Teeth are held in the jaws by their roots. Front teeth normally have one root, but teeth further back have more.
At the core of each tooth is a soft mass of tissue called the pulp. In a healthy tooth, the pulp contains living fibres, cells, nerves and a blood supply, extending into the root(s) through the root canal(s).
Decay or injury can destroy the living pulp. Because dead pulp lacks a blood supply, it is more prone to infection, leading to an abscess and toothache.
Root canal treatment (also known as root filling or endodontics) means removing damaged or dead pulp and filling the space left. The remaining tooth can then be repaired.
Pulp damage can cause toothache but the pain will usually end very quickly when the root canal is cleaned out.
Without a root filling, a tooth with a dead pulp would probably have to be taken out in the end. There is also a possibility of infection spreading beyond the tooth itself.
Root-fillings are usually successful and can last many years, but re-treatment is also possible if infection recurs. Occasionally, if inflammation persists at the tip of the root, surgery can be carried out to remove part of the root, clean the area and put in a filling. This is known as apicectomy.