A tooth that has been infected by bacteria will become decayed. A tooth with caries should be okay with a simple tooth filling, but if the disease is allowed to spread and infect the deeper tissues, a simple restorative filling will no longer be indicated. When the infection has spread into the pulp, the diseased pulp will have to be removed for the tooth to be saved and this is what is done with a root canal treatment.
A root canal treatment is a pulp therapy procedure that is performed so that a tooth can be spared from a tooth extraction. As long as the roots are of considerable health and stability under the bone, the tooth can receive a pulp therapy and it can be preserved. After which, this tooth can be restored with a crown.