Root canal treatment is required for two main reasons. The first is an infection. The second reason for a root canal is damage to the pulp that can’t be fixed. An untreated cavity is a common cause of pulp infection. The decay erodes the enamel and dentin of the tooth until it reaches a root canal. This allows bacteria to infect the pulp. Antibiotics can’t get to infections inside teeth. The inflammation caused by the infection reduces the blood supply to the tooth. The reduced blood supply also keeps the pulp from healing.