IGF1 and periodontitis: Yeh et al. reported that combination of osteogenic protein-1 (OP1) with either IGF-1 or interleukin-6 enhanced OP1-induced increase in cell proliferation, alkaline phosphatase (ALP) activity and bone nodule formation;6, 7 while combined treatment with platelet-derived growth factor and IGF-1 improved the periodontal structure healing of periodontitis-affected teeth.8 These studies indicated that cytokine combinations have a synergistic effect on bone healing and tissue regeneration, and hence represent a potential therapeutic strategy for the repair of bone defects.