A crown (sometimes incorrectly called a cap) is a tooth form produced by a dental technician. Materials used to make crowns include precious metal alloy, semiprecious metal alloy, porcelain, or one of the reinforced aluminosilicate-type ceramic systems such as Procera.

Why use a crown?

A very badly damaged tooth may be difficult or impossible to restore to correct form and function using a direct dental restorative material such as amalgam or dental composite . These materials are placed in the damaged tooth and carved to shape by the dentist in the mouth. This limits their strength. Contamination by saliva and blood may lead to discolouration and inhibition of dentine bonding systems used to prevent microleakage .

Therefore the tooth may require an indirect restoration made outside the mouth by a dental technician, who can work to produce a customised tooth shape in the chosen material that will fit the patients damaged tooth exactly, a little like a thimble fits over a finger to protect it.

The stages involved:

1. Patient presents with badly damaged tooth. Tooth may be restored using a direct filling material to act as a core for the crown.

2.Dentist prepares the tooth using a dental drill, removing some tooth and core to allow sufficient thickness of crown material to cover the damaged tooth and restore its strength. At this stage the dentist will also prepare the margins of the crown preparation ie. the join between the natural tooth and the crown. There are several designs in the literature, the common types being a chamfer (typically used for gold and other metal crowns), and a shoulder (used for porcelain where thickness is important for good strength and aesthetics.

3. Dentist takes an impression of the teeth and records how the teeth meet. Typically a polyvinylsiloxane putty and a lightbody wash system are used to record the shape of the prepared tooth. Dentist chooses the shade and material of the crown, and writes a prescription for the technician to follow.

4. A temporary crown is fabricated by the dentist and placed over the prepared tooth.

5. The models of the teeth are sent to the dental laboratory where the technician makes the crown according to the prescription.

6. The finished crown is returned to the dentist for fitting. The crown is cemented over the damaged tooth, using a luting cement , restoring the tooth to a good strength and function.