Experimental Study Of Pulp Regeneration Via Cell Homing By Stromal Cell Derived Factor-1

Objection:In order to investigate the role of stromal cell-derived factor-1(SDF-1)in regenerative endodontic treatment,SDF-1 was applied into non-vital root canals and SDF-1 antibodies were applied in vivo to neutralize SDF-1,a byproduct of pulp revascularization.Methods:1.8-week-old sixty female SD rats were enrolled in the study.Bilateral mandibular first molars were used as experimental teeth.We removed the dental pulp to establish non-vital root canals model.2.The experimental methods of the study were as follows:(1)Establishment of non-vital root canals model.(2)Stimulating root tip bleeding by injuring it.(3)SDF-1? hydrogel was implanted into the root canals.(4)Local injection of SDF-1 serum antibodies into the vestibular sulcus of the mandibular first molar.The experiments were randomly divided into 5 groups,each group contains 12 rats.According to the above methods,different groups of experimental teeth were treated in a single or combined manners,as follows: Group Blood Clot(Group BC),Group Blood Clot +SDF-1? hydrogel(Group BC+ SDF-1?),Group SDF-1? hydrogel(Group SDF-1?)and Group Blood Clot + SDF-1 Neutralizing Antibody(Group BC + antiSDF-1).Unlike the experimental groups,no treatment was performed in the control group.3.Collection and testing the samples: after each group was treated accordingly with above methods,12 rats in each group were sacrificed by excessive anesthesia at the corresponding period,that was 14 days and 30 days(6 rats per time point).Bilateral sides of mandibles were used for histological specimen.These slices were stained with hematoxylin-eosinstaining(HE)and immunohistochemistry(IHC).Qualitative and quantitative analysis procedures were done in the new tissues of the root canals.Result:Histology of HE stain(1)The control group: no treatment was performed after removing of dental pulp.There was no neonatal connective tissues in the root canals for both 14 days and 30 days.Only a few inflammatory cells were found near the apical foramen.The cells in the periodontal ligament of the apical region were found to have little tendency to extend from the apical foramen into the root canal.(2)Histology of HE stain in expermental groups14 days histology: in the Group BC,Group BC+SDF-1? and Group SDF-1?,irregularly mineralized matrixes and dense connective tissues were found in the root canals.These dense connective tissues was composed of fibroblast-like cells and a small number of small blood vessels were found at the apical direction of the root canals.The cells in the periodontal ligament of apical regions from the above three groups clearly showed the tendency of extending from the apical foramen into the root canals.The small blood vessels in the neonatal connective tissues of Group BC+SDF-1? and the Group SDF-1? were more abundant than that of Group BC.There was no obvious neonatal connective tissues in the root canals 2 out of 8 samples in Group BC+anti SDF-1 and no extending of the periodontal ligament cells in apical region as well.However,there were large number of immature fibroblasts and abundant blood vessels accumulated near the apical foramen,but did not find to have the tendency to grow into the root canals.The histological patterns of the remaining samples were similar to that of the BC group.30 days histology: the histological pattern of the periodontal ligament around the apical foramen and root canals in each experimental group was found to be similar.A lot of irregularly mineralized matrixes were deposited at the coronal portion of the root canals.Dense connective tissues which composed of fibroblast-like cells and a few small blood vessels were developed in the apical direction of the root canals.The morphology of these connective tissues was similar to those of the periodontal ligament structures and also connected to the periodontal ligament through apical foramen.(3)The histology of IHC stain in expermental groups14 days IHC stain: CXCR4-positive cells were expressed in the periodontal ligament of the apical area of all experimental groups while in the root canals regions the CXCR4-positive cells were expressed only in Group BC,Group BC+SDF-1? and Group SDF-1?.30 days IHC stain: CXCR4-positive cells were expressed in the root canals of Group BC,Group BC+SDF-1?.However,there was no CXCR4-positive cells in the root canals of the remaining groups.There were full of mineralized tissues but no CXCR4-positive cells were expressed in the root canals of Group SDF-1?.In the periodontal ligament of the apical area CXCR4-positive cells were expressed in all experimental groups.(4)Statistical analysis of the area ratios of new tissues in the root canalsIn 14 days,the mean ratios of Group BC,Group BC+SDF-1? and Group SDF-1? were higher than that of Group BC+antiSDF-1 but there were no significant differences among all the experimental groups(p>0.05).In 30 days,the mean ratios of Group BC,Group BC+SDF-1? and Group SDF-1? were also higher than that of Group BC+antiSDF-1 and there were statistical differences among all the experimental groups(p < 0.05).When calculating the pairwise comparison,mean ratio of Group BC+SDF-1? was higher than Group BC and Group BC+SDF-1?(p<0.05).In addition,there was statistical difference between mean ratio of GroupSDF-1? and Group BC+antiSDF-1(p<0.05).Conclusion:1.SDF-1? can recruit endogenous cells that express CXCR4 into the root canals for tissue regeneration.To some extent,the usage of SDF-1 could increase the amount of new tissues in the root canals after pulp revascularization.2.Topical application of SDF-1 antibody can prevent CXCR4-positive cells from homing into the root canals and participated in pulp tissue regeneration.3.SDF-1?/CXCR4 signal axis plays a key role in the homing of cells to the root canals for tissue regeneration.