NBDE Endodontics 3 — Questions and Answers
Question 1: Which obturation technique involves heating gutta-percha and compacting it into the canal using a carrier?
- Cold lateral condensation
- Thermoplastic injection
- Carrier-based obturation (Thermafil) (Correct answer)
- Continuous wave condensation
Correct answer: Carrier-based obturation (Thermafil)
Carrier-based systems like Thermafil use a plastic or metal carrier coated with alpha-phase gutta-percha that is heated and inserted to fill the canal.
Question 2: A patient develops paresthesia of the lower lip after root canal treatment of a mandibular second molar. What is the most likely cause?
- Over-instrumentation beyond the apex compressing the inferior alveolar nerve (Correct answer)
- Failure to achieve adequate anesthesia
- Vertical root fracture
- Lateral perforation into the furcation
Correct answer: Over-instrumentation beyond the apex compressing the inferior alveolar nerve
Overfilling or aggressive instrumentation beyond the apex of mandibular molars can impinge on or chemically injure the inferior alveolar nerve, causing paresthesia.
Question 3: What distinguishes a Type IV canal configuration (Weine classification) from Type III?
- Two separate canals that merge into one before the apex
- One canal that divides into two at the apex with two foramina (Correct answer)
- Two separate canals with two separate foramina
- One canal with one foramen
Correct answer: One canal that divides into two at the apex with two foramina
Weine Type IV begins as one canal and divides near the apex into two separate canals with two distinct apical foramina.
Question 4: Which condition is an absolute contraindication to performing a pulpotomy on a primary molar?
- Deep caries approaching the pulp
- Physiologic root resorption of one-third of the root
- Pathologic internal root resorption (Correct answer)
- Absence of a permanent successor
Correct answer: Pathologic internal root resorption
Pathologic internal root resorption indicates the radicular pulp is irreversibly inflamed and infected, making pulpotomy (which preserves the radicular pulp) contraindicated.
Question 5: The zone of coagulation necrosis seen after MTA or calcium hydroxide apexification therapy heals primarily by which process?
- Resolution and complete regeneration of pulp tissue
- Calcific bridge formation via dentinogenesis
- Fibrous connective tissue scar replacement
- Cementum deposition over the apex (cementogenesis) (Correct answer)
Correct answer: Cementum deposition over the apex (cementogenesis)
Calcium hydroxide and MTA promote apical closure primarily through cementogenesis, with cementum-like hard tissue deposited over the open apex.
Question 6: A mandibular first molar shows a 'J-shaped' periapical radiolucency extending along the lateral root surface. What is the most likely cause?
- External inflammatory root resorption
- Vertical root fracture (Correct answer)
- Lateral canal with accessory foramen
- Dentigerous cyst
Correct answer: Vertical root fracture
A J-shaped radiolucency along the lateral root surface extending to the apex is pathognomonic of a vertical root fracture.
Question 7: In regenerative endodontic procedures (REP), blood clot scaffold creation requires instrumentation to what level?
- Working length (apical foramen)
- 3mm short of working length
- 1mm beyond the apex to induce bleeding (Correct answer)
- Mid-root level only
Correct answer: 1mm beyond the apex to induce bleeding
Files or instruments are intentionally extended 1–2mm beyond the apex to lacerate periapical tissues and induce bleeding into the canal space to form a blood clot scaffold.
NBDE Endodontics 3
Which obturation technique involves heating gutta-percha and compacting it into the canal using a carrier?