Biofilms in endodontic infection

Bacterial biofilms are very prevalent in the apical root canals of teeth with primary and post‐treatment apical periodontitis. These bacterial endodontic communities are often found adhered to or at least associated with the dentinal canal walls, with bacterial cells encased in an extracellular amorphous matrix and often facing host inflammatory cells. This pattern of bacterial community arrangement in the root canal system is consistent with the acceptable criteria for including apical periodontitis in the set of biofilm‐mediated diseases. Whereas intraradicular biofilms are common in teeth with apical periodontitis lesions, extraradicular biofilms are found much less frequently and usually in association with symptoms. Morphological studies reveal that the structure of endodontic biofilms can vary from case to case and a unique pattern has not been established. Bacterial biofilms are expected to be even more prevalent in the root canals of teeth associated with long‐standing pathologic processes, including large apical radiolucencies and cysts. The very high frequency of biofilms in the root canals of treated teeth with post‐treatment disease may be interpreted as indirect evidence that, depending on location and possibly species composition, biofilms can be a challenge for proper root canal disinfection.