Elaboração de elementos finitos para estudos biomecânicos em prostodontia

Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas MonizO método dos elementos finitos tornou-se na técnica mais utilizada na análise de fenómenos físicos no campo da estrutura, mecanismos sólidos e fluidos. Na biomecânica, este método sofreu avanços consideráveis quer na investigação quer como instrumento de ensino e pode ser usado para encontrar factos ou processos de estudo que com outro instrumento não seriam possíveis (3). A análise por elementos finitos é um método numérico e tem vantagens consideráveis na fotoelasticidade. É muito útil na análise de geometrias complexas e permite a determinação das tensões e distorções sofridas por um componente tridimensional. Estes elementos finitos são formados pela divisão da estrutura original numa série de secções de forma adequada, onde cada uma delas conserva as mesmas propriedades dos materiais reais (4,5). Muitos destes métodos têm sido aplicados em estudos de medicina dentária restauradora, que consegue preservar e restaurar dentes cariados, restaurações defeituosas, dentes perdidos ou traumatizados. Em geral, o método dos elementos finitos é especialmente indicado para prever tendências e realizar análises paramétricas (2). Obviamente, é muito importante conhecer em detalhe as propriedades dos materiais anisotrópicos e as suas relações constituintes para desenvolver um modelo válido de elementos finitos (1). Portanto, é uma ferramenta útil que permite a realização de um grande número de análises em componentes e estruturas complexas, difíceis de obter pelos métodos analíticos clássicos. Um programa de elementos finitos consiste num software complexo onde convergem inúmeras operações. A preparação dos dados e a análise dos resultados numéricos que aparecem como produto do cálculo são tarefas que tendem a ser integradas no próprio software. Os cálculos de elementos finitos são efetuados num processador no qual estão incluídas todas as ajudas para a preparação dos dados e produção dos resultados, e num pós-processador que facilita a análise e interpretação dos mesmos, geralmente sob a forma de gráficos (traçado de curvas, gráficos tridimensionais, tabelas, etc.) O objetivo desta tese é rever a literatura de forma a compreender como é feito um elemento finito que permita o estudo biomecânico dos diferentes tipos de próteses feitas pelo médico dentista. No âmbito da investigação, serão revistos os diferentes tipos de materiais utilizados atualmente e o seu comportamento com as forças interpretadas na boca, bem como os movimentos de mastigação e os contactos dentários na oclusão. Isto dará ao médico dentista uma ideia geral sobre a seleção de materiais de acordo com o tipo de reabilitação (10).The finite element method has become the most widely used technique for the analysis of physical phenomena in the field of structure, solid and fluid mechanisms. For biomechanics, this method has received considerable advances in research and as a teaching tool, it can be used to find facts or study processes that with another tool are not possible (3). Finite element analysis is a numerical method and has important advantages over photoelasticity. It is very useful in the analysis of complex geometries and allows the determination of the stresses and distortions experienced by a three-dimensional component. These finite elements are formed by dividing the original structure into a series of suitably shaped sections, each of which retains the same properties as real materials (4,5). Many of these methods have been applied in studies of restorative dentistry, which can pre-serve and restore teeth that have decay, defective restorations, lost and traumatized teeth. In general, the finite element method is especially suitable for predicting trends and performing parametric analysis (2). Obviously, it is very important to know in detail the properties of anisotropic materials and their constituent relationships to develop a valid finite element model (1). Therefore, it is a useful tool that allows performing a large number of analyses on complex components and structures, which are difficult to obtain by classical analytical methods. A finite element program is a complex piece of software in which numerous operations converge. The preparation of the data and the analysis of the numerical results that appear as a product of the calculation are tasks that tend to be integrated into the software itself. Finite element calculations consist of a processor which includes all the aids for the preparation of the data and generation of the results, and a post-processor which facilitates the analysis and interpretation of the results, usually in the form of graphs (plotting curves, three dimensional graphs, tables, etc.). As part of the research, the different types of materials currently used and their behavior with the forces interpreted in the mouth, as well as chewing movements and tooth contacts in occlusion will be reviewed. This will give the dentist a general idea about the selection of materials according to the type of rehabilitation

Global Survey of Outcomes of Neurocritical Care Patients: Analysis of the PRINCE Study Part 2

BACKGROUND: Neurocritical care is devoted to the care of critically ill patients with acute neurological or neurosurgical emergencies. There is limited information regarding epidemiological data, disease characteristics, variability of clinical care, and in-hospital mortality of neurocritically ill patients worldwide. We addressed these issues in the Point PRevalence In Neurocritical CarE (PRINCE) study, a prospective, cross-sectional, observational study. METHODS: We recruited patients from various intensive care units (ICUs) admitted on a pre-specified date, and the investigators recorded specific clinical care activities they performed on the subjects during their first 7 days of admission or discharge (whichever came first) from their ICUs and at hospital discharge. In this manuscript, we analyzed the final data set of the study that included patient admission characteristics, disease type and severity, ICU resources, ICU and hospital length of stay, and in-hospital mortality. We present descriptive statistics to summarize data from the case report form. We tested differences between geographically grouped data using parametric and nonparametric testing as appropriate. We used a multivariable logistic regression model to evaluate factors associated with in-hospital mortality. RESULTS: We analyzed data from 1545 patients admitted to 147 participating sites from 31 countries of which most were from North America (69%, N = 1063). Globally, there was variability in patient characteristics, admission diagnosis, ICU treatment team and resource allocation, and in-hospital mortality. Seventy-three percent of the participating centers were academic, and the most common admitting diagnosis was subarachnoid hemorrhage (13%). The majority of patients were male (59%), a half of whom had at least two comorbidities, and median Glasgow Coma Scale (GCS) of 13. Factors associated with in-hospital mortality included age (OR 1.03; 95% CI, 1.02 to 1.04); lower GCS (OR 1.20; 95% CI, 1.14 to 1.16 for every point reduction in GCS); pupillary reactivity (OR 1.8; 95% CI, 1.09 to 3.23 for bilateral unreactive pupils); admission source (emergency room versus direct admission [OR 2.2; 95% CI, 1.3 to 3.75]; admission from a general ward versus direct admission [OR 5.85; 95% CI, 2.75 to 12.45; and admission from another ICU versus direct admission [OR 3.34; 95% CI, 1.27 to 8.8]); and the absence of a dedicated neurocritical care unit (NCCU) (OR 1.7; 95% CI, 1.04 to 2.47). CONCLUSION: PRINCE is the first study to evaluate care patterns of neurocritical patients worldwide. The data suggest that there is a wide variability in clinical care resources and patient characteristics. Neurological severity of illness and the absence of a dedicated NCCU are independent predictors of in-patient mortality.status: publishe

SARS-CoV-2 vaccination modelling for safe surgery to save lives: data from an international prospective cohort study

Background Preoperative SARS-CoV-2 vaccination could support safer elective surgery. Vaccine numbers are limited so this study aimed to inform their prioritization by modelling. Methods The primary outcome was the number needed to vaccinate (NNV) to prevent one COVID-19-related death in 1 year. NNVs were based on postoperative SARS-CoV-2 rates and mortality in an international cohort study (surgical patients), and community SARS-CoV-2 incidence and case fatality data (general population). NNV estimates were stratified by age (18-49, 50-69, 70 or more years) and type of surgery. Best- and worst-case scenarios were used to describe uncertainty. Results NNVs were more favourable in surgical patients than the general population. The most favourable NNVs were in patients aged 70 years or more needing cancer surgery (351; best case 196, worst case 816) or non-cancer surgery (733; best case 407, worst case 1664). Both exceeded the NNV in the general population (1840; best case 1196, worst case 3066). NNVs for surgical patients remained favourable at a range of SARS-CoV-2 incidence rates in sensitivity analysis modelling. Globally, prioritizing preoperative vaccination of patients needing elective surgery ahead of the general population could prevent an additional 58 687 (best case 115 007, worst case 20 177) COVID-19-related deaths in 1 year. Conclusion As global roll out of SARS-CoV-2 vaccination proceeds, patients needing elective surgery should be prioritized ahead of the general population.The aim of this study was to inform vaccination prioritization by modelling the impact of vaccination on elective inpatient surgery. The study found that patients aged at least 70 years needing elective surgery should be prioritized alongside other high-risk groups during early vaccination programmes. Once vaccines are rolled out to younger populations, prioritizing surgical patients is advantageous