What causes an endodontically treated tooth to need additional treatment?

Most teeth can be treated. Occasionally, a tooth can’t be saved because the root canals are not accessible, the root is severely fractured, the tooth doesn’t have adequate bone support, or the tooth cannot be restored. However, advances in endodontics are making it possible to save teeth that even a few years ago would have been lost. And, when endodontic treatment is not effective, endodontic surgery may be able to save the tooth.