ABE Endodontic Microbiology and Pathology 3 — Questions and Answers
Question 1: Which anaerobic species is considered a 'keystone pathogen' capable of restructuring the entire microbial community in endodontic infections despite low abundance?
- Streptococcus mutans
- Porphyromonas endodontalis (Correct answer)
- Actinomyces israelii
- Lactobacillus acidophilus
Correct answer: Porphyromonas endodontalis
P. endodontalis, like P. gingivalis, can modulate the local microbiome and immune response disproportionate to its numbers, fitting the keystone pathogen model.
Question 2: Condensing osteitis (focal sclerosing osteomyelitis) is best characterized as:
- An acute suppurative infection of bone
- A reactive bone formation response to low-grade pulpal inflammation (Correct answer)
- A central giant cell granuloma variant
- A periapical cyst with calcified walls
Correct answer: A reactive bone formation response to low-grade pulpal inflammation
Condensing osteitis represents reactive periapical bone sclerosis in response to chronic, low-grade pulpal infection or irritation.
Question 3: Which component of gram-negative bacterial cell walls is most responsible for stimulating macrophages to release IL-1β and TNF-α in periapical tissues?
- Peptidoglycan
- Lipoteichoic acid
- Lipopolysaccharide (LPS) (Correct answer)
- Muramyl dipeptide
Correct answer: Lipopolysaccharide (LPS)
LPS (endotoxin) from gram-negative bacteria is a potent stimulator of macrophage-derived pro-inflammatory cytokines via TLR4 signaling.
Question 4: During the transition from pulp necrosis to periapical abscess formation, which process represents the earliest response at the periapex?
- Osteoclastic bone resorption
- Cyst epithelial proliferation
- Vascular dilation and neutrophil emigration (Correct answer)
- Fibroblast collagen deposition
Correct answer: Vascular dilation and neutrophil emigration
The earliest periapical response involves vascular dilation and neutrophil emigration as the acute inflammatory response begins.
Question 5: Extra-radicular infection most commonly involves which microbial structure adherent to the external root surface?
- Planktonic bacteria in periapical fluid
- Bacterial biofilm on the root apex (apical biofilm) (Correct answer)
- Bacterial spores in cementum
- Viral particles in PDL fibers
Correct answer: Bacterial biofilm on the root apex (apical biofilm)
Extra-radicular infection often manifests as an apical biofilm on the external root surface, which may explain persistent periapical pathology after adequate root canal treatment.
Question 6: Which histological finding is MOST characteristic of a periapical abscess as opposed to a periapical granuloma?
- Plasma cell infiltration
- Giant cell formation
- Central area of liquefactive necrosis with neutrophils (Correct answer)
- Dystrophic calcifications
Correct answer: Central area of liquefactive necrosis with neutrophils
A periapical abscess is characterized by central liquefactive necrosis with a predominance of neutrophils (pus formation).
Question 7: Sodium hypochlorite's antimicrobial efficacy in the root canal is primarily attributed to its:
- Low pH causing bacterial DNA denaturation
- Release of free chlorine and oxidation of bacterial proteins (Correct answer)
- Chelation of calcium from bacterial cell walls
- Disruption of quorum sensing molecules
Correct answer: Release of free chlorine and oxidation of bacterial proteins
NaOCl releases free chlorine (hypochlorous acid) which oxidizes and denatures bacterial proteins, destroying cell membranes and inactivating enzymes.
ABE Endodontic Microbiology and Pathology 3
Which anaerobic species is considered a 'keystone pathogen' capable of restructuring the entire microbial community in endodontic infections despite low abundance?