature reaches
11500
C after a 20 minute holding time the plunger presses the
ceramic under vacuum (0.3-0.4 MPa) into the mold, in which it is
held under pneumatic pressure (for a 45-minute period) to allow
complete and accurate fill of the mold.

      Veneering: Shade reproduction may be carried out either by
the :
•  Staining technique : In the staining technique, the selected
dentinal stain is applied and thinned to the desired consistency
with glazing stains before firing and repeated until the necessary
shade is achieved Individual characterization can be achieved
with final stain firing.
• Layering technique : In the layering technique, the dentinal
core is cut back and wash fired. The latter provides an optimum
bond between the dentinal core and layering material. Appropriate
incisal and neutral materials are mixed with IPS Empress build-up
liquid and then applied in thin layers before drying. This is
repeated until the correct shape and shades are achieved. The final
restoration is glazed and fired before polishing is carried out.
Internal crown surfaces can be roughened by etching;  silaned and
bonded to tooth using resin-based luting agents. www.indiandentalacademy.com

Properties : Reported flexural strengths are in the range of 160
to I80MPa. The increase in strength has been attributed to :
      The pressing step which increases the density of leucite
crystals.
       Subsequent heat treatments which initiate growth of
additional leucite crystals.

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

Advantages :
      Lack of metal or an opaque ceramic core
      Moderate flexural strength (120-180MPa range)
      Excellent fit (low-shrinkage ceramic)
      Improved esthetics (translucent, fluorescence)
      Etchable
      Less susceptible to fatigue and stress failure
      Less abrasive to opposing tooth
      Biocompatible material
      Unlike previous glass-ceramic systems IPS Empress does not
require ceramming to initiate the crystalline phase of leucite crystals
(They are formed throughout the various temperature cycles). www.indiandentalacademy.com

Disadvantages :
      Potential to fracture in posterior areas.
      Need for special laboratory equipment such as pressing
oven and die material (expensive)
       Inability to cover the colour of a darkened tooth
preparation or post and core, since the crowns are relatively
translucent.
      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

Uses :
 Full contour restorations (inlays, veneers full crowns)
 Alternately used as a core material, veneered with
conventional feldspathic porcelain (similar to Optec HSP).

Leucite
content
Convention
al
Porcelain
Dicor Glass-
ceramic
IPS Empress
Pressable
ceramic
30-35% 50-60% 80-85%

IPS EMPRESS 2 (Ivoclar) -Second generation of pressable
materials for all-ceramic bridges. It is made from a lithium
disilicate framework with an apatite layered ceramic. The
glass-ceramic ingots are made from lithium silicate glass
crystals with crystal content of more than 60 volume%. The
apatite crystals incorporated are responsible for the improved
optical properties (translucency, light scattering) which
contribute to the unique chameleon effect of leucite glass-
ceramic materials.
IPS Empress 2 is used with special investment material, an
EP500 press furnace and a fully automatic high-tech furnace.
Other applications : Cosmopost and IPS Empress cosmoingot
- core build-up system with the pre-fabricated zircon oxide
root canal posts and the optimally coordinated ingot.

IPS
Empress
IPS Empress 2 (frame work)
Flexural
strength
Upto 150
MPa
> 400 Mpa

Advantages claimed by manufacturer :
      High biocompatibility
      Excellent fracture resistance
      High radiopacity
     Outstanding translucency.

INFILTRATED
CERAMICS

In-Ceram Alumina
In – Ceram In – Ceram Spinell
In – Ceram Zirconia

In-Ceram: Strengthening of porcelain by incorporation of
crystalline material like alumina particles is limited due to the
resultant porosity in the final product. An improved high
aluminous porcelain system termed In-Ceram (Vita
Zahnfabrik, Bad Sackingen, Germany) was developed by a
French scientist and dentist Dr. Michael Sadoun (1980) and
first introduced in France in  1988.
The In-Ceram Crown (Vident) process involves three basic
steps :
      Making an intensely dense core by slip casting of fine
grained alumina particles and  sintering.
      The sintered alumina core is infiltrated with molten glass
to yield a ceramic coping of high density and strength.
 The infiltrated core is veneered with feldspathic
porcelain and fired.

The densely packed alumina crystals limit crack propagation,
while the glass infiltration eliminated residual porosity and
improves flexural strength upto 2-5 times that of glass-ceramic
and feldspathic porcelain.

Composition: In-Ceram ceramic consists of two three-
dimensional interpenetrating phases :
 Alumina/ Al2
03
crystalline (Volume fraction) 99.56 wt%
of with a particle size distribution averaging 3.8µm
 An Infiltration glass lanthanum aluminosilicate with
small amounts of sodium and calcium (Lanthanum-decreases
the viscosity of the glass to assist infiltration and increases its
refractive index to improve translucency). www.indiandentalacademy.com

Fabrication stages :
      Slip casting
      Glass infiltration
      Veneering of core
Slip casting :
A slip is a suspension of fine insoluble particles in a liquid. Slip
casting is the art or science of preparing stable suspensions and
forming ware by building up a solid layer on the surface of a porous
mold that sucks up the liquid phase by means of capillary forces
(Kingery, 1958). Slip casting is an ancient process used to make
common objects such as beer steins, where a much more watery slip
(a dispersion of alumina particles in water) is poured into a porous
split mold (usually Plaster Of Paris). Slip casting was also used for
the fabrication of ceramic tableware. Sadoun (1989) refined the slip
casting technique to produce In-Ceram. www.indiandentalacademy.com

Slip casting for In-Ceram restorations :
      A special ultrasonic device (In-Ceram Vitasonic II) is used
for the preparation of the slip. Liquid (water), fine grained (1-
5um) alumina powder and an additive are combined and stirred
under ultrasonic agitation until a homogenous mass with so-called
rheopex properties (when a liquid mass stiffens under sudden
pressure) is achieved.
       The slip is painted on a special plaster model made of
porous refractory matrix (In-Ceram Special Plaster, Vita
Zahnfabrik) needed to compensate for the sintering shrinkage of
the  slip casting (The slip is applied with an acrylic brush in quick
strokes, so that previously applied masses do not dry).
      As the liquid from the slip cast is absorbed into the die by
capillary action, additional layers are added (0.5 to 0.7mm thick)
causing the porcelain particles to aggregate and condense tightly
forming a dense layer.

       The mass can be cut with a scalpel, so that the
framework is shaped roughly before the first firing.
       The alumina layer is allowed to dry (30 mins), and a
stabilizer is applied to the frame-work, followed by sintering
(10 hour firing cycle of upto 1120 0
C) in a special furnace (In-
Ceramat, Vita Zahnfabrik) to produce an organized
microstructure with 0.3% sintering shrinkage. The sintered
alumina particles in the coping are partially fused at their
grain boundaries, hence the coping is fragile and porous in
nature.
      The plaster shrinks during sintering, so that the sintered
frameworks are easily removed from the die.

Glass – infiltration :
A specially formulated low-fusing glass-infiltrate (lanthanum glass)
powder of appropriate shade and matching thermal expansion is
mixed with distilled water.
The frameworks are set on a platinum-gold foil (Pt-95; Au-5) and
the glass-water slurry is amply applied (to avoid air impactions)
over the external surface of the porous substructure.
The infiltration firing is performed for 4 to 6 hours at 11000
C (in
the In-Ceramat furnace), depending on the size of the restoration
(number of units). The glass infiltrate melts at 800°C and at 1100°C
the molten glass infiltrates / diffuses through the interstitial spaces
of the porus alumina core by capillary action and encapsulates the
fine grain alumina particles. This infiltration firing with glass not
only confers the selected shade to the core, it also increases the
strength of the core to about 20 times its original strength and
flexural strength of upto 446 Mpa have been reported. www.indiandentalacademy.com

Castable Ceramics: A Guide to Dicor Glass-Ceramics

Castable Ceramics: A Guide to Dicor Glass-Ceramics

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