Abstract: Abstract：Objective To investigate the presence and distribution of extraradicular biofilm on the apical root surfaces of human teeth with persistent periapical periodontitis. Methods Ten apex samples of single-rooted teeth with persistent periapical periodontitis were collected during root-end surgery. Five single-rooted teeth extracted for orthodontic reasons were selected as controls. All samples were initially evaluated using scanning electron microscopy after freeze-drying. The same samples were then processed with Brown and Brenn-modi?ed Gram staining. Results The root outside surfaces of teeth extracted for orthodontic reasons were covered by fibers and there was no cementum resorption or microorganisms. Extraradicular biofilm and cementum resorption were found in all teeth with persistent periapical periodontitis. The extraradicular bacteria were predominantly rods and filaments, and surrounded by a varying amount of amorphous extracellular material. Conclusions The extraradicular biofilm may be one of the important factors which cause persistent periapical periodontitis.

Key words: persistent periapical periodontitis, extraradicular biofilm, scanning electron microscopy