NBDE Knowledge 4 — Questions and Answers
Question 1: Which of the following is the primary buffer system in saliva?
- Bicarbonate-carbonic acid system (Correct answer)
- Phosphate buffer system
- Protein buffer system
- Ammonia buffer system
Correct answer: Bicarbonate-carbonic acid system
The bicarbonate-carbonic acid system is the dominant salivary buffer, especially at high flow rates, neutralizing acids produced by oral bacteria.
Question 2: The cell-rich zone of Höhl in the dental pulp is located:
- Immediately beneath the cell-free zone (Correct answer)
- Adjacent to the odontoblast layer
- In the central pulp core
- At the apical foramen
Correct answer: Immediately beneath the cell-free zone
The cell-rich zone of Höhl lies immediately beneath the acellular cell-free zone of Weil and contains fibroblasts and undifferentiated mesenchymal cells.
Question 3: Which landmark is used to locate the mental foramen during a mental nerve block?
- Between the first and second mandibular premolars (Correct answer)
- Distal to the mandibular canine
- Mesial to the first mandibular molar
- At the symphysis menti
Correct answer: Between the first and second mandibular premolars
The mental foramen is typically located between the apices of the first and second mandibular premolars, slightly below the apices.
Question 4: Which histologic feature is pathognomonic of ameloblastoma?
- Stellate reticulum-like cells within follicles lined by palisaded columnar cells (Correct answer)
- Calcified ghost cells
- Rushton bodies
- Asteroid bodies
Correct answer: Stellate reticulum-like cells within follicles lined by palisaded columnar cells
Ameloblastoma mimics the enamel organ with peripheral palisaded columnar cells and a central stellate reticulum pattern in follicular arrangements.
Question 5: During mandibular development, Meckel's cartilage primarily:
- Serves as a template that is later replaced by intramembranous ossification (Correct answer)
- Directly ossifies to form the mandible
- Forms the condylar cartilage
- Persists as the mandibular symphysis
Correct answer: Serves as a template that is later replaced by intramembranous ossification
Meckel's cartilage acts as a scaffold alongside which the mandible forms by intramembranous ossification; the cartilage itself mostly disappears.
Question 6: Which complement pathway is activated by antigen-antibody complexes?
- Classical pathway (Correct answer)
- Alternative pathway
- Lectin pathway
- Terminal pathway
Correct answer: Classical pathway
The classical complement pathway is initiated by C1q binding to antigen-antibody (IgG or IgM) complexes on pathogen surfaces.
Question 7: A radiolucent lesion at the apex of a vital tooth most likely represents:
- Periapical cemento-osseous dysplasia (early stage) (Correct answer)
- Periapical abscess
- Periapical granuloma
- Periapical cyst
Correct answer: Periapical cemento-osseous dysplasia (early stage)
Early periapical cemento-osseous dysplasia presents as a radiolucency at the apex of vital teeth, most commonly mandibular anterior teeth in middle-aged women.
NBDE Knowledge 4
Which of the following is the primary buffer system in saliva?