Dental crowns are used when substantial tooth structure has been lost through decay or injury, but the root is still firm enough to anchor a protective coating. Crowns can also be used to improve the appearance of a tooth. In dental bridgework – a method employed to fill gaps left by extracted teeth – a crown may be used to support an adjacent replacement tooth. Crowns are made by dental technicians. They are often fabricated from gold and semi-precious metals; porcelain is used to mimic tooth appearance and can be used on its own, or as a facing. The dentist prepares the tooth to accept the crown and records an impression of it by getting the patient to bite into a block of quick-setting material such as silicone gel. A plaster mould is made from the impression, from which the crown can be contructed. The crown is made to match the colour shade, contour and character of the remaining teeth. For crowns not normally visible gold is often preferred, although some people like to reveal a little gold! Although crowns cover most of the tooth’s exposed surface they must be well maintained to prevent plaque from building up at the tooth’s junction with the crown. Looked after in this way crowns can last many years, preserving the form and appearance of the teeth.