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At least 1,009 records · Page 56Linked to original sources
PubMed1997

Fluoride release and shear bond strengths of three light-cured glass ionomer cements.

Little is known about the release of fluoride from light-cured glass ionomer cements when used as orthodontic bonding agents. Fluoride release from three "hybrid" light-cured glass ionomer cements was measured during a 42-day period after initial curing in an in vitro test that simulated their use as orthodontic bonding agents. On day 48, the bonded teeth were exposed for 30 seconds to a stannous fluoride gel and checked for fluoride release during the following week. One cement (BL) released the most fluoride after initial cure and after an exposure to a stannous fluoride gel on day 48. The other two hybrid cements exhibited both significantly less fluoride release than material (BL) and resembled for most of the 55-day duration the composite resin control. After the 55-day duration, shear bond strengths of the composite resin control were significantly higher than the three light-cured glass ionomer cements. The light-cured glass ionomer cements in this study released fluoride after initial curing and after exposure to a topical fluoride gel. This property may help reduce or possibly even prevent enamel decalcifications seen around bracket bases. At present, the shear bond strengths of the light-cured glass ionomer cements tested appear to be too low for routine orthodontic bonding agents.

Analysis of Variance↗
PubMed1999

Decalcification and bond failure: A comparison of a glass ionomer and a composite resin bonding system in vivo.

Decalcification during orthodontic treatment is a serious problem. A glass ionomer agent is now available to bond orthodontic brackets as an alternative to composite resins. This prospective study was a clinical trial to determine if a glass ionomer bonding system (Fuji Ortho LC) decreases the incidence of decalcification without increasing the amount of bonding failures. A prospective clinical trial with 16 patients encompassing a total of 298 teeth was conducted. The 149 control teeth were bonded with a light-cured composite resin (Reliance Light Bond) whereas the 149 experimental teeth were bonded with the light-cured glass ionomer agent. Patients were followed for a period of 12 to 14 months. All teeth were evaluated for breakage (bonding failure rate), and all maxillary anterior teeth (96) were evaluated for decalcification on a graded scale. The glass ionomer failure rate was 24.8%, and was higher than the composite resin failure rate of 7.4% (P <.001). There were more glass ionomer bond failures in 12 of 16 patients (P <.001). Enamel decalcification was similar in the 2 bonding systems.

Acid Etching, Dental↗
PubMedDate not supplied

The acquisition of breaking and broken glass.

A set of experiments tested the idea that an examiner can distinguish glass acquired by backward fragmentation from that acquired by contact with already-broken glass. A window was broken. The exterior surface of the breaker's clothing was brushed and hair-combings taken and these were searched for glass fragments. Wearing the same clothing the breaker then cleared up the broken glass and further hair-combings and brushings of the clothing surface were taken. The size, shape and presence or absence of an original flat surface was recorded for the recovered fragments. The distributions within these parameters were compared for the two methods of acquisition and association between the method and the parameters was tested using contingency tables. It was found that fragment shape does not identify the method of acquisition and that a high proportion of fragments retaining the original outer surface shows that the glass was acquired by backward fragmentation.

Criminology↗
PubMed2000

Laser spectroscopic studies of Tb3+-doped oxyfluoroborate glass.

Tb3+-doped oxyfluoroborate glasses have been prepared for different concentrations of Tb. The absorption, fluorescence and photoacoustic spectra of these have been recorded and studied. It is marked that the fluorescence intensity of different fluorescence transitions decreases with the increase of Tb ion concentration in the glass. This quenching at higher concentration is due to the energy transfer among the excited and nearest neighbor unexcited Tb ions in the glass. The lifetime measurement confirms it, as the lifetime of a particular state was found to decrease with the increase of Tb ion concentration in the glass. The mechanism of the energy transfer process was determined to involve quadrupole quadrupole interaction. We have also studied the energy transfer from Tb3+-->Pr3+ when both the rare earths are doped together in the glass. A decrease in the lifetime of the 5D4 level of Tb3+ with the increase of Pr3+ concentration confirms this.

Absorption↗
PubMed2003

Optical properties of Dy3+ doped calibo glass on addition of lead oxide.

The effects of PbO on optical properties of dysprosium doped calibo glass have been studied. The content of PbO in the glass has been varied from 0 to 60 mol%. The absorption and fluorescence spectra are analyzed in terms of the Judd-Ofelt theory. It is observed that the fluorescence yield is maximum for the glass containing 40 mol% PbO. The I-R absorption spectra of these glasses have also been recorded and interpreted in terms of changes in the structure of the glasses.

Dysprosium↗
PubMed2004

Characterization of a polymeric adsorbed coating for DNA microarray glass slides.

A new method was developed to covalently attach target molecules onto the surface of glass substrates such as microwell plates, beads, tubes, and microscope slides, for hybridization assays with fluorescent targets. The innovative concept introduced by this work is to physically adsorb onto underivatized glass surfaces a functional copolymer, able to graft amino-modified DNA molecules. The polymer, obtained by radical copolymerization of N,N-dimethylacrylamide, N-acryloyloxysuccinimide, and 3-(trimethoxysilyl)propyl methacrylate, copoly(DMA-NAS-MAPS), self-adsorbs onto the glass surface very quickly, typically in 5-30 min. The film, formed on the surface, bears active esters, which react with amino-modified DNA targets. The surface layer is stable in an aqueous buffer containing various additives (SDS, urea, salt), even at boiling temperature. It should be emphasized that the coating is formed by the immersion of glass slides in a diluted aqueous solution of the polymer. Therefore, the procedure is fast, inexpensive, robust, and reliable, and it does not require time-consuming glass pretreatments. Slides, coated with copoly(DMA-NAS-MAPS), were profitably used as substrates for the preparation of low-density DNA microarrays. The density and the thickness of the films were evaluated by X-ray reflectivity measurements whereas the extent of reaction of functional groups with DNA molecules was determined by a functional test. The experiments indicate that half of the active groups present on the surface reacts with oligonucleotide probes.

Acrylamides↗
PubMed1975

Growth hormone covalently bound to sepharose or glass. Analysis of ligand release rates and characterization of soluble radiolabeled products.

Purified boveine growth hormone labeled enzymatically with iodine-125 was covalently coupled to cyanogen bromide activated Sepharose 4B gel and to diazotized zirconia-clad glass beads. Under the conditions employed, an average of 0.8 and 7.3 mg of hormone were bound per ml of Sepharose and glass, respectively. When the conjugates were incubated in Krebs-Ringer bicarbonate buffer (pH 7.4), three separate radioactive species were detected in the incubation supernatant by chromatography on Sephadex G-75. The elution volumes of two of the species were identical with those of 125-I-labeled growth hormone and Na-125I controls, while the third component eluted as a moleucle of intermediate size. The rate of release of each species from the solid matrix was linear with time over 4 days and increased with temperature from 4 to 37 degrees. Although significantly less growth hormone was released from glass (0.14%/day) than from Sepharose (0.40%/day) at 37 degrees, active hormone in amounts sufficient to be detectable in a biological assay was nevertheless liberated from the former after as little as 4 hr of incubation. By contrast, the rate of release of 125-Iminus- and the intermediate-size compound from glass was significantly greater than from Sepharose, suggesting that protein bound to glass supports is more susceptible to degradation from exposure to ionizing radiation.

Animals↗
PubMed2002

Effect of molecular scale roughness of glass beads on colloidal and bacterial deposition.

Molecular-scale surface roughness and charge heterogeneity have been hypothesized as factors that can affect the deposition rates of colloids during their transport in porous media. To test their relative importance, a single batch of cleaned glass beads was divided in half and chemically treated with acid or base to alter surface roughness. Analysis of the topography of 20 glass beads with an atomic force microscope (AFM) indicated that the chromic acid-treated (rough) beads had a root-mean-square roughness of 38.1 +/- 3.9 nm, while the sodium hydroxide-treated (smooth) beads had root-mean-square surface roughness of 15.0 +/- 1.9 nm. AFM force volume imaging of glass bead surfaces did not reveal surface charge heterogeneity. Filtration experiments with inorganic colloids (latex microspheres, 1 microm diameter) consistently demonstrated that there was a greater retention of latex microspheres on rough than smooth glass beads suspended in either low (10(-5) M) or higher (10(-1) M) ionic strength (IS) solutions. Collision efficiencies for rough beads were 30-50% larger than for smooth beads. Collision efficiencies of bacteria using rough glass beads were also equal to or greater than those measured for smooth beads. In experiments with the perchlorate-reducing bacterial isolate KJ, collision efficiencies were significantly greater on rough rather than smooth beads for two different ionic strength solutions (IS = 0.05 or 1 M). In another case (IS = 0.1 M) for KJ, and in filtration experiments with E coli, collision efficiencies were not significantly different between the rough and smooth beads. We hypothesize that the consistently greater deposition rates of microspheres, but not bacteria, on rough rather than smooth beads are due in part to the presence of polymers on the surfaces of bacteria.

Bacteria↗
PubMed2006

Electrostatic-gated transport in chemically modified glass nanopore electrodes.

Electrostatic-gated transport in chemically modified glass nanopore electrodes with orifice radii as small as 15 nm is reported. A single conical-shaped nanopore in glass, with a approximately 1 microm radius Pt disk located at the pore base, is prepared by etching the exposed surface of a glass-sealed Pt nanodisk. The electrochemical response of the nanopore electrode corresponds to diffusion of redox-active species through the nanopore orifice to the Pt microdisk. Silanization of the exterior glass surface with Cl(Me)(2)Si(CH(2))(3)CN and the interior pore surface with EtO(Me)(2)Si(CH(2))(3)NH(2) introduces pH-dependent ion selectivity at the pore orifice, a consequence of the electrostatic interactions between the redox ions and protonated surface amines. Nanopore electrodes with very small pore orifice radii (< approximately 50 nm) display anion permselectively at pH < 4, as demonstrated by electrochemical measurement of transport through the pore orifice. Ion selective transport vanishes at pH > 6 or when the pore radius is significantly larger than the Debye screening length, consistent with the observed ion selectivity resulting from electrostatic interactions. The ability to introduce different surface functionalities to the interior and exterior surfaces of glass nanopores is demonstrated using fluorescence microscopy to monitor the localized covalent attachment of 5- (and 6)-carboxytetramethylrhodamine succinimidyl ester to interior pore surfaces previously silanized with EtO(Me)(2)Si(CH(2))(3)NH(2).

Biosensing Techniques↗
PubMed2004

Synthesis of highly luminescent glasses incorporating cdte nanocrystals through sol-gel processing.

Highly photoluminescent glass was prepared by embedding water-soluble nanocrystals in a glass matrix using a novel sol-gel process. Thiol-stabilized CdTe nanocrystals and aminopropyltrimethoxysilane were found to be the best combination in the preparation. The synthesis process had to be optimized to avoid nanocrystal agglomeration. The nanocrystals thus embedded in the glass matrix did not show any deterioration of the surface condition. The obtained glass combines excellent optical properties of nanocrystals with the high stability of glass; it emits light of various colors with narrow emission spectra and high photoluminescent efficiency (41%).

Alloys↗
PubMed2004

Carbonate formation on bioactive glasses.

The system termed 58S is a sol-gel-synthesized bioactive glass composed of SiO2, CaO, and P2O5, used in medicine as bone prosthetic because, when immersed in a physiological fluid, a layer of hydroxycarbonate apatite is formed on its surface. The mechanism of bioactive glass 58S carbonation was studied in the vacuum by means of in-situ FTIR spectroscopy with the use of CO2, H2O, and CD3CN as probe molecules. The study in the vacuum was necessary to identify both the molecules specifically involved in the carbonation process and the type of carbonates formed. Bioactive glass 58S was compared to a Ca-doped silica and to CaO. On CaO, ionic carbonates could form by contact with CO2 alone, whereas on 58S and on Ca-doped silica carbonation occurred only if both CO2 and an excess of H2O were present on the sample. The function of H2O was not only to block surface cationic sites, so that CO2 could not manifest its Lewis base behavior, but also to form a liquid-like (mono)layer that allowed the formation of carbonate ions. The presence of H2O is also supposed to promote Ca2+ migration from the bulk to the surface. Carbonates formed at the surface of CaO and of Ca-bearing silicas (thus including bioactive glasses) are of the same type, but are produced through two different mechanisms. The finding that a water excess is necessary to start heavy carbonation on bioactive glasses seemed to imply that the mechanism leading to in-situ carbonation simulates, in a simplified and easy-to-reproduce system, what happens both in solution, when carbonates are incorporated in the apatite layer, and during sample shelf-aging.

Apatites↗
PubMed2000

Mössbauer spectroscopy indicates that iron in an aluminosilicate glass phase is the source of the bioavailable iron from coal fly ash.

Iron speciation by Mössbauer spectroscopy indicates that ferric iron in an aluminosilicate glass phase is the source of the bioavailable iron in coal fly ash and that this iron species is associated with combustion particles, but not with crustal dust derived from soil minerals. Urban particulate has been shown to be a source of bioavailable iron and has been shown to be able to induce the formation of reactive species in cell culture experiments. Crustal dust and laboratory-generated coal fly ash have been studied as surrogates for two sources of metal-bearing particles in ambient air. As much as a 60-fold difference in the amount of iron mobilized by the chelator citrate was observed between fly ash and crustal dust samples with similar total iron contents. The extent of iron mobilization by citrate in vitro has been shown to correlate with indirect measures of excess iron in cultured cells and with assays for reactive oxygen species generation in vitro. Mössbauer spectroscopy of coal fly ash, before and after treatment with the chelator desferrioxamine B, showed that the iron in an aluminosilicate glass phase was preferentially removed. The removal of the glass-phase iron greatly reduced the amount of iron that could be mobilized by citrate and prevented the particles from inducing interleukin-8 in cultured human lung epithelial (A549) cells. Ferric iron in aluminosilicate glass is associated with particles formed at high temperatures followed by rapid cooling. The observation that ferric iron in aluminosilicate glass is the source of bioavailable iron in coal fly ash suggests that particles from ambient sources and other specific combustion sources should be examined for the presence of this potential source of bioavailable iron.

Air Pollutants↗
PubMed2004

Injectable bioactive glass/biodegradable polymer composite for bone and cartilage reconstruction: concept and experimental outcome with thermoplastic composites of poly(epsilon-caprolactone-co-D,L-lactide) and bioactive glass S53P4.

Injectable composites (Glepron) of particulate bioactive glass S53P4 (BAG) and Poly(epsilon-caprolactone-co-D,L-lactide) as thermoplastic carrier matrix were investigated as bone fillers in cancellous and cartilagineous subchondral bone defects in rabbits. Composites were injected as viscous liquid or mouldable paste. The glass granules of the composites resulted in good osteoconductivity and bone bonding that occurred initially at the interface between the glass and the host bone. The bone bioactivity index (BBI) indicating bone contacts between BAG and bone, as well as the bone coverage index (BCI) indicating bone ongrowth, correlated with the amount of glass in the composites. The indices were highest with 70 wt % of BAG, granule size 90-315 microm and did not improve by the addition of sucrose as in situ porosity creating agent in the composite or by using smaller (<45 microm) glass granules. The percentage of new bone ingrowth into the composite with 70 wt % of BAG was 6-8% at 23 weeks. At the articular surface cartilage regeneration with chondroblasts and mature chondrocytes was often evident. The composites were osteoconductive and easy to handle with short setting time. They were biocompatible with low foreign body cellular reaction. Results indicate a suitable working concept as a filler bone substitute for subchondral cancellous bone defects.

Animals↗
PubMed2004

A structural model for metallic glasses.

Despite the intense interest in metallic glasses for a variety of engineering applications, many details of their structure remain a mystery. Here, we present the first compelling atomic structural model for metallic glasses. This structural model is based on a new sphere-packing scheme-the dense packing of atomic clusters. Random positioning of solvent atoms and medium-range atomic order of solute atoms are combined to reproduce diffraction data successfully over radial distances up to approximately 1 nm. Although metallic glasses can have any number of chemically distinct solute species, this model shows that they contain no more than three topologically distinct solutes and that these solutes have specific and predictable sizes relative to the solvent atoms. Finally, this model includes defects that provide richness to the structural description of metallic glasses. The model accurately predicts the number of solute atoms in the first coordination shell of a typical solvent atom, and provides a remarkable ability to predict metallic-glass compositions accurately for a wide range of simple and complex alloys.

Crystallography↗
PubMedDate not supplied

The effect of maturation on in-vitro erosion of glass-ionomer and other dental cements.

The clinical durability of restorations made using water-based materials depends upon the type of material used. Current specification tests cannot predict durability, possibly because these are carried out on samples matured for 24 hours whereas longer maturation times may be more relevant. The lactic acid jet test was selected as a test method, being believed capable of ranking materials in the same order of erosion resistance in vitro as found in vivo. The powder/liquid interaction (glass or zinc oxide with polymeric or phosphoric acid) was investigated by selecting glass-ionomer, zinc polycarboxylate, silicate and zinc phosphate cements, with emphasis placed on glass ionomers. Two test times, 24 hours and 2 months, were chosen, with eight samples for each material tested at each time. All glass ionomers showed a significant reduction in erosion rate with time; two zinc polycarboxylates also showed some reduction but not to a significant degree. The silicate and zinc phosphate cements increased in erosion rate but not significantly. It was concluded that materials using polymeric acids had erosion rates which reduced with time, significantly so for glass ionomers. This might explain their longevity over silicate cements.

Dental Cements↗
PubMed2003

Effects of thermocycling on the bond strength of a resin-modified glass ionomer cement: an in vitro comparative study.

This study investigated the effects of thermally induced stresses (thermocycling) on the shear bond strength of resin-modified, chemically cured, glass ionomer cement for use as an orthodontic bonding agent. A conventional no-mix composite resin was also used as a control. Mesh-based metal orthodontic brackets were bonded to extracted human premolars using either the resin-modified glass ionomer cement or the no-mix composite resin. Specimens were stored either in water at 37 degrees C for 24 hours for baseline data or thermocycled between 5 degrees C and 55 degrees C for 200 and 20,000 cycles before testing the in vitro shear bond strengths. Thermocycling reduced shear bond strengths for all specimens. The resin-modified glass ionomer cement showed a 11.1% decrease after 200 thermocycles and 26.5% decrease after 20,000 thermocycles, whereas the no-mix adhesive resin showed only 5.7% and 17.9% reductions, respectively. Analysis of variance showed statistically significant differences between the mean shear bond strengths of the groups at the P < .001 level of significance. For the resin-modified glass ionomer cement groups, the predominant bond failure site was at the bracket-adhesive interface. The results of this study suggest strongly that resin-modified glass ionomer cements offer a viable alternative to conventional no-mix composite resins, with satisfactory in vitro shear bond strength even after 20,000 thermocycles.

Analysis of Variance↗
PubMed1997

Curing of a silane coupling agent and its effect on the transverse strength of autopolymerizing polymethylmethacrylate-glass fibre composite.

The aim of this study was to determine how curing gamma-methacryloxypropyltrimethoxysilane (gamma-MPS) to the surface of E-glass fibre affects the transverse strength of autopolymerizing polymethylmethacrylate-glass fibre composite (PMMA-GF). For this purpose, unidirectional glass fibres treated with gamma-MPS solution and cured for various lengths of time at different temperatures (+50 degrees C, +100 degrees C and +150 degrees C) were used as a strengthener of PMMA test specimens (n = 10 per group). The mean concentration of glass fibres in the test specimens was 17 wt%. The unreinforced test specimens and the test specimens reinforced with unsilanized fibres were compared, but no statistical difference in their transverse strengths was found (P = 0.568). The results also revealed that when the curing temperatures of the gamma-MPS were compared, the highest transverse strength (152 MPa) for the PMMA-GF composite was obtained by curing the MPS for 120 min at +100 degrees C; the lowest strength (91 MPa) was obtained by polymerizing the MPS at +150 degrees C (P < 0.001). However, SEM photomicrographs taken from the interface of the glass fibre and PMMA showed that the fibre adhered equally well to the PMMA treated at +100 degrees C or at +150 degrees C. This suggests that reduction in transverse strength of composite test specimens is caused by other factors, for example, by improper impregnation of PMMA into the fibre bundle, rather than by inadequate adhesion.

Adhesiveness↗
PubMed1998

Some aspects of the tensile strength of undirectional glass fibre-polymethyl methacrylate composite used in dentures.

The aim of this study was to determine the tensile strength and E-modulus of unidirectional denture glass fibre-polymethyl methacrylate (GF-PMMA) composite with various fibre contents. The experimental values of tensile strength and E-modulus were compared with values obtained by a theoretical calculation. Autopolymerized PMMA test specimens (n = 6, per group) were reinforced with unidirectional E-glass fibres which had been wetted in a mixture of PMMA powder and monomer liquid. After storing the test specimens for 40 days in water at 37 degrees C, the tensile strength and E-modulus of the test specimens were measured. The increased amount of fibres in the PMMA matrix (up to 14.8% by weight) increased the mean tensile strength of the test specimens from 40.5 MPa to 91.2 MPa (P < 0.001) and the E-modulus from 2057 MPa to 3751 MPa (P < 0.001). The experimental tensile strength and Emodulus values were considerably lower than those based on the theoretical calculations. This was assumed to be due to the percentage of glass fibres unimpregnated with the PMMA resin. The presence of unimpregnated glass fibres was determined using light microscopy. The results of this study suggest that a new method of incorporating the glass fibres into the PMMA resin matrix should be developed in order to obtain a well-impregnated fibre composite reinforcement with high durability.

Analysis of Variance↗