CHARACTERISTICS OF DENTAL CAD/CAM SYSTEMS PRINCIPLES OF OPERATION. ACCESSORIES

CAD\CAM technologies have taken a strong place among modern methods of manufacturing dentures. The abbreviation “CAD/CAM” stands for the first letters of the phrase “Computer Assisted Design /Computer Aided Manufacturing”, which in Russian sounds like “computer design (modeling)/production (manufacturing) under computer control”. These technologies are borrowed from industry, where they have been successfully used for a long time. Various parts are designed using a computer and then manufactured automatically. However, the main difference between dental CAD\CAM systems is that these systems produce parts only in a single copy. Computer-aided design of the structure is associated with the individual shape of the prosthetic bed, the relief of which must be digitized and transmitted to a computer with high accuracy and speed.

Manufacturing with the help of computers is carried out by two main methods: the subtraction method, when everything superfluous is removed from an entire block of material (for example, milling) and the addition method, when the object is built layer by layer (rapid prototyping). Most modern systems are based on automated manufacturing of prosthetic frames by milling and subsequent manual application of facing material.

The special advantages of milling CAD/CAM systems include higher accuracy (edge fit is up to 20-30 microns), the possibility of using materials that are not available to traditional technologies, high productivity, compact equipment.

CAD\CAM systems for the manufacture of dentures have long ceased to be only interesting scientific developments, having proved their practical effectiveness. They open up new unique opportunities in orthopedic dentistry.
Most modern CAD/CAM systems are based on the automated manufacture of dentures by milling. During intraoral scanning and impression scanning, milling can be used to make models of dentition and jaws. In addition, surgical guide templates for implantation can be made by milling.

An important characteristic of the machines used for CAM milling is the number of degrees of freedom when processing the part. The machines used in dentistry are 3, 4 and 5 axis. The more degrees of freedom, the more complex the part can be made.

For accurate and efficient milling, such characteristics as the displacement step of the workpiece and the milling cutter, the nature of the workpiece retention, the number of workpieces that can be processed automatically are important.

The smaller the offset step, the greater the milling accuracy.

Modern machines provide a displacement step of up to 0.5 microns.

The workpiece for milling can be held in different ways. Given the rather large dimensions of the workpieces, it is appropriate to assume that the unilateral retention of the workpiece determines a large amount

possible milling error of the part on the side removed from the fixing point in the holder. Fixing the workpiece along the entire perimeter reduces the amount of error.

Most milling machines provide manual replacement of workpieces for milling. To increase productivity in some machines, it is possible to install two blanks at once. Large industrial machines, the so-called mini-factories, provide not only automatic replacement of tools, but also processed workpieces.
The milling cutter must move along a closed curve. This reduces the milling time and increases its accuracy.

In the milling strategy, the following must be strictly coordinated: the direction of movement and the speed of movement of the cutter, the speed of its rotation, the type of material and the thickness of the material. A special computer program calculates milling modes (diameter, trajectory, speed of movement, speed of rotation of the cutter. Brittle materials should be processed at a high speed of rotation of the cutter, viscous and plastic materials at a low speed.

During its rotation, the spindle holding the milling cutter can additionally perform high-frequency vertical oscillations (30 kHz). This reduces the necessary degree of pressure on the workpiece, which makes it possible to produce thin-walled parts, increases the service life of the cutter, optimizes the surface to be processed, reducing the likelihood of microcracks in the material.

The zone of rough processing and fine processing is allocated. The zone of fine processing is considered to be the area near the finishing line of preparation. In case of rough processing, a larger diameter milling cutter is selected and a larger step of the milling cutter movement is set. In the case of fine machining, on the contrary, the thinnest milling cutter and the minimum step of movement are selected. In this case

the total milling time is reduced while ensuring high accuracy of the products.
At the same time, it should be borne in mind that when scanning and subsequent processing ITSELF, the density of measurement points or the density of the triangulation grid should be different in different parts of the object. This optimizes the resources of the computer and the speed of its operation.

The compatibility of the type of milling cutter and the material used must be observed. For zircon, a diamond milling cutter is used, for metal – carbide, for plastic – carbide with a special pattern that prevents plastic from sticking to the cutter, for wax – aluminum.

These requirements are taken into account in the software that controls the operation of the milling machine. In addition, the program optimizes the distribution of manufactured parts in the volume of the workpiece.

The heavier the bed of the milling machine, the smaller the possible amplitude of vibrations when milling metal workpieces. When milling plastic and baked zircon, this indicator is not so significant.

Cooling of the workpiece during milling with a liquid is absolutely necessary when milling titanium, due to the danger of its ignition. However, this is extremely impractical due to the possible contamination of workpieces from other materials, the inconvenience of cleaning the working chamber of the machine. Therefore, many systems implement dry milling of materials (with the exception of titanium).

Classification of CAD/CAM technologies.

All CAD/CAM systems are divided into two types: “open” and “closed”.

“Closed” systems include equipment that can only work with certain consumables (disks or blocks made of zirconium dioxide, etc.), usually produced by one company.

Open CAD/CAM systems have an advantage for users. First of all, it is an opportunity to choose CAD/CAM material from the range available on the market for milling finished restoration. Secondly, both the scanner for digitizing the impression or the remaining substance of the tooth and the milling machine are selected by the operator. That is, the images obtained by the clinician using an intraoral scanning camera of one open CAD/CAM system can be freely used for modeling in the software of another open system and milled on the machine of a third open system of another manufacturer.

According to the second basic classification, all CAD/CAM technologies are divided into medical and laboratory. Actually, there is no clear separation of systems. It is considered that the classic CAD /CAM system, for example, CEREC. It includes a shooting unit (CEREC AC, for example) with software for modeling and manufacturing a limited range of restorations (inlays, frameless ceramic crowns, temporary plastic crowns and bridges of three units) and a milling machine for grinding these restorations.

Medical CAD/CAM systems can also be assembled from a scanning intraoral camera and a small-capacity milling machine of two different open technologies. It is also possible to have only an intraoral scanner in the clinic, when a digitized snapshot of the existing situation after dissection in the oral cavity is transmitted via the Internet to the laboratory. But the latter option will satisfy only a part of the needs of the patient at the orthopedic reception, since in this case it is possible to make the pharmacological structures only using the “silicone key” technique, whereas a milling machine could grind a temporary plastic restoration in a matter of minutes from the image before dissection.

Laboratory CAD/CAM systems have a wide range of manufactured dentures, both frameless and framed, both removable and non-removable orthopedic structures, as well as a number of auxiliary (polymer models, ashless compositions for casting, surgical templates, etc.). Such a system includes: a laboratory scanner designed to digitize the entire plaster model or impression, a laptop with dental software with great modeling capabilities, an industrial milling machine, a high-temperature furnace for the sinterization of zirconium dioxide frames and a low-temperature one for glazing and firing ceramic cladding or all-ceramic fired restorations.

It is impossible to talk about the advantage of laboratory systems over clinical ones. Each type of CAD/CAM system performs certain functions in the process of planning prosthetics and orthopedic treatment itself. The main purpose of the digital technology at the patient’s chair is to restore the lost hard tissues of the tooth in one visit with high–precision and highly aesthetic clinical restorations made of ceramics (inlays, single crowns), as well as the manufacture of pharmacological structures to protect the prepared teeth under the frame complex laboratory orthopedic structures and the patient’s non-departure from the social environment during prosthetics.

Advantages of CAD/CAM systems

compared to the traditional method. The CAD/CAM system is known for its high speed of operation and relative ease of operation, which significantly reduces training costs and increases labor productivity. The system is reliable and stable even during the daily processing of complex products. Another important aspect to increase the profitability of the clinic is to attract patients with high aesthetic requirements with a minimum of time spent in the dentist’s chair.

The CAD/CAM system performs work of the highest accuracy (size deviation of 10-20 microns in comparison with 50-70 microns during casting). High qualification and extensive experience of the system operator are not required to work with the technology (manufacturing companies, as a rule, are interested in professional development of specialists using their products, and conduct frequent master classes and field training courses). The system can be serviced by one person (the manufacturer also provides regular maintenance of the devices and conducts software upgrades).

A big plus of the clinical system is the saving of the workplace. Any CAD/CAM system saves working time, is characterized by clean operation and high productivity (up to 120 units per day).

To date, the dental market offers an extensive selection of 3D scanners for both prints and plaster models. Manufacturers promise a quick transition to digital format in dentistry, noting the ease of operation of scanners, high performance, a wide range of types of prosthetics and the highest accuracy (up to 10 microns). Each manufacturing company invites you to training courses for obtaining digital casts, modeling future restoration in a CAD program. The scanning object in the equipment is fixed quickly, and the scanning process is started with a single click in a convenient program.

All dental 3D scanners can be divided into two categories: medical (intraoral chambers) and laboratory (in the usual sense of the device). Each category has its advantages and disadvantages.

The main advantages of intraoral scanning cameras:

• the presence of an intraoral scanner does not require the cost of impression material,
• the camera is portable and is slightly larger than a toothbrush,
• reproduces a realistic image of the actual situation in the oral cavity,
• automatic or semi-automatic detection of central occlusion,
• less financial investment to buy a camera.

Advantages of laboratory scanners:

• the ability to convert a large number of objects into digital form within a short time interval,
• the best visualization of structures outside the oral cavity, the highest scanning accuracy.

The disadvantages of each type of scanners arise from their advantages, namely: shrinkage of the impression material, disadvantages of the impression or plaster model, expansion of gypsum lead to a decrease in the accuracy of future CAD/CAM restoration when scanning in laboratory equipment. Negative aspects when scanning with an intraoral camera are less visibility of the prosthetic bed (especially in the cervical region), increased scanning time, tremor of the operator’s hand.

Basically, scanners are part of an open system, with the help of which digital images are obtained in a single format, which makes it possible to process the received images in the software of other manufacturers.

Intraoral scanners were developed primarily for the manufacture of ceramic and temporary plastic restorations at the patient’s chair. At the moment, intraoral cameras are sometimes not inferior to laboratory scanning accuracy, so it would be wrong to call them an integral part of only a medical CAD/CAM system.

To obtain an optical impression using an intraoral camera, for some representatives, it is necessary to pre-coat the prepared hard tissues of the tooth with anti-reflective powder (for example, CEREC Bluecam, Sirona camera). But most modern cameras do not require additional manipulations before taking a picture, since digital casts are obtained using a laser.

Representatives of intraoral scanners.

The pioneer in the development of intraoral scanning devices was the company Sirona. In 2015, 30 years have passed since CEREC technologies have been successfully used in dental practice for a wide range of indications. The evolution of the intraoral scanner has evolved from a camera using infrared radiation in the thermal spectrum (CEREC 1, 2, 3, 3D), through blue rays (Bluecam, CEREC AC) to a full-color Omnicam laser camera (CEREC AC).

Intraoral scanners CEREC Bluecam and CEREC Omnicam

At the moment, Sirona has two current models of intraoral scanners: CEREC Bluecam and CEREC Omnicam, which are equipped with the CEREC AC camera unit.

CEREC Bluecam is a previous development, it must be used after applying matting powder to the prepared hard tissues of the tooth. The camera has high accuracy, great depth of field, automatic image capture, adaptation image and its stabilization. Blue rays, which are used to scan tissues, contribute to better visibility in the oral cavity.

virtual model after scanning with a camera of dissected teeth in the oral cavity

CEREC Omnicam is the latest version of the Sirona intraoral scanner. It scans with laser beams, which does not require powder coating of the scanned objects, is functional, lightweight, a full-color picture immediately appears on the monitor screen in real time.

CEREC Omnicam Scanning Camera

the picture of prosthetic bed tissues scanned by her

Technological progress always generates new technologies that can be perfectly integrated into the workflow of manufacturing dental restorations. Therefore, in addition to intraoral scanning devices, the FACE HUNTER facial scanning device (Zirkonzahn 5 TEC system) has already been presented to the dental public. Introducing the Face Hunter device, Zirkonzahn company offers a new scanner for photographically realistic digitization of the patient’s face in three-dimensional format.

The work can be performed on the basis of the patient’s physiognomy, which allows for axial positioning and combining facial scanning data with models in a virtual articulator.

Thus, it is possible to “virtually control” even the facial arc and, if necessary, adjust its position through modeling software.

Combining scan data from FaceHunter with a model obtained by digitizing Scanner S600 ARTI in a virtual articulator (Zirkonzahn)

The use of three-dimensional facial scanning data offers a number of advantages for dental technicians, dentists and patients. With the help of new technology, a dental technician can create restorations based on data on the patient’s facial features, and the dentist receives an image of the final result of almost photographic quality. At the same time, the scanner acts not only as a marketing tool, it is mainly used for consulting and issuing recommendations to the patient, who thus gets a clearer idea of what the final work will look like.

The facial scan data is entered into the Zirkonzahn program crack.Modellier through a patented information transfer system and are placed there together with the data received from the S600 ARTI scanner. Then the image of the face and the situational conditions are compared with each other, which makes it possible to perform work based on the characteristics of the face. Using the device in combination with the Reality Mode CAD/CAM software module (display mode in natural color) allows you to view the results as close to reality as possible.

Representatives of laboratory scanners.

3Shape produces a number of laboratory scanners. The choice of scanning device depends on the required performance of the device.

The D500 laboratory 3D scanner for CAD/CAM systems is the optimal choice for a small laboratory. The scanner has two 1.3-megapixel cameras that allow scanning plaster models with antagonists, prints, multiple stamps on a standard plate for fixing the model with an accuracy of up to 10 microns. The scanner has a blue LED backlight, two plaster models are placed in the scanning compartment at once. The software is Dental System. In terms of time, scanning of a single crown takes 40 seconds, of a triple bridge prosthesis – 115 seconds. The scanner’s manufacturing country is Denmark.

3Shape’s most advanced scanner is the D900L scanner. It has the highest scanning speed and accuracy among the scanners in its line. It is used to translate the above objects into digital files, but with an accuracy of 7-8 microns. Four 5.0-megapixel cameras are mounted in the scanner, scanning a single crown in 15 seconds in color, and a bridge-shaped prosthesis of three units in 35 seconds.

Laboratory 3D Scanner D500 (3Shape)

3D Сканер D900L (3Shape)

Milling machines.

Like scanners, milling machines for CAD/CAM systems come in several types, differing in power, performance and range of manufactured structures.

Small grinding machines, most often included in the “medical” CAD/CAM systems, include such representatives: CORiTEC 140i, CORiTEC 250i (imes-icore); Planmeca PlanMill™ 40 (Planmeca); CEREC MC, CEREC MC-X (Sirona); Milling unit M1 (Zirkonzahn) and others . All these devices are high–precision milling machines designed for grinding restorations at the patient’s chair. The focus of milling is on full-anatomical single restorations. Such grinding machines are compact and allow you to save space, thanks to their minimal size. Basically, these are 4-axis milling cutters designed for dry and wet grinding of all basic materials: plastics, wax, nanocomposite, zirconium and all types of ceramics. Each of the devices provides computer control of the process – the system determines and prompts the user about the need to replace tools or water.

The Planmeca PlanMill™40 high-precision milling machine for the dental clinic has two spindles built in (50,000 rpm), there is an automated feed system for 6 cutters (3 on each side), automatic quality control of the cutters after each milling, produces simultaneous 4-axis milling, working with blocks up to 60 mm.

Planmeca PlanMill ™ 40 Milling Machine

The CEREC MC milling machine is aimed at manufacturing full-anatomical single restorations with a block size of up to 20 mm (inlay, onlay, overlay tabs, all-ceramic crowns). The simple operation of the device is suitable for the work of novice specialists.

Milling machine CEREC MC (Dentsply-Sirona)

The CEREC MC X milling machine grinds a full range of designs “at the patient’s chair” – inlays, all-ceramic crowns, veneers with block sizes up to 40 mm, as well as temporary bridges, abutments, surgical templates. The software of this milling machine has an additional CEREC Premium SW update (for the manufacture of laboratory restorations) and a surgical manual (production of surgical templates with guides).

CEREC MC X grinds quickly and accurately – crown milling takes only about 11 minutes.

Milling machine CEREC MC X (Dentsply-Sirona)

The Dentsply-Sirona laboratory grinding unit is CEREC MC XL. This milling machine grinds both clinical and laboratory types of restorations. With the Premium Package software package, it is possible to grind all types of CAD/cam materials (feldspar ceramics, glass ceramics, disilicate lithium ceramics, full-anatomic restorations of zirconium dioxide, hybrid ceramics, polymers and metals). CEREC MC XL grinds blocks up to 85 mm long. The device is equipped with four motors and a user-friendly touch screen. Surgical manual and endo grinding option (the thinnest) are available. The manufacturer recommends the purchase of a milling machine complete with CEREC Speedfire furnace for the synterization of full-anatomical restorations made of zirconium dioxide in one visit.

Milling machine CEREC MC XL (Dentsply-Sirona)