This paper summarizes 6 cases with multi-fracture of dental instruments in tooth root canal treated in our hospital from June 2011 to July 2013,the creation of a straight pathway,establishment of collateral bypass ,ultrasonic vibration,prevention of root perforation and secondary instrument fracture were emphasized,a reference in dealing with similar situations was provided.

Objective To investigate the polymorphisms of human cytomegalovirus ( HCMV ) UL146 gene in asymptomatic children. Methods Urine samples were collected from 47 asymptomatic chil-dren who were positive for HCMV DNA. PCR was performed to amplify the open reading frame ( ORF) of UL146 gene. Positive bands were sequenced and variations in UL146 gene were analyzed by using bioinfor-matics software. Results Seventeen samples were successfully amplified and sequenced. Variations spread all over the sequence of UL146 gene and the variability in nucleotide and amino acid sequences ranged from 0％ to 42. 5％ and 0％ to 67. 7％ respectively. Compared with the Towne strain, there was diversity in sig-nal sequence and C-terminal region. Phylogenetic analysis indicated that UL146 in the 17 asymptomatic chil-dren belonged to four genotypes, which were G1, G8, G9 and G11. Forms of post-translational modification varied greatly among the four genotypes, while the important functional region of ELRCXC chemokine was highly conservative. Secondary structure prediction showed that random-coli conformation was the predomi-nant structure of active proteins. Isoelectric point ( PI) and molecular weight ( MW) were dissimilar among the four genotypes. Conclusion HCMV UL146 gene in asymptomatic children was hypervariable in both nucleotide sequence and amino acid structure. However, the important functional region was highly con-served. The predominant genotypes of UL146 in these children were G1, G8, G9 and G11, and the geno-type distribution in them showed no significant difference with previous findings in children with symptomatic HCMV infection.

Objective: To explore cyberbullying and risk factors of middle school students, and to provide a reference for cyberbullying prevention in school settings. Methods: A stratified cluster random sampling method was used to select 12 940 students from three junior high schools and four senior high schools in Yixing City of Jiangsu Province, China, to conduct a questionnaire survey from March 1 to May 31, 2019. The Chi -square test was performed to compare differences in the prevalence of cyberbullying among groups with different sociodemographic characteristics, and the multivariate Logistic regression model was employed to analyze the risk factors. A risk predictive nomogram model was constructed and then verified. Results: Middle school students were found to be victims of cyberbullying at a rate of 12.3%. The Logistic regression results showed that alcohol use ( OR =1.93), lack of emotional management ( OR =1.30), feeling unsafe ( OR =1.70), not trusting people ( OR =1.66), increased daily online time ( OR =1.39), higher frequency of using social software or websites ( OR =2.24), poor relationships with family members ( OR =1.46), parental neglect ( OR =1.50), class leadership ( OR =1.30) and poor relationships with classmates ( OR =1.34) were risk factors for middle school students who were victims of cyberbullying ( P <0.05). Based on these 10 independent risk factors, the nomogram prediction model, had good discrimination ( AUC =0.73). Conclusion Cyberbullying is common among middle school students. Internet use, parental neglect and class leadership all have an impact on cyberbullying.