Microbial diversity in failed endodontic root-filled teeth

Background Persistent/secondary infections of human root canals play an important role in the failure of endodontic treatment. This study used 16S rRNA sequencing to assess microbial diversity in root-filled teeth associated with failed endodontic treatment. Methods DNA was extracted from 15 teeth with persistent intraradicular infections, and the 16S rRNA of all present bacteria were amplified by PCR, followed by cloning and sequencing of the 16S rRNA amplicons. Results All sample extracts were positive for PCR amplification using the universal 16S rRNA gene primers. Negative control reactions yielded no amplicons. Sixty-five phylotypes belonging to seven phyla were identified from 760 clones; a mean of 9.4 phylotypes were detected in each sample （range 3-15）. Twenty-eight phylotypes were detected in more than one sample, revealing a high inter-sample variability. Parvimonas micra （60%, 9/15）, Solobacterium moore （47%, 7/15）, Dialister invisus （33%, 5/15）, Enterococcus faecalis （33%, 5/15）, Filifactor alocis （27%, 4/15）, and Fusobacterium nucleatum （27%, 4/15） were the prevalent species. Nineteen as-yet-uncultivated phylotypes were identified, comprising a substantial proportion of the bacteria in many cases. Conclusions Persistent intraradicular infections were present in all root-filled teeth associated with failed endodontic treatment. The current observations reveal new candidate endodontic pathogens, including as-yet-uncultivated bacteria and phylotypes that may participate in the mixed infections associated with post-treatment apical periodontitis.

Morphology of bacterial flora in root canals associated with apical abscesses

Background Apical abscess is an inflammatory process in the peri-radicular tissues caused by biofilms in the necrotic root canal systems. Therefore, a comprehensive analysis of the bacterial colonization is required for a better understanding of the pathogenesis. This study aimed to investigate the patterns of bacterial infection of root canals of teeth with apical abscesses and to determine whether histological and microbiological findings correlated with clinical conditions. Methods Eighteen samples from 18 teeth with apical pathological lesions were analyzed. Nine patients with acute apical abscesses experienced severe pain, and nine patients were asymptomatic with a sinus tract. After extraction, each affected root was divided into two halves. One half was processed for histobacteriologic analysis and examined using light microscopy, and the other half was analyzed using scanning electron microscopy （SEM） to determine the patterns of microbial colonization of the root canals. Results The appearance of each sample subjected to SEM was consistent with the histobacteriologic findings despite the presence or absence of clinical symptoms. Intraradicular biofilms comprising cocci, rods, and/or filaments of amorphous materials were observed in the apical third of the main root canals in all samples. The bacterial biofilms covering the main root canal walls also penetrated the dentinal tubules to varying depths. The morphologies of biofilms varied, and a unique pattern of intraradicular infection was not identified. Conclusion Intraradicular infections formed complex and variable multispecies biofilms and their presence did not correlate with clinical symptoms.