NBDE Microbiology and Pathology 3 — Questions and Answers
Question 1: Which hepatitis virus is transmitted parenterally and poses the greatest occupational risk to dental healthcare workers through needlestick injuries?
- Hepatitis B virus (HBV) (Correct answer)
- Hepatitis A virus (HAV)
- Hepatitis C virus (HCV)
- Hepatitis E virus (HEV)
Correct answer: Hepatitis B virus (HBV)
HBV has the highest risk of transmission via needlestick (6–30%) compared to HCV (1.8%) or HIV (<0.3%), making vaccination essential for dental workers.
Question 2: A patient with recurrent herpetic labialis is under stress. Which statement best describes the pathogenesis of the recurrence?
- HSV-1 reactivates from latency in the trigeminal ganglion (Correct answer)
- Re-infection occurs from a new exogenous HSV-1 source
- HSV-1 persists actively in epithelial cells between outbreaks
- Antibody levels drop below protective thresholds
Correct answer: HSV-1 reactivates from latency in the trigeminal ganglion
HSV-1 establishes latency in the trigeminal ganglion and reactivates due to triggers like stress, UV exposure, or immunosuppression.
Question 3: An ameloblastoma is best characterized histologically by which pattern?
- Follicular islands with peripheral columnar cells and stellate reticulum (Correct answer)
- Sheets of basaloid cells with peripheral palisading and necrosis
- Mucus-secreting glandular elements within a fibrous stroma
- Calcified ghost cells within an epithelial neoplasm
Correct answer: Follicular islands with peripheral columnar cells and stellate reticulum
The follicular pattern of ameloblastoma shows islands of odontogenic epithelium with reverse-polarized columnar basal cells and a stellate reticulum core.
Question 4: Which organism is implicated as the primary etiologic agent of localized aggressive periodontitis (previously juvenile periodontitis)?
- Aggregatibacter actinomycetemcomitans (Correct answer)
- Treponema denticola
- Prevotella intermedia
- Tannerella forsythia
Correct answer: Aggregatibacter actinomycetemcomitans
Aggregatibacter actinomycetemcomitans produces leukotoxin and is the primary pathogen in localized aggressive periodontitis affecting first molars and incisors.
Question 5: A painless, slowly enlarging radiolucency at the angle of the mandible is found in a 25-year-old. Histology shows a parakeratinized stratified squamous epithelium lining. The diagnosis is:
- Odontogenic keratocyst (OKC) (Correct answer)
- Radicular cyst
- Lateral periodontal cyst
- Dentigerous cyst
Correct answer: Odontogenic keratocyst (OKC)
OKC is characterized by a thin, parakeratinized epithelium with a corrugated surface and high recurrence rate, often associated with Gorlin syndrome.
Question 6: In the complement system, which component is shared by both the classical and alternative pathways and is essential for membrane attack complex formation?
- C3 (Correct answer)
- C1q
- C2
- Factor B
Correct answer: C3
C3 is the central convergence point for both pathways; its cleavage to C3b initiates the terminal complement cascade leading to MAC formation.
Question 7: Which staining technique is used to identify acid-fast organisms such as Mycobacterium tuberculosis in tissue sections?
- Ziehl-Neelsen stain (Correct answer)
- Gram stain
- PAS stain
- Silver methenamine stain
Correct answer: Ziehl-Neelsen stain
The Ziehl-Neelsen (carbol fuchsin) stain identifies acid-fast mycobacteria, which retain red dye after acid-alcohol decolorization.
NBDE Microbiology and Pathology 3
Which hepatitis virus is transmitted parenterally and poses the greatest occupational risk to dental healthcare workers through needlestick injuries?