Free NBDE Endodontics Questions and Answers — Questions and Answers
Question 1: A patient presents with a chief complaint of a severe, spontaneous toothache in the lower right quadrant that awakens them at night. A cold stimulus applied to tooth #30 elicits a sharp pain that lingers for over 30 seconds. The tooth is not tender to percussion. Radiographs reveal a deep composite restoration but no periapical radiolucency. What is the most likely pulpal diagnosis?
- Reversible Pulpitis
- Pulp Necrosis
- Symptomatic Irreversible Pulpitis (Correct answer)
- Asymptomatic Apical Periodontitis
Correct answer: Symptomatic Irreversible Pulpitis
The classic signs of symptomatic irreversible pulpitis are spontaneous pain (especially at night), and a sharp, lingering pain in response to thermal stimuli (typically cold). Reversible pulpitis involves sharp pain that subsides immediately after the stimulus is removed. Pulp necrosis would not respond to cold testing. Asymptomatic apical periodontitis is a periapical diagnosis, not a pulpal one, and is associated with a necrotic pulp.
Question 2: Which of the following is the primary active ingredient in endodontic irrigating solutions responsible for dissolving necrotic pulp tissue and the organic components of the smear layer?
- Ethylenediaminetetraacetic acid (EDTA)
- Sodium hypochlorite (NaOCl) (Correct answer)
- Chlorhexidine gluconate
- Calcium hydroxide
Correct answer: Sodium hypochlorite (NaOCl)
Sodium hypochlorite (NaOCl) is a potent proteolytic and antimicrobial agent that is unique among common irrigants for its ability to dissolve organic tissue, such as pulpal remnants and the organic collagen matrix of the smear layer. EDTA removes the inorganic component, chlorhexidine is primarily an antibacterial rinse with no tissue-dissolving properties, and calcium hydroxide is an intracanal medicament.
Question 3: A dentist is performing a root canal on a mandibular first molar. Based on typical root and canal morphology, what is the most common configuration they should expect to find?
- One root with one canal
- Three separate roots (MB, DB, and Palatal)
- Two roots; one mesial and one distal, with one canal in each root
- Two roots; one mesial root with two canals and one distal root with one or two canals (Correct answer)
Correct answer: Two roots; one mesial root with two canals and one distal root with one or two canals
The mandibular first molar most commonly has two roots: a mesial and a distal root. The mesial root is wider and almost always contains two canals (mesiobuccal and mesiolingual). The distal root typically contains one large canal, but the presence of two canals is also a frequent variation.
Question 4: A 12-year-old patient presents with an avulsed permanent maxillary central incisor (#8) with a closed apex. The tooth was stored dry for 75 minutes before presentation. According to current IADT guidelines, what is the primary therapeutic goal of replanting this tooth?
- To encourage revascularization of the pulpal tissue.
- To allow for regeneration of the periodontal ligament.
- To maintain the alveolar bone contour via eventual ankylosis and replacement resorption. (Correct answer)
- To ensure the immediate return of normal proprioceptive function.
Correct answer: To maintain the alveolar bone contour via eventual ankylosis and replacement resorption.
After an extra-oral dry time exceeding 60 minutes, the periodontal ligament (PDL) cells are considered non-viable. Therefore, the goal of replantation is not to achieve true PDL healing but to use the tooth as a natural space maintainer. The tooth will undergo replacement resorption (ankylosis), which preserves the height and width of the alveolar bone, facilitating a future implant placement. Revascularization is not possible in a mature tooth.
Question 5: The primary purpose of using a 17% EDTA solution as a final rinse during chemo-mechanical debridement of a root canal is to:
- Kill resistant bacterial strains like E. faecalis.
- Remove the inorganic, mineralized component of the smear layer. (Correct answer)
- Dissolve any remaining vital pulp tissue.
- Act as a long-term intracanal medicament between appointments.
Correct answer: Remove the inorganic, mineralized component of the smear layer.
EDTA (Ethylenediaminetetraacetic acid) is a chelating agent. Its primary function in endodontics is to bind with calcium ions in the dentin, thereby removing the inorganic (mineralized) component of the smear layer that is created during instrumentation. This action unplugs the dentinal tubules, allowing for better disinfection and sealer adaptation. It does not dissolve organic tissue.
Question 6: Which of the following microorganisms is a facultative anaerobe most frequently implicated in persistent or secondary endodontic infections and is known for its resistance to common intracanal medicaments?
- Porphyromonas gingivalis
- Streptococcus mutans
- Actinomyces israelii
- Enterococcus faecalis (Correct answer)
Correct answer: Enterococcus faecalis
Enterococcus faecalis is a gram-positive facultative anaerobe renowned for its ability to survive in the harsh environment of an obturated root canal. It can form biofilms, invade dentinal tubules, and is notably resistant to high pH environments, such as those created by calcium hydroxide, making it a common culprit in failed endodontic treatments.
Free NBDE Endodontics Questions and Answers
A patient presents with a chief complaint of a severe, spontaneous toothache in the lower right quadrant that awakens them at night.
A cold stimulus applied to tooth #30 elicits a sharp pain that lingers for over 30 seconds.
The tooth is not tender to percussion.
Radiographs reveal a deep composite restoration but no periapical radiolucency.
What is the most likely pulpal diagnosis?