Investigation of Cultivable Bacteria Isolated from Longstanding Retreatment-Resistant Lesions of Teeth with Apical Periodontitis

Lesions of endodontic origin (LEO), as described by Schilder in the 1960 or more conventionally called chronic apical periodontitis, are the bane of both the general dentist and Endodontist.  The Toronto Study: Phase II, done by Friedman et al, JOE 2004, looked at the success rate of endodontic retreatment.  Friedman’s group found a retreatment success rate 79% for teeth with pre-existing LEO’s.

The question when observing retreatment failure is why?  With contemporary endodontic methodology, enhanced microscopic vision, cone beam CT’s, targeted irrigation protocols, and most recently laser assisted disinfection we are better than ever at removing bacteria from the root canal system. 

Schilder wrote in his classic 1974 article “Cleaning and Shaping of the Root Canal System” that all LEO’s have the ability to heal if the root canal system has been adequately cleaned, shaped and disinfected.  This is often misquoted as all LEO’s will heal.  Sadly, while poor endodontic technique and inadequate coronal seal will ensure long-term failure the opposite is not always a given.  Failure still occurs.  Could it be possible that there are extra-radicular sources of infection?

Jacinto et al, JOE 39:10, 2013, set out to answer this vexing question.  The group surgically removed, under aseptic conditions, the lesions from 20 teeth with persistent, symptomatic LEO’s which had been present radiographically for a minimum of one year.  All teeth had been retreated under strict chemo-mechanical protocols.  Teeth with sinus tracts, periodontal probing >4 mm, or root fractures (allowing oral vectors of bacterial contamination) as well as patients treated with antibiotics within the previous 3 months were excluded from the study.  CBCT’s were obtained in all cases to ensure that all intra-radicular anatomy had been found, cleaned, shaped, and filled 3 dimensionally.

The LEO’s were collected surgically under strict asepsis protocols to minimize the possibility of contamination from the oral cavity.  Care was taken not to touch the apical root segment preventing contaminating the lesion with bacteria colonizing the external surface of the root.  The samples were cultured for both aerobic and anaerobic bacteria.

The authors were able to culture bacteria from 95% of surgically obtained lesions of endodontic origin.  Cysts were found in 65% of samples with the remainder being granulomas.  Up to 7 species of bacteria were found with strict anaerobes predominating (84% of all species detected).

These results expand on our understanding of the pathogenicity of lesions of endodontic origin, their ability to heal with conventional endodontic treatment, and the reasons behind the occasional failure of otherwise good conventional endodontics we experience in our offices.  Other microbial studies have shown the tenacious nature of these infections and the complexity of the biofilms associated with extra-radicular infections including their resistance to both lesion penetration and efficacy of anti-microbial’s as well as the patients’ own immune system (Rhen et al Nat Immun 2002). Systemic factors such as Diabetes or immune deficiencies further reduce host healing capacity.

These failures are often frustrating for both patient and dentist.  Many patients are upset that they have to invest further time and funds when they hoped (or expected) that their problems would be solved.  Many dentists feel obligated to “fix” the problem and some may not understand or adequately convey to the patient that extra-radicular sources of infection may exist that are beyond the scope of conventional treatment protocols.

Endodontic failures may occasionally lead to relationship breakdown between the dentist and patient when these issues are not adequately understood and communicated.  One of the challenges for the Endodontist is to make sure the patient understands the biology of their endodontic infection and their treatment options.  An informed patient can take responsibility for their health care choices and most often are understanding, though not necessarily happy, when faced with adverse treatment outcomes.


Dr. Bittner was born and raised in the Surrey/Langley area. Following his pre-dental training at Simon Fraser University, he received his Doctor of Dental Medicine from the University of British Columbia in 1982 and his Certificate in Advanced Graduate Studies in Endodontics from Boston University’s Goldman School of Dental Medicine in 1995.

Dr. Bittner was in private practice in general dentistry for 11 years in Langley prior to his Endodontic specialty training. He has been practicing the Dental Specialty of Endodontics since 1995.

In his free time, Dr. Bittner loves to participate in a variety of sports including most recent, golfing! He also enjoys being a new grandfather, which if you ask him is just the best!

On December 9, 2014, posted in: News for Doctors by