| Background:Tooth is the hardest organ of human body,which is composed of enamel,dentin,cementum and pulp.Dentin is the main structure of tooth tissue.When the enamel is destroyed and the dentin is exposed,the odontoblasts are stimulated and degenerated or even necrotic.The dental pulp stem cells which are the undifferentiated mesenchymal cells in the deep layer of dental pulp can move here to differentiate into dentin cells,secrete dentin matrix,and then mineralize to form the third stage dentin,as known as restorative dentin.Matrix metalloproteinase（MMPs）are a group of important proteolytic enzymes,and they are named for their need of Ca2+,Zn2+and they have similar structures.They can be divided into five categories.MMP-2、9 belong to gelatinases,their substrates are collagenⅣ,Ⅴ,Ⅸ,Ⅹbesides denatured collagen.There are different amounts of MMP-2,MMP-8 and MMP-9 in the dentin of human primary teeth and permanent teeth.The content of MMP-2 was the highest in the dentin of human primary teeth,followed by MMP-8 and MMP-9.Besides,in the permanent dentin,the content of MMP-8 in dentin with higher calcification degree is less than that in dentin with lower calcification degree.MMP-8 can break down type I collagen which is the main protein in dentin to form two peptide chains,and MMP-2 and MMP-9 can enzymatically break these two peptide chains into shorter peptide chains.In addition,the product formed by MMP-2 decomposing dentin protein-1 can promote the differentiation of dental pulp stem cells into odontoblasts.And MMP-9 is involved in the early stages of tooth formation and development.Therefore,studying the mechanism of differentiation of dental pulp stem cells into odontoblasts plays an important role in the treatment of tooth defects and even tooth loss.Objective:The mechanism of odontoblast differentiation of DPSCs was explored by studying the expression of MMP-2 and MMP-9 in DPSCs differentiating into odontoblasts in vitro.And then we can provide support in the treatment of dental defects.Methods:The primary cells of DPSCs were selected from the young permanent teeth without caries by the modified tissue enzymatic method.The primary cells are cultured to the fourth generation.The fourth generation dental pulp stem cells were induced to differentiate to the direction of odontogenesis by the odontogenic（osteogenic）inducer.The differentiation ability and degree of odontogenic direction were identified by detecting the activity of alkaline phosphatase and the content of dentin siaphoprotein after the induction for one week,two weeks,three weeks and four weeks.The content of MMP-2 and MMP-9 was determined by enzyme-linked immuno sorbent assay.Result:DPSCs were cultured successfully.DPSCs cultured in odontogenic induction medium can produce mineralized nodules.The activity of ALP and the content of DPSS in DPSCs which were cultured by the odontogenic（osteogenic）inducer were significantly higher than those in the control group.This indicated that it differentiated to odontogenic（bone）.In the first three weeks,there was no significant difference in the content of MMP-2 between the experimental group and the control group,.At the fourth week,the content of MMP-2 was significantly higher than that of the control group.However,the content of MMP-9 in DPSCs which were cultured by the odontogenic（osteogenic）inducer was significantly lower during the four weeks.Conclusion:The expression of MMP-9 decreased in the odontogenic phase of DPSCs,nevertheless,there was an upward trend in the expression of MMP-2. |
