PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Silicon Compounds”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources
PubMed2000

Characteristics of pharmaceutical grade phyllosilicate powders.

The purpose of this paper was to evaluate the possible use of three types of pharmaceutical grades of phyllosilicates as pharmaceutical excipients. Seven samples (two smectites, three palygorskites, and two sepiolites) were studied. A complete mineralogical and chemical characterization of each material was made and powder texture was established by image analysis of scanning electron micrographs. Powder flow properties were then determined and the influence of textural characteristics on powder rheology and particle packing was assessed. Mineral contents were adequate for the sepiolites (> 90% of main mineral) and smectites (78 and 95%), but should be improved on the palygorskite samples (around 50% of main mineral in two of the studied samples). According to the textural characterization, the samples presented almost equal size distributions, but exhibited two different morphologies (i.e., laminar for smectites and fibrous for sepiolites and palygorskites). Both sepiolites possessed high flowability, whereas this factor varied from medium to low in the other materials. The compressibility of smectites was adequate, whereas that of palygorskites was high and that of the sepiolites was low. All of the samples studied would be useful as solid dosage form excipients (some samples would require improvement of their flow properties or treatment to reduce the amount of mineral impurities).

Bentonite↗
PubMed1987

Potential health risks from the use of fibrous mineral absorption granulates.

Attapulgite (palygorskite) and sepiolite are fibrous clay minerals used commercially as components in a wide variety of products including oil and grease adsorbents, carriers for pharmaceuticals, cosmetics, and pesticides. They are also components of drilling muds and animal litter and they are used as paint thickeners. The current annual worldwide production of these minerals exceeds one million tons. Although fibrous in nature, the fibre length may vary greatly depending on the location of the geological deposits. American attapulgite is short (0.1-2.5 micron in length, median of 0.4 micron) but palygorskite from other parts of the world is much longer (30% longer than 5 micron). Several samples of these materials have been submitted to scanning transmission electron microscopy (STEM). This paper reports the results of microscopic evaluations and makes a comparison with the data from experimental carcinogenicity studies and it is concluded that fibre length is a most important carcinogenic property.

Environmental Exposure↗
PubMed1984

Oscillatory wear tests of dental composites.

The wear behavior of 12 commercial restorative composites (conventional and microfilled) and an unfilled restorative material was evaluated using an in vitro wear test referred to as an oscillatory wear test. The effect of varying test conditions was evaluated in a series of preliminary experiments in order to define test conditions for material evaluation. The materials were tested after being aged in water at 37 degrees C for periods of from seven days to one year. The results indicated consistently lower wear rates for the microfilled materials as compared with those of the conventional composites. Aging did not result in significant differences in wear rates measured by this method. Scanning electron micrography of worn surfaces suggested a possible effect of filler particle shape and bonding to the matrix to explain this difference. Although the relevance of the results to clinical behavior is not yet known, the study indicated the importance of material variables on wear.

Acrylic Resins↗
PubMed1995

A room temperature vulcanizing silicone rubber sport splint.

Athletic hand and wrist injuries may be treated by immobilizing the affected extremity in a rigid splint to protect the injury site for an extended time period. For athletes, this means a reduction in playing time, perhaps being out for an entire playing season. The use of a room temperature vulcanizing silicone rubber compound allows for a playing splint that complies with athletic regulations. Proper application of the room temperature vulcanizing silicone rubber provides an excellent, reliable protective playing splint allowing for safe, functional athletic performance for the injured player during the game. This article describes the fabrication process of a silicone rubber protective playing splint for athletic hand and wrist injuries. The effectiveness of the silicone rubber protective playing splint is illustrated via case studies.

Adolescent↗
PubMed2003

[Change of leukocytic phagocytosis during repeat hemoperfusion with cross-linked agar beads entrapped attapulgite clay].

The leukocytic phagocytosis rate and the index of phagocytosis of rats on cross-linked agar beads entrapped attapulgite clay (CAA) hemoperfusion were studied. The results revealed that the leukocytic phagocytosis rate and the index of phagocytosis descended significantly after 1 hour and rose gradually after 6 hours. Finally it reached the normal level after 48 hours. Hemoperfusion repeated two times gave similar results. In conclusion, the function of leukocytic phagocytosis declined temporarily during CAA hemoperfusion. Many times hemoperfusion will not notably affect the body's defense system of rats.

Agar↗
PubMedDate not supplied

Surface geometry of three packable and one hybrid composite after polishing.

This study evaluated the surface quality of four composite materials after polishing with six different polishing techniques. Eighty specimens were made using three packable composites (Definite/Degussa, SureFil/ Dentsply and Solitaire/Heraeus-Kulzer) and one hybrid composite (Herculite XRV/Kerr). Five specimens of each material were polished using flexible Sof-Lex discs. The remaining 75 specimens of each composite were prepared using three finishing protocols: a single 30 microm diamond (n = 25), two finishing diamonds (30/20 microm; n = 25) and a 30 microm diamond followed by a tungsten carbide finishing bur (n = 25). Final polishing of each of the three finishing groups was accomplished with SuperBuff, Diafix-oral, OneGloss, Astropol and HaWe Composite Polishers (n = 5, each). Surface roughness was evaluated quantitatively by laser-stylus profilometry. Average roughness (R(a)) was calculated; statistical analysis of the data was performed with two-way ANOVA and Scheffé post-hoc tests. The polished surfaces were examined qualitatively by SEM. The results showed significant effects on surface roughness from the different composites (p = 0.011) and polishing systems (p < 0.001). After polishing, the Solitaire surfaces (R(a) = 0.72 microm) were smoother than Definite (R(a) = 0.87 microm) and SureFil (R(a) = 0.89 microm) and significantly smoother than Herculite (R(a) = 0.92 microm; p = 0.011). Three of the polishing methods (SuperBuff, Diafix-oral and Astropol) achieved lower R(a)-values than Sof-Lex discs. The polishing quality of the one-step systems SuperBuff and Diafix-oral was strongly affected by the initial finishing protocol.

Aluminum Oxide↗
PubMed1997

Some silicates.

Explore the source record for details and available documents.

Animals↗
PubMedDate not supplied

Chemiluminescent derivatization of adenyl compounds with glyoxal derivatives in the presence of heteropoly acids and its application to the simple and sensitive determination of DNA.

A chemiluminescence (CL) determination of adenyl compounds is described. CL derivatization of adenyl compounds with methylglyoxal dimethyl acetal was performed in the presence of tungstosilicic acid and propan-2-ol. CL from adenyl compounds was produced by hydrogen peroxide and L-cysteine ethyl ester in DMF and water. The proposed method is highly sensitive and specific to compounds containing adenine. Adenine was determined in the range 1.0 x 10(-3)-5.0 x 10(-8) M with the detection limit of 3.0 x 10(-8) M (150 fmol per assay). The method was applied to the determination of DNA and detection limits of a few nanograms of DNA achieved.

Acetone↗
PubMed1989

High-resolution electron microscopy of ceramic interfaces.

Three observations described here were chosen not only to represent our recent interface studies in ceramics, but also to demonstrate how different the present status of interface research is with respect to the level of high-resolution electron microscopy. Certain common features may be found among the problems of ceramic interface studies. Importance of basal plane grain boundary, for example, is one of the characteristics of this type of heterogeneous compound. The crystalline heterogeneity has been ignored largely in the grain boundary structure study since it has been developed primarily for cubic metals. The new area of basic grain boundary interface structure study is opened now that description of this type of interface has become engineeringly important.

Aluminum↗
PubMed1990

A randomized, open-label comparison of nonprescription loperamide and attapulgite in the symptomatic treatment of acute diarrhea.

The efficacy of nonprescription doses of loperamide hydrochloride (Imodium A-D) was compared with nonfibrous activated attapulgite (Diasorb) in a randomized, parallel, open-label study of adult patients with acute diarrhea. The results of the study showed loperamide to be more effective than attapulgite in the control of diarrhea. Loperamide significantly reduced stool frequency compared with attapulgite, particularly within the first 12-hour period following the start of therapy, and significantly shortened the mean time to last unformed stool (loperamide, 14.2 hours, versus attapulgite, 19.5 hours). Subjective evaluations of severity of enteric symptoms, overall relief following treatment, and overall relief after 48 hours of treatment were equivalent for both drugs. Both treatments were well tolerated, and there was no difference between treatments with respect to the proportion of patients reporting adverse experiences.

Acute Disease↗
PubMed1992

Surface roughness of finished composite resins.

This study evaluated the results of polishing composite resin by using the following finishing and polishing techniques: Arkansas stone burs; eight-blade tungsten-carbide burs; diamond burs; aluminum-oxide disks; no polishing; and 12- and 30-blade tungsten-carbide burs. The results were compared to ascertain which technique delivers the smoothest surface. The study was done with 120 class V restorations on extracted human teeth distributed in two groups (I and II) of 60 restorations each. Group I teeth samples were filled with microfilled composite resin and Group II with a hybrid composite resin. Readings were made with a profilometer to evaluate the final polishing. The conclusions from the results of the study were that microfilled composite resins provided a better finish when treated with aluminum-oxide disks. These results were statistically significant (p < 0.001). When hybrid composites were used the control group recorded the lowest values.

Aluminum Oxide↗
PubMed2005

Microtensile bond strength of different components of core veneered all-ceramic restorations.

OBJECTIVES: The present study aims to evaluate the core-veneer bond strength and the cohesive strength of the components of three commercial layered all-ceramic systems. Two surface treatments for the core surface finish and different veneering ceramics with different thermal expansion coefficients (TEC) were applied. The selected systems were two CAD-CAM ceramics; Cercon and Vita Mark II and one pressable system; (IPS)Empress 2 for layering technique. METHODS: Standardized core specimens were fabricated according to the manufacturer's instructions, or polished with 1200 siliconcarbide polishing paper. The core specimens were veneered with either its manufacturer's veneer or an experimental veneer with higher TEC. The obtained micro-bars were subjected to the microtensile bond strength test. The obtained data were analyzed using one and two-way ANOVA. A finite element analysis (FEA) model of the test setup was analyzed. Scanning Electron Microscopy (SEM) was carried out at the fracture surface. RESULTS: The core materials were significantly stronger than the veneering materials and the layered core-veneer specimens of which the results were statistically comparable. Polishing the core surfaces did not have an effect on the core-veneer bond strength. Experimental veneer with higher TEC resulted in massive fractures in both the core and veneering material. SEM and FEA demonstrated fracture pattern and mechanism of failure. SIGNIFICANCE: The core-veneer bond strength is one of the weakest links of layered all-ceramic restorations and has a significant role in their success. To exploit fully the high strength of zirconium oxide cores, further research work is needed to improve its bond with its corresponding veneering material.

Biocompatible Materials↗
PubMed1998

Depth-resolved Raman microprobe examination of a commercial dental porcelain exposed to a simulated oral environment.

OBJECTIVES: The specific aims were investigation of the chemical transformations into the interior of a commercial dental porcelain upon exposure to a simulated oral environment and identification of structural alterations that contribute to the strengthening of the porcelain. METHODS: Samples of a commercial dental porcelain, Duceram LFC, were exposed to refluxing dilute acetic acid for 0, 1, 5, 10, and 72 h to simulate exposure to the oral environment. The control and refluxed samples were examined using a depth-resolved Raman microprobe system covering the low (0-2550 cm-1) and high (2000-4000 cm-1) frequency ranges. Spectra were processed using exploratory factor analysis. Significant factors were retained, accounting for 99.999% of the variance. RESULTS: The porcelain was found to be significantly depolymerized prior to acid-refluxing. Exposure to water and to acid resulted in the formation of a better-ordered region near the surface. In that region, three intermingled zones of chainlike metaborate and pyroborate, of boroxol rings, and of a mixture of borate and silicate tetrahedra were identified. The borate/silicate factor was dependent on refluxing time. Hydroxyl groups were detected in all of the samples, but no changes to the hydroxyl environment were noted until after 10 or more hours of refluxing. Then, molecular water and isolated hydroxyls/SiOH were detected. After 72 h, an additional unassigned factor around 2800-2950 cm-1 was noted. SIGNIFICANCE: Acid refluxing causes generation of ordered boron-containing species near the surface of the porcelain.

Boron Compounds↗
PubMed2004

Nanoporous SiC: a candidate semi-permeable material for biomedical applications.

We have fabricated free-standing SiC nanoporous membranes in both p -type and n -type material. We showed that these membranes will permit the diffusion of proteins up to 29000 Daltons, while excluding larger proteins. By using radioactively labeled albumin, we also show that porous SiC has very low protein adsorption, comparable to the best commercially available polymer nanoporous membrane.

Adsorption↗
PubMedDate not supplied

Interaction of different ocular endotamponades as a risk factor for silicone oil emulsification.

PURPOSE: To investigate the influence of other substances used intraoperatively in vitreoretinal surgery on the emulsification of silicone oil in patients' eyes. METHODS: Gas chromatography coupled mass spectroscopy of the headspace (GC/MS/HS) was 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. RESULTS: Some samples of nonemulsified explanted silicone oil were not different in their content of volatile substances measured by GC-MS/HS. In all explanted samples of emulsified silicone oil volatile substances could be detected, which do not exist or are at the detection limit in native silicone oil for ophthalmic use. The majority of contaminants are heavy liquids, cleaning substances, and oligosiloxanes. CONCLUSION: The contact of silicone oil with all types of substances should be reduced to a minimum. Reuse of tubing sets must be avoided. If a direct exchange between heavy liquids and silicone oil seems necessary, turbulence at the interfaces must be avoided and the contact time between these two endotamponades must be kept as short as possible. If these precautions are obeyed, the risk of emulsification of silicone oil used as an ocular endotamponade can be significantly reduced, down to the influence of individual patients' conditions.

Device Removal↗
PubMed1989

Carborundum pneumoconiosis. Fibers in the mineral activate macrophages to produce fibroblast growth factors and sustain the chronic inflammatory disease.

Carborundum is a synthetic abrasive manufactured through fusion of high grade silica sand and finely ground carbon in an electric furnace at 2,400 degrees C. It had been considered an inert dust until recently. Two recent epidemiologic studies in Quebec have documented an excess of interstitial lung disease in plant workers and some 30 workers have received workman compensation. Histopathologic lesions have been described in four of the workers. To further investigate the carborundum pneumoconiosis, nine groups of eight sheep were exposed once in the tracheal lobe to either 100 ml saline, 100 mg latex beads in 100 ml saline, 100 mg graphite in 100 ml saline, 100 mg carborundum particles in 100 ml saline, 100 mg ashed carborundum particles in 100 ml saline, 100 mg of quartz (Minusil-5) in 100 ml saline, 100 mg crocidolite fibers in 100 ml saline, 100 mg carborundum fibers in 100 ml saline, and 100 mg ashed carborundum fibers in 100 ml saline solutions. The animals had BAL at two-month intervals and autopsy at month 8. The BAL analyses of cellularity, cytotoxicity and fibrogenicity, in association to necropsy histopathology, documented that all particles except for quartz were inert. The two-carborundum fiber samples produced a similar sustained nodular fibrosing alveolitis and crocidolite asbestos fibers produced a peribronchiolar fibrosing alveolitis of comparable severity. Thus, the major bioactive dusts in the carborundum manufacturing process are quartz particles and the carborundum fibers generated in the process. The latter have fibrogenic activities comparable to asbestos fibers of similar size and are likely to contribute to the pathogenesis of the interstitial lung disease of carborundum workers.

Animals↗
PubMed1993

Effectiveness of different types of clay for reducing the detrimental effects of aflatoxin-contaminated diets on performance and serum profiles of weanling pigs.

Three trials were conducted with recently weaned pigs (n = 198) to determine the effects of feeding different types of clay in conjunction with aflatoxin-contaminated diets. In Trial 1, pigs (n = 54; trial length 4 wk) were assigned to either an uncontaminated treatment (NC), 800 ppb of aflatoxin from contaminated corn (AC), or AC with one of four clays. In Trial 2 (n = 81; trial length 5 wk), pigs were assigned to NC, AC (500 ppb of aflatoxin from rice starch), or AC with one of seven types of clay. In both trials, pigs fed AC had decreased ADG and gain:feed ratios (P < .05) compared with controls. The clays differed in their ability to produce gains similar to those of controls. The clays did reduce changes in the serum measurements normally affected by aflatoxin, including albumin, total protein, gamma glutamyltransferase (GGT), and alkaline phosphatase (ALP) levels, in a manner similar to their effect on ADG. In Trial 3, pigs (n = 63) were assigned to one of seven diets for 4 wk: NC, AC (800 ppb of aflatoxin) with no clay, AC with one of four levels of a treated Ca bentonite (.25, .5, 1, and 2%), or AC and .5% hydrated sodium calcium aluminosilicate. The addition of treated Ca bentonite to AC improved ADG (P < .05) and ADFI (P < .01) linearly. Gain:feed ratios were not affected by treatments. The inclusion of treated Ca bentonite to the AC diet linearly decreased aspartate aminotransferase (AST) levels and quadratically decreased ALP and GGT levels (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxins↗