Delayed Recruitment of Immunocompetent Cells in Denervated Rat Periodontal Ligament Following Experimental Tooth Movement

It has previously been shown that the number of mononuclear phagocytic cells in the periodontal ligament (PDL) of orthodontically moved rat molars is significantly increased (p ≤ 0.05) at 3, 7, and 14 days compared with the controls. Since these changes coincide with increased density of peptidergic nerve fibers, it was of particular interest to investigate a possible relation between the immunocompetent cells and sensory nerve fibers in the PDL of experimentally moved and denervated rat molars. Twenty-two young animals had the first right mandibular molar moved mesially, 7, 14, and 21 days after ipsilateral inferior alveolar nerve axotomy. The left side served as unoperated control. An immunohistochemical procedure was carried out on alternate, serial, cryostat sections with antibodies against CDllb (macrophages, dendritic cells) and class II major histocompatibility complex (MHC) molecules (RT1B). At 7 and 14 days, the number of CDllb+- and RTlB-expressing cells in the denervated PDL showed no significant difference compared with the contralateral side. However, at 21 days, when periodontal tissue re-innervation is established, the number of the investigated immunocompetent cells in the PDL of the denervated and experimentally moved mandibular molars demonstrated a significant difference compared with the contralateral and control molars (p ≤0.05). It can be concluded that axotomy of the inferior alveolar nerve delays the recruitment of macrophage-like and class II MHC molecule-expressing cells in the PDL of orthodontically moved rat molars. The results further indicate that sensory nerve fibers interact with immunocompetent cells and participate in their mobilization to locally inflamed tissues.