Strengthening of porcelain by ion exchange subsequent to thermal tempering

The purpose of this study was to test the hypothesis that high-leucite content feldspathic porcelain can be strengthened best by thermal tempering followed by ion exchange, compared with either thermal tempering or ion exchange alone. The results of biaxial flexure testing indicate that thermal tempering was the most effective way of strengthening the porcelain among the three methods tested. The combined procedure did not yield the greatest strengthening effect as hypothesized, but one that is only slightly stronger than that produced by ion exchange alone. Weibull analysis indicated that the ion-exchange treatment resulted in a narrower distribution of biaxial flexural strength compared with that of untreated or thermally tempered porcelain. The narrower distribution of biaxial flexural strength is considered desirable for enhancing the longevity of ceramic-based dental restorations.

Tumors of the heart. An analysis of 79 cases

There were 79 cases of cardiac tumors seen from 1957 to July 1988. 49 (62.0%) of them were benign and 30 (38.0%) malignant. All the 49 benign tumors except 2 were surgically excised and found to be myxoma. Of them, 18 patients were male and 31 female. 85.7% of the tumors were located in the left atrium, 12.2% in the right atrium and 2.0% in the left ventricle. Palpitation, dyspnea, chest oppression, fever, episodes of syncope and hemiplegia, cough, diastolic and systolic murmurs at the apical or tricuspid area were the common symptoms and signs. Atrial fibrillation was found only in 2 cases. Echocardiographic findings were diagnostic while ECG and X-ray findings were nonspecific. Four patients died after operation. Of the 30 cases of malignant tumors, 15 were secondary tumors metastasized mainly from the lung or mediastinal malignancies. Of 11 primary tumor cases (7 males and 4 females), 3 were malignant lymphoma, 2 mesothelioma of pericardium, 2 malignant myxoma, 1 angiosarcoma, 1 leiomyosarcoma, 1 fibrosarcoma and 1 rhabdomyosarcoma. Another 4 cases were not studied histopathologically. The clinical manifestations, ECG and X-ray findings of the 11 primary tumors were nonspecific but echocardiography was helpful to the diagnosis. Six patients were operated on and 1 died during hospitalization.

Effects of ammonium and lactate on hybridoma cell growth and metabolism

The effects of ammonium and lactate at different concentrations on the growth of 2F7 hybridoma cells, involving glucose consumption, lactate accumulation and cell viability, are investigated. The results suggest that growth inhibition occurs at 2.5 mM ammonium and 2.5 mg/ml lactate, and that severe inhibition occurs at 5 mM ammonium and 5.0 mg/ml lactate.

Analysis of ras gene mutations in gastrointestinal cancers

Point mutations of c-Ki-ras genes were analyzed in 33 samples of human gastrointestinal malignancy. DNA extracted from the frozen tissue was amplified by polymerase chain reaction (PCR) and analyzed by direct sequencing and slot-blot hybridization at codons 12, 13 and 61 of c-Ki-ras. In 7 cases out of 19 colorectal cancers, point mutations were found: 3 cases at codon 12, 1 at codon 13, 2 at codon 61 of c-Ki-ras and one case had double mutations at codon 12 and codon 13. In 11 cases of gastric cancer, 4 showed point mutations: 1 at codon 12 and 3 at codon 13 of c-Ki-ras. In 3 pancreatic carcinomas, 2 had point mutations: one at codon 12 and the other at codon 13 of c-Ki-ras. The results indicate that c-Ki-ras gene point mutations are involved in the tumorigenesis of the human gastrointestinal system.

[A study of histamine receptors in peripheral lymphocytes in asthmatic subjects]

The identification and quantitative analysis of specific histamine H1 and H2 receptors on lymphocytes were acquired and histamine-induced suppressor cell activity was examined by using 3H-histamine radioligand-binding assay and co-culture technique. The quantitative analysis of H2 receptors decreased on the lymphocytes of extrinsic asthmatic subjects. Peripheral-lymphocytes from asthmatic subjects generated less histamine-induced suppressor activity than did those from normal individuals. In the asthmatics, the functional suppressor-cell abnormality positively correlated with the decreased quantity of H2 receptors on the lymphocytes.

New inhibitors of aldose reductase: anti-oximes of aromatic aldehydes

Aldose reductase is an NADPH-dependent enzyme which catalyzes the reduction of glucose to sorbitol. Specific potent inhibitors of aldose reductase are of potential pharmacological use because elevated levels of sorbitol produced by this enzyme in lens, peripheral nerve, retina, and renal glomeruli may be responsible for the pathogenesis associated with chronic diabetes. These inhibitors could also serve as probes of the mechanism of action of aldose reductase. anti-Oximes of aromatic aldehydes (e.g., benzaldoxime and 4-fluorobenzaldoxime) have proved to be effective inhibitors of aldose reductase rivaling pharmacological agents currently used to inhibit this enzyme in vivo. The kinetic patterns of inhibition in which benzyl alcohol is used as the oxidizable substrate suggest that the inhibition is due to the formation of a stable ternary complex composed of aldose reductase, NADP+, and the anti-oxime. Analogus ternary complexes are formed at the active site of horse liver alcohol dehydrogenase which is also inhibited by anti-oximes of efficient substrates.

Influence of initial flaw size on crack growth in air-tempered porcelain

Tempering of dental porcelain by forced convective cooling in air has been shown previously to inhibit the sizes of cracks induced in porcelain surfaces. However, the depth of compressive stress that is produced by tempering of feldspathic porcelain has not been determined. It can be assumed that the potential of tempered specimens to inhibit crack formation is reduced as the flaw size exceeds some critical value, since the compressive stress decreases with distance from the surface. The objective of this study was to test the hypothesis that the effectiveness of tempering stress in porcelain decreases with the increasing size of initial surface flaws. Body porcelain discs, 16 mm in diameter and 2 mm in thickness, were tempered (T) by forced convective cooling in air from an initial temperature of 982 degrees C at a pressure of 0.34 MPa for 90 s. Nontempered control discs (NT) were slowly cooled by termination of power to the furnace. The half crack-lengths (c) of surface cracks induced by a Vickers microhardness indenter at loads ranging from 2.0 to 39.2 N were determined initially and over a period of 24 h. The initial half crack-lengths, co, for the tempered specimens were significantly smaller (p less than 0.05) than the corresponding values for the slow-cooled specimens. The mean value of the stress corrosion susceptibility coefficient (n), which is inversely related to the slope of log crack size vs. log time, was only slightly smaller for the NT specimen groups (15.3), compared with the mean value for the T groups (17.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Prebiotic synthesis of histidyl-histidine

Histidyl-histidine (His-His) has been synthesized in a yield of up to 14.4% under plausible prebiotic conditions using histidine (His), cyanamide, and 4-amino-5-imidazole carboxamide. A trace amount of His trimer was also detected. Because the imidazole group of His is involved in a number of important enzymatic reactions, and His-His has been shown to catalyze the prebiotic synthesis of glycyl-glycine, we expect this work will stimulate further studies on the catalytic activities of simple His-containing peptides in prebiotic reactions.

Prebiotic synthesis of histidine

The prebiotic formation of histidine (His) has been accomplished experimentally by the reaction of erythrose with formamidine followed by a Strecker synthesis. In the first step of this reaction sequence, the formation of imidazole-4-acetaldehyde took place by the condensation of erythrose and formamidine, two compounds that are known to be formed under prebiotic conditions. In a second step, the imidazole-4-acetaldehyde was converted to His, without isolation of the reaction products by adding HCN and ammonia to the reaction mixture. LC, HPLC, thermospray liquid chromatography-mass spectrometry, and tandem mass spectrometry were used to identify the product, which was obtained in a yield of 3.5% based on the ratio of His/erythrose. This is a new chemical synthesis of one of the basic amino acids which had not been synthesized prebiotically until now.

The effect of glutaraldehyde base disinfectants on denture base resins

The effect of two alkaline glutaraldehyde base disinfectants on a heat-cured denture base resin was evaluated by the flexural strength, the repair flexural strength, and the surface morphology of the material that had been immersed up to 12 hours in the disinfecting solutions. The flexural strength of the material was not significantly affected by either disinfectant. The disinfectant with phenolic buffer caused surface pitting of the material after 10 minutes of immersion, and softening and swelling of the surface after 2 hours of immersion. No apparent surface change was observed with the regular alkaline formulation, however. Between the two repair resins, the autopolymerized resin yielded greater repair flexural strength than the light-cured repair resin. However, the repair flexural strength of autopolymerized resin seemed to be influenced by either disinfecting solution whereas the light-cured repair resin was not affected.

Prebiotic synthesis of imidazole-4-acetaldehyde and histidine

The prebiotic synthesis of imidazole-4-acetaldehyde and imidazole-4-glycol from erythrose and formamidine has been demonstrated as well as the prebiotic synthesis of imidazole-4-ethanol and imidazole-4-glycol from erythrose, formaldehyde and ammonia. The products were identified by TLC, HPLC, and LC-MS by comparison with authentic samples. The maximum yields of imidazole-4-acetaldehyde, imidazole-4-ethanol, and imidazole-4-glycol obtained in these reactions are 1.6, 5.4, 6.8% respectively, based on the erythrose. Imidazole-4-acetaldehyde would have been converted to histidine on the primitive earth by a Strecker synthesis, and several prebiotic reactions would convert imidazole-4-glycol and imidazole-4-ethanol to imidazole-4-acetaldehyde.

Assessment of microleakage of restorative materials by a diffusion model

The time-dependent microleakage behaviour of two types of restorative materials, a microfilled composite resin and a glass ionomer, was studied. A dentine bonding agent was also included. This study was based on a diffusion model of microleakage. It was found that the initial gap sizes of the restorations increased progressively for restorations microfilled with bonding agent, microfilled alone, and glass ionomers, in that order. Analysis of microleakage over some periods suggests that the gap size of the restorations by microfilled with bonding agent may increase with time, and that while restorations by glass ionomer and microfilled composite resin decrease in gap sizes with time, glass ionomer restorations show a faster rate of decrease.

Controlled release of fluoride in connection with dental composite resins

A delivery system of F- in connection with dental restorations was tested. The system utilized the gap space which often exists between the restorative material and the tooth structure. A known quantity of fluoride compound was placed at a site within prepared plastic cavity blocks prior to restoring with composite resins. It was found that each specimen exhibited a unique steady-state release of F- during a certain period of the experiment. The rate and duration of the steady-state release of fluoride were independent of the types of composites used. This phenomenon was explained in terms of the gap size which could have been influenced by the manipulation and the nature of the materials. The benefit of this delivery system in dental application is its ability to maintain a high concentration of F- within the gap.

Interactive effect of stress and temperature on creep of PFM alloys

The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the glass transition temperature of dental porcelains. In comparison, a Ni-Cr alloy and a Pd-Co alloy demonstrated superior creep resistance at high-stress, low-temperature conditions. This indicates a relatively low potential for deformation due to stresses which may result from a thermal contraction differential between these two alloys and incompatible dental porcelains.

Effects of canal lubrication on retention of cemented posts

The effect of lubricating the canal space prior to making a custom acrylic post pattern was studied in regard to the retention of cast posts cemented with zinc phosphate. Ways of removing the lubricant before cementation were also evaluated.

The prebiotic synthesis and catalytic role of imidazoles and other condensing agents

In the past decade significant advances have been made in the synthesis of oligonucleotides and other polymers by means of imidazoles and other condensing agents. In spite of the current knowledge of the chemistry of imidazoles and their importance as prebiotic catalysts, their formation under primitive earth conditions has not been properly demonstrated. We have now been able to synthesize imidazole as well as its 2-methyl and 4-methyl derivatives under plausible prebiotic conditions. One method utilizes an aldehyde (formaldehyde or acetaldehyde), glyoxal and ammonia as the starting materials for the formation of imidazole and 2-methylimidazole. The other method uses a carbohydrate and ammonia as the key reagents for the synthesis of 4-methylimidazole. The importance of imidazole and related compounds (e.g., cyanamide) in the synthesis of oligonucleotides has been studied by us as well as others. Apparently the charge relay group (-N-C-N-) present in imidazoles, carbodiimides, cyanamide, or the histidine and arginine of enzyme active centers is essential for the synthesis of phosphodiester and pyrophosphate bonds.

Antibodies from patients with connective tissue diseases bind specific subsets of cellular RNA-protein particles

We characterized the RNA-containing antigens precipitated by sera from 260 patients with positive antinuclear antibodies. 49 individuals, most of whom had systemic lupus erythematosus or Sjögren's syndrome, possessed antibodies that precipitated the previously identified RNP, Sm, Ro, and La antigens either singly or in combinations. These antigens, which are located on discrete sets of small nuclear or cytoplasmic RNA-protein particles, exhibited a number of antigenic interrelationships. One patient's serum recognized a new particle containing a small RNA which we have called Th; it also precipitated the Ro complexes. Other patients with systemic lupus erythematosus, hepatitis B virus infection, juvenile rheumatoid arthritis, myositis, and rheumatoid arthritis had antibodies that precipitated specific subsets of ribosomal RNA and transfer RNA. One patient's serum contained a monoclonal immunoglobulin G that precipitated ribosomes. Most of these antibodies identified antigenic determinants constituted at least in part of protein. The specificity of the proteins bound to particular cellular RNA, probably explains the exquisite precision with which antibodies from rheumatic disease patients discriminate among RNA subsets. Such sera should be useful probes for investigating specific roles that different RNA and RNA-protein complexes play in cellular metabolism.

Effect of K2SO4 and CaSO4 dihydrate solutions on crystallization and strength of gypsum

Crystal formation obtained from evaporating clear filtrates of dental stone mixed with various solutions were examined with an optical and scanning electron microscope. It was found that when K2SO4 was present in any concentration, a spherulitic structure dissimilar to that of CaSO4. 2H2O and K2SO4 was dominant. It is concluded that syngenite (a complex compound of CaSO4 and K2SO4) forms at the center of the nuclei of crystallization and is responsible for spherulitic formation. The use of K2SO4 solution and saturated CaSO4 solution was also found to improve the strength both at one and 24 h.

A 31P-NMR study of the cross-membrane pH gradient induced by ATP hydrolysis in mitochondria

31P-NMR has been used to study the increase of delta pH in mitochondria by externally added ATP. Freshly prepared mitochondria was treated with N-ethylmaleimide to inhibit the exchange between internal and external P(i). Upon addition of ATP, phosphocreatine (30 mM) and creatine kinase to a NMR sample of mitochondria suspension (approx. 120 mg protein/ml) at 0 degrees C, an increase of delta pH by approx. 0.5 pH unit was observed. However the increased delta pH could not be maintained, but slowly decayed along with the increase of external ADP/ATP ratio. Further addition of valinomycin to the suspension induced a larger delta pH (approx. 1) which was maintained by the increased rate of internal ATP hydrolysis as seen in the growth of the internal P(i) peak intensity in NMR spectra and the concomitant decrease of the external phosphocreatine peak. The external P(i) and ATP peaks stayed virtually constant. When carboxyatractyloside was added to inhibit the ATP/ADP translocase, the internal P(i) increase was stopped and the delta pH decayed. These observations in conjunction with those made earlier in respiring mitochondria clearly show the reversible nature of the ATPase function in which the internal ATP hydrolysis is associated with outward pumping of protons.

Sugar pucker geometries at the intercalation site of propidium diiodide into miniature RNA and DNA duplexes in solution

We have evaluated the sugar pucker geometry at the intercalation site of propidium diiodide into the self-complementary dinucleoside monophosphate duplexes cytidylylguanosine and deoxycytidylyldeoxyguanosine as a function of the nucleotide/drug ratio in aqueous solution. Our solution results support the observation by Sobell and coworkers [Sobell, H.M., Tsai, C.C., Jain, S.C. & Gilbert, S.G. (1977) J. Mol. Biol. 114, 333--365] of a C3' endo (3'-5')C2' endo sugar pucker geometry in the 2:2 intercalation complex of ethidium bromide into the iodocytidylylguanosine duplex in the crystalline state. We demonstrate further that the mixed sugar pucker observed for the intercalation of propidium diiodide into the miniature RNA duplex in solution persists in the intercalative complex of this trypanocidal drug into the corresponding miniature DNA duplex in solution.

Leucine aminopeptidase from swine kidney: purification, molecular weight, subunit and amino acid composition

A homogeneous leucine aminopeptidase was obtained from mixed breed swine kidneys by means of chromatography on a special column. After coupling an inhibitor, N-sulfanilyl N'-butylcarbamide, to Sepharose 6B, the derivative did not absorb the enzyme, but absorbed a non-enzymatically active protein. The enzyme showed a single band on disc-gel electrophoresis. The molecular weight of the enzyme has 320,000 daltons. In 6 M guanidine solution containing 0.5% 2-mercaptoethanol at pH 8, the enzyme exhibited a molecular weight of 53,000 on equilibrium centrifugation. A similar value, 54,000, for the subunit of the enzyme was found on SDS-gel electrophoresis. The amino acid composition of the enzyme is also reported.

Free acid, anion, alkali, and alkaline earth complexes of lasalocid a (X537A) in methanol: structural and kinetic studies at the monomer level

We report below on nuclear magnetic resonance investigations of the structure and exchange kinetics for the free acid, anion, sodium complex, and barium complex of the ionophore lasalocid A (X537A) in methanol solution. A comparison between the proton and carbon longitudinal relaxation times of lasalocid in nonpolar and polar solvents demonstrates that the free acid (HX) is a monomer in methanol solution. Parallel proton and carbon relaxation measurements demonstrate that the anion (X-), sodium complex (NaX), and barium complex (BaX+) are also monomeric in methanol solution. These results are in contrast to the Na2X2 dimer and the BaX2-H20 dimer observed in crystals and in nonpolar (cyclohexane and methylene chloride) solutions. Large downfield shifts on complex formation (X- to NaX and BaX+) are detected for protons located on the polar face of the ionophore with their C-H bonds directed towards and proximal to the metal ion. The exchange of lasalocid anion between free (X-) and complexed (BaX+) states in methanol can be monitored from the temperature-dependent line shapes of the proton resonances at superconducting fields. The exchange rates are independent of the reactant concentrations and are characteristic of a rate-determining dissociation of BaX+ in methanol solution with activation parameters delta H++ = 6.5 kcal mol-1 (25 degrees) and delta S++ = -20.0 cal mol-1 degree -1 (1 cal = 4.184 J). The rate constants for dissociation and formation of BaX+ complex in methanol, 25 degrees, are 5.2 X 10(3) sec-1 and 1.5 X 10(10) M-1 sec-1, respectively. These studies were extended to derive the activation parameters for the exchange of lasalocid anion between BaX+ and NaX and between BaX+ and HX in methanol, while the exchange among HX, X-, and NaX is too rapid to be monitored on the time scale of nuclear magnetic resonance.

Structural and kinetic studies of lasalocid A (X537A) and its silver, sodium, and barium salts in nonpolar solvents

The ionophore lasalocid A (X537A) and its metal salts have been investigated by high resolution (270 MHz and 360 MHz) proton nuclear magnetic resonance spectroscopy to obtain structural and kinetic information in nonpolar solution. The proton resonances were assigned from double resonance studies on lasalocid A and on its salts, homologs, isomers, and chemically modified derivatives. Studies of proton and carbon longitudinal relaxation time suggest that lasalocid A exists as a monomer, whereas the sodium and barium salts exist as dimers in nonpolar solvents. A study of the magnitude of the vicinal proton coupling constants and the chemical shifts and linewidths of the hydroxyl resonances suggest that the backbone conformation and intramolecular hydrogen bonds are similar for lasalocid A and its sodium and barium salts in nonpolar solvents. Nuclear magnetic resonance studies on the role of bound solvent molecules suggest a tightly bound water molecule in the barium complex dimer (crystallized from water-ethanol) and a weakly bound ethanol molecule in the lasalocid A monomer (crystallized from ethanol) in cyclohexane. The selective changes in proton chemical shift on complexation [where the polar faces of two lasalocid anions coordinate the metal cation(s) in nonpolar solvents have been analyzed in terms of the proximity of the resonances to the cation, their linkage to the coordinating oxygen atoms, and the magnetic anisotropy effects of the polar groups of one ligand on the resonances of its partner in the dimer. The nuclear magnetic resonance studies in solution are compared with earlier observations on lasalocid A and its salts in the crystalline state. Thus, the short Ag-C5 distance in the crystal structure of silver complex dimer is also observed in the solution structure. The kinetic parameters associated with the exchange between lasalocid A and its barium complex in chloroform have been measured from an analysis of the resonance line shapes as a function of temperature.