In dentistry, a crown most commonly refers to a dental cap, a type of dental restoration that completely caps or encircles a tooth or dental implant. A crown may be needed when a large dental cavity threatens the health of a tooth. A crown is typically bonded to the tooth by dental cement. They can be made from various materials, which are usually fabricated using indirect methods. Crowns are used to improve the strength or appearance of teeth and to halt deterioration. While beneficial to dental health, the procedure and materials can be costly. The most common method of crowning a tooth involves taking a dental impression of a tooth prepared by a dentist, then fabricating the crown outside of the mouth. The crown can then be inserted at a subsequent dental appointment. This indirect method of tooth restoration allows use of strong restorative material requiring time-consuming fabrication under intense heat, such as casting metal or firing porcelain, that would not be possible inside the mouth. Because of its compatible thermal expansion, relatively similar cost, and cosmetic difference, some patients choose to have their crown fabricated with gold. Computer technology is increasingly employed for crown fabrication in CAD/CAM dentistry. Indications for dental crowns Crowns are indicated to: Replace existing crowns which have failed. Restore the form, function and appearance of badly broken down, worn or fractured teeth, where other simpler forms of restorations are unsuitable or have been found to fail clinically. Improve the aesthetics of unsightly teeth which cannot be managed by simpler cosmetic and restorative procedures. Maintain the structural stability and reduce the risk of fractures of extensively restored teeth including those which have been endodontically treated. Restore the visible portion of a single dental implant. Restoration of endodontically treated teeth Traditionally, it has been proposed that teeth which have undergone root canal treatment are more likely to fracture and therefore require cuspal protection by providing occlusal coverage with an indirect restoration like crowns. This led to routine prescribing of crowns for root-treated teeth. However, recent review of literature reveals that there is no strong evidence to show that crowns are better than other routine restorations to restore root-filled teeth. The general advice is that dentists should use their clinical experience in view of the patient's preferences when making the decision of using a crown. As a rule of thumb, the use of crowns and other indirect restorations