Florid cemento-osseous dysplasia (FCOD) is benign and exhibits multifocal involvement of tooth-bearing areas of the jaw. Initially, the lesions are radiolucent but become mixed. In late stages, the lesions change into a radiopaque mass with a thin radiolucent rim. Most FCOD cases are asymptomatic, and conservative treatment is recommended. However, surgical intervention is necessary in secondary infected cases. Because of hypovascularity, infected lesions are difficult to manage and do not respond to antibiotic medications. This clinical report describes the treatment of secondary infection of an FCOD lesion with both conservative and surgical interventions.

Osteogenic sarcoma is primary malignant bone tumor. It can arise de novo or from the benign precursors lesions, like Paget’s disease, giant cell tumor, chronic osteomyelitis, osteoblastoma, and fibrous dysplasia. Here, we present a case of osteogenic sarcoma arising from florid osseous dysplasia appearing as a rapidly growing bony bulging mass in 44‐year‐old Korean female who had at first been non‐symptomatic, but later suffered from the numbness of chin and lower lip. The radiologic images revealed the mixed radiopaque‐ radiolucent intraosseous lesions throughout the mandible, which were diagnosed as florid osseous dysplasia pathologically. But only after 6 months, the lesions were substituted by the radiological ill‐defined diffuse bony sclerotic lesion with bone destruction, accompanying the interrupted periosteal bone formation, which were pathologically diagnosed as osteogenic sarcomas. These serial clinicopathologic changes imply the malignant progression of florid osseous dysplasia rather than the collision of benign condition, florid osseous dysplasia and malignant tumor, osteogenic sarcoma. The possibility for fibro‐osseous lesion of the jaw as premalignant lesion should not be overlooked; therefore, periodic check‐ups for the lesions are necessary. Proper evaluation and interpretation for clinical neural symptom and radiologic change of bone density may lead to the correct differential diagnosis and therapeutic intervention.

Florid cemento-osseous dyspl잃ia with concommitant traumatic bone cyst is uncommon condition. We report a case of florid cemento 。，sseous dysplasia involving four quadrants of the jaws and associated with large cystic lesion of the mandible misdiagnosed as a multiple odontogenic keratocysts in a 37-year-old Korean woman. Histological examination revealed unencapsulated fibroblastic proliferation with formation of bone and cementum, showing different developmental stages, and cys디c lesions resembling a traumatic bone cyst.