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At least 109 records · Page 6Linked to original sources
PubMed2004

Release of silica, calcium, phosphorus, and fluoride from glass ionomer cement containing bioactive glass.

The aim of this study was to examine the release of silica (Si), calcium (Ca), phosphorous (P), and fluoride (F) from conventional glass ionomer cement (GI) and resin-modified glass ionomer cement (LCGI), containing different quantities of bioactive glass (BAG). Further aim was to evaluate in vitro biomineralization of dentine. The release of Si increased with the increasing immersion time from the specimens containing BAG, whereas the amount of Ca and P decreased indicating in vitro bioactivity of the materials. LCGI with 30wt% of BAG showed highest bioactivity. It also showed CaP-like precipitation on both the surface of the test specimens and on the dentin discs immersed with the material. Within the limitations of this study, it can be concluded that a dental restorative material consisting of glass ionomer cements and BAG is bioactive and initiates biomineralization on dentin surface in vitro.

Biocompatible Materials↗
PubMed1989

Evaluation of the ability of glass-ionomer cement to bond to glass-ionomer cement.

This study investigated the cohesive bond strengths of glass-ionomer cement at three setting and etching intervals and compared these bonds to the shear strength of the material itself. Bonded cylinders were created and then sheared using the Instron Universal Testing Machine. Analysis of bond values of glass ionomer added to glass ionomer indicate bond variability and low cohesive bond strength of the material. Bond values of unbonded glass-ionomer material indicate that the material itself is stronger than bonds established between bonded samples.

Dental Bonding↗
PubMed2001

Interactions of bioactive glasses with osteoblasts in vitro: effects of 45S5 Bioglass, and 58S and 77S bioactive glasses on metabolism, intracellular ion concentrations and cell viability.

In a cell culture model of murine osteoblasts three particulate bioactive glasses were evaluated and compared to glass (either borosilicate or soda-lime-silica) particles with respect to their effect on metabolic activity, cell viability, changes in intracellular ion concentrations, proliferation and differentiation. 45S5 Bioglass caused extra- and intracellular alkalinization, a rise in [Ca2+]i and [K+]i, a small plasma membrane hyperpolarization, and an increase in lactate production. Glycolytic activity was also stimulated when cells were not in direct contact with 45S5 Bioglass particles but communicated with them only through the medium. Similarly, raising the pH of culture medium enhanced lactate synthesis. 45S5 Bioglass had no effect on osteoblast viability and, under most conditions, did not affect either proliferation or differentiation. Bioactive glasses 58S and 77S altered neither the ion levels nor enhanced metabolic activity. It is concluded that: (1) some bioactive glasses exhibit well-defined effects in osteoblasts in culture which are accessible to experimentation; (2) 45S5 Bioglass causes marked external and internal alkalinization which is, most likely, responsible for enhanced glycolysis and, hence, cellular ATP production; (3) changes in [H+] could contribute to alternations in concentrations of other intracellular ions; and (4) the rise in [Ca2+]i may influence activities of a number of intracellular enzymes and pathways. It is postulated that the beneficial effect of 45S5 on in vivo bone growth and repair may be due to some extent to alkalinization, which in turn increases collagen synthesis and crosslinking, and hydroxyapatite formation.

Animals↗
PubMed2004

Glass transition and the Coulomb gap in electron glasses.

We establish the connection between the presence of a glass phase and the appearance of a Coulomb gap in disordered materials with strongly interacting electrons. Treating multiparticle correlations in a systematic way, we show that in the case of strong disorder a continuous glass transition takes place whose Landau expansion is identical to that of the Sherrington-Kirkpatrick spin glass. We show that the marginal stability of the glass phase controls the physics of these systems: it results in slow dynamics and leads to the formation of a Coulomb gap.

Journal Article↗
PubMed2006

Spin-glass transition of the three-dimensional Heisenberg spin glass.

It is shown, by means of Monte Carlo simulation and finite size scaling analysis, that the Heisenberg spin glass undergoes a finite-temperature phase transition in three dimensions. There is a single critical temperature, at which both a spin glass and a chiral glass ordering develop. The Monte Carlo algorithm, adapted from lattice gauge theory simulations, makes it possible to thermalize lattices of size L = 32, larger than in any previous spin-glass simulation in three dimensions. High accuracy is reached thanks to the use of the Marenostrum supercomputer. The large range of system sizes studied allows us to consider scaling corrections.

Journal Article↗
PubMed1991

From contacts and bondings between bone and bioactive glass to bonding of bioactive glass and porcelain to metal alloys, different methods of fracture repair.

Bioactive glass has the ability to bond to bone. In this article the contact between glass and bone is discussed and the development of core alloy for an implant coated with bioactive glass and the oxidation of metal surface in ceramic fusion has been studied. Good bonding of coating materials to core alloys is necessary in dental implants. Using a pull test method we studied the bond strengths between various alloys and some composite materials clinically used to repair fractures of porcelain-veneered dental crowns. An experimental bioglass material was also studied. The bonding of composite materials to metal surfaces etched with hydrofluoric acid was almost as good as the bonding between metal and porcelain, or glass.

Adhesives↗
PubMed2004

Toughening of dental glass ionomer cements with reactive glass fibres.

A fibre reinforced glass ionomer cement (FRGIC) for dental applications was loaded with 20 vol% short fibres (430 microm) with a glass composition in the system SiO(2)-Al(2)O(3)-CaF(2)-Na(3)AlF(6). The fracture toughness and the total energy release rate were examined. A 20% anisotropic fibre alignment was observed, perpendicular to the loading direction. An increase of fracture toughness of 140% and of total energy release rate of 440% was achieved compared to the unreinforced glass ionomer cement. Matrix-fibre interface reaction is supposed to exert the major influence on mechanical behaviour of FRGIC by controlling fibre pull-out and thus the total energy release rate.

Anisotropy↗
PubMed2005

Glass transition-related changes in molecular mobility below glass transition temperature of freeze-dried formulations, as measured by dielectric spectroscopy and solid state nuclear magnetic resonance.

The purpose of this study was to explore why changes in the molecular mobility associated with glass transition, the timescale of which is on the order of 100 s, can be detected by measuring the nuclear magnetic resonance relaxation times that reflect molecular motions on the order of 10 kHz and 1 MHz. The molecular motions in freeze-dried dextran 40k, dextran 1k, isomaltotriose (IMT), and alpha-glucose comprising a common unit but with different glass transition temperatures, were investigated by dielectric spectroscopy (DES) in the frequency range of 0.01 Hz to 100 kHz and in the temperature range of -20 degrees to 200 degrees C, in order to compare with the molecular motions reflected in nuclear magnetic resonance relaxation times. The alpha-relaxation process for freeze-dried alpha-glucose was visualized by DES, whereas those for freeze-dried dextran 40k, dextran 1k, and IMT were too slow to be visualized by DES. The latter freeze-dried cakes exhibited quasi-dc polarization because of proton-hopping-like motion rather than alpha-relaxation process. The correlation time (tau(c)) for the backbone carbon of dextran 40k and IMT, calculated from the measured value of spin-lattice relaxation time in the rotating frame, was found to be close to the relaxation time of proton-hopping-like motion determined by DES (tau(DES)) at temperatures around glass transition temperature. The timescales of molecular motions reflected in the tau(c) and tau(DES) were significantly smaller than that of motions leading to molecular rearrangement (molecular rearrangement motions), which correspond to alpha-relaxation. However, the shapes of temperature dependence for the tau(c) and tau(DES) were similar to that of the calorimetrically determined relaxation time of molecular rearrangement motions. Results suggest that the molecular motions reflected in the tau(c) and tau(DES) are linked to molecular rearrangement motions, such that enhancement of molecular rearrangement motions enhances the molecular motions reflected in the tau(c) and tau(DES). Thus, the tau(DES) and tau(c) can reflect changes in molecular mobility leading to unwanted changes in amorphous formulations, and are thought to be a useful measure for evaluating the stability of formulations.

Dextrans↗
PubMed1995

Surface modifications of a glass and a glass-ceramic of the MgO-3CaO.P2O5-SiO2 system in a simulated body fluid.

A glass of nominal composition (wt%) 17.25 MgO-52.75 3CaO.P2O5-30 SiO2 and a glass-ceramic obtained from it showed surface modifications when immersed in an acellular medium having a composition similar to that of human blood plasma. A (Ca, P)-rich layer, with an approximate Ca/P atomic ratio of 1.7, identified as hydroxyapatite, developed on both samples. The precipitated film on the glassy sample was weakly bonded, whereas that formed on the glass-ceramic was strongly adherent. The apatite precipitated during the in vitro tests on both samples grew as a needle-like structure with crystals about 150-200 nm long and 50-70 nm thick, as measured on specimens soaked for 1 month in the simulated body fluid (SBF). The presence of calcium and phosphate ions in the SBF contributed to the precipitation of the (Ca, P)-rich layers on both specimens.

Binding Sites↗
PubMed1990

SEM study of surface alterations of bioactive glasses and glass--ceramics in a bony implantation bed.

Back scattered electron (BSE) images of glasses and glass-ceramics with different degrees of bone-bonding behaviour have been investigated. After the implantation of probes in the femur of rats changes of the surface material, induced by leaching and corrosion (material response) and of the tissue in the drill hole (host response), were studied. The results demonstrate advantages of using BSE images and give further information for understanding the sequential changes in the implant material which occur mainly in bone-bonding materials. The density of the leached zone was not homogeneous and it therefore might be possible that preferential leaching of the glass matrix contributes to the mineralization of extracellular matrix. These findings could be of use for further development of surface reactive materials.

Animals↗
PubMed2005

Compressive strength and surface characterization of glass ionomer cements modified by particles of bioactive glass.

OBJECTIVES: The aim of this study was to determine compressive strength, Young's modulus of elasticity, and Vickers' surface hardness, of conventional cure and resin-modified glass ionomer cements after the addition of bioactive glass (BAG) particles into the cements. METHODS: Experimental glass ionomer cement (GIC)-BAG materials were made by mixing 10- or 30-wt% of BAG particles with conventional cure and resin-modified GIC powders. Materials were processed into cylindrical specimens and immersed in water for 1, 3, 7, 14, 30 and 180 days before mechanical tests. SEM and EDS analysis was used to characterize the changes in surface topography and the main elemental composition. RESULTS: The compressive strength of the test specimens decreased with the increasing amount of BAG. The compressive strength of resin-modified GIC increased during the immersion, but remained at a lower level than that of the other materials. The conventional cure GIC-based materials had on average 55% higher surface microhardness than the resin-modified materials. In the elemental composition, more Ca was detected in the BAG-containing materials than in the pure GICs. The amount of F was significantly higher (p < 0.001) on all resin-modified materials, being highest on resin-modified GIC with 30-wt% of BAG after 180d of immersion. SIGNIFICANCE: The addition of BAG to GIC compromises the mechanical properties of the materials to some extent. Thus, their clinical use ought to be restricted to applications where their bioactivity can be beneficial, such as root surface fillings and liners in dentistry, and where high compressive strength is not necessarily needed.

Analysis of Variance↗
PubMed1998

Marginal adaptation and retention of a glass-ionomer, resin-modified glass-ionomers and a polyacid-modified resin composite in cervical Class-V lesions.

OBJECTIVES: An 18-month follow-up clinical trial of one conventional glass-ionomer (HIFI Master Palette), three resin-modified glass-ionomers (Fuji II LC, Vitremer, 3M Exp. 155) and one polyacid-modified resin composite (Dyract) was conducted to evaluate their clinical effectiveness in Class-V cervical lesions. In addition, the interface between dentin and two resin-modified glass-ionomers and one polyacid-modified resin composite was examined by scanning electron microscopy (SEM). METHODS: After evaluation of the restorations immediately following placement (baseline), all patients were subjected to a strict recall schedule with controls at 6, 12 and 18 months. The clinical effectiveness was recorded in terms of retention and marginal integrity, clinical microleakage, caries recurrence, and tooth vitality. A chi 2-test (p < 0.05) was used to test for significant differences between materials. In case of restoration loss or special defects, a replica was made to examine the surface texture and restoration margins by SEM. In vitro, the interface was examined by SEM after an argon-ion-beam etching technique was used to enhance surface relief and disclose interfacial substructures. RESULTS: Retention appeared to be good for all the materials tested. Marginal discrepancies were localized at the incisal enamel and/or the cervical dentin margin, except for the polyacid-modified resin composite that showed most of the defects at the incisal enamel margin. None of the systems could guarantee margins free of microleakage for a long time. In vitro, the type of dentin pre-treatment defines to a great extent the morphology of the resultant interface between dentin and the restorative material tested. SIGNIFICANCE: In this clinical study, the retention rate of the tested materials was good and even excellent for some products. Perfect marginal adaptation deteriorated too fast. The marginal adaptation of the polyacid-modified resin composite at the enamel site would probably have been better by the use of selective enamel or total acid etching. Marginal sealing remains a problem. Future research should concentrate on improving the marginal adaptation and sealing capacities before a broader clinical use can be advocated.

Acrylic Resins↗
PubMed1997

Changes in compressive strength on ageing in glass polyalkenoate (glass-ionomer) cements prepared from acrylic/maleic acid copolymers.

Previous studies have shown that glass-ionomers made from acrylic/maleic copolymers stored in water reach a maximum strength at about 1 week, and after 4 months have become significantly weaker. This finding, which contrasts with the behaviour of glass-ionomers based on poly(acrylic acid), was originally attributed to hydrolytic instability. This interpretation has been tested in the current work. Specimens of glass-ionomer prepared from acrylic/maleic acid copolymer have been stored for up to 4 months in different media, namely deionized water, dry air and vegetable oil, then tested for compressive strength. Specimens were in the form of cylinders of dimensions 6 mm high x 4 mm diameter, and storage temperature was 37 degrees C. Data were analysed using two-way analysis of variance (ANOVA) and in all three media specimens became weaker at 4 months than they had been at 1 week (P < 0.05). However, for the specimens stored in dry air and in water, the 1-week values were not the maximum. The fact that there was a loss of strength under all conditions led to the conclusion that it is not, after all, due to hydrolysis.

Acrylates↗
PubMed1992

Microleakage of glass ionomer/composite resin restorations: a laboratory study. 1. The influence of glass ionomer cement.

Acid-etching of enamel margins, often combined with bevelling and use of a low viscosity resin, has resulted in improved sealing of composite restorations. When enamel is absent and margins involve dentine or cementum, microleakage is more often observed. The use of glass ionomer cement, as both a restorative material and as a base combined with a veneer of composite resin, has been advocated as a means of minimizing microleakage where margins are placed in dentine or cementum. Four restorative techniques incorporating glass ionomer cement were used, in vitro, to restore cervical cavities. After thermal cycling, dye penetration was scored along occlusal and gingival margins. In all instances the gingival margin exhibited a less reliable seal than the occlusal margin. The sandwich restorations produced a superior seal at both occlusal and gingival margins when compared with glass ionomer restorative cement.

Acid Etching, Dental↗
PubMed1977

Modifications of glass microelectrodes: a self-filling and a semifloating glass microelectrode.

A simple and inexpensive method for constructing a double capillary was developed for preparing a self-filling glass microelectrode. The modified method uses a thin capillary instead of a bundle of glass fibers and fuses it to the outer capillary wall with flame before pulling the latter with a puller. The validity of the new electrode was proven by measuring the proximal cell PD of the rat kidney slices (mean of the stable cell PDs lasting longer than 30 min,--69 mV). A semifloating electrode was modified from the original floating electrode to be applicable to the in vivo kidney preparation whose pulsatile and respiratory movements had hindered yielding a stable cell PD. This electrode is constructed simply by replacing the shaft of the Ling-Gerard glass microelectrode with a length of flexible silcone-rubber tubing. The cell PD recorded by this electrode is found to be more stable and can withstand minor tissue distortion in mammalian kidney cells in vivo and also in such a contractile tissue as the secretory coil of the eccrine sweat gland.

Animals↗
PubMed1998

Mechanical properties of bioactive glasses, glass-ceramics and composites.

The application of bioactive glass and glass-ceramics has been widely documented over the past twenty years but the high modulus and low fracture toughness has made them less applicable for clinical, load bearing, applications. The development of non-resorbable polyethylene and polysulphone matrices for these materials has improved the mechanical properties. However, the primary concern of whether the bioactivity of the composites is reduced is still unresolved. The more recent development of resorbable carrier systems, dextran and collagen, for bioactive glasses does not introduce such problems, hence making this form of composite suitable for novel soft tissue applications. The development of a simple quality index has enabled some of the materials described within this paper to be ranked by their ability to replace bone, thus enabling possible new research directions to be emphasized.

Biocompatible Materials↗
PubMedDate not supplied

A clinical comparison of glass ionomer, resin-modified glass ionomer and resin composite restorations in the treatment of cervical caries in xerostomic head and neck radiation patients.

Controversy exists as to whether there is less secondary caries at the margins of glass ionomer restorations compared with other materials that do not release fluoride. This study examined the incidence of secondary caries for three types of restorative materials in Class V restorations in xerostomic patients. The study group consisted of 45 high caries-risk adult patients who had undergone head and neck irradiation for the treatment of cancer. All were substantially xerostomic and in need of at least three restorations in the same arch. Every patient received a restoration with each of the test materials, a conventional glass ionomer (GI), a resin modified glass ionomer (RMGI) and a resin composite (C). Patients were instructed in the daily use of a neutral pH sodium fluoride gel in custom trays. Recall appointments were made at 6, 12, 18 and 24 months, and the restorations were examined for material loss, marginal integrity and recurrent caries at the restoration margin. Fluoride compliance was determined at each recall period and recorded as the percentage of recommended use during that interval. Patients were categorized at the end of the study as fluoride non-users if their average compliance was 50% or less. Those with greater than 50% compliance were categorized as fluoride users. In the latter group, no recurrent caries was found for any of the restorations, whereas a material-dependent incidence of recurrent caries was found in the fluoride non-user group. None of the GI, one RMGI and eight C restorations failed due to recurrent caries. For the fluoride non-user patients, Fishers exact test (p=0.05) showed no statistical difference between GI and RMGI but statistical differences were found among those materials and resin composite at each recall period. Recurrent caries reductions for GI and RMGI relative to C were greater than 80% in xerostomic patients not using topical fluoride supplementation.

Adult↗
PubMed2003

[Four-glass or two glass test for chronic prostatitis].

Chronic pelvic pain syndrome is still an important clinical problem. The NIH prostatitis classification introduced in 1998 for diagnosis and treatment measures is based on extended microbiological analysis of urine and expressed prostate secretion (4-glass test). In 1997 J.C. Nickel proved that the culture and microscopic examination of urine before and after prostatic massage leads to the same results as the 4-glass test. In our prospective study on 143 patients with a diagnosis of chronic prostatitis, we analyzed this statement and came to the same results. We therefore recommend replacing the expensive and time-consuming 4-glass test by a simple preprostatic and postprostatic massage urine culture. Further examinations should only be performed in special cases.

Adult↗