A 22 year old male patient came to the maxillofacial surgery department of the Hospital San José referred by his dentist for a painless increase in volume in relation to the body and left mandibular branch of undetermined evolution. The patient had no previous morbid or surgical history.
On extraoral examination there was an increase in volume involving the body and left mandibular ramus that had not previously been detected by the patient. There was no skin involvement and no adenopathy. There was also no associated sensory involvement and the mandibular functional examination was normal.

On intraoral examination the patient presented partial edentulousness due to the absence of the lower left canine and molars, and an increase in volume with a dented surface involving the body and ramus on the same side. The overlying mucosa had whitish areas, was painless to palpation and hard in consistency.

A panoramic radiograph was requested, showing a well-defined, bilocular, radio-opaque, mixed lesion, extending from the root of the lower right lateral incisor to the middle of the left mandibular ramus, with a diameter of 12cm in its largest diameter and 4cm in its smallest diameter. Included in the lesion were the tooth germs of the left lower canine, first and second molar. The anterior border of the ramus, alveolar ridge and basilar border were expanded.

A CT scan was requested which showed thinning of the bony cortices, mainly of the vestibular cortical bone. Based on this, a stereolithographic model was requested to plan the definitive surgery.

An incisional biopsy of the lesion was performed. Histopathological examination stained with haematoxylin-eosin showed a lesion consisting mainly of fibroblastic stroma with variable cellularity, containing multiple calcified structures of different sizes and irregular distribution. The histopathological diagnosis was FO.

With this diagnosis, definitive surgery was planned. A 2.4 reconstruction plate was modelled on the stereolithographic model and extended at the level of the basilar border from the right lower first molar to the upper area of the left mandibular ramus.
The mandible was exposed via a cervical approach and the mandibular segment involved was resected en bloc, taking the tumour borders as the limits. Subsequently, mandibular reconstruction was performed using a microvascularised fibula graft, which was adapted to the reconstruction plate and sectioned into three parts to facilitate its adaptation to the plate.

Post-operative management of the patient involved antibiotic therapy and conventional analgesia together with revulsives and a soft diet. The latter was prolonged for one month.
After one year postoperatively, the patient underwent oral rehabilitation with the placement of osseointegrated implants on which a hybrid prosthesis was made.

The patient continues to have regular clinical and radiographic check-ups. Currently, after 5 years, he is in very good condition.