Dental Polishers
In dentistry and dental technology very different materials require smoothing and polishing. This ranges from exceptionally hard natural tooth enamel to the surfaces of filling materials (composites, compomers or amalgam), fixed restorations (metal alloys or ceramics), implant components (titanium, other metals or zirconia), appliances, splints or dentures (all types of hard and soft materials).
The dental polishers used in standard handpieces are rotary instruments with a metal or plastic shank. The smoothing and polishing section of the instrument is attached to the shank – whether rigidly connected or via press-on, clamp or screw connection (e.g. with mandrels). Some polishers are not active themselves and require the additional use of polishing pastes as consumable materials (in particular for prophylaxis).
Easy, clean results are produced with all other polishers. In this case the working section is made of rubber or silicone. Abrasive materials (e.g., silicon carbide or corundum and mainly diamonds are used for very hard materials, in particular ceramics) of a suitable, selected grit size are embedded in the surface or impregnate the entire working section.
A wide range of polisher shapes is available for different applications. Typical shapes are points, cups and discs for the dental practice and wheels, cylinders/arbor bands and torpedoes for the dental laboratory.
A dental polisher
Surfaces of materials are smoothed and polished in one or more working stages. Technically, the individual processing stages vary either in the different pressure applied and/or motor speed but mainly by using abrasives/polishers with different degrees of hardness and grit sizes (specific for each stage). Polishing techniques often differentiate between two-step pre-polishing (coarse polish) and high-lustre polishing (fine polish), depending on the material, initial condition, required final state and up to three steps. The first/coarsest step is frequently a transition from preparing/contouring; at this stage significant (macroscopic) amounts of material are still removed. In the subsequent steps the main focus of the work is more on reducing (increasingly microscopic) surface irregularities (surface roughness). The final step produces a smooth surface, in general with a silky sheen or high-lustre/shining finish. Often the different colours of the polishers facilitate the assignment of specific instruments to the respective working stages. All diamond grit polishers have uniformly standardised coloured rings for identifying the different fineness of each polishing step.
To rule out cross contamination between patients in clinical dental medical applications, preference should be given to polishers, which are either suitable for sterilisation in an autoclave to ensure safe multiple use or which are designed as single-use products from the outset (use for one single patient only).
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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. |