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Transcript of 77562247-CAD-CAm
CAD/CAM RESTORATIONS
CAD/CAM RESTORATIONS
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CAD/CAM RESTORATIONS
CONTENTS
INTRODUCTION
HISTORY OF MACHINING SYSTEMS
MACHINING SYSTEMS & THEIR CLINICAL PROCEDURE’S
STAGES OF FABRICATION : COMPUTERIZED SURFACE DIGITIZATION
COMPUTER-AIDED DESIGN
COMPUTER-ASSISTED MANUFACTURING
COMPUTER-AIDED ESTHETICS
COMPUTER-AIDED FINISHING
MACHINABLE CERAMICS
ADVANTAGE OF CAD/ CAM SYSTEMS
DISADVANTAGES OF CAD/ CAM SYSTEMS
ANALOGOUS SYSTEMS (COPYING / PANTOGRAPHY METHODS )
SUMMARY
CONCLUSIONS
BIBLIOGRAPHY
PHOTOGRAPHS
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TERMINOLOGY
CAD-CAM ceramic - a machinable ceramic material formulated for the
production of inlays and crowns through the use of a computer-aided design, computer-
aided machining process.
Castable dental ceramic - a dental ceramic specially formulated to be cast
using a lost-wax process.
Ceramic - a compound of metallic and non-metallic elements.
Ceramic, dental - a compound composed of metals (such as aluminium,
calcium, lithium, magnesium, potassium, sodium, tin, titanium, and zirconium) and
nonmetals (such as silicon, boron, fluoride, and oxygen) that may be used as a single
structural component, such as when used in a CAD-CAM inlay, or as one of several
layers that are used in the fabrication of a ceramic-based prosthesis. Dental ceramics are
formulated to provide one or more of the following properties: castability, mouldability,
injectability, color, opacity, translucency, machinability, abrasion resistance, strength,
and toughness. Note: all porcelains and glass ceramics are ceramics, but not all ceramics
are porcelains or glass-ceramics.
Copy - milling - a process of machining a structure using a device that traces
the surface of a master metal, ceramic, or polymer pattern and transfers the traced spatial
positions to a cutting station where a blank is cut or ground in a manner similar to a key-
cutting procedure.
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Core ceramic - a dental ceramic material that provides a mechanically strong
base onto which a body ceramic (also called dentine or gingival ceramic) can be
veneered.
Feldspathic porcelain - a ceramic composed of a glass matrix phase and one
or more crystal phases. An important crystal phase is leucite (K2O. Al2O3.4SiO2), which is
used to create a high-expansion porcelain that is thermally compatible with gold-based,
palladium-based and nickel-based alloys. A more technically correct name for this class
of dental ceramics is leucite porcelains, because feldspar is not present in the final
processed porcelain nor is it necessary as a raw material to produce leucite crystals.
Glass-ceramic - a solid consisting of a glassy matrix and one or more crystal
phases produced by the controlled nucleation and growth of crystals in the glass.
Glass-ceramic core - the substructure of a restoration, typically made by
casting glass containing a nucleating agent into a mould, divesting the cast structure,
removing the sprue extensions, and ceramming to produce a specific volume fraction of
crystals. If necessary for colour and opacity control, the core may then be veneered with a
specially formulated porcelain or other ceramic at an elevated temperature. An example
is Dicor glass ceramic.
Glass-infiltrated dental ceramic - a minimally sintered Al2O3 or MgAl2O4
core with a void network that has been sealed by the capillary flow of molten glass.
Examples include In-ceram (Al2O3) and In-ceram Spinell (MgAl2O4) core.
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Injection-moulded ceramic - a glass or other ceramic material that is used
to form the ceramic core of an inlay, veneer, or crown by heating and compressing a
heated ceramic into a mold under pressure. An example is IPS Empress.
Porcelain jacket crown (PJC) - one of the first types of all-ceramic crown,
made from a low-strength aluminous core porcelain and veneering porcelain (with
matching thermal contraction coefficient) without the use of a supporting metal substrate
except, in some instances, for a thin platinum foil (see ceramic jacket crown).
Shade guide, ceramic - a series of ceramic tooth-shaped tabs mounted on
metal or plastic strips that is designed for comparison of hue/ value, and chroma
characteristics with those of natural teeth or existing ceramic restorations. The letter and
number code on the metal strip allows the dentist to communicate the perceived
appearance properties to a dental technologist who may not be able to observe the teeth to
be restored.
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INTRODUCTION
Ceramics are thought to be the first material ever made by man. Dental Ceramic
- a compound composed of metals (such as aluminium, calcium, lithium, magnesium,
potassium, sodium, tin, titanium, and zirconium) and nonmetals (such as silicon, boron,
fluoride, and oxygen) that may be used as a single structural component, such as when
used in a CAD-CAM inlay, or as one of several layers that are used in the fabrication of a
ceramic-based prosthesis. Dental ceramics are formulated to provide one or more of the
following properties: castability, mouldability, injectability, color, opacity, translucency,
machinability, abrasion resistance, strength, and toughness. Note: all porcelains and
glass ceramics are ceramics, but not all ceramics are porcelains or glass-ceramics.
They are among the earliest group of inorganic materials to be structurally
modified by man. Although routine use of ceramics in restorative dentistry is a recent
phenomenon, the desire for a durable and esthetic material is ancient. Dental ceramics are
the most natural appearing replacement material for missing tooth substance available in
a range of shades and translucencies to achieve life like results. However, the mechanical
properties and physical properties and the manufacturing technique of so-called
conventional dental ceramics have revealed certain clinical shortcomings i.e. excessive
brittleness, crack propagation, low tensile strength, fracture of the restoration, wear of
antagonists and sintering shrinkage. These shortcomings among other factors have
limited the indications for dental ceramics. However regardless of the advanced state of
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the 300 year old technique of casting each it its steps could induces errors in the final
castings.
Until 1988, indirect ceramic restorations were fabricated by conventional method
(sintering, casting, and pressing) and neither was pore free. Pore free restorations can be
alternately produced by machining blocks of pore free industrial quality ceramics. The
tremendous advances in computers and robotic could also be applied to revolutionize
dentistry and provide both precision and reduce time consumption with the combination
of opto electronics computer technique and sinter technology, the morphologic shape of
the crown 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 face. The introduction of CAD/CAM
systems in later 1980s to restorative dentistry represents a major technological
breakthrough. Its possible to design and fabricate ceramic restorations at single
appointment as opposed to the traditional method of making impressions, fabricating
prosthesis and using a laboratory for development of the restoration. The sophisticated
processing of advanced ceramics for dental restoration lead to the further development of
CAD/CAM technologies. The sophisticated processing of advanced ceramic for dental
restoration lead to the further development of CAD/CAM. The techniques necessitates
digitizing of the prepared teeth or the planned restoration itself and surfacing of the
acquired digital data surface before milling paths can be generated. CAD/CAM offers,
esthetic anterior crowns / bridges, veneers, as well as posterior restorations. In addition,
the use of dental CAD / CAM is supposed to eliminate potential sources of errors in the
craftsmanship of the conventional procedure for the manifesting of restoration. In order
to access the complex free form surfaces to be dealt within dentistry, 3D computers aided
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approaches appears to be most promising. Technical, recent material and clinical
innovation in restorative dentistry has increased the complexity of treatment planning and
decision making. Many of these advances have not replaced, but have augmented a wide
variety of existing materials or treatment protocols, as well as clinical technique and
skills. Dentists today can choose from a variety of ceramic materials in dentistry; hence,
should be familiar with the range of CAD/CAM systems and all-ceramic materials
available for fabrication of CAD/CAM ceramic restorations. This review outlines the
developments in the evolution of CAD/CAM ceramic restorations over the last three
decades and considers the state of the art in the several extended and innovative
applications of dental ceramics.
CAD/CAM is an acronym for Computer Aided Design/ Computer Aided
Manufacturing (or Milling).
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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.
1999- The third generation Cerec 3 (Sirona,Benheim,Germany)
2003- Cerec 3D (Sirona,Benheim,Germany)
Since 1971 a considerable activity in research & development has emerged in the field of
machined restoration/reconstruction at different universities & industrial companies.
Parallel to CEREC, many other types of systems were introduced into the market. They
are CAP, COMET, DENStech, Inlac, Nissan, DCS-Precident & LAVA.
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Application of CAD/ CAM techniques was actively pursued by three
groups of researches
A. Group supported by Henson International of France.
B. Combined group effort between the University of Zurich and Brains,
Brandestini Instruments of Switzerland.
C. 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
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A. Optical impression – Laser scanner
B. Data processing – By Shape recognition software
C. 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
processing - 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
A. Optical impression - Photograph based system using a 35-mm camera with
magnifying lens.
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B. Data processing - 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:
A. Data acquisition
B. Restoration design
C. 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:
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Digital Systems (CAD/ CAM)
Direct
Indirect
Three steps :
1. 3-dimensional surface scanning
2. CAD - Modelling of the restoration
3. Fabrication of the restoration.
Analogous systems (Copying methods)
Copy Milling/ Copy Grinding or Pantography Systems
Two steps:
1. Fabrication of prototype for scanning;
2. Copying and reproducing by milling
Erosive techniques
Sono Erosion
Spark Erosion
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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
Erosonic
DFE Procera
Cerec 3
TRIAD OF FABRICATION
Traditional technique High technology
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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
CONTACT DIGITIZER
LASER
CAMERA
IMPRESSION
DATA
ACQUISITION
CASTS & DIE
COMPUTERIZED DESIGN
WAX PATTERN
RESTORATION
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DESIGN
INVEST
ELECTRICAL DISCHARGE MACHINE
MACHINE
SINTER
Fabrication
CAST
TRADITIONAL LOST – WAX TECHNIQUE CAD / CAM
Creation of a restoration with traditional & CAD/ CAM techniques
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
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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 inclusion
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:
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CAD/CAM RESTORATIONS
1. Photogrammetry
2. Moiré
3. Laser scanning .
4. Computerized tomography (CT) scanning
5. Magnetic resonance imaging (MRI)
6. Ultrasound
7. Contact profilometry
Mechanical scanning conducted by a profilometer or pinpoint sensor is 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 TECHNIQUE 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
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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
The entire process of electronic designing and subsequent milling of a ceramic restoration
requires approximately 10 to 15 minutes.
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Chairside Economical Restoration of Esthetic Ceramics
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CAD/CAM RESTORATIONS
Cerec System
The CEREC (Ceramic Reconstruction) system ( Siemen/sirna corp.) was originally
developed by Brains A.G. 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 :
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• 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)
The Optical impression
A small hand held video camera with a 1cm 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 – TiO2 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.
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• 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 the 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 continuous 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
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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
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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 liters 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.
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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 the 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 or cuts (200-400) 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 retrieved.
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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 an mm.
• During the milling operation, the screen continuously informs the operator of the
percentage of completion.
• A continuous readout is displayed concerning the cutting efficiency of the
diamond wheel, thereby indicating the probable need for replacement.
Clinical shortcomings 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
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CAD/CAM RESTORATIONS
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 major changes include :
• Enlargement of the grinding unit from 3 axes to 6 axes.
• Upgrading of the software with more sophisticated technology which allows
machining of the occlusal surfaces 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.
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• 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 the foot control and the 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 grinding of the grinding
disk (#6um particle, 18000rpm and cutting speed 38m/s).
• Extended machining 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+38µm for Cerec 1
to 56+27µm for 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
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• Pore-free
• 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 :
• Etching the fitting surface for bonding 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 fabrications of metal alloys or titanium have only been
investigated for crowns, copings and bridges.
Machinable Ceramics
The industrially prefabricated ceramic ingots/ blanks used are practically pore-
free which do not require high temperature processing and glazing, hence have a
consistently high quality. The blanks measure approximately 9mm x 9mm x 13mm and
are industrially fabricated using conventional dental porcelain techniques. E.g.: Vitadur
353 N (Vita Zahnfabrik, Bad Sackingen, West Germany) frit powder is mixed with
distilled water, condensed into a 10mm x 10mm x l5mm steel die and fired under vacuum
(the temperature is increased at a rate of 60OC/min to 950oC and held for one minute).
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Two classes of machinable ceramics available are :
• 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.
Cerac Vitabloc Mark II : This is also 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 mica plates are smaller
(average diameter 2µm) 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 (in-vitro study results).
MGC - F (Corning Inc.) : Machinable glass ceramic developed to overcome the
deficiencies of the Vita Mark II and Dicor MGC. It is tetrasilic mica glass-ceramic with
minor compositional and microstructural changes from Dicor MGC to enhance its
fluorescence and machinability.
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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 shades.
Celay : This material can be used in both copy milling and CAD/ CAM techniques.
According to the manufacturer, it is fine-grained feldspathic porcelain used to reduce
abrasiveness with a composition identical to that of Cerec Vitabloc Mark II. In addition,
both In-Ceram and Spinell(Vita) are available for processing in the green state in
conjunction with Celay.
Y-TCP (Yttria Stabilized Tetragonal Circonia Polycrystal): is considered to be the
most successful oxide ceramic for dental-medical application. Outstanding mechanical
features of Y-TCP combined with light color and translucence provide fascinating
possibilities in modern ceramics restoration. The combination of this new material from
firm VITA with SIRONA INLAB SYSTEM opens the futuristic perspectives to its user.
Confirmed CAD/CAM technology breaks the technical limits of up to now applied dental
ceramic restoration in the maximal aesthetic way. Y-TCP confirmed its excellent
biological withstanding by over a 30-year long clinical using for hip joint prosthesis in
human body. After passing the sintering procedure suggested by firm VITA, with 3
points it possesses the density of bending to DIN EN ISO 6872 of more than 900 Mpa,
that is the one of maximal that can be achieved in dental application of ceramics
LAVA
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The Lava all-ceramic system (3M ESPE Dental Products, Seefeld, Germany) also uses a
CAD/CAM procedure, to produce a framework consisting of a Y-TZP-based ceramic
supplemented by a specially designed veneer ceramic.-The frameworks are fabricated
using contemporary CAD/ CAM procedures (scanning, computer-aided framework
design and milling) from presintered Y-TZP blanks .The shade of the core material may
also be stained to correspond with 1 to 7 shades of the Vita Classic shade system
resulting in the ability to develop shading of the restoration which, in turn, may provide
the technician with less of a challenge than when required to mask an opaque white
ceramic or a grey metal core.This may also eliminate the need to veneer the lingual and
gingival aspects of the bridgework connectors.'° In this respect, the Y-TZP core utilized
for the Lava system has been considered to exhibit increased translucency in comparison
with other zinconia-based ceramic core materials. The manufacturers have suggested that
an ideal translucency may be achieved as a result of inherent material properties and a
low wall thickness.
Lava relies on non-contact, photo-optical recording of the surfaces of dies prepared from
an impression of the teeth to be restored.The dies and bite registration are digitized by the
scanner and are viewed three-dimensionally on the computer screen. The bridge or crown
framework may be designed on the computer within the parameters of
the system, which set the thickness of the framework and the square area (9 mm') of
bridge connectors. Pontic designs are retrieved from a library of designs held by the
computer system. It could be considered that the solely computer-aided design is an
advantage over other systems which require the technician to make a wax build-up.
Long-term clinical data on restorations formed in Lava are not yet available, but
communication with a laboratory producing large numbers of Lava frameworks in the
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UK have not indicated any problems, such as fracture of the framework (Littlejohn L,
personal communication, August 2005). Laboratory experimentation by Sorensen with
the Lava system for CAD/CAM production of highstrength precision fixed
prosthodontics" has demonstrated excellent marginal fit of Lava bridges, while results of
a series of laboratory experiments carried out on Lava discs by Curtis and co-workerS14"
have indicated that Lava does not lose strength in moist condition,its not adversely
affected by grinding by a 20-40 pm bur with water coolant,Following surface loading at
simulated masticatory loads flexural strength is not affected and the possibility of
inducing a transformation toughening mechanism (counteracting crack propagation) may
have been identified.
These are promising results, indicating that Lava does not suffer from a common problem
with dental ceramics, namely, the adverse effect of oral fluids on their strength. For the
clinician, these data show that, if adjustment of the framework is required, this should be
carried out using a fine bur with water coolant.
At the time of writing, three Lava milling centres are in operation in the UK, while other
countries with a number
of milling centres include the USA, Italy and Germany. Technicians wishing to utilize the
Lava system for construction of bridge or crown frameworks cast dies in the conventional
manner, prior to sending these to the milling centre.
Other machinable ceramics being developed include :
• Bioglass (Alldent Corp., Rugell, Liechtenstein)
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CAD/CAM RESTORATIONS
• DFE (Keramik/Krupp Medizintechnir, 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
filled in with composite resin during the cementation. Straight walls with right angles are
recommended The 4-6 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 5-15 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 the
placement of retraction cord, or by use of electrosurgery/ incision surgery.
Cementation
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CAD/CAM RESTORATIONS
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 the 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.
• Translucency and colour of porcelain very closely approximate the natural dental
hard 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
opposing tooth. A tight marginal fit is provided by the adhesive system used
between the etched ceramic porcelain and enamel surfaces. The essential
measures are:
• Porcelain ceramic etching (HF 5% for 60 seconds): microretentive 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
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CAD/CAM RESTORATIONS
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 FPDs. 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.
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 Measuring Technique, Steinbichler Optotechnik, 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.
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CAD/CAM RESTORATIONS
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 )
It was commercially introduced in 1990/ 91 in France, but is apparently no longer
available.
The REKOW System (Digital Dental System)
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CAD/CAM RESTORATIONS
It 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 system
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 on traditional models and dies for tracing the image.
The DUX’s system/ The Titan System (DCS groups Dental, Allschwill, Switzerland)
were 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 the contact
stylus. This system is currently distributed under the brand name DCS -President (DCS/
Girrbach).
Advantage of CAD/ CAM(Cerec system) over other systems :
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CAD/CAM RESTORATIONS
• Eliminates the procedures like 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.
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CAD/CAM RESTORATIONS
• Using industrially prefabricated ceramic blanks compared to those 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 be easily 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 or blood).
• Incompatibility with other imaging systems.
• 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.
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CAD/CAM RESTORATIONS
• 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 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.
Erosion methods
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CAD/CAM RESTORATIONS
It needs a copy-suitable pre-version (e.g.: pro-inlay) in the form of a negative
model of the interior and exterior contour of the restoration for its fabrication. The
(metal-based) negative form is prepared either by wax molding and casting or by
intensive copper plating of the impression.
• Sono erosion - for ceramic restorations
• Spark erosion - for metal restorations
Sono erosion
It is based on ultrasonic methods. First, metallic negative moulds (so-called
sonotrodes) of the desired restoration are produced, 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
It 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
work piece 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.
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CAD/CAM RESTORATIONS
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.
The 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
lightening 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.
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CAD/CAM RESTORATIONS
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-axis for effective bulk reduction. For milling a
coping, the lumen of the coping is scanned and milled with coarse ball and round
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CAD/CAM RESTORATIONS
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,
Switzerland) 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, Switzerland). This powder is removed
on contact with the tracing instruments so that areas already scanned can be
differentiated from the 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 are
marked and reworked with repeated scanning.
• The internal surface is either acid-etched or air-abraded before silanization and
cementation.
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
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CAD/CAM RESTORATIONS
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.
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CAD/CAM RESTORATIONS
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 a 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).
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CAD/CAM RESTORATIONS
• 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
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 8-10 minutes. The internal surface of the titanium coping is air
abraded (120μm particles of Al2O3) 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.
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CAD/CAM 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 restorations
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)
They 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.
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CAD/CAM RESTORATIONS
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).
SUMMARY
Ceramic materials have been used in dentistry for well over 200 years. They are
the most biocompatible dental restorative materials, because they are chemically very
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CAD/CAM RESTORATIONS
stable. A desirable feature of ceramics is that their appearance can be customized to
simulate the colour, translucency and flourescence of natural teeth. A major problem with
the use of ceramics as tooth replacement materials is their very low fracture toughness,
and the fact that fracture occurs at a very low strain of about 0.1%. In other words, the
ceramic structure only exhibits a very low flexibility before fracture. Another problem is
that if the ceramic structure is formed by the condensation and sintering of fine frit
particles, fusion is accompanied by a relatively large firing shrinkage. Newer ceramic
materials and innovative ceramic processing techniques have been introduced in
restorative dentistry since the early 1980’s. Some of these ceramics still share roots with
research that originated in Europe in the 18th century. Today as in the era of Nicholas
Dubois De Chemant,most advances are derived from collaborations with the ceramics
engineering community. Notable recent progress includes; the advent of predictable
ceramic materials and techniques for esthetic complete crowns, partial coverage and
laminate veneer restorations; improved metal ceramic esthetics with the advent of
opalescent porcelains and framework modifications; introduction of CAD/CAM and
machining as a route to fabrication of restorations; improved understanding of the clinical
response of all ceramic prostheses and of the material factors that influence clinical
longevity. Strong scientific and collaborative foundations presently exist for continued
development and improvement of ceramic systems by increasingly well-informed teams
of researchers and dentists.
No currently available restorative system can be considered the ideal replacement
for natural tooth structure. However, in recent years there has been a great amount of
attention given to research on and development of ceramic systems for restorative use.
Ceramics are playing an increasingly important role in restorative dentistry, and further
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CAD/CAM RESTORATIONS
improvements in fracture resistance and wear properties will no doubt enhance their
restorative use. The demand for esthetic dentistry is expected to continue and will be
influencial in determining the range of the products available.
In the future we expect to see dramatic improvements by the turn of the century,
not only in esthetic dental materials, but also the techniques of using these materials. The
creativity and artistic skill of the dental ceramists will be paramount in creating a realistic
illusion using these technologies. High technology will continue to improve the way we
diagnose and design treatment plans for patients with esthetic dental concerns. As high-
tech costs diminish, more dentists will introduce these technologies into their practices to
meet the ever increasing demand.
CONCLUSION
The aim of restorative and esthetic dentistry is to restore the decayed or missing
part of the teeth with a bio-compatible material that matches natural enamel in
appearance and physical characteristics and maintain occlusal anatomy to promote proper
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CAD/CAM RESTORATIONS
oral function. Dental ceramic technology is one of the fastest growing areas of dental
material research and development. The past decades have seen the development of
several new groups of ceramics.
The diversity of dental ceramics continues to stimulate laboratory and clinical
research. Systems such as Dicor and Empress are now established, and data regarding the
in vitro and in vivo performance of such restorations have been reported widely.
Modifications to several systems have been suggested or introduced to overcome certain
disadvantages. The potential of the In-Ceram system, remains to be exploited to the full.
The diversity and sophistication of some of the CAD-CAM systems may prove to be
influential in the future.
Each system has its own merits, but may also have shortcomings. Combinations
of materials and techniques are beginning to emerge which aim to exploit the best
features of each. Glass-ceramic and glass-infiltrated alumina blocks for CAD-CAM
restoration production are examples of these and it is anticipated that this trend is likely
to continue….
BIBLIOGRAPHY
Text Book References
1. John. W. McLean - The Science & Art of Dental Ceramics, Vol. I; Quintessence
- 1979.
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2. John W. McLean - Science and Art of Dental Ceramics (Bridge Design & Lab
procedures), Vol II. Quintessence - 1980.
3. Jack. D. Preston - Perspectives in Dental Ceramics; Quintessence - 1985.
4. G.J. Chiche, Alain Pinault - Essentials of Dental Ceramics - 1988.
5. J. F. Roulet, S. Herder - Bonded Ceramic Inlays; Quintessence - 1991.
6. Barry G. Dale, Kenneth W. Ascheim - Esthetic Dentistry - 1993.
7. R. G. Craig - Restorative Dental Materials 9th ed. - 1993.
8. Ralph W. Phillips - Skinner's Science of Dental Materials 9th ed. - 1994.
9. Sturdevant C, M. Roberson, T. M. Heymann H.O., Sturdevant j.r. - The art
and Science of Operative Dentistry, 3rd ed. - 1995.
10. H. T. Shillingberg - Fundamentals of Fixed Prosthodontics ; 3rd edition - 1997.
11. William F. P. Malone, David L. Koth - Tylman's theory and Practice of Fixed
Prosthodontics, 8th ed., St Louis - 1997.
Journal References
1. Council on Dental Material, Instruments and Equipment (ADA Report) –
Recent developments in materials and processes for ceramic crowns - JADA
1985;10(4):548-9.
2. Dianne Rekow - Computer-aided design and manufacturing in dentistry : A
review of the state of the art - JPD 1987; 58(4):512-6.
3. K. A. Malament - The Cast Glass - Ceramic restoration – JPD I987;57(6):674-
83.
4. F. Duret, Blouin, B. Duret - CAD-CAM in dentistry - JADA 1988;117:715-22.
5. John. W. McLean - Ceramics in clinical dentistry - BDJ 1988; Mar19:187-94.
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6. Karl. F. Leinfelder, Barry P. Isenberg, Milton E. Essig - A new method for
generating ceramic restorations : a CAD-CAM system - JADA 1989;118:703-7.
7. W.H.Mormann, M. Brandestini, F. Lutz, F. Barbakow - Chairside Computer-
aided direct ceramic inlays - Q Int 1989;20(5):329-39.
8. J. E. Qualtrough, N. H. F. Wilson, G.A. Smith, - The Porcelain Inlay: A
Historical View - Op Dent 1990;15:61-70.
9. Rill G. Banks - Conservative posterior ceramic restorations - A literature review
– JPD 1990;63(6):619-26.
10. E. Dianne Rekow - Dental CAD-CAM Systems : what is the state of the art? –
JADA 1991;122:43-8.
11. S. O. Hondrum - A review of the strength properties of dental ceramics – JPD
1992;67(6):859-65.
12. N. B. Van Roekel - Electrical Discharge Machining in Dentistry – IJP
1992;5(2):114-21.
13. E. Dianne Rekow - High-Technology Innovations and Limitations For
Restorative Dentistry. – DCNA 1993;37(3):521-24.
14. Heiner Weber, Gerd Frank - Spark erosion procedure : A method for extensive
combined fixed and removable prosthodontic care – JPD 1993;69(2):222-27.
15. Kenneth J. Anusavice - Recent Developments in Restorative Dental Ceramics –
JADA 1993;124:72-84.
16. M. Vander Zel – Ceramic-fused-to-metal restorations with a new CAD/ CAM
system - Q Int. 1993;24(11):769-78.
17. K. Kawai, M. Hayashi, M. Torii, Y. Tsuchitani -Marginal Adaptability and Fit
of Ceramic Milled Inlays - JADA 1995;126:1414-9.
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18. H. O. Heymann, S. C. Bayne, J. R. Sturdevant, A. D. Wilder Jr, T. M.
Roberson –The Clinical performance of CAD-CAM generated ceramic inlays (A
four-year study) - JADA 1996;127:1171-4.
19. J. Robert Kelly, I. Nishimura, S. D. Campbell - Ceramics in dentistry :
Historical roots and current perspectives - JPD 1996;75(1):18-32.
20. M. Andersson, L. Carlsson, M. Persson, B. Bergman - Accuracy of machine
milling and spark erosion with a CAD/ CAM system – JPD 1996;76(2):187-93.
21. Sven Rinke, A. Huls - Copy-milled aluminous core ceramic crowns : A Clinical
report. - JPD 1996;76(4):343-6.
22. W. H. Mormann, A. Bindl - The new creativity in ceramic restorations : Dental
CAD-CAM - Q. Int. 1996;27(12):821-8.
23. Marc.A.Rosenblum, Allan.Schulman - A Review of All-Ceramic Restorations.
– JADA 1997;128:297-307.
24. R. Hickel, W. Dasch, A. Mehl, L. Kremers - CAD-CAM: Fillings of the future?
- IDJ 1997;47(5):247-58.
25. Irfan Ahmad - Yttrium-Partially Stabilized Zirconium Dioxide Posts : An
approach to Restoring Coronally Compromised Non-vital Teeth - Int. J.
Periodont. Rest. Dent. 1998;18(5):455-65.
26. Derek. W.Jones - A brief Overview of Dental Ceramics - J. Can.Dent Assoc
1998;64(9):648-50 & Dental Abstracts 1999;44(2):61.
27. P.Ottl, A. Piwowarczyk, Hans Chritoph Laue, E. A. Hegenbarth - The
Procera All-Ceram System - Int. J. Periodont. Rest. Dent. 2000;20(2):151-5
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