Rigid Rod Polymer Fillers in Acrylic Denture and Dental Adhesive Resin Systems

Polymeric materials have been used in dental applications for decades. Adhesion of polymeric materials to each other and to the tooth substrate is essential to their successful use. The aim of this series of studies was two-folded. First, to improve adhesion of poly(paraphenylene) based rigid rod polymer (RRP) to other dental polymers, and secondly, to evaluate the usability of a new dentin primer system based on RRP fillers. Poly(paraphenylene) based RRP would be a tempting material for dental applications because of its good mechanical properties. To be used in dental applications, reliable adhesion between RRP and other dental polymers is required. In this series of studies, the adhesion of RRP to denture base polymer and the mechanical properties of RRP-denture base polymer-material combination were evaluated. Also adhesion of BisGMA-TEGDMA-resin to RRP was determined. Different surface treatments were tested to improve the adhesion of BisGMA-TEGDMA-resin to RRP. Results were based on three-point bending testing, Vickers surface hardness test and scanning electron microscope analysis (SEM), which showed that no reliable adhesion between RRP and denture base polymer was formed. Addition of RRP filler to denture base polymer increased surface hardness and flexural modulus but flexural strength decreased. Results from the shear bond strength test and SEM revealed that adhesion between resin and RRP was possible to improve by surface treatment with dichloromethane (DCM) based primer and a new kind of adhesive surface can be designed. The current dentin bonding agents have good immediate bond strength, but in long term the bond strength may decrease due to the detrimental effect of water and perhaps by matrix metalloproteinases. This leads to problems in longevity of restorations. Current bonding agents use organic monomers. In this series of studies, RRP filled dentin primer was tested in order to decrease the water sorption of the monomer system of the primers. The properties of new dentin primer system were evaluated in vitro by comparing it to commercial etch and rinse adhesive system. The results from the contact angle measurements and SEM showed that experimental primer with RRP reinforcement provided similar resin infiltration to dentin collagen and formed the resin-dentin interface as the control primer. Microtensile bond strength test and SEM revealed that in short term water storing, RRP increased bond strength and primer with BMEP-monomer (bis[2-(methacryloyloxy)-ethyl]phosphate) and high solvent concentration provided comparable bonding properties to the commercial control primers. In long term water storing, the high solvent-monomer concentration of the experimental primers decreased bond strength. However, in low solvent-monomer concentration groups, the long-term water storing did not decrease the bond strength despite the existence of hydrophilic monomers which were used in the system. These studies demonstrated that new dentin primer system reached the mechanical properties of current traditional etch and rinse adhesive system in short time water storing. Improved properties can be achieved by further modifications of the monomer system. Studies of the adhesion of RRP to other polymers suggest that adhesion between RRP and other dental polymers is possible to obtain by certain surface treatments.

Purification and fractionation by nanotiltration in dairy and sugar and sweetener industry applications

Nanotiltration is a membrane separation method known for its special characteristic of rejecting multivalent ions and passing monovalent ions. Thus, it is commonly applied with dilute aqueous solutions in partial salt removal, like in drinking water production. The possibilities of nanofiltration have been studied and the technique applied in a wide branch of industries, e.g. the pulp and paper, the textile and the chemical processing industry. However, most present applications and most of the potential applications studied involve dilute solutions, the permeating stream being generally water containing monovalent salts. In this study nanotiltration is investigated more as a fractionation method. A well-known application in the dairy industry is concentration and partial salt removal from whey. Concentration and partial demineralization is beneficial for futher processing of whey as whey concentrates are used e.g. in baby foods. In the experiments of this study nanotiltration effectively reduced the monovalent salts in the whey concentrate. The main concern in this application is lactose leakage into the permeate. With the nanofiltration membranes used the lactose retentions were practically ? 99%. Another dairy application studied was the purification and reuse of cleaning solutions. This is an environmentally driven application. An 80% COD reduction by nanofiltration was observed for alkaline cleaning-in-place solution. Nanofiltration is not as commonly applied in the sugar and sweeteners industry as in the dairy industry. In this study one potential application was investigated, namely xylose purification from hemicellulose hydrolyzate. Xylose is raw material for xylitol production. Xylose separation from glucose was initially studied with xylose-glucose model solutions. The ability of nanofiltration to partially separate xylose into the permeate from rather concentrated xylose-glucose solutions (10 w-% and 30 w-%) became evident. The difference in size between xylose and glucose molecules according to any size measure is small, e.g. the Stokes diameter of glucose is 0.73 nm compared to 0.65 nm for xylose. In further experiments, xylose was purified into nanoliltration permeate from a hemicellulose hydrolyzate solution. The xylose content in the total solids was increased by 1.4—1.7 fold depending on temperature, pressure and feed composition.

The Influence of Certain Processing Factors on the Durability of Yttrium Stabilized Zirconia Used As Dental Biomaterial

In dentistry, yttrium partially stabilized zirconia (ZrO2) has become one of the most attractive ceramic materials for prosthetic applications. The aim of this series of studies was to evaluate whether certain treatments used in the manufacturing process, such as sintering time, color shading or heat treatment of zirconia affect the material properties. Another aim was to evaluate the load-bearing capacity and marginal fit of manually copy-milled custom-made versus prefabricated commercially available zirconia implant abutments. Mechanical properties such as flexural strength and surface microhardness were determined for green-stage milled and sintered yttrium partially stabilized zirconia after different sintering time, coloring process and heat treatments. Scanning electron microscope (SEM) was used for analyzing the possible changes in surface structure of zirconia material after reduced sintering time, coloring and heat treatments. Possible phase change from the tetragonal to the monoclinic phase was evaluated by X-ray diffraction analysis (XRD). The load-bearing capacity of different implant abutments was measured and the fit between abutment and implant replica was examined with SEM. The results of these studies showed that the shorter sintering time or the thermocycling did not affect the strength or surface microhardness of zirconia. Coloring of zirconia decreased strength compared to un-colored control zirconia, and some of the colored zirconia specimens also showed a decrease in surface microhardness. Coloring also affected the dimensions of zirconia. Significantly decreased shrinkage was found for colored zirconia specimens during sintering. Heat treatment of zirconia did not seem to affect materials’ mechanical properties but when a thin coating of wash and glaze porcelain was fired on the tensile side of the disc the flexural strength decreased significantly. Furthermore, it was found that thermocycling increased the monoclinic phase on the surface of the zirconia. Color shading or heat treatment did not seem to affect phase transformation but small monoclinic peaks were detected on the surface of the heat treated specimens with a thin coating of wash and glaze porcelain on the opposite side. Custom-made zirconia abutments showed comparable load-bearing capacity to the prefabricated commercially available zirconia abutments. However, the fit of the custom-made abutments was less satisfactory than that of the commercially available abutments. These studies suggest that zirconia is a durable material and other treatments than color shading used in the manufacturing process of zirconia bulk material does not affect the material’s strength. The decrease in strength and dimensional changes after color shading needs to be taken into account when fabricating zirconia substructures for fixed dental prostheses. Manually copy-milled custom-made abutments have acceptable load-bearing capacity but the marginal accuracy has to be evaluated carefully.

Airway surgery for obstructive sleep apnea and partial upper airway obstruction during sleep

This study analyzed the feasibility and efficacy of surgical therapies in patients with sleep-disordered breathing ranging from partial upper airway obstruction during sleep to severe obstructive sleep apnea syndrome. The surgical procedures evaluated were tracheostomy, laser-assisted uvulopalatoplasty (LUPP) and uvulopalatopharyngoplasty (UPPP) with laser or ultrasound scalpel. Obstructive sleep apnea and partial upper airway obstruction during sleep were measured with the static charge-sensitive bed (SCSB) and pulse oximeter. The patients with severe obstructive sleep apnea syndrome were treated with tracheostomy. Palatal surgery was performed only if the upper airway narrowing occurred exclusively at the soft palate level in patients with partial upper airway obstruction during sleep. The ultrasound scalpel technique was compared to laser-assisted UPPP. The efficacy of LUPP to reduce partial upper airway obstruction during sleep was assessed and histology of uvulopalatal specimen was compared to body fat distributional parameters and sleep study findings. Tracheostomy was effective therapy in severe obstructive sleep apnea. Partial upper airway obstruction and arterial oxyhemoglobin desaturation index during sleep decreased significantly after LUPP. The minimal retropalatal airway dimension increased and soft palate collapsibility decreased at the level where the velopharyngeal obstruction had occurred before the surgery. Ultrasound scalpel did not offer any significant benefits over the laser-assisted technique, except fewer postoperative haemorrhage events. The loose connective tissue as a manifestation of edema was the only histological finding showing correlation with partial upper airway obstruction parameters of SCSB. Tracheostomy remains a life-saving therapy and also long-term option when adherence to CPAP fails in patients with obstructive sleep apnea syndrome. LUPP effectively reduces partial upper airway obstruction during sleep provided that obstruction at the other levels than the soft palate and uvula were preoperatively excluded. Technically the ultrasound scalpel or laser surgeries are equal. In patients with partial upper airway obstruction the loose connective tissue is more important than fat accumulation in the soft palate. This supports the hypothesis that edema is a primary trigger for aggravation of upper airway narrowing during sleep at the soft palate level and evolution towards partial or complete upper airway obstruction during sleep.

Use of fiber-reinforced composite framework and thermochromic pigment in maxillofacial prostheses

The purpose of this investigation was to evaluate the possibility to enhance certain qualities of facial prostheses. Polymethyl methacrylate is still being used as base mate¬rial or clip carrier material, but it is hard and heavy, and debonding of the silicone from the acrylic base material is a frequent problem. This thesis aims to evaluate the use of fiber-reinforced composite (FRC) as framework material for maxillofacial silicone prostheses. FRC has been used as reinforcement in removable and fixed partial dentures since the 1990s. This material is lightweight and can be fabricated to compress the margins of the prosthesis slightly, to keep it tightly against the skin during jaw movements and facial expressions. Additionally, the use of a thermochromic pigment, colorless in room temperature and red in a cold environment, was studied in order to evaluate the possibility of using this color changing pigment in facial prostheses to mimic the color change of facial skin in cold weather. The tensile bond strength between pre-impregnated, unidirectional FRC and maxillofacial silicone elastomer was studied. Three different bonding agents or primers were compared. Bond strength was improved by one of the primers and by roughening the surface. The effect of a skin compressing glass fiber-reinforced composite framework on facial skin blood flow was studied by using a face mask, constructed with a compression pad corresponding to the outer margin of a glass fiber-reinforced framework beam of a facial prosthesis. The skin blood flow of ten healthy volunteers, aged 23-25 years, was measured during touch, light, and moderate compression of the skin, by using laser Doppler imaging technique. None of the compressions showed any marked effects on local skin blood flow. There were no significant differences between blood flow during compression and at baseline. Maxillofacial silicone elastomer was colored intrinsically with conventional color pigments: a control group containing only conventional pigments was compared to two test groups with 0.2 wt% and 0.6 wt% thermochromic pigment added. The color of the material was measured with a spectrophotometer in room temperature and after storage in a freezer. The color stability of the maxillofacial silicone elastomer colored with thermo¬chromic pigment was evaluated by artificial aging. The color dif¬ference of the L* (lightness) and a* values (redness), comparing color after the samples were stored at room temperature and in a freezer (-19°C), was statistically significant for both 0.2 wt% and 0.6 wt% thermo¬chromic pigment groups. The differences in the b* values (yellowness) were statistically significant for the 0.6 wt% group. Exposure to ultraviolet (UV) radiation led to visually noticeable and statistically signifi¬cant color changes (ΔE) in all color values in both test groups. The specimens containing thermochromic pigment were very sensitive to UV radiation. In conclusion, a framework of fiber-reinforced composite can successfully be bonded to maxillofacial silicone elastomer, and a framework beam, compressing the facial skin, did not remarkably alter the skin blood flow on healthy, young adults. The thermochromic pigment showed color change in maxillofacial silicone elastomer. However, artificial aging showed that it was too sensitive to UV radiation to be used, as such, in maxillofacial prostheses.

Susteinable steelmaking by process integration

Environmental issues, including global warming, have been serious challenges realized worldwide, and they have become particularly important for the iron and steel manufacturers during the last decades. Many sites has been shut down in developed countries due to environmental regulation and pollution prevention while a large number of production plants have been established in developing countries which has changed the economy of this business. Sustainable development is a concept, which today affects economic growth, environmental protection, and social progress in setting up the basis for future ecosystem. A sustainable headway may attempt to preserve natural resources, recycle and reuse materials, prevent pollution, enhance yield and increase profitability. To achieve these objectives numerous alternatives should be examined in the sustainable process design. Conventional engineering work cannot address all of these substitutes effectively and efficiently to find an optimal route of processing. A systematic framework is needed as a tool to guide designers to make decisions based on overall concepts of the system, identifying the key bottlenecks and opportunities, which lead to an optimal design and operation of the systems. Since the 1980s, researchers have made big efforts to develop tools for what today is referred to as Process Integration. Advanced mathematics has been used in simulation models to evaluate various available alternatives considering physical, economic and environmental constraints. Improvements on feed material and operation, competitive energy market, environmental restrictions and the role of Nordic steelworks as energy supplier (electricity and district heat) make a great motivation behind integration among industries toward more sustainable operation, which could increase the overall energy efficiency and decrease environmental impacts. In this study, through different steps a model is developed for primary steelmaking, with the Finnish steel sector as a reference, to evaluate future operation concepts of a steelmaking site regarding sustainability. The research started by potential study on increasing energy efficiency and carbon dioxide reduction due to integration of steelworks with chemical plants for possible utilization of available off-gases in the system as chemical products. These off-gases from blast furnace, basic oxygen furnace and coke oven furnace are mainly contained of carbon monoxide, carbon dioxide, hydrogen, nitrogen and partially methane (in coke oven gas) and have proportionally low heating value but are currently used as fuel within these industries. Nonlinear optimization technique is used to assess integration with methanol plant under novel blast furnace technologies and (partially) substitution of coal with other reducing agents and fuels such as heavy oil, natural gas and biomass in the system. Technical aspect of integration and its effect on blast furnace operation regardless of capital expenditure of new operational units are studied to evaluate feasibility of the idea behind the research. Later on the concept of polygeneration system added and a superstructure generated with alternative routes for off-gases pretreatment and further utilization on a polygeneration system producing electricity, district heat and methanol. (Vacuum) pressure swing adsorption, membrane technology and chemical absorption for gas separation; partial oxidation, carbon dioxide and steam methane reforming for methane gasification; gas and liquid phase methanol synthesis are the main alternative process units considered in the superstructure. Due to high degree of integration in process synthesis, and optimization techniques, equation oriented modeling is chosen as an alternative and effective strategy to previous sequential modelling for process analysis to investigate suggested superstructure. A mixed integer nonlinear programming is developed to study behavior of the integrated system under different economic and environmental scenarios. Net present value and specific carbon dioxide emission is taken to compare economic and environmental aspects of integrated system respectively for different fuel systems, alternative blast furnace reductants, implementation of new blast furnace technologies, and carbon dioxide emission penalties. Sensitivity analysis, carbon distribution and the effect of external seasonal energy demand is investigated with different optimization techniques. This tool can provide useful information concerning techno-environmental and economic aspects for decision-making and estimate optimal operational condition of current and future primary steelmaking under alternative scenarios. The results of the work have demonstrated that it is possible in the future to develop steelmaking towards more sustainable operation.

Fiber-reinforced composite fixed dental prostheses: Studies of the materials used as pontics

Fiber-reinforced composite fixed dental prostheses – Studies of the materials used as pontics University of Turku, Faculty of Medicine, Institute of Dentistry, Department of Biomaterials Science, Finnish Doctoral Program in Oral Sciences – FINDOS, Annales Universitatis Turkuensis, Turku, Finland 2015 Fiber-reinforced composites (FRC), a non-metallic biomaterial, represent a suitable alternative in prosthetic dentistry when used as a component of fixed dental prostheses (FDPs). Some drawbacks have been identified in the clinical performance of FRC restorations, such as delamination of the veneering material and fracture of the pontic. Therefore, the current series of studies were performed to investigate the possibilities of enhancing the mechanical and physical properties of FRC FDPs by improving the materials used as pontics, to then heighten their longevity. Four experiments showed the importance of the pontic design and surface treatment in the performance of FRC FDPs. In the first, the load-bearing capacities of inlay-retained FRC FDPs with pontics of various materials and thicknesses were evaluated. Three different pontic materials were assessed with different FRC framework vertical positioning. Thicker pontics showed increased load-bearing capacities, especially ceramic pontics. A second study was completed investigating the influence of the chemical conditioning of the ridge-lap surface of acrylic resin denture teeth on their bonding to a composite resin. Increased shear bond strength demonstrated the positive influence of the pretreatment of the acrylic surfaces, indicating dissolution of the denture surfaces, and suggesting potential penetration of the monomer systems into the surface of denture teeth. A third study analyzed the penetration depth of different monomer systems on the acrylic resin denture teeth surfaces. The possibility of establishing a durable bond between acrylic pontics and FRC frameworks was demonstrated by the ability of monomers to penetrate the surface of acrylic resin denture teeth, measured by a confocal scanning type microscope. A fourth study was designed to evaluate the load-bearing capacities of FRC FDPs using the findings of the previous three studies. In this case, the performance of pre-shaped acrylic resin denture teeth used as pontics with different composite resins as filling materials was evaluated. The filling material influenced the load-bearing capacities, providing more durable FRC FDPs. It can be concluded that the mechanical and physical properties of FRC FDPs can be improved as has been shown in the development of this thesis. The improvements reported then might provide long lasting prosthetic solutions of this kind, positioning them as potentially permanent rehabilitation treatments. Key words: fiber-reinforced composite, fixed dental prostheses, inlay-retained bridges, adhesion, acrylic resin denture teeth, dental material.