ABE Endodontic Microbiology and Pathology 2 — Questions and Answers
Question 1: Which virulence factor produced by Porphyromonas gingivalis allows it to evade host immune responses in periapical infections?
- Lipopolysaccharide (LPS)
- Cysteine proteases (gingipains) (Correct answer)
- Hydrogen peroxide
- Bacteriocins
Correct answer: Cysteine proteases (gingipains)
Gingipains are cysteine proteases that degrade immunoglobulins and complement proteins, enabling P. gingivalis to evade host defenses.
Question 2: In a tooth with symptomatic apical periodontitis, which inflammatory mediator is primarily responsible for sensitizing nociceptors and causing spontaneous pain?
- Interleukin-10
- Prostaglandin E2 (PGE2) (Correct answer)
- Transforming growth factor-beta
- Interleukin-4
Correct answer: Prostaglandin E2 (PGE2)
PGE2 lowers the pain threshold of nociceptors and is a key mediator of pain in acute apical periodontitis.
Question 3: A periapical granuloma is histologically distinguished from a radicular cyst by the:
- Presence of plasma cells
- Absence of an epithelial lining (Correct answer)
- Presence of Russell bodies
- Absence of macrophages
Correct answer: Absence of an epithelial lining
A periapical granuloma lacks an epithelial lining, while a radicular cyst has a stratified squamous epithelial lining.
Question 4: Which microorganism is most commonly associated with failed root canal treatment and persistent periapical pathology?
- Fusobacterium nucleatum
- Treponema denticola
- Enterococcus faecalis (Correct answer)
- Prevotella intermedia
Correct answer: Enterococcus faecalis
E. faecalis is highly resistant to intracanal medicaments and is the species most frequently isolated from failed root canals.
Question 5: The 'phoenix abscess' is best described as:
- An acute exacerbation of a pre-existing chronic periapical lesion (Correct answer)
- A primary acute apical abscess with no prior infection
- A sterile abscess caused by chemical irritation
- A periapical cyst that becomes secondarily infected
Correct answer: An acute exacerbation of a pre-existing chronic periapical lesion
A phoenix abscess is an acute inflammatory flare-up superimposed on a chronic periapical lesion, often triggered by instrumentation.
Question 6: Biofilm within the root canal system is significant because bacteria in biofilm state exhibit:
- Increased susceptibility to antibiotics compared to planktonic forms
- Reduced virulence due to nutrient limitation
- Up to 1000-fold greater resistance to antimicrobials (Correct answer)
- Decreased ability to communicate via quorum sensing
Correct answer: Up to 1000-fold greater resistance to antimicrobials
Biofilm bacteria can be up to 1000 times more resistant to antimicrobials than planktonic (free-floating) bacteria.
Question 7: Which cell type is the predominant effector in chronic apical periodontitis and is primarily responsible for bone resorption via RANKL signaling?
- Neutrophils
- Mast cells
- T lymphocytes (Correct answer)
- Natural killer cells
Correct answer: T lymphocytes
T lymphocytes, particularly Th1 and Th17 subsets, produce RANKL and inflammatory cytokines that drive osteoclast-mediated bone resorption in chronic periapical lesions.
ABE Endodontic Microbiology and Pathology 2
Which virulence factor produced by Porphyromonas gingivalis allows it to evade host immune responses in periapical infections?