Imaging of extraradicular biofilm using combined scanning electron microscopy and stereomicroscopy.

Microorganisms are able to survive and induce persistent infection in extraradicular areas. The objective of this study was to evaluate the relationship between extraradicular biofilm and persistent periapical periodontitis. Thirty-five apical samples with different stages of pulp and periapical pathology (vital pulp, pulp necrosis without radiographically visible periapical lesions, chronic periapical periodontitis that had not received root canal therapy and persistent periapical periodontitis) were initially evaluated using scanning electron microscopy. The same samples were then processed using Brown and Brenn-modified Gram staining. We detected extraradicular biofilm in all samples with persistent periapical periodontitis and in three samples with chronic periapical periodontitis. The extraradicular bacteria predominantly had rod and filament morphology and were surrounded by varying amounts of amorphous extracellular material. The surfaces outside the root of the apical samples with vital pulp and pulp necrosis were covered by fibers, and no extraradicular microorganisms were present, which suggests that extraradicular biofilm is closely associated with failed endodontic treatments, thus resulting in persistent infection.