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Prevention of dental tissue loss by composite restoration repairs. Long-term durabillity of composite to composite bond in various environments.
Comba, Lukáš ; Bradna, Pavel (advisor) ; Veverka, Jan (referee) ; Roubalíková, Lenka (referee)
in english Introduction: Composite restorations in the oral cavity are exposed to an aggressive environment and mechanical challenge that gradually impairs their physical and mechanical properties. This may result in an enhanced wear rate, loss of esthetic properties and an increased risk of a restoration fracture or its marginal failure with a negative impact on the restoration's durability. Worn or failed restorations are usually completely replaced, which increases the irreversible loss of dental hard tissues. Repair of composite restorations by their partial replacement is therefore a minimally invasive, preventive and less time-consuming alternative to their complete replacement and increases their longevity. In the oral cavity, the adhesive bond between the existing composite restoration and the repair composite resin is exposed to various chemical substances and mechanical stress, e.g. surfactants in toothpastes, which can initiate its degradation. By decreasing the surface tension, the penetration of water into the adhesive joint can be enhanced, accelerating the hydrolysis of the adhesive and reducing the composite repair strength. The major and not yet fully resolved issue of composite repairs is how to achieve a strong and durable bond between the existing and repair composite materials....
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Tungsten-steel and tungsten-chromium composites prepared by RF plasma spraying
Matějíček, Jiří ; Klečka, Jakub ; Čížek, Jan ; Veverka, Jakub ; Vilémová, Monika ; Chráska, Tomáš ; Ganesh, V.
For future fusion reactors, materials able to withstand harsh environments are needed. In particular, this concerns the plasma-facing components which are foreseen to consist of tungsten based plasma-facing armor and structural and cooling part made of steel. Currently, joining of these materials presents a significant challenge. The stress concentration at their interface, which arises due to thermal exposure and the difference in thermal and mechanical properties, can be reduced by composite/graded interlayers. Plasma spraying is among the prospective technologies for their preparation. In this work, tungsten-steel and tungsten-chromium composites were prepared by radio-frequency inductively coupled plasma (RF-ICP) spraying. Initial optimization of the spraying process for pure materials as well as their mixtures was carried out. Basic characterization of the layers for their structure, porosity and composition is presented.
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Oral Health in Patients with Cardiovascular Diseases
Chalupová, Miroslava ; Hecová, Hana (advisor) ; Bartáková, Věra (referee) ; Veverka, Jan (referee)
Cardiovascular diseases are some of the most common health and society problems in the present population. The question of influencing cardiovascular diseases by the state of oral health has been discussed for a long time. Opinions on this issue have undergone long-term development. The state of oral health influencing the overall health has been overestimated and underestimated over the years. This thesis has summarized contemporary knowledge of the metastatic opportunistic infection of oral etiology and evaluated the state of oral health of 187 patients from the Department of Stomatology, Faculty of Medicine and University Hospital in Pilsen, Charles University, who were examined by a dentist as a part of the preoperative examinations before planned cardiac surgery in 2015-2018. The experimental part of the study was focused on the detection of oral bacteria on pathologically changed heart valves from 41 patients operated on the Department of Cardiosurgery, Faculty of Medicine and University Hospital in Pilsen, Charles University. The summary of the results of the prospective epidemiological study of 187 patients undergoing a planned cardiosurgical operation has brought information about the neglected state of oral health of these patients. More than half of the examined patients (64.17%) were at...
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Thin nitride layers as permeation barriers
Veverka, Jakub ; Matějíček, Jiří ; Lukáč, František ; Pospíšil, D. ; Cvrček, L. ; Nemanič, V.
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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Powder feeding analysis in RF-ICP
Zlatník, Rostislav ; Veverka, Jakub (referee) ; Čížek, Jan (advisor)
The work is focused on the problematics of inductively coupled plasma, which is used for deposition of layers. We focused on two goals in the work. The first one focused on powder feeder, which is working on the vibration principle and is used in an apparatus that is using inductively coupled plasma. The aim is to determine its properties, dependence on different input parameters and working conditions. Is important to verify the suitability of its use for this kind of application. The assumption was to find the ideal configuration of the feeder for the given powder. After an overall assessment of the feeder properties, it was recognized as inappropriate for this application. The second goal is to spray tungsten layers with three different tungsten powders. Layers made with an inductively coupled plasma technology delivers promising results, but this issue needs to be intensively addressed in the future.
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Alternative Methods of Permeation Barriers Preparation
Veverka, Jakub ; Matějíček, Jiří
Permeation barriers represent one of the crucial fields in materials development for thermonuclear fusion. Primary objective of the barriers is to suppress the permeation of hydrogen isotopes (mainly tritium) from future thermonuclear fusion facilities. Secondary objective is to reduce their retention in structural materials. Expected reactor conditions put high demands on the material, as well as on the final barrier quality. Key properties are tritium permeation reduction, absence of defects (especially cracks), high-temperature stability and corrossion resistance, and compatibility with structural materials (mostly ferritic-martensitic steels). Thin nitride layers, identified as promising permeation barriers, were prepared by diffusion-based nitridation and physical vapour deposition (PVD), and characterized.
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The return of Poland and Czechoslovakia and the entry of Hungary to International Monetary Fund.
Veverka, Jan ; Svoboda, Karel (advisor) ; Mlsna, Petr (referee)
Bachelor thesis "The Return of Poland and Czechoslovakia and the Entry of Hungary to International Monetary Fund" deals with the early membership of these three central European countries - Czechoslovakia, Poland and Hungary - in the International Monetary Fund. First the thesis deals with how both Czechoslovakia and Poland were involved in the process of setting up the IMF and how they both terminated their membership in the beginning of the fifties, later the thesis deals with the circumstances leading to the Hungarian membership in the International Monetary Fund in 1982, to Polish membership renewal in 1986 as well as to Czechoslovak membership renewal talks in the 1980s. There has been a substantial change in economic and political setting in Hungary, Czechoslovakia and Poland after thirty years of disparate economic evolution and political separation via "iron curtain". At the same time, the character of IFM changed as well, and it was this coincidence that lead to the change in the attitude towards the IMF membership on the side of all above mentioned states as well as of the international organization itself.
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Long-term durability of composite restoration margins in environments with increased corrosion risk
Roubíčková, Adéla ; Bradna, Pavel (advisor) ; Veverka, Jan (referee) ; Halačková, Zdena (referee)
Introduction: An adhesive bond between hard dental tissues and composite reconstructions is exposed to mechanical load, water, bacteria, enzymes and different chemical compounds. These factors could impair durability and resistance of composite reconstructions. In contrast with extensive research of negative influence of water on degradation of adhesive bonds, the influence of chemical substances on adhesive bond has not been investigated to a greater extent. Aim: The aim of the experimental part of the thesis was to evaluate the influence of hydrogen peroxide containing tooth-whitening products and mouth rinses containing chlorhexidine and fluoride on a long-term stability of class V composite restorations created using four contemporary adhesive systems by a microleakage method. Materials and methods: The following adhesive systems were investigated: total-etch Gluma Comfort Bond (GLU), and self-etch adhesives Clearfil SE Bond (CLF), Adper Prompt (ADP) and iBond (IBO). Standardized class V cavities were prepared in 192 extracted human teeth (one cervical margin in the cementum and one in the enamel). Subsequently, the cavities were restored using microhybride composite Charisma. The specimens were then exposed to the tooth whitening system Opalescence PF 20, mouth rinse Corsodyl containing...
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