Polymerization stress of resin composites as a function of system compliance

Objectives. Evaluate the effect of testing system compliance on polymerization stress and stress distribution of composites. Methods. Composites tested were Filtek Z250 (FZ), Herculite (HL), Tetric Ceram (TC), Helio Fill-AP (HF) and Heliomolar (HM). Stress was determined in 1-mm thick specimens, inserted between two rods of either poly(methyl methacrylate), PMMA, or glass. Experimental nominal stress (sigma(exp)) was calculated by dividing the maximum force recorded 5 min after photoactivation by the cross-sectional area of the rod. Composites` elastic modulus (E) was obtained by three-point bending. Data were submitted to one-way ANOVA/Tukey`s test (alpha = 0.05). Stress distribution on longitudinal (sigma(y)) and transverse (sigma(x)) axes of models representing the composites with the highest and lowest E (FZ and HM, respectively) were evaluated by finite element analysis (FEA). Results. sigma(exp) ranged from 5.5 to 8.8 MPa in glass and from 2.6 to 3.4 MPa in PMMA. Composite ranking was not identical in both substrates, since FZ showed or sigma(exp) statistically higher than HM in glass, while in PMMA FZ showed values similar to the other composites. A strong correlation was found between stress reduction (%) from glass to PMMA and composite`s E (r(2) = 0.946). FEA revealed that system compliance was influenced by the composite (FZ led to higher compliance than HM). sigma(x) distribution was similar in both substrates, while cry distribution showed larger areas of compressive stresses in specimens built on PMMA. Significance. sigma(exp) determined in PMMA was 53-68% lower than in glass. Composite ranking varied slightly due to differences in substrates` longitudinal and transverse deformation. (c) 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Thermal/mechanical simulation and laboratory fatigue testing of an alternative yttria tetragonal zirconia polycrystal core-veneer all-ceramic layered crown design

This study evaluated the stress levels at the core layer and the veneer layer of zirconia crowns (comprising an alternative core design vs. a standard core design) under mechanical/thermal simulation, and subjected simulated models to laboratory mouth-motion fatigue. The dimensions of a mandibular first molar were imported into computer-aided design (CAD) software and a tooth preparation was modeled. A crown was designed using the space between the original tooth and the prepared tooth. The alternative core presented an additional lingual shoulder that lowered the veneer bulk of the cusps. Finite element analyses evaluated the residual maximum principal stresses fields at the core and veneer of both designs under loading and when cooled from 900 degrees C to 25 degrees C. Crowns were fabricated and mouth-motion fatigued, generating master Weibull curves and reliability data. Thermal modeling showed low residual stress fields throughout the bulk of the cusps for both groups. Mechanical simulation depicted a shift in stress levels to the core of the alternative design compared with the standard design. Significantly higher reliability was found for the alternative core. Regardless of the alternative configuration, thermal and mechanical computer simulations showed stress in the alternative core design comparable and higher to that of the standard configuration, respectively. Such a mechanical scenario probably led to the higher reliability of the alternative design under fatigue.

Design, modelling and analysis of a six component force balance for hypervelocity wind tunnel testing

A combination of modelling and analysis techniques was used to design a six component force balance. The balance was designed specifically for the measurement of impulsive aerodynamic forces and moments characteristic of hypervelocity shock tunnel testing using the stress wave force measurement technique. Aerodynamic modelling was used to estimate the magnitude and distribution of forces and finite element modelling to determine the mechanical response of proposed balance designs. Simulation of balance performance was based on aerodynamic loads and mechanical responses using convolution techniques. Deconvolution was then used to assess balance performance and to guide further design modifications leading to the final balance design. (C) 2001 Elsevier Science Ltd. All rights reserved.

Adverse effect of alcohol drinking: the role of oxidative stress

Atualmente, o álcool tem um papel importante na saúde pública e surge como um dos principais problemas sociais no mundo, dado que é a droga mais viciante aceite em encontros sociais. Provavelmente, por essa razão, os riscos do consumo abusivo do álcool são subestimados pelos jovens, mulheres grávidas e idosos. O álcool, quando ingerido em altas proporções, pode afetar todos os órgãos e desencadear inúmeras doenças, tais como a doença cardíaca coronariana, doença neurodegenerativa, as doenças crónicas e câncer. O álcool afeta ainda o estado psicológico, induzindo a violência, o estado antissocial e situações de risco de comportamentos. Por estas razões, o álcool tornou-se um foco principal da investigação, avaliando os seus efeitos sobre o corpo humano. Nesta pesquisa, foram suscitadas amostras de sangue de um grupo de pacientes em tratamento psicológico e/ou farmacêutico que serão analisadas com quatro métodos: Teste de Radicais Livres do Oxigénio (FORT), Defesa contra Radicais Livres do Oxigénio (FORD), cromatografia gasosa (GC) e cromatografia líquida de alta pressão (HPLC). Ambos os métodos FORT e FORD avaliam o stress oxidativo pela quantificação de radicais livres e a capacidade de antioxidantes em eliminar esses radicais livres, respetivamente. O stress oxidativo é o efeito do excesso de consumo de álcool, que é reduzido pela capacidade de ação dos antioxidantes. A boa reprodutibilidade, precisão e exatidão de ambos os métodos indicam que estes podem ser aplicados em rápidos diagnósticos. Para o método FORT e considerando o início do tratamento, os pacientes alcoólicos apresentaram uma média de 3,59±1.01mmol/LH2O2 e o grupo de controlo uma média de 1,42±0.53mmol/LH2O2, o que mostra uma diferença significativa entre os dois grupos (P=0,0006). Para o método FORD, pacientes alcoólicos apresentam uma média de 1,07±0.53mmol/LH2O2 e o grupo de controlo, uma média de 2,81±0.46mmol/LH2O2, mostrando também uma média significativa (P=0,0075). Após 15 dias de tratamento observou-se que há uma diferença entre os dois grupos de pacientes alcoólicos, mas não há nenhum melhoramento em relação ao grupo de pacientes em tratamento. No método FORT os grupos mostram uma diferença significativa (P=0,0073), tendo os pacientes sem tratamento farmacêutico melhores resultados (2.37±0.44mmol/LH2O2) do que os pacientes com tratamento (3.72±1,04mmol/LH2O2). O oposto ocorre no método FORD, os pacientes em tratamento farmacêutico presentam melhores resultados (1.16±0.65mmol/LH2O2) do que o outro grupo (0.75±0.22mmol/LH2O2), não sendo, no entanto, uma diferença significativa entre os dois grupos (P=0.16). Os resultados obtidos para a concentração de MDA pelo método de HPLC mostraram que o grupo de controlo tem valores mais baixos do que os pacientes alcoólicos, embora a diferença não seja muito significativa (P = 0,084), mas é ainda elevada. Além disso, os dois grupos de pacientes não apresentaram uma diferença significativa entre os seus resultados no início (P=0,77) e no fim (P=0,79) do tratamento. De acrescentar ainda que, os resultados da concentração de álcool no sangue determinados pelo método de CG mostraram que só alguns pacientes sem tratamento consumiram álcool durante o período de tratamento, o que influencia negativamente a conclusão sobre o efeito do tratamento. Contudo, outros fatores externos podem ainda influenciar os resultados finais, tais como o estado nutricional e estado psicológico dos pacientes, se o paciente continua a beber durante o tempo de tratamento ou até mesmo se o paciente é exposto a outros tipos de substâncias nocivas. Existe ainda a possibilidade de o tempo de aplicação do tratamento não ser suficiente para apresentar um efeito positivo em relação ao stress oxidativo e este é um outro fator que contribui para a impossibilidade de confirmar sobre o efeito, quer seja positivo ou negativo, do tratamento antioxidante.

Effect of plug-filling, Testing velocity and temperature on the tensile strength of strap repairs on aluminium structures

In this work, an experimental study was performed on the influence of plug-filling, loading rate and temperature on the tensile strength of single-strap (SS) and double-strap (DS) repairs on aluminium structures. Whilst the main purpose of this work was to evaluate the feasibility of plug-filling for the strength improvement of these repairs, a parallel study was carried out to assess the sensitivity of the adhesive to external features that can affect the repairs performance, such as the rate of loading and environmental temperature. The experimental programme included repairs with different values of overlap length (L O = 10, 20 and 30 mm), and with and without plug-filling, whose results were interpreted in light of experimental evidence of the fracture modes and typical stress distributions for bonded repairs. The influence of the testing speed on the repairs strength was also addressed (considering 0.5, 5 and 25 mm/min). Accounting for the temperature effects, tests were carried out at room temperature (≈23°C), 50 and 80°C. This permitted a comparative evaluation of the adhesive tested below and above the glass transition temperature (T g), established by the manufacturer as 67°C. The combined influence of these two parameters on the repairs strength was also analysed. According to the results obtained from this work, design guidelines for repairing aluminium structures were

Stress Ratio Effects on the fatigue Properties of Biaxially Loaded Tubular FRP-Specimens – Experimental Study

In this work tubular fiber reinforced specimens are tested for fatigue life. The specimens are biaxially loaded with tension and shear stresses, with a load angle β of 30° and 60° and a load ratio of R=0,1. There are many factors that affect fatigue life of a fiber reinforced material and the main goal of this work is to study the effects of load ratio R by obtaining S-N curves and compare them to the previous works (1). All the other parameters, such as specimen production, fatigue loading frequency and temperature, will be the same as for the previous tests. For every specimen, stiffness, temperature of the specimen during testing, crack counting and final fracture mode are obtained. Prior to testing, a study if the literature regarding the load ratio effects on composites fatigue life and with that review estimate the initial stresses to be applied in testing. In previous works (1) similar specimens have only been tested for a load ratio of R=-1 and therefore the behaviour of this tubular specimens for a different load ratio is unknown. All the data acquired will be analysed and compared to the previous works, emphasizing the differences found and discussing the possible explanations for those differences. The crack counting software, developed at the institute, has shown useful before, however different adjustments to the software parameters lead to different cracks numbers for the same picture, and therefore a better methodology will be discussed to improve the crack counting results. After the specimen’s failure, all the data will be collected and stored and fibre volume content for every specimen is also determinate. The number of tests required to make the S-N curves are obtained according to the existent standards. Additionally are also identified some improvements to the testing machine setup and to the procedures for future testing.

Adverse Effect of Alcohol Drinking: The Role of Oxidative Stress

Atualmente, o álcool tem um papel importante na saúde pública e surge como um dos principais problemas sociais no mundo, dado que é a droga mais viciante aceite em encontros sociais. Provavelmente, por essa razão, os riscos do consumo abusivo do álcool são subestimados pelos jovens, mulheres grávidas e idosos. O álcool, quando ingerido em altas proporções, pode afetar todos os órgãos e desencadear inúmeras doenças, tais como a doença cardíaca coronariana, doença neurodegenerativa, as doenças crónicas e câncer. O álcool afeta ainda o estado psicológico, induzindo a violência, o estado antissocial e situações de risco de comportamentos. Por estas razões, o álcool tornou-se um foco principal da investigação, avaliando os seus efeitos sobre o corpo humano. Nesta pesquisa, foram suscitadas amostras de sangue de um grupo de pacientes em tratamento psicológico e/ou farmacêutico que serão analisadas com quatro métodos: Teste de Radicais Livres do Oxigénio (FORT), Defesa contra Radicais Livres do Oxigénio (FORD), cromatografia gasosa (GC) e cromatografia líquida de alta pressão (HPLC). Ambos os métodos FORT e FORD avaliam o stress oxidativo pela quantificação de radicais livres e a capacidade de antioxidantes em eliminar esses radicais livres, respetivamente. O stress oxidativo é o efeito do excesso de consumo de álcool, que é reduzido pela capacidade de ação dos antioxidantes. A boa reprodutibilidade, precisão e exatidão de ambos os métodos indicam que estes podem ser aplicados em rápidos diagnósticos. Para o método FORT e considerando o início do tratamento, os pacientes alcoólicos apresentaram uma média de 3,59±1.01mmol/LH2O2 e o grupo de controlo uma média de 1,42±0.53mmol/LH2O2, o que mostra uma diferença significativa entre os dois grupos (P=0,0006). Para o método FORD, pacientes alcoólicos apresentam uma média de 1,07±0.53mmol/LH2O2 e o grupo de controlo, uma média de 2,81±0.46mmol/LH2O2, mostrando também uma média significativa (P=0,0075). Após 15 dias de tratamento observou-se que há uma diferença entre os dois grupos de pacientes alcoólicos, mas não há nenhum melhoramento em relação ao grupo de pacientes em tratamento. No método FORT os grupos mostram uma diferença significativa (P=0,0073), tendo os pacientes sem tratamento farmacêutico melhores resultados (2.37±0.44mmol/LH2O2) do que os pacientes com tratamento (3.72±1,04mmol/LH2O2). O oposto ocorre no método FORD, os pacientes em tratamento farmacêutico presentam melhores resultados (1.16±0.65mmol/LH2O2) do que o outro grupo (0.75±0.22mmol/LH2O2), não sendo, no entanto, uma diferença significativa entre os dois grupos (P=0.16). Os resultados obtidos para a concentração de MDA pelo método de HPLC mostraram que o grupo de controlo tem valores mais baixos do que os pacientes alcoólicos, embora a diferença não seja muito significativa (P = 0,084), mas é ainda elevada. Além disso, os dois grupos de pacientes não apresentaram uma diferença significativa entre os seus resultados no início (P=0,77) e no fim (P=0,79) do tratamento. De acrescentar ainda que, os resultados da concentração de álcool no sangue determinados pelo método de CG mostraram que só alguns pacientes sem tratamento consumiram álcool durante o período de tratamento, o que influencia negativamente a conclusão sobre o efeito do tratamento. Contudo, outros fatores externos podem ainda influenciar os resultados finais, tais como o estado nutricional e estado psicológico dos pacientes, se o paciente continua a beber durante o tempo de tratamento ou até mesmo se o paciente é exposto a outros tipos de substâncias nocivas. Existe ainda a possibilidade de o tempo de aplicação do tratamento não ser suficiente para apresentar um efeito positivo em relação ao stress oxidativo e este é um outro fator que contribui para a impossibilidade de confirmar sobre o efeito, quer seja positivo ou negativo, do tratamento antioxidante.

Soluble ST2 Testing: A Promising Biomarker in the Management of Heart Failure

Abstract ST2 is a member of the interleukin-1 receptor family biomarker and circulating soluble ST2 concentrations are believed to reflect cardiovascular stress and fibrosis. Recent studies have demonstrated soluble ST2 to be a strong predictor of cardiovascular outcomes in both chronic and acute heart failure. It is a new biomarker that meets all required criteria for a useful biomarker. Of note, it adds information to natriuretic peptides (NPs) and some studies have shown it is even superior in terms of risk stratification. Since the introduction of NPs, this has been the most promising biomarker in the field of heart failure and might be particularly useful as therapy guide.

Monetary policy rules and financial stress: does financial instability matter for monetary

We examine whether and how main central banks responded to episodes of financial stress over the last three decades. We employ a new methodology for monetary policy rules estimation, which allows for time-varying response coefficients as well as corrects for endogeneity. This flexible framework applied to the U.S., U.K., Australia, Canada and Sweden together with a new financial stress dataset developed by the International Monetary Fund allows not only testing whether the central banks responded to financial stress but also detects the periods and type of stress that were the most worrying for monetary authorities and to quantify the intensity of policy response. Our findings suggest that central banks often change policy

Pelvic organ prolapse surgery with and without tension-free vaginal tape in women with occult or asymptomatic urodynamic stress incontinence: a randomised controlled trial.

INTRODUCTION: We set out to determine if insertion of a retropubic tension-free vaginal tape (TVT) sling at the time of pelvic organ prolapse surgery improves continence outcomes in women with pre-operative occult stress incontinence (OSI) or asymptomatic urodynamic stress incontinence (USI). METHODS: We conducted a randomised controlled study of prolapse surgery with or without a TVT midurethral sling. The pre- and post-operative assessment at 6 months included history, physical examination and urodynamic testing. Quality of life (QOL) and treatment success was assessed with the UDI-6 SF, IIQ-7 SF and a numerical success score. The primary outcome was symptomatic stress urinary incontinence (SUI) requiring continence surgery (TVT) at 6 months. Long-term follow-up continued to a minimum of 24 months. Secondary outcomes were quality of life parameters. RESULTS: Eighty women received prolapse surgery alone (n = 43) or prolapse surgery with concurrent TVT (n = 37). Six months following prolapse surgery 3 out of 43 (7 %) patients in the no TVT group requested sling surgery compared with 0 out of 37 (0 %) in the TVT group (ARR 7 % [95 %CI: 3 to 19 %], p = 0.11). After 24 months there was one further participant in the no TVT group who received a TVT for treatment of SUI compared with none in the TVT group (4 out of 43, 9.3 % versus 0 out of 37; ARR 9.3 % [95 %CI: -1 to 22 %], p = 0.06). Both groups showed improvement in QOL difference scores for within-group analysis, without difference between groups. CONCLUSION: These results support a policy that routine insertion of a sling in women with OSI at the time of prolapse repair is questionable and should be subject to shared decision-making between clinician and patient.

Antecedents of Job Satisfaction, Organizational Commitment and Stress in a Public Hospital: A P-E Fit Perspective

This article tests different P-E fit dimensions in order to assess their impact on three work outcomes: job satisfaction; organizational commitment; and stress perception. Findings shows that P-E fit dimensions have differentiated effects on its dependent variables. This study contributes to several important academic discussions. The first concerns the model tested, which contains several P-E fit dimensions. The second scientific contribution is to consider P-E fit dimensions as antecedents of three job outcomes. The third contribution concerns the development and testing of a new P-E fit dimension called "person-reforms" fit.

Anxiety and Psychological Stress Before Prenatal Screening in First-Time Mothers Who Conceived Through IVF/ICSI or Spontaneously.

Mothers' general anxiety, anxiety about the well-being of the child and psychological stress before prenatal testing was studied by comparing women who conceived through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) with women who conceived naturally. Before the first trimester screening test for Down's syndrome, a group of 51 women who conceived through IVF/ICSI and a group of 54 women who conceived spontaneously completed the State Scale of the State-Trait Anxiety Inventory (S-Anxiety; Spielberger, 1983), the Fear of Bearing a Physically or Mentally Handicapped Child Subscale of the Pregnancy-related Anxiety Questionnaire (PRAQ-R; Huizink et al., 2004), the Psychological Stress Measure (PSM; Lemyre & Tessier, 1988), and the Prenatal Psychosocial Profile (PPP; Curry, Campbell, & Christian, 1994). Women who conceived through IVF/ICSI had more elevated levels of general anxiety and psychological stress than the women who conceived naturally; however, no difference was observed between the two groups for anxiety specifically related to the health of the child. These results underline the need to monitor women's emotional state after conception via IVF/ICSI-when counseling usually ends-and around the time of the first trimester screening. Counseling might thus be extended.

Testing the predictive adaptive response in a host-parasite system

1. Harsh environmental conditions experienced during development can reduce the performance of the same individuals in adulthood. However, the 'predictive adaptive response' hypothesis postulates that if individuals adapt their phenotype during development to the environments where they are likely to live in the future, individuals exposed to harsh conditions in early life perform better when encountering the same harsh conditions in adulthood compared to those never exposed to these conditions before. 2. Using the common vole (Microtus arvalis) as study organism, we tested how exposure to flea parasitism during the juvenile stage affects the physiology (haematocrit, resistance to oxidative stress, resting metabolism, spleen mass, and testosterone), morphology (body mass, testis mass) and motor performance (open field activity and swimming speed) of the same individuals when infested with fleas in adulthood. According to the 'predictive adaptive response' hypothesis, we predicted that voles parasitized at the adult stage would perform better if they had already been parasitized with fleas at the juvenile stage. 3. We found that voles exposed to fleas in adulthood had a higher metabolic rate if already exposed to fleas when juvenile, compared to voles free of fleas when juvenile and voles free of fleas in adulthood. Independently of juvenile parasitism, adult parasitism impaired adult haematocrit and motor performances. Independently of adult parasitism, juvenile parasitism slowed down crawling speed in adult female voles. 4. Our results suggest that juvenile parasitism has long-term effects that do not protect from the detrimental effects of adult parasitism. On the contrary, experiencing parasitism in early-life incurs additional costs upon adult parasitism measured in terms of higher energy expenditure, rather than inducing an adaptive shift in the developmental trajectory. 5. Hence, our study provides experimental evidence for long term costs of parasitism. We found no support for a predictive adaptive response in this host-parasite system.

Effect of multiple oral doses of androgenic anabolic steroids on endurance performance and serum indices of physical stress in healthy male subjects.

Anabolic androgenic steroids (AAS) are doping agents that are mostly used for improvement of strength and muscle hypertrophy. In some sports, athletes reported that the intake of AAS is associated with a better recovery, a higher training load capacity and therefore an increase in physical and mental performances. The purpose of this study was to evaluate, the effect of multiple doses of AAS on different physiological parameters that could indirectly relate the physical state of athletes during a hard endurance training program. In a double blind settings, three groups (n = 9, 8 and 8) were orally administered placebo, testosterone undecanoate or 19-norandrostenedione, 12 times during 1 month. Serum biomarkers (creatine kinase, ASAT and urea), serum hormone profiles (testosterone, cortisol and LH) and urinary catecholamines (noradrenalin, adrenalin and dopamine) were evaluated during the treatment. Running performance was assessed before and after the intervention phase by means of a standardized treadmill test. None of the measured biochemical variables showed significant impact of AAS on physical stress level. Data from exercise testing on submaximal and maximal level did not reveal any performance differences between the three groups or their response to the treatment. In the present study, no effect of multiple oral doses of AAS on endurance performance or bioserum recovery markers was found.

Spare non-occupational HIV post-exposure prophylaxis by active contacting and testing of the source person.

OBJECTIVE: HIV-1 post-exposure prophylaxis (PEP) is frequently prescribed after exposure to source persons with an undetermined HIV serostatus. To reduce unnecessary use of PEP, we implemented a policy including active contacting of source persons and the availability of free, anonymous HIV testing ('PEP policy'). METHODS: All consultations for potential non-occupational HIV exposures i.e. outside the medical environment) were prospectively recorded. The impact of the PEP policy on PEP prescription and costs was analysed and modelled. RESULTS: Among 146 putative exposures, 47 involved a source person already known to be HIV positive and 23 had no indication for PEP. The remaining 76 exposures involved a source person of unknown HIV serostatus. Of 33 (43.4%) exposures for which the source person could be contacted and tested, PEP was avoided in 24 (72.7%), initiated and discontinued in seven (21.2%), and prescribed and completed in two (6.1%). In contrast, of 43 (56.6%) exposures for which the source person could not be tested, PEP was prescribed in 35 (81.4%), P < 0.001. Upon modelling, the PEP policy allowed a 31% reduction of cost for management of exposures to source persons of unknown HIV serostatus. The policy was cost-saving for HIV prevalence of up to 70% in the source population. The availability of all the source persons for testing would have reduced cost by 64%. CONCLUSION: In the management of non-occupational HIV exposures, active contacting and free, anonymous testing of source persons proved feasible. This policy resulted in a decrease in prescription of PEP, proved to be cost-saving, and presumably helped to avoid unnecessary toxicity and psychological stress.