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PubMed1983

The chloride corrosion behaviour of four orthodontic wires.

Potentiodynamic cyclic polarization of four orthodontic alloys (wires), namely Permachrome, Elgiloy, a beta-titanium alloy and Nitinol in a 1% NaCl solution within -500 mV and +300 mV (SCE) indicated the first three alloys to be passive whereas breakdown of passivity was observed on Nitinol. The SEM examination of the pre- and post-polarized alloy surfaces provided evidence which was consistent with the electrochemical measurements, in that the first three alloys exhibited no appreciable corrosion damage whereas pitting corrosion was observed on Nitinol. The results obtained from X-ray analysis of the pitted surface indicated that this pitting could be due to selective dissolution of nickel from Nitinol.

Chemical Phenomena↗
PubMed1980

Electron microprobe analysis of zinc incorporation into rumen protozoa.

With the aid of electron microprobe analysis on ciliate spreads, we detected zinc in ciliates and its accumulation in the endoplasm. A correlation was found between the amount of zinc accumulation and its concentration in the medium. By the same microprobe analysis of of ultrathin sections, we determined semiquantitatively the zinc accumulation in the intracytoplasmic granules and its presence in macronuclei and in intra- and extracellular bacteria.

Animals↗
PubMed2001

Mobilization of selenite by Ralstonia metallidurans CH34.

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.

Absorptiometry, Photon↗
PubMed1995

Electron spectroscopic imaging of encapsidated DNA in vaccinia virus.

We have used electron spectroscopic imaging to locate the phosphorus in vaccinia DNA in situ in unstained, ultrathin sections of virions. The phosphorus of the DNA backbone appeared to form a halo on the core periphery surrounding a phosphorus-impoverished central element. These results constrain models for how DNA could be packaged into mature vaccinia particles.

DNA, Viral↗
PubMed1984

Hydrolytic degradation of dental composites.

The leakage of filler elements from four composites after storage in water was investigated by use of atomic absorption spectrophotometry. The results confirmed previous findings that leaching of silicon from different composites is strongly dependent on filler composition. Consideration of the total filler surface of each composite material indicated that quartz as well as pyrolytic silica-containing composites leached less silicon than did composites containing fillers of strontium and/or barium glasses. A correlation between leakage and crack formation in the matrix appeared to exist for all composites except for the microfilled resin. These cracks were explained as a result of osmotic pressure built up at the matrix-filler interface due to hydrolytic degradation of the filler. Of the investigated materials, the microfilled resin was found to be the most stable material in a wet environment with respect to crack formation. This finding was explained by filler composition, filler form, and the specific structure of the microfilled resin.

Aluminum↗
PubMed1985

Microstructures of duplex (beta + gamma) silver-tin alloys.

The microstructures of (beta + gamma) silver-tin alloys are especially influenced by both homogenization temperature and subsequent heat treatment. When the alloy is cooled from homogenization temperatures above approximately 200 degrees C, lenticular regions of the ordered orthorhombic gamma phase precipitate from within the disordered h.c.p. beta phase on three structurally equivalent planes, (1210), (1120), and (2110), to form a Widmanstatten structure. When the duplex alloys were homogenized at temperatures below approximately 200 degrees C, where the beta/(beta + gamma) phase boundary is vertical, these structures were not observed.

Chemical Phenomena↗
PubMed1998

Surface chemistry of a high-copper dental amalgam.

In amalgam, mercury is intended to take the form of stable intermetallic compounds. Any mercury leakage must therefore come from free mercury not involved in such compounds. Thus, a knowledge of the exact surface chemistry of dental amalgam is necessary if this phenomenon is to be understood. From XPS and EDS analyses, a model of the surface chemistry of amalgam is proposed which fully characterizes all the phases that are present. The data show the surface to have a composition different from that of the bulk, being comprised of a hydrocarbon deposit and adsorbed water covering the intermetallic phase gamma2 (Sn(6-8)Hg), tin (iv) oxide, and mercury in a free state. After amalgamation, the amount of mercury at the surface decreases with time and eventually attains a constant concentration, where it is all involved in the gamma2 phase, leaving no free mercury. A model is proposed for the surface of amalgam and the changes in this model with time.

Copper↗
PubMed1992

[Concentration and form of asbestos fibers in tap drinking water contaminated from a water supply pipe with asbestos-cement].

The identification and concentration of asbestos fibers in tap drinking water supplied in a central area of Akita Prefecture, Japan, were determined by phase-contrast microscopy and a scanning electron microscope equipped with an energy-dispersive X-ray microanalyzer. The following results were obtained. 1. Asbestos fibers were found in the tap water from two areas in which an asbestos-cement pipe was used for public water supply. The concentrations of asbestos fibers in the tap water were 2.7 x 10(4) to 27.0 x 10(4) fibers per liter of water in area A and 10.0 x 10(4) to 21.0 x 10(4) in area B. On the other hand, no asbestos fiber contamination was observed in tap water of area C, which shared a common water source with area A. A vinyl chloride pipe was used over the entire length of the water supply in route C. 2. Crocidolite was the predominant type of asbestos fiber detected in the tap water. Chrysotile and a mixture of chrysotile and amosite were also observed. 3. Almost all asbestos fibers detected in the tap water possessed the form of thick or sheaved fibers with lengths ranging from ca. 5 to 10 microns. Their shapes were very different from those of asbestos fibers found in the atmosphere. The typical form of the latter is short (ca. 1 micron in length) and needle-like. 4. It was suggested that the contamination of asbestos fibers in the tap water was caused by erosion and peeling off of the inner wall of the asbestos-cement pipe used as a conduit. In order to evaluate the safety of drinking water in Japan, an extensive survey on asbestos-fiber contamination in tap water is necessary.

Asbestos↗
PubMed2002

Changes of element ratios of cultured cells from dune reed under adverse environmental conditions.

Dune reed, as an ecotype of reed plant (Phragmites communis Trin.), is an ideal material for studies on the adaptations of plant to environmental conditions. Scanning electron microscope, energy-dispersive X-ray analysis, and plant tissue culture techniques were used to investigate the effect of extreme temperature, salt, and polyethylene glycol-induced osmotic stress on the intracellular elements K, Na, Ca, and Cl in cultured cells from dune reed and swamp reed (as control). The results indicated that the percentages of the studied elements in dune reed cells exposed to various stresses increased or decreased obviously compared to the swamp reed cells. It has been found that a pattern of absorbing K and discharging Na exists in dune reed cells, which did not exist in swamp reed cells. The pattern is thought to be a significant physiological mechanism of the dune reed response to adverse environmental factors. In addition, the percentages of Ca and Cl in dune reed cells were also shown to increase at high temperature. The growth of cells along with their surface features under different stress conditions were observed and the results are discussed.

Cells, Cultured↗
PubMed2006

Effects of plaque control on the patency of dentinal tubules: an in vivo study in beagle dogs.

BACKGROUND: The aim of this in vivo study was to evaluate the effects of plaque control on the patency of dentinal tubules using vital teeth of beagle dogs. METHODS: Class V cavities were prepared on the cervical areas of the mandibular and maxillary molars in each dog with a diamond point. To simulate the state of dentinal hypersensitivity, the teeth were etched with 50% citric acid for 2 minutes to obtain patent dentinal tubules. Plaque control was achieved by brushing the left-side teeth every day, whereas no plaque control was performed for the right-side teeth. A dentin biopsy was performed after 1, 2, and 3 weeks using the cylindrical diamond point to obtain dentin specimens. RESULTS: In the plaque control group, some of the dentinal tubules were occluded with precipitate (Ca/P=1.49), and the diameter of the dentinal tubules decreased from 2.42+/-0.33 microm (mean+/-SD) to 1.11+/-0.51 microm after 7 days, although most of the dentinal tubules remained open. In contrast, no precipitate was observed in the dentinal tubules of the non-plaque control group. Also, the diameter of the dentinal tubules increased from 2.42+/-0.33 to 2.9+/-0.49 microm, due to the demineralization of the peritubular and intertubular dentin. CONCLUSION: Plaque control plays a key role in reducing the patency of dentinal tubules and, therefore, might promote the natural repair of dentinal hypersensitivity.

Analysis of Variance↗
PubMed2001

Ultrastructure of selected calcium oxalate-containing urinary calculi from dogs.

OBJECTIVE: To elucidate the ultrastructural details of calcium oxalate-containing urinary calculi from dogs. Sample Population-38 specimens selected from a collection of 8,297 oxalate-containing urinary calculi from dogs: 22 specimens composed of calcium oxalate (calcium oxalate monohydrate [COM], calcium oxalate dihydrate [COD], or COM and COD) and 16 specimens composed of calcium oxalate with amorphous calcium phosphate. PROCEDURE: Analyses of specimens included use of plain, reflected, and polarized light microscopy, X-ray diffractometry, scanning electron microscopy (SEM) with backscattered electron (BSE) imagery, and electron microprobe analysis. RESULTS: Four texture types were observed in calcium oxalate calculi; 4 texture types of calcium oxalate-calcium phosphate-mixed calculi were recognized. Texture types were delineated through differences in calcium oxalate crystal sizes, which were affected by urine supersaturation and abundance of crystal nucleation sites. Segregation of calcium oxalate from calcium phosphate indicated they do not precipitate under the same conditions. Deposition of calcium phosphate between calcium oxalate crystals decreased the volume of pore spaces within calculi. Porosity was observed along boundaries between COM and COD. Minute pores increased the surface area of calculi exposed to urine, and this increase in liquid-solid interface promotes interaction of crystals with the surrounding urine. CONCLUSIONS AND CLINICAL RELEVANCE: Calcium oxalate urolithiasis is of major concern, because it is often a recurrent disease among dogs, principally treated by surgical removal of calculi, with few effective dissolution strategies. Understanding the ultrastructure and mineralogic content of calcium oxalate and its association with amorphous calcium phosphate is a step toward the solution of this increasingly important medical problem.

Animals↗
PubMed1992

Short-term plasma-cleaning treatments enhance in vitro osteoblast attachment to titanium.

The purpose of this research was to characterize the in vitro cellular behavior of osteoblast-like cells on titanium surfaces prepared with argon plasma-cleaning (PC) treatments for various lengths of time. The highest levels of cell attachment were observed for surfaces which had been plasma-treated for one min. Surface analyses indicated that although PC treatments dramatically improved surface wettability, the presence of inorganic contaminants was observed with longer treatment times and may have interfered with cell attachment. Further work is suggested to investigate the longer-term phenotypic expression of osteoblasts when grown on implant surfaces.

Analysis of Variance↗