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
Crowns Crowns Crowns can be fitted on natural teeth (preparation) or the intraoral sections and abutments of implants. Crowns are retained by cementation and/or adhesion; it is also possible to fabricate screw-retained restorations on abutments. The long-term seal of the crown margin (marginal integrity) is very important for maintaining the health of the surrounding marginal periodontium and prevention of secondary caries.
Crowns are fabricated using a single material (full cast crown, all-ceramic crown) or by the combination of different materials (e.g. bonded crown). Very different procedures are used for this, e.g. casting (cast crown), milling, trimming, sintering (CAD-CAM), pressing (press-ceramic crown) or electroforming (electroformed crown). With a metal-ceramic crown a coping (framework) is first fabricated using metal and then coated with ceramic (veneered) to achieve optical similarity with the tooth. Historical techniques include soldering of crown parts (banded crowns).
Prefabricated steel crowns can be used for treating severely destroyed deciduous teeth. Temporary (short, medium or long-term) custom-adapted prefabricated, frequently intraorally (direct) or extraorally fabricated temporary crowns (mainly using resins) bridge the period until a permanent crown is fitted. Crowns fulfil various functions. As protective crowns they absorb masticatory forces to prevent teeth with weakened structures breaking apart and/or seal endodontically treated teeth against penetration of bacteria. They also protect the tooth against chemical and thermal irritation. Anchor or abutment crowns retain bridges whereas support crowns anchor retentive and support elements such as rests and clasps. Connectors, e.g. attachments can also be integrated into the crown (attachment crowns). Crowns can be fabricated individually (single crowns) or connected with other crowns (splinted crowns).
In the specific case of the telescope crown (conical telescope crown, parallel telescope crown) the crown consists of a fixed inner crown (primary crown) and an outer crown (secondary crown), which fits on the primary crown in the removable restoration. If a telescope crown is fabricated using the electroforming technique, it can be adhesively retained later in a tertiary crown fabricated over it. |
Anterior crown preparations
Implant-borne metal-ceramic crown
Three metal full cast crowns
Upper anterior crowns