Each tooth is comprised of a crown and a root. In a regular dental filling procedure, only the decayed part of the crown is drilled out. With root canal therapy, however, the drilling goes beyond the crown and into the root, removing all the tissue inside the root, including the nerve. The hollow root is then cleaned and filled with a medicated material, and the remaining tooth is prepared and fitted with a dental crown, returning the tooth to its original shape and structure. In most cases, the whole process can be completed in one or two visits.