In this paper, a mandibular prognathism with suspected large hemangioma was reported. The patient was a 35-year-old male with the chief complaint of prognathism. Calcification in the sublingual, submandibular, and pterygomandibular region were found by X-ray examination, however, the mass and cystic leision was not found by CT examimation. It was difficult that the clinical diagnosis could be established from the clinical findings and X-ray and CT examinations. The leision was suspected to be myositis ossificans, but the pathological diagnosis of biopsy specimen, extracted from the submandibular region, was not suggested to be myositis ossificans. The biopsy specimen of calcification was observed by scanning electron microscopy (SEM) and X-ray microanalysis. SEM showed a layer pattern in the calcification. As the result of X-ray microanalysis, the main detected component elements in calcification were Ca and P, whose calculated Ca/P ratio was 1.52. These findings suggested that the calcification was a plebolith. Sagittal splitting osteotomy could be performed by the Obwegeser method without any trouble. The postoperative course was uneventful for four years.
