Delayed recruitment of immunocompetent cells in denervated rat periodontalligament following experimental tooth movement

It has previously been shown that the number of mononuclear phagocytic cell s in the periodontal ligament (PDL) of orthodontically moved rat molars is significantly increased (p less than or equal to 0.05) at 3, 7, and 14 days compared with the controls. Since these changes coincide with increased de nsity of peptidergic nerve fibers, it was of particular interest to investi gate a possible relation between the immunocompetent cells and sensory nerv e fibers in the PDL of experimentally moved and denervated rat molars. Twen ty-two young animals had the first right mandibular molar moved mesially, 7 , 14, and 21 days after ipsilateral inferior alveolar nerve axotomy. The le ft side served as unoperated control. An immunohistochemical procedure was carried out on alternate, serial, cryostat sections with antibodies against CD11b (macrophages, dendritic cells) and class TI major histocompatibility complex (MHC) molecules (RT1B). At 7 and 14 days, the number of CD11b(+)- and RT1B-expressing cells in the denervated PDL showed no significant diffe rence compared with the contralateral side. However, at 21 days, when perio dontal tissue re-innervation is established, the number of the investigated immunocompetent cells in the PDL of the denervated and experimentally move d mandibular molars demonstrated a significant difference compared with the contralateral and control molars (p less than or equal to 0.05). It can be concluded that axotomy of the inferior alveolar nerve delays the recruitme nt of macrophage-like and class II MHC molecule-expressing cells in the PDL of orthodontically moved rat molars. The results further indicate that sen sory nerve fibers interact with immunocompotent cells and participate in th eir mobilization to locally inflamed tissues.