Intracellular calcium response to hydraulic pressure in human periodontal ligament fibroblasts

Human periodontal ligament fibroblasts in culture were exposed to the controlled change in hydraulic pressure and were monitored continuously with an electric pressure gauge, and the concentration of intracellular calcium was measured in real time by a calcium-binding fluorescent dye, fluo-3. The elevation of hydraulic pressure to a level ranging from 20 to 50 mm Hg induced transient elevation of the intracellular calcium concentration in about 10% of the fibroblasts observed, indicating that these cells could respond to the pressure change. The results supported further an idea that periodontal ligament fibroblasts, responding to the pressure exerted by orthodontic force, would initiate the chain of events in orthodontic tooth movement, including alveolar bone remodeling. The threshold level of pressure (27 to 68 g/cm(2)) obtained in this experiment, at which the fibroblasts started to respond, would provide a biochemical basis to determine the optimal magnitude of stress for clinical orthodontics.