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PubMed1989

Toxicity of an attapulgite sample studied in vivo and in vitro.

Conflicting data are found in the literature concerning the carcinogenic potency of attapulgite. We tested the carcinogenic potency of French attapulgite in rats, and compared it with 2 chrysotile samples: Rhodesian UICC (Ch A) and short Canadian fibres (Ch C). The mean length of the fibres was 0.77 micron (attapulgite), 3.21 microns (Ch A) and 1.25 microns (Ch C). The mean diameter was 0.06 micron in the 3 samples. The particles (20 mg) in saline were inoculated into the pleural cavity of Sprague-Dawley rats allowed to survive for their full lifespan. The incidence rates of mesothelioma were: 0% (saline controls), 0% (attapulgite), 19% (ChC) and 48% (Ch A). In vitro studies were carried out using cultures of rat pleural mesothelial cells (RPMC). Attapulgite and Ch C did not modify cell growth except at high doses of 10 micrograms/cm2. Unscheduled DNA synthesis (UDS) was detected using [3H]thymidine incorporation in confluent RPMC (GoG1 arrested) and a scintillation method. UDS was stimulated with either Ch A or Ch C at doses ranging from 2 to 10 micrograms/cm2. In contrast, attapulgite did not significantly enhance [3H]thymidine incorporation at doses ranging from 2 to 20 micrograms/cm2. The results show that the attapulgite tested here had no carcinogenic potency. The in vivo and in vitro reactivity of the fibres used in this experiment might perhaps be related to the fibre size; however, other parameters may also be important.

Animals↗
PubMed1991

Repairability of type II glass polyalkenoate (ionomer) cements.

Two Type II glass polyalkenoate (ionomer) cements were evaluated for their repairability by measuring tensile bond strength of new material added to previously placed cement. Variables included time of repair (20 min vs. 24 h) and surface condition prior to repair (smooth and unetched, smooth and etched, rough and unetched, rough and etched). Failures were evaluated using light microscopy and categorized as cohesive, adhesive, or mixed. Scanning electron microscopy was employed to view the cement surfaces following each of the four pretreatments. Surface pretreatment was found to significantly affect both materials when repaired at 20 min (P less than 0.05). The highest bond strength was achieved when bonding to the smooth, unetched surface. Surface pretreatment did not significantly affect bond strength when the cements were repaired at 24 h (P greater than 0.05). Tensile bond strengths were greater for repairs made at 20 min than for those made at 24 h, but the differences were not always statistically significant.

Acid Etching, Dental↗
PubMed2003

Enhanced compositional contrast in imaging of nanoprecipitates buried in a defective crystal using a conventional TEM.

In this article, we show that nanometer-sized precipitates of atomic numbers higher than those of the surrounding crystalline matrix can be clearly revealed in a conventional transmission electron microscope by high-angle, centered dark-field imaging after minimizing the diffraction contrast. The effect is similar to that of Z-contrast STEM, albeit with a spatial resolution limited to 1 nm. Its sensitivity to atomic number differences between precipitates and matrix is about 10, which is demonstrated for precipitates formed after Er, Ge, Cr, and Si ion implantation into SiC.

Carbon Compounds, Inorganic↗
PubMed1992

Effect of procedure on diametral tensile strength of composite resin.

The sensitivity of the test for diametral tensile strength to variations in testing procedure was investigated. Composite resin specimens of four different surface roughnesses at both ends of the specimens were loaded at one of three crosshead speeds. The diametral tensile strength values varied between 43.9 and 65.7 MPa. Diametral tensile strength was found to decrease with increasing loading rate, with decreasing roughness of the specimens, and with increasing length of the cylindrical specimens. The significant influence of the surface roughness is suggested to be a result of the correlation between roughness and length of specimens, and not the expression of a true influence on diametral tensile strength of surface roughness of the specimens' ends.

Analysis of Variance↗
PubMed2000

Effects of whisker-to-silica ratio on the reinforcement of dental resin composites with silica-fused whiskers.

Resin composites need to be strengthened to improve their performance in large stress-bearing restorations. This study aimed to reinforce composites with whiskers and to investigate the effects of the whisker:silica ratio. It was hypothesized that changing the whisker-silica ratio would affect the whisker-matrix bonding and the filler's distribution, and hence alter the composite properties. Silica particles and whiskers were mixed at various whisker:silica mass ratios, thermally fused, and combined with a dental resin at filler mass fractions of 0-65%. Whisker:silica ratio and filler level had significant effects on composite properties. At 60% filler level, the silica composite (whisker:silica = 0:1) had a flexural strength (mean +/- SD; n = 6) of 104 +/- 21 MPa; that at a whisker:silica ratio of 1:0 was 74 +/- 36 MPa. However, that of the silica-fused whisker composite (whisker:silica = 5:1) was 210 +/- 14 MPa, compared with 109 +/- 23 MPa and 114 +/- 18 MPa of two prosthetic controls. Mixing silica with whiskers minimized whisker entanglement, improved filler distribution in the matrix, and facilitated whisker silanization and bonding to the matrix, thus resulting in substantially stronger composites.

Carbon Compounds, Inorganic↗
PubMed1995

A scanning electron microscope study comparing the effectiveness of different types of sharpening stones and curets.

The effects of various types of sharpening stones on standard carbon steel Gracey type curets, and the influence of the sharpened curets on periodontally involved root surfaces, during in vitro scaling and root planing, was evaluated by means of scanning electron microscopy (SEM). Six different sharpening stones of varying texture, two of aluminum oxide, two India, and two Arkansas stones were assigned to sharpen six groups of 10 curets each. The curets were first examined under SEM and photographed and all exhibited edge irregularities. They were then sharpened with the different stones and again examined and photographed using SEM. The sharpness of each instrument was graded, related to the type of stone used, and the data compared statistically. A positive correlation was found between the texture of stone used and the surface sharpness it produced on the cutting edge of the instrument. The curets were then used to root plane the root surfaces on periodontally involved, extracted teeth. Replicas of the root surfaces were examined with SEM before and after removal of the smear layer with 10% EDTA. The planed and cleaned root surfaces revealed the effects of the sharpened instruments, with the relative surface roughness of the instrument being imparted to the tooth surface. The curets sharpened with finger grit stones produced smoother surfaces than those sharpened with the rough or coarse grit stone. It may be concluded that the sharpness of curets is related to the type of sharpening stone used and in turn to the smoothness of the planned root.

Aluminum Oxide↗
PubMed1991

[Toxicological study of materials for artificial heart valves].

The toxicological study was performed in order to establish the optimum carbon thromboresistant coat of titanium in creating new constructions of the artificial heart valves under conditions of chronic experiments in albino rats. Fine samples of carbon coats made by different techniques were studied. The biological activity of only one coat made by the method of ionoplasmic spraying with using chemically pure carbon target was established.

Animals↗
PubMed1987

Pleural carcinogenic potency of mineral fibers (asbestos, attapulgite) and their cytotoxicity on cultured cells.

The carcinogenicity of several samples of mineral fibers was tested following injection of 20 mg in the pleural cavity of noninbred Sprague-Dawley rats. Three samples of chrysotile asbestos (mean length: 3.2, 2.1, and 1.2 micron) induced mesotheliomas at a rate of 48, 52, and 19%, respectively. The first sample was acid leached prior to intrapleural injection; in that group, the percentage of mesotheliomas was reduced to 25%. Treatment with amosite and crocidolite resulted in the occurrence of 57 and 56% of mesotheliomas. Acid-treatment of amphiboles did not significantly modify the percentage of mesotheliomas. When the Stanton's fiber dimensions were taken into consideration to correlate with mesothelioma incidence, the observed number of mesotheliomas in the chrysotile-treated animals was much lower than that expected, suggesting that other fiber parameters (chemistry, physicochemistry) play a role in the carcinogenicity. Attapulgite fibers (mean length: 0.77 micron) did not induce tumor, and the mean survival time was of the same order as that observed in the control groups. The injection of quartz resulted in no mesothelioma but did result in 6 malignant histiocytic lymphomas (17%) and 2 malignant schwannomas (6%). In vitro experiments did not show strong correlation between cytotoxicity and the carcinogenic potency of these minerals, but the qualitative cellular responses might give some indications on the fiber's potency. In addition, the in vitro effects of the fibers seem to be modulated by their size.

Animals↗
PubMed1996

High-Pressure Framework Silicates

Recent syntheses of high-pressure alkali and alkaline earth silicates reveal a class of framework structures with corner-linked 4- and 6-coordinated silicon. These compounds possess the structural formula (A4-2x1+Bx2+)SimVI(SinIVO2(m+n)+2), where x, m, and n specify the amounts of alkaline earth, 6-coordinated silicon, and 4-coordinated silicon, respectively. Appropriate values of m and n yield a range of high-pressure structures, from fully 4-coordinated to fully 6-coordinated silicate frameworks. Recognition of this class of framework silicates leads to predictions of high-pressure structures as well as room-pressure isomorphs of high-pressure silicates.

Journal Article↗
PubMed1974

Superficial and deep juxtaglomerular apparatus renin activity of the rat kidney. Effect of surgical preparation and NaCl intake.

The intrarenal gradient of renin activity was determined in rats by using superficial (S) and deep (D) cortical juxtaglomerular apparatuses (JGA's), identified and microdissected after silicone-rubber compound injection. Angiotensin generated from single JGA's using partially purified sheep renin substrate was quantified by rat bioassay. When, in rats on a normal NaCl diet, silicone-rubber was injected into a carotid artery, alone or with abdominal aorta catheterization, S:D renin activity ratios were 1.18+/-0.08 (SEM) and 1.21+/-0.12, respectively. The S:D renin activity ratios obtained when silicone-rubber was injected into the abdominal aorta (2.52+/-0.09) or a chronic carotid artery catheter (3.44+/-0.40) were significantly higher (P < 0.001). The lower S:D renin activity ratios after carotid artery manipulation were due to significantly higher D-JGA renin activities. This increased D-JGA renin activity and the lack of a renin gradient appear to be related to acute carotid artery manipulation. Alterations in JGA renin activity were examined relative to NaCl intake. 2 wk after high-NaCl diet the absolute net renin activity decreased (P < 0.001) more in S (5.84+/-0.11 ng AI.JGA(-1).h(-1)) than D (1.73+/-0.06 ng AI.JGA(-1).h(-1)) JGA's, and the intrarenal renin gradient was lost (S:D-JGA renin activity, 1.00+/-0.07), as compared to the regular NaCl diet. 2 wk of a low-NaCl diet resulted in a greater (P < 0.01) increase in S (14.28+/-1.47 ng AI.JGA(-1).h(-1)) than D (9.62+/-1.19 ng AI.JGA(-1).h(-1)) JGA renin activity and a renin gradient (S:D-JGA renin activity) of 1.75+/-0.12. These results demonstrate that NaCl intake clearly influences total JGA renin content and may also affect the relative intrarenal distribution of renin activity.

Angiotensin II↗
PubMed1999

Mechanical and histological investigations on pressureless sintered SiC dental implants.

The effect of sinterability manufacturing conditions, such as Si/C ratio, additives, firing temperature on mechanical properties of pressureless sintered SiC having electrical resistivity and oxidation behaviour in moist were studied. In order to evaluate the possibility of dental implant application of SiC, the implant study using rat femurs was performed. SiC was implanted in the drilled hole of the femurs and the histologic reaction to SiC was investigated under light microscopy and CMR. SiC provoked endosteal as bone formation. At 1-3 weeks, it was observed the formation of callus around the SiC implant. Finally, the intervening fibrous tissue between the encapsulating bone and SiC was replaced by bone tissue which was outgowing from the encapsulating bone surface. The observed interface between bone and SiC was similar to the bone-HA interface as to morphology. These results indicate the clinical application of SiC as a dental implant.

Animals↗
PubMed2005

Effect of texture of polishing particle on the surface roughness of a cobalt-chromium alloy using a centrifugal shooting type polishing machine.

In a previous report, we investigated the influence of the shooting angle of polishing particle on the surface roughness of a cobalt-chromium (Co-Cr) alloy using a centrifugal shooting type polishing machine. In the present work, we examined the effects of the texture of polishing particle and polishing time on the surface roughness of Co-Cr alloy cast specimens. Nine different textures of polishing particle were investigated with respect to core material and particle abrasiveness: three different elastic body cores (core A, hard chloroprene rubber; core B, soft chloroprene rubber; core C, natural rubber) and three different green carborundum powders as abrasives (#800, #3000, and #6000). Polishing was performed under a fixed shooting angle of 30 degrees for six different polishing times (1, 2, 3, 5, 7, and 10 minutes). Surface roughness (Ra, Sm) and cutting depth on the polished surface were measured after each polishing stage. Surface roughness was significantly improved within three minutes, particularly using a polishing particle with rough carborundum powder (#800 or #3000) and a heavy core (core A or core B). Cutting depth increased in proportion to polishing time and roughness of carborundum powder, and was least with core C. These results suggested that a polishing particle composed of core B and #3000 carborundum paste was superior for the intermediate polishing of a Co-Cr alloy, and that polishing time should be limited to within three minutes.

Analysis of Variance↗
PubMed1988

Study of fatty acids in atheroma induced in rabbits by an atherogenic diet with or without silicon i.v. treatment.

Fifty-two rabbits were submitted for two months to an atherogenic diet with or without addition of silicon in the form of an I.V. silicon organic compound and compared to a control group of 21 rabbits. Out of the 26 rabbits receiving cholesterol alone, 23 showed atheromatous lesions; out of the 26 rabbits receiving cholesterol + silicon, only 8 had lesions. Free fatty acids, total fatty acids and esters were studied in the plasma and in the aorta. During atheroma, saturated fatty acids decrease, in particular 18:0, unsaturated fatty acids increase, in particular 18:1, 18:2, 20:4; with added silicon the variations are less important: in free fatty acids in plasma, there is a decrease of 20:4; in cholesterol esters in plasma and aorta an increase of 18:0 and a decrease of 18:2. There is a negative correlation between atheromatous lesions and myristic and stearic acids, and a positive correlation between oleic, linoleic and arachidonic acids and atheroma. Arachidonic acid, involved in phenomena of lipid peroxidation, decreased in the silicon treated rabbits.

Animals↗
PubMed1990

Thermodynamic study of phase transfer of precipitates on SiC whisker reinforced glass ceramics.

Physiochemical properties of glass ceramics in weakly buffered, supersaturated, metastable calcium and phosphate solution were studied. Formations of calcium phosphate precipitates were also analyzed thermodynamically. All biomaterials examined here showed primarily dissolution process and subsequent nucleation. Dissolution was enhanced in those which contained Na2O and/or SiC. The dissolution of calcium and phosphate ions from biomaterials and subsequent nucleation of calcium phosphate salts after induction time resulted in a stable equilibrium having solubility characteristics similar to octacalcium phosphate (OCP). The most soluble material, CPSN-SiC, showed an initial transient equilibrium with amorphous calcium phosphate (ACP). From above results, calcium phosphate ceramics had certain driving force of its own which kept the equilibrium of solution to OCP thermodynamically for 7 days. Despite the favorable solubility equilibrium attained, there still remain problems for clinical application.

Biocompatible Materials↗