Cellular response to orthodontically-induced short-term hypoxia in dental pulp cells

Orthodontic force application is well known to induce sterile inflammation, which is initially caused by the compression of blood vessels in tooth-supporting apparatus. The reaction of periodontal ligament cells to mechanical loading has been thoroughly investigated, whereas knowledge on tissue reactions of the dental pulp is rather limited. The aim of the present trial is to analyze the effect of orthodontic treatment on the induction and cellular regulation of intra-pulpal hypoxia. To investigate the effect of orthodontic force on dental pulp cells, which results in circulatory disturbances within the dental pulp, we used a rat model for the immunohistochemical analysis of the accumulation of hypoxia-inducible factor-1α in the initial phase of orthodontic tooth movement. To further examine the regulatory role of circulatory disturbances and hypoxic conditions, we analyze isolated dental pulp cells from human teeth with regard to their specific reaction under hypoxic conditions by means of flow cytometry, immunoblot, ELISA and real-time PCR on markers (Hif-1α, VEGF, Cox-2, IL-6, IL-8, ROS, p65). In vivo experiments showed the induction of hypoxia in dental pulp after orthodontic tooth movement. The induction of oxidative stress in human dental pulp cells showed up-regulation of the pro-inflammatory and angiogenic genes Cox-2, VEGF, IL-6 and IL-8. The present data suggest that orthodontic tooth movement affects dental pulp circulation by hypoxia, which leads to an inflammatory response inside treated teeth. Therefore, pulp tissue may be expected to undergo a remodeling process after tooth movement.