Air-abrasion units in dentistry
Air-abrasion units attached to standard handpiece couplings of dental units (or as stand-alone units) are always operated in dental medicine (unlike the sandblasters in dental technology) using a mixed jet of downstream separated (avoids clumping) water, compressed air and powder. The powder is stored in a refillable reservoir ("powder chamber") in the unit.
Introduced as far back as the mid-20th century, air-abrasion units have again been used since about the year 2000 ("cavity air polishers") operating at a pressure of between 4 and 10 bar for reducing hard tooth structure (air abrasion, "kinetic cavity preparation", abbreviated as "KCP"). The impact of water-insoluble aluminium oxide particles (equivalent to dental technological "abrasive grit") prepares non-contact (no tactile sensation), smaller, minimally invasive cavities quietly and with only low pain, without generating heat (unlike rotary instruments). The cavities, however, are not prepared with predictable geometries (undefined margins). Other areas of application are the intensive cleaning of fissures before sealing and conditioning (roughening, creation of micro-retention and/or chemical changes) of restorations or tooth surfaces for improving the bond strength, particularly of adhesive systems (also to veneering porcelains, e.g. for intraoral repairs).
The more widely used powder/water jet units (since approx. 1980) operate at a pressure of 2 to 3 bar with angular crystals made from water-soluble, very salty tasting, sodium hydrogen carbonate (NaHCO3, "natron"; obsolete also "sodium bicarbonate") powder (due to "refined" hydrophobic substances), later also reputedly less abrasive, water-insoluble "floury" calcium carbonate (CaCO3). They are used for targeted supragingival removal of discoloration from enamel (professional cosmetic teeth cleaning).
The classically used "salt jet" can cause damage to adjacent restoration surfaces, exposed dentine surfaces or injury to the gingiva. Applied at an unfavourable angle, the jet of air can lead to gingival emphysema, in the worst-case scenario later to air embolisms. When using air-abrasion units, special safety precautions should also be taken to avoid germ transfer, blocked tubing, damage to objects, inhalation or eye injuries.
In recent years, water-soluble amino acid glycine has been increasingly used for "perio-polishing", i.e. for subgingival removal of accretion and bacteria from the gingival pockets for prophylactic and periodontal therapy purposes. In the absence of calculus, this procedure is deemed superior to scaling with instruments.
Guided Biofilm Therapy (GBT) is a synonym for systematic prophylaxis and guarantees a uniformly high standard of quality in oral medical prevention, prophylaxis and therapy. GBT unites the most important scientific experience with technically state-of-the-art instruments – minimally invasive yet maximally preventive – all in a single holistic treatment session.
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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. |