"Shot on Target": A Case of an Unusual Peripheral Ossifying Fibroma of the Edentulous Upper Jaw Irritated by the Only Teeth of the Lower Jaw.

A peripheral ossifying fibroma (POF) is a benign, localized lesion that originates from the periosteum or periodontal ligament after traumatic or calculus irritation. The lesions typically manifest in females throughout their second and third decades of life. The diagnosis of a POF is challenging from both clinical and histological standpoints, as it exhibits overlapping features with numerous other clinical entities. This case describes an unusual occurrence of POFs in the anterior maxilla of a 66-year-old female patient who is edentulous at this jaw, but the last two teeth of the lower jaw affect it. The radiographic evaluation revealed no discernible alterations within the bone structure. The diagnosis of POFs was determined through histological investigation. The microscopic examination revealed scattered immature osteoid dystrophic calcified depositions in deep positions, whereas the overlying stratified squamous epithelium manifested frictional keratosis (hyperplasia). The stromal fibroblasts of the collagenous stroma displayed ovoid, normochromatic nuclei, without atypia. Interestingly, the particular importance of this POF case indicates the possibility of an atypical formation in terms of age and location suggesting the role of local chronic irritation as the most critical parameter. Regardless of the initial causative factor, which may be the remnants of the periodontal ligament, the periosteum, or the gingival fibroblasts, ultimately mechanical trauma constitutes the crucial prerequisite so that reactive hyperplasias may be induced.