Made available in DSpace on 2014-06-12T22:57:25Z (GMT). No. of bitstreams: 2 arquivo4012_1.pdf: 567312 bytes, checksum: 7691dbf0dd11facca327c9b9aca128b9 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / O objetivo deste estudo foi avaliar o tempo de recontaminação de canais radiculares obturados com cones ProTaper Universal® e, expostos ao meio bucal. Metodologia Cinqüenta pré-molares unirradiculares humanos foram preparados usando o sistema rotatório ProTaper Universal , sendo divididos aleatoriamente em seis grupos, quatro experimentais e dois controles. Os grupos experimentais, com dez espécimes cada, foram separados de acordo com o a técnica obturadora e o calibre do cone principal utilizado. Em seguida, a superfície externa dos espécimes foi impermeabilizada, sendo então montados no sistema experimental. A detecção de infiltração foi determinada pela visualização da turbidez do meio e a identificação da espécie bacteriana, que infiltrou o canal radicular, foi realizada pela análise da fisiologia das colônias, coloração de Gram e análises bioquímicas. Os dados obtidos foram analisados com o auxílio do teste de Kaplan-Meier para análise de sobrevivência, sendo aplicado o teste de Longrank para comparar as curvas de sobrevivência e os pareamentos dos grupos. Resultados As infiltrações microbianas ocorreram 22,5% dos espécimes obturados no intervalo entre o 12º e 80º dia. O teste de Long-rank revelou que não houve diferença estatisticamente significativa entre as diferentes técnicas obturadoras e entre os diâmetros dos cones utilizados. Conclusões As técnicas de condensação lateral e de cone único associadas ao cimento AH Plus® não proporcionaram um total vedamento contra a infiltração bacteriana, independentemente do diâmetro do cone utilizado

La mélatonine, hormone "donneuse de temps de l’organisme", en plus de sa synthèse principale dans la glande pinéale est produite dans la rétine où sa régulation et ses fonctions restent partiellement connues chez les mammifères. Le but de mon projet a été de caractériser l’expression temporelle et spatiale de la mélatonine et d’examiner son rôle potentiel dans la physiopathologie rétinienne. Une première partie a révélé au moins deux sites de production de la mélatonine dans la rétine : une synthèse nocturne de l'hormone dans les photorécepteurs de type cône ainsi qu'une production diurne dans les cellules ganglionnaires. Nos résultats ont démontré que la mélatonine peut agir par l'intermédiaire de son récepteur nommé MT1, localisés dans chacune des trois couches rétiniennes. Une seconde partie a mis en évidence que la mélatonine augmente la survie des photorécepteurs chez les rongeurs âgés en modulant l'activation de la voie de survie cellulaire via ses récepteurs MT1 et MT2. / Melatonin, a major hormonal "Zeitgeber" in the body, is produced in the pineal gland as well as the retina. In mammals its regulation and functions in this tissue are only partially understood. The aim of my project was to characterize the temporal and spatial expressions of melatonin as well as its potential roles in retinal physiopathology. In the first part, we identified the timing and sites of melatonin production. Notably, nocturnal synthesis occurs in the cones while diurnal production is seen in the ganglion cells. Our work also establishes that melatonin can act via its MT1-type receptors localized in the three retinal nuclear layers. The second axis demonstrated that melatonin increases photoreceptors viability via its receptors during the course of aging by modulating activation of an intracellular survival pathway.

This thesis explores Voxel Cone Tracing as a possible Global Illumination solutionon mobile devices.The rapid increase of performance on low-power graphics processors hasmade a big impact. More advanced computer graphics algorithms are now possi-ble on a new range of devices. One category of such algorithms is Global Illumi-nation, which calculates realistic lighting in rendered scenes. The combinationof advanced graphics and portability is of special interest to implement in newtechnologies like Virtual Reality.The result of this thesis shows that while possible to implement a state of theart Global Illumination algorithm, the performance of mobile Graphics Process-ing Units is still not enough to make it usable in real-time.

Magister Scientiae - MSc / Nowadays, the availability of radiographic modalities from conventional radiography to more advanced approaches such as medical computed tomography as well as cone beam computed tomography have been useful in providing insights of relevant anatomy prior to surgical procedures. The increased popularity of cone beam computed tomography has prompted interest in the utility of this approach for diagnostic application in dentistry, including the assessment of the proximity of impacted mandibular third molars to the inferior alveolar canal. It is important to understand the reliability of conventional panoramic radiograph in the assessment of this criterion since it is more commonly used as first line radiographic approach due to its availability and lower radiation dose. This study is aimed to investigate the reliability of conventional panoramic radiograph in the evaluation of the proximity of impacted mandibular third molar root tip to the inferior alveolar canal by correlating the results with cone beam computed tomography. A retrospective study of forty nine patients who underwent panoramic radiography as well as cone beam computed tomography for examination of impacted mandibular third molars was conducted. Two observers were participated in all image evaluation. In this study, both observers recorded statistically significant differences in the measurement of the apices of vertically impacted third molars and the inferior alveolar canal from panoramic radiographs and cone beam computed tomography images. The low reliability of panoramic radiograph to assess the vertical proximity between these two anatomical structures suggests the importance of additional assessment with cone beam computed tomography in cases where panoramic radiograph shows superimposition of the third molar root on the roof of the canal, presence of root below the roof of the canal and presence of bone height of less than one millimetre separating the third molar from the inferior alveolar canal.

Cone-beam computed tomography (CBCT) has become increasingly popular in dentistry. It is usually associated with radiation doses that are lower than those seen with conventional computed tomography (CT) but greater than those seen with dental radiography. Because exposure to ionising radiation is associated with risks, the radiation protection principles of justification and optimisation should be applied. These are especially important in children and young people due to their greater risk of developing stochastic effects. Justification requires a balancing of the radiation risk with the potential benefits and the latter is dependent on diagnostic efficacy. There has been a proliferation of articles published on dental CBCT and there is a need to review this systematically so that diagnostic efficacy can be judged. In terms of optimisation, radiation dose reduction can be achieved in various ways, but the use of barrier materials to protect younger patients in CBCT has not been adequately tested. Reduction in exposure parameters in CBCT will lower doses but at the expense of a loss of image quality. While some efforts have been made to relate radiation exposure and image quality in CBCT, there is a need to develop low-dose CBCT protocols specifically for children and young people. The first aim of this thesis was to survey current uses of CBCT in children and young people in three United Kingdom dental hospitals. The second aim was to determine the efficacy of thyroid shielding in a child phantom testing several different designs, materials and thickness of thyroid shields. The third aim was to evaluate the evidence on diagnostic efficacy of dental CBCT for root fractures in permanent, non-endodontically treated, anterior teeth by conducting a systematic review. The fourth aim was to evaluate objective and subjective image quality in a laboratory study to determine a low-dose CBCT protocol which maintains adequate diagnostic image quality for a clinical indication in children. Finally, the aim was to evaluate this low-dose protocol in terms of image quality in real clinical situations. A high adherence to the European guidelines No 172 on radiation protection in dental CBCT was found amongst the surveyed hospitals. Thyroid shielding was found to be effective in dose reduction when performing a large field of view CBCT scan in a child phantom, but design influenced efficacy. The systematic review showed that research articles investigating CBCT diagnostic accuracy for vertical and horizontal root fractures had deficiencies in methodology, while only one study was identified addressing higher levels of diagnostic efficacy. A low-dose imaging protocol was identified in a laboratory study, which has been shown to be an effective tool in dose reduction providing an adequate diagnostic image quality and reducing radiation doses considerably for clinical indications in the anterior maxilla in children and young people.

Today mines produce metals which are used for everyday products by people worldwide. When metals are produced, waste products known as tailings are generated. These tailings are commonly stored in impoundments, surrounded by embankment dams. The demands from the society are constantly increasing regarding the quality and safety of dams. One step in development towards a better control regarding safety and quality of tailing dams, could be to compact the beach. Today there is a lack of methods to easy check the dry densities over large areas for a compacted material. Since these dams can be large structures with embankment lengths of several kilometers, it is necessary to be able to check the density with a fast method. In this thesis it was investigated if the dry density, and correspondingly the compaction, can be checked with a Dynamic Cone Penetrometer (DCP). In the thesis the dry density of tailings was compared with penetration rate of the DCP. A laboratory setup was made with a test box filled with tailings provided by Boliden AB from the Aitik mine. Six different box tests were performed, each test with different compaction. From the tests a trend was observed, for which the tailings increased in density as the DCP indexes showed an increased resistance. A relationship between DCP index and dry densities was found. Though a relationship was found, it is important to emphasize that the tests were carried out in an environment that was easy to control. One test with high water content showed that water was influencing the DCP index results. Therefore it was concluded that if the DCP will be used in field, the water content also has to be checked.

No description available.

This thesis investigates laser micromachining using a high pulse repetition frequency (high-PRF) femtosecond fibre laser. Three different types of industrial-grade metals, Stainless steel, Copper, and Aluminium are investigated. The impact of the processing parameters on material removal is studied. Finally the feasibility of the technology in three dimensional micro structuring is explored. The thesis contributes to clarify the main interaction mechanisms occurring in high-PRF femtosecond laser processing. Heat accumulation and particle shielding are identified as main material removal influencing mechanisms. As a result of heat accumulation, lowered ablation thresholds are detected for Aluminium (0.16 J/cm² at 1.02 MHz versus 0.33 J/cm² at 20 kHz) and Stainless steel (0.088 J/cm² at 1.02 MHz versus 0.11 J/cm² at 20 kHz). For the high heat conductive Copper heat accumulation is largely ruled out. Particle shielding is investigated by ultra high speed camera imaging. It is shown that the ablation plumes enlarge at the higher pulse repetition rates. A parameter study investigates material ablation. From this study, appropriate machining parameters are derived with regard to both high ablation rate and removal efficiency, and small roughness: Aluminium: 5 μm pulse spacing / 5 μJ pulse energy, Copper: 7.5 μm pulse spacing / 7 μJ pulse energy, Stainless steel: 5 μm pulse spacing / 3 μJ pulse energy. In addition experimentally and theoretically determined volume ablation rates are compared. For this, a material removal calculation model is designed. Good agreements between theoretical and experimental values are obtained by taking into account effective penetration instead of optical penetration for energy transport. A surface temperature calculation model is designed, providing useful insights into heat accumulation. Heat accumulation observed for Aluminium and Stainless Steel is confirmed by surface temperature rise, calculated based on the remaining energy. Improvement of the model by enhanced energy coupling yields surface temperatures above the melting temperature. This is conclusive to experimental observations. Finally the feasibility of the high-PRF femtosecond laser technology in micromachining is demonstrated by micro mould fabrication. Utilising these moulds, micro-fluidic plastic demonstrators are fabricated by micro-injection moulding.

The RTT80 cone beam x-ray computed tomography system, developed by Rapiscan Systems Ltd, uses switched x-ray sources and fixed offset detector rings to remove the time consuming mechanical rotations of earlier imaging systems. This system produces three-dimensional images in real time. A Geant4 Monte Carlo simulation has been developed to investigate scattered radiation in the uncollimated detector machine, showing high levels of scatter behind highly attenuating objects. A new scatter correction method is proposed which estimates scatter to each detector, in each projection, from 1cm³ voxels of the computerised object. The scatter distributions from different materials are pre-determined using a Geant4 Monte Carlo simulation. The intensity of scatter from each voxel is based on measured data. The method is applied to two simulated test objects, a water box simulated with a monoenergetic input spectrum and a test suitcase simulated with a polyenergetic spectrum. The test suitcase is broken down into separate components to analyse the method further. The results show that the method performs well for low attenuating objects, but the results are sensitive to the intensity values. However, the method provides a good basis for a scatter correction method.

Changes occur to the mandible with dental loss and senescence. However, the influence that these changes have on sex and ancestry estimations remains unclear. The purpose of this study was to investigate the influence of dental loss and senescence on changes in mandibular morphology. The outcome has implications for both forensic anthropology and restorative dentistry. The study sample consisted of 717 mandibles consisting of both male and female South Africans of African (SAA) and European ancestry (SAE). To minimise the effects of variation in dentition amongst sex-ancestry groups, the sample included individuals with a spectrum of tooth loss patterns, namely efficient and inefficient occlusions as well as no occlusions. Dentition was considered efficient when the remaining teeth in occlusion were evenly distributed between the sides. Linear measurements as well as geometric morphometric shape analyses were performed. Shape analyses of the complete mandible were performed on models from digitised landmarks by using a MicroScribe G2. Detailed shape analyses of the ramus and chin area as well as measurements of the cortical thickness at specific sites were executed on images generated by cone beam computed tomography (CBCT). A comprehensive assessment of changes in shape, size and cortical thickness of the mandible with age and dental loss were made. Shape and size differences of the mandible were evaluated for discriminant abilities between sex and ancestry groups. Although most dimensions decreased with tooth loss, the greatest impact was noted in the loss of alveolar bone. The mandibular angle increased minimally in size when a few teeth were lost, but recovered to some extent with further tooth loss. The cortical thicknesses at the mental foramen lingually as well as in the midline in females, were relatively spared with tooth loss. Male individuals of SAA were often the most resilient to tooth loss. In general external linear dimensions were maintained with age despite tooth loss. Conversely, measurements of cortical bone thickness decreased slightly, but could have been influenced by dental loss. The shape of the chin and gonial area was more affected by aging in SAE. The sex and ancestry discriminant ability of the linear dimensions when considered collectively approximated 90%, in general improving further when tooth loss was taken into account. All linear measurements were smaller in females and in general tooth loss accentuated sex differences. SAA exhibited greater dimensions, apart from maximum ramus height, bigonial breadth and cortical thickness at the gonion. The mental tubercles were more prominent than the pogonion in SAE (square chin) and vice versa in individuals of SAA (pointed chin). The gonial area in individuals of African ancestry was broad and more convex and the gonial eversion more prominent with a more upright ramus. Discriminant qualities of the gonial shape for sex in individuals of African ancestry reached 90% within dentition groups. Ramus flexure and chin shape were not found to be useful in sex estimation. In conclusion, this research elucidated the effects of tooth loss and senescence on the morphology of the mandible for the forensic anthropological setting. / Thesis (PhD)--University of Pretoria, 2015. / tm2015 / Anatomy / PhD / Unrestricted