ABSTRACT
BACKGROUND:Zirconia is considered to be one ofthe promising prosthodontics materials because of its high strength, high hardness, excelent wear resistance and excelent corrosion resistance. However, the development of zirconia is hindered owing to the uncertainty in long-term stability of zirconiaal-ceramic crowns such as the cracking (chipping) of veneering porcelain and deterioration of mechanical properties of zirconia dental crowns under intraoral conditions. OBJECTIVE:To summarize the preparation of zirconia bioceramic and its application progress in the field of prosthodontics. METHODS:The properties, crystal structure, preparation and use of zirconia in prosthodontics were reviewed. Reasons that affected the stability of zirconia were also discussed. The future development of zirconia was forecasted. RESULTS AND CONCLUSION:Preparation of zirconia bioceramics involves the folowing aspects:powder synthesis, biscuit molding, and ceramic sintering.To improvethe istability of zirconia al-ceramic crowns,we optimize the preparation of zirconia powder topromotethe purity, mechanical properties, biological properties and stability. Furthermore, it is necessary to explore the effects of crystal nucleation, growth, second phase and grain size on crystal stability and biomechanical propertiesof thetooth abutment, as wel astoconduct an in-depth theoretical analysis on the effect oftooth abutmentand lattice matching of porcelain crowns on the interface.
ABSTRACT
BACKGROUND:Cobalt chloride (CoCl2) may promote the proliferation of human umbilical cord-derived mesenchymal stem cels (hUC-MSCs) in a time- and concentration-dependent manner, and meanwhile, CoCl2 can regulate the expression of genes and proteins in hUC-MSCs. OBJECTIVE:To explore the effects of CoCl2 induced-hypoxia on the proliferation of hUC-MSCs and gene and protein expressions in hUC-MSCs, thereby establishing an effective method for MSCs culture and amplificationin vitro. METHODS: hUC-MSCs were extracted using tissue explant method. Under hypoxia conditions induced by CoCl2 (0, 100, 150, 200, 250 μmol/L) for different periods (0, 1, 2, 3, 4 days), flow cytometry was used to identify cel surface-associated antigens; cel counting kit-8 was used to detect cel proliferation; RT-PCR was used to determine levels of hypoxia inducible factor-1α, inducible nitric oxide synthase, stromal cel-derived factor-1, interleukin-6, transforming growth factor-β mRNA; western blot assay was used to detect protein expression of hypoxia inducible factor-1α. RESULTS AND CONCLUSION:The cels were positive for CD29, CD73, CD90, CD105, while negative for CD31, CD14, CD34, CD45, CD11b, HLA-DR. Moreover, the antigen expression was not affected by CoCl2 induced-hypoxia. CoCl2 induced-chemical hypoxia could promote the proliferation of hUC-MSCs in a time- and concentration-dependent manner. RT-PCR results showed thatunder hypoxia, hypoxia inducible factor 1α, inducible nitric oxide synthase and stromal cel-derived factor-1 mRNA expressions were significantly up-regulated, but interleukin-6 and transforming growth factor-β mRNA expressions were down-regulated significantly (P < 0.05). Additionaly, the protein expression of hypoxia inducible factor 1α was increased under hypoxia conditions. These findings indicate that CoCl2 induced-hypoxia environment may promote the proliferation of hUC-MSCs and the optimal concentration of CoCl2 is 200μmol/L. However, a higher concentration of CoCl2 (≥ 250μmol/L) inhibits the proliferation of hUC-MSCs, and the mechanism may be related to the increase of hypoxia inducible factor-1α at protein and mRNA levels.
ABSTRACT
Objective To investigate the effect of salt-induced kinase 2 (SIK2) in the G2/M checkpoint in response to ionizing radiation and the possible mechanism.Methods HeLa cells were irradiated with 60Co γ-rays.The cell model of knockdown SIK2 expression was constrcuted by transfecting HeLa cells with a pSicoR-based lentivirus vector of expressing SIK2 shRNA by lipofectamin 2000.Western blot and flow cytometry were performed to measure the changes of SIK2 protein level and cell cycle distribution.The phosphorylated histone protein H3 on Ser 10 was used as a molecular marker of mitotic cells for detecting the function of G2/M checkpoint.Results The expression level of SIK2 protein increased in HeLa cells after 60Co γ-ray irradiation.A cell model of knockdown SIK2 expression was successfully generated by transfecting the specific shRNA against SIK2.Depression of SIK2 significantly increased the cellular sensitivity at 1,2,4,6 Gy post-irradiation (t =-3.445,-2.581,-3.251,-2.553,P ＜0.05),and led cells to release earlier from the G2/M boundary arrest compared to control cells at 5,6 h post-irradiation (t =4.341,6.500,P ＜ 0.05).Western blot analysis indicated that the irradiation-induced phosphorylated CHK2/T68 in SIK2 knock-down cells was earlier than that in control cells.Conclusions salt-induced kinase 2 (SIK2) participates in the regulation of G2/M checkpoint induced by ionizing radiation and affects cellular radiosensitivity.