Pulpal inflammation commonly extends to the periodontal area through the furcation area because it contains multiple lateral and accessory canals that connect the pulp chamber with the periodontal ligament. These anatomical communications act as pathways for inflammatory cells and bacterial products, especially in multi-rooted teeth where the furcation is a convergence zone. This connection facilitates the spread of infection from the pulp to the surrounding periodontal structures, leading to combined endodontic-periodontal lesions. Recognizing the furcation area's role is crucial during surgical intervention to prevent persistent infection.

Reference: Pathways of the Pulp, Cohen & Hargreaves, 12th Edition.