FREE NBDE Endodontics 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?

Accepted Answer

Symptomatic Irreversible Pulpitis

Answer

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?

Accepted Answer

Sodium hypochlorite (NaOCl)

Answer

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?

Accepted Answer

Two roots; one mesial root with two canals and one distal root with one or two canals

Answer

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?

Accepted Answer

To maintain the alveolar bone contour via eventual ankylosis and replacement resorption.

Answer

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:

Accepted Answer

Remove the inorganic, mineralized component of the smear layer.

Answer

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.

NBDE - National Board Dental Examination Practice Test

NBDE - National Board Dental Examination Practice Test

FREE NBDE Endodontics Questions and Answers