Endodontics is a branch of dentistry recognized by the American Dental Association involving treatment of the pulp (root canal) and surrounding tissues of the tooth. When you look at your tooth in the mirror, what you see is the crown. The rest of the tooth, the portion hidden beneath the gum line, is called the root. Though the outer portion of the root is a hard tissue called dentin, the inside channel — or “root canal” — contains a pulp of soft tissue, blood vessels and nerves.