Sandblasters in dental technology
Frameworks are processed in the abrasive technique using appropriate sandblasters.
Handpieces are used in microblasters for manual blasting of individual frameworks. Recycling sandblasters are also available with integrated (adjustable) nozzles, which can also be used for simultaneously sandblasting several similar frameworks (e.g. CoCr castings) automatically in a slowly rotating blasting basket. Combination sandblasters incorporate the two functions.
Sandblasters are equipped with reservoirs (abrasive tanks) for one or more different abrasives (different grit sizes). Modern units often have a modular design and can simply be extended with other abrasive tanks as required for additional applications. Color-coding is used to facilitate identification and assignment of abrasives, handpieces/nozzles and system controls.
A sandblaster
The abrasive is directed onto the surface to be sandblasted using compressed air (preferably filtered, free from oil and water) as a jet through a fine nozzle, made from a highly resistant material (e.g. boron carbide). Accurate focusing of the jet increases the sandblasting precision and at the same time reduces the material consumption. The blasting chamber forms a self-contained work area. Used abrasive is trapped by filter systems and extractors, preventing indoor air contamination. Separators remove contaminants from the abrasive.
Viewing glass (the service-life is increased by using optional mesh guards), lighting and additional magnifying systems ensure a good view. Gloves (cuffs), which are permanently fixed in the unit housing, enable manipulation of the frameworks. Sandblasting is often activated using a foot-switch in order to keep the hands free.
Precise coordination of sandblasting pressure, grit size of the abrasive and distance and angle of the nozzle to the framework to be sandblasted are crucial in ensuring optimum sandblasting in the least possible and therefore more cost-effective time.
Modern sandblasters are suitable for universal use in all areas of application, e.g. the removal of residual investment and metal oxides, roughening to create retentive surfaces, high-luster or matt sandblasting, compacting metal surfaces as well as special applications such as cold silanization for coating surfaces in the RocatecTM system.
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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. |