A crown is an artificial restoration that fits over a broken or decayed tooth and makes it look like a proper tooth again. Other reasons to have a crown or cap are:
- to restore teeth that are badly discoloured
-to change the shape of a tooth to make it look better
-to strengthen a tooth that has been root-filled and is hence weakened
-together with other crowns joined, to form a bridge to replace a missing tooth

There are different materials that can be used to make a crown:
-porcelain
-porcelain fused to precious metal alloy
-ceramic
-glass
-precious metal alloy or gold
-non-precious metal alloy

These materials vary considerably in their strength. Gold alloy is much stronger than porcelain or ceramic and a crown can therefore be made quite thin and still be strong enough to withstand the forces of chewing. As the crown fits over a tooth, a certain amount of tooth must be taken away to allow for this, or the crown will stand proud of the other teeth and interfere with the closing of the mouth. A gold crown, being inherently strong in thin section, will require only a relatively modest reduction in the tooth, whereas a porcelain crown which has to be made much thicker to be adequately strong, will require much more tooth tissue to be taken away before placement. The material used for the crown will therefore have a strong bearing on how the tooth is prepared.

In general the dentist will anaesthetize the tooth and shape it with the dental drill by removing layers from the outside, keeping the overall shape slightly tapered so that a crown can slide on to it once it has been made to fit. The shape of the core for the crown will be determined by how much tooth tissue needs to be removed, but it will end up more or less cylindrical with a shoulder or margin that will be set either just above or just below the gum level all round depending on circumstances.

The dentist then takes an impression of the prepared tooth with a tray full of soft rubbery material. Sometimes an impression is also taken of the teeth in the opposing jaw. These moulds are sent to a laboratory where they are cast in a strong plaster and then the crown is constructed on the model.

Whilst waiting for the crown to be made, the patient will have some kind of temporary restoration or cover over the tooth. This can be made from a variety of materials, but is commonly acrylic.

The finished crown, back from the laboratory is fitted at the next visit. The dentist checks for fit, and that the crown does not interfere with chewing movements of the jaws. The crown is made to match the other teeth as far as possible, especially near the front of the mouth where it is likely to show. When dentist and patient are happy, the crown is fixed into place with dental cement.
A crown always feels strange and alien to begin with but usually after a couple of days the patient gets used to it and forgets about it. If it is still noticeable, or feels “in the way,” then it’s best to return to the dentist for some slight adjustment. With proper care a crown can be expected to last for many years.

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