Endodontic treatment is prescribed for teeth that have been diagnosed with an abscess, irreversible pulpitis, chronic apical periodontitis, inflammatory resorption or are necrotic (filled with non-living blood vessel and nerve tissue). Endodontic treatment is also prescribed if the clinical crown of the tooth (the part that is visible protruding through the gum tissues) is badly broken down and would require structural posts to be placed in order to restore the tooth to normal function.
Sometimes a tooth that requires endodontic treatment will be obvious from an X-ray image (radiograph), if there are obvious changes in the bone near the root tip(s)—even in the absence of symptoms. Sometimes teeth with deep decay (caries) require root canal treatment even though they may not hurt or be sensitive. A tooth that is particularly sensitive to hot temperatures, but is relieved by cold likely has gas from bacteria inside of it