[Effect of pulsed electromagnetic fields (PEMF) on human periodontal ligament in vitro. Alterations of intracellular Ca2+].

The concept of orthodontic tooth movement is based on the hypothesis that teeth move as a result of the biological response of periodontal tissues to the mechanical forces applied. There is a widely held hypothesis that mechanical stress generates an electrical signal which sets in motion the subsequent events, as in bone exposed to mechanical forces electrical currents are produced affect bone growth and remodeling. This implies a transduction mechanism which translates the electrical signal into a biochemical message, recognizable by the cellular machine. This study is aimed at the identification of the message and the investigation of its control. In fact, the effect of Pulsed Electromagnetic Fields (PEMF) on the intracellular second messenger, cytoplasmic Ca2+ in Human Periodontal Ligament Fibroblasts (HPLF) was investigated. The resting intracellular ionized calcium concentration ([Ca+2]i) of HPLF cells was 232.7 +/- 25.0 nM, and with PEMF [Ca2+]i increased from 12 hrs to 499.0 +/- 115.5 nM up to 12 hrs, then reached to a steady level through 24 hrs. The PEMF were also found to decrease the responses towards epidermal growth factor (EGF) and serum, when the degree of response was based on the intracellular Ca2+ transient. These effects of PEMF were mimicked by 12-0-tetradecanoyl phorbol 13-acetate (TPA), a potent activator of protein kinase C. Some reports have suggested that fibroblasts of the periodontal ligament contain high alkaline phosphatase (ALPase) activity as much as osteoblast. Since similar results concerning the [Ca2+]i were obtained in osteoblast (OB)-like cells, this experiment also supports the hypothesis that fibroblasts of periodontal ligament have osteoblastic features.