Browsing by Author "Machado, Joana"
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- Analysis of the Use of Cylindrospermopsin and/or Microcystin-Contaminated Water in the Growth, Mineral Content, and Contamination of Spinacia oleracea and Lactuca sativaPublication . Llana-Ruiz-Cabello, Maria; Jos, Angeles; Cameán, Ana; Oliveira, Flavio; Barreiro, Aldo; Machado, Joana; Azevedo, Joana; Pinto, Edgar; Almeida, Agostinho; Campos, Alexandre; Vasconcelos, Vitor; Freitas, MarisaCyanobacteria and cyanotoxins constitute a serious environmental and human health problem. Moreover, concerns are raised with the use of contaminated water in agriculture and vegetable production as this can lead to food contamination and human exposure to toxins as well as impairment in crop development and productivity. The objective of this work was to assess the susceptibility of two green vegetables, spinach and lettuce, to the cyanotoxins microcystin (MC) and cylindrospermopsin (CYN), individually and in mixture. The study consisted of growing both vegetables in hydroponics, under controlled conditions, for 21 days in nutrient medium doped with MC or CYN at 10 μg/L and 50 μg/L, or CYN/MC mixture at 5 + 5 μg/L and 25 + 25 μg/L. Extracts from M. aeruginosa and C. ovalisporum were used as sources of toxins. The study revealed growth inhibition of the aerial part (Leaves) in both species when treated with 50µg/L of MC, CYN and CYN/MC mixture. MC showed to be more harmful to plant growth than CYN. Moreover spinach leaves growth was inhibited by both 5 + 5 and 25 + 25 µg/L CYN/MC mixtures, whereas lettuce leaves growth was inhibited only by 25 + 25 µg/L CYN/MC mixture. Overall, growth data evidence increased sensitivity of spinach to cyanotoxins in comparison to lettuce. On the other hand, plants exposed to CYN/MC mixture showed differential accumulation of CYN and MC. In addition, CYN, but not MC, was translocated from the roots to the leaves. CYN and MC affected the levels of minerals particularly in plant roots. The elements most affected were Ca, K and Mg. However, in leaves K was the mineral that was affected by exposure to cyanotoxins.
- Bone Immobilization devices and consolidation mechanisms: Impact on healing timePublication . Flores, Andreia; Marques, Arcelina; Machado, Joana; Marta, Miguel; Vaz, MárioThe human skeleton is formed by living tissues that react to loads and ensures the support of the remaining tissues of human body like muscles, ligaments, tendons, etc. However, its integrity can be compromised due to fractures or injuries of the bone tissue that require orthopedic surgery and immobilization methods, such as external fixators, intramedullary nail or osteosynthesis plates.One of the most important characteristics of living tissue is its capacity of self-regeneration. It is a complex process that implies several mechanisms during the consolidation time. Therefore, the knowledge of the involved mechanisms and their interdependence on external factors, will allow accelerating the regeneration process and contributing to the success of the rehabilitation process. Several techniques have been developed to characterizing characterize the mechanical loads acting in fractured bone to better understand the fracture consolidation and obtain useful information for the orthopedic doctors. This information is relevant to enable each patient follow-up and optimize the clinic procedures. As such, it is important to understand what happens during fracture consolidation to predict the necessary structural immobilization time and mechanical stimulus which shorten the healing process. The purpose of this work is twofold: primarily, to study the consolidation process using different immobilization systems, and secondarily, to explore the necessary time for bone consolidation by recording the relevant mechanical parameters time story.
- Currently used systems of dental posts for endodontic treatmentPublication . Machado, Joana; Almeida, Paulo; Fernandes, Sampaio; Marques, Arcelina; Vaz, MárioAn advanced stage of a tooth decay promotes an extremely damaged tooth that needs endodontic treatment to be restored. When satisfactory coronal tooth structure remains, an artificial crown can be placed without a post. On the other hand, the treatment of seriously damaged teeth often require an endodontic post. The main reason for using post is to enable rebuilding of the tooth structure prior to crown restoration. Dentists believe that endodontic posts provide a stable and solid restoration of the tooth, as well as providing strengthening of the tooth root, which constitutes the solid basis for a dental crown restoration. However, some authors reported that the strength of the tooth is directly related to the remaining dentin, and because of that, an endodontic treatment can present a higher risk of biomechanical failure. A number of different materials have been used for the manufacturing of dental posts. The fundamental posts requirements include high tensile strength, high fatigue resistance to occlusal and shear loading and a good distribution of the forces affecting the tooth root. The purpose of this article is to review the current literature and identify the various characteristics of a dental post, as well as some principles on the endodontic treatment for tooth decay.
- Currently used systems of dental posts for endodontic treatmentPublication . Machado, Joana; Almeida, Paulo; Fernandes, Sampaio; Marques, Maria Arcelina; Vaz, MárioAn advanced stage of a tooth decay promotes an extremely damaged tooth that needs endodontic treatment to be restored. When satisfactory coronal tooth structure remains, an artificial crown can be placed without a post. On the other hand, the treatment of seriously damaged teeth often require an endodontic post. The main reason for using post is to enable rebuilding of the tooth structure prior to crown restoration. Dentists believe that endodontic posts provide a stable and solid restoration of the tooth, as well as providing strengthening of the tooth root, which constitutes the solid basis for a dental crown restoration. However, some authors reported that the strength of the tooth is directly related to the remaining dentin, and because of that, an endodontic treatment can present a higher risk of biomechanical failure. A number of different materials have been used for the manufacturing of dental posts. The fundamental posts requirements include high tensile strength, high fatigue resistance to occlusal and shear loading and a good distribution of the forces affecting the tooth root. The purpose of this article is to review the current literature and identify the various characteristics of a dental post, as well as some principles on the endodontic treatment for tooth decay.
- Effects of Chrysosporum (Aphanizomenon) ovalisporum extracts containing cylindrospermopsin on growth, photosynthetic capacity, and mineral content of carrots (Daucus carota)Publication . Guzmán-Guillén, Remedios; Campos, Alexandre; Machado, Joana; Freitas, Marisa; Azevedo, Joana; Pinto, Edgar; Almeida, Agostinho; Cameán, Ana M.; Vasconcelos, VitorNatural toxins produced by freshwater cyanobacteria, such as cylindrospermopsin, have been regarded as an emergent environmental threat. Despite the risks for food safety, the impact of these water contaminants in agriculture is not yet fully understood. Carrots (Daucus carota) are root vegetables, extensively consumed worldwide with great importance for human nourishment and economy. It is, therefore, important to evaluate the possible effects of using water contaminated with cyanotoxins on carrot cultivation. The aim of this work was to investigate cylindrospermopsin effects on D. carota grown in soil and irrigated for 30 days, with a Chrysosporum ovalisporum extract containing environmentally relevant concentrations of cylindrospermopsin (10 and 50 μg/L). The parameters evaluated were plant growth, photosynthetic capacity, and nutritional value (mineral content) in roots of carrots, as these are the edible parts of this plant crop. The results show that, exposure to cylindrospermopsin did not have a clear negative effect on growth or photosynthesis of D. carota, even leading to an increase of both parameters. However, alterations in mineral contents were detected after exposure to crude extracts of C. ovalisporum containing cylindrospermopsin. A general decline was observed for most minerals (Ca, Mg, Na, Fe, Mn, Zn, Mo, and P), although an increase was shown in the case of K and Cu, pointing to a possible interference of the cyanobacterial extract in mineral uptake. This study is the first to evaluate the effects of C. ovalisporum extracts on a root vegetable, however, more research is necessary to understand the effects of this toxin in environmentally relevant scenarios.
- Influence of an innovative dental post approach in dentin mechanical behaviorPublication . Lopes, Carla; Machado, Joana; Almeida, Paulo; Fernandes, Sampaio; Marques, Maria Arcelina; Vaz, MárioThe restoration of seriously damaged teeth often requires an endodontic post. A number of different materials and shapes of dental posts have been manufactured, which leads to different mechanical behaviors. The currently used post systems frequently result in failure or fracture of the tooth, due to the difference between tooth and dentin mechanical properties. Recently, a bundle of fine individual posts made of reinforced fiberglass has been developed. This new approach is not a single-post and it can be spread apart, being individually distributed in the tooth canal. With this configuration, the fine posts can adapt to suit into any root canal anatomy. Biomechanical properties similar to the dentin are being reported as an advantage for the use of this new dental post. The purpose of this study is to understand if the bundle post introduces an improvement in the results of endodontic treatment, compared with the currently used post systems. This study was carried out using the finite element method to determine the influence of stress distribution on dentin, when these two different approaches are used. The results show that stresses at the dentin changed with the dental post used. The use of bundle post appears to better accommodate the developed stress, reducing the stresses in the tooth.
- Mechanical behavior of external fixator on fracture healing processPublication . Lopes, Carla; Flores, Andreia; Marques, Maria Arcelina; Machado, Joana; Marta, Miguel; Vaz, MárioSucceeding a fracture of a long bone, there are multiple approaches to perform the bone fracture immobilization.The external fixation has traditionally been used under clinical indications, and can be a definitive optionin cases where risks of infection are high. The currently used system scannot predict or measure the complete bone consolidation[1, 2]. The purpose of the present study is to understand the phases of healing and to predict functional bone consolidation.This study was carrying out using the finite element analysis (FEA)to determine the influence of stress distribution along the tibia and the rods of the fixator.This information gathered by the present study is relevant to help medical and scientific communities to know the real fracture healing process.