咬合创伤致咀嚼肌疼痛的中枢机制研究

目的观察咬合创伤后咬肌区的化学和机械伤害性刺激对中枢神经系统c- fos、P物质（ SP）表达的影响。方法在!面洞型内放入一个2 mm牙用固位钉造成咬合干扰，咬合创伤形成后7 d，咬合创伤机械刺激组和机械刺激对照组在麻醉下对左侧咬肌区行机械性刺激，记录有疼痛反应次数，2 h后处死动物。咬合创伤化学刺激组和化学刺激对照组在麻醉下左侧咬肌区注射体积分数为5%甲醛，2 h后处死动物。取大鼠脑干组织，用SABC漂染法检测c- fos、SP表达，并定量分析。结果机械刺激和化学刺激后，c- fos在脑干obex水平和颈髓C1- 2水平有两个表达高峰，咬合创伤机械刺激组和咬合创伤化学刺激组动物c- fos表达均明显高于其对照组（ P<0.05）。咬合创伤机械刺激组机械性刺激后脑干SP表达明显高于其对照组（ P<0.05），在颈髓C1- 2水平SP表达咬合创伤机械刺激组比其对照组增高，但无统计学差异（ P=0.072）。结论咬合创伤可引起脑干和颈髓中枢神经元的敏化，是咬合创伤致咀嚼肌疼痛的中枢机制之一。

Central mechanisms of masticatory muscle pain induced by occlusal interference

OBJECTIVE: To study c-fos and substance P expression in the central nervous system following mechanical and chemical nociceptive stimulation to the masseters in rats with occlusal interference. METHODS: Occlusal interference was made by bonding a 2 mm long dentin screw in the pulp cavity of the first maxillary molar in the left side. Seven days after occlusal interference, the rats in occlusal interference and mechanical stimulus group and mechanical stimulus control group were light anesthetized and nociceptive mechanical stimulus were applied to the ipsilateral masseter. Pain response was recorded and all the animals were killed 2 hours later. The rats in the other two groups were deep anesthetized and 100 microL 5% formalin was injected into the ipsilateral masseter, killed 2 hours later. The brainstem and cervical spinal cord were processed c-fos and substance P immunoreactivity and data were quantitatively analyzed. RESULTS: Both mechanical and chemical stimulus to the ipsilateral masseter induced increasing neuronal c-fos expression in the trigeminal nucleus and in the cervical spinal dorsal horn in occlusal interference and mechanical stimulus group and occlusal interference and chemical stimulus group (P < 0.05). Following mechanical stimulation to the ipsilateral masseter, substance P expression in the trigeminal nucleus transition zone was increased in occlusal interference and mechanical stimulus group (P < 0.05). CONCLUSION: The central neuronal sensitization in the brainstem may play an important role in the masticatory muscle pain induced by occlusal interference.