Histomorphologic evidence supports a hyperplastic pathogenesis of fibromatous epulis of periodontal ligament origin/peripheral odontogenic fibroma and proposal of fibromatous hyperplasia of the gingival ligament as unifying nomenclature

Fibromatous epulis of periodontal ligament origin (FEPLO), also known as peripheral odontogenic fibroma (POF), is a benign gingival lesion that occurs frequently in dogs. Common use of both names is cumbersome and confusing yet persists due to disagreement regarding pathogenesis. With the objective of clarifying the histogenesis and pathogenesis, 100 canine FEPLO/POF lesions that had been surgically excised en bloc were evaluated histologically to characterize the lesion’s relationship to surrounding anatomic structures and to document concurrent pathologies in those tissues. No lesions involved the periodontal ligament space, although 88/100 (88%) lesions attached to alveolar bone, similar to the normal anatomy of the gingival ligament. The lesions consist of fibrous tissue with osteogenic potential, and 54/100 (54%) lesions had bone or cemento-osseous matrix. Odontogenic epithelium was evident in 63/100 (63%) lesions, and the paradental location of the epithelium suggests that the origin of most odontogenic epithelium in FEPLO/POF lesions is a result of hyperplastic junctional epithelium extending into the lesion. Hypercellularity was interpreted as a feature of reactive lesions since 15/17 (88%) hypercellular lesions were ulcerated and 15/17 (88%) were inflamed. Frequent concurrent histologic findings included hypercementosis at the cementoenamel junction of the adjacent tooth (79/89, 89%), reactive alveolar bone (90/100, 90%), and inflammation of alveolar bone (67/100, 67%). While the pathogenesis cannot be determined with absolute certainty, available evidence supports a reactive, hyperplastic process rather than neoplastic. The authors believe that fibromatous hyperplasia of the gingival ligament is an anatomically correct name that accurately reflects the likely etiopathogenesis.