Experimental Study On The Changes Of Root Canal Tissue And The Expression Of Stromal Cell Derived Factor 1 After Periapical Injury

OBJECTIVE: Periapical tissues were stimulated to cause damage and bleeding effect after non-vital maxillary first molar root canal model established.The characteristic changes of root canal tissues,the expression and distribution of stromal cell-derived factor-1 in root canals and periapical tissues,the changes in concentration of serum SDF-1 were investigated before and after the injury.To evaluate the role of SDF-1 in revascularization of the pulp tissues.METHODS: Sixty-four 6-8 weeks male SD rats weighted 180-220 g with SPF grade were used.After the establishment of non-vital maxillary first molar root canal model,the experimental animals were subjected to periapical stimulation to induce root canal bleeding(n = 56).The injury group was sub-divided into 7groups: 12 h,1d,2d,4d,7d,10 d,14d,according to the different time points after periapical injury.The animals were given the lethal dose of anasthesia to collect the blood and maxilla from them.The SDF-1 levels in serum were detected by enzyme-linked immunosorbent assay(enzyme linked immunosorbent assay,ELISA).The maxilla were fixed and artificially decalcified then the changes of tissues and the characteristics of SDF-1 in root canal were observed by HE staining and immunohistochemistry.RESULTS:Periapical blood flowed into the root canal where the formation of blood clot occurred.The morphology of the root canal tissues was fibrins encapsulated with blood clots and blood cells at 1d,2d and 4d after injury.In the later stage of injury,the blood clots dissolved and the inflammatory cells gradually reduced.The close correlation occured between tissues and also between dentin and tissues structures.After 14 days of injury,the new vessels and cell structures appeared between the tissues and the root canal wall.Immunohistochemical staining showed that SDF-1 was expressed in the blood clots and inflammatory cells of the root canal after injury,then the expression of SDF-1,blood clot and inflammatory cells were decreased overtime.ELISA showed that the concentration of SDF-1 in the serum of the 12 h group and the4 d group were significantly higher than that of the control group(P <0.05),the difference was statistically significant,the results of rest time quantum have no significant changes when compared with that before injury.CONCLUSION:1.The expression of SDF-1 in the root canal was significantly correlated with the situation of blood clot and inflammatory cell after stimualtion-induced hemorrhage at the root apex.2.Increased concentrations of SDF-1 in serum can be seen in Group 12 h and Group 4d after periapical injury,but it has no continuity throughout the whole healing process.The evidences of bone marrow stem cells homing passing through blood circulation through periapical injury are needed further experiments to confirm.