NBDE Endodontics 4

Question 1

Which microorganism is most commonly isolated from teeth with failed root canal treatment (persistent infection)?

Accepted Answer

Enterococcus faecalis

Answer

Enterococcus faecalis dominates persistent endodontic infections due to its ability to survive in nutrient-poor, alkaline environments and resist calcium hydroxide treatment.

Question 2

A patient presents with a draining sinus tract on the attached gingiva near tooth #30. The tract is traced with a gutta-percha cone. Where does the cone most likely terminate?

Accepted Answer

Periapical region of the offending tooth

Answer

Sinus tracts from endodontic origin typically track through bone and soft tissue to terminate at the periapical area of the causative tooth.

Question 3

Which sealer type is considered the current gold standard for biocompatibility and bond strength in root canal obturation?

Accepted Answer

Epoxy resin-based sealers (AH Plus)

Answer

Epoxy resin-based sealers like AH Plus demonstrate superior bond strength to dentin, low solubility, and excellent long-term clinical performance.

Question 4

During access preparation of a mandibular second premolar, the clinician should anticipate which unusual canal configuration?

Accepted Answer

Possible two canals that may or may not merge

Answer

Mandibular premolars have notoriously variable canal anatomy, with two canals present in a significant percentage that may merge or remain separate — a major source of treatment failure.

Question 5

When calcium hydroxide is used as an intracanal medicament, its primary antimicrobial mechanism is:

Accepted Answer

Disruption of bacterial membranes by hydroxyl ions raising pH above 11

Answer

The high pH (>11) generated by hydroxyl ion release denatures bacterial proteins and enzymes, disrupts membrane integrity, and damages bacterial DNA.

NBDE - National Board Dental Examination Practice Test

NBDE - National Board Dental Examination Practice Test

NBDE Endodontics 4