Crowns:

The outside of each tooth is made of enamel, which is extremely hard. Although teeth are strong and difficult to break, trauma (such as a fall) may chip or break them.

Tooth decay may also severely weaken a tooth, with a high risk that the tooth may fall apart. Root canal treatment, where the pulp of the tooth containing nerves and blood vessels is removed, can also weaken a tooth, especially if it has large fillings. Teeth may also wear down over time.

In these cases, a crown is often the best way to save a tooth and strengthen it. A crown fits over the existing natural tooth and replaces the natural crown; the part of the tooth seen above the gums.

Teeth have many functions apart from chewing and biting, so missing teeth should be replaced for the following reasons:
- to improve appearance
- to prevent stresses causing damage to other teeth
- to prevent the teeth near the gap from shifting
- to maintain the natural bite
- to improve chewing ability.

Crowns and bridges are usually made of porcelain or gold alloy. Porcelain is strong and can be made to match the colour of the natural teeth. It is resistant to staining and can be cleaned if it becomes stained.
Gold alloy is used for its strength, hardness and durability. It is especially useful for molars which must withstand the forces of grinding and crushing. Gold alloy and porcelain are well tolerated by the gum and cheek. An allergic reaction to gold alloy or porcelain is rare.