NBDE Periodontics and Endodontics 5 — Questions and Answers
Question 1: What is the function of EDTA in endodontic treatment?
- Dissolves organic tissue in the canal
- Chelates calcium to remove the smear layer (Correct answer)
- Kills anaerobic bacteria in the canal
- Lubricates files to prevent fracture only
Correct answer: Chelates calcium to remove the smear layer
EDTA (ethylenediaminetetraacetic acid) chelates calcium ions in dentin, removing the smear layer and opening dentinal tubules to improve sealer penetration and disinfection.
Question 2: Which periodontal surgery technique uses an envelope flap to access root surfaces without creating vertical releasing incisions?
- Modified Widman flap
- Papilla preservation flap (Correct answer)
- Apically positioned flap
- Undisplaced full-thickness flap
Correct answer: Papilla preservation flap
The papilla preservation flap design maintains the interdental papilla intact, providing better esthetic outcomes and blood supply to the flap while accessing root surfaces.
Question 3: A tooth with a root canal-treated tooth develops a new periapical lesion 3 years post-treatment. What is the FIRST step in management?
- Immediate surgical apicoectomy
- Nonsurgical endodontic retreatment (Correct answer)
- Extraction and implant placement
- Long-term antibiotic therapy
Correct answer: Nonsurgical endodontic retreatment
Nonsurgical retreatment is the first-line approach for failed root canal therapy, as it addresses the most common cause of failure (inadequate debridement/seal) with less morbidity than surgery.
Question 4: Which microorganism is MOST commonly found in persistent/failed root canal infections?
- Porphyromonas gingivalis
- Enterococcus faecalis (Correct answer)
- Treponema denticola
- Fusobacterium nucleatum
Correct answer: Enterococcus faecalis
Enterococcus faecalis is the dominant organism in persistent endodontic infections due to its resistance to calcium hydroxide, ability to invade dentinal tubules, and survival in nutrient-poor environments.
Question 5: During a periodontal examination, 'bleeding on probing' (BOP) is MOST accurately described as an indicator of:
- Permanent bone loss
- Active periodontal infection at that site
- Gingival inflammation (Correct answer)
- Tooth mobility
Correct answer: Gingival inflammation
Bleeding on probing (BOP) is primarily an indicator of gingival inflammation; its absence is more useful as a negative predictor of disease activity than its presence is as a positive predictor.
Question 6: A patient presents with pain only on release of bite pressure on a specific tooth. This symptom is MOST consistent with:
- Acute apical abscess
- Cracked tooth syndrome (Correct answer)
- Reversible pulpitis
- Chronic periodontitis
Correct answer: Cracked tooth syndrome
Pain upon release of biting pressure (rebound pain) is pathognomonic of cracked tooth syndrome, as the crack opens and closes during function, stimulating pulpal nerves on release.
Question 7: What is the purpose of using calcium hydroxide as an intracanal medicament between endodontic appointments?
- To dissolve the smear layer
- To provide antimicrobial action and induce hard tissue formation (Correct answer)
- To lubricate canals for the next appointment
- To temporarily obturate the canal space
Correct answer: To provide antimicrobial action and induce hard tissue formation
Calcium hydroxide's high pH (~12.5) provides broad antimicrobial action and, when placed at the apex, can stimulate hard tissue formation (apexification) in teeth with open apices.
NBDE Periodontics and Endodontics 5
What is the function of EDTA in endodontic treatment?