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Objective@#To explore the prevalence of depressive symptoms among middle school students in Nanjing and the relationship between screen time, sleep duration and depressive symptoms, and to provide a scientific reference for depression prevention in adolescents.@*Methods@#Using stratified cluster random sampling method, a total of 2 010 students from 5 middle schools in urban areas and 3 middle schools in suburban counties were selected. Screen time and sleep duration were evaluated through questionnaires, and depressive symptom was assessed by the Center for Epidemiological Studies Depression Scale (CES-D).@*Results@#The prevalence of depressive symptoms (CES-D≥16) was 27.71%(557). Logistic regression analysis showed that students with screen time >2 h/d( OR=1.90, 95%CI =1.53-2.37), sleep duration <7 h/d ( OR=2.54, 95%CI =1.88-3.42) were statistically associated with depressive symptoms. stratified analysis showed that, sleep duration of <7 h/d was associated with increased odds of depressive symptoms, the magnitude among students with screen time >2 h/d( OR=2.46, 95%CI =1.64-3.71) was higher than those with screen time ≤2 h/d( OR=2.35, 95%CI =1.51-3.65).@*Conclusion@#High prevalence of depressive symptoms was observed among middle school students in Nanjing. Prolonged screen time and insufficient sleep duration are associated with increased odds of depressive symptoms. Attention should be paid to the mental health of adolescents with the combined exposure of screen based activities and lack of sleep.
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Objective@#To analyze Internet behaviors of children and adolescents and their influencing factors, and to provide scientific basis for health education guidance and prevention measures.@*Methods@#A stratified cluster sampling method was used. From January to June 2019, 30 955 primary school students in 16 provinces (municipalities), from eastern, central, and western economic zones of China were selected to conduct a questionnaire survey, regarding general demographics, diet and exercise, tobacco, alcohol and sleep, Internet and electronics usage, etc.@*Results@#Among them, 43.1% of students had never been online with girls (44.7%) higher than boys (41.8%)(χ2=21.04, P<0.01); 1.3% of students reported online time for more than 4 hours a day, boys were significantly higher than girls(χ2=15.87, P<0.01); Internet addiction was detected in 2.4% of elementary school students, with boys (3.0%) higher than girls(1.7%)(χ2=331.77, P<0.01), and the trend increases with grade. With sixth grade (3.3%) were significantly higher than children from the first grade (0.8%) and other grades(χ2=163.96, P<0.01). Children’s tendency to Internet addiction was 11.9%, of which boys were 13.0% and girls were 10.6%, boys were significantly higher than girls(χ2=117.66, P<0.01). Pearson correlation analysis revealed that, after controlling gender age, boarding school, family relationship, single parents and regrouped families, smoking, drinking sugary drinks, eating fried foods, and left-behind were positively related to Intenet addiction(r=0.06, 0.07, 0.27, 0.44, 0.07, 0.11, 0.09, P<0.01), while medium and high intensity sports, effective physical education, health education in school, AIDS education and parental restrictions on TV and computer games, were negatively associated with internet addiction(r=-0.74, -0.65, -0.04, -0.05, -0.63, P<0.01).@*Conclusion@#The internet addiction of Chinese primary school students is common and increases by year. High-intensity, high-density sports, effective physical education, and health education could help prevent Internet addiction among children.
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<p><b>OBJECTIVE</b>To compare the shaping ability and the influence on apical foramen among hand ProTaper, stainless steel K-files and rotary ProTaper in preparing different curved root canal.</p><p><b>METHODS</b>Forty simulated resin root canal blocks were randomly divided into four groups and prepared by hand ProTaper, stainless steel K-file and rotary ProTaper, respectively. Of them, 12 blocks in group A, B, C consist of six 200 curved root canals and six 30 degrees curved root canals each group. The curvature of the other 4 blocks in group D was less than 5 degrees. Taking photos of the models to the root canal orthotopically and apical foramen using digital camera before and after instrumentation. Finally, the transportation of root canal and the size of apical foramen were analyzed using special image software Auto-CAD.</p><p><b>RESULTS</b>The transportation of center in group B was the highest than that in group A and group C (P<0.05). In some portions of root canal, the transportation of center in group C was higher than that in group A. The size of the apical foramen in group B was significantly bigger than the other groups and the size of the apical foramen in 30 degrees root canal was significantly bigger than that in 20 degrees root canal after instrumentation (P<0.05). There was no significantly different between group A and group C, though the size of apical foramen in group C was bigger than that in group A at the same curvature, and that in 30 degrees root canal was bigger than in 20 degrees root canal (P>0.05).</p><p><b>CONCLUSION</b>Both of the two instruments engender root canal transportation, and curvature is the main reason of transportation. Comparing with stainless steel K-files, NiTi files can maintain the shape of the root canal and apical foramen well.</p>