Chronic Apical Periodontitis

Chronic apical periodontitis (CAP) is the most prevalent periapical pathology — a low-grade, persistent inflammatory reaction of periradicular tissues to bacterial products from a necrotic infected root canal. Unlike its acute counterpart, CAP is typically asymptomatic, discovered incidentally on radiographs as the characteristic periapical radiolucency.

The periapical lesion in CAP is predominantly a granuloma (75–85% of lesions) — a mass of chronically inflamed granulation tissue containing macrophages, lymphocytes, plasma cells, and fibroblasts — or a radicular cyst (15–25%) — an epithelium-lined pathological cavity containing fluid or semi-solid material.

The biological debate over whether periapical cysts can heal with non-surgical root canal treatment or require surgical enucleation has evolved with CBCT evidence showing that most lesions, regardless of histological type, resolve after adequate endodontic therapy.

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.