The Tooth That Jumped Mid-Treatment

Correct answer: A. Vital, inflamed pulp tissue remains in one of the canals

• A. CORRECT. Pulp necrosis is frequently PARTIAL. A multi-rooted tooth can have a necrotic pulp in one canal — producing the negative cold response and the apical lesion — while another canal, most often the palatal or the second mesiobuccal, still contains VITAL, INFLAMED tissue. That tissue is exquisitely sensitive, and the file contacting it produces exactly this sudden sharp pain. The correct response is supplemental anaesthesia: intraligamentary or, most reliably, INTRAPULPAL injection directly into the responsive canal.
• B. A separated instrument is a mechanical complication. Broken metal in a canal does not itself cause pain — there is no nerve to stimulate if the tissue is necrotic.
• C. Apical perforation would cause pain on exceeding the apex — but the tooth is necrotic, and the periapical tissue is anaesthetised by the block. It also would not explain the persistent bleeding later.
• D. If the block had failed entirely, the patient would have been uncomfortable from the moment of access, not at one specific point in one canal.

Note: ⚑ FLAG. The recall keyed 'broken file'. A separated file causes no pain. The finding that the tooth is asymptomatic yet has an apical lesion, combined with sudden pain on instrumentation, points squarely to residual vital tissue. Pulp testing gives a single answer for a tooth with several canals — that is its limitation.

Correct answer: B. Vital tissue remains near the apex, or the working length has been exceeded

• A. Coronal over-instrumentation causes strip perforation or a weakened root, not apical bleeding.
• B. CORRECT. Persistent bleeding after apparently complete instrumentation means either that VITAL TISSUE REMAINS in the apical portion of the canal, or that the instruments have passed BEYOND the apical constriction into the vascular periapical tissues. Both are corrected the same way: re-establish an accurate working length with an apex locator, confirm radiographically, and complete cleaning and shaping to that length.
• C. Sodium hypochlorite at any clinical concentration does not cause bleeding — it dissolves tissue. Extruded hypochlorite causes sudden severe pain, rapid swelling and ecchymosis, a very different picture.
• D. Local anaesthetic does not cause intracanal bleeding.

Note: Two useful checks: an apex locator reading that will not stabilise, and a paper point that comes back blood-soaked at the tip only. Both indicate the apical constriction has been breached.

Correct answer: B. To protect the patient from aspirating or swallowing instruments and irrigants

• A. Soft-tissue retraction is a convenience benefit.
• B. CORRECT. PATIENT PROTECTION is the primary and non-negotiable reason. The rubber dam prevents aspiration or ingestion of files, burs and irrigants, and shields the soft tissues from sodium hypochlorite — a hypochlorite accident in an unprotected mouth causes chemical burns to the mucosa and can be sight-threatening if it reaches the eye. This is why rubber dam use during endodontic treatment is regarded as the STANDARD OF CARE, and its omission has been the basis of successful malpractice claims.
• C. Aerosol reduction is a real ancillary benefit, but not the primary rationale.
• D. Moisture control and asepsis are genuine and important benefits — the dam prevents salivary bacteria from re-contaminating the canal system — but they are secondary to patient safety.

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.