ABE Endodontic Microbiology and Pathology 5

Question 1

Calcium hydroxide's antimicrobial mechanism in root canals is primarily due to:

Accepted Answer

The high pH (~12.5) causing membrane damage and enzyme inactivation

Answer

Ca(OH)2 produces a strongly alkaline environment (pH ~12.5) that disrupts bacterial cytoplasmic membranes and denatures essential enzymes.

Question 2

Which cytokine plays a DUAL role in apical periodontitis — promoting inflammation in early stages but also stimulating osteoblast activity and bone repair in healing phases?

Accepted Answer

Interleukin-6 (IL-6)

Answer

IL-6 has pleiotropic effects — it promotes acute inflammation and B-cell differentiation but also stimulates osteoblasts and contributes to bone healing after infection control.

Question 3

Fusobacterium nucleatum's role in endodontic infections is best described as a:

Accepted Answer

Bridge organism connecting early and late colonizers in polymicrobial biofilms

Answer

F. nucleatum acts as a bridge species in polymicrobial biofilms, co-aggregating with early colonizers (streptococci) and late colonizers (Porphyromonas, Prevotella), facilitating complex community development.

Question 4

A tooth that has undergone root canal treatment is still symptomatic 6 months post-treatment. A periapical biopsy reveals hyphae and yeast forms. The most likely causative organism is:

Accepted Answer

Candida albicans

Answer

Candida albicans is the most commonly identified fungal species in persistent endodontic infections, demonstrating both yeast and hyphal (dimorphic) forms.

Question 5

The periapical rarefaction seen radiographically in chronic apical periodontitis results primarily from:

Accepted Answer

Osteoclastic bone resorption driven by RANKL/OPG imbalance

Answer

RANKL (from activated T cells and fibroblasts) promotes osteoclast differentiation and activity, while inflammatory cytokines suppress OPG, leading to net bone resorption visible as periapical radiolucency.

(ABE) American Board of Endodontics Practice Test

(ABE) American Board of Endodontics Practice Test

ABE Endodontic Microbiology and Pathology 5