Development of metal-resin composite restorative material. Part 2. Effects of acid and heat treatments of silver-tin filler particles on flexural properties of metal-resin composite.
(17/1192)
The effects of acid and heat treatments of silver-tin filler particles on the flexural properties of metal-resin composite restorative materials were investigated. Five metal-resin composite restorative materials containing different silver-tin filler particles treated under different conditions were experimentally prepared. The conditions of the alloy particles were; 1) as atomized (NT), 2) 1.8% HCl acid-treated (AT), 3) heat-treated at 150 degrees C for 5 min after AT (A15), 4) heat-treated at 200 degrees C for 5 min after AT (A20) and 5) heat-treated at 250 degrees C for 5 min after AT (A25). The flexural strength and the flexural modulus of elasticity were measured for the five metal-resin composites to evaluate the effects of the acid and heat treatments. The flexural strength of the prepared composites was significantly influenced by the surface condition of the filler particles (p < 0.01), and increased significantly when the as atomized particles (NT) were acid-treated (AT) or acid- and heat-treated at 150 degrees C (A15), but then significantly decreased as the heat treatment temperature increased (A20 and A25). The strength of the A15 composite was significantly higher than those of the other composites, and exceeded that (about 60 MPa) of the previous composite with no treatment. No significant difference was found in the flexural modulus of the composites. (+info)
Metal-resin composite restorative material using powder-liquid system.
(18/1192)
In order to further improve the mechanical properties of a metal-resin composite and avoid the problems which were found in the previous metal-resin composite using a 2-paste system, another type of metal-resin composite using a powder-liquid system was developed. In the new system 4-META treatment was carried out at low temperature and DMPT was separated from the 4-META treated particles. The efficacy of this system as well as the effects of 4-META concentration, duration of 4-META treatment (immersion time) and filler content on the flexural properties, working time and setting time were investigated. The flexural strength of the powder-liquid composite was significantly affected by two main factors, immersion time and filler content, and the other properties (flexural modulus, working time and setting time) were by all three main factors. The highest flexural strength of the prepared composite was 91.8 MPa, which was higher than that of the 2-paste composite (64.0 MPa) by about 43%. This was achieved at a 0.1 ratio of 4-META concentration, 30 s immersion time and 94 mass% filler content. The working time and setting time ranged between 2.3-13.6 min and 4.2-20.1 min, respectively, and those of the highest strength composite were 3.0 and 5.2, respectively. The results of the present study indicate that the powder-liquid system is effective to improve the properties of the metal-resin composite. (+info)
Isothermal age-hardening behaviour in a multi-purpose dental casting gold alloy.
(19/1192)
The isothermal age-hardening behaviour of a multi-purpose dental casting gold alloy was investigated by means of hardness testing, X-ray diffraction study, scanning electron microscopic observations and energy dispersive spectroscopy. By ageing of the solution-treated specimen at 400-500 degrees C, two phases of the Au-rich alpha 1 phase with an f.c.c. structure and the alpha 2 phase with an ordered f.c.c. structure based on Pt3In were transformed into three phases of the alpha 1 phase, the alpha 2 phase and the beta phase with an ordered f.c.t. structure based on PtZn. Hardening was attributed to the fine nodular precipitation resulting from the formation of the beta phase in the alpha 1 matrix. Softening was due to the coarsening of the fine nodular precipitates as the result of consumption of the alpha 2 phase. (+info)
Development of metal-resin composite restorative materia. Part 1. Experimental composite using silver-tin alloy as filler and 4-META as coupling agent.
(20/1192)
Metal-resin composites, using metal particles instead of inorganic particles as the filler and 4-META as the coupling agent, were experimentally prepared under 20 different conditions (five different concentrations of 4-META, and four different contents of metal particles). The flexural strength of the prepared metal-resin composites was in the range of about 14.5-61.3 MPa. The flexural strength was significantly influenced by the 4-META concentration, the metal particle content and their interaction. The highest strength was estimated at 2-3 mass% of 4-META concentration and 92.0-93.5 mass% metal filler content. The flexural modulus of the metal resin composite ranged approximately from 7.8 GPa to 15.5 GPa. The flexural modulus of the metal resin composite significantly increased with the metal particle content. The effect of the 4-META concentration on the flexural modulus was not significant. (+info)
Prognostic significance of DNA ploidy pattern and nucleolar organizer regions (AgNOR) in colorectal carcinoma.
(21/1192)
AIM: To investigate the prognostic significance of DNA ploidy and silver stained nucleolar organizer regions (AgNOR), as well as their relation to the histological grade and Dukes' stages of colorectal carcinomas, and the relation of tumor cells proportion in the S-phase and Dukes' stage, histologic grade, DNA ploidy, or AgNOR count. METHODS: DNA flow cytometric analysis and AgNOR were performed on 94 surgically removed colorectal carcinomas. The mean AgNOR count was calculated in 200 tumor cells for each case. Survival rates and tests for significance were evaluated using the log-rank test and Cox regression model. RESULTS: There were no significant correlations between the ploidy pattern, histological grade, and Dukes' stage. Diploid tumors had a significantly lower AgNOR count (median 2.5, range 2.1-7.7) than aneuploid (median 6.2, range 2.0-7.9). Dukes' C stage tumors exhibited higher AgNOR count than Dukes' A or B stages. The proportion of tumor cells in S-phase did not correlate with any other parameter. Each of these parameters failed to show any correlation with survival. After dividing the tumors into those with high (>5) and low AgNOR count (<5), no correlation was found in the latter group between AgNOR and any other studied parameters, whereas in the group with high AgNOR count correlations to Dukes' stage, DNA ploidy, and histological grade were established.Conclusions. The difference in survival between well, moderately, and poorly differentiated tumors were significant in the group with high AgNOR counts. Dukes' C stage and aneuploid tumors had the worst prognosis. (+info)
The perineuronal proteoglycan surface coat in the adult rat brain, with special reference to its reactions to Gomori's ammoniacal silver.
(22/1192)
The present study showed that many neurons in the adult rat brain possessed a perineuronal sulfated proteoglycan surface coat which reacted to cationic iron colloid and aldehyde fuchsin. This surface coat was stained supravitally with Ehrlich's methylene blue and doubly stained with Ehrlich's methylene blue and aldehyde fuchsin. The surface coat was also stained with Gomori's ammoniacal silver and doubly stained with Gomori's ammoniacal silver and cationic iron colloid. The surface coat was usually expressed together with a nerve cell surface glycoprotein net detectable with lectin Wisteria floribunda agglutinin. These findings indicate that the perineuronal proteoglycan surface coat is identical to Cajal's superficial reticulum and contains some collagenous elements. It was further demonstrated that collagenase digestion erased Gomori's ammoniacal silver impregnation within the perineuronal proteoglycan surface coat. (+info)
Suppression of leukocyte chemotaxis in vitro by chemotherapeutic agents used in the management of thermal injuries.
(23/1192)
Polymorphonuclear leukocytes from burned patients exhibit suppressed chemotaxis possibly related to the susceptibility of such patients to opportunistic infection. This study assesses the effect of normal serum upon burn-suppressed leukocytes and the effects of three commonly used topical chemotherapeutic agents upon the chemotaxis exhibited by granulocytes from normal controls. In vitro incubation with normal serum restored chemotaxis to normal in the suppressed granulocytes from burned patients. The serum factor responsible for this restoration was heat labile. Serum albumin alone did not exhibit this effect. Both mafenide and silver sulfadiazine suppressed the chemotactic function of granulocytes obtained from normal controls, while silver nitrate exhibited no such activity. Studies of the chemotactic function of control granulocytes after incubation with sera from burned patients yielded similar results; only the sera from patients treated with silver nitrate failed to suppress normal leukotaxis. The chemotactic impairment found in leukocytes from burned patients, however, while related to burn size and predictive of prognosis, did not vary with the agent used for the topical therapy. These data suggest the presence of a reversible intrinsic defect in leukotaxis consequent to burn injury, related to some factor deficient in burn serum. In addition, extrinsic impairment of normal granulocyte leukotaxis by two commonly used chemotherapeutic agents is demonstrated. (+info)
Role of a Candida albicans P1-type ATPase in resistance to copper and silver ion toxicity.
(24/1192)
Copper ion homeostasis is complicated in that copper is an essential element needed for a variety of cellular processes but is toxic at excess levels. To identify Candida albicans genes that are involved in resistance to copper ion toxicity, a library containing inserts of C. albicans genomic DNA was used to complement the copper sensitivity phenotype of a Saccharomyces cerevisiae cup1Delta strain that is unable to produce Cup1p, a metallothionein (MT) responsible for high-level copper ion resistance. A P1-type ATPase (CPx type) that is closely related to the human Menkes and Wilson disease proteins was cloned. The gene encoding this pump was termed CRD1 (for copper resistance determinant). A gene encoding a 76-amino-acid MT similar to higher eukaryotic MTs in structure was also cloned, and the gene was termed CRD2. Transcription of the CRD1 gene was found to increase upon growth with increasing copper levels, while the CRD2 mRNA was expressed at a constant level. Strains with the CRD1 gene disrupted were extremely sensitive to exogenous copper and failed to grow in medium containing 100 microM CuSO(4). These crd1 strains also exhibited increased sensitivity to silver and cadmium, indicating that Crd1p is somewhat promiscuous with respect to metal ion transport. Although strains with the CRD2 gene disrupted showed reduced growth rate with increasing copper concentration, the crd2 mutants eventually attained wild-type levels of growth, demonstrating that CRD2 is less important for resistance to copper ion toxicity. Crd1p is the first example of a eukaryotic copper pump that provides the primary source of cellular copper resistance, and its ability to confer silver resistance may enhance the prevalence of C. albicans as a nosocomial pathogen. (+info)