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1. Introduction
Traditional methods for the production of indirect restorations
usually include impression making, die or model making and final
manufacture. Inaccuracies can occur at any stage, and if introduced early
on, may have an exaggerated effect on the final restoration.
- Costs can be high, in terms of clinical and laboratory time and
expertise.
- The costs of producing remake restorations must be borne either
by the dentist or the laboratory.
- Extra chairside time and visits are unwelcome to the patient, who
may find them inconvenient and stressful.
One visit treatment for indirect restorations has been made
possible by technological development which enable distilization and
replication of the complex topography of the tooth surface using
computer-aided design / computer-aided manufacture (CAD/CAM).
Several techniques of varying degrees of sophistication, have
been introduced. The concept common to all the systems is that spatial
information relating to soft or hard tissues may be processed as
numerical data and manipulated by computer. Additionally the
machining or manufacturing system is not material specific.
1

2. Definition:
CAD/CAM systems that can produce dental prosthesis with
robots or computers.
The first report on CAD/CAM, published in 1973, made it clear
that the optical impression technique, or dental CAD/CAM,
encompasses, all methods of analysis including diagnosis and treatment,
working in space, ad developing means of measurement that preferably
optical.
CAD/CAM means manufacturing the prosthesis directly with the
data taken from the patient’s mouth and at the utmost, it means staying
analogical. In short, it is proceeding directly from paste to crown. The
most topical example of a CAD/CAM system in the non-dental world is
copying a drawing or sculpture with a pantograph.
History
CAD/CAM technologies introduced to the dental profession in
1971.
In 1979, Heitlinger and Rodder milled the equivalent of the stone
model used by a dental technician to make the crown, inlay or pontic. In
1980 Moermann and Brandestini took a single picture and milled only
the internal surface of the inlay.
2

3. During the next 5 years, little was heard. The first dental
CAD/CAM prototype was presented at the Ganaciene Conference
(France) in 1983 and the first crown was publicly milled and installed
in a mouth without any laboratory involvement in 1985.
Though 1985 was a decisive year for computer aided dentistry
there was still a long way to go. Several engineers took 2 hours to
operate the first usable system in a dental office. Nevertheless this
demonstration French Congress indicated principles established 14 years
earlier.
Two new names appeared at this time, the Aoki team in Japan
and Diane Rekown at the university of Minnesota.
Dr. Rekow chose a photogrammetric method to acquire the third
dimension and used the principle of the critical tooth for her second and
third steps. It should also be mentioned that Raggie Candill (1988) at the
university of Alabana, started a project aimed in the same direction.
Uses
a) All CAD/CAM systems permit the production of restorations at
the chairside.
b) Eliminate potential inaccuracies associated with the traditional,
multistage production of indirect restoration.
c) Their use also minimizes cross infection.
3

4. General principles of CAD/CAM
All true CAD/CAM systems exhibit there computer-linked
functional components, although the degree of sophistication may differ.
a) A means of data acquisition.
b) Restoration design.
c) Restorative production.
The first stage requires digital data to be collected from the
patient’s mouth this is equivalent to traditional impression taking. The
information may be stored in the form of three-dimensional coordinates
of poils, on the surface of the oral tissues obtained with the aid of an
intraoral camera on physical sensor, resolution depends on the design of
the individual system, but it follow, that a laser beam offers greater
accuracy than a contacting probe, whether in relation to soft tissue, tooth
surface or cavity preparation.
Restoration design even when aided by computer, still relies to a
large extent on the operators clinical knowledge but may be aided by the
availability of digital information from the unprepared dentition and a
library of performs. Future development of artificial intelligence
systems may offer further assistance.
4

5. Commercially available systems:
1) CELAY introduced in 1990
Manually controlled, rather than computer-controlled, the Celay
system (developed by Mikrona Technologie, Spreitenbach, Switzerland)
has two main features.
1. A hand-operated contacting probe that traces the external
contour of an acrylic or wax inlay, previously fabricated
directly in the mouth.
2. A milling arm, following the probe by means of a
pantographic arm with eight degrees of freedom, that cuts
a copy of the ‘pro-inlay’ from a porcelain or glass-ceramic
block.
Both inlays and onlays may be produced using this method.
Manufacturing details:
A wax or resin model of the required restoration is produced by
the clinician at the chairside. The topography of this ‘pro-inlay’ is traced
by a disc-shaped contacting sensor and the information simultaneously
transmitted, via the pantographic arm, to a diamond-coated wheel which
mills a copy restoration from a pre-manufactured ceramic block. The
initial cut is carried out using a relatively coarse (126µm) diamond-
5

6. tipped wheel under liquid coolant. The cut is repeated with a liner wheel
(64µm) to smooth the surface. Fine anatomical detail can be achieved
using conical and cylindrical diamond points.
Points:
a. This is a relatively simple technique for the production of inlays.
b. The accuracy of the final restoration depends on fit of the resin
prototype at the First International Celay Symposium, it was
reported that marginal fit ranged from 50 to 80µm.
The system was first introduced in 1992 in Europe.
A technique for manufacturing crowns using the Celay system,
which allows replication of fitting surfaces, was introduced in 1993:
• A light-cured replica of the crown core is
produced, scanned and milled from a Vita-Celay alumina blank.
• This core is strengthened by the addition of a
colour-matched glass, applied in the form of an aqueous slurry.
2) PROCERA introduced in 1987, designed by Anderson and
developed by Bobelpharma.
The Procera system (Nobelpharma Inc. Goteborg,
Sweden) combined pantographic reproduction with electrical
discharge (spark-erosion) machining. It allows the production of
6

7. titanium copings, which are subsequently veneered with a
compatible porcelain (Ti-Ceram) or composite to form crowns or
bridges, the latter requiring laser welding of the individual titanium
units.
Manufacturing details:
A traditional die is produced from a conventional impression of
the prepared tooth and is placed under the reading head of a
pantograph. A copy of milling device produces several replicas, one
from titanium and two or three more from graphite cylinders. These
dies are used as electrodes in an electro-erosion apparatus to
precisely manufacture the interior fitting contour of a titanium
coping.
Points:
• This is a lengthy, expensive procedure, the
accuracy of which is dependent on the accuracy of the
conventionally produced stone die and the precision of the copy
milling and spark erosion apparatus.
• The outer ceramic contour is formed manually by
traditional porcelain fused-to-metal techniques.
7

8. 3) SOPHA
This sophisticated French system, invented by Duret, allows for
the production of inlays, anterior and posterior crowns and bridges. It
also permits consideration of both static and dynamic occlusal factors.
An impression of the tooth is taken using a lager imaging system and
holography. Information from the light source is then digitized by the
camera, presented on a video display and transferred to a CAD/CAM
program that creates a model of the preparation.
The complex software allows the dentist to access a library of
theoretical teeth, which may be adapted and modified according to the
requirements of the oral situation.
Manufacturing details:
The laser probe scans the tooth and the signal is relayed to the
computer. A final view is taken with the teeth in a selected occlusal
position of reference. The complete set of pictures is displayed on a
high-resolution video screen, and the restoration designed in a series of
stages starting with the fitting surface, then going on to the external and
occlusal surfaces. The CAD system is also linked to a proprietary
articulator (the Access articulator), which provides data related to
dynamic jaw movements.
8

9. Points:
• This procedure is lengthy and very expensive. It
is technique sensitive.
• Marginal accuracy has been reported to range
from 0 to 60µm.
4) CICERO
The Cicero (Computer-integrated crown reconstruction) system
makes use of optical scanning, near net-shaped metal and ceramic
sintering and computer-aided fabrication techniques.
Manufacturing details:
Information is digitized from a gypsum cast, using a fast
laserstripe scanning method. Up to 100,000 surface points may be
recorded per minute. An appropriate tooth is selected from a
collection of generic forms of theoretical teeth in the programme’s
library. Mesial and distal contacts of the proposed restoration are
outlined by the operator on a video screen and the margin of the new
crown adjusted to the preparation. Working, balancing and
protrusive pathways for the new restoration are also computed at this
stage. After interior and exterior tooth surfaces have been defined,
the interfaces between cement and metal, and between dentine and
9

10. incisal porcelains, are delineated. Built into the software is
accommodation for the overall thickness of cement and metal
substructure.
Milling of a pre-formed refractory block is followed by sintering
a thin layer of a gold alloy powder onto the milled surface. The
appropriate dentine shade of fine-grained, leucite reinforced ceramic
in the form of a colloidal vacuum-kneaded paste is cold pressed onto
the metal-covered refractory shape and vacuum fired. The dentine
porcelain is automatically ground back. Enamel porcelain is then
added and the restoration re-fired before final milling of the external
contour. The last step includes individual staining and glazing
5) CEREC
Invented by Mormann and Brandestini and developed by
Siemens, Cerec was introduced to the dental profession in 1987. It is
the most widely investigated and reported CAD/CAM system to
data. The main features comprise an intra-oral camera, an image-
processing unit linked to a viewing screen and a micro milling
machine. The production and placement of inlays and veneers,
milled either from blocks of feldspathic porcelain or from ceramic,
may be accomplished in one visit.
10

11. Manufacturing details:
The cavity is prepared according to precise criteria (e.g. 90°
axio/floor line angle no cavo/surface bevel) determined by the
mechanical limitations of the machining process. The preparation
and abutment teeth are coated with a reflecting powder and a non-
contacting scan head, incorporating a light-emitting diode and lens
system, is positioned over the tooth surfaces. Information relating to
three teeth may be stored at an one time. This system also
incorporates a monitor that displays the preparation data being
processed, permitting visual verification. All pulpal and cervical
borders are manually outlined on the video screen determines the
occlusal and proximal cavosurface margins and the marginal ridge
position.
Inlay fabrication is accomplished with a three axis N/C milling
machine. A liquid-cooled, high-speed turbine powers a diamond bur
that is rigidly attached to a y axis platform.
The restoration tried into the prepared cavity and assessed for
accuracy of fit. Once clinically acceptable the proximal surface is
polished and the fitting surface etched and treated with a silane
coupling agent.
11

12. Points:
• Pulpal floors must be as flat as possible because
any contour irregularities on the pulpal or gingival floors cannot
be reproduced.
• Simultaneous milling by both a milling disc and
a cylindrical diamond bur takes place.
• The additional use of a cylindrical diamond bur
allows the production of restorations that could not have been
machined using the milling disc alone. Therefore, a wider range
of restorations, such as inlays, onlays, partial crowns and veneers,
may be produced at the chairside in this way.
• The process of tracing and recording the
preparation details is relatively easily learned, and could be
delegated to the trained dental surgery assistant.
• One of the main advantages of this system is that
restorations may be produced at the chairside. However, initial
financial outlay may well be prohibitive. Proposed solutions
include leasing or sharing equipment.
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13. 6) DUX
The Dux system, also known as the Titan system (DCS, Dental
Allschwill, Switzerland) consists of a miniature contact digitizer, a
central computer and a milling unit. The manually operated tracing unit,
which is said to have an average accuracy of 3µm, consists of a table
that shifts a die or model beneath a contact stylus. The central computer
converts the three-dimensional model data into a CNC milling
programme. Titanium crown and bridge substructures may be produced
using this technique.
Points:
• Accuracy of the Dux system is claimed to be in
the order of 30 (±20)µm and the milling process takes about 10
minutes.
• This system is also applicable to quality control
and model and tool manufacturing.
7) DENTICAD
The DentiCAD system (BEGO, Bremen, Germany and
DentiCAD, Waltham Mass, USA) consists of a miniature robot arm
digitizer, CAD/CAM software with a facility for fully automated
design and a milling machine. The robot arm can be used either
13

14. intra-orally or indirectly on conventional dies or models. The milling
process is directly controlled by computer.
Points:
This is the most fully automated system, allowing production of
inlays, copings, crowns and bridges. The user needs only to digitize
the required teeth (preparation, opposing and abutment teeth) and the
rest of the procedure is carried out automatically.
8) The Japanese system:
Under the supervision of Professor Tsutsumy, this system has the
three usual CAD/CAM components, i.e. the camera, the CAD and
the NCMT. The system is only at the development stage, but its
inventor, Dr. Fujita, has already produced some crowns with it. No
clinical experience has been reported to date.
9) The Dens system:
Developed by Rohleder and Kammer in Berlin, this system is still
in its early stages of development. However, a prototype was
introduced in Cologne this year. It comprises an optical sensor that is
very fast and a NCMT that can work titanium and was developed to
this end. It has no CAD yet. No clinical experience has been reported
to date.
14

15. 10) The Krupp system:
This system deserves to be mentioned because it fails between
the traditional method and the robot. Made with a special wax, the
prosthesis is used to mould special electrodes that will reproduce the
external and internal surfaces, separated at the line of the most
important contours. The two moulded electrodes are used, as with
the Procera system, to process by electro-erosion non-and semi
precious metals of the Dentitan or Endocast type. It is possible to
produce all-metal pieces like crowns and bridges using this system.
No clinical experience has been reported to date, but the precision
recognized by all who tried it is in the order of 40µm.
Benefits and shortcomings of CAD/CAM
By comparing modern CAD/CAM systems copying techniques
with previous ceramic systems which have been used in a
constructive-modelling way various benefits and shortcomings may
be set against each other.
Advantages and shortcomings of conventional inlays versus
subtractive processing (e.g. CAD/CAM)
15

16. Dental technician subtractive
Preparation (demands)
Choice of materials
Quality of material
Occlusal contouring
Marginal fit
Repeatability
Appointments
System price
Inlay fees
+
++
+
++
+
-
2
-
- -
-
(+)
++
+
(+)
++
1 or 2
- -
-
1. The main disadvantages of CAD/CAM systems specified
repeatedly by practitioners are lower fitting accuracy of the
inlays and insufficient creation of the occlusal surface with
Cerec. Nevertheless investigations of Celay as well as of Cerec 2
show that with exact preparation a precision comparable to
ceramic inlays (order of 50-100µm) can be produced by dental
technicians. Should indistinct preparation margins be present the
dental technician is superior to the CAD/CAM systems
(especially with regard to Cerec). Occlusion may be produced by
means of copying techniques, for example very well with Celay
and also to a high degree with Cerec 2, whereas details like side
fissures cannot be ground with Cerec 2.
16

17. 2. With CAD/CAM systems partial higher demands are made on
the preparation. In order to let a software process run as trouble-
free as possible, for example the automatic detection of the
cavity margins with the edge finder algorithm, an accurate
preparation border is necessary. With subtractive fabrication of
restorations, possibly sharp internal angles of the restoration
cannot be worked out in detail with grinding instruments of a
certain size.
3. Furthermore there were particular limitations with Cerec 1 with
respect to requirements during preparation to produce an inlay.
The grinding wheel limited clinical application in several
situations. Buccal extensions for instance must not become wider
buccally as non-grindable undercuts would have otherwise
occurred. Similar constraints applied to shoulder preparations at
cusp substitution. These limitations no longer exist with Cerec 2
due to the additional cylindrical grinder.
4. Purchasing costs for subtractive systems generally exceed those
for conventional ceramic systems. Laboratory costs for ceramic
inlays made by subtractive techniques is, in Germany however,
mostly slightly less than that for inlays fabricated conventionally
by dental technicians. A Cerec users opinion poll conducted by
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18. the German Association for Restorative Computer-aided
Dentistry revealed that 88 per cent enjoyed working with Cerec.
Currently the enthusiasm of dentists for CAD/CAM plays an
important role in the decision to buy such a unit.
Future Developments
Contouring the occlusal surface
In the last years our research team already presented different
possibilities as to how to create occlusal surfaces via computer. Based
on various situations three different possibilities have been suggested:
 With an existing suitable occlusal surface
(either natural or restored) a scan is taken from the occlusal
surface before preparation and the pictures of the ‘initial state’
and ‘post-cavity preparation’ will be superimposed. The software
necessary for that purpose has already been developed in the
authors department. This option has also been incorporated into
Cerec 2.
 With medium-sized defects with remaining cusp
slopes there is the possibility of reconstructing further trends of
cusp slopes including fissures by means of CAD (Hermite-
Splines) (meanwhile also included with Cerec 2).
18

19.  Extensive defects pose the most difficult
problem. In this case reference to a data bank of different teeth
with average values is required, and adaptation of the occlusal
surface considering the antagonists by means of CAD/CAM
needs-to take place. This technique, however, is still in a stage of
development.
Quality control by error analysis
Once the CAD-calculation of the grinding process and the
geometrical data of the restorations are present, online error analyses can
be conducted. This can provide quality control by warning of potential
problems. For example, if a projected inlay falls below a specified
minimum thickness (depending on the used material) the system is able
to provide a warning that there may be fracture-sensitive marginal areas,
thereby reducing handling errors.
Computer-aided preparation
Another interesting development is at present being pursued at
the University of Frankfurt / Main (Germany) with the CAM-system
(Computer Aided Cavity). Uniquely, the system attempts to take a
picture of the tooth after caries removal and rough cavity preparation
and to plot the cavity borders approximately on the screen. Thereupon a
program calculates the outer contouring of the cavity estimating that a
19

20. certain cylindrical stone is suitable to follow the contouring without
problems. In the next step the preparation diamond with right-angle
handpiece will be fixed in the mouth and the cavity will be completely
prepared, controlled by computer. With respect to the now known
coordinates an inlay may be ground out of ceramic. As many cavity
designs recur in their extensions again and again it may be quite possible
that a few basic designs of inlays can be present and that the computer
prepares a cavity suitable for the inlay and corresponding to the given
defect size. One immediate problem is that an additional loss of tooth
structure may will sometimes be suffered.
Conclusion
The introduction of CAD/CAM in dentistry will influence the
direction of clinical practice and research at universities. Results
achieved must be analyzed with caution, but the extraordinary speed of
development of this technology in industry affirms that it will be rapidly
and definitively accepted in the dental profession. Its future evolution
could be spectacular considering its numerous possibilities.
All these systems offer an alternative to the currently practiced
impressions-die-lost wax-casting technique. Potentially each can save
the dentists time by providing restorations that accurately fit the patient
without requiring chairside adjustments. In addition, they can provide
20

21. more consistency in restorative design and open the possibility of a
array of different restorative materials, including machinable tooth-
colored ceramics.
References:
1) Francois Deret et al : CAD/CAM in dentistry. Journal of
American Dental Association, 1988; 117: 715-721.
2) Diame Rekow : Computer-aided design and manufacturing in
dentistry. A review of the state of the art. Journal of Prosthetic
Dentistry, 1987; 58: 512-516.
3) Cripsin B.J. : Computerised design and manufacturing of
aesthetic dental restorations. Dent. Clin. North Amer., 1992; 36:
797-807.
21

22. CAD-CAM IN DENTISTRY
Contents
• Introduction
• Definition
• History
• Uses
• General principles of CAD/CAM
• Commercially available systems
• Benefits and shortcomings of CAD/CAM
• Future developments
22

23. RETENTION AND RESISTANCE FORM IN FIXED PARTIAL
DENTURES
Introduction
Retention form
a. Magnitude of dislodging forces.
b. Geometry of the tooth preparation.
c. Materials being cemented.
d. Type of luting agent.
e. Film thickness of luting agent.
PATH OF INSERTION
Resistance form
a. Magnitude and direction of dislodging forces.
b. Geometry of tooth preparation.
c. Physical properties of the entity agent.
Enhancement of internal features
a. Pens.
b. Grooves.
c. Box.
23

24. d. Dowel cores.
Crown lengthening procedures.
Cores – in case of attritional or fractured teeth.
Introduction
Teeth do not possess the regenerative ability found in most other tissues.
Therefore, once enamel or dentin is lost as a result of caries, trauma, or
wear, restorative materials must be used to reestablish form and
function. Teeth require preparation to receive restoration and these
preparations must be based on fundamental principles from which basic
criteria can be developed that help predict the success of prosthodontic
treatment. Retention are resistance form are a part of these principles of
tooth preparation and are the property of today’s discussion.
24