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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Focus text of the month
Fixed restorations are a part of prosthetics. In particular crowns (though they often do not replace a tooth but only supplement the lost tooth structure of an existing tooth) and bridges as well as bar… Fixed restorations are a part of prosthetics. In particular crowns (though they often do not replace a tooth but only supplement the lost tooth structure of an existing tooth) and bridges as well as bar restorations are described as fixed restorations. Implants replace "fixed" tooth roots in the bone but are not defined as fixed restorations. In contrast to removable restorations, fixed restorations are rigidly bonded to teeth or implant abutments using adhesive retention or cementation. Restorations, which are fixed for the patient (e.g. by screw-retention or temporary cementation) but are designed to be removable by the dentist, are called "operator-removable". If restorations, which are removable for the patient, are retained on fixed crowns they are called fixed-removable restorations. A minimum of four periodontally healthy abutments in a favourable alignment (quadrangular) is essential for ensuring stable, statically balanced support per jaw for purely fixed restorations. However, for purely implant-borne fixed restorations in particular, a minimum of six abutments is required in the mandible and even eight abutments in the maxilla due to the lower bone quality. An increase in the number of abutments (e.g. using implants) and also a combination using removable (tissue-borne) restorations can help relieve the natural residual teeth.
Features of fixed restorations are periodontal support on abutments, a rigid, immovable connection with the abutment and the subjective sensation of patients of wearing "their own teeth". Care and repair are more difficult compared with removable versions and extending the restoration is generally impossible – especially in the case of (primary) connections with adjacent single crowns for increasing the stability. This is why the previously generally accepted superiority of fixed restorations should be qualified according to each individual case. A fixed restoration is not only impossible in edentulous cases but also with implants if, as a result of massive bone resorption, the distance between the alveolar ridge level and occlusal plane is too large, which would lead to an excessively forceful leverage effect. Fixed restorations can be fabricated provisionally (temporary; generally using acrylic and rarely from metal or ceramic), e.g. for testing a new occlusal relationship or for bridging the time required for fabrication of the permanent restoration or other treatment. Individual components of fixed restorations can be prefabricated (e.g. attachments, other connectors or implant abutments); these can remain unchanged or they can be customised. Final (permanent) fixed restorations are fabricated either from a single material, combinations of materials or by joining different materials using very different procedures, e.g. casting, milling, soldering, welding, grinding, sintering (CAD-CAM), pressing or electroforming. Temporary luting (short, medium or long-term) can be used for trying in fixed restorations. |
Pontic 42, labial view of single-winged bridge
Pontic 42, clinical view of single-winged bridge