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PubMed2005

Dynamic mechanical analysis of provisional resin materials reinforced by metal oxides.

In this study, several provisional resin materials were investigated by dynamic mechanical analysis (DMA). The materials were autopolymerized PMMA and PEMA, light cured PMMA. Autopolymerized PMMA has the highest T(g) (131 degrees C) compared to that of the autopolymerized PEMA (102 degrees C) and light cured PMMA (120 degrees C). The storage moduli for autopolymerized PMMA, autopolymerized PEMA and light cured PMMA are 2.9, 1.8 and 2.3 GPa, respectively. The loss moduli of the same resins are 330, 300 and 350 MPa, respectively. Each of these resins were reinforced with 1%, 3% and 5% of each of metal oxides of MgO, ZrO2 and Al2O3 and then studied with DMA. Small changes were observed for dynamic mechanical properties tested. However, the changes are not systematic and noticeable. This is most probably due to smaller size of metal oxides particles compared to that of polymer particle size.

Aluminum Oxide↗
PubMed1985

[Cerestore].

Explore the source record for details and available documents.

Aluminum Oxide↗
PubMed2001

Application of spinel-type cobalt chromite as a novel catalyst for combustion of chlorinated organic pollutants.

Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants. A spinel-type cobalt chromite (CoCr2O4) among others was proven to be a very promising catalyst showing higher activity and higher CO2 selectivity than traditional alumina supported chromia. Even if both Cr3+ and Cr6+ species were observed on the surface of CoCr2O4, the Cr6+ species was stable under reducing environment. The presence of Cr3+-Cr6+ pair sites and the effect of redox treatments on the activity were investigated to explain the nature of possible active sites for TCE decomposition. Higher selectivity to CO2 of CoCr2O4 was ascribed to the abundance of its Cr3+ species, together with its activity for water gas shift reaction.

Aluminum Oxide↗
PubMed1998

Effects of magnesia and potassium sulfate on gypsum-bonded alumina dental investment for high-fusing casting.

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.

Aluminum Oxide↗
PubMed2000

Interfacial oxidations of pure titanium and titanium alloys with investments.

External oxides of a commercially pure titanium (cpTi), Ti6Al4V alloy, and an experimental beta-type titanium alloy (Ti 53.4 wt%, Nb 29 wt%, Ta 13 wt%, and Zr 4.6 wt%) were characterized after heating to 600, 900, 1150, and 1400 degrees C in contact with three types of investments (alumina cement, magnesia cement, and phosphate-bonded) in air. XRD studies demonstrated that MgO, Li2TiO3 and/or Li2Ti3O7 were formed through reactions with the metal and the constituents in the magnesia cement-investment after heating to 900, 1150, and 1400 degrees C. Except for these conditions, TiO2 (rutile) was only formed on cpTi. For titanium alloys, the other components apart from Ti also formed simple and complex oxides such as Al2O3 and Al2TiO5 on Ti6Al4V, and Zr0.25Ti0.75Nb2O7 on the beta-type titanium alloy. However, no oxides containing V or Ta were formed. These results suggest that the constituents of titanium alloys reacted with the investment oxides and atmospheric oxygen to form external oxides due to the free energy of oxide formation and the concentration of each element on the metal surface.

Alloys↗
PubMedDate not supplied

Strength of magnesia-core crown with different body porcelains.

The diametral strengths of magnesia-core crowns made with different body porcelains, Will-Ceram, Crystar, Ceramco II, and Vita VMK 68, were measured. The results were compared to the diametral strengths of aluminous-core crowns and Renaissance crowns. A one-way analysis of variance showed that there were no significant differences in the strengths of magnesia-core crowns or the aluminous-core crowns, but the Renaissance crown strengths were significantly lower.

Aluminum Oxide↗
PubMed1996

Surface reaction between titanium castings and investments.

The selection of investments suitable for titanium castings is critical because the surface-reacted layer greatly affects their mechanical properties. This study analyzed the interfacial zone of titanium castings obtained from various commercial investments and examined the relationship between the surface-reacted layer and the hardness. CP titanium disks (20 mm diameter, 1 mm thick, n = 5) were cast using eight commercial casting systems and investments for titanium casting: two alumina-based investments (T-invest, CD-titan investment), two spinel-based investments (Titanmold, Titavest MZ), three zirconia-based investments (Asahivest-D, Titaniumvest EX, Tycast investment TM), and a magnesia-based investment (Selevest CB). The Vickers hardness of cast disks in cross-section was tested at 50 microns intervals from the surface to 0.5 mm in depth. The cross-section was observed metallurgically, and an elemental mapping measurement of the reacted layer was conducted under the EPMA. The Vickers hardnesses at 50 microns from the surface of the specimens ranged 312 to 624 and were significantly different among the investments (p < 0.01). The thickness of the reacted layer, rich in O, Si, Al, Zr, Mg, and P, ranged from 10 to 60 microns. No correlation was seen between the thickness of reacted layer and the hardness (p > 0.05). However, the specimens cast with alumina-based and zirconia-based investments were harder than the spinel-based and magnesia-based investments at 500 microns. Although the free energies of metal oxide formation of alumina and zirconia were lower than titania, these data suggest that silica, alumina and zirconia were reduced by contact with molten titanium. Accordingly, silicon, aluminum and zirconium diffused to the interior of the titanium castings and changed their mechanical properties.

Aluminum Oxide↗
PubMed1993

Titanium. A review of investments for high temperature casting.

Conventional silica (SiO2) based dental casting investments are used for the casting of pure titanium using casting machines specifically developed for this metal. Highly reactive molten titanium reduces SiO2 and titanium is in turn oxidised. For this reason possible alternatives to SiO2 have been studied in the past decade and MgO and Al2O3 are the most common in current commercial investments released for titanium casting. The surface of titanium castings presents a layered structure and its evaluation in relation to clinical performance requires further study. It is also urgently required to know setting and thermal behaviour of the newly developed investments for successful compensation of metal shrinkage.

Aluminum Oxide↗
PubMedDate not supplied

Esthetic improvements and in vitro testing of In-Ceram Alumina and Spinell ceramic.

The original In-Ceram material (In-Ceram Alumina), composed of sintered aluminum oxide subsequently infused with a glass, features interesting mechanical properties. In-Ceram Spinell was marketed more recently to improve the esthetic potential. This study compared the flexural strength of various combinations of sintered alumina and spinel infiltrated with the associated glasses. In addition, the influence of vacuum during the infusion process was investigated using density measurements. The characteristic strength (load at which 63% of the specimens had failed) was 530 MPa for the original material, 523.7 MPa when the same material was infiltrated under vacuum, 481.4 MPa when sintered alumina was infused under vacuum with the glass originally marketed for the spinel, and 283.1 MPa for the sintered spinel infiltrated under vacuum with the associated glass. A significant increase in density was observed when the infiltration firing of sintered alumina was performed under vacuum. Furthermore, the in vivo evaluation of specific esthetic parameters inherent to different types of cores was made and revealed the relative opacity of alumina; spinel was found to have the ability to blend in with the underlying substrate. Both materials demonstrated a general lack of fluorescence.

Aluminum Oxide↗
PubMed2006

Activities of rat cytochrome P450 3A and 2C isoforms are increased in vivo by magnesium sulfate as evidenced by enhanced oxidation of bupivacaine and testosterone in liver microsomes.

We previously reported that magnesium sulfate (MgSO(4)) increases the threshold dose of bupivacaine in inducing seizure in rats. Cytochrome P450 (P450) isoforms involved in the biotransformation of bupivacaine to three oxidative metabolites and the effects of MgSO(4) in vivo on the P450 activities in rats were investigated. Of six cDNA-expressed rat P450 isoforms tested, CYP3A2 and CYP2C11 had high rates for N-debutlylation and 3'-hydroxylation of bupivacaine, respectively. The liver microsomes prepared from male rats pretreated with intravenous administration of MgSO(4) (a bolus dose of 25 mg/kg, followed by infusion of 2.0 mg/kg/min for 6 h) showed increased V(max) values for N-debutylation and 3'-hydroxylaiton of bupivacaine compared to the liver microsomes from control rats. Administration of MgSO(4) also increased the activities of testosterone 6beta- and 16alpha-hydroxylation. Although the level of expression of CYP3A and CYP2C isoforms in the liver microsomes were unchanged, NADPH-P450 reductase and cytochrome b(5) were found to be induced by intravenous administration of MgSO(4). These results suggest that CYP3A and CYP2C isoforms are activated by MgSO(4) in vivo as a consequence of enhanced microsomal electron transfer due to induction of NADPH-P450 reductase and cytochrome b(5), leading to the increased metabolism and clearance of bupivacaine.

Anesthetics, Local↗
PubMed2002

Strength and fracture toughness of MgO-modified glass infiltrated alumina for CAD/CAM.

OBJECTIVE: This study was conducted to investigate the effect of MgO additive to Al2O3 on the flexural strength, fracture toughness of glass infiltrated alumina for CAD/CAM application. METHODS: Alumina blanks with additive of 0.5 wt% MgO were prepared via isostatic pressing and sintering at 1400 degrees C for 2h, and then alumina-glass composites were fabricated by infiltrating the molten glass into the partially sintered alumina compact. Flexural strength and fracture toughness were determined using three point bending methods and a single edge notched beam method. The mechanism of crack propagation was observed under a field emission scanning electron microscope. RESULTS: The three-point flexural strength and fracture toughness of partially sintered alumina and alumina-glass composite were 210 MPa, 1.86 MPam(1/2), and 432.2 MPa, 5.12 MPam(1/2), respectively, and they were free of shrinkage during the processing of glass infiltration. The field emission SEM micrograph indicated that indentation caused a non-planar crack propagation including crack deflection and crack bowing. SIGNIFICANCE: MgO was used as an additive to alumina to improve the strength and fracture toughness of partially sintered alumina and alumina-glass composite. The high strength and toughness are related to toughening by the distribution of alumina with uniform particle sizes, crack bowing, crack deflection and the beneficial wetting properties of the particle surface.

Aluminum Oxide↗
PubMed1989

Pulmonary alveolar proteinosis and cement dust: a case report.

Pulmonary alveolar proteinosis developed in a 29-year-old white man within 2 years of working as a cement truck driver. Pulmonary alveolar proteinosis (PAP), an uncommon respiratory disorder characterized by the accumulation of phospholipid material within the alveoli, has been described in association with exposure to silica, aluminum oxide, and a variety of dusts and fumes. Although a link between exposure to Portland cement and PAP has not been previously noted, this type of cement contains nearly 20% silica. Lung biopsy material, originally used to diagnose PAP, was reviewed under electron dispersive spectroscopy. Analysis indicated the presence of silica particles within the alveolar fluid and macrophages. A number of items support a causal relationship between exposure to cement dust and PAP: (1) the temporal sequence between assuming job duties and the development of the illness, (2) improvement following removal from further exposure, (3) dusty, unprotected working conditions, (4) the presence of silica within the cement, and (5) the alveolar fluid from periodic acid-Schiff-positive lung tissue.

Adult↗