Root canal therapy is needed when the nerve of a tooth is affected by decay or infection. In order to save the tooth, the pulp (the living tissue inside the tooth), nerves, bacteria, and any decay are removed and the resulting space is filled with special, medicated, dental materials, which restore the tooth to its full function. Reasons for root canal therapy: decay has reached the tooth pulp (the living tissue inside the tooth), infection or abscess have developed inside the tooth or at the root tip, injury or trauma to the tooth. An access opening is made on top of the tooth and a series of root canal files are placed into the opening, one at a time, removing the pulp, nerve tissue, and bacteria. If tooth decay is present, it will also be removed with special dental instruments. Once the tooth is thoroughly cleaned, it will be sealed with either a permanent filling or, if additional appointments are needed, a temporary filling will be placed. At the next appointment, usually a week later, the roots and the inside cavity of the tooth will be filled and sealed with special dental materials. A filling will be placed to cover the opening on top of the tooth. In addition, all teeth that have root canal treatment should have a crown (cap) placed. This will protect the tooth and prevent it from breaking, and restore it to its full function.