Bite registration material
Bite registration is an extremely important step in the fabrication of diagnostic models, restorations, bite-raising appliances, orthodontic appliances etc. It is used for precise, clear indexing of the three-dimensional alignment of maxilla and mandible in the required relationship.
Bite registration material
In addition to increasingly popular, yet technically still very costly primary digital (virtual) procedures, analogue registration methods are still mainly used today. Reversible thermoplastic (wax, resin, gutta percha), chemically-curing (ZnO, acrylics) and irreversible elastic (e.g. PVS = polyvinyl siloxane) bite registration materials are generally available for analogue registrations. These are applied either directly on natural or prosthetic opposing teeth or used for the fixation/indexing of custom-fabricated bite blocks, in full and partial denture prosthetics, for example in the form of an acrylic base (previously also shellac) with wax bite rims attached or as a connection between the upper and lower plates (acrylic, metal) in Gothic arch registration.
Zink oxide bite registration material
Silicone bite registration (check)
Addition-curing silicone bite registration materials (A-silicones), which are closely related to impression materials, offer the advantages of flowability (low bite resistance, avoids bite displacement) and positional stability (no uncontrolled flow) due to thixotropy, detailed representation (crisp details), dimensional stability (withdrawal from undercuts), thermal stability, good processability (grinding and/or trimming) and insensitivity to moisture or mechanical stress (compressive, tensile) after curing. Colour, transparency or opacity, setting time and final hardness (Shore A to Shore D), and scannability can be modified to a wide extent, depending on the area of application. They are used mainly as two-component bite registration materials (base + catalyst/activator) in standardised cartridges, which are mixed and applied using mixing guns and mixing tips.
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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. |