Computer Aided Design and Manufacturing (CAD/CAM)
Introduction :
The single prosthesis fixed alone or on implant is the area in which impression taking and machining remain the most used, two things that today the advent of digital technology has considerably modified their stages and the processes of the development of dental prostheses.
Many things have changed since François Duret’s research on optical imprinting, and in fact; the invention of CAD/CAM in Dentistry.
To fully understand the developments in dental CAD/CAM, you need to know how it works.
I: Reminder of the fixed single prosthesis (crowns):
The single fixed prosthesis can have two types of support pillar: a natural dental pillar or an artificial implant pillar. This depends on whether a natural or artificial root (implant) is used as the basic support.
Crowns are fixed prostheses, as opposed to removable. They are prosthetic pieces that will cover the coronal part of the tooth to restore the aesthetic and functional morphology.
They can be single or multiple (in the case of bridge prostheses) and can be made on the dental tissue remaining after preparation or on a false metal or ceramic prosthetic stump.
We speak of a fixed prosthesis because the crown will be secured to the tooth or the false stump by sealing or bonding (or screwing in the case of a prosthesis on an implant).
Different materials can be used to make a crown, depending on the material used an aesthetic gradient will be proposed to the patient and by association an economic gradient:
Cast crowns (CC) : the least aesthetic and therefore the least expensive, they are made by casting a molten semi-precious alloy. Previously, gold was used for this type of crown, today, given the cost of gold, an alloy such as Nickel Chrome or Cobalt Chrome will be preferred (in the case of Nickel allergy)
Mixed crowns : they combine two materials, a support material (alloy or metal) and an aesthetic cosmetic material (ceramic), we distinguish:
Vestibular Inlay Crowns (CIV) , only the vestibular face is covered with a resin shell (old) or ceramic. They are an aesthetic/cost compromise, they should still be avoided in the mandible where only the metal part will be visible.
Ceramic-Metal Crowns (CCM) , a cast coping completely covers the dental surface or the false stump, on this coping is added the cosmetic ceramic. The crown is more aesthetic than a CIV because only a lingual/palatal metal band can be visible, the rest is cosmetic. It is therefore more expensive than a CIV.
Ceramic-Ceramic Crowns (CCC) : they are entirely composed of ceramic, the coping in very resistant ceramic (most often Zirconia) and the more aesthetic cosmetic part on top. These are the most aesthetic but the most expensive.
Whatever the type of crown placed, only the aesthetic gradient is likely to vary, like any reconstruction placed in the mouth, the crown must restore function and meet the bio-functional requirements of the oral cavity.
II: CONCEPT ON CAD/CAM
Definition :
The acronym CFAO is the abbreviation for Computer Aided Design and Manufacturing,
In English CAD/CAM (Computer-Aided Design/Manufacturing)
This acronym is used to designate the combination
CAD (Computer Aided Design )
and FAO (Computer Aided Manufacturing), which consists of the use of digital tools in the service of the digital chain ranging from modeling to the manufacturing of prostheses
This technology used both in the laboratory and in the dental office can be applied to inlays, onlays, veneers, inlay-cores, fixed prostheses (single and multiple), fixed prostheses on implants (glued or screwed).
For each family, the manufacturing processes differ but the digital processes remain essentially the same.
Computer Aided Design and Manufacturing (CAD/CAM)
Figure 2: Part of the CAD/CAM museum (the first known Hennson system)
Materials used in dental CAD/CAM:
Figure 3: Materials machinable by dental CAD/CAM
The materials available are more numerous than those offered by the traditional method, and the most frequently used in conventional prosthetics are accessible to CAD/CAM, however, not all current CAM systems on the market provide access to all materials.
1-metals:
Metals are either machined from blocks or discs or shaped by
Laser techniques, in CAD/CAM, titanium and Cobalt-Chromium are the most used.
2-ceramics :
In fact, it is for ceramics that CAD/CAM has provided the maximum research, especially by developing high-resistance ceramics.
All ceramic prostheses must first and foremost meet certain standards, such as
ISO 6872 standard.
Ceramics usable for CAD/CAM depending on the chemical nature of their crystalline phase:
2.1 Feldspathic ceramics:
Figure 5: Feldspathic ceramic plot for machining with transparent view of the future
Prosthesis.
This type of ceramic is indicated for the manufacture of single crowns in the anterior sector.
2.2 Glass-ceramics: These blocks are used for anterior single crowns on pulped teeth.
Figure 6: Glass-ceramic pads for machining.
2.3. Infiltrated ceramics:
2.3.1 IN CERAM SPINELL(MgAL2O4)
It is a highly translucent ceramic, with excellent optical properties for very bright anterior teeth.
2.3.2 IN CERAM ALUINA (AL203)
This ceramic is mainly used for the creation of infrastructures for single crowns.
2.3.3 IN CERAM ZIRCONIA (33% Zr and 66% alumina)
It is mainly used to hide a colored support, or for example an inlay-core, or in the case where the mechanical properties must be reinforced (posterior unit infrastructures, small bridges).
2.4 Polycrystalline ceramics:
This is the perfect example of materials that were not accessible before the advent of CAD/CAM. In this category, we distinguish Alumina and Zirconia.
2.4.1 PURE ALUMINA
These are blocks of pre-sintered pure alumina.
It is used for single crowns and small bridges.
2.4.2 PURE ZIRCONIA: ZrSiO4
– ZIRCONIA TZ
Examples of zirconia prosthetic parts obtained by CAD/CAM from a block.
-THE HIP ZIRCONIA
It is said to be pure: its zirconia content is at least 93.6%.
3-composites:
Composite resin materials were traditionally used in direct chairside restorations with the limitation of their posterior use being their low strength. In recent years, significant progress has been made in improving their properties allowing their use in posterior molar sectors.
With the development of CAD/CAM, their indications have been expanded from a direct restorative material to a machinable material in the form of a composite block for the manufacture of indirect prosthetic parts such as veneers, inlays, onlays and crowns.
How dental CAD/CAM works:
1.1 General principles of dental CAD/CAM
Dental CAD/CAM consists of three steps:
• The imprint:
1◦ conventional prints:
You should know that if you want to use CAD/CAM, you can make a conventional print but you will have to combine this technique with a digital print at a later stage (often a table scanner).
2 ◦ digital fingerprints :
optical digital fingerprints:
• intra-oral
• table scanner: the aim is to scan a plaster model or a conventional impression
mechanical digital impressions: probes
• Computer Aided Design CAD : The software receives the impression of the preparation, either in open file format (STL), or in closed file format, specific to the brand used. Its purpose is to model the future prosthesis (inlay, crown, bridge, etc.) using CAD software and taking into account several parameters: occlusion, contact points with adjacent teeth, available prosthetic height, choice of material, etc.
• Computer Aided Manufacturing (CAM) : The file containing the modeled prosthetic part is sent to the machine tool which can manufacture it in different ways: by subtraction or by addition.
1.2 Computer Aided Design, concepts of open and closed systems:
– free format: this is the STL format which means StereoLithography or Surface Tesselation
Language. This file format can be used universally by different CAD software. We therefore speak of an open system.
– proprietary format: the file can then only be used by software of the same brand as the intraoral camera. We are therefore talking about a closed system.
But it is sometimes possible to buy additional software, allowing to convert these proprietary files into STL format (as for the CEREC system with the SIRONA Connect software allowing to open the files). We will therefore speak of a “semi-open” system.
The functionalities of CAD software are generally similar: it is possible to modify the shape of the future prosthesis, to enlarge and change the orientation of the virtual model, to trace the limits of the preparations, to adjust the occlusal contact points and those with adjacent teeth, to estimate the thickness of the prosthetic material.
CAD of a prosthesis according to Zheng et al. (2011)
1.3 Computer Aided Manufacturing:
After having modeled the future prosthetic part using CAD software, it must now be manufactured. For this, there are different techniques: either subtractive methods or additive methods. We will present how each of the techniques works.
1.3.1. Subtractive method: Machining
Subtraction manufacturing techniques work on a simple principle: a block of material is machined by a machine tool. This has several axes on which cutters are fixed, allowing the desired part to be shaped. In our field, the number of axes varies from 3 to 5.
The more axes a machine tool has, the faster it will be because several types of cutters will be able to machine the block of material. This is why 3-axis machine tools are capable of machining crowns, simple bars, bridges and copings. 4-axis machine tools can machine implant abutments, in addition to all the other elements previously mentioned. 5-axis machines can also machine complex prosthetic parts and several implant abutments at the same time.
The materials that can be machined by these machine tools are numerous: alumina, zirconia, glass-ceramic, cobalt-chrome, titanium, resins, wax, etc.
This allows rapid manufacturing of prosthetic parts, with very satisfactory precision.
1.3.2. Additive methods:
Additive manufacturing consists of shaping an object by adding material by stacking successive layers (unlike machining, which shapes an object by removing material). In this case, we speak of “direct manufacturing” because a part is formed directly from its 3D digital representation, without going through a mold or machining a block.
There are several additive manufacturing methods:
a. 3D printers:
They allow modeling by selective deposition in multiple jets of a wax hardened by heating or of a liquid photosensitive resin hardened by UV polymerization.
-b. Stereolithography:
It consists of modeling by selective UV polymerization of a wax/photosensitive liquid resin mixture contained in a tank.
-c. Microfusion (or Laser Sintering):
The process consists of melting the powder according to the geometric parameters defined from the CAD file, then the melted powder is solidified quickly forming beads of solid material. This technique is today the most suitable for the manufacture of hard metal frames and chassis, because it is faster and more cost-effective than the casting or machining process.
The indications for these manufacturing methods are numerous: they can be used to manufacture temporary prostheses (in wax or resin) as well as to manufacture permanent prostheses (in metal, composite, ceramic, etc.). The major advantage of these techniques is the possibility of manufacturing a multitude of shapes, allowing the prosthetic part to adapt perfectly.
1.4. The different digital channels:
1. “Direct”, “semi-direct” or “indirect” CAD/CAM:
In direct CAD/CAM
The practitioner performs the restoration in the office and in a single session. The intra-oral optical impression is processed on site, by the practitioner who also performs the restoration on site, using a numerically controlled machining unit. Since this technique only allows full-mass machining of ceramic or synthetic material blocks, the practitioner’s machine manufactures inlays, onlays, ceramic veneers, single crowns or bridges using the direct method.
Crown design:
. Digital design requires having dedicated software, as well as being equipped with a machining center. The prosthetic offer is a little more limited than in the case of semi-direct CAD/CAM. But nothing prevents the practitioner from sending the optical impression to the prosthetic laboratory (via the Internet) and thus delegating all or part of the modeling and manufacturing phase to it. This work can be very easily carried out in a short time and with qualitative results equivalent and sometimes superior to those obtained in the laboratory using conventional techniques.
In semi-direct CAD/CAM , the optical impression recorded by the practitioner is sent via the Internet to a laboratory or a partner machining center.
Computer Aided Design and Manufacturing (CAD/CAM)
Digitalization of the clinical situation in the dental office using an intraoral optical impression camera. The practitioner takes an optical impression in the office, checks it and sends the file with his order to the prosthetist by sending a digital file. The laboratory will design the prosthetic element digitally from the optical impression, then it will machine the part and finish it. All the practitioner will have to do is place the prosthetic element.
In indirect CAD/CAM :
Laboratories can be equipped with a CAD or CAM system or both CAD/CAM. In the first case, the laboratory will scan the plaster model and develop the prosthetic part that it will send to a CAM machining laboratory that will produce the part in a non-exhaustive choice of materials: feldspar ceramic, zirconia, titanium, hybrid ceramic, cobalt chrome, etc.
Indirect CAD/CAM chain
In the case where the laboratory is equipped with a CAD/CAM system: it will scan the plaster model or use a digital impression made in the dental office. It will design a prosthetic part assisted by computer and modeling software. It will then machine this part most often in zirconia. “Full zirconia”: consists of the production of a prosthesis entirely in zirconia, particularly solid, perfectly indicated in the posterior sector for single elements and bridges.
Zirconia ceramics: the prosthetist creates a zirconia framework, always computer-assisted; this part will be machined from a zirconia disc and after sintering, the prosthetist will finish the prosthesis using a conventional ceramic technique. This technique allows the creation of very aesthetic prostheses and is therefore particularly suitable for previous creations. For the digitization of plaster models, there are different types of scanner: by light scanning or by successive taking of shots.
The contribution of the CFAO chain in daily practice:
Computer Aided Design and Manufacturing (CAD/CAM)
Table. 1.4. Comparative table of the steps between the different CAD/CAM methods compared to the classical method; in red, the laboratory steps
CAD/CAM throughout its process (optical impression, CAD, CAM) tends to reduce the risk of inaccuracies and offers numerous advantages:
At the level of the intraoral optical impression:
– patient and practitioner comfort
– refrain from imprint materials, their storage (indirect imprecision linked to the environment), their disinfection, their dimensional variations and errors linked to their handling
– analysis (enlargement) and possibilities of correction of the preparation during the impression thanks to the unitary virtual model
– start of the digital prosthetic chain from the impression in direct and semi-direct technique
– precision of the imprint and storage of digital data in an archivable and unalterable manner (no dimensional variations)
– short duration of 2 to 5 min
– sending data possible, quickly and easily via the Internet.
– can facilitate color taking, when it has an integrated spectrocolorimeter
– possible use in the implant field, directly on the healing abutment, or in
using a specific system on the implant head (scanbody)
Scanner contribution:
The digitalization of the plaster model is obvious; it is only a matter of moving from a real model to a virtual model, thanks to the scanner. This narrow vision of the plaster model is neither more nor less than a kind of information storage in a real and palpable form.
Today, storing the model in digital form using the scanner on a USB key is an act similar to casting the real model in plaster but the purpose or result is very different.
In both cases, they are a memorization of the shape of the mouth. In the first case, it is a non-reproducible model.
While in the other case it is an accessible memory, infinitely reproducible and storable in an infinity of identical modular units but which can always return to its initial state. Two surface memorizations, two different availabilities.
Contribution of the STL system:
PLY and STL files of a bottom optical impression
This allows for constant collaboration between the dentist and the prosthetist:
When the prosthesis is modeled, it returns to the office, in reverse order but in a file interpretable by a machine tool located in the office (not in real form) and it is the prosthetist who, remotely, controls the machining for the final production, so in summary: In the past, our work was transmitted to the laboratories in the form of a plaster model and only returned in the form of a finished prosthesis.
At the CAD level:
– refrain from casting models, infectious risks, dimensional variations.
– creation and conservation of virtual models
– possibility of reproducing all traditional gestures on CAD software
– permanent control of the design of the future prosthesis
– speed of execution
At FAO level:
– traceability of materials used
– fast and precise machining and possibility of making sequences in the laboratory
– machining of zirconia possible
– reproducible protocol
– possibility of performing the restoration in a single session using direct technique
– possibility of producing a physical working model to open up possibilities for complex cases.
Indirect techniques
Occupy a very important place in the general practice activity of the dental surgeon in the office.
These techniques allow for greater longevity, aesthetics and precision compared to direct methods but they require an intermediate laboratory step for the production of the prosthetic piece (veneer, inlay, onlay or crown) and the placement of a temporary restoration.
The interposition of the laboratory stage and the installation of a provisional restoration may be sources of problems.
By multiplying the number of sessions and going through an intermediate step, we increase the risks of errors because we send different information to the prosthetist via various materials with different properties and degrees of precision.
Impression of the preparation(s) and its limits, adjacent teeth.
Imprint of the antagonist arch
Inter-arcade report.
This is the context in which CAD/CAM is included. The measurement, design and manufacturing systems combined in a single location (the dental office) will allow the practitioner to produce the prosthetic part himself.
In the “all-in-one” or chairside system , the participation of the prosthetist is no longer necessary. This imposes a new dynamic in the care timeline and a new organization of care in the chair.
As we have seen, traditional indirect restorations are carried out in at least 3 stages, two in the chair and one in the prosthetic laboratory:
In the chair 1st session: preparation, impression, inter-arch report, choice of shade, placement of the temporary prosthesis.
In the laboratory: casting of plaster models, assembly in articulator/occluder, production of the prosthetic part and finishing.
In the chair 2nd session: removal of the restoration/temporary tooth, fitting of the prosthetic part, sealing or bonding.
With the direct CAD/CAM system, the practitioner carries out all of these steps in a single session.
Patient installation, anesthesia and tooth preparation
Optical impression and design of the part by computer with the patient in the chair, choice of shade
Manufacture of the prosthetic part by the manufacturing unit, the patient waits in the waiting room.
Possibly make-up and icing of the piece, finishing touches
Trying on the part and gluing while benefiting from the effects of anesthesia
This brings many practical and comfort advantages for the patient:
A single session without aesthetic deficit or inconveniences linked to temporary
A single anesthesia
Technological innovation (robotics)
For the practitioner:
Save time
A single anesthesia
No temporary sealing
No intermediary (courier, prosthetist)
It should be noted, however, that make-ups and glazes require some experience, so the prosthetist can participate in the design to improve the final aesthetics of the prosthetic piece.
Conclusion :
The single session is one of the major advantages of CAD/CAM, it is the implementation of modern dentistry: depending on the patient’s requirements, the communication and trust that can be established with the care team, as well as the speed of implementation, this technology is a valuable tool! With more efficient and comfortable sessions, patients have the feeling of a “tailor-made” and truly personalized treatment.
Like any new process, its use requires training, particularly in the choice of materials. But we can say that today, this type of restoration developed by CFAO meets the expected quality and reliability criteria, in compliance with “proven medical knowledge”.
Good oral hygiene Regular scaling at the dentist Dental implant placement Dental x-rays Teeth whitening A visit to the dentist The dentist uses local anesthesia to minimize pain