Etiology
Partial eruption of the mandibular third molar is the prerequisite anatomical condition. The operculum — a flap of gingival tissue — traps food debris and bacteria between the flap and the tooth crown.
The subgingival microenvironment is anaerobic and warm, ideal for mixed anaerobic flora: Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia, Treponema species, and Peptostreptococcus.
Precipitating factors include: trauma from the opposing maxillary third molar biting into the operculum, upper respiratory tract infections (which may activate latent pathogens), stress and fatigue (immune compromise), and poor oral hygiene.
Systemic factors that impair immune response — diabetes, HIV, chemotherapy — significantly increase risk of severe infection and spread.