Oxytalan-positive peripheral ossifying fibromas express runt-related transcription factor 2, bone morphogenetic protein-2, and cementum attachment protein. An immunohistochemical study

Background The peripheral ossifying fibroma (POF) represents one of the most common lesions of the periodontal tissues that may originate from the gingival soft tissues, the periosteum, or the periodontal ligament. Aim To investigate the immunohistochemical expression of runt‐related transcription factor 2 (Runx‐2), bone morphogenetic protein‐2 (BMP‐2), and cementum attachment protein (CAP) in oxytalan‐positive POF, to establish the use of POF as an in vivo model for the study of the periodontal ligament. Materials and Methods Thirty tumors that presented clinical and histologic features of POF, as well as oxytalan fibers, were included in the study. Immunohistochemical expression of Runx‐2, BMP‐2, and CAP was evaluated by light microscopy. Results Runx‐2, BMP‐2, and CAP were abundantly expressed by POFs; 22 of 30 tumors expressed positive staining for Runx‐2, twenty‐six tumors for BMP‐2, and twenty‐five tumors for CAP. The expression of Runx‐2 was abundant in POFs where bone was histologically present ( P = 0.04) and of BMP‐2 in POFs where dystrophic calcifications were present ( P = 0.03). Conclusion It is suggested that oxytalan‐positive POFs, purportedly originating from the periodontal ligament, express molecules that are specific to bone and cementum (Runx‐2, BMP‐2), or cementum only (CAP). Thus, the cell populations present in the lesion belong to the mineralized‐tissue‐forming cell lineages, the cementoblastic or osteoblastic lineage.