What's a root canal

The pulp and nerve in a tooth are removed and the tooth is sealed.

Root Canals: Process, Causes, Problems, Surgery, Recovery, and More (http://www.webmd.com/oral-health/dental-root-canals)

Thank you.

The canals contain the nerves and blood vessels, which lead to the pulp chamber. Any trauma or infection of the nerve will result in the need for a root canal. In short, just as JudyKayTee said. Common reasons for root canal therapy include; Tooth decay penetrating through the enamel and then the dentin in to the pulp, abscesses, or trauma.