Function of immunocompetent cells in the tension zone of periodontal ligament in tooth movement

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Tissue reaction of the tension zone of periodontal ligament ( PDL ) during orthodontic tooth movement has been simplified as tugging of PDL fibers and bone formation. However, PDL fibers in the tension zone are forced to strong tugging, which causes involvement of defense system. We examined an involvement of immune system in the tension zone of PDL in early stage of tooth movement, using histological and immunohistochemical methods. Periodontal space was enlarged to more than 130 % and the PDL fibers showed a strong tugging aspect 6 hours after initiation of tooth movement. ED1 positive cells ( macrophage and monocyte ) were increased. However, fibroblasts also showed localization of IL-1B and MMP12. This indicats that fibroblasts involve in defense reaction of the PDL, prior to rearrangement of the PDL and bone formation on the alveolar bone in the very early stage of periodontal reaction in the tension zone.