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Objective: To analyze the root canal diameter of the mandibular first premolar by using finite element analysis to simulate the stress distribution of dentin under three different preparation methods, and to provide the basis for clinical root canal preparation strategies of the mandibular first premolars. Methods: Twenty-one patients with complete cone beam computed tomography (CBCT) images were selected. The original DICOM format data from CBCT were imported into Mimics 21. 0 software to measure the root canal diameter at 3, 6, 9, and 12 mm from the apex and the root canal taper was segmentally calculated. Based on this, three-dimensional finite element models of the dental and periodontal tissues were constructed. Control group, maximum diameter preparation group, uniform preparation group, and 0. 06 taper instrument preparation group were designed. In ANSYS Workbench 17. 0 finite element analysis software, a 200 N load was applied to the buccal, lingual, and occlusal surfaces in various groups, and the stresses on dentin in various groups were analyzed. Results: The analysis of root canal taper at 3-6 mm, 6-9 mm, and 9-12 mm from the apex of mandibular first premolar teeth showed that the taper was similar in the mesial-distal direction at 3-6 mm from the apex. The average taper in the buccal-lingual direction at 6-9 mm from the apex was 0. 29, which was greater than the taper in the apical 1/3 and coronal 1/3. Under the same load, the peak stress values in dentin of mandibular first premolar teech in various groups were increased sequentially: 4. 693 6, 16. 304 0, 14. 278 0, and 18. 682 0 MPa. The stress in maximum diameter preparation group concentrated on the canal wall with the highest stress value. The stress in uniform preparation group concentrated on the root surface, and the stress values on each section were lower than those in maximum diameter preparation group. The stress in 0. 06 taper instrument preparation group concentrated on the apical 1/3 of the root surface. Conclusion: The root canal of the mandibular first premolar has a unique elliptical taper shape, and there are significant differences in diameter and taper between the mesial-distal and buccal-lingual directions. Different preparation methods result in different stress distributions on the canal wall, and the uniform preparation is the best method for enlarging the canal. [ABSTRACT FROM AUTHOR]

Objective: To discuss the effect of long-term use of chlorhexidine on the resistance of Enterococcus faecalis (E. faecalis), and to clarify its mechanism. Methods: The standard strain of E. faecalis was repeatedly exposed to chlorhexidine for 10 generations, and the minimum inhibitory concentration (MIC) was recorded at each passage. The bacteria collected from the 10th generation with increased MIC values were designated as the E. faecalis chlorhexidine-resistant strains (E. faecalis-Cs). The growth curves of two strains were drawn; the morphology of two strains were observed by transmission electron microscope; the number of biofilm formation of two strains was detected by crystal violet staining; the bacterial hydrophobicities of two strains were detected by microbial adhesion to hydrocarbons (MATH)method; the expression levels of S-ribosylhomocysteine lyase (LuxS)mRNA in the bacterial biofilms of two strains were detected by real-time fluorescence quantitative PCR (RT-qPCR)method. Results: From the 0th to the 10th generation, the MIC values of E. faecalis were gradually increased. The growth curves of E. faecalis and E. faecalis-Cs showed no significant differences. The transmission electron microscope observation results showed that both E. faecalis and E. faecalis-Cs appeared oval or diplococcal, with intact cell wall structures, smooth edges, and evenly distributed cytoplasm. There were no significant differences in the morphology, size, cell wall thickness, or integrity between two types of bacteria. The crystal violet staining results showed that compared with E. faecalis, the number of biofilm formation of E. faecalis-Cs was significantly increased (P<0. 05). The MATH results showed tha the hydrophobicity of E. faecalis-Cs was significantly higher than that of E. faecalis (P<0. 05). The RT-qPCR results showed that the expression level of LuxS mRNA in the biofilms of E. faecalis-Cs was significantly higher than that of E. faecalis (P<0. 05). Conclusion: E. faecalis develops the resistance after repeated exposure to the chlorhexidine, and the pathogenicity of the resistant strain is enhanced. The high expressin of quorum sensing (QS)system LuxS gene and stronger biofilm forming ability of bacteria may be the potential mechanism for E. faecalis to tolerate the chlorhexidine. [ABSTRACT FROM AUTHOR]

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This paper researched on the task dividing method based on the architecture of the network emulation for the fusion of virtualization and digital simulation to improve the performance. This method took into account the advantages of virtualization and digital simulation, and divided the emulation network topology into virtualization topology area and digital simulation topology area. And then aiming at load balancing and remote traffic minimizing, it divided the two topology area combined with given physical resources. Extensive experiments show that using the proposed method to divide the network emulation task, it reduced the remote traffic by 33. 7%, 25. 1% averagely, and improved the degree of load balancing by 56.3%, 38.0% averagely, compare with the random algorithm and the uniform load balancing algorithm. The task dividing method can effectively reduce the remote traffic and improve the degree of load balancing. [ABSTRACT FROM AUTHOR]

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