CAD/CAM software in dental technology
CAD programmes for use in dental technology receive scan data directly from the mouth ("optical impression-taking") or indirectly by scanning impressions, bite registrations or models produced using conventional methods. Scanning can be performed using laser scanners, stripe-light scanners, mechanical scanning or other techniques. In addition, libraries are often available with datasets of prefabricated industrially fabricated components such as implants/platforms, abutments or connectors on the one hand and on the other hand templates of anatomically contoured copings, occlusal surfaces, crowns, bridge pontics etc.
CAD programmes have an important key function in the dental technology production chain. They enable imaging, linking and processing of the recorded electronic data. The user can plan and optimise the required restoration virtually taking into account the various parameters (such as material thickness, anatomical design, proximal contacts, antagonistic contacts in static and dynamic occlusion [in virtual articulators], aesthetics, coordination with other components).
Once computer-aided design (CAD) is complete, the design is transferred to and the restoration fabricated using computer-aided manufacturing (CAM). This can take place immediately afterwards and in the vicinity or at a later time and in a different location.
The same CAD and/or CAM programme can be integrated in the product of various third-party suppliers as "OEM" software.
In principle, any dental restoration can now be designed up to 100% using CAD/CAM software and fabricated using a wide range of materials, whether an inlay, CrCo framework, customised abutment, four-unit bridge, temporary crown, telescope crown tertiary structure, surgical stent or bite-raising appliance.
Essential requirements of CAD/CAM programmes used in dental technology are import and export compatibility (interfaces) with conventional data formats (in this case mainly STL format in which three-dimensional surfaces are broken down into minute, geometrical easily describable triangles). "Open" data formats can be used on any production machines (e.g. milling units or machines for generative production) for material processing. "Closed" systems in contrast provide "confidential" (i.e. company-specific, proprietary) data formats, which can only be further processed on certain, company or licensed machines.
As exceptionally high precision is required - the accuracy of dental scanners today is in the range of 5 µm to 30 µm, the accuracy required of the final fit allows a maximum error tolerance of 50 µm – suitable CAD/CAM programmes must be able to handle the extremely large datasets involved, which provide the respective computer and manufacturing system with a high data processing capacity and speed.
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polishing debris | Polierreste |
Wax build-up technique Wax build-up technique The various anatomical structures (such as cusp tips and slopes as well as marginal ridges) are usually built up one after another by adding small portions of wax (often using differently coloured waxes for didactic purposes). The firm, special waxes first have to be melted at room temperature. This can be carried out by warming small portions on differently shaped working tips of hand instruments in an open flame (such as a gas burner) or using electrically heated instruments which provide for more accurate temperature control and avoid contamination (e.g. electric wax-knife, induction heaters, wax dipping units). The wax is applied drop-by-drop to ensure that the warmer molten wax added last fuses seamlessly with the firm, cooler material. After hardening, the wax pattern can be reduced by sculpting, milling guidance surfaces or drilling to add retainers. Modern procedures include flexible, occlusal preforms for adding contours to soft wax. In addition, wax preforms, such as for occlusal surfaces or bridge pontics, are available in various shapes and sizes. Recently, irreversible, light-curing materials have been introduced for use instead of reversible thermoplastic waxes. Wax preforms To ensure that the wax pattern can be released without being damaged, model surfaces, opposing dentition and preparations must be hardened/sealed with special lacquer (applied by spraying, brushing or dipping). These waxes are mostly relatively rigid/elastic after cooling. Attaching wax sprues to a removable framework supported on double crowns using a hand instrument When employing the lost wax technique, prefabricated wax sprues, bars and reservoirs are attached to the patterns. Once the pattern has been released and its sprues waxed onto the crucible former, it is invested in a casting ring with refractory investment material. The wax can then be burnt out residue-free and casting completed. Unlike standard wax build-up techniques, a diagnostic wax-up is not intended for fabricating an indirect restoration, but rather for simulating the appearance and/or external contouring for producing orientation templates. |