| ObjectiveThe movement of orthodontic teeth is built on the basis of the biological alterations in the course of periodontal tissue being forced. The movement-related alterations of orthodontic tooth, includ the cementum, periodontal ligament and alveolar bone remodeling. Among the periodontal tissues a variety of tissues, cells, and molecules are involved in this complex biological process.The interaction of different tissues, cells, and molecules maintain the physiological alterations and the dynamically stable of the periodontal tissue during the movement of orthodontic tooth.When the tooth is under the pressure of the orthodontic force,the periodontal ligament cells, extracellular matrix and nerve endings feel the mechanical stimulation firstly and then release growth factors, inflammatory mediators, hormonal substances and nerve peptides etc,which involved in the process of tooth movement every cycle.Nerve growth factor (NGF) is a nerve cell growth regulator with the function of Neurons nutrition and promoting neurite out growth, which is synthesized and secreted by the target tissue cells that are guided by the effective of neurons. It has an important role in the regulation of central and peripheral neuronal development, differentiation, growth, regeneration and expression s of functional properties. NGF is a member of neurotrophic factor family, and it can bind with TrkA receptor and P75receptor. P75is low-affinity binding receptor of NGF.It has been proved that NGF and P75can promote proliferation, differentiation and apoptosis of neuron. It has reported that after the movement of orthodontic tooth the expressions of NGF in the trigeminal ganglia is regular,which is closely related to pain response. However, it has been reported hardly about its expression and significance in the periodontal tissue at home and abroad.This study is designed to study the expression change of NGF and its receptor P75in rats periodontal tissue in the early stage of orthodontic force on periodontal ligament and its roles and possible mechanisms in periodontal tissue remodeling process.MethodThe thirty six male SD rats of eight weeks old are divided into two groups. One is the Control group, of which the teeth of six rats are not forced, and the other group is the experimental group, which can be divided into another five groups, these are groups of4h,1d,3d,5d,7d of different force time. The object of this study is the first molar of right maxilla of rats. The anchorage tooth is maxillary incisor and it is that using orthodontic force of0.39N to pull the right maxillary first molar to simulate the moving process of the mesial movement of orthodontic tooth. The animals are killed at the different force time and the tissues are maked to tissue slices, which include the the tissues of maxillary first molar. The technique of Immunohistochemistry is used to dective the expression of NGF and P75in periodontal tissues.Result1. Compared with the control group, with the changes of force time, in the experimental group the periodontal ligament gap of pressure side is gradually narrowing, the inflammatory component increases, periodontal ligament fiber arranges in disorders gradually, the numbers of osteoclasts increases and alveolar trap nest of bone absorption deepen.2. In the control group, Both NGF and P75of periodontal tissues are weakly positive expressed. After being forced for3d, IOD is strongly positive expression, and then decrease gradually. At the time of7d it is only slightly higher than that in the control group. Conclusion1. The NGF and P75also can be expressed in periodontal tissues in the normal state.2. After some load is ued to the maxillary first molar of rats, the expressions of NGF and P75in periodontal tissue have showed a trend of increase first and then decrease.3. The NGF and its receptor P75involve in early pain response of orthodontic treatment and may involve in the early stage of inflammation of periodontal tissue and remodeling of alveolar bone. |
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