Microbial flora of root canal-treated teeth associated with asymptomatic periapical radiolucent lesions

This study aimed to investigate the composition of microflora in endodontic ally treated teeth associated with asymptomatic periapical lesions in south ern Chinese patients. Twenty-four teeth which had received nonsurgical root canal treatment more than 4 years previously, and which presents an accept able coronal restoration with a periapical radiolucent area, were re-treate d nonsurgically. Bacteriological samples were obtained after removal of the old root canal filling. The samples were inoculated on enriched trypticase soy agar and four selective media for incubation at 37 degreesC in both a carbon dioxide-enriched atmosphere and anaerobically. Eighteen teeth that h ad received gutta-percha root canal fillings were grouped for analysis, 12 (66.7%) of which contained cultivable microorganisms. The total colony form ing units per ml of transport medium ranged from 0 to 2.3 X 10(5). The numb er of bacterial genera recovered ranged between 0 and 6, with facultative g ram-positive cocci being the most prevalent group of bacteria isolated. Fac ultative anaerobic bacteria were present in all, whereas strict anaerobic b acteria were found in 3 out of the 12 teeth with positive growth. The size of the periapical rarefaction did not show any relationship with the quanti ty of microorganisms recovered. Coagulase-negative staphylococci, streptoco cci and Pseudomonas aeruginosa were most frequently isolated in this group of patients. The possible origin of these organisms is discussed.