On-Bone Fixation of Free Gingival Graft Induces the Expression of Osteogenic Differentiation Markers in the Mandible of Miniature Pigs.

Abstract

To study the distribution of markers of mesenchymal stem cells (clusters of differentiation-29 and -44), osteoblasts (osteocalcin), and transforming growth factor-β1 in the mandibular tissue of miniature pigs after on-bone fixation of a free gingival graft. Six outbred male miniature pigs 2 years of age were used in the study. In the external surface of the mandible, the periosteum was excised from all over the free gingival graft fixation area. A free gingival graft was placed on the wound and fixed. In control animals, instead of free gingival graft, a piece of mucoderm (porcine accellular dermal matrix, Botiss Biomaterials) was placed on the wound and fixed. Three months after the surgery, a portion of bone tissue was sampled from the free gingival graft insertion area. The samples were immunohistochemically stained using antibodies against osteoblast and mesenchymal stem cell markers. Three months after surgery, high expression levels of the aforementioned markers were detected in the contact zone between the graft and alveolar bone. Clusters of differentiation-29- and -44-immunopositive cells predominated at the border of the new bone tissue and gingival lamina propria as well as in Haversian canals. Osteocalcin-positive cells were observed mainly in the layer of outer circumferential lamellae, on the surface of concentric lamellae of young osteons forming Haversian canals, and in the Haversian canals in the immediate vicinity of the graft. The bulk of transforming growth factor-β1-expressing cells occurred in the connective tissue Volkmann and Haversian canals and the adventitious and inner vascular membranes. On-bone free gingival graft fixation results in remodeling of the alveolar bone and is accompanied by a change in the immunoreactivity against factors controlling osteogenic differentiation. Clusters of differentiation-29 and -44 expression in mandibular bone tissues suggest that free gingival graft placement results in activation of mesenchymal stem cells and their transforming growth factor-β1-mediated differentiation into osteocalcin-containing osteoblasts.