Etiology
Etiology
Chronic apical periodontitis develops when the host-pathogen balance in an infected root canal establishes a stable, low-grade equilibrium. Bacteria in the apical portion of the root canal system continuously release antigens that provoke periapical inflammation, but the immune response contains rather than eliminates the infection.
Intraradicular biofilm dominates the microbiology — polymicrobial communities with Fusobacterium, Prevotella, Actinomyces, Streptococcus, and others form robust biofilms on canal walls, in ramifications, isthmuses, and accessory canals that resist irrigation and instrumentation.
Extraradicular infection (biofilm on root surfaces, periapical actinomycosis) accounts for a minority of persistent lesions but is critical to recognize as it does not respond to non-surgical treatment. Periapical actinomycosis — Actinomyces species forming sulfur granules visible histologically — is the classic example.