NBDE MCQ 3 — Questions and Answers
Question 1: The canine eminence is formed by the root prominence of which tooth?
- Maxillary first premolar
- Maxillary canine (Correct answer)
- Mandibular canine
- Maxillary lateral incisor
Correct answer: Maxillary canine
The maxillary canine has the longest root in the dentition, creating a prominent bony ridge called the canine eminence on the anterior maxilla.
Question 2: Which type of hypersensitivity reaction is responsible for allergic contact stomatitis from dental materials?
- Type I (IgE-mediated)
- Type II (cytotoxic)
- Type III (immune complex)
- Type IV (cell-mediated) (Correct answer)
Correct answer: Type IV (cell-mediated)
Allergic contact stomatitis is a Type IV delayed hypersensitivity reaction mediated by sensitized T-lymphocytes reacting to haptens from dental materials.
Question 3: During mandibular nerve block, the needle tip should be positioned adjacent to which structure?
- Coronoid notch
- Pterygomandibular raphe
- Mandibular foramen (Correct answer)
- External oblique ridge
Correct answer: Mandibular foramen
The inferior alveolar nerve block targets the mandibular foramen on the medial ramus where the inferior alveolar nerve enters the mandibular canal.
Question 4: A white, non-removable plaque-like lesion of the oral mucosa that cannot be characterized as any other condition is called:
- Candidiasis
- Leukoplakia (Correct answer)
- Lichen planus
- Leukoedema
Correct answer: Leukoplakia
Leukoplakia is a clinical diagnosis of exclusion — a white patch that cannot be scraped off and cannot be identified as another specific lesion, with malignant potential.
Question 5: The working length in endodontic treatment is measured to:
- The cemento-enamel junction
- 1 mm short of the radiographic apex
- The major foramen
- The minor constriction (apical constriction) (Correct answer)
Correct answer: The minor constriction (apical constriction)
Working length is established to the apical constriction (minor foramen), typically 0.5–1 mm from the radiographic apex, to preserve the apical seal.
Question 6: Which enzyme is primarily responsible for initiating caries by metabolizing sucrose to form insoluble glucans?
- Lactate dehydrogenase
- Glucosyltransferase (Correct answer)
- Phosphoenolpyruvate transferase
- Fructokinase
Correct answer: Glucosyltransferase
Glucosyltransferase (GTF) from Streptococcus mutans synthesizes insoluble glucans from sucrose, enabling bacterial adhesion and biofilm formation.
Question 7: In a Class II cavity preparation, the gingival floor should be positioned:
- At the cemento-enamel junction
- Coronal to the contact area
- Apical to the contact area by at least 0.5 mm (Correct answer)
- At the height of contour
Correct answer: Apical to the contact area by at least 0.5 mm
The gingival floor must be placed apical to the proximal contact to allow adequate separation for matrix placement and to ensure margins are accessible for finishing.
NBDE MCQ 3
The canine eminence is formed by the root prominence of which tooth?