NBDE Endodontics 2 — Questions and Answers
Question 1: Which radiographic finding is most characteristic of a periapical abscess compared to a periapical granuloma?
- Well-defined radiolucency with corticated border
- Diffuse radiolucency with poorly defined margins (Correct answer)
- Small radiolucency less than 1mm
- Hyperdense lesion at the apex
Correct answer: Diffuse radiolucency with poorly defined margins
Periapical abscesses typically appear as diffuse, poorly defined radiolucencies due to rapid bone destruction, whereas granulomas have more defined borders.
Question 2: A patient presents with a tooth that tests vital with cold but has a periapical radiolucency. What is the most likely diagnosis?
- Irreversible pulpitis with periapical abscess
- Periapical scar
- Non-odontogenic lesion or anatomical landmark (Correct answer)
- Chronic apical periodontitis
Correct answer: Non-odontogenic lesion or anatomical landmark
A vital pulp response with a periapical radiolucency suggests a non-odontogenic etiology or an anatomical structure (e.g., mental foramen, incisive canal) rather than pulpal pathology.
Question 3: During root canal preparation, the working length shortens by 2mm unexpectedly. What is the most likely cause?
- Ledge formation (Correct answer)
- Instrument separation
- Perforation
- Canal transportation
Correct answer: Ledge formation
Ledge formation creates a false canal wall that blocks instrument passage to the apex, causing an apparent reduction in working length.
Question 4: Which irrigant is most effective at dissolving organic pulp tissue remnants during root canal treatment?
- EDTA (17%)
- Chlorhexidine (2%)
- Sodium hypochlorite (5.25%) (Correct answer)
- Hydrogen peroxide (3%)
Correct answer: Sodium hypochlorite (5.25%)
Sodium hypochlorite is the only endodontic irrigant with proven ability to dissolve organic tissue due to its proteolytic action.
Question 5: What is the primary purpose of the smear layer removal step using EDTA in root canal treatment?
- Sterilize the canal walls
- Dissolve organic tissue
- Open dentinal tubules to improve sealer penetration (Correct answer)
- Whiten the dentin
Correct answer: Open dentinal tubules to improve sealer penetration
EDTA chelates calcium ions and removes the inorganic smear layer, exposing dentinal tubule openings to allow deeper sealer penetration.
Question 6: A tooth with a symptomatic irreversible pulpitis most commonly presents with which combination of symptoms?
- Mild, short-duration pain to cold that resolves quickly
- Spontaneous pain and lingering pain to thermal stimuli (Correct answer)
- No response to electric pulp test
- Pain only on percussion with no thermal response
Correct answer: Spontaneous pain and lingering pain to thermal stimuli
Symptomatic irreversible pulpitis is characterized by spontaneous pain and prolonged, lingering response to thermal stimuli lasting more than 30 seconds.
Question 7: Which rotary file system design feature reduces the risk of instrument separation?
- Increased taper (0.12)
- Asymmetric cross-section with off-center design (Correct answer)
- Multiple flutes with tight pitch
- Stainless steel composition
Correct answer: Asymmetric cross-section with off-center design
Asymmetric (off-center) cross-sections reduce the contact area with dentin walls, lowering torsional stress and the risk of fracture.
NBDE Endodontics 2
Which radiographic finding is most characteristic of a periapical abscess compared to a periapical granuloma?