CAD CAM – Grow Big !

CAD CAM – Grow Big !

Now say goodbyes to traditional methods for the production of indirect restorations usually include impression making, die or model making and switch to CAD/CAM.

Inaccuracies can occur at any stage, and if introduced early on, may have an exaggerated effect on the final restoration.

Costs can be high with CAD/CAM, 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 enables digitalization and replication of the complex topography of the tooth surface using computer-aided design / computer-aided manufacture (CAD/CAM).

What is a CAD/CAM?

        CAD/CAM systems 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 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 CAD/CAM system in the non-dental world is copying a drawing or sculpture with a pantograph.

Uses of CAD/CAM

a)     With a CAD/CAM system you can produce restorations chairside.

b)    Eliminate potential inaccuracies associated with the traditional, multistage production of a restoration.

c)     CAD/CAM use also minimizes cross infection.

General principles of CAD/CAM

All CAD/CAM systems exhibit three-dimensional computer-linked functional components

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 a 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 the physical sensor, resolution depends on the design of the individual system, but it follows, 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 a computer, still relies to a large extent on the operator’s 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.

Commercially available systems

CELAY

introduced in 1990

Manually controlled, rather than computer-controlled.

Celay system (developed by Mikrona Technologie, Spreitenbach, Switzerland) has two main features –

1.     A hand-operated contacting probe that traces the external contour of 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 puts a copy of the ‘pro-inlay’ from porcelain or glass-ceramic block.

        Both inlays and onlays are 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 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-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

    This is a relatively simple technique for the production of inlays.

   The accuracy of the final restoration depends on the fit of the resin prototype and the marginal fit ranges from 50 to 80µm.

        The system was first introduced in 1992 in Europe.

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 titanium copings, which are subsequently veneered with 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 the milling device produces several replicas, one from titanium and two or three more from graphite cylinders.

These dies are used as electrodes in an electroerosion apparatus to precisely manufacture the interior fitting contour of 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.

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.

Points

        This procedure is lengthy and very expensive. It is technique sensitive.

        Marginal accuracy has been reported to range from 0 to 60µm.

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 laser stripe 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 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

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.

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 a 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 determine 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 but 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.

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.

 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.

 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 intra-orally or indirectly on conventional dies or models.

The milling process is directly controlled by a 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.

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.

The Dennis 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 an NCMT that can work titanium and be developed to this end.

It has no CAD yet.

No clinical experience has been reported to date.

The Krupp system

  This system deserves to be mentioned because it falls between the traditional method and the robot.

Made with a special wax, the prosthesis is used to mold special electrodes that will reproduce the external and internal surfaces, separated at the line of the most important contours.

The two molded 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 of this CAD/CAM 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-modeling way various benefits and shortcomings may be set against each other.

Advantages and shortcomings of conventional versus CAD/CAM

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 even 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.

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 are, in Germany however, mostly slightly less than that for inlays fabricated conventionally by dental technicians.

A Cerec users opinion poll conducted by the German Association for Restorative Computer-aided Dentistry revealed that 88 percent enjoyed working with Cerec.

Use CAD/CAM and run a successful dental practice..

SP



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