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

Its chelating effect on bacterial calcium channels

Answer

Release of chlorine ions from calcium salts

Answer

Inhibition of quorum sensing autoinducers

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

Interleukin-17 (IL-17)

Answer

Tumor necrosis factor-alpha (TNF-α)

Answer

Bone morphogenetic protein-2 (BMP-2)

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

Primary pathogen that initiates disease independently

Answer

Pioneer colonizer of the root canal biofilm

Answer

Obligate synergist that only grows with E. faecalis

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

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Answer

Histoplasma capsulatum

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

Hypermineralization of periapical bone

Answer

Displacement of cancellous trabeculae by expanding cyst fluid

Answer

Vascular thrombosis causing avascular bone necrosis

Question 6

Which property makes Treponema denticola particularly virulent in endodontic infections?

Accepted Answer

Production of a dentilisin protease that degrades host defense proteins and penetrates dentin tubules

Answer

Ability to form endospores under adverse conditions

Answer

Resistance to calcium hydroxide via biofilm formation alone

Answer

Aerobic metabolism enabling survival in oxygenated environments

Question 7

An internal resorption defect noted on CBCT is histologically characterized by:

Accepted Answer

Odontoclasts within dentinal tubules resorbing dentin from the canal lumen outward

Answer

Cementoclasts resorbing dentin from the external root surface inward

Answer

Osteoclasts resorbing alveolar bone adjacent to the root

Answer

Fibroblasts depositing reparative dentin within the canal