National Repository of Grey Literature 18 records found  1 - 10next  jump to record: Search took 0.13 seconds. 
Preparation and characterization of highly filled composite materials for dental applications
Gavroňová, Ivana ; Bystřický, Zdeněk (referee) ; Poláček, Petr (advisor)
Master thesis deals with highly filled particulate composite materials for dental applications. In the practical part, the dimetacrylate matrix was filled with a mixture of particles of different types and different sizes to achieve the maximum possible packing. Moreover, filler content and the influence of filler on composite material was studied. Hydrolytic stability was also tested on composite materials. The methods used to characterize composite materials were bending test, thermogravimetric analysis (TGA), differential scanning photocalorimetry (DPC), dynamic-mechanical analysis (DMA) and scanning electron microscopy (SEM). Curing of the matrix was characterized by the degree of conversion, the heat of polymerization and the polymerization rate. Furthermore the polymerization shrinkage was measured. The glass transition temperature, the dynamic modulus at 40 °C and 100 °C, the modulus of elasticity, the strength, the critical value of the stress factor and the critical energy release rate were found in the tested samples.
Effect of Structure of FRC and Adhesive on the Bond Strength of Joint between FRC and Particulate Filled Dental Composite
Bystřický, Zdeněk ; Přikryl, Radek (referee) ; Poláček, Petr (advisor)
This bachelor’s thesis investigates how is the strength of adhesive bond between dental FRC (Fiber Reinforced Composite) and adhesive affected by the type of reinforcement of dental FRC and by the type of adhesive. The nature of the fracture was investigated also. The strength of adhesive bond of the experimentally designed samples was measured using universal tensile testing machine in the specially constructed jaws. The nature of the fracture was viewed by the confocal microscope. The obtained results suggest that the strength of adhesive bond is mostly affected by the type of reinforcement of the FRC provided that there is a good wetting on the FRC surface. In this case, interlaminar strength of FRC was the limiting factor. The strength was lower in the case of FRC with multidirectional (spliced) glass fibers. The strength was also affected in a certain manner by the creation of locations where the stress was concentrated. This effect was most notably in the case of adhesives with the high cohesive strength. The impact of aqueous environment on the stability of adhesive joint was most major in the case of the low - crosslinked resins and in the case when the molecules of water penetrates into the interface between materials in consequence of poor wetting.
Hybrid dental composites combining short fibers and particulate fillers
Klieštiková, Nikola ; Přikryl, Radek (referee) ; Bystřický, Zdeněk (advisor)
This work deals with the hybrid composite material combining particulate filler with short fibers for dental applications. The barium micro-filler and the short glass fibers were treated with -methacryloxypropyltrimethoxysilane in cyclohexane using n-propylamine. The barium micro-filler and the short glass fibers were mixed with the matrix based on a dimethacrylate resin. The effects of the addition of short glass fibers on mechanical properties were studied. Surface treatment of the filler was characterized by thermogravimetric analysis (TGA) and diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). Fracture surfaces and the adhesion to the matrix was observed by scanning electron microscope (SEM). The modulus of elasticity and strenght was determined by three point bending flexural test. Critical values of the stress intensity factor annd energy release rate were determined using the three point bending flexural test of notched specimens. The particulate filler increased the flexural modulus of elasticity and fragility. The addition of short fibers had little effect on flexural modulus of elasticity, but increased the flexural strength and fracture toughness of the specimen.
Photopolymerization kinetics of dimethacrylate dental resin
Vaněk, Martin ; Bystřický, Zdeněk (referee) ; Poláček, Petr (advisor)
Aim of magister´s thesis was to study reaction kinetics of dental materials. Thesis was focused on dimethacrylate dental polymers, which are for example used for dental restoration, tooth repair and creating now teeth. First part of the thesis concentrates on influence of molar ratio on reation kinetics by addition of other monomer to polymer resin. Second part concentrates on influence of addition of additive silica on reaction kinetics of polymerization. Essential variables know as a polymerization ratio, conversion, gel point, glass transition temperature and storage modulus were studied. Firstly, polymerization ratio and conversion were observed by differential scanning calorimetry (DSC). Secondly rheology was observed by photoreometr. Finally, glass transition temperature and storage modulus were observed by dynamic mechanical analysis (DMA). Behaviour changes caused by addion of monomer or filler point out decrease of polymeration ratio and converstion. Same behaviour was observed by short exposure. In order to established network formation, values of gel point increased by higher concentration of monomer or filler. Glass transition temperature and storage modulus measured by DMA were evaluated. Those valuables had variable tendency due to monomer acting like filler at higher concentration. Also contradictory impact of different material conversion and filler concetration was discussed.
Hybrid composite based on dental matrix
Almásyová, Zuzana ; Bystřický, Zdeněk (referee) ; Přikryl, Radek (advisor)
This bachelor´s thesis deals with the study of the effect of alumina fillers addition on mechanical properities of experimental composite based dimethacrylate matrix. Important properities and aspects of particle composite, composite mechanics and surface treatments methods were described in the theoretical section of this work. As a studied system was dimethacrylate matrix with micro-filler in form of barium glass and nano-filler in form of alumina. The filler was modified by two silanization methods. Surface treatment of the filler was studied by termogravimetry and infrared spectroscopy. Morphology of fracture areas was examined using scanning electron microscopy with the aim to characterize dispersion of particles in the matrix. Mechanical properties of prepared composite materials were established by the testing of the flexural properties. The best silanization method of particular filler was determined. The addition of alumina had a negative effect on the resulting mechanical properties of prepared composite.
Thermal Stability/Degradation of High Viscosity Dental Resins
Bystřický, Zdeněk ; Trautmann, Radoslav (referee) ; Poláček, Petr (advisor)
This diploma thesis deals with the influence of long term thermal load on the stability of high-viscous resins used for dental composites matrix. The process of polymerization was also investigated in connection with type and ratio of monomer units, mass content of the initiator system and the presence of nanosilica filler. Prepared resins were characterized by differential compensation photocalorimetry (DPC) and dynamic mechanical analysis (DMA). The dependence of the heat flow on time was measured by DPC. Based on the experimental data, the dependence of conversion on time and the dependence of polymerization rate on conversion were determined. Viscoelastic properties of the cured resins were determined by DMA. Experimentally measured data implies that by the influence of elevated temperature both the degree of conversion and the polymerization rate decreased. With a higher content of the initiator system incorporated in resin the decrease was more significant. Therefore, we can conclude that when the resin was exposed to the elevated temperature one of the components of the initiator system was inactivated. For the photopolymerized resins presence of two glass transition temperatures is typical due to the inhomogenous morphology of the cured resin. There are two types of domains with varying relative composition. However, after the degradation only one glass transition temperature was detected. That was caused by reducing the resin viscosity due to the increased temperature. Higher mobility of the initiator system molecules and monomers itself resulted in more homogenous structure of the cured resin. In case of elevated temperature exposed resins more significant decrease of the elastic modulus was observed. The curing process is considerably influenced by the type and ratio of the monomer units and by the presence of filler.
Morphogenesis and Viscoelastic Properties of Dimethacrylate Networks
Bystřický, Zdeněk ; Lehocký, Marián (referee) ; Bradna, Pavel (referee) ; Jančář, Josef (advisor)
Tato dizertační práce se zabývá studiem morfogeneze dimethakrylátových sítí. V práci byly využity zjednodušené systémy založené na monomerech, které bývají typicky využívány jako složky matric pryskyřičných kompozitních materiálů využívaných v oblasti záchovné stomatologie. Kinetika a mechanismy formování polymerních sítí byly studovány především s ohledem na strukturu jednotlivých monomerů, jejich vzájemný molární poměr a koncentraci iniciačního systému využitého pro radikálovou polymeraci. Vypočtené profily konverze funkčních skupin a reakčních rychlostí byly využity jako základ pro pochopení a interpretaci mechanismů morfogeneze sítí a porovnání se známými modely. Dále byla studována kinetika termické degradace, která je s morfologií vytvrzených sítí přímo spjata. V rámci takto charakterizovaných systémů byla stanovena teplotní závislost dynamického modulu a byl popsán vztah mezi supra-molekulární strukturou dimethakrylátových sítí a jejich viskoelastickou odezvou v daném teplotním rozmezí. Kinetika polymerace byla studována pomocí diferenční kompenzační foto-kalorimetrie (DPC) a infračervené spektroskopie (FTIR). Proces termické degradace byl analyzován pomocí termo-gravimetrické analýzy (TGA). Viskoelastické parametry byly charakterizovány pomocí dynamicko-mechanické analýzy (DMA). Reaktivita jednotlivých systémů je přímo odvozena od molekulární struktury monomerů, která ovlivňuje mobilitu reagujících složek v průběhu polymerace. Kinetika polymerace je řízena především difúzí, přičemž její rychlost je dána tuhostí monomerní páteře, koncentrací funkčních skupin a vlivem fyzikálních interakcí. Omezená mobilita rostoucích řetězců, postranních funkčních skupin i samotných monomerů vede k monomolekulární terminaci makro-radikálů a omezení stupně konverze funkčních skupin. Vzhledem k tomu, že k zásadnímu omezení mobility dochází již v počáteční fázi polymerace, tj. v bodu gelace, je případná termodynamická nestabilita vedoucí k fázové separaci polymerujícího systému potlačena a proces kopolymerace je ve své podstatě náhodný. To bylo prokázáno i prostřednictvím identifikace jedné teploty skelného přechodu u charakterizovaných kopolymerů. Heterogenní charakter morfogeneze je spjat s rozdílnou reaktivitou postranních funkčních skupin. V počátečních fázích polymerace dochází k propagaci reakcí postranní funkční skupiny s radikálem na stejném rostoucím řetězci, což vede ke vzniku tzv. primárního cyklu. Pravděpodobnost cyklizace souvisí především s flexibilitou monomerní páteře. Heterogenita polymerace je charakterizována vznikem vnitřně zesítěných struktur, tzv. mikrogelů, a jejich následným spojováním. Tuhost monomeru naopak přispívá k vyšší efektivitě zesítění a více homogenní morfologii vytvrzené sítě. Heterogenita dimethakrylátových sítí se odráží v mechanismu termické degradace, přičemž přítomnost strukturně odlišných domén vede k rozkladu ve dvou krocích. Průběh soufázového modulu a teplota skelného přechodu korelují s tuhostí polymerních sítí, efektivitou zesítění a přítomností fyzikálních interakcí, které vyztužují strukturu sítě nad rámec kovalentního zesítění. Heterogenní morfologie sítí se projevuje rozšiřováním spektra relaxačních časů. Experimentální data jsou v kvalitativní shodě s existujícími numerickými modely popisujícími kinetiku radikálové polymerace multifunkčních monomerů.
Plasma surface modification of powder fillers
Štulrajterová, Lujza ; Bystřický, Zdeněk (referee) ; Přikryl, Radek (advisor)
This bachelor’s thesis deals with the study of particulate-filled composite materials and the influence of filler surface modifications on the properties of the composite. Important aspects of particulate fillers, used fillers and possible surface treatments were characterized in the theoretical section of this work. Dimethacrylate matrix with halloysite nanotubes as filler was chosen as a studied system. The filler was modified by low-temperature plasma under low pressure and by silanization. Surface of the modified filler was studied by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Particle size distribution was measured by photon cross-correlation spectroscopy and dynamic light scattering (DLS). Mechanical properties of prepared particulate composites were established by the testing of the flexural properties. Fracture areas were analyzed by using scanning electron microscopy (SEM). The results showed no effects of the plasma treatment on the mechanical properties. Silane treatment of the filler surface illustrated improvement of the composite material strength.
Optimization of interfaces in filled dental composites
Gavroňová, Ivana ; Bystřický, Zdeněk (referee) ; Přikryl, Radek (advisor)
The bachelor's thesis deals with the particulate composite materials, especially dental composite materials and their properties, production methods and possible adjustments in either the particles themselves as a filler or modification of the interface between the filler and the matrix. In this bachelor's thesis also examines testing properties of particulate composite materials.
Photopolymerization kinetics of dimethacrylate dental resin
Vaněk, Martin ; Bystřický, Zdeněk (referee) ; Poláček, Petr (advisor)
Aim of magister´s thesis was to study reaction kinetics of dental materials. Thesis was focused on dimethacrylate dental polymers, which are for example used for dental restoration, tooth repair and creating now teeth. First part of the thesis concentrates on influence of molar ratio on reation kinetics by addition of other monomer to polymer resin. Second part concentrates on influence of addition of additive silica on reaction kinetics of polymerization. Essential variables know as a polymerization ratio, conversion, gel point, glass transition temperature and storage modulus were studied. Firstly, polymerization ratio and conversion were observed by differential scanning calorimetry (DSC). Secondly rheology was observed by photoreometr. Finally, glass transition temperature and storage modulus were observed by dynamic mechanical analysis (DMA). Behaviour changes caused by addion of monomer or filler point out decrease of polymeration ratio and converstion. Same behaviour was observed by short exposure. In order to established network formation, values of gel point increased by higher concentration of monomer or filler. Glass transition temperature and storage modulus measured by DMA were evaluated. Those valuables had variable tendency due to monomer acting like filler at higher concentration. Also contradictory impact of different material conversion and filler concetration was discussed.

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