Activation of Glia in Spinal Trigeminal Nucleus following tooth movement

Purpose: Glial activation is known to contribute to pain hyperalgesia following peripheral injury and inflammation. Orthodontic therapy is frequently associated with the occurrence of dental pain and orofacial pain. This study investigated response of glial cells in SpVc after experimental tooth movement (ETM). Methods: 1) Tooth movement was induced by Waldo's method, which a piece of elastic band (3M Unitek, 1/8) was inserted between the first and second upper molars on the left side. 2) A series of von Frey filament were used to determine hyperalgesia of masseter to mechanical stimulation according to Ren's method. Minocycline or saline vehicle was injected intraperitoneally 1h before ETM and continued daily to day 14 after ETM. 3)Activation of microglia and astrocytes was monitored at 1, 3, 7 and 14 days using immunohistocheminal analysis with OX-42 and GFAP antibodies, respectively. Results: A significant reduction of the relative escape threshold on ipsilateral masseter was observed at 3-9 days after saline treated ETM as compared to that of pre-ETM controls (P<0.05). The relative escape threshold of mincocycline treated ETM rats was higher than that of the saline treated ETM rats at 3-9 days, which didn't reach statistical significance (P>0.05). In normal control group, a few OX-42-IR microglia were observed in SpVc, they appeared a small cell body and thin process. Bilateral microglial activation was observed at 1-7 days after ETM, maximal at 3 days. Conclusions: These results suggest that microglial activation have a role in tooth pain and masticatory muscles hyperalgesia following ETM. Supported by the National Natural Science Foundation of China (No. 30471909).