Sympathectomy causes increased root resorption after orthodontic tooth movement in rats: immunohistochemical study.

Accumulating evidence suggests that the sympathetic nervous system modulates inflammatory responses and bone remodeling. We have studied the effects of sympathectomy and orthodontic tooth movement (OTM) on root resorption, immunocompetent cell recruitment, neuropeptide, neurokinin-1 receptor (NK1-R), and interleukin 6 (IL-6) expression. Experimental rats (n=8) had the right superior cervical ganglion surgically removed, whereas control rats (n=6) underwent sham surgery. Three days later, all rats had the right maxillary first molar moved mesially by an orthodontic appliance. The rats were perfused 13 days later, and the right maxillae were processed for immunohistochemistry by using primary antibodies directed against ED1 antigen, CD43, substance P (SP), NK1-R, neuropeptide Y (NPY), and IL-6. Following OTM, sympathectomized (SCGx) rats had significantly more root resorption (P<0.01) and SP-immunoreactive (IR) fibers (P=0.01) in the compressed periodontal ligament (PDL) compared with control rats. There was a significant decrease in recruitment of CD43+ cells in the pulp after OTM in SCGx rats compared with control rats (P=0.02). An upregulation of NK1-R immunoreactivity was observed surrounding the hyalinized tissue, and an increase in the number of NK1-R IR cells and density of SP-IR fibers was present in first molar pulp of all rats. NPY-IR fibers were absent in the compressed PDL of SCGx and control rats. Thus, OTM induces remodeling not only around the periodontal tissues, but also in the dental pulp. The sympathetic nerves have an inhibitory effect on hard tissue resorption and a stimulatory effect on CD43+ cell recruitment after OTM.