Biological reactions to orthodontic tooth movement.

Understanding the biological basis of tooth movement is crucial to orthodontics. Identifying the components of the signal transduction pathway initiated after force application will permit their manipulation, leading to better results. To examine the effects of mechanical stimulation in the periodontium, human periodontal ligament cells were isolated, cultured and characterized. In contrast to gingival fibroblasts, human PDL-fibroblasts in culture exhibit characteristics typical of osteoblast-like cells. To assess the role of mechanical stimulation the relevant orthodontic forces were simulated in vitro. For this purpose PDL-cells were cultured in Petri dishes with a flexible bottom. This bottom can be stretched over a convex template so that the adherent cells will be also stretched. The results of the stretching experiments demonstrate that human PDL-cells respond to mechanical stretch by a signal transduction pathway which most likely includes specific small GTP-binding proteins, such as Rab and Rho, as well as well defined transcription factors (c-Jun and c-Fos).