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:
Why 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.