Figure 1. Schematic illustrations summarizing potential effects of sympathetic nerves on teeth. Stimulating effects of sympathetic nerves are indicated with (+), and inhibitory effects by (-). Top left panel illustrates a peripheral post-ganglionic sympathetic nerve terminal containing vesicles with noradrenaline (NA) or neuropeptide Y (NPY), which are released upon stimulation. Figs. below illustrate rat molar teeth in 3 different conditions. (A) Normal uninflamed pulp with sympathetic imbalance caused by unilateral sympathectomy recruits immunoglobulin-producing cells. (B) Electrical stimulation of sympathetic nerves causes recruitment of CD 43+ granulocytes in the normal dental pulp. During experimental orthodontic tooth movement (OTM), sympathetic nerves have an inhibitory effect on hard tissue resorption and a stimulating effect on CD 43+ cell recruitment in the dental pulp and PDL. (C) The inflamed pulp shows increased reparative dentin formation and sprouting of sympathetic nerve fibers, while the periapical lesion shows decreased IL-1 production and number of osteoclasts compared with a denervated sympathectomized tooth.