Endodontics · patient case question
Which organisms predominate in a primary endodontic infection?
Patient case: The Tooth That Jumped Mid-Treatment
Patient: 39-year-old male
Chief Complaint: Referred for root canal treatment of tooth #14. He reports no symptoms at all.
Background: Large restoration placed years ago. Routine radiograph revealed an apical lesion.
Medications: None
Vital Signs: BP 122/76 mmHg · HR 72 bpm · RR 16 · T 98.4°F
Findings: Tooth #14 is asymptomatic and does not respond to cold, with a well-defined apical radiolucency. Under local anaesthesia the canals are being negotiated when the patient suddenly jumps in pain as a file advances. Later in the appointment, after instrumentation, one canal bleeds persistently on irrigation.
Show answer and explanation
Correct answer: C. Obligate anaerobes
- A. Facultative organisms are present but are a minority in PRIMARY infections. They become important in SECONDARY and PERSISTENT infections — Enterococcus faecalis is the classic facultative organism of failed root canal treatment, surviving because it tolerates high pH and nutrient deprivation.
- B. Microaerophiles are a minor component, not the predominant group.
- C. CORRECT. Primary endodontic infections are POLYMICROBIAL and dominated by OBLIGATE ANAEROBES — typically 90% or more of the flora. The necrotic canal has no circulation, no oxygen and a low redox potential, which selects strongly for anaerobic growth. Common isolates include Porphyromonas, Prevotella, Fusobacterium, Peptostreptococcus and Dialister.
- D. Obligate aerobes cannot survive in the anoxic environment of a necrotic root canal.
Note: Clinical link: this is why metronidazole (active only against anaerobes) is a rational adjunct in endodontic infection, and why the shift to E. faecalis in retreatment cases changes the disinfection strategy.