ABSTRACT
To understand orthodontic tooth movement and determine optimal orthodontic force from a biological viewpoint, nitric oxide production in cultured human periodontal ligament fibroblasts was measured at varying levels of hydraulic pressure. The fibroblasts in a culture flask were exposed to the controlled change in hydraulic pressure, and intracellular nitric oxide levels were measured in real time by a nitric oxide-binding fluorescent dye, diaminofluorescein-2. The fibroblasts produced a significantly larger amount of nitric oxide at the pressure of 75 and 100 mmHg, compared with the pressure of 0, 25, and 50 mmHg (P <.0001, one-way ANOVA, and P <.05, Tukey-Kramer test). Immunohistochemically, the cultured fibroblasts expressed brain nitric oxide synthase. The pressure level to enhance nitric oxide production was comparable to the magnitude of clinically used orthodontic force (80 g/cm(2)). Nitric oxide might be a key regulator in orthodontic tooth movement.
Subject(s)
Nitric Oxide/biosynthesis , Periodontal Ligament/metabolism , Analysis of Variance , Cell Separation , Cells, Cultured , Fibroblasts/chemistry , Fibroblasts/metabolism , Humans , Immunohistochemistry , Nitric Oxide/analysis , Periodontal Ligament/chemistry , Periodontal Ligament/cytology , Pressure , Spectrometry, FluorescenceABSTRACT
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/cm2) 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.
