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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Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic… Composites also composite (from the Latin componere = to compose) are tooth-coloured filling materials with plastic properties used in dental treatment. In lay terms they are often referred to as plastic fillings, also erroneously sometimes confused with ceramic fillings due to their tooth colour. After being placed in a cavity they cure chemically or by irradiating with light or a combination of the two (dual-curing). Nowadays, composites are also used as luting materials. The working time can be regulated with light-curing systems, which is a great advantage both when placing fillings and during adhesive luting of restorations. Dual-curing luting materials are paste/paste systems with chemical and photosensitive initiators, which enable adequate curing, even in areas in which light curing is not guaranteed or controllable. Composites were manufactured in 1962 by mixing dimethacrylate (epoxy resin and methacrylic acid) with silanized quartz powder (Bowen 1963). Due to their characteristics (aesthetics and advantages of the adhesive technique) composite restorations are now used instead of amalgam fillings.
The material consists of three constituents: the resin matrix (organic component), the fillers (inorganic component) and the composite phase. The resin matrix mainly consists of Bis-GMA (bisphenol-A-glycidyldimethacrylate). As Bis-GMA is highly viscous, it is mixed in a different composition with shorter-chain monomers such as, e.g. TEGDMA (triethylene glycol dimethacrylate). The lower the proportion of Bis-GMA and the higher the proportion of TEGDMA, the higher the polymerisation shrinkage (Gonçalves et al. 2008). The use of Bis-GMA with TEGDMA increases the tensile strength but reduces the flexural strength (Asmussen & Peutzfeldt 1998). Monomers can be released from the filling material. Longer light-curing results in a better conversion rate (linking of the individual monomers) and therefore to reduced monomer release (Sideriou & Achilias 2005) The fillers are made of quartz, ceramic and/ or silicon dioxide. An increase in the amount of filler materials results in decreases in polymerisation shrinkage, coefficient of linear expansion and water absorption. In contrast, with an increase in the filler proportion there is a general rise in the compressive and tensile strengths, modulus of elasticity and wear resistance (Kim et al. 2002). The filler content in a composite is also determined by the shape of the fillers.
Minimally-invasive preparation and indiscernible composite restoration
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