Endodontics

With proper care, most teeth that have had endodontic (root canal) treatment can last as long as other natural teeth. Root canals performed by endodontists (root canal specialists) have a 95% success rate. In some cases, however, a tooth that has received endodontic treatment fails to heal. Occasionally, the tooth becomes painful or diseased months or even years after successful treatment. 

Why do I need retreatment?

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. 
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.