Sometimes a tooth is considered so threatened (because of internal cracking, etc.) that future infection is considered likely or inevitable, and a pulpectomy is advisable to prevent it. But usually some inflammation and/or infection is already present, within or below the tooth. To cure the infection and save the tooth, it is necessary for the dentist to drill into the pulp chamber, and remove the infected pulp by scraping it out of the root canals. Once that is done, the dentist fills the cavity with an inert material and seals up the opening. This procedure is known as root canal therapy. If enough of the tooth has been damaged, or removed as a result of the treatment, a crown may be required.