[Bacterial biofilm on the apical external root surfaces of human teeth associated with chronic periradicular lesions].

Objective: To investigate the patterns of microbial infection on the apical external root surfaces of treated and untreated teeth associated with chronic apical periodontitis and to study bacteria in the biofilm in order to find out the species, constitution and origination of bacteria in periapical biofilm.

Methods: Ten teeth with chronic apical periodontitis from patients of the Department of Stomatology of People's Hospital, Peking University: 5 untreated teeth with a radiographically visible chronic periradicular lesions and 5 teeth with extensive carious lesions, radiolucent lesions of varying sizes and attached periradicular tissues were selected for study. Using aseptic techniques and sterile instruments, bacterial samples of the root canals were taken, inoculated and separated according to usual practice. After extraction, ten teeth were fixed and the apical 5 mm portion of one root was sectioned. Root tips were dehydrated, sputter coated with gold, and then examined for the occurrence of bacteria on the apical root surfaces using scanning electron microscope. Five healthy teeth with vital pulp were used as controls.

Results: Microbial study showed that ten specimens yielded bacterial growth. The most prevalent bacteria were P. micros and F. nueleatum. In the 5 untreated teeth, bacterial cells were usually observed close to the apical foramen in only 1 specimen. Morphologically, these bacteria consisted of cocci. In the 5 treated teeth, a dense bacterial aggregation composed mainly of cocci and rods was observed surrounding the apical foramen of all specimens. Besides rods, other bacterial morphological types were recognized, including coaggregations of cocci and filaments, characterizing a fully developed "corn-cob". No microorganisms were found in the healthy controls.

Conclusion: Bacterial biofilm was always present in teeth with post-treatment endodontic disease. The presence of apical bacterial biofilm is clinically important, and it may cause failure of endodontic treatment as a consequence of persistent infection.