Modelação 3D de uma mandíbula humana. Análise de elementos finitos em actividade mastigatória

A mandíbula humana é uma estrutura anatómica de grande complexidade biomecânica. Vários autores 1-3 desenvolveram malhas de elementos finitos, com diferentes graus de complexidade, para efectuar análise de tensões instaladas neste osso mediante determinadas condições. Pretendeu-se com este estudo optimizar a malha desenvolvida por Reis Campos2, através da inserção dos músculos envolvidos na mastigação

Análise por elementos finitos do comportamento mecânico de uma mandíbula humana parcialmente edêntula em função da densidade óssea trabecular

Purpose: To present a methodological procedure to obtain the geometric and discrete models of a human mandible for numerical simulation of the biomechanical behavior of a partially edentulous mandible as a function of cancellous bone density. Methods: A 3D finite element method was used to assess the model of a partially edentulous mandible, Kennedy Class I, with dental implants placed at the region of teeth 33 and 43. The geometric solid model was built from CT-scan images and prototyping. In the discrete model a parametric analysis was performed to analyze the influence of cancellous bone density (25 %, 50 %, 75 %) on the development of mandibular stress and strain during simulation of masticatory forces in the anterior region. Results: Maximum von Mises stress and equivalent strain values in cancellous bone were found close to the loading area (masticatory forces). The peak stress and strain values occurred in the mandibular anterior region, and for the same masticatory force the equivalent stresses increased with bone density. Conclusion: The results suggest that the stresses and strains developed in the mandibular model were affected by cancellous bone density during the simulation of masticatory activity. Objetivo: Apresentar uma metodologia para modelamento geométrico de uma mandíbula humana e obtenção de um modelo discreto para simular numericamente o comportamento biomecânico de uma mandíbula parcialmente edêntula em função de diferentes densidades do osso trabecular. Metodologia: Utilizou-se o método de elementos finitos 3D para realizar um estudo numérico sobre um modelo de mandíbula humana, desdentada parcial tipo Classe I de Kennedy, com implantes nas regiões dos dentes 33 e 43. O modelo sólido geométrico foi determinado por tomografia computorizada e prototipagem. No modelo discretizado foi realizada uma análise paramétrica para verificar a influência da densidade óssea do osso trabecular (25 %, 50 %, 75 %) no desenvolvimento de tensões e deformações da mandíbula durante a aplicação de forças mastigatórias na região anterior. Resultados: As tensões máximas de von Mises e deformações equivalentes no osso trabecular foram desenvolvidas próximo às regiões de aplicação das forças de mordida. Os picos de valores de tensões/deformações localizaram-se na região anterior da mandíbula, sendo que, para o mesmo valor de esforço de mordida, as tensões equivalentes aumentaram com a densidade óssea. Conclusão: Os resultados sugerem que as tensões e deformações desenvolvidas no modelo mandibular testado foram afetadas pelo grau de densidade do osso trabecular durante simulação de atividade mastigatória

Does Doing the Right Thing Pay? Comparing Youths Who Abstain from Risk Behaviors to Their Risk-taking Peers

Purpose: To assess whether young people not engaging in risk behaviors do better than their risk-taking peers. Methods: Data were drawn from the GenerationFRee study, a cross-sectional in-school survey including 5179 youths aged 15-24. Six risk behaviors were studied: smoking, alcohol misuse, cannabis use, use of other illegal drugs, violent behavior and antisocial behavior. A score obtained after adding the behaviors permitted to divide the subjects into Abstainers (score=0; N=1920) and Risk-takers (score>0; N=3259). Groups were compared on personal, familial, academic characteristics. All variables significant at the bivariate level were included in a logistic regression using Risk-takers as the reference category. Results are given as adjusted Odds Ratios (aOR) with 95% confidence interval

More Important Than You Thought: Some Chronically Ill Adolescents Rely a Lot on Their Health Professional

Purpose: To assess who do chronically ill adolescents rely on in their entourage. Methods: Data were drawn from the GenerationFRee study, a cross-sectional survey including 5149 youths aged 15-24 divided into 3 groups: healthy controls (HC; N=4529), chronically ill without limitations (CI; N=517) and chronically ill with limitations (CIWL; N=103). Groups were compared on perceived health status, socio-demographic variables and whether they could rely a lot on their father, their mother, their girl/boyfriend, their best friend or their health professional in case of difficulty. All variables significant at the bivariate level were included in a multinomial logistic regression using HC as the reference category. Results are given as Relative Risk Ratios (RRR) with 95% CI

Is Being Overweight or Obese Really a Problem?

Purpose: To assess whether there are individual, familial, academic or social differences between youths being overweight, obese or normal weight. Methods: Data were drawn from the GenerationFRee study, a cross-sectional survey including 5179 youths aged 15-24. Using Cole’s cut-off points of body mass index (BMI), individuals were divided into normal weight (NW; N=4291), overweight (OW; N=646), and obese (OB, N=242). Groups were compared on age, gender, emotional wellbeing, self-reported health status, family structure, relationship with father and with mother, life satisfaction, socioeconomic status, pubertal timing, popularity among peers, easiness to make friends, at risk for eating disorders, parents nationality, own nationality, and academic track. All variables at the bivariate level were included in multinomial logistic regression using NW as the reference category. Results are given as Relative Risk Ratios (RRR) with 95% confidence interval

Gambling and Risk Behaviors: Characteristics of Young Problematic Gamblers in Switzerland

Purpose : To assess the characteristics and associated risk factors of young problematic gamblers. Methods: Data were drawn from the GenerationFRee study, a Swiss cross-sectional in-school survey including 5179 youths aged 15-24 (mean age 18.3). Among these participants, 1371 (26.5%) reported having gambled in the last 12 months and were included in the study. Gamblers were divided into two groups according to the South Oaks Gambling Screen (SOGS) scale adapted for adolescents: non-problematic gamblers (SOGS<2; N=1116) and at risk/problematic gamblers (SOGS>=2; N=255). Participants reported demographic, family and academic data, risk behaviors (current smoking, alcohol misuse, cannabis use, use of other illegal drugs, violent and antisocial acts, and Internet addiction) and sensation seeking. All variables significant at the bivariate level were included in a logistic regression analysis to assess the variables associated with at risk/problematic gambling using non-problematic gamblers as the reference category. Data are presented as adjusted odds ratios (aOR) with 95% confidence interval

Influência do osso trabecular no comportamento biomecânico de uma mandíbula humana em actividade mastigatória

A mandíbula humana é um dos elementos anatómicos de difícil análise biomecânica, pois combina, com uma elevada sofisticação, uma complexa geometria que inclui osso cortical e trabecular, tecido dentário, ligamentos, nervos e vasos sanguíneos. Neste artigo é efectuado um estudo numérico sobre um modelo de um desdentado com implantes, detenninado por tomografia computorizada. É efectuada uma análise paramétrica para verificar a influência das propriedades do osso trabecular no comportamento biomecânica da mandíbula durante actividade mastigatória. O resultado da deformação permite concluir que a actividade de ósseo integração é mais adequada para maiores valores de densidade do tecido ósseo. Os resultados demonstram ainda que para o mesmo valor de esforço de mordida, as tensões equivalentes crescem com a densidade do tecido

Neoproterozoic crustal evolution in Southern Chad: Pan-African ocean basin closing, arc accretion and late- to post-orogenic granitic intrusion.

International audienceIn the Lake Léré region, southern Chad, Neoproterozoic terrains are distributed in four lithostructural groups that reveal the geotectonic evolution of a part of the Pan-African orogenic domain. The first group includes basaltic volcanic rocks and fine-grained detrital sedimentary rocks of pre-tectonic basins that were emplaced in an extensional regime, close to a volcanic arc. The second and third groups include calc-alkaline gabbroic intrusions emplaced at an upper crustal level and a midcrustal tonalite, respectively, that are interpreted to be the roots of an active margin volcanic arc. These first three groups experienced WNW to ESE compression, and may belong to a fore-arc basic—volcanic arc—back-arc basin system that was accreted eastward to the Palaeoproterozoic Adamaoua-Yadé Block. The fourth group includes post-tectonic granite plutons invading the older groups. This paper documents the accretion processes in the southern margin of the Saharan Metacraton

Unraveling the phase behavior, mechanical stability, and protein reconstitution properties of polymer-lipid hybrid vesicles

Hybrid vesicles consisting of natural phospholipids and synthetic amphiphilic copolymers have shown remarkable material properties and potential for biotechnology, combining the robustness of polymers with the biocompatibility of phospholipid membranes. To predict and optimize the mixing behavior of lipids and copolymers, as well as understand the interaction between the hybrid membrane and macromolecules like membrane proteins, a comprehensive understanding at the molecular level is essential. This can be achieved by a combination of molecular dynamics simulations and experiments. Here, simulations of POPC and PBD22-b-PEO14 hybrid membranes are shown, uncovering different copolymer configurations depending on the polymer-to-lipid ratio. High polymer concentrations created thicker membranes with an extended polymer conformation, while high lipid content led to the collapse of the polymer chain. High concentrations of polymer were further correlated with a decreased area compression modulus and altered lateral pressure profiles, hypothesized to result in the experimentally observed improvement in membrane protein reconstitution and resistance toward destabilization by detergents. Finally, simulations of a WALP peptide embedded in the bilayer showed that only membranes with up to 50% polymer content favored a transmembrane configuration. These simulations correlate with previous and new experimental results and provide a deeper understanding of the properties of lipid-copolymer hybrid membranes