Two patients with cementifying fibroma occurring centrally in the mandible were reported. The first case was a 64-year-old man with a walnut-sized, radiopaque lesion with sharp demarcation of the site in the mandible 5-7, and resection of the tumor was performed. The second case was a 29-year-old woman with an oval semiradiopaque lesion with sharp demarcation of the site in the mandible ranging from the 7 mesial root to the sigmoid notch, and partial resection was performed. Histologically, various amounts of cementum were formed in fibrous tissues in both patients, but there were some differences in the amounts of cellular components and hard tissues present. Tumors were found to consist of fibroblastic cells, cementoblastic cells and undifferentiated mesenchymal cells electron microscopically. The cementum-like, hard tissues were formed irregularly along the collagen fibers, but signs of early calcification were observed in the form of irregular aggregations of small bristle-like, osmophilic crystals. A small number of matrix vesicle-like structures were also present around the aggregation. The first and second cases show favorable courses without relapse at present, three years and three months and three years and one month, respectively, after resection.
