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.     

Fracture strength of Er,Yag laser treated PMMA denture-based polymer (DBP) colonized with C. albicans,S. aureus,S.mutans,and E.coli

AimTo assess and equate the efficacy of different disinfection protocols autoclave, chlorhexidine (CHX), PDT utilizing Rose Bengal (RB), chitosan, and Er, Yag laser and their effect on fracture strength of PMMA denture-based polymer (DBP) colonized with C. Albicans, S. aureus, S.mutans, and E.coli.Material and methodsA total of 50 (n = 10) PMMA DBP were manufactured and adulterated with the American Type Culture Collection (ATCC) of diverse microbial colonies inhabited by C. Albicans, S. aureus, S.mutans, and E.coli. The specimens were subjected to different denture disinfection approaches by randomly distributing in into five groups i.e., Er, Yag laser, RB, autoclave, CHX, and Chitosan, respectively for appraising antimicrobial effectiveness. PMMA fracture load was also assessed and statistical analysis was performed for CFU/mL (log10) of exposed C. Albicans, S. aureus, S.mutans, and E.coli by one-way ANOVA and Tukey's multiple comparison test at a significance level of p < 0.05.ResultsIntergroup comparison disclosed that denture disinfection with Er, Yag laser, autoclave, Chitosan, and CHX (control) validated comparable antimicrobial efficacy to denture against all inspected CFU/mL (log10) (p>0.05). The intragroup comparison revealed that DBP sanitization with Er, Yag laser, autoclave, Chitosan, RB, and CHX substantiated equivalent effective antimicrobial efficacy in plummeting CFU/mL (log10) of S. mutans and E. coli (p>0.05) but in consideration to S.aureus and C.albicans, all groups resulted in declining their count except 5µm RB activated by PDT(p < 0.05). No significant difference was perceived in fracture load of PMMA denture base among Er, Yag laser, RB, chitosan, and CHX (control) (p > 0.05) except autoclave decontamination procedure that indicated the least fracture strength of DBP when disinfected (p < 0.05).ConclusionEr, Yag laser, and Chitosan activated by PDT have the potential to be used as an alternative to chlorhexidine for disinfecting Polymethyl methacrylate denture base as they demonstrated the highest antimicrobial efficacy against E. coli, C. Albicans, S aureus, and S. mutans with optimal fracture load.     

英语学界对“母乳不足”现象的认知进化

“母乳最好”的宣传话语在目前育龄人群中几乎耳熟能详,但很多信奉科学育儿、希望母乳喂养的都市女性却发现母乳喂养困难重重,其中遭遇“母乳不足”的案例较为多见。回顾历史发现,“母乳不足”的现象全球普遍存在,这个话题在20世纪80年代的英语学术圈曾引起热议。经过十余年讨论后,学者们基本认同大部分遭遇母乳不足的女性并不是真正的“母乳不足”,而是由于种种社会文化因素干扰造成母乳喂养失败的这一结论,其中产后初期的奶瓶介入是重要原因。术语也由insufficient milk syndrome变为perceived insufficient milk,以此来强调“母乳不足”不是一种病理现象,而更多是一种文化感知。     

Grouped-sampling technique to deal with unbalance in Raman spectral data modeling

Due to limitations in disease prevalence and hospital specificity, spectral data are often collected with unbalanced sample size. To solve this problem, a new sampling method – grouped-sampling was proposed in this research, which is shown to be effective for unbalanced data. It avoids over-fitting of over-sampling and overcomes under-sampling utilization of under-sampling. In this study, we applied grouped-sampling to two unbalanced datasets where the sample proportions are 199:40 and 75:225. And then verified from two classic models: PCA-SVM (Principal Component Analysis-Support Vector Machine) and the deep learning algorithm GoogLeNet. The accuracy of these two datasets were 85.11% and 96.15% in PCA-SVM and 85.10% and 84.61% on GoogLeNet. Also, the F1-score were evaluated to measure the classification balance of sampling method, and result shows that F1-score of grouped-sampling is always the highest compared to over-sampling and under-sampling. In summary, compared to traditional sampling methods, grouped-sampling performs better on prediction for classes with smaller sample size, which means grouped-sampling can improve the balance of classification results and the potential of practical application. Therefore, we develop a group sampling method that distinguishes between under- and over-sampling, which greatly improves the accuracy and balance of predictions for unbalanced samples.     

三七片DNA条形码分子鉴定及方法学考察

目的为研究DNA条形码技术在中成药鉴定中的应用,以三七片为研究对象,对方法的适用性、专属性与精密度进行考察。方法收集15批次市售三七片样品,考察三七片DNA提取条件,并对"中药材DNA条形码分子鉴定法指导原则"中PCR扩增、序列获得、结果判定等方法适用性进行确认;收集三七、人参、西洋参,制作三七片及其掺伪品,考察方法的专属性和重现性。结果三七片取样量100 mg,56℃水浴8 h所获得DNA的质量浓度平均值为60.7 ng/μL,PCR扩增、序列获得和结果判定均可获成功;三七、人参和西洋参的ITS2序列长度均为230bp,三七与人参、三七与西洋参的序列间均存在7个稳定的SNP位点,自制三七片和掺伪三七片均可成功获得ITS2序列,不同比例三七与人参、三七与西洋参的测序峰图在SNP位点处呈现相应峰高比的SNP套峰具备专属性;重复性、中间精密度和重现性考察符合《中国药典》2015年版(通则9101)相关要求。结论 ITS2序列作为DNA条形码能够稳定、准确鉴定三七片的原料药材,具备良好的专属性和精密度,三七片DNA条形码分子鉴定法将为保障三七片临床用药安全提供新的技术手段,并对《中国药典》其他收载单方制剂的鉴定提供参考。     

美国新药技术成熟度评价研究

目的研究提出适合我国新药研发和药品安全管理的技术成熟度评价机制。方法借鉴美国新药研发技术成熟度等级(biomedical technology readiness level,BTRL)评价标准与方法,结合我国新药研发、监管和产业化特点,提出我国成熟度评价等级和指标,并在重大新药创制科技重大专项研发管理中开展探索分析。结果与结论探索建立我国化学药和生物制品技术成熟度评价等级标准,将为我国新药研发科研项目和保障药品安全提供管理与评估工具,为其他行业领域提供参考借鉴。     

Hospital concentration and low-income populations: Evidence from New York State Medicaid

While a large body of evidence has examined hospital concentration, its effects on health care for low-income populations are less explored. We use comprehensive discharge data from New York State to measure the effects of changes in market concentration on hospital-level inpatient Medicaid volumes. Holding fixed hospital factors constant, a one percent increase in HHI leads to a 0.6% (s.e. = 0.28%) decrease in the number of Medicaid admissions for the average hospital. The strongest effects are on admissions for birth (-1.3%, s.e. = 0.58%). These average hospital-level decreases largely reflect redistribution of Medicaid patients across hospitals, rather than overall reductions in hospitalizations for Medicaid patients. In particular, hospital concentration leads to a redistribution of admissions from non-profit hospitals to public hospitals. We find evidence that for births, physicians serving high shares of Medicaid beneficiaries in particular experience reduced admissions as concentration increased. These reductions may reflect preferences among these physicians or reduced admitting privileges by hospitals as a means to screen out Medicaid patients.     

基于转录组测序方法研究加替沙星对小鼠的肝损伤作用

目的： 探讨加替沙星（GAT）对小鼠肝脏的损伤作用及其机制。方法： 选取32只SPF级雄性昆明小鼠作为研究对象，随机分为4组：低、中、高剂量（分别为25、50、100 mg/kg） GAT组和对照组。给药体积按10 mL/kg，连续灌胃给药7 d，对照组给予对应体积的生理盐水。通过检测各组小鼠血清中的谷丙转氨酶（ALT）、谷草转氨酶（AST）、碱性磷酸酶（AKP）、肌酐（CRE）和甘油三酯（TG）浓度，初步评价加替沙星导致的小鼠肝组织损伤。进一步利用转录组测序技术检测各组小鼠肝脏的基因表达谱，筛选差异表达基因，对差异基因进行基因本体论（GO）功能分类，并采用京都基因与基因组百科全书（KEGG）数据库进行信号通路富集分析。结果： 与对照组比较，高剂量GAT组小鼠肝脏质量显著降低（P<0.01）；低、中剂量GAT组肝脏系数显著降低（P<0.01）；低、中剂量GAT组小鼠血清ALT浓度显著降低（P<0.05或0.01）；低剂量GAT组小鼠血清AST浓度显著降低（P<0.01）。与对照组比较，中剂量GAT组共筛选出27个差异表达基因（包括20个上调基因，7个下调基因）。GO功能分类提示这些基因主要富集在免疫系统、多细胞生物、多生物及生殖过程等17个生物过程中。KEGG通路分析提示差异基因主要富集于脂质代谢、萜类化合物和聚酮化合物的代谢等22条通路中。结论： GAT可导致小鼠肝功能发生变化，并通过影响小鼠肝脏内胆汁酸和胆固醇等内分泌系统和脂质代谢等的平衡，造成肝组织损伤。     

The intracorrelation of family health insurance and job lock

This paper tests for the presence of job lock and “health insurance plan lock” stemming from the health shock of a child family member. Using the onset of an acute, unanticipated health shock, I estimate a 7–14 percent decreased likelihood of all family members leaving their current health insurance network and health plan within one year of the emergency. This corresponds to a reduced one-year job mobility rate of approximately 13 percent for the health plan’s primary policyholder. Furthermore, the non-portability of health insurance products may contribute to the observed job and health plan lock.