A root canal may be needed if the decay has reached the tooth's nerve.
Essentially, a root canal involves cleaning out a tooth's infected root, then filling and sealing the canal.

Procedure:
1) An opening is made through the crown of the tooth into the pulp chamber.
2) The pulp is removed, and the root canals are cleaned, enlarged and shaped.
3) The infected area is medicated.
4) The root canals are filled.
5) The crown opening is filled with a temporary filling.

Causes of a Root Canal
A cavity that has been left untreated can become larger. Once the cavity reaches the pulp of the tooth, an infection forms at the base of the root canal, causing an abscess. This abscess is generally painful and will need to be removed.