Effects of magnesia and potassium sulfate on gypsum-bonded alumina dental investment for high-fusing casting.
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The purpose of this study was to improve the characteristics of gypsum-bonded alumina investments using magnesia and potassium sulfate as chemical additives. Magnesia content improved fluidity, delayed setting reaction, increased green strength, and decreased setting expansion, when mixed with distilled water. When the investment was mixed with potassium sulfate, the setting time and setting expansion were reduced, and the thermal expansion increased, however, the green strength decreased. Therefore, the investment with a small amount of magnesia mixed with potassium sulfate was considered a suitable composition, having adequate setting behavior, enough green strength and sufficient compensate expansion for casting. (+info)
Amsorb: a new carbon dioxide absorbent for use in anesthetic breathing systems.
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BACKGROUND: This article describes a carbon dioxide absorbent for use in anesthesia. The absorbent consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide but includes two setting agents (calcium sulphate and polyvinylpyrrolidine) to improve hardness and porosity. METHODS: The resultant mixture was formulated and subjected to standardized tests for hardness, porosity, and carbon dioxide absorption. Additionally, the new absorbent was exposed in vitro to sevoflurane, desflurane, isoflurane, and enflurane to determine whether these anesthetics were degraded to either compound A or carbon monoxide. The performance data and inertness of the absorbent were compared with two currently available brands of soda lime: Intersorb (Intersurgical Ltd., Berkshire, United Kingdom) and Dragersorb (Drager, Lubeck, Germany). RESULTS: The new carbon dioxide absorbent conformed to United States Pharmacopeia specifications in terms of carbon dioxide absorption, granule hardness, and porosity. When the new material was exposed to sevoflurane (2%) in oxygen at a flow rate of 1 l/min, concentrations of compound A did not increase above those found in the parent drug (1.3-3.3 ppm). In the same experiment, mean +/-SD concentrations of compound A (32.5 +/- 4.5 ppm) were observed when both traditional brands of soda lime were used. After dehydration of the traditional soda limes, immediate exposure to desflurane (60%), enflurane (2%), and isoflurane (2%) produced concentrations of carbon monoxide of 600.0 +/- 10.0 ppm, 580.0 +/- 9.8 ppm, and 620.0 +/-10.1 ppm, respectively. In contrast, concentrations of carbon monoxide were negligible (1-3 ppm) when the anhydrous new absorbent was exposed to the same anesthetics. CONCLUSIONS: The new material is an effective carbon dioxide absorbent and is chemically unreactive with sevoflurane, enflurane, isoflurane, and desflurane. (+info)
Formulation of glutaraldehyde disinfectant for alginate impressions.
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The effect of buffer agents incorporated in glutaraldehyde disinfectants on the surface quality of dental models was examined by the measurement of surface roughness, X-ray diffraction analysis and SEM observation. Seven experimental glutaraldehyde disinfectants were prepared using two buffer agents, potassium acetate alone or potassium acetate and sodium hydrogen carbonate in combination. Four kinds of sulfate--zinc, calcium, potassium and magnesium sulfate--were added to these disinfectants in order to accelerate the hydration of calcium sulfate hemihydrate. The impressions treated with the experimental disinfectants for 1 h produced stone surfaces which had significantly lower surface roughness values than those treated with the commercial disinfectants (p < 0.05). The X-ray diffraction analysis and SEM observation showed that these superior surfaces were produced as a result of significant reductions in the amount of residual calcium sulfate hemihydrate. Replacement of buffer agents in commercial glutaraldehyde disinfectants with chemicals such as those studied in the present study will improve the surface quality of dental stone. (+info)
Properties of a hybrid plaster-fibreglass cast.
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OBJECTIVE: To examine the suitability of a plaster-fibreglass hybrid cast for orthopedic applications, comparing them to plaster of Paris (POP) and fibreglass constructs. METHOD: Groups of 10 standardized hybrid, POP and fibreglass casts were studied. An Instron servohydraulic system was used to test the casts in 3-point bending and shear. OUTCOME MEASURES: Strength, stiffness, weight, thickness and cost of the 3 types of cast, and shear strength at the interface between the POP and fibreglass in the hybrid casts. RESULTS: The hybrid casts were twice as strong as the POP constructs, were stiffer and weighed 14% less but were thicker and cost 2.5 times more. They were almost as strong as and less than half the cost of the fibreglass constructs but were thicker, not as stiff, and weighed 42% more. The shear strength of the POP-fibreglass interface in the hybrid casts was higher than the 3-point bending strength of this construct by a factor of 3. CONCLUSIONS: Plaster-fibreglass hybrid casts should be considered for orthopedic use on the basis of their strength, stiffness, weight and cost, combined with their acknowledged advantages of good moulding ability and water resistance. (+info)
Solar forcing of drought frequency in the Maya lowlands.
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We analyzed lake-sediment cores from the Yucatan Peninsula, Mexico, to reconstruct the climate history of the region over the past 2600 years. Time series analysis of sediment proxies, which are sensitive to the changing ratio of evaporation to precipitation (oxygen isotopes and gypsum precipitation), reveal a recurrent pattern of drought with a dominant periodicity of 208 years. This cycle is similar to the documented 206-year period in records of cosmogenic nuclide production (carbon-14 and beryllium-10) that is thought to reflect variations in solar activity. We conclude that a significant component of century-scale variability in Yucatan droughts is explained by solar forcing. Furthermore, some of the maxima in the 208-year drought cycle correspond with discontinuities in Maya cultural evolution, suggesting that the Maya were affected by these bicentennial oscillations in precipitation. (+info)
Elution characteristics of vancomycin, teicoplanin, gentamicin and clindamycin from calcium sulphate beads.
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The in vitro release of vancomycin, teicoplanin, gentamicin and clindamycin from biodegradable calcium sulphate (CaSO(4)) carrier beads is described. All antibiotics showed prolonged release from the carrier beads, which was elevated during the first 24 h, with peak levels exceeding 2500 microg/bead. Doubling the antibiotic load of the beads revealed a more prolonged elution and a two-fold increase in antibiotic release. Local carrier-associated antibiotic treatment with CaSO(4) beads may prove to be effective in the management of chronic bone infections. (+info)
Efficacy of calcium sulfate plus decompression bone in lumbar and lumbosacral spinal fusion: preliminary results in 40 patients.
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OBJECTIVE: To compare the efficacy of calcium sulfate pellets plus bone obtained from decompression with fresh autologous iliac crest bone in lumbar and lumbosacral spinal fusion with decompression. DESIGN: A prospective randomized clinical trial. SETTING: Four tertiary care centres in Halifax, NS. PATIENTS: All were consenting, skeletally mature and suffering from degenerative disc disease or spondylolisthesis. The first 40 patients from a single test centre are reported; 32 of these had completed 1-year follow-up. INTERVENTIONS: Posterolateral lumbar or lumbosacral spinal fusion with spinal canal decompression and randomized placement of test material (decompression bone plus an equal volume of calcium sulfate pellets) on one side and control material (autologous posterior iliac crest bone of equal volume to the test material) on the contralateral side, which allowed subjects to act as their own control. OUTCOME MEASURES: Assessment of bone formation by radiographic evaluation at 6 and 12 months after fusion by an independent musculoskeletal radiologist blinded to the placement of test material. RESULTS: At 6 and 12 months after fusion, 78% and 88% of patients, respectively, showed bone formation at the test site that was 75% to 100% of, equal to or more than that at the control site. Increases in bone formation at 6 and 12 months were almost identical at both sites. Smoking status, patient gender or age, instrumentation used and volume of graft used were not predictive of outcome. CONCLUSIONS: Calcium sulfate pellets plus decompression bone provided bone formation equivalent to autologous iliac crest bone in a majority of patients. Calcium sulfate pellets plus decompression bone may provide a viable alternative to autologous iliac crest as a graft material for spinal fusion. (+info)
Effect of pH and calcium on short-term NO3- fluxes in roots of barley seedlings.
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The effect of pH and Ca2+ on net NO3- uptake, influx, and efflux by intact roots of barley (Hordeum vulgare L.) seedlings was studied. Seedlings were induced with NO3- or NO2-. Net NO3- uptake and efflux, respectively, were determined by following its depletion from, and accumulation in, the external solution. Since roots of both uninduced and NO2(-)-induced seedlings contain little internal NO3- initial net uptake rates are equivalent to influx (M. Aslam, R.L. Travis, R.C. Huffaker [1994] Plant Physiol 106: 1293-1301). NO3-, uptake (influx) by these roots was little affected at acidic pH. In contrast, in NO3(-)-induced roots, which accumulate NO3-, net uptake rates decreased in response to acidic pH. Under these conditions, NO3- efflux was stimulated and was a function of root NO3- concentration. Conversely, at basic pH, NO3- uptake by NO3- and NO2(-)-induced and uninduced roots decreased, apparently because of the inhibition of influx. Calcium had little effect on NO3- uptake (influx) by NO2(-)-induced roots at either pH 3 or 6. However, in NO3(-)-induced roots, lack of Ca2+ at pH 3 significantly decreased net NO3- uptake and stimulated efflux. The results indicate that at acidic pH the decrease in net NO3- uptake is due to the stimulation of efflux, whereas at basic pH, it is due to the inhibition of influx. (+info)