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Hybrid Composites Combining Short Deformable Fibers and Particulate Fillers in Polymeric Matrix
Smrčková, Markéta ; Pavelka,, Vladimír (referee) ; Poláček, Petr (advisor)
In this work, the effect of adding short deformable polyvinylalcohol fibers into dimethacrylate resins on mechanical properties of composite materials was investigated. Furthermore, micro- or nano-fillers were added into the matrix. The effect of filler/short fibers combination on mechanical properties of so-called hybrid composites was studied. Composites were characterized by differential compensation photocalorimetry (DPC), termogravimetric (TGA) and dynamic mechanical (DMA) analysis. The fracture surfaces were examined using scanning electron (SEM) and confocal laser (CLSM) microscopy. Elastic modulus and strength, the critical value of stress intensity factor and strain energy release rate and the viscoelastic properties of composite materials were measured. The mechanical properties of composite materials are affected not only by the type of filler/reinforcement, but also by properties of the matrix. These properties also depend on the way of network formation during photo-initiated polymerization. For this reason, heat of polymerization, degree of conversion and the maximum polymerization rate of mixture of dimethacrylate monomers were determined.
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Effect of preparation conditions on the structure and properties of hybrid light curing composites
Škriniarová, Nina ; Ing. Vladimír Pavelka. Ph.D. (referee) ; Jančář, Josef (advisor)
The purpose of this thesis was to implement and evaluate series of experiments focused on the impact of mixing conditions and component dispensing on the structure and properties of hybrid polymer composite materials for resistant dental fillings. There were suggested some preparation methods and subsequently some mechanical properties of prepared samples were measured. Short non-formable polymer fibers in combination with filler particles of various particle sizes were added into the matrix. As matrix a polymer, light curable monomer mixture based on urethandimethacrylate and dodecandioldimethacrylate was used. Tensile deformation curves of prepared samples were measured. Morphology of prepared composites was observed by surface fractography using scanning electron microscopy (SEM). Samples were evaluated by comparing of tensile curves and morphology observed on SEM slides. The best way of component mixing and dispensing was evaluated based on comparison of experiment results and properties predicted by existed models.
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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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Adhesion Strength and Fracture Morphology between FRC Root Canal Post and Particulate Filled Composite Core
Kročová, Blanka ; Pavelka,, Vladimír (referee) ; Poláček, Petr (advisor)
This bachelor thesis examines the influence of composition and structure of the dental pin on its mechanical properties. It deals with the adhesion strength and fracture morphology of adhesive joints between composite, fiber stiffened root pin (FRC) and a core of particle composite. There is observed adhesive strength dependence on the diameter of the pin FRC, the fiber content of the pin and the use of the composite particle in which the pin is embedded. Shear, adhesive joint strength was measured using a universal testing instrument with specially-made jaws. Fracture morphology was analyzed by the scanning electron microscope (SEM). Obtained data shows that the shear strength of adhesive joints for the used materials is most affected by the quality of wetting the surface of the FRC. Effect on the results could be stress distribution in adhesive strength measurements because the used jaws were not in an ideal proportion for all diameters of the samples. In another part of thesis the samples of dental pins were tested in three point bending. For the study of fracture analysis, selected samples were tested by impact in bending and test was captured with high-speed camera. With the dental pin composed of more FRC posts with a smaller diameter at the same time there is not so extensive the quarry, as in the case of using the post with a large diameter. Character of a fracture in a compound dental pin is also influenced by the type of connecting material and quality of adhesion between the material and individual posts.
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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.
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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.
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Short Fibers Reinforced Particulate Filled Composites
Kročová, Blanka ; Pavelka, Vladimír (referee) ; Poláček, Petr (advisor)
This diploma thesis examines the effect of short fiber reinforcement in particle composite with a polymer matrix and the effect of its structure on the mechanical properties. It studies the refraction toughness depending on the addition of short polyvinylalcohol fibers (PVAL), nanosilica and pulverized polymethylacrylate (PMMA) to a dimethylacrylate matrix. Matrix strengthening was characterised with the help of differential compensation photocalorimetry. The inner structure of the composite and the morphology of fracture were studied using a scanning electron microscope. For the tested samples, the modules of elasticity and toughness were measured, the critical values of stress intensity factor and the energy release rate were determined. The findings suggest that the limit value of short fibers content is 4 vol. %. This content of fibers significantly increases the tenacity of the material but at the same time the uniform distribution of fibers and the ease of preparation of the material decrease. Within the possible applications, the manipulation of this material worsens as well. The fibers content of 2 ± 0.5 vol. % is an acceptable compromise between good treatability, uniform distribution of fibers and the required mechanical properties. During the study of the fracture surfaces of the material, different types of fibers disruption were witnessed (extraction from the matrix, plastic deformation, fibrillation on the surface of the fibers, fracture) depending on the type of used matrix and filling.
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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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Dental materials and imunne reaction
Chrástová, Iveta ; Bártová, Jiřina (advisor) ; Prokešová, Ludmila (referee)
Adverse reactions to metals is relatively frequent in sensitive individuals, and may lead to the development of various diseases, such as lichen planus and lichenoid reaction and was also described effect of amalgam to the pathology of autoimmune diseases. In sensitive patients with known reactions to metals leads to atrophy of the oral mucosa and discomfort (burning, cutting, excessive salivation). Adverse effects of dental materials are described as an allergic reaction type IV delayed hypersensitivity. It disrupt the immune system, increased vascular permeability, tissue is often damaged by chronic inflammation and it is also activated antigen- nonspecific component of immunity. Monocytes are the key cells of the immune system, which act as antigen presenting cells, in particular after conversion in the tissues into macrophages are directly involved in the activation of immune responses and their stimulation is therefore crucial for the development of adverse reactions to dental materials. In the thesis was measured cytokine production by monocytes after stimulation with metal salts. To determine the extent of the patients' responses to the metals was used lymphocyte proliferation assay (MELISA® ), which was developed and patented in Sweden. We compared lymphocyte proliferation after stimulation...
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