Fatigue analysis of restored teeth longitudinally cracked under cyclic loading

ObjectiveTo investigate the fatigue behavior of restored teeth, in particular the mechanisms of longitudinal dentinal cracking under cyclic mechanical loading, using finite element analysis (FEA) and the stress-life (S-N) approach.MethodsTen root-filled premolars restored with resin composites were subjected to step-stress cyclic loading to produce longitudinal cracks. Fracture loads and number of cycles completed at each load level were recorded. FEA was used to predict the stress amplitude of each component under the global cyclic load. Both intact and debonded conditions were considered for the dentin-composite interface in the FEA. The predicted stress concentrations were compared with the fracture patterns to help elucidate the failure mechanisms. The S-N approach was further used to predict the lifetimes of the different components in the restored teeth. Cumulative fatigue damage was represented by the sum of the fractions of life spent under the different stress amplitudes.ResultsLongitudinal cracks were seen in ~50% of the samples with a mean fracture load of 770 ± 45 N and a mean number of cycles to failure of 32,297 ± 12,624. The longitudinal dentinal cracks seemed to start near the line angle of the cavity, and propagated longitudinally towards the root. The sum of fractions of life spent for the dentin-composite interface exceeded 1 after ~7000 cycles when that for dentin was much lower than 1, indicating that interfacial debonding would occur prior to dentin fracture. This was supported by micro-CT images showing widened interfacial space in the cracked samples. In the debonded tooth, FEA showed dentinal stress concentrations at the gingival wall of the cavity, which coincided with the longitudinal cracks found in the cyclic loading test. The sum of fractions of life spent for dentin was close to 1 at ~30,000 cycles, similar to the experimental value.SignificanceDebonding of the dentin-composite interface may occur prior to longitudinal cracking of dentin in root-filled teeth under cyclic loading. The approximate time of occurrence for these events could be estimated using fatigue analysis with stresses provided by FEA. This methodology can therefore be used to evaluate the longevity of restoration designs for root-filled teeth.     

增进积极体验为目标的健康干预对抑郁症病人抑郁情绪及生活质量的影响

目的:探讨增进积极体验为目标的健康干预对抑郁症病人抑郁情绪及生活质量的影响。方法:选择2019年9月—2021年3月在医院就诊的68例抑郁症病人为研究对象,按照随机数字表法分为观察组与对照组,每组34例。对照组予以常规护理,观察组在常规护理基础上予以增进积极体验为目标的健康干预。干预前后分别采用汉密尔顿抑郁量表(HAMD)、世界卫生组织生存质量测定量表简表(WHOQOL-BREF)评估病人的抑郁情绪和生活质量,同时对两组病人的护理满意度进行比较。结果:干预后观察组病人抑郁评分低于对照组(P<0.05);两组病人的生理功能、心理功能、社会功能及环境功能指标均较干预前有明显改善,且观察组评分均高于对照组(P<0.05);观察组病人对护理干预的总满意度为97.06%,高于对照组的61.76%(P<0.05)。结论:增进积极体验为目标的健康干预可明显缓解抑郁症病人的抑郁情绪,提高病人的生活质量。     

Brilliance型16排螺旋CT的故障分析与维修

针对日常使用中遇到的Brilliance 16排螺旋CT高压系统、机架以及控制器局域网络(CAN)通讯等故障现象进行分析与维修,最终通过更换滤波电容、机架数据采集控制器(DMC)电源以及信号刷等配件得以排除故障。通过对故障准确判断以及合理运用厂家Service模式下的维修工具软件快速解决故障,保障了影像科检查工作的顺利进行,从而提高设备的稳定性。     

多元化联合教学模式在超声引导下疼痛介入治疗中的应用

目的探讨多元化联合教学模式在超声引导下疼痛介入治疗教学中的应用效果。方法选择2018年1月至2020年12月在北京大学第三医院疼痛科进修的30名医师作为研究对象,将其分为对照组与观察组;对照组采用常规教学模式;观察组采用多元化联合教学模式,比较两组医师技能考核成绩、教学质量评分和满意度评分。结果观察组医师技能考核成绩优良率为93.3%,高于对照组的73.3%(P<0.05);观察组医师对基础理论知识掌握、临床思维能力的提高、学习兴趣的激发、疾病诊治能力的提高4个方面的评分均高于对照组(P<0.01)。结论多元化联合教学模式可促进超声引导下疼痛介入治疗技能的提高,有利于提高学员的综合临床能力。     

Effect of orbital wall resection areas in the treatment of patients with endocrine orbitopathy

In patients treated by orbital wall decompression for endocrine orbitopathy (EO) there is limited evidence on the effect of orbital wall resections. Thus, the aim of this study was to evaluate the effect of one, two, and three-wall resections on orbital parameters to determine if any such correlations exist. Preoperative and postoperative data from all patients at a tertiary care centre who underwent decompression surgery from 2010 - 2020 were digitally analysed. The effect of the number and area of resected walls on orbital area, orbital volume, and Hertel value, and the effect of lateral rim advancement (LARA) were determined. A total of 131 orbital areas showed an increase from a mean (SD) preoperative area of 42.0 (4.6) cm² to 47.3 (6.1) cm² postoperatively (p<0.001). In total, the mean (SD) area of osseous wall removed in all patients was 6.2 (1.7) cm² at the lateral orbit (n = 129), 6.7 (2.3) cm² at the orbital floor (n = 123), and 5.8 (1.8) cm² at the medial orbital wall (n =30). The mean (SD) orbital volume increased by 6.0 (3.0) cm³ after decompression. There was also a significant reduction in exophthalmos of 7.3 (3.2) mm (from 25.2 (3.9) to 17.9 (3.5), p<0.001). LARA was performed in 50 patients. Changes in volume and area, and reduction in exophthalmos were not significantly different with or without LARA. The postoperative effects of orbital wall resection are predictable and exhibit a relation with six units of change. Two-wall resection is the most common intervention.     

Efficient polymer nanoparticle-mediated delivery of gene editing reagents into human hematopoietic stem and progenitor cells

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