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 |
|---|---|
| auxiliary tool | Schwesternwerkzeug, Hilfsinstrument, Hilfswerkzeug |
Focus text of the month
Sleep apnoea Sleep apnoea Compared with healthy sleep, there is a great increase in breathing cessations (AHI = apnoea/hypopnoea index > 10 per hour), in the form of complete apnoea or reductions in airflow (hypopnoea). Central nervous system causes are rarer than the much more common OSA (obstructive sleep apnoea) of local (peripheral) origin. This itself causes central cessations, so mixed forms often occur (approx. 90%). OSAS (obstructive sleep apnoea syndrome) is nearly always associated with heavy snoring that disturbs other sleepers. The interaction of a number of factors, such as supine sleeping position, slack pharyngeal musculature, especially involving the soft palate and uvula and also the hypopharynx (e.g. due to alcohol consumption, sleeping pills), physiological and pathological anatomy (obstructed nasal breathing, enlarged tonsils, macroglossia, obesity) causes temporary complete obstruction of the airways during inspiration. This causes a drop of about 4% in the blood's oxygen saturation, which is normally 95% to 100% so the oxygen supply to the tissues is impaired. If the episode lasts longer, hypercapnia (a rise in carbon dioxide level) may occur. This then triggers frequent "micro-arousals" via chemosensors, which often do not lead to full awakening; sleep is disturbed with shortened deep sleep phases and an overall reduction in sleep quality with lower relaxation and recovery, which can lead to an increased need for sleep and increased daytime tiredness, daytime somnolence (hypersomnia) and a tendency to fall asleep. In the long term, apart from quality of life and energy levels, life expectancy is also affected as OSA is associated with high blood pressure, cardiac arrhythmias and depression and there is an increased tendency to stroke, heart attack and accidents. The diagnosis can be confirmed by recording relevant parameters during sleep at home (cardiorespiratory polygraphy) or in hospital (polysomnography when the patient spends the night in the sleep laboratory); these include ECG, pulse oximetry, EEG, video recording, etc.
Various approaches are used in treatment, alone or in combination:
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Polysomnogramme with hypnogramme