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 |
|---|---|
| cartridge nozzle | Kartuschendüse |
Focus text of the month
Zircon Zircon
Compaction of highly pure zirconium dioxide powder and binding agents without heat treatment produces a press blank, known as a green compact or green body. Shrinkage of 25% at a later stage must be taken into account. A presintering process is then completed at approx. 1000°C, during which the binding agents are eliminated, shrinkage of approx. 5% occurs. This produces a partially sintered blank. In this partially sintered state the zirconium dioxide can be processed using many conventional dental CAD-CAM milling systems. Subsequent shrinkage of 20% at the (post) sinter firing stage must be factored into the calculation by respective enlarged manufacturing. |
All-zirconia bridgework and crowns
Zirconium dioxide free-end bridge
Lingual view of single-winged bridge