Ultrastructural Examination of Failed Molar Retreatment with Secondary Apical Periodontitis: An Examination of Endodontic Biofilms in an Endodontic Retreatment Failure Gary B. Carr, DDS,* Richard S. Schwartz, DDS, † Christoph Schaudinn, PhD, ‡ Amita Gorur, MSc, § and J. William Costerton, PhD k¶ Abstract A light and electron microscope examination of the re- sected root tip of a failing endodontically re-treated lower molar was examined. The tooth had been initially treated 10 years ago and then re-treated 2 years ago. The resected root tip was sectioned axially, and thin sections were examined through the entire length of the specimen. Thin sections were examined with a trans- mission electron microscope. The thin sections were randomly chosen along the isthmus areas between the mesiobuccal and mesiolingual canals. Our findings suggest that a complex, variable, multispecies biofilm was present the entire length of the specimen. (J Endod 2009;35:1303–1309) Key Words Apical periodontitis, biofilm, endodontic failure, endodontic retreatment, ultrastructural P rimary apical periodontitis is one of the most common bacterial diseases of humans, afflicting as many as 60% of all individuals worldwide at some point in their life span (1). It has been established conclusively that the cause of the disease stems from the microbial colonization of the root canal space by oral microorganisms, leading to subsequent periapical breakdown from the spread of these organisms, or their toxins, into the periodontal ligament space and bone (2–4). Of the more than 700 species of bacteria thought to be present in the mouth (5), it appears only a limited number of species are capable of surviving and per- sisting in the root canal environment, and an even smaller number are capable of surviving endodontic treatment regimens whose sole purpose is directed toward eliminating them (6–10). Contemporary research has also tried to make a distinction between primary apical periodontitis and secondary apical periodontitis (6–12). The distinction proposed is that in primary apical periodontitis (disease present before any treatment) the organisms are predominately gram-negative obligate or facultative anaerobes that are multispecies in character, whereas in secondary disease (post-treatment disease) the organisms are facultative gram-positive organisms of a very limited species distri- bution and are perhaps even monoinfections (11–13). There is much recent work that demonstrates that the most likely disease model for endodontics is a biofilm model, just as it is in periodontal disease, and that although acute disease might be caused by planktonic organisms, the source for all these organ- isms is from a preexisting and ever-present biofilm (14–19). By using combined light and electron microscopy, Nair et al (18–20) have shown conclusively that in both primary and secondary apical periodontitis, the organisms colonizing the root canal space are growing in verdant biofilms. One might suspect that the organisms capable of surviving treatment rendered 10 years ago and then re-treated to a very high standard with 30 days of Ca(OH)2 would show a less verdant biofilm structure, given the extreme nutrient scarcity in such cases, and that such a biofilm would consist of only a very small number of species. Certainly the culturing model and the literature predict that (21). This work attempts to test that viewpoint by carefully examining one such case in great detail. Materials and Methods The patient was a 39-year-old woman in good general health with no signif- icant medical history. She presented in 2005 with periodic spontaneous pain and tenderness at tooth #30. Clinical tests revealed #30 was mildly tender to percussion. It had a periapical radiolucency associated with the distal root and widening of the periodontal ligament at the apex of the mesial root. There were no significant probing depths and no evidence of a sinus tract. The adjacent teeth were non- tender and responded normally to cold. According to the patient, the original root canal treatment was performed in about 1995 and had ‘‘bothered her on and off’’ over the years. After discussing the options of retreatment, surgery, or extraction, the patient made the decision to re-treat. Access was made through her metal-ceramic crown, and gutta-percha was removed from 3 canals. There was an untreated distobuccal From *Pacific Endodontic Research Foundation, San Diego, CA; † Private practice, San Antonio, TX; ‡ Center for Biofilms, USC School of Dentistry, Los Angeles, CA; § Lawrence Berkeley National Laboratory, Berkeley, CA; k Department of Orthopedic Surgery, Allegheny General Hospital, Pittsburgh, PA; and ¶ Center for Genomic Sciences, Allegheny-Singer Research Institute, Pittsburgh, PA. Address requests for reprints to Dr Gary B. Carr, Pacific Endodontic Research Foundation, 6235 Lusk Blvd, San Diego, CA 92121. E-mail address: gary@tdo4endo.com. 0099-2399/$0 - see front matter Copyright ª 2009 American Association of Endodontists. doi:10.1016/j.joen.2009.05.035 Case Report/Clinical Techniques JOE — Volume 35, Number 9, September 2009 Failed Molar Retreatment with Secondary Apical Periodontitis 1303