Effects of irradiation on cementum matrix cytokins function during periodontal regeneration

The influence of gamma-ray irradiation on a cementum-impregnated gelatine membrane (CGM) was analyzed with emphasis on its function during periodontal regeneration. In brief, proteins were extracted from gamma-ray irradiated cementum (gammaC). With the gammaC protein, sample cells (gingival fibroblasts, periodontal ligament cells, and alveolar bone cells) were co-cultured, and cytological parameters (cell attachment, cell differentiation and alkaline phosphatase activity) were analyzed. Additionally, kinetics of some gene expression was analysed using reverse transcript RT-PCR, which included osteoproteogerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) mRNA. BMP-2 and osteonectin were resistant to gamma-rays, and other cytokines involved in regeneration were decreased. Thus, the attachment activity of osteoblasts to gammaC protein was higher than that of non-irradiated cementum (control C). The expression of OPG/OCIF mRNA was lower in co-cultured cells with gammaC protein than those with in control C protein. Together the results imply that some cytokine in intact cementum prevents the attachment (differentiation) of bone cells onto the root surface, which may explain why the introduction of CGM following gingival flap surgery induces new cementum, new ligament and new bone formation, but CGM irradiated with gamma-rays for clinical use causes ankylosis.