Shade-taking for restorations
Shade-taking for restorations
Mimicking the positioning, contours and optical surface properties of adjacent and opposing natural teeth as realistically as possible is an important part of integrating dental prostheses inconspicuously into the mouth. The optical surface properties are summarized by the term "tooth shade" despite the fact that they include a wide range of parameters such as shade, shade gradient, brightness, shade saturation, translucency (light shimmering through light-scattering material) versus opacity (due to scattering of light), fluorescence or phosphorescence (light emission due to, e.g. UV light), glaze (due to reflection of light).
The virtually infinite spectrum comprising millions of naturally occurring tooth shades subjectively perceptible to the human eye can be reduced to a few standardised shades (clearly defined and described for objective documentation and communication) and only incur minimal aesthetic sacrifices. These are then incorporated into so-called shade guides (mostly one-dimensional/linear, rarely multi-dimensional, encompassing various parameters) such as for prefabricated denture tooth. These shade tabs are usually contoured like teeth, made of the restorative (e.g. composite or porcelain) and used for comparing with patients' teeth and/or restorations.
Shade guide
Shade guides are also available in gingival shades for imitating soft tissues such as mucosa.
As each specific surface appears differently (metamerism) when illuminated with light of differing intensities or wavelengths (sun, cloudy, dawn, artificial lighting), in order to achieve predictable results wherever possible shade-taking must be carried out under reproducible, standardised lighting conditions. To achieve these, various technical aids such as identical ring lights for dentist and technician, cameras with white balance or special electronic devices which measure spots or use standardised photos for "surveying" the various areas of the tooth (such as the incisal, dentine, cervical and proximal regions) and displaying the results to correspond with standard shade guides are employed.
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Word of the day
| English | German |
|---|---|
| firm | standfest, standhaft, formstabil |
Focus text of the month
Bite registration material 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.
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. |
Bite registration material
Zink oxide bite registration material
Silicone bite registration (check)