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At least 433 records · Page 24Linked to original sources
PubMed1987

Study of rat lung alveoli using corrosion casting and freeze fracture methods coupled with digital image analysis.

Relative areas and volumes can be estimated from vascular corrosion casts of rat lung alveoli using a calibration obtained from bulk frozen hydrated tissue. These morphometric measurements are roughly independent of the shrinkage and distortion artifacts known to arise in the corrosion casting procedure. Digital image processing of the SEM micrographs is employed to facilitate the measurement of casts and frozen tissue. The vascular corrosion casting technique is modified also to permit successful casting of alveolar air passages. The modified technique produces faithful casts of dead-ended luminal structures where continuous perfusion of casting medium into the tissue is not possible. The casts of alveolar air passages and their corresponding vasculature are compared to determine the volume of a single alveolus. By utilizing the calibrated measurements of lung areas and volumes, an estimate of lung vascular surface area per unit volume is obtained. This number, when multiplied by the respiratory tidal volume of the rat, may represent the total lung vascular surface are available for physiological gas exchange during normal respiration.

Animals↗
PubMed1997

[Cellular antigen stimulation test (CAST)--applicability in the diagnosis of insect toxin allergies].

In the CAST, blood leukocytes are prestimulated with the cytokine IL-3 and exposed to allergen(s). Mainly basophiles react by synthesizing sulfidoleukotrienes (sLT), namely LTC4 and its metabolites LTD4 and LTE4. They are detected by ELISA technique. 66 patients with suspected allergy to hymenoptera venoms were evaluated. Allergic reactions comprised all severity grades (I-IV ref. H. L. Mueller). The workup included skin tests (up to 1 microgram/ml, Pharmacia), measurement of specific serum IgE with RAST-CAP (Pharmacia), and CAST with three concentrations of bee (Apis mellifera) and wasp (Vespula spec.) venom (Aquagen ALK). A control group of 13 nonallergic, RAST-CAP negative individuals was established. CAST demonstrated pronounced variations of individual s-LT synthesis in patients and controls. The use of elevated cut-offs improved the results, while the use of three allergen concentrations did not increase reliability. Diagnostic accuracy of CAST was evaluated by comparison with skin tests as the "gold standard". With bee venom and a cut-off at 3 standard deviations, a sensitivity and specificity of 73%/71% was obtained. Wasp venom showed better results at 2 standard deviations, with a sensitivity and specificity of 68%/100%. CAST results were not influenced by the severity of the allergic reaction nor by the time lapse since the sting had occurred. In conclusion, CAST is a valuable test in insect sting allergy. However, established methods such as skin tests and RAST-CAP achieve better results. CAST should therefore be considered a supplementary method in cases where established methods fail. It remains to be shown whether CAST can be used as a parameter for monitoring patients who have undergone immunotherapy.

Adolescent↗
PubMed1979

The relationship of pattern position to the flow of gold and casting completeness.

To minimize the possibility of incomplete casting due to improper pattern orientation relative to the sprue and direction of the casting arm motion, the following precautions should be taken. 1. Locate the pattern in the trailing half of the casting ring 90 to 135 degrees away from the sprue position. 2. Once the pattern is in the position described, locate it downward in the lower outer quarter of the trailing half of the casting ring and secure it in that position. 3. Mark the ring or sprue former so that the invested pattern can be oriented properly in the casting arm. 4. When using an electric casting machine, be certain that the pyrometer is correct. If in doubt, it is advisable to check the melt state of the gold before casting.

Dental Casting Investment↗
PubMed1995

Mold filling of Ti castings using investments with different gas permeability.

OBJECTIVES: The aim of this work was to study mold filling during casting of standardized five-unit Ti bridges vs. the gas permeability of the investments. METHODS: An Ar arc casting machine with a separate melting and mold chamber was used. Both chambers were evacuated before Ar was introduced into the melting chamber. A rubber sealer was inserted between the top of the steel ring of the mold and the steel floor between the two chambers. The mold cavity required the same Ar pressure as the melting chamber prior to casting. Four different investments for Ti casting were investigated: 1) Bellavest T (BEGO), 2) Rematitan Plus (Dentaurum), 3) Titavest CB (Morita) and 4) Titanium Vest (Ohara Co.). Three castings were made with each investment. The molds were fired according to the manufacturers' instructions and cooled to room temperature. The Ar gas pressures in the two chambers were recorded during casting, and the mold filling was evaluated initially by visual inspection and subsequently by studying the margins of the crowns in a microscope. RESULTS: In the melting and molding chambers, the Ar pressure was found to be: 1) Bellavest T: 400 and 1 torr; 2) Rematitan Plus: 600 and 85 torr; 3) Titavest CB:600 and 150 torr; and 4) Titanium Vest: 600 and 85 torr, respectively. This indicates substantial differences in the gas permeability of the molds. Bellavest T produced poorly filled molds, Rematitan Plus and Titanium Vest resulted in poor margins and Titavest CB produced complete castings. SIGNIFICANCE: Proper mold filling is promoted by investments with a high gas permeability, so the gases in the mold cavity can escape through the investment to the mold chamber.

Argon↗
PubMed2003

Adherence of investment to Au-Pd-Ag alloy using a vacuum-argon pressure casting machine.

OBJECTIVE: The removal of adhered investment material from marginal metal surfaces represents a possible risk of poor marginal adaptation. The aim of this work was to evaluate the effects of argon on investment adherence to the casting surface and on the alloy surface microstructure. METHODS: A die of stainless steel was used. 10 wax copings were cast by vacuum-argon pressure, while 10 copings by vacuum-air pressure using a Combilabor CLG-77 A in a graphite crucible; supply was direct with curved sprues of slashed circle 3.5 mm. The alloy used was Herabond. After coarse investment, removal of all specimens were investigated with scanning electron microscopy and semi-quantitative digital densitometry. RESULTS: The specimens cast under vacuum-argon pressure showed less amount of investment adhered (unpaired t test of grouped specimens, difference 2.896x10(5)pixel; p=0.002) while the grain size on the casting surface increased significantly p=0.000 (difference 5.968(microm). SIGNIFICANCE: Vacuum-argon pressure supply during casting reduces the investment adherence to the metal surface, and increases the packing density and size of the grains, especially on the casting surface. These minimize the risk of marginal distortions due to casting cleaning procedures and facilitate the finishing and polishing procedures.

Adhesiveness↗
PubMed1999

Titanium full crown casting: thermal expansion of investments and crown accuracy.

OBJECTIVES: The aim of the present study was to establish a statistical model between thermal expansion values of investments and dimensional accuracy of cast titanium full crowns. METHODS: Thermal expansion (TE) measurements were made on cylindrical specimens (5O x 20 mm) dried to constant mass and full crown wax patterns were prepared from metal dies having the same design. Castings were made using a one-chamber high-pressure casting machine. Dimensional accuracy of the cast crowns was expressed by the discrepancy (micron) between the wax pattern and a casting prepared from the same die. A simple least squares linear regression analysis was made on data accumulated over the last five years. RESULTS: A high correlation coefficient (R = 0.87) was found between dimensional accuracy (Y) and thermal expansion value (X), and the accuracy was predicted by a formula Y = 1040.50X - 1004.45 microns. For zero discrepancy, a thermal expansion of 0.97% was required. SIGNIFICANCE: The dimensional accuracy expressed as the discrepancy between wax pattern and casting is easy to understand and less confusing than the traditional percentage value. The crown accuracy was highly predictable (R = 0.87) from the thermal expansion value of investments determined under controlled laboratory measuring conditions. New investments being released for titanium casting can be under constant modification. For this, regular monitoring of their TE behaviour is essential and use of the same batch is preferable for expansion measurement and crown accuracy assessment.

Analysis of Variance↗
PubMed2004

The thickness effects of titanium castings on the surface reaction layer.

In this study, wedge-shaped CP titanium castings and Ti-6Al-7Nb alloy castings were produced by three types of investment. The effects of the castings' thickness on surface reaction layer were investigated by measuring Vickers hardness, observing the microstructure, and analyzing the oxygen concentration. It was found that the thickness of the surface reaction layer was affected by the thickness of the wedge-shaped castings, and that the hardness value near the surface became lower toward the tip of the wedge-shaped CP titanium and Ti-6Al-7Nb alloy castings. The surface reaction layer of the Ti-6Al-7Nb alloy castings was thinner than that of the CP titanium castings.

Dental Alloys↗
PubMed2004

Study of resin-bonded calcia investment. Part 3: Hardness of titanium castings.

The Vickers hardness of the cross-sectioned area of titanium castings made from an experimental resin-bonded calcia investment and three commercial investments was evaluated. The microstructure and element distribution of the surface zone were analyzed using an EPMA. The results showed that the high hardness of the casting surface could be decreased using the experimental investment. The hardness of the castings made from the experimental investment at a 25-50 microm depth was lower than those from the other investments, and the thickness of the hardened casting surface was 125 microm. Layered structures with fewer layers were formed on the surfaces of the castings made from the experimental investment. The layered structures were influenced by both the investment components and the mold temperature at casting. The less contaminating nature of the experimental investment components and the technology of the room temperature mold contributed to the improved surface properties of the resulting castings.

Calcium Compounds↗
PubMed2004

Dimensional accuracy and surface property of titanium casting using gypsum-bonded alumina investment.

The aim of the present study was to evaluate the dimensional accuracy and surface property of titanium casting obtained using a gypsum-bonded alumina investment. The experimental gypsum-bonded alumina investment with 20 mass% gypsum content mixed with 2 mass% potassium sulfate was used for five cp titanium castings and three Cu-Zn alloy castings. The accuracy, surface roughness (Ra), and reaction layer thickness of these castings were investigated. The accuracy of the castings obtained from the experimental investment ranged from -0.04 to 0.23%, while surface roughness (Ra) ranged from 7.6 to 10.3microm. A reaction layer of about 150 microm thickness under the titanium casting surface was observed. These results suggested that the titanium casting obtained using the experimental investment was acceptable. Although the reaction layer was thin, surface roughness should be improved.

Aluminum Oxide↗
PubMed2006

Titanium casting using commercial phosphate-bonded investments with quick heating method.

The purpose of this study was to investigate the possible use of quick heating method for titanium casting using two commercial investments (Rematitan Plus and Tancovest). The resulting characteristics of the investments with the quick heating method were as follows: residual thermal expansion at the casting temperature was in the range of 0.39 to 0.64%; green strength and fired strength ranged from 4.4 to 10.3 MPa and from 13.8 to 17.6 MPa, respectively. Five full crown titanium castings from each casting condition were obtained using an argon arc melting and gas pressure casting machine. The thickness of cast surface reaction layer was approximately 200 microm, regardless of heating methods or investments. Further, the heating method did not significantly influence either the accuracy or surface roughness of the titanium castings. These results therefore suggested that these commercial investments for titanium could be used for the quick heating method.

Analysis of Variance↗
PubMedDate not supplied

The effect of five investing techniques on air bubble entrapment and casting nodules.

Five different investing techniques were used to invest lost-wax casting patterns. The use of an investing technique that subjects the invested casting ring to air pressure (40 lb per square inch) during setting was found to produce less air bubble/cast nodule incidence than did the other four techniques investigated. Not all cast nodules can be seen by the unaided eye; magnification is needed. More cast nodules than air bubbles were seen at the interface of pattern and investment, showing that there may be many air bubbles below the investment surface that are entered by the incoming alloy during casting. The effect of a surface-tension reducing (STR) agent on the air bubble incidence between pattern and investment depends on the investing technique used, although all techniques used showed a reduction in cast nodule incidence when an STR agent was used. Sprue direction was also found to influence the incidence of casting nodules.

Air↗
PubMedDate not supplied

Interfacial reactions of cast titanium with mold materials.

PURPOSE: Dental casting requires replication of complex shapes with high fidelity. To achieve this objective, the problem of scale formation on titanium dental castings must be overcome. Scaling occurs readily at high temperatures because of the high reactivity of molten titanium with investment materials. The purpose of this study was to examine the effectiveness of using stable oxide coatings on the mold surface to reduce the interfacial reactions. MATERIALS AND METHODS: A traditional phosphate-bonded dental investment, a commercial titanium investment, and an experimental oxide coating were used for the molds. Pure titanium samples were cast, divested, and prepared for scanning electron microscopic and energy dispersive x-ray spectroscopic analyses. RESULTS: Layers of 7- to 10-micron-thick scale were formed on titanium castings during reaction with traditional mold materials. Interface reaction was reduced between the molten titanium and the investment material when yttrium oxide or zirconium oxide coatings were applied to the mold before casting. CONCLUSION: Less titanium-mold interfacial reactions occurred when protective coatings were used as diffusion barriers for titanium casting. Y2O3-coating oxide particles applied without binder were entrapped in the cast titanium surface layer. Further study of a binder system for Y2O3 coating is needed.

Dental Casting Investment↗
PubMed1993

New aspects of microvascular corrosion casting: a scanning, transmission electron, and high-resolution intravital video microscopic study.

We used intravital microscopy of small intestine and pancreas in order to show dynamic interactions between vascular wall and undiluted Mercox, because previous studies of ours have shown that Mercox diluted with monomeric methylmethacrylate penetrates cells in the vascular wall. Scanning and transmission electron microscopy were used to show three-dimensional pathways and correlating tissue structures, which cannot be identified in vivo. The microvascular diameters were not altered when the vasculature was flushed with saline/dextran solution using perfusion pressures between 70 and 140 mm Hg, but, in circumscribed areas, contraction of vascular wall was observed immediately after Mercox injection. This phenomenon was carried out by endothelial cells; pericytes were never present at the site of constrictions. Extravasation, i.e., leakage of the resin into the surrounding tissue, occurred in circumscribed areas regardless of the applied perfusion pressure. The resin also filled routes, which were not perfused with blood before casting. Scanning microscopy of corresponding specimens showed flattened cast channels, with impressions of valves and endothelial cell nuclear imprints characteristic of lymphatics. These results show that undiluted Mercox is a stimulus for vascular cellular components and that it changes the vascular wall permeability, resulting in extravasation and filling of lymphatics. Transmission electron microscopy showed that large vessels were homogeneously filled with resin and that cellular structures were not infiltrated with Mercox. Cut sections of the gold-coated surface of casts showed grooves up to 20 nm wide, suggestive of minimal deformation, while the abluminal surface of the metal film was almost smooth. Another proof of minimal deformation of undiluted Mercox casts is that the diameter of vessels was not altered during and after polymerization. Obtained casts are not fragile, as are casts of diluted Mercox, and phase separation does not occur, which would result in penetration of the cells in the vascular wall. For these reasons, the use of undiluted Mercox is recommended. Mixing 10 ml Mercox with 1 g catalyst resulted in complete polymerization within 5.5-7 min. This mixture can be used for casting biological specimens.

Animals↗
PubMed1998

Staining tissue with methacrylate casts for light microscopy.

Scanning electron microscopy (SEM) of methyl methacrylate casts and light microscopy (LM) of tissue are well-established methods for studying the microcirculation. The two are complimentary, but methacrylate is transparent and thus its presence is often not appreciated by LM. Applying histologic stains to sections of tissue embedded in methyl methacrylate would allow the relationships of light microscopic and scanning electron microscopic views of cast vasculature to be better appreciated. We sought to test different stains on cast tissue to find one that would accent the cast. Surgically removed and autopsied human lungs were cast with methacrylate and processed by routine light microscopic methods. They were stained with the hematoxylin and eosin, Masson trichome, elastic--van Gieson, Grocott methenamine silver, Brown-Brennan, and Ziehl-Neelsen methods. The Ziehl-Neelsen procedure stained the methacrylate best, giving it a red color. This procedure also worked well without heating. We conclude that (1) cast methacrylate lung can be processed for routine LM with excellent results; (2) methacrylate stains well with the Ziehl-Neelsen technique; (3) the acid--fast stained cast lung shows capillaries and cells in both normal and diseased lung better than the routine hematoxylin and eosin stain; (4) this technique can be used to assess filling and correlate findings on the same tissue with the two different microscopic methods.

Corrosion Casting↗
PubMed2002

Functional treatment after surgical repair of acute Achilles tendon rupture: wrap vs walking cast.

The aim of this study was to compare the clinical outcome for patients treated with walking cast immobilization and wrap early mobilization after surgical repair of acute Achilles tendon ruptures. A total of 39 consecutive patients with complete ruptures of the Achilles tendon were identified, treated, and functionally rehabilitated with either a walking cast or a wrap. Because the randomization was quasi-random, chi-square and t-tests were performed to compare the baseline characteristics. A statistically significant difference was present only for the injured side ( p<0.05). Therefore, groups were considered comparable for analysis of outcome. All patients were evaluated at an average follow-up of 6.7 years (range 5-8 years). Functional postoperative treatment with a wrap allowed a significantly shorter hospital stay ( p<0.05) as well as a shorter period to return to pre-injury sports level ( p<0.01) compared with treatment with a walking cast. According to the modified Rupp score, 91.3% of patients in the walking cast group had a good or excellent result, as did 93.8% in the wrap group ( p=0.9). Slight atrophy of the calf muscles was reported in 3 patients in the walking cast group (13.0%) and in 4 in the wrap group (25.0%). One re-rupture was reported in the walking cast group (4.3%). Functional treatment after surgical Achilles tendon repair is safe, and there is no increased risk of re-rupture or wound healing problems. Functional treatment with a wrap is preferable to treatment with a walking cast with respect to hospitalization time and return to sports.

Achilles Tendon↗
PubMed2006

The value of a pantaloon cast test in surgical decision making for chronic low back pain patients: a systematic review of the literature supplemented with a prospective cohort study.

The results of lumbar fusion in chronic low back pain (LBP) patients vary considerably, and there is a need for proper patient selection. Lumbosacral orthoses have been widely used to predict outcome, however, with little scientific support. The aim of the present study was to determine the value of a pantaloon cast test in selecting chronic LBP patients for lumbar fusion or conservative management. First, a systematic review of the literature was carried out in which two independent reviewers identified studies in Medline, Cochrane and Current Contents databases. Three papers met the selection criteria. In the only study with a control group, a significantly better outcome after fusion compared to conservative treatment was found in patients who reported significant pain relief while in a cast (i.e. a positive cast test). The results of lumbar fusion, however, were not significantly different for patients with a positive and those with a negative cast test. In addition to the review, a clinical cohort study of 257 LBP patients, who had been allocated to either lumbar fusion or conservative management by a temporary external transpedicular fixation trial, was performed. Prior to allocation, all had undergone a pantaloon cast test. Patients with no history of prior spine surgery and with a positive pantaloon cast test had a better outcome after lumbar fusion than those treated conservatively (P = 0.002, chi (2 )test). In patients with previous spine operations the outcomes were poor and the test was of no value. From the literature and the present patient cohort, it was concluded that only in chronic LBP patients without prior spine surgery, a pantaloon cast test with substantial pain relief suggests a favorable outcome of lumbar fusion compared to conservative management. The test has no value in patients who have had previous spine surgery.

Adult↗
PubMed1987

Factors affecting the retention and fit of gold castings.

A study was designed to simulate clinical conditions. Several factors were evaluated for effect on retention and fit (margin adaptation) of gold castings. Twenty-six castings (13 pairs) were made by different investigators using a standard preparation but with varying fabrication techniques. One of each pair of castings was made on a spaced die and one on an unspaced die. A significant difference in the postcementation retention was observed in the varying techniques of each investigator. Retentive values varied from 29 to 129 lbs. Complete seating of the castings during cementation was improved by the use of die spacer. Castings made on the spaced dies had more retention than corresponding unspaced castings. Die spacing has positive benefit when properly used. Moderate roughness of axial surfaces improves retention when zinc phosphate cement is used. Physical properties of restorative materials are important, but the individual technique and care of each investigator has a major effect on the ultimate fit and retention of the cast restoration.

Cementation↗
PubMed2005

Feto-feto-fetal transfusion syndrome in monozygotic monochorionic triamniotic triplets: vascular evaluation by a cast model.

A unique cast model of the placenta in a rare case of feto-feto-fetal triplet transfusion syndrome (FFFTTS) allowed the demonstration of why the transfusion syndrome developed in one fetus and not in the other two in that single placenta. The vasculature anatomy of a monochorionic triamniotic triplet placenta with FFFTTS of three healthy infants (one donor, two recipients) born in the 35th week of gestation was cast by means of dental casting materials. After the cast hardened, the tissue was corroded, revealing the cast blood vessels. The diameters and lengths of the chorionic blood and intraplacental vessels of the cast placenta were measured with a digital caliper. The cast revealed two artery-artery (A-A) anastomoses on the chorionic plate between the two recipients and the donor. Seven artery-vein (A-V) deep anastomoses connected only the arteries of the donor and the veins of the two recipients. The blood vessel connections among the fetuses allowed the evaluation of a pathologic case with its own control in a single placenta. From the vascular appearance, we speculate that the A-A anastomoses between the two fetuses protected them from developing blood transfusions, but that the A-V anastomoses contributed to their development.

Adult↗