Viral shedding in day-care children and students infected with norovirus in outbreaks / 上海预防医学

Objective:This study aimed to investigate the time duration of norovirus shedding among day-care children and students during norovirus outbreaks， as well as influencing factors affecting the viral shedding. Methods:Suspected cases of norovirus infection and their close contacts were collected from child care and school settings during norovirus outbreaks in Xuhui District， Shanghai， from 2017 through 2019. Specimens were detected using real-time RT-PCR to determine whether children had been infected with norovirus. Subsequently， further specimens were collected every 3-7 days from infected children until specimens tested negative for norovirus. Results:A total of 76 outbreaks were reported involving 1 014 suspected cases. In the 421 suspected cases， 311 confirmed cases were diagnosed after examination. Furthermore， a total of 58 confirmed cases participated in this study with informed consent， with a participation rate of 18.65%. The average time duration of norovirus shedding was （16.24±13.80） days， in which 79.31% had viral shedding more than 7 days， 37.93% more than 14 days and 17.24% more than 21 days. A Cox proportional-hazards model showed that children with more severe symptoms （HR=2.06，P=0.040）， day-care children （HR=4.13，P=0.012）， and confirmed cases in 2019 （HR=0.11，P<0.001） had longer duration of viral shedding. Conclusion:Children may remain shedding norovirus after their recovery and back to class. Improvement in sanitation for these recovered children in child care and schools is especially necessary， which may avert secondary transmission.

Toxicity testing of four silver nanoparticle-coated dental castings in 3-D LO2 cell cultures / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

To address the controversial issue of the toxicity of dental alloys and silver nanoparticles in medical applications, an in vivo-like LO2 3-D model was constructed within polyvinylidene fluoride hollow fiber materials to mimic the microenvironment of liver tissue. The use of microscopy methods and the measurement of liver-specific functions optimized the model for best cell performances and also proved the superiority of the 3-D LO2 model when compared with the traditional monolayer model. Toxicity tests were conducted using the newly constructed model, finding that four dental castings coated with silver nanoparticles were toxic to human hepatocytes after cell viability assays. In general, the toxicity of both the castings and the coated silver nanoparticles aggravated as time increased, yet the nanoparticles attenuated the general toxicity by preventing metal ion release, especially at high concentrations.

Application of digital photography in color matching in dentistry / 浙江大学学报·医学版

<p><b>OBJECTIVE</b>To develop a new color matching method in dentistry by application of digital photography.</p><p><b>METHODS</b>Digital photographs were obtained of Vitapan 3D-Master shade guide and natural teeth under the same condition, the L*a*b* values of each digital photography were assessed and analyzed by Photoshop CS4.</p><p><b>RESULTS</b>The Vitapan 3D-Master shade guide was divided into 5 groups, the L* values were similar in each group, but decreased from group 1 to 5. The a* values of L1.5 and L2.5 were minimum, R1.5 and R2.5 were maximum and M1-M3 were intermediate. Compared with Vitapan 3D-Master shade guide, the L*a*b* values of natural teeth were higher.</p><p><b>CONCLUSION</b>Digital photography can basically reflect the color of Vitapan 3D-Master shade guide, and provides a reference for color matching in dentistry.</p>

Effect of pH value and fluoride ions on corrosion resistance of pure Ti and Ni-Cr-Ti alloy in artificial saliva / 浙江大学学报·医学版

<p><b>OBJECTIVE</b>To investigate the effect of pH value and fluoride ions on the corrosion resistance of pure Ti and Ni-Cr-Ti alloy in the artificial saliva.</p><p><b>METHODS</b>Electrochemical technique was used to measure the electric potential of corrosion (Ecorr), current density of corrosion (Icorr) and polarization resistance (Rp) of pure titanium and Ti-Ni-Cr alloy in the artificial saliva with different pH value and fluoride concentrations. After electrochemical analysis, microstructure and phase diffraction were examined by FSEM.</p><p><b>RESULTS</b>With the lower pH value, the Ecorr and Icorr of pure titanium and Ti-Ni-Cr alloy increased, the Rp decreased, there was a significant difference (P<0.05). The Ecorr and Icorr increased markedly, the Rp significantly reduced in the artificial saliva containing 0.2% NaF (P<0.01). FSEM showed that pure titanium and Ti-Ni-Cr alloy surface corrosion, pure titanium in the artificial saliva containing 0.2% NaF was most serious.</p><p><b>CONCLUSION</b>Lower pH value decreases the corrosion resistance of pure titanium and Ti-Ni-Cr alloy and the artificial saliva containing fluoride ions decreases the corrosion resistance of pure titanium.</p>