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PubMed2005

Micro/nanoscale mechanical and tribological characterization of SiC for orthopedic applications.

Micro/nanomechanical and tribological characterization of SiC has been carried out. For comparison, measurements on SiC, CoCrMo, Ti-6Al-4V, and stainless steel have also been made. Hardness and elastic modulus of these materials were measured by nanoindentation using a nanoindenter. The nanoindentation impressions were imaged using an atomic force microscope (AFM). Scratch, friction, and wear properties were measured using an accelerated microtribometer. Scratch and wear damages were studied using a scanning electron microscope (SEM). It is found that SiC exhibits higher hardness, elastic modulus, scratch resistance as well as lower friction with fewer and smaller debris particles compared to other materials. These results show that SiC possesses superior mechanical and tribological properties that make it an ideal material for use in orthopedic and other biomedical applications.

Biocompatible Materials↗
PubMed1996

Benign response to particles of diamond and SiC: bone chamber studies of new joint replacement coating materials in rabbits.

Wear particles from total joint replacements are thought to accelerate prosthetic loosening. Diamond coating may improve the smoothness and wear characteristics of the femoral head component of total hip replacements, and thus increase their longevity. The brittleness of a thin diamond coat may be overcome by using an SiC-whisker diamond composite. This study describes the reactions of regenerating bone tissue to phagocytosable particles of diamond and SiC, using implanted bone harvest chambers in rabbits. The particles were dispersed in hyaluronan and introduced into a canal transversing the implant. The tissue that entered the canal during the following 3 weeks was then harvested. In previous studies using this model, particles of high density polyethylene, bone cement and chromium-cobalt all caused an inflammatory reaction and a marked decrease in the amount of ingrown bone. In the present study, neither the diamond nor the SiC particles caused any decrease in bone formation. It appears that particles of diamond and SiC are comparatively harmless.

Animals↗
PubMed2003

Study on fluoride emission from soils at high temperature related to brick-making process.

Characteristics of fluoride emission from 12 soils at temperatures of 400-1,100 degrees C related to the brick-making process were studied. The results obtained in this study indicate that fluoride emission as gaseous HF and SiF4 was related to the firing temperature, soil total fluoride content, soil composition and calcium compounds added to soils. Soils began to release fluoride at temperatures between 500 and 700 degrees C. Marked increases of the average fluoride mission rate from 57.2% to 85.4% of soil total fluoride were noticed as the heating temperature was increased from 700 to 1,100 degrees C. It was found that the major proportion (over 50%) of the soil total fluoride was emitted from soils at approximate 800 degrees C. The amount of fluoride released into the atmosphere when heated depended on the total fluoride contents in the soils. Correlation analysis showed that the soil composition, such as cation exchange capacity, exchangeable calcium and CaCO3, had some influence on fluoride emission below 900 degrees C, but had no influence at temperatures above 900 degrees C. Addition of four calcium compounds (CaO, CaCO3, Ca(OH)2, and CaSO4) at 1.5% by weight raised the temperature at which fluoride began to be released to 700 degrees C. The greatest decrease in fluoride emission among the four calcium compound treatments was found with CaCO3.

Air Pollutants↗
PubMed1995

Superoxide anion release by alveolar macrophages exposed to respirable industrial fibres: modifying effect of fibre opsonisation.

Phagocyte-derived free radicals are considered to play a role in fibre-related pathology and the components of the lung lining fluid could modify the surface of fibres. Therefore we examined the ability of long amosite asbestos and a range of man-made fibres to stimulate release of superoxide anion from rat alveolar macrophages when they were in their native form (unopsonised) and opsonised by incubation in rat Immunoglobulin G. We also assessed the specific amount of opsonin adsorbed to each fibre type. In the uncoated form all of the fibres produced modest amounts of superoxide release from macrophages. When they were opsonised however there was an effect on stimulation of release of superoxide that was fibre-specific. Both MMVF21 and RCF 1 were dramatically enhanced in their ability to stimulate release and this was related to a high affinity of their surface for IgG. Code 100/475 and SiC were not substantially affected by opsonisation and this was reflected in their low affinity for IgG. Long amosite had low affinity for IgG but showed dramatic enhancement of capacity to stimulate superoxide release. These fibre-specific differences in the effect of a coating of material that is found in the lung lining points out the problems of interpretation of in vitro data and more work on this important area is warranted.

Air Pollutants, Occupational↗
PubMed2004

Using microabrasive material to remove fluorosis stains.

BACKGROUND: Increased public access to fluoride has decreased the prevalence of caries and increased the prevalence of fluorosis staining. This article provides a case report involving a conservative method of removing fluorosis stain, as well as describes an in vitro test of the method. CASE DESCRIPTION: A healthy man sought treatment at New York University College of Dentistry for removal of severe, dark brown fluorosis staining on his anterior teeth. To remove the stain, the treating clinician used a microabrasive material, which leaves enamel intact, instead of a tooth-whitening agent, which requires removal of all affected enamel. METHODS: To demonstrate that enamel structure is not disturbed by the microabrasive material, the authors performed a study using scanning electron microscopy, or SEM. They viewed enamel structure under SEM at x1,000 magnification. They viewed untreated microabraded enamel and compared it with enamel that had been treated for 20 seconds with 37 percent phosphoric acid. RESULTS: An etch pattern was not discernible on the tooth treated with the microabrasive material. The enamel prisms remained intact and the cores were not exposed. CLINICAL IMPLICATIONS: Microabrasion removes intrinsic fluorosis stain effectively while protecting enamel. In this case, an enamel shade of brown not in the range of any tooth color shade guide was reduced.

Adult↗
PubMed2004

Structural characterization of organic multilayers on silicon(111) formed by immobilization of molecular films on functionalized Si-C linked monolayers.

Silicon(111)-H surfaces were derivatized with omega-functionalized alkenes in UV-mediated and thermal hydrosilylation reactions to give Si-C linked monolayers. Additional molecular layers of organic compounds were coupled either directly or via linker molecules to the functionalized alkyl monolayers. In the first instance, amino-terminated monolayers were prepared from a tert-butoxycarbonyl-protected omega-aminoalkene followed by removal of the protecting group. Various thiols were coupled to the monolayer using a heterobifunctional linker, which introduced maleimide groups onto the surface. In the second system, N-hydroxysuccinimide (NHS) ester-terminated monolayers were formed by reaction of Si-H with N-succinimidyl undecenoate. The reactivity of the NHS ester groups was confirmed by further modification of the monolayer. The stepwise assembly of these multilayer structures was characterized by X-ray reflectometry and X-ray photoelectron spectroscopy.

Alkenes↗
PubMed2005

Design and implementation of a novel mechanical testing system for cellular solids.

Cellular solids constitute an important class of engineering materials encompassing both man-made and natural constructs. Materials such as wood, cork, coral, and cancellous bone are examples of cellular solids. The structural analysis of cellular solid failure has been limited to 2D sections to illustrate global fracture patterns. Due to the inherent destructiveness of 2D methods, dynamic assessment of fracture progression has not been possible. Image-guided failure assessment (IGFA), a noninvasive technique to analyze 3D progressive bone failure, has been developed utilizing stepwise microcompression in combination with time-lapsed microcomputed tomographic imaging (microCT). This method allows for the assessment of fracture progression in the plastic region, where much of the structural deformation/energy absorption is encountered in a cellular solid. Therefore, the goal of this project was to design and fabricate a novel micromechanical testing system to validate the effectiveness of the stepwise IGFA technique compared to classical continuous mechanical testing, using a variety of engineered and natural cellular solids. In our analysis, we found stepwise compression to be a valid approach for IGFA with high precision and accuracy comparable to classical continuous testing. Therefore, this approach complements the conventional mechanical testing methods by providing visual insight into the failure propagation mechanisms of cellular solids.

Aluminum↗
PubMed2005

Recent developments in nanofabrication using focused ion beams.

Focused ion beam (FIB) technology has become increasingly popular in the fabrication of nanoscale structures. In this paper, the recent developments of the FIB technology are examined with emphasis on its ability to fabricate a wide variety of nanostructures. FIB-based nanofabrication involves four major approaches: milling, implantation, ion-induced deposition, and ion-assisted etching of materials; all these approaches are reviewed separately. Following an introduction of the uniqueness and strength of the technology, the ion source and systems used for FIB are presented. The principle and specific techniques underlying each of the four approaches are subsequently studied with emphasis on their abilities of writing structures with nanoscale accuracy. The differences and uniqueness among these techniques are also discussed. Finally, concluding remarks are provided where the strength and weakness of the techniques studied are summarized and the scopes for technological improvement and future research are recommended.

Carbon↗
PubMed2003

Grindability of cast Ti-Cu alloys.

OBJECTIVE: The purpose of the present study was to evaluate the grindability of a series of cast Ti-Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. METHODS: Experimental Ti-Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm x 8.5 mm x 30.5 mm), from which the hardened surface layer (250 microm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1min. Data were compared to those for CP Ti and Ti-6Al-4V. RESULTS: For all speeds, Ti-10% Cu alloy exhibited the highest grindability. For the Ti-Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. SIGNIFICANCE: By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti(2)Cu among the alpha-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

Carbon Compounds, Inorganic↗
PubMed1997

Carborundum, a bulk similar to dietary fibers but chemically inert, does not decrease colon carcinogenesis.

Dietary fibers might lower the risk of colorectal cancer, maybe because of their bulking effect. We tested the protection afforded by an inert bulk against carcinogenesis. Thirty rats received an azoxymethane injection and were allocated to a control diet, or to a diet supplemented with 10% carborundum. After 100 days the colons were scored for aberrant crypt foci. Compared to controls, the fecal weight was doubled in carborundum-fed rats (P < 0.001), but the aberrant crypt foci multiplicity was not changed (P = 0.92). The results do not support the hypothesis that intestinal dilution by an inert bulk can protect against colon cancer.

Alkaline Phosphatase↗
PubMed2004

Subwavelength-scale tailoring of surface phonon polaritons by focused ion-beam implantation.

Recent advances in optical nanotechnologies by controlling surface plasmon polaritons in metallic nanostructures demonstrate high potential for subwavelength-scale waveguiding of light, data storage, microscopy or biophotonics. Surprisingly, surface phonon polaritons-infrared counterparts to surface plasmon polaritons-have not been widely explored for nanophotonic applications. As they rely on the infrared or terahertz excitation of lattice vibrations in polar crystals they offer totally different material classes for nanophotonic applications, such as semiconductors and insulators. In an initial step towards nanoscale surface phonon photonics we show evidence that the local properties of surface phonon polaritons can be tailored at a subwavelength-scale by focused ion-beam modification of the crystal structure, even without significant alteration of the surface topography. Such single-step-fabricated, monolithic structures could be used for controlling electromagnetic energy transport by surface phonon polaritons in miniaturized integrated devices operating at infrared or terahertz frequencies. We verify the polaritonic properties of an ion-beam-patterned SiC surface by infrared near-field microscopy. The near-field images also demonstrate nanometre-scale resolved infrared mapping of crystal quality useful in semiconductor processing or crystal growth.

Carbon Compounds, Inorganic↗
PubMed2002

Dentin morphology and permeability after brushing with different toothpastes in the presence and absence of smear layer.

BACKGROUND: The purpose of this study was to evaluate the morphology and permeability of dentin after brushing with different toothpastes in the presence and absence of smear layers. METHODS: Dentin discs were prepared from extracted third molars. Dentin permeability was measured using a hydraulic pressure apparatus working at 70 cm H2O pressure. Dentin was treated with 0.5 M EDTA for 5 minutes and washed to remove a smear layer and to establish the maximum permeability of each dentin disc, which was expressed as 100%. A new smear layer was then created on the upper surface using a #400 carbide paper under water for 30 seconds. Dentin permeability of the smear layer-covered dentin was measured and expressed as a percentage of the maximum permeability of that specimen, permitting each specimen to serve as its own control. Each sample was then brushed by a mechanical device under water for 3 minutes with constant pressure of 250 g using a medium toothbrush and permeability remeasured. Finally, 1 of 5 different toothpastes was applied on the dentin and brushed for 3 minutes. In another group, the same procedures were performed with the exception of the smear layer production, so it was possible to calculate changes in the permeability of dentin with open tubules following brushing. Scanning electron microscopic (SEM) examination of dentin was obtained before and after treatments with brushing and toothpastes. RESULTS: Dentin permeability was reduced by brushing procedures when the smear layer was absent, but it was increased when the smear layer was present. Toothpaste application reduced dentin permeability when no smear layer was present on the top of the surface, but modified and increased permeability of samples with smear layers. SEM observations demonstrated the presence of dentifrice particles on dentin surfaces and inside dentinal tubules, and this may be responsible for the observed reductions in permeability. Smear plugs produced during dentin brushing were not removed by the dentifrices. CONCLUSIONS: Dentin permeability and morphology are significantly affected by toothbrushing and by the type of dentifrice used. The presence of smear plugs in the dentin may decrease severity.

Adult↗
PubMed1997

Mortality from nonmalignant respiratory diseases among male workers in Norwegian ferroalloy plants.

OBJECTIVES: This study examined mortality from nonmalignant respiratory diseases among ferroalloy workers. METHODS: The cohort comprised 14730 men employed for the first time in 1933-1990 and for at least 6 months in 1 of 12 plants. The duration of work in specific departments and exposure to amorphous silica in the ferrosilicon/silicon-metal (FeSi/Si-met) plants, estimated from a job-exposure matrix, were the main exposure variables. Deaths were observed during 1962-1990. The mortality was analyzed with the use of standardized mortality ratios (SMR) and internal comparisons of rates. RESULTS: Overall mortality from nonmalignant respiratory diseases was not increased, but mortality from bronchitis, emphysema, and asthma combined was significantly increased among the men with at least 3 years of FeSi/Si-met furnace work (SMR 1.82, 16 deaths). A Poisson regression analysis of the mortality from these causes among 6359 employees in the FeSi/Si-met plants showed a significant increase of 0.06 per unit of amorphous silica exposure observed 10-20 years after the exposure. Six men died of pneumonia while still employed in a ferromanganese/silicomanganese (FeMn/SiMn) plant. No corresponding deaths occurred among employees in FeSi/Si-met plants. Only 2 deaths from pneumoconiosis were observed in the total cohort. CONCLUSIONS: Among employees in FeSi/Si-met plants increased mortality from bronchitis, emphysema, and asthma may be associated with previous exposure to amorphous silica. Deaths from pneumonia among FeMn/SiMn workers may be associated with manganese exposure.

Adult↗
PubMed2004

Effect of a whitening agent application on enamel bond strength of self-etching primer systems.

PURPOSE: Though reduction in bond strength after tooth whitening has been reported, little is known about it's effect on enamel bond strength of two-step bonding systems that exclude phosphoric acid etching prior to bonding agent application. The purpose of this study was to determine the effect of whitening procedure using an in-office whitening agent on enamel bond strength of self-etching primer systems. METHODS: Three self-etching primer systems, Imperva Fluoro Bond, Mac Bond II, Clearfil SE Bond, and a one-bottle adhesive system Single Bond as a control material, were used. Bovine mandibular incisors were mounted in self-curing resin and the facial enamel or dentin surfaces were ground wet on 600-grit SiC paper. An in-office whitening agent, Hi-Lite was applied on the tooth surface according to the manufacturer's instruction. Bonding procedures were done soon after rinsing off the whitening agent or after 24 hours storage in distilled water. Specimens without whitening procedure were prepared as controls. Fifteen specimens per test group were stored in 37 degrees C distilled water for 24 hours, then shear tested at a crosshead speed of 1.0 mm/minute. One-way ANOVA followed by Duncan multiple range test were used for statistical analysis of the results. RESULTS: For the specimens made soon after rinsing off the whitening agent, a significant decrease in enamel bond strength was observed for all the bonding systems used. For the specimens made after 24 hours storage in water, a small decrease in enamel bond strength was observed and no significant differences were found compared to those of controls (without whitening). From the results of this study, enamel bond strengths of the self-etching primer systems might be affected to a lesser degree after rinsing with water followed by 24 hours storage in water.

Analysis of Variance↗
PubMed2006

The phenomenon of "sticky" silicone oil.

BACKGROUND: To investigate the reasons for difficulties removing silicone oil from the vitreous cavity due to putative adherence to the retina. METHODS: Gas chromatography-coupled mass spectroscopy of the headspace (GC/MS/HS) and gel permeation chromatography (GPC) were used to detect volatile compounds in silicone oil samples explanted from patients, qualitatively as well as quantitatively. Surface and interfacial tensions of the explanted samples were measured using the pendent-drop technique. To simulate the removal of silicone oil from the vitreous cavity, the contact between silicone oil and differently treated surfaces and various aspiration techniques were tested in vitro. RESULTS: The median concentration of perfluorodecalin in seven "sticky" samples was 2.4 times higher than in 14 non-sticky samples. In the sticky samples, the median surface tension of the aqueous phase was lower. The difficulty of aspirating silicone oil could be reproduced in vitro by reducing the surface tension of the aqueous environment of the silicone oil. CONCLUSION: The observed stickiness of silicone oil seems to be a matter of reduced surface tension of the surrounding aqueous material and/or contamination of silicone oil with perfluorocarbon liquid, which creates interruption of the material flow, giving the impression of adherence of the silicone oil to the retina.

Adhesiveness↗
PubMed2004

Effect of heat treatments on machinability of gold alloy with age-hardenability at intraoral temperature.

OBJECTIVE: This study investigated the effect of heat treatment on the machinability of heat-treated cast gold alloy with age-hardenability at intraoral temperature using a handpiece engine with SiC wheels and an air-turbine handpiece with carbide burs and diamond points. METHODS: Cast gold alloy specimens underwent various heat treatments [As-cast (AC); Solution treatment (ST); High-temperature aging (HA), Intraoral aging (IA)] before machinability testing. The machinability test was conducted at a constant machining force of 0.784N. The three circumferential speeds used for the handpiece engine were 500, 1,000 and 1,500 m/min. The machinability index (M-index) was determined as the amount of metal removed by machining (volume loss, mm(3)). The results were analyzed by ANOVA and Scheffé's test. RESULTS: When an air-turbine handpiece was used, there was no difference in the M-index of the gold alloy among the heat treatments. The air-turbine carbide burs showed significantly (p<0.05) higher M-indexes than the diamond points after any heat treatments. With the SiC wheels, increasing the circumferential speed increased the M-index values for each heat treatment. The specimens heat-treated with AC, HA and IA had similar M-indexes at the lower speeds (500 and 1,000 m/min). The ST specimens exhibited the lowest M-index at the lower speeds. However, at the highest speed (1,500 m/min), there were no significant differences in the M-indexes among the heat treatments except for HA, which showed the highest M-index. CONCLUSION: There was no effect of heat treatment on the machinability of the gold alloy using the air-turbine handpiece. The heat treatments had a small effect on the M-index of the gold alloy machined with a SiC wheel for a handpiece engine.

Body Temperature↗