As occasionally happens with any dental or medical procedure, a tooth may not heal as expected after initial treatment for a variety of reasons:
Narrow or curved canals were not treated during the initial procedure.
Complicated canal anatomy went undetected in the first procedure.
The placement of the crown or other restoration was delayed following the endodontic treatment or the restoration did not prevent salivary contamination to the inside of the tooth.
In other cases, a new problem can jeopardize a tooth that was successfully treated. For example, new decay can expose the root canal filling material to bacteria, causing a new infection in the tooth.
A loose, cracked or broken crown or filling can expose the tooth to new infection. After your endodontist completes retreatment, you will need to return to your dentist as soon as possible to have a new crown or other restoration placed on the tooth to protect and restore it to its full function.