Objective To analyze probable risk factors to Henoch-Sch?nlein purpura (HSP) in Tibetan children so as to bring evidences for correct identification of high-risk children in plateau areas. Methods 140 high-altitude Tibetan children with HSP admitted to Shannan People's Hospital of Tibet Autonomous Region from October 2015 to October 2018 were enrolled, and 140 high-altitude Tibetan healthy children and 140 plain area HSP children were selected as the control. Gender, age, family history, allergy, past history (rheumatic disease, autoimmune disease, asthma), clinical phenotype, biochemical markers (antibody positive rate, platelet count and hemoglobin), clinical efficacy and recurrence were retrospective analyzed. The risk factors of HSP in the high-altitude Tibetan children were analyzed by univariate and multivariate Logistic regression analysis. Results It was shown by univariate analysis that the proportion of allergic history and past history of high-altitude HSP children was higher than those of high-altitude healthy children (allergic history: 35.7% vs. 11.4%, past history: 21.4% vs. 5.7%, both P < 0.05). Compared with plain area HSP children, the age of high-altitude HSP children was increased (years old: 6.5±2.3 vs. 5.3±2.2), the clinical phenotype was more complex (37.9% vs. 57.1% for simple skin and limb type, 21.4% vs. 14.3% for abdominal type, 28.6% vs. 21.4% for renal type, 7.1% vs. 5.0% for brain or lung type, 5.0% vs. 2.2% for complex type), the positive rate of antibody was increased (64.3% vs. 50.0%), platelet count was decreased (×109/L: 116.2±12.3 vs. 176.8±35.4), hemoglobin level was increased (g/L: 125.6±15.7 vs. 113.8±10.9), recurrence rate was lower (4.3% vs. 10.7%), and the difference was statistically significant (all P < 0.05). It was shown by multivariate Logistic regression analysis that age, allergic history and past history were independent risk factors for HSP in high-altitude Tibetan children [age: odds ratio (OR) = 1.263, 95% confidence interval (95%CI) = 1.063-1.968; allergic history: OR = 1.765, 95%CI = 1.326-2.452, past history: OR =1.421, 95%CI = 1.102-2.232, all P < 0.05]. Clinical phenotypic and biochemical indexes were important risk factors affecting the clinical efficacy of high-altitude Tibetan HSP children (non-simple skin and limb type: OR = 2.123, 95%CI =1.623-2.869; antibody positive: OR = 1.865, 95%CI = 1.502-2.768; both P < 0.05). Conclusions It is different of HSP occurrence in Tibetan children from plateau and plain areas. Attention should be paid to screening age, allergy history, past history, clinical phenotype, antibody positive and other high risk children. Early and effective intervention can improve clinical curative effect and reduce recurrence.

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.