With the appropriate care, a tooth that has had endodontic treatment will last as long as other natural teeth. Yet, a tooth that has received treatment may fail to heal or continue to cause pain if certain underlying factors are present. These factors include, but are not limited to 1) canals that are missed in the original root canal treatment, 2) canals that are improperly cleaned or sealed, 3) the presence of a root fracture, or 4) failure to permanently restore the tooth.  Sometimes, the pain may occur months or years after the initial endodontic treatment. If so, endodontic retreatment may be needed.  The use of the surgical operating microscope by Dr. Lewis is critical in finding canal space that was missed or improperly cleaned.  In addition, the combination of light and magnification allows for the detection of many root fractures and their extent, which is critical in determining a tooth's long term prognosis.  In general, most deficiencies which cause endodontic failure can be corrected.  However, in certain situations, underlying problems cannot be corrected by endodontic retreatment, leading to surgical intervention or extraction.