Application of sintered titanium alloys to metal denture bases: a study of titanium powder sheets for complete denture base.
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The purpose of this study was the fabrication of titanium powder sheets to enable the application of sintered titanium alloys as metal denture bases. The effects of titanium particle shape and size, binder content, and plasticizer content on the surface smoothness, tensile strength and elongation of titanium powder sheets was investigated. To select a suitable ratio of powdered metal contents for application as a metal denture base, the effects of aluminum content in Ti sheets and various other powder metal contents in Ti-Al sheets on the density, sintering shrinkage, and bending strength were evaluated. Based on the results of the above experiments, we developed a mixed powder sheet composed of 83Ti-7Al-10Cr with TA45 titanium powder (atomized, -45 microm), and 8 mass% binder content. This titanium alloy sheet had good formability and ductility. Its sintered titanium alloy had a density of 3.2 g/cm3, sintering shrinkage of 3.8%, and bending strength of 403 MPa. The titanium alloy sheet is clinically acceptable for fabricating denture bases. (+info)
Changing paradigms in implant dentistry.
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This review focuses on five paradigms of implant dentistry which have undergone considerable modifications in recent years. An attempt was made to select and include all the relevant citations of the past 10 years. These five paradigms document the debate in the clinical and scientific community and include the aspects of (1) smooth vs. rough implant surfaces, (2) submerged vs. non-submerged implant installation techniques, (3) mixed tooth-implant vs. solely implant-supported reconstructions, (4) morse-taper abutment fixation vs. butt-joint interfaces, and (5) titanium abutments vs. esthetic abutments in clinical situations where esthetics is of primary concern. (+info)
Stent coating with titanium-nitride-oxide for reduction of neointimal hyperplasia.
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BACKGROUND: Coronary stents prevent constrictive arterial remodeling but stimulate neointimal hyperplasia. Stainless steel induces a metallic foreign body reaction, which is absent for titanium. The hypothesis of the present study was that titanium renders the stent surface biologically inert, with reduced platelet and fibrinogen binding. METHODS AND RESULTS: Twelve pigs were instrumented with a stainless steel and 2 titanium-nitride-oxide-coated stents (TiNOX 1, ceramic; TiNOX 2, metallic). Animals were restudied after 6 weeks. Histological specimens of stented segments were analyzed by digital morphometry. Platelet adhesion and fibrinogen binding studies were performed in the perfusion chamber. Under in vitro conditions, TiNOX 1 showed reduced platelet adhesion (65+/-3%) compared with TiNOX 2 (72+/-5%; P<0.05) and stainless steel (71+/-4%; P<0.05). Platelet adhesion 48 hours after incubation with human plasma, however, was not different between TiNOX 1 (17+/-3%) and 2 (15+/-3%) but was significantly higher with stainless steel (23+/-2%; P<0.05). Fibrinogen binding was significantly reduced with TiNOX 2 (54+/-3%) compared with TiNOX 1 (82+/-4%, P<0.05) or stainless steel (100%, P<0.05). Histomorphometry revealed a significantly larger neointimal area in stainless steel (2.61+/-1.12 mm(2)) than in TiNOX 1-coated (1.47+/-0.84 mm(2), P<0.02) or TiNOX 2-coated (1.39+/-0.93 mm(2), P<0.02) stents. The reductions were 44% and 47%, respectively. CONCLUSIONS: TiNOX coating significantly reduces neointimal hyperplasia in stainless steel stents. The antiproliferative effect was similar for both TiNOX coatings, suggesting that the electrochemical properties are more important for attenuation of neointimal proliferation than the observed differences in platelet adhesion and fibrinogen binding. (+info)
Cold crucible levitation melting of biomedical Ti-30 wt%Ta alloy.
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Recently, titanium-tantalum alloys have been studied as implant materials for dental and orthopedic surgery. However, titanium and tantalum are difficult to mix by common arc melting and induction melting, because of their high melting point and the marked difference between their densities (Ti: 1,680 degrees C, 4.5 g/cm3, Ta: 2,990 degrees C, 16.6 g/cm3). Thus, the Cold Crucible Levitation Melting (CCLM) method was chosen to produce a Ti-30 wt%Ta binary alloy in the present study. The CCLM furnace, with 1 kg capacity, consisted of a water-cooled crucible comprising oxygen-free high purity copper segments and coils wrapped around the crucible and connected to a frequency inverter power supply. A qualified ingot of 1.0 kg of Ti-30 wt%Ta alloy was obtained. The ingot was characterized from the surface quality, chemical composition distribution and microstructure, and finally the melting process was discussed. (+info)
History dependence of protein adsorption kinetics.
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The behavior of proteins at biological and synthetic interfaces is often characterized by a strong history dependence caused by long relaxation times or irreversible transitions. In this work, we introduce the rate of adsorption as a means to systematically quantify the extent, and identify the underlying causes, of history dependence. We use multistep kinetic experiments in which the i'th step is an exposure of a Si(Ti)O(2) surface to a flowing fibronectin or cytochrome c solution of concentration c(i) for a time t(i) (c(i) = 0 corresponds to a rinse) and measure the protein adsorption by optical waveguide light mode spectroscopy. The rate of adsorption is sensitive to the structure of the adsorbed layer, and we observe it to greatly increase, for a given adsorbed density, when going from a first to a subsequent adsorption step. This increase is most pronounced when the duration of the initial adsorption step is long. We attribute these observations to the gradual and irreversible formation of protein clusters or locally ordered structures and use them to explain previous underestimates of kinetic data by mesoscopic model descriptions. A thorough understanding of these complex postadsorption events, and their impact on history dependence, is essential for many physiological and biotechnological processes. Optical waveguide lightmode spectroscopy is a promising technique for their macroscopic quantification. (+info)
Agglomerates of ultrafine particles of elemental carbon and TiO2 induce generation of lipid mediators in alveolar macrophages.
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Agglomerates of ultrafine particles (AUFPs) may cause adverse health effects because of their large surface area. To evaluate physiologic responses of immune cells, we studied whether agglomerates of 77-nm elemental carbon [(EC); specific surface area 750 m2/g] and 21 nm titanium dioxide (TiO(2) particles (specific surface area 50 m(2)/g) affect the release of lipid mediators by alveolar macrophages (AMs). After 60-min incubation with 1 microg/mL AUFP-EC (corresponding to 7.5 cm(2) particle surface area), canine AMs (1 x 10(6) cells/mL) released arachidonic acid (AA) and the cyclooxygenase (COX) products prostaglandin E(2) (PGE(2), thromboxane B(2), and 12-hydroxyheptadecatrienoic acid but not 5-lipoxygenase (5-LO) products. AUFP-TiO(2) with a 10-fold higher mass (10 microg/mL) than AUFP-EC, but a similar particle surface area (5 cm(2) also induced AMs to release AA and COX products. Agglomerates of 250 nm TiO(2) particles (specific surface area 6.5 m(2)/g) at 100 microg/mL mass concentration (particle surface area 6.5 cm(2) showed the same response. Interestingly, 75 cm(2)/mL surface area of AUFP-EC and 16 cm(2)/mL surface area of AUFP-TiO(2) additionally induced the release of the 5-LO products leukotriene B(4) and 5-hydroxyeicosatetraenoic acid. Respiratory burst activity of stimulated canine neutrophils was partially suppressed by supernatants of AMs treated with various mass concentrations of the three types of particles. Inhibition of neutrophil activity was abolished by supernatants of AMs treated with COX inhibitors prior to AUFP-incubation. This indicates that anti-inflammatory properties of PGE(2) dominate the overall response of lipid mediators released by AUFP-affected AMs. In conclusion, our data indicate that surface area rather than mass concentration determines the effect of AUFPs, and that activation of phospholipase A(subscript)2(/subscript) and COX pathway occurs at a lower particle surface area than that of 5-LO-pathway. We hypothesize a protective role of PGE(2) in downregulating potential inflammatory reactions induced by ultrafine particles. (+info)
The effect of zigzag elastics in the treatment of Class II division 1 malocclusion subjects with hypo- and hyperdivergent growth patterns. A pilot study.
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The aim of this study was to investigate the effect of zigzag elastics in the treatment of Class II division 1 malocclusion subjects with hypo- or hyperdivergent growth patterns. Two groups were established, each consisting of 10 subjects classified as hypo- or hyperdivergent according to their pre-treatment SN-GoGn angle. The cephalometric radiographs taken before and after an elastic application period of approximately 4 months were used to generate 22 variables. In both groups, there were no statistically significant differences in the vertical position of the lower molars, the SN-GoGn angle or the inclination of the lower incisors, whereas the sagittal skeletal relationship was improved as a result of an increase in the SNB angle and the mandibular length (P < 0.01). Upper incisor extrusion was statistically significant in both groups (P < 0.05). The downward rotation of the occlusal plane and the increase in overbite were found to be significant in the hypodivergent group (P < 0.05). Significant differences were observed between the groups in the extrusion of the upper incisor, the inclination of the occlusal plane, and the amount of overbite (P < 0.05). The results show that the zigzag elastic system is preferable, especially in hyperdivergent Class II division 1 subjects, as the use of such elastics does not cause an unfavourable effect on vertical jaw base relationship. (+info)
Intramolecular capture of pummerer reaction intermediates by an aromatic nucleophile: selective construction of 1,4-benzothiazine and indole ring systems.
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The simple alkyl sulfoxide 6 carrying two aromatic nucleophiles, when treated with trifluoroacetic anhydride at room temperature (Pummerer reaction conditions), underwent an intramolecular aromatic sulfenylation of the 6-exo-tet process in an exclusive manner to yield two regioisomeric 1,4-benzothiazine derivatives, 8 and 9. On the other hand, a similar reaction of the alpha-acyl sulfoxide 7, possessing identical aromatic nucleophiles, caused an intramolecular aromatic alkylation of the 5-exo-trig process to produce the 3-oxo-indole derivative 14 in a quantitative yield. These results demonstrate that the construction of 1,4-benzothiazine and indole ring systems can be achieved in a selective manner by proper choice of the sulfoxide side chain. (+info)