Insulin-like growth factor system components in the periodontium during tooth root resorption and early repair processes in the rat

There is evidence that growth factors, such as the insulin-like growth factors (IGFs), are involved in biological and pathological processes in oro-dento-facial tissues. To investigate their roles in tooth movement, root resorption, and repair, the occurrence of components of the IGF system, including the ligands IGF-I and -II, the IGF receptor 1 (IGF1R) and six IGF-binding proteins (IGFBP-1 to -6), was investigated by immunohistochemistry on sections from rat maxillae where the first molar had been moved mesially by means of an orthodontic appliance for 9 d to induce root resorption. After force deactivation on day 0, early repair was studied after a further 5, 7, 10, 12, 14, and 17 d. The immunostaining pattern in the periodontal ligament, cementum, and bone of control animals showed similarities known from studies in human teeth. Increased immunostaining for nearly all components in pressure sides and resorption lacunae indicated an involvement in resorption processes and clastic activities. During early stages of repair, the occurrence of several components (e.g. IGF-II, IGFBP-5 or -6) within lacunae and in cementoblasts showed an involvement in the resorption-repair sequence, which is considered to be a coupling process as known from bone.     

Immunohistochemical localization of components of the insulin-like growth factor-system in human deciduous teeth

To investigate the occurrence of components of the insulin-like growth factor (IGF) system during the resorption process of shedding human deciduous teeth, we investigated sections of 13 decalcified and paraffin-embedded deciduous teeth immunohistochemically with antibodies against IGF-I and -II, six IGF binding proteins (IGFBPs 1-6) and the IGF receptors IGF1R and IGF2R. The teeth were in different stages of resorption and all showed reparative cementum formation. It was found that acellular extrinsic fiber cementum, reversal lines and reparative cellular intrinsic fiber cementum were immunoreactive for both IGFs and various IGFBPs. Therefore, in human deciduous teeth, all subgroups of cementum, but not dentine, may represent sources of components of the IGF system. Odontoclasts did not carry IGFs or the IGF1R, but IGFBPs and the IGF2R. Therefore, these cells, in contrast to osteoclasts, may not respond to IGFs, but may be involved in the release and sequestration of IGFs from cementum during the resorption process. In contrast to odontoclasts, cementoblasts and periodontal ligament (PDL) fibroblasts carried IGF1R. The influence of the IGF system on the function of these cells with respect to periodontal matrix turnover and cementogenesis is discussed. On the behalf of the IGFBP immunoreactivities found, the PDL extracellular matrix can be considered to be a reservoir for IGF system components, where binding proteins may regulate IGF distribution and activity.