The modern techniques of endodontic treatments result in very high percentages of success. Especially in the cases that the treatment has been done by an Endodontist, based on bibliography, the chances of success, reach as high as 95%.

The unsuccessful removal of the bacteria from the pulp chamber or the non protection from a new infection after the completion of the endodontic treatment may lead to failure.

The reasons of failure could vary:

• The morphology of the tooth may be unusual or complicated and may not have been properly diagnosed.
• The root canals may be narrow or with extreme curve.
• The existence of iatrogenic problems like separated files.
• Inadequate restoration that doesn’t protect the tooth thoroughly from the oral environment which is full of bacteria.

Sometimes, after several years a new problem may arise and put in danger a successful endodontic treatment. Such problems are:

• New decay underneath the filling which caused a new bacterial infection of an endodontically treated tooth.
• A “loose”, broken, disrupted restoration could expose the tooth to a new infection.
• The tooth may fracture.

When something of the above happens, the endodontic treatment may fail and retreatment will be needed.