A Study On NGF Changes In Periphery Tissues And Sensitization Of Primary Sensory Center Induced By Traumatic Occlusion

Traumatic occlusion causes a variety of deleterious effects both to local dental and masticatory system. Clinically, some patients suffer from toothache but no significant defects on dentin or in periodontal tissue except occlusion trauma. Dental pain disappears after occlusal adjustment, which demonstrates traumatic occlusion may lead to orofacial pain.Tissue damaging stimuli are intimately associated with the sensation of pain. Pain is a common symptom after tissue injury and it is also psychical adjunct of protective reflexes. Chronic pain states have been the subject of intense study in recent years but have received little attention in the dental literature especially in traumatic occlusion.Much of cytokinn is believed to participate in pulpitis or periodontium injury. A major contributor to produce hyperalgesia has been shown recently to be the neurotrophin nerve growth factor- NGF. NGF induces mechanical and thermal hyperalgesia in adult rats. Administration of anti-NGF serum or trkA-IgG fusion proteins substantially reduces inflammation hypersensitivity. NGF plays an important role in neuronal differentiation, maturation and survival. These effects are mediated largely via the high-affinity neurotrophic receptor tyrosine kinase A (TrkA).Until now, mechanical stimulation give rise to traumatic occlusion pain is not completely clearly. Whether NGF level changes in periphery tissue, whether trkA and some neuropeptides, such as preprotachykinin A (PPTA) expression variety in trigeminal ganglion (TG), and whether occlusal trauma excites primary sensory center are still not yet known. In this study, we want to discuss new data highlighting the distinct properties of orofacial pain from traumatic occlusion and identify any relationship between NGF and the etiology of dental pain and the mechanisms of NGF participate in traumatic occlusion pain.Objective The present study was designed to (1) establish traumatic occlusion animal model. (2) investigate the role of NGF and TrkA in orofacial pain induced by trauma occlusion. (3) provide more evidence in understanding the possible mechanisms of orofacial pain and explore potential therapic methods to this disease.Methods The occlusal surfaces of the first and second maxillary right molars in 15 dogs were unilaterally raised 1.5 mm with the casting Ni-Cr inlays which were fixed in Class I hole. The retention of inlays was observed during 2 months .On days 3,7,14,30 and 60 after teeth operation, X-Ray pictures of the upper and lower molars in the traumatic side were taken. Other 3 dogs without traumatic occlusion were used as control group. Periodontium ligament and pulp tissue were detached from root cementum and pulp cavity respectively. TG and caudalis subnucleus of trigeminal spinal tract nucleus (Vc) were also removed. NGF and trkA expression both in mRNA and protein level in periodontium and pulpal tissue, and trkA, PPTA mRNA in TG and c-fos mRNA in Vc were also detected by reverse transcription-polymerasechain reaction (RT-PCR), sandwich enzyme-linked immunosorbent assay (ELISA) and Western-blotting, respectively.The results were as below:1. None of inlay was loose or dislocation during experiment observation period. Abrasion on the occlusal surface and widen periodontium ligament were detected by X-Ray photos on both 30 and 60 days after traumatic occlusion induced.2. There were less expression of NGF and TrkA mRNA in control adult dog's periodontium. NGF and TrkA mRNA expression up-regulated from 3 to 30 days and 7 to 60 days compared with the control group respectively (P<0.05) and reached peak level during 14 to 30 days after traumatic occlusion was induced. NGF mRNA was about three-fold on day 30 in trauma periodontium ligament compared with control group. The expression of NGF and TrkA mRNA in the trauma periodontium side was stronger than that in contralateral side and control group (P<0.01). An upregulation expression level of NGF mRNA in contralateral sides was also observed during 3 to 7 days; NGF protein was increased gradually duri...