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At least 1,405 records · Page 78Linked to original sources
PubMed1995

In vitro enamel remineralization at orthodontic band margins cemented with glass ionomer cement.

Demineralization adjacent to orthodontic bands remains a clinical concern. The release of fluoride from glass ionomer cement has been shown to inhibit demineralization. The purpose of this study was to examine the remineralization effects of a glass ionomer cement adjacent to orthodontic bands. Forty extracted molars were painted with an acid-protective varnish, excluding a 2 x 6 mm window on the buccal surfaces. Artificial caries-like lesions were created in the exposed enamel with an acidified gel. Half the lesion on each tooth was then painted with an acid-protective varnish. An orthodontic band was cemented with a glass ionomer cement or zinc phosphate cement, the gingival margin of the band located at the level of the artificial carious lesion. The teeth were placed in separate closed environments of a nonfluoridated artificial saliva for 3 months. The teeth were then sectioned and photographed with polarized light microscopy in imbibition medias of water and Thoulet's (R.I.: 1.41, 1.47), representing a minimum of 5%, 10%, and 25% pore volume, respectively. With a sonic digitizer, the area of the body of the lesion was measured in each imbibition media, comparing the maintained varnished out lesions to the lesions exposed to the cement. Results demonstrated a statistically significant reduction in the body of the lesions (p < 0.005) for those exposed to the glass ionomer cement.

Dental Caries↗
PubMed1995

Clinical comparison between a glass ionomer cement and a composite for direct bonding of orthodontic brackets.

The clinical performance of a glass ionomer cement for direct bonding of orthodontic brackets was compared with a composite resin routinely used in this procedure. Brackets were bonded, using both materials, in alternate quadrants of 16 patients of the Orthodontic Clinic of the State University of Rio de Janeiro. A total of 225 teeth, 112 in the glass ionomer cement group and 113 in the composite group, were tested. Bond failure frequencies were recorded for 12 months, and chi-square statistical test was carried out comparing the failure rates of the materials. The composite showed a statistically significant lower failure rate (7.96%) than the glass ionomer cement (50.89%), regardless of the dental arch tested. Although the glass ionomer cement presents important properties not observed in the composite, it is necessary to increase its cohesive strength to permit its clinical use for direct bonding of orthodontic brackets.

Adolescent↗
PubMed2000

Non-bridging oxygens in borate glasses: characterization by 11B and 17O MAS and 3QMAS NMR.

The concentrations of non-bridging oxygens (NBO) in oxide glasses has major effects on their properties and on those of their precursor glass melts. In borate and borosilicate glasses, the presence of NBO bonded to boron has generally been inferred from 11B NMR spectra and mass balance considerations. Here we report the direct observation of such NBO using 17O MAS and 3QMAS techniques, and compare estimates of their populations with those derived from high-resolution 11B MAS spectra. For the latter, two independent methods are used, based on the ratios of trigonal to tetrahedral boron and on the concentrations of trigonal boron sites with large quadrupolar asymmetry parameters. We include data on crystalline sodium pyroborate (Na4B2O5) and sodium metaborate (NaBO2), and several sodium and barium borate glasses. 17O chemical shifts and quadrupolar coupling constants for NBO bonded to boron vary considerably depending on their coordination environment. In borosilicates, peaks for this species may be hidden by overlap with B-O-Si or Si-O-Si resonances.

Borates↗
PubMed2002

An AFM determination of the effects on surface roughness caused by cleaning of fused silica and glass substrates in the process of optical biosensor preparation.

The covalent attachment of organic films and of biological molecules to fused silica and glass substrates is important for many applications. For applications such as biosensor development, it is desired that the immobilised molecules be assembled in a uniform layer on the surface so as to provide for reproducibility and speed of surface interactions. For optimal derivatisation the surface must be appropriately cleaned to remove contamination, to create surface attachment sites such as hydroxyl groups, and to control surface roughness. The irregularity of the surface can be significant in defining the integrity and density of immobilised films. Numerous cleaning methods exist for fused silica and glass substrates and these include gas plasmas, and combinations of acids, bases and organic solvents that are allowed to react at varying temperatures. For many years, we have used a well established method based on a combination of washing with basic peroxide followed by acidic peroxide to clean and hydroxylate the surface of fused silica and glass substrates before oligonucleotide immobilisation. Atomic force microscopy (AFM) has been used to evaluate the effect of cleaning on surface roughness for various fused silica and glass samples. The results indicate that surface roughness remains substantial after use of this common cleaning routine, and can provide a surface area that is more than 10% but less than 30% larger than anticipated from geometric considerations of a planar surface.

Biosensing Techniques↗
PubMed2002

Optimisation of glass surfaces for optical immunosensors.

The surfaces of glass sensor chips were modified with dextran to generate a layer protecting the sensor surface from unspecific protein binding and also serving as a matrix for covalent protein immobilisation. Dextran was coupled to the glass surface in different concentrations either covalently on amino-functionalised glass chips or via biotin-avidin binding. Unspecific binding of BSA was monitored with the grating coupler system, and was increasingly suppressed with increasing dextran concentrations. Using a solution with 100 mg/ml carboxymethylated dextran decreased the signals to approximately 2% of those obtained at an untreated glass chip. Antibodies were successfully immobilised in the dextran and binding to the corresponding Cy5-labelled antigen was repeatedly monitored using a fluorescence sensor system (total internal reflection fluorescence (TIRF)).

Animals↗
PubMed1998

Pulp reaction to a tri-cure resin-modified glass ionomer.

OBJECTIVE: This study evaluated the pulp response to a tri-cure resin-modified glass ionomer cement and compared this response to those elicited by a zinc oxide-eugenol cement and a silicate cement. Materials were placed in nonexposed class V cavity preparations on human teeth. STUDY DESIGN: Sixty premolars were selected in orthodontic patients in a voluntary group of teenagers. All cavities were prepared according to International Dental Federation specifications. Resin-modified glass ionomer and silicate applications were carried out according to the manufacturers' instructions. RESULT: All teeth were asymptomatic. Pulp responses to the resin-modified glass ionomer cement were slightly greater than to the zinc-oxide-eugenol cement. Bacterial staining attempts were inconclusive with regard to time intervals and pulp responses. No necrotic pulps were seen in any teeth. CONCLUSION: The tri-cure resin-modified glass ionomer cement elicited a slightly greater adverse pulp response than did the zinc-oxide-eugenol cement with respect to the healing process of the pulp.

Composite Resins↗
PubMedDate not supplied

Modeling glasses using the reverse Monte Carlo algorithm: addition of nuclear magnetic resonance and expanded coordination number constraints.

In simple oxide glasses the coordination number and oxidation state of the glass-forming element can be predicted directly from the "8--n" rule. Tellurite glasses, however, are unusual in that the coordination number of oxygen around tellurium varies without a corresponding change in the oxidation state of tellurium. To model sodium tellurite glasses successfully using the reverse Monte Carlo algorithm several new constraints have been added. Changes include extending the original coordination constraint to allow multiple coordination numbers, and the addition of a new coordination constraint to keep the oxidation state of tellurium constant by limiting the number of bridging and nonbridging oxygens bonded to each tellurium atom. In addition, the second moment of the distribution of dipolar couplings for sodium atoms obtained from a spin-echo NMR experiment was added as a new constraint. The resulting real-space models are presented and the effectiveness of the new constraints is discussed.

Algorithms↗
PubMed2001

Spectroscopic properties of Er3+, Yb3 + and Er3 + /Yb3+ doped metaphosphate glasses.

The absorption and emission spectroscopies of Er3+ doped and Er3+/Yb3+ codoped Ca(PO3)2, Sr(PO3)2 and Ba(PO3)2 glasses have been studied. From the Judd-Ofelt intensity parameters, the spontaneous emission probabilities of some relevant transitions and the radiative lifetimes of several excited states of Er3+ have been calculated. The decay curves of the Er3+ emission at 1.5 microm have been measured at different temperatures. The data have been fitted using a stretched exponential function and the obtained experimental lifetimes have been compared with the calculated radiative lifetimes. The difference between the experimental and calculated lifetimes is attributed to the presence of traces of OH groups in the host glasses. The absolute OH content in some glasses has been determined from the infrared spectra. The emission spectra at 1.5 microm of the Er3+ ion in the codoped glasses have been measured at different temperatures. The integrated emission intensities decrease significantly on passing from room temperature to 13 K, suggesting a temperature dependence of the rate of the energy transfer process between Yb3+ and Er3+.

Biophysical Phenomena↗
PubMed2001

Optical spectroscopy of lanthanide ions in ZnO-TeO2 glasses.

Zinc tellurite glasses of compositions 19ZnO-80TeO2-1Ln2O3 with Ln = Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f-->f transitions the Judd-Ofelt parameters ohm(lambda) were obtained. The values of the ohm(lambda) parameters are in the range usually observed for oxide glasses. For Nd3+ and Er3+, luminescence spectra in the near infrared were measured and the stimulated emission cross sections sigma(p) were evaluated for some laser transitions. The high values of sigma(p), especially for Nd3+, make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu3+ doped glass were measured at 20 K, and the energies of the Stark components of the 7F1 and 7F2 states were obtained. A crystal field analysis was carried out assuming a C2v site symmetry. The behaviour of the crystal field ratios B22/B20 and B44/B40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu3+ sites appears to be very low compared to other oxide glasses.

Biophysical Phenomena↗
PubMed2001

A factorial analysis of silanization conditions for the immobilization of oligonucleotides on glass surfaces.

The modification of glass surfaces with (3-mercaptopropyl)trimethoxysilane and the application of this to DNA chip technology are described. A range of factors influencing the silanization method, and hence the number of surface-bound, chemically active thiol groups, were investigated using a design of experiment approach based on analysis of variance. The number of thiol groups introduced on glass substrates were measured directly using a specific radiolabel, [14C]cysteamine hydrochloride. For liquid-phase silanization, the number of surface-bound thiol groups was found to be dependent on both postsilanization thermal curing and silanization time and relatively independent of silane concentration, reaction temperature, and sample pretreatment. Depending on the conditions used in liquid-phase silanization, (1.3-9.0) x 10(12) thiol groups/cm2 on the glass samples were bound. The reliability and repeatability of liquid- and vacuum-phase silanization were also investigated. Eighteen-base oligonucleotide probes were covalently attached to the modified surfaces via a 3'-amino modification on the DNA and subsequent reaction with the cross-linking reagent N-(gamma-maleimidobutyryloxy) succinimide ester (GMBS). The resulting probe levels were determined and found to be stoichiometric with that of the introduced thiol groups. These results demonstrate that silanization of glass surfaces under specific conditions, prior to probe attachment, is of great importance in the development of DNA chips that use the simple concept of the covalent attachment of presynthesized oligonucleotides to silicon oxide surfaces.

Factor Analysis, Statistical↗
PubMed2005

Lithium isotope composition of basalt glass reference material.

We present data on the lithium isotope compositions of glass reference materials from the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) determined by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). Our data on the USGS basaltic glass standards agree within 2 per thousand, independent of the sample matrix or Li concentration. For SIMS analysis, we propose use of the USGS glasses GSD-1G (delta(7)Li 31.14 +/- 0.8 per thousand, 2sigma) and BCR-2G (delta(7)Li 4.08 +/- 1.0 per thousand, 2sigma) as suitable standards that cover a wide range of Li isotope compositions. Lithium isotope measurements on the silica-rich NIST 600 glass series by MC-ICPMS and TIMS agree within 0.8 per thousand, but SIMS analyses show systematic isotopic differences. Our results suggest that SIMS Li isotope analyses have a significant matrix bias in high-silica materials. Our data are intended to serve as a reference for both microanalytical and bulk analytical techniques and to improve comparisons between Li isotope data produced by different methodologies.

Glass↗
PubMedDate not supplied

New application of silane coupling agents for covalently binding antibodies to glass and cellulose solid supports.

Bifunctional silane reagents (3-iodopropyl)trimethoxysilane (1), (gamma-glycidoxypropyl)trimethoxysilane (2), and [1-(trimethoxysilyl)-2-(m- (or p-)chloromethyl)phenyl]ethane (3) were used to covalently link goat anti-mouse (GAM) antibodies (Ab) to glass microbeads and cuprammonium rayon hollow-fiber dialyzers. An average of 0.79 and 0.83 microgram of GAM Ab/cm2 was immobilized on the hollow-fiber dialyzers and the glass beads, respectively. The antibodies immobilized on glass microbeads or on hollow-fiber dialyzers were then used to selectively deplete CD34+ cells or CD4+ peripheral blood mononuclear cells (PBMC), respectively. Glass microbeads depleted 80% CD34+ cells with good selectivity, and the hollow-fiber dialyzers depleted an average of 81% CD4+ PBMC.

Animals↗
PubMedDate not supplied

Cellulose and glass fiber affinity membranes for the chromatographic separation of biomolecules.

Macroporous cellulose and glass membranes were prepared from filter paper and glass fiber filter, respectively. To enhance their stability, the cellulose membranes were crosslinked with epichlorohydrin, and the glass membranes were crosslinked with glutaraldehyde or organic bifunctional silanes. Several pathways for the modification, activation, and ligand immobilization were used and compared. For cellulose membranes, the diazotization method provided the best results, whereas the glutaraldehyde method provided the best performance for glass membranes, regarding both their stability and ligand immobilization capacity. The characterization of the membranes was made by using a triazine dye, bovine serum albumin, and trypsin as test ligands. The membrane morphologies and the uniformities of ligand distribution across the membrane cartridges were investigated. Numerous affinity ligands were immobilized onto the membranes, and the prepared affinity membranes have been used to separate or purify concanavalin A, peroxidase, protease inhibitors, globulin, fibronectin, and other biomolecules.

Biopolymers↗
PubMed2003

Adhesive properties of corn zein formulations on glass surfaces.

Adhesive properties on glass of commercial zein and an inexpensive zein-lipid mixture isolated from dry-milled corn were investigated. A method was developed for uniformly preparing bonded glass panels and measuring the amount of pull required to separate the panels. The adhesive strength of commercial zein to glass was greater at 29% than at 52% relative humidity (RH). Bonded samples prepared from zein isolates were less sensitive to changes in RH. Bonds using commercial zein formulations containing plasticizer reached a maximum strength at 10% poly(ethylene glycol) regardless of RH. Formulations that required the least amount of ethanol (35-42%) were obtained by adjusting its pH to 3 or 10 with a volatile acid or base. These formulations completely bonded to the glass panels at low sample concentrations as estimated by 100% cohesive failure and exhibited lower Young's Modulus values than most of the other bonding materials tested. Samples bonded with a polyvinyl acetate emulsion adhesive were not as strong as the zein-bonded samples and were sensitive to changes in RH.

Adhesiveness↗
PubMed2006

Glass transition and enthalpy relaxation of amorphous food saccharides: a review.

Many food materials exist in a disordered amorphous solid state due to processing. Therefore, understanding the concept of amorphous state, its important phase transition (i.e., glass transition), and the related phenomena (e.g., enthalpy relaxation) is important to food scientists. Food saccharides, including mono-, di-, oligo-, and polysaccharides, are among the most important major components in food. Focusing on the food saccharides, this review covers important topics related to amorphous solids, including the concept and molecular arrangement of amorphous solid, the formation of amorphous food saccharides, the concept of glass transition and enthalpy relaxation, physical property changes and molecular mobility around the glass transition, measurement of the glass transition and enthalpy relaxation, their mathematical descriptions and models, and influences on food stability.

Carbohydrates↗
PubMed1999

Glass transition temperature of honey as a function of water content as determined by differential scanning calorimetry.

The glass transition of pure and diluted honey and the glass transition of the maximally freeze-concentrated solution of honey were investigated by differential scanning calorimetry (DSC). The glass transition temperature, of the pure honey samples accepted as unadulterated varied between -42 and -51 degrees C. Dilution of honey to 90 wt % honey content resulted in a shift of the glass transition temperature by -13 to -20 degrees C. The concentration of the maximally freeze-concentrated honey solutions, as expressed in terms of honey content is approximately 102-103%, i.e., slightly more concentrated in sugars than honey itself. The application of DSC measurements of and in characterization of honey may be considered, but requires systematic study on a number of honeys.

Calorimetry, Differential Scanning↗
PubMed2004

Vesicle adsorption and lipid bilayer formation on glass studied by atomic force microscopy.

The adsorption of phosphatidylcholine (PC) vesicles (30, 50, and 100 nm nominal diameters) and of dye-labeled PC vesicles (labeled with 6% Texas Red fluorophore (TR) and encapsulated carboxy fluorescein (CF)) to glass surfaces was studied by contact mode atomic force microscopy in aqueous buffer. These studies were performed in part to unravel details of the previously observed isolated rupture of dye-labeled PC vesicles on glass (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), specifically to differentiate partial rupture, that is, pore formation and leakage of entrapped dye, from full rupture to form bilayer disks. In addition, the adhesion potential of PC vesicles on glass was calculated based upon the adhesion-driven flattening of adsorbed vesicles and a newly developed theoretical model. The vesicles were found to flatten considerably upon adsorption to glass (width-to-height ratio of approximately 5), which leads to an estimate for the adhesion potential and for the critical rupture radius of 1.5 x 10(-4) J/m2 and 250 nm, respectively. Independent of vesicle size and loading with dye molecules, the adsorption of intact vesicles was observed at all concentrations below a threshold concentration, above which the formation of smooth lipid bilayers occurred. In conjunction with previous work (Johnson, J. M.; Ha, T.; Chu, S.; Boxer, S. G. Biophys. J. 2002, 83, 3371-3379), these data show that 6% TR 20 mM CF vesicles adsorb to the surface intact but undergo partial rupture in which they exchange content with the external buffer.

Adsorption↗
PubMed2002

Development of a remote electrode system for monitoring the water content of materials inside a glass vial.

PURPOSE: This article explores the use of a remote electrode dielectric measurement system to monitor the water content of hydrated ovalbumin inside a glass vial. METHODS: The intrinsic dielectric properties of hydrated ovalbumin were characterized first using conventional parallel plate electrodes. The second stage was to simulate a remote electrode measurement by placing nonconductive, nondispersive polyethylene films between the sample and electrodes. Finally, a study on the dielectric measurement of ovalbumin contained in a 10 ml glass vial was undertaken with the electrodes external to the glass vial. RESULTS: The dielectric behavior of hydrated ovalbumin was characterized by charge transfer (i.e., protons) in the hydrogen bonded network of water molecules in the bulk sample. The mechanism was identified as an anomalous low-frequency dispersion and a dielectric loss peak (epsilon3). The dielectric relaxation time, tau3, of the epsilon3 dispersion was especially sensitive to water content. Moreover, a good correlation (R2 = 93%) was observed between relaxation times tau3 obtained from measurements using conventional parallel plate electrodes and the remote electrode system. CONCLUSIONS: Dielectric measurements using remote electrodes attached to a glass vial are therefore applicable for the in situ measurement of water content in materials. The application of this technology to the determination of the lyophilization end point is suggested.

Electrodes↗