The tooth consists of three layers. The outer layer is called enamel, the layer underlying the enamel is called the dentin and the innermost layer of the tooth is called the pulp. The pulp is the only living structure in the tooth. When the pulp is infected, a root canal treatment is to be performed to save the tooth.
When a tooth is infected, the infection tends to start on the surface of the tooth, the enamel. As the infection / cavity spreads, it tends to start affecting the dentine and later the pulp. There is no pain when the enamel alone is infected. As the cavity progresses into the dentine, sensitivity or pain starts to develop. When the cavity is not treated at this stage, the cavity further spreads into the pulp. When the cavity is confined to the enamel or dentine region alone, a normal filling can be done. In case the cavity spreads into the pulpal region, there are only two choices left. One is to perform a Root canal treatment and save the structure of the tooth. The other is to go for extraction of the tooth.
The spread of infection into the pulp can be diagnosed only through a radiological examination. A full mouth x ray or a small x ray confined to the infected tooth and surrounding teeth can help confirm the involvement of infection in the pulp.
A root canal treatment is recommended in most cases where the infection of the pulp is minimum and the outcome of the treatment is predicted to be good. During a root canal treatment, the pulpal tissue is fully removed. The pulp canal is then cleaned and is filled with a material called the gutta percha.