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At least 469 records · Page 26Linked to original sources
PubMed2000

A rapid phospholipase D assay using zirconium precipitation of anionic substrate phospholipids: application to n-acylethanolamine formation in vitro.

Activation of phospholipase D (PLD) is involved in a number of signal transduction pathways in eukaryotic cells. The most common method for determination of PLD activity in vitro involves incubation with a radiolabeled substrate and lipid extraction followed by thin-layer chromatography in order to separate and quantify substrate and product(s). A more rapid assay can be used when utilizing phosphatidylcholine as a substrate because one of the products, choline, is water soluble and therefore easily separated from the substrate. However, this separation principle is not applicable in evaluating N-acylphosphatidylethanolamine (NAPE)-hydrolyzing PLD activity, which produces two lipophilic products, N-acylethanolamine (NAE) and phosphatidic acid. Therefore, we developed a rapid assay for the routine detection of NAPE-hydrolyzing PLD activity. This assay is based on precipitation of radiolabeled substrate (NAPE) in the presence of ZrOCl(2), followed by quantification of radiolabeled NAE released into a methanolic supernatant. The precipitation involves a chemical reaction of the zirconyl cation with the phosphate anion. Conditions were optimized for the complete precipitation of NAPE, whereas N-acyllysophosphatidylethanolamine and glycerophospho(N-acyl)ethanolamine were precipitated at least 95%. Furthermore, this precipitation method can be extended to assays of other anionic phospholipid-hydrolyzing PLD activities by selecting an optimal pH of the precipitation solution. For example, 98;-99% precipitation of phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine was achieved.Consequently, this new assay allows for a convenient examination of PLD activities toward a variety of phospholipid substrates, and in particular allows for the analysis of NAE formation from NAPE in vitro, a feature that will facilitate a more complete biochemical characterization of this anandamide-generating enzyme.

Animals↗
PubMedDate not supplied

Bond strength of luting cements to zirconium oxide ceramics.

PURPOSE: This study was conducted to determine the bond strength of some resin luting cements to zirconia ceramic. The hypothesis was that adhesive bonding capacity is influenced by different surface pretreatments designed for milled ceramic inlays. MATERIALS AND METHODS: Composite cylinders 5 mm x 5 mm were light cured on the ceramic surfaces for a shear test conducted in a test jig. Five surface treatments were studied: as received (from the milling machine), sandblasting with either 250- or 50-micron alumina sand, hydrofluoric acid treatment, and grinding with diamond burs. The tested luting cements were Panavia 21, Twinlook, and Superbond C&B. RESULTS: All debonding occurred at the interface between ceramic and composite cement. Superbond demonstrated the highest bond strength regardless of the surface treatments. Grinding the surface with diamond burs improved the bonding slightly for Twinlook and Panavia 21 and also showed the roughest texture. Washing with hydrofluoric acid had no significant influence on bond strength. CONCLUSION: Bond strengths for Twinlook and Pananvia 21 were quite low, and only Superbond showed a bond strength reasonably acceptable for clinical use; however, as no standard for bond strength has been established for inlay therapy, the other cements cannot be rejected as luting cements for inlays.

Acid Etching, Dental↗
PubMed2000

[Clinical study of zirconium oxide bridges in the posterior segments fabricated with the DCM system].

Today's dental reconstructive therapeutic concepts require restoration of high esthetic quality and excellent biocompatibility. Full ceramic reconstructions accomplish these requirements but only for anterior teeth and premolars. For all-ceramic bridges the mechanical strength was insufficient to withstand the posterior chewing forces. Frequently the interdental connectors cracked, and the only way to prevent these fractures was to overconture the connectors to a size of approx. 16 mm2. The high-tech ceramic zirconia is a potential alternative for three-to five-unit full ceramic bridges in the functionally loaded posterior segments. Experimental zirconia bridges which were fabricated using the DCM system (Direct Ceramic Machining System at the ETH Zurich, were tested in vitro. The frameworks were digitally enlarged by 20% and were easily milled from a presintered yet porous zirconia blank. After the milling process, the framework was densely sintered and shrank to its original size. Due to these positive in-vitro results a clinical investigation was started. 22 veneered zirconia bridges were luted; 19 molars and 25 premolars were prepared. The connectors, max. 7 mm2, of all these bridges, have been functionally loaded by antagonists. After a mean observation time of 385 days (307 days to 488 days), all 22 bridges did not show any cracks in the framework or in the veneering porcelain. The patients commented particularly on the low heat conduction rate of zirconia. The only endodontic problem which occurred could not be directly connected to the type of bridge framework. The reliability of zirconia bridges in this investigation was connected to the DCM-Process. No statement about other zirconia-systems can be made on the results of this study.

Dental Alloys↗
PubMedDate not supplied

Preparation and antibacterial evaluation of some nitrone derivative and their zirconium (IV) chloride complexes.

Some new complexes of the general formula ZrCl3.L where L = [N-(p-anisole)-alpha-(2-xanthatophenyl)nitrone], L1, and [N-(p-chlorophenyl)-alpha-(2-xanthatophenyl)nitrone], L2, have been prepared and characterized by elemental analysis, i.r. and molar conductances. The antibacterial activities of these compounds have been studied against five species of bacteria in vitro at concentration ranging from 1-10 micrograms/ml. A remarkable activity was exhibited by the ligand L2 against Staph. aureus and Bacillus subtilis.

Anti-Bacterial Agents↗
PubMed2001

[Effects of the mold temperature on the castability of titanium zirconium alloy for dental clinical use].

OBJECTIVE: The aims of this study were to investigate the influence of the mold temperature on the castability of Ti-Zr alloy and find out the reasonable method for casting Ti-Zr alloy in clinic. METHODS: Ti-Zr alloy, pure titanium and Ti-6Al-4V alloy were casted respectively, by using a mold made of a zircon (ZrO2.SiO2) investment and a casting machine (China) designed, with a program of vacuum, pressure and centrifuge casting at three mold temperatures (room temperature, 300 degrees C, 600 degrees C). The castability value was obtained by counting the complete segment of the cast alloy grid. The wax pattern provided a grid with 112 segments. The percentage of complete cast segments was calculated by divided by 112, and multiplied by 100. The mesh castability values of Ti-Zr alloy, pure titanium and Ti-6Al-4V alloy were examined. RESULTS: The castability of three titanium alloys was high when the mold temperature was high. The castability values of Ti-Zr alloy at three mold temperatures were 88.57% for the room temperature, 94.55% for 300 degrees C, and 96.67% for 600 degrees C. Ti-Zr alloy casted at the room temperature showed significantly lower castability value than that casted at 300 degrees C and 600 degrees C (P < 0.05), but no significant difference was found between the castability values of 300 degrees C and 600 degrees C (P > 0.05). The castability values of pure titanium at three mold temperatures were 95.33% for room temperature, 98.70% for 300 degrees C, and 98.90% for 600 degrees C. The castability values of Ti-6Al-4V alloy at three mold temperatures were 95.37% for room temperature, 96.00% for 300 degrees C, and 98.78% for 600 degrees C. When casted at room temperature, the castability values of Ti-Zr alloy were significantly decreased comparing with those of pure titanium and Ti-6Al-4V alloy (P < 0.05), but no significant difference was found when cast alloys were casted at 300 degrees C and 600 degrees C (P > 0.05). CONCLUSION: The mold temperature is one of the major factors influencing cast quality. This study suggests that in order to obtain high castability of dental Ti-Zr alloy castings in clinic, the optimal mold temperature should be higher than 300 degrees C.

Dental Alloys↗
PubMed2001

[Transverse deflection study of casted titanium zirconium alloy for dental clinic use].

OBJECTIVE: The aim of this study was to obtain the reasonable thickness of Ti-Zr alloy used for denture base material. METHODS: According to the "Revised ADA Specification No. 12 for denture base polymers", the transverse deflection tests of Ti-Zr alloy after casting were performed. Pure titanium, Ti-6Al-4V alloy and Co-Cr alloy were examined as the control. Three groups of wax patterns with different thickness were designed. Ti-Zr alloy, pure titanium and Ti-6Al-4V alloy were casted into molds at 300 degrees C, which were made of zircon (ZrO2.SiO2) investment, using a casting machine (China), with a program of vacuum, pressure and centrifuge casting. Co-Cr alloy was casted by normal method in clinic. The transverse deflections of these four alloys castings with three different thicknesses were measured using a transverse testing machine. RESULTS: When the thickness is 0.65 mm for Ti-Zr alloy, pure titanium and Ti-6Al-4V alloy, and 0.57 mm for Co-Cr alloy, the transverse deflections could satisfy the requirement. CONCLUSION: The transverse deflection is one of the key indexes for evaluating the ability of dental material to bear biting forces. The reasonable thickness of Ti-Zr alloy used as denture base material is 0.65 mm.

Dental Alloys↗
PubMed2000

[A surface reacted layer study of titanium-zirconium alloy after dental casting].

OBJECTIVE: To investigate the influence of the mold temperature on the surface reacted layer of Ti-Zr alloy castings. METHODS: Ti-Zr alloy was casted into a mold which was made of a zircon (ZrO2.SiO2) for inner coating and a phosphate-bonded material for outer investing with a casting machine (China) designed as vacuum, pressure and centrifuge. At three mold temperatures (room temperature, 300 degrees C, 600 degrees C) the Ti-Zr alloy was casted separately. The surface roughness of the castings was calculated by instrument of smooth finish (China). From the surface to the inner part the Knoop hardness and thickness in reacted layer of Ti-Zr alloy casting was measured. The structure of the surface reacted layer was analysed by SEM. Elemental analyses of the interfacial zone of the casting was made by element line scanning observation. RESULTS: The surface roughness of the castings was increased significantly with the mold temperature increasing. At a higher mold temperature the Knoop hardness of the reactive layer was increased. At the three mold temperature the outmost surface was very hard, and microhardness data decreased rapidly where they reached constant values. The thickness was about 85 microns for castings at room temperature and 300 degrees C, 105 microns for castings at 600 degrees C. From the SEM micrograph of the Ti-Zr alloy casting, the surface reacted layer could be divided into three different layers. The first layer was called non-structure layer, which thickness was about 10 microns for room temperature group, 20 microns for 300 degrees C and 25 microns for 600 degrees C. The second layer was characterized by coarse-grained acicular crystal, which thickness was about 50 microns for three mold temperatures. The third layer was Ti-Zr alloy. The element line scanning showed non-structure layer with higher level of element of O, Al, Si and Zr, The higher the mold temperature during casting, the deeper the Si permeating and in the second layer the element Si could also be found. CONCLUSION: The mold temperature is one of the major factors influencing to casting quality. In order to reduce the surface reacted layer of Ti-Zr alloy castings, the lower mold temperature and the investment without Si should be chosen.

Dental Alloys↗