The Morphological Study Of The Tooth Movement Induced Primary Central Sensitization

Pain is frequently associated with dental care. Although many dentists may be unaware of their patients' pain experiences during treatment, up to 77% of dental patients report some degree of pain during their visits to the dentist. In orthodontics, the situation does not seem to be very different. In a retrospective study of dental discomfort and pain among 203 adult Chinese patients in Singapore wearing fixed orthodontic appliances, 91% reported pain caused by their appliances. In 39% of these patients, tooth pain and discomfort were experienced during each step of the treatment, when a new archwire or elastic force was applied. Prospective investigations of both children and adults by Scheurer and Kvam revealed that 95% of the patients reported experiencing pain during orthodontic treatment. In recent Chinese investigation, the malocclusion rate is 51.84% ~ 72.92% which is much higher than 1960's. With the aesthetic request, more and more people ask for orthodontic treatment. But the orthodontic pain makes the patient fear and even give up the treatment. Animal experiment shows that tooth movement can stimulate the Fos protein expression and many neurotransimitter in spinal trigeminal subnucleus caudalis, one of the important relay nuclei for processing the nocicetptive information from the oro-facial region. It means that tooth movement may induce the sensitization in Vc. The recently researchs show that glia, including astrocyte and microglia, play an important role in the initial induction and maintenance of chronic pain in the spine. Several inflammation animal model show oro-facial stimulus canactive the trigeminal glia. Can tooth movement stimulate the trigeminal glia? If so, it will provide an surprising explanation for the orthodontic pain. The results will be useful for the future treatment research.Objective: â‘  To set up the tooth movement animal model related to behavior. (2) In this animal model, to observe spatial and temporal distribution of Fos protein and actived glia, including astrocyte and microglia. (3) To observe the spatial and temporal character of P2X receptors, NR2A/B receptor, EAAT1 and to investigate the mechanism of trigeminal glia activation and central sensitization induced by tooth movement.Methods: The experimental tooth movement was initiated in the rat upper molars by the method described by Waldo. Briefly, under light anesthesia with a gas mixture of ethyl ether and oxygen, a piece of the elastic band(3M Unitek, 1/8) was inserted unilaterally between the first and second upper molars (left side). â‘  Mechanical nociceptive threshold measurement: according to Ren's method, von Frey filaments were used to assess the muscle mechanical threshold, head withdrawal, leg raising and crying were observed as painful actions, survive for 2 h after the onset of tooth movement. (2)Immunohistochemistry: The free-floating sections were processed by the avidin-biotin complex ABC method to assess the Fos, GFAP and P2X. â‘¢Confocal methods: FITC and Texas Red was used to obsever the Fos/OX42,NR2/EAAT1.Results:â‘ The upper first molar moved to the maximum distance, 0.8 mm, in the 7th day. The bilateral masseter muscles and temporal muscles exhibited hyperalgesia from 3rd to 9th day, which the peak was the 5th to 7th day.â‘¡In normal animals, Fos-LI neurons were rarely observed in the SpVc and spinal cervical cord horn. The number of Fos-LI neurons increased significantly from 1 to 2h following the induction of experimental tooth movement, reaching a maximum at 2h, and then decreasing gradually. Most of the neurons were localizedin the superficial layers of the ipsilateral spinal cervical cord horn and the ipsilateral SpVc near the obex, but a few were observed at the ventral portion of the SpVc, NTS and VLM. The neurons at the superficial layers and ventral portion of the contralateral SpVc also showed Fos-like immunoreactivity, but their numbers were significantly smaller than those on the ipsilateral side.(3)Glial fibrillary acidic protein (GFAP) was labeled by immunohistochemistry and served as a marker for Astrocytes. Increased GFAP immunoreactivity was found in the bilateral spinal cervical horn and trigeminal nucleus nucleus within 1-7 days after tooth movement. No side differences were observed in the Vi after tooth movement.â‘£Complement receptor 3, which is recognized by the antibody OX42, served as a marker for Microglias. Activated microglia was found in the SpVc and AP from 1st to 3 rd day, and light 0X42 immoreactivity was found in the Vi, VLM and ION. The peak expression was the 1st day.(5)In normal animals, P2X4 receptor was rarely expressed. Increased P2X4 immunoreactivity was found in the ipsilateral spinal cervical horn and SpVc and MVZ; While the P2X7 is only expressed on the contralateral spinal horn and ipsilateral SpV.?The central glutamatergic system has been implicated in the pathogenesis of europathic pain, and a highly active central glutamate transporter (GT) system regulates the uptake of endogenous glutamate. Here we demonstrate that both the expression and uptake activity of spinal GTs changed after tooth movement and contributed to neuropathic pain behaviors in rats. Tooth movement induced an initial GT upregulation up to at least postoperative day 3 primarily within the ipsilateral spinal cord dorsal horn and SpV, which was followed by a GT downregulation when examined on postoperative days 7 by immunohistochemistry. Increased EAAT1 immunoreactivity was observed within the ipsilateral SpV, and the contralateral SpV showed no difference in the experiment time. Tooth movement induced an initial GT upregulation up to at least postoperative day...