Root Canal Microbiology — ORE Part 1 MCQ

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ModerateEndodonticsRoot Canal MicrobiologyORE Part 1

A root-filled tooth has a persistent periapical radiolucency and is being treated by nonsurgical endodontic retreatment. Which organism is most commonly isolated from the root canal in this setting?

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Correct answer: E — Enterococcus faecalis

Explanation lettering: E = shown as A · C = shown as B · D = shown as C · B = shown as D · A = shown as E

A is correct. In persistent intraradicular infection associated with failed root-canal treatment and a persisting periapical lesion, Enterococcus faecalis is the most frequently recovered organism. Its ability to survive adverse canal conditions and form biofilm helps explain its association with post-treatment endodontic disease. The qualification that the tooth is root-filled and undergoing retreatment is decisive: the microbial profile of an untreated primary infection is more polymicrobial and anaerobe-rich. Streptococcus mutans and Lactobacillus acidophilus are principally associated with dental caries. Staphylococcus aureus is not a typical dominant organism in persistent endodontic infection. Porphyromonas gingivalis may occur in endodontic infections, particularly alongside other anaerobes, but it is not the most commonly isolated organism in this post-treatment setting.

Reference: Pinheiro ET, Gomes BPFA, Ferraz CCR, et al. Microorganisms from canals of root-filled teeth with periapical lesions. International Endodontic Journal. 2003;36(1):1-11. https://pubmed.ncbi.nlm.nih.gov/12656508/