Objective: To investigate eye care behaviors among primary students in Wenzhou during Novel Coronavirus epidemic(COVID-19),and to provide a basis for eye care education and myopia prevention strategy. Methods: A total of 1 127 students from grade one to grade six of six primary schools in Wenzhou were selected to participate in an on-line invistigation regarding class attendance and eye care behaviors during the epidemic, March 6-9, 2020. Results: During the epidemic period, the primary school students in Wenzhou mainly took classes on the Internet (936, 83.1%), and the main learning tools were computers (391, 34.7%) and mobile phones (344, 30.5%), with an average of 3.00 h of online class. On average, students needed 2.00 h to complete homework and 1.00 h of extracurricular reading every day. In addition to learning, the daily use of mobile phone or ipad, computer and TV was 1.00,0.50,1.00 h respectively. Limited by the epidemic situation, the average daily exercise time of students was 0.81 h, including 0.00 h of outdoor activities; the average daily sleep was 9.00 h . During the epidemic period, 553 pupils (49.1%) reported eye discomfort, of which the most common was dry eyes (379, 47.4%). Multivariate Logistic regression analysis showed that the main learning tools of non-electronic products, reading distance > 30 cm or not reading, exercise time >0.5 h and outdoor activity time > 0.5 h were the protective factors of ocular discomfort (P<0.05). More than 2 h homework and recreational screen time higher than 0.5 h were risk factors for ocular discomfort(P＜0.05). Conclusion During the epidemic period, online learning increasedeye strain.Time of electronic devices usage,correct posture for reading,moderate level of ourdan physical activity,as well as prevention and treatment of eye strain should be strictly monitored.

OBJECTIVETo establish a method for the determination of N-butylbenzene in the workplace atmosphere by gas chromatography.

METHODSN-butylbenzene in the workplace atmosphere was collected by activated charcoal tube, desorbed using carbon disulfide, and determined by capillary column gas chromatography.

RESULTSThe method showed a linear relationship within the range of 0∼100 µg/ml. The regression equation was y = 0.870x-0.014, with the correlation coefficient r being 0.999 9. The limit of detection was 0.32 µg/ml. The minimum detectable concentration was 0.21 mg/m³ (with sampled air volume of 1.5 L). The average spike recovery rate was 97.8%∼102.6%. The within-run precision was 3.06% and the between-run precision was 3.64%. The rate of average desorption was 99.6%. The breakthrough volume was 6.34 mg. The sampling efficiency was 100%. The samples could be stored for at least 7 days at room temperature.

CONCLUSIONAll parameters of the method meet the requirements of GBZ/T 210.4-2008 "Guide for establishing occupational health standards-Part 4 Determination methods of air chemicals in workplace" and can be applied for the determination of N-butylbenzene in workplace atmosphere.

Air ; analysis ; Air Pollutants, Occupational ; analysis ; Benzene Derivatives ; analysis ; Chromatography, Gas ; methods ; Linear Models ; Workplace

Objective : To evaluate the clinical outcomes of all-ceramic crowns whose oral digital impressions were scanned by 3Shape Trios. Methods : All the impressions were scanned by Trios and all the crowns were fabricated according to the standard procedure. The restoration quality were evaluated using modified United States Public Health Service (USPHS) criteria one year after treatment. Restoration integrity、 marginal adaptation、enamel wear、 color satisfaction and gingival index (GI) of the prostheses were evaluated according to the modified USPHS criteria. Results: The clinical 1 year survival rate of 92 porcelain crowns fabricated by 3-shape Trios digital impression and made by CAD/CAM was 100%. The scored A rates of restoration integrity、 marginal adaptation、 enamel wear、 secondary caries、color satisfaction and gingival index of the prostheses were 100%、91.3%、 98%、95.6%、96.7% and 94.7% after 1 year, respectively. Conclusion The clinical outcomes of all-ceramic crowns whose oral digital impressions were scanned by 3Shape Trios and whose crowns were made by CAD-CAM are satisfying.

Objective : To evaluate the clinical outcomes of all-ceramic crowns whose oral digital impressions were scanned by 3Shape Trios. Methods : All the impressions were scanned by Trios and all the crowns were fabricated according to the standard procedure. The restoration quality were evaluated using modified United States Public Health Service (USPHS) criteria one year after treatment. Restoration integrity、 marginal adaptation、enamel wear、 color satisfaction and gingival index (GI) of the prostheses were evaluated according to the modified USPHS criteria. Results: The clinical 1 year survival rate of 92 porcelain crowns fabricated by 3-shape Trios digital impression and made by CAD/CAM was 100%. The scored A rates of restoration integrity、 marginal adaptation、 enamel wear、 secondary caries、color satisfaction and gingival index of the prostheses were 100%、91.3%、 98%、95.6%、96.7% and 94.7% after 1 year, respectively. Conclusion The clinical outcomes of all-ceramic crowns whose oral digital impressions were scanned by 3Shape Trios and whose crowns were made by CAD-CAM are satisfying.

Objective: The objective of this study was to compare the early clinical effects of zirconia all⁃ceramic crowns using two different impression methods. Zirconia ceramic crowns were produced using digital models based on either a silicone rubber impression perfusion model in vitro or a 3D mouth scanner. Methods : A total of 50 patients with a planned restoration of the first permanent molar with zirconia all⁃ceramic crowns after root canal therapy were se⁃ lected and randomly divided into two groups: a digital impression by intraoral 3D scanning group and a digital impres⁃ sion by extraoral scanning after silicone rubber impression group. Zirconia all⁃ceramic crowns were created by CAD/ CAM in both groups. Marginal adaptation, proximal contact, and occlusal contact were compared between groups. Results: There was no significant difference between the two groups in marginal adaptation (P > 0.05). For proximal con⁃ tact and occlusal contact, no significant differences regarding the number of cases for the criteria of level A and level B were found between two groups (P > 0.05), while the misfit value in level B was smaller in the first group than in the second group (P < 0.05). Conclusion Zirconia all⁃ceramic crowns with intraoral 3D scanning show excellent early clinical performance.