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Objective:To apply knowledge maps to systematically evaluate problem-based learning (PBL) literatures from the past 50 years, so as to explore the law of development and related important documents.Methods:All peer-reviewed studies were retrieved from Web of Science (WOS) Citation Database on PBL of the year from 1970 to 2019. Bibliometrix package of R was used to analyze following items: annual growth law of PBL literature, literature cumulative growth law, literature citation status and top 30 important documents. Based on the results, the law of development of PBL research, important literatures and time nodes was analyzed.Results:After literature cleaning, 2 401 documents were finally included into the analysis. The analysis revealed that: in accordance with the law of development disciplines, PBL study experienced three periods, early birth (Period Ⅰ), PBL study early development (Period Ⅱ) and PBL large-scale development (Period Ⅲ). Now PBL is currently in a period of large-scale development. In the development process, 1983, 1986, 1993, 2003, 2005, 2007, 2011, 2012 and 2014 has become important research time nodes, and there have been five important documents promoting PBL development (ALBANESE MA, 1993, ACAD MED; VERNON DTA, 1993, ACAD MED; NORMAN GR, 1992, ACAD MED; BARROWS HS, 1986, MED EDUC; HMELO-SILVER CE, 2004, EDUC PSYCHOL REV).Conclusion:Nowadays, PBL theory and method has been perfected, which has been developed significantly, and it's an important period of application and promotion. The PBL has become an important method to cultivate clinical skills or other disciplines with strong practicality.
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Cas1-and-Cas2-mediated new spacer acquisition is an essential process for bacterial adaptive immunity. The process is critical for the ecology of the oral microflora and oral health. Although molecular mechanisms for spacer acquisition are known, it has never been established if this process is associated with the morphological changes of bacteria. In this study, we demonstrated a novel Cas2-induced filamentation phenotype in E. coli that was regulated by co-expression of the Cas1 protein. A 30 amino acid motif at the carboxyl terminus of Cas2 is necessary for this function. By imaging analysis, we provided evidence to argue that Cas-induced filamentation is a step coupled with new spacer acquisition during which filaments are characterised by polyploidy with asymmetric cell division. This work may open new opportunities to investigate the adaptive immune response and microbial balance for oral health.
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Objective:To compare the compression strength of three provisional restorative materials. Methods:Eighteen cylinder specimens were fabricated with 12mm in diameter and 30mm in height according to the GB/T 7314-2005 standards. Six specimens were made of self-curing resin,Switf-Temp and Protemp Ⅱ respectively. Then all specimens were compressively loaded and the data were recorded by MTS880 testing machine. Results:There were significantly statistical differences (P0.05)in terms of compression strength. Conclusion:The self-curing resins have higher compression strength than those of Switf-Temp and Protemp Ⅱ. The dentists must be aware of different situations of teeth and choose the provisional material appropriate for each tooth.