Tissue Engineering of the Periodontal Ligament Stimulated by Orthodontic Treatment

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AIM: In our study using rat occlusal hypofunction model, we have reported the changes in width of the periodontal ligament (PDL), the number and the size of blood vessels, distribution of the extracellular matrix, and the distribution and the morphology of mechanoreceptors. In this study, we applied various mechanical stresses on hypofunctional tooth in this model to clarify the mechanism of recovery in the function of periodontal ligament. Further, we also examined the possibility to regenerate the periodontal ligament stimulated by orthodontic forces.MATERIALS AND METHODS: Occlusal hypofunctional rat model was prepared by extracting molars or setting bite-plate on incisors. Occlusal force or 2-10 gf orthodontic force was continuously or intermittently applied to the hypofunctional teeth. Distribution of the extracellular matrix and Nitric Oxide synthase, tooth movement and root resorption was observed histochemically and immunohistochemically.RESULTS: The distance of the tooth movement in the hypofunctional model was different from normal model. Root resorption was induced when the strong force were applied to the hypofunctional teeth. It was suggested that lighter force could move teeth smoothly without inducing pathological changes. Distribution and synthesis of the extracellular matrix and nitric oxide synthase was influenced by mechanical stress, to maintain the function of the PDLCONCLUSION: The effect of mechanical stress on periodontal ligament of the. hypofunctional tooth was different from the normal tissue. Therefore strength, type and/or duration of the force must be changed to avoid pathological change such as root resorption. However, mechanical stress such as occlusal force or orthodontic force can recover atrophically changed PDL, which suggest that appropriate mechanical stimuli are useful in recovering and regenerating PDL.