Abstract: BACKGROUND: The research of dental stem cells in the fields of regenerative medicine and tissue engineering has been deepening, bringing hope for the repair of tooth-related tissues and the treatment of systemic diseases. However, there is a lack of systematic research and analysis on the biological characteristics of dental stem cells in different age groups. 
OBJECTIVE: To explore the biological characteristics of the human deciduous tooth and permanent tooth pulp stem cells cultured in umbilical cord blood platelet lysate to provide a reliable basis for human platelet lysates to replace fetal bovine serum.  
METHODS: The pulp tissues of deciduous teeth, juvenile permanent teeth and adult permanent teeth were taken out and cultured in DMEM/F-12 medium supplemented with 10% fetal bovine serum or different concentrations (5%, 10% and 15%) of human platelet lysates. Cell proliferation in the four groups was detected by cytometry. The optimal concentration of human platelet lysates was selected for subsequent experiments. Under the optimal concentration of human platelet lysates, human deciduous tooth and juvenile and adult permanent tooth pulp stem cells were cultured in vitro. The cell growth status was observed under the microscope. The specific antigen on the cell surface was detected by flow cytometry. The cell proliferation ability was tested by the cell counting method and CCK-8 assay. The cell differentiation ability in vitro was observed by a three-line differentiation assay.
RESULTS AND CONCLUSION: (1) The cell proliferation rate of the 10% human platelet lysate group was the highest. (2) In all three groups, fusiform fibrous cells grew and expanded from around the tissue block. There was no significant difference between deciduous teeth and juvenile permanent tooth cells, but the adult permanent tooth cells were larger than the deciduous and juvenile permanent tooth cells of the same generation. (3) The results of flow cytometry showed that deciduous teeth, juvenile permanent teeth and adult permanent teeth conformed to the phenotypic characteristics of mesenchymal stem cells. (4) The proliferative capacity of adult permanent dental pulp stem cells was significantly lower than those of deciduous teeth and juvenile permanent dental pulp stem cells (P < 0.01). (5) mRNA expressions of osteoblast-related genes alkaline phosphatase and bone morphogenetic protein 2, lipoprotein lipase and peroxisome proliferator-activated receptor γ2, mRNA expressions of chondroblast related gene type II collagen α1 and cartilage oligomeric matrix protein in adult pulp stem cells of permanent teeth were significantly lower than those of deciduous teeth and juvenile permanent teeth pulp stem cells (P < 0.01). (6) Compared with adult dental pulp stem cells, human deciduous teeth and juvenile permanent teeth dental pulp stem cells have the stronger proliferative capacity and multidirectional differentiation potential, and are more suitable for clinical research and disease treatment.

Key words: platelet lysate, dental pulp, stem cell, differentiation, aging change