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At least 577 records · Page 32Linked to original sources
PubMed2006

A novel comonomer-free light-cured glass-ionomer cement for reduced cytotoxicity and enhanced mechanical strength.

OBJECTIVE: The objective of this study was to develop a novel comonomer-free light-cured glass-ionomer system based on the 4-arm star-shape poly(acrylic acid). The mechanical strengths and in vitro cytotoxicity of the formed system were evaluated and compared with those of several representative commercial glass-ionomer cements. MATERIALS AND METHODS: The 4-arm poly(acrylic acid) was synthesized using ATRP and tethered with glycidyl methacrylate (GM). The GM-tethered polymer was formulated with water, photo-initiators, and Fuji II LC filler. Fuji II, Fuji II LC and Vitremer were used for comparison. Compressive strength (CS) and MTT assay were used as tools to evaluate the mechanical strengths and in vitro cytotoxicity of the cements, respectively. RESULTS: The experimental cement exhibited significantly high compressive, diametral tensile and flexural strengths as compared to commercial glass-ionomer cements, Fuji II, Fuji II LC and Vitremer. The effects of polymer/water (P/W) ratio, GM-grafting ratio, glass powder/polymer liquid (P/L) ratio and aging in water on strengths were significant. Similar to conventional glass-ionomer cement Fuji II, the eluates from the experimental cement showed little in vitro cytotoxicity to Balb/c mouse fibroblast cells, as compared to Fuji II LC and Vitremer that contain HEMA as a comonomer. CONCLUSIONS: It appears that this novel comonomer-free light-cured glass-ionomer cement will be a promising dental restorative because it demonstrated significantly improved mechanical strengths and almost no in vitro cytotoxicity as compared to current commercial light-cured glass-ionomer cements.

Acrylic Resins↗
PubMed2006

Comparison between effectiveness of a low-viscosity glass ionomer and a resin-based glutaraldehyde containing primer in treating dentine hypersensitivity--a 25.2-month evaluation.

OBJECTIVES: The null-hypothesis tested was; there is no difference in effectiveness between a new low-viscosity glass ionomer and a resin-based glutaraldehyde containing primer in treating hypersensitive teeth after 2 years. METHODS: Using a split-mouth design, hypersensitive teeth in 14 adult patients were randomly assigned to 2 treatment groups. Hypersensitive tooth surfaces were covered with a low-viscosity glass ionomer (Fuji VII) and a resin-based glutaraldehyde containing primer (Gluma Desensitizer). The discomfort interval scale (DIS) ranging from 0 to 4 was used to test the level of hypersensitivity before and after treatment, and at 3 months using compressed air blown for 2 s, and at 1 and 25.2 months using a telephone interview. Differences between and within the treatment groups were tested using the sign rank test. RESULTS: Evaluations in the gluma group were discontinued after 3 months. The mean DIS score for hypersensitive teeth in the glass ionomer group was statistically significantly lower than that in the gluma group, immediately after application (p=0.0005), after 1 month (p=0.02) and after 3 months (p=0.003). After 3 months, 11/14 of the hypersensitive teeth in the glass ionomer group and 2/14 in the gluma group were free of sensitivity. The mean DIS score for hypersensitive teeth in the glass ionomer group remained low after 19.2 months (0.25: S.E.=0.13) and 25.2 months (0.22: S.E.=0.15). CONCLUSIONS: The null-hypothesis was rejected. The low-viscosity glass ionomer (Fuji VII) is more effective in treating hypersensitive teeth than Gluma Desensitizer after 3 months. The positive treatment effect of the glass ionomer continued until 25.2 months.

Adult↗
PubMed2005

Up-conversion luminescence analysis in ytterbium-sensitized erbium-doped oxide-halide tellurite and germanate-niobic-lead glasses.

Ytterbium-sensitized erbium-doped oxide-halide tellurite and germanate-niobic-lead glasses have been synthesized by conventional melting method. Intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions 2H11/2-->4I15/2, 4S3/2-->4I15/2 and 4F9/2-->4I15/2, respectively, were simultaneously observed at room temperature in these glasses. The quadratic dependence of the 525, 546 and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs. Tellurite glass showed a weaker up-conversion emission than germanate-niobic-lead glass, which is inconsistent with the prediction from the difference of maximum phonon energy between tellurite and germanate-niobic-lead glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. Our results reveal that the phonon density and the maximum phonon energy of host glasses are both important factors in determining the up-conversion efficiency.

Erbium↗
PubMed2005

Fluorescence properties of Eu3+ ions doped borate and fluoroborate glasses containing lithium, zinc and lead.

The influence of glass composition on the fluorescence properties of Eu3+ ions doped borate and fluoroborate glasses modified with Li+, Zn2+ and Pb2+ cations have been investigated. The magnitude of splittings of 7F1 levels are analyzed using crystal-field (CF) analysis. The relative intensities of 5D0 --> 7F2 to 5D0 --> 7F1 transitions, crystal-field strength parameters and decay times of the 5D0 level have been determined and are found to be lower for Pb based glasses than those of Zn/Li based glasses. The lifetimes of 5D0 level are found to increase when borate glasses are modified with pure fluorides than with oxides and oxyfluorides. The fluorescence decay of 5D0 level fits perfect single exponential in the Eu3+:glass systems studied which indicates the absence of energy transfer between Eu3+ ions in these glasses.

Borates↗
PubMed2005

Structural, optical, physical and electrical properties of V2O5.SrO.B2O3 glasses.

The present work aims to study the structure and variation of optical band gap, density and dc electrical conductivity in vanadium strontium borate glasses. The glass systems xV2O5.(40-x)SrO.60B2O3 and xV2O5.(60-x)B2O3.40SrO with x varying from 0 to 20 mol% were prepared by normal melt quench technique. Structural studies were made by recording IR transmission spectra. The fundamental absorption edge for all the glasses was analyzed in terms of the theory proposed by Davis and Mott. The position of absorption edge and hence the value of the optical band gap was found to depend on the semiconducting glass composition. The absorption in these glasses is believed to be associated with indirect transitions. The origin of Urbach energy is associated with the phonon-assisted indirect transitions. The change in both density and molar volume was discussed in terms of the structural modifications that take place in the glass matrix on addition of V2O5. dc conductivity of the glass systems is also reported. The change of conductivity and activation energy with composition indicates that the conduction process varies from ionic to polaronic one.

Boron Compounds↗
PubMed2006

Fluorescence properties of Nd3+-doped tellurite glasses.

The compositional and concentration dependence of luminescence of the (4)F(3/2)-->(4)I(J) (J=13/2, 11/2 and 9/2) transitions in four Nd(3+)-doped tellurite based glasses has been studied. The free-ion energy levels obtained for 60TeO(2)+39ZnO(2)+1.0Nd(2)O(3) (TZN10) glass have been analysed using the free-ion Hamiltonian model and compared with similar results obtained for Nd(3+):glass systems. The absorption spectrum of TZN10 glass has been analysed using the Judd-Ofelt theory. Relatively longer decay rates have been obtained for Nd(3+)-doped phosphotellurite glasses. The emission characteristics of the (4)F(3/2)-->(4)I(11/2) transition, of the Nd(3+):TZN10 glass, are found to be comparable to those obtained for Nd(3+):phosphate laser glasses. The non-exponential shape of the emission decay curves for the (4)F(3/2)-->(4)I(11/2) transition is attributed to the presence of energy transfer processes between the Nd(3+) ions.

Fluorescence↗
PubMed2005

Reuse of ground waste glass as aggregate for mortars.

This work was aimed at studying the possibility of reusing waste glass from crushed containers and building demolition as aggregate for preparing mortars and concrete. At present, this kind of reuse is still not common due to the risk of alkali-silica reaction between the alkalis of cement and silica of the waste glass. This expansive reaction can cause great problems of cracking and, consequently, it can be extremely deleterious for the durability of mortar and concrete. However, data reported in the literature show that if the waste glass is finely ground, under 75mum, this effect does not occur and mortar durability is guaranteed. Therefore, in this work the possible reactivity of waste glass with the cement paste in mortars was verified, by varying the particle size of the finely ground waste glass. No reaction has been detected with particle size up to 100mum thus indicating the feasibility of the waste glass reuse as fine aggregate in mortars and concrete. In addition, waste glass seems to positively contribute to the mortar micro-structural properties resulting in an evident improvement of its mechanical performance.

Conservation of Natural Resources↗
PubMed2005

Extraction of heavy metal ions from waste colored glass through phase separation.

A new method utilizing phase separation phenomena for the extraction of heavy metal ions used as colorants in colored glass is proposed. Colored soda-lime-silica glass containing Co or Cr as a colorant was remelted with B2O3 to yield soda-lime-borosilicate glass. The soda-lime-borosilicate glass thus obtained was leached in 1M nitric acid at 90 degrees C to dissolve the borate phase. All cations (Na, Ca, Cr and Co) concentrated in the borate phase are successfully leached out with the dissolution of the borate phase, when the amount of the B2O3 added to the glass and heat treatment conditions are properly chosen. Porous silicate glass powders with high SiO2 purity are obtained as the result of the leaching. Porous glass can also be formed as bulk material by controlling the composition of additives during the remelting.

Chemistry Techniques, Analytical↗
PubMed1979

Electrochemical properties of Na+- and K+-selective glass microelectrodes.

Electrochemical properties of Na+-selective glass microelectrodes were studied and compared with those of K+-selective glass microelectrodes. The selectivity of Na+-selective glass microelectrodes depended on the ion concentration of test solutions. With aging, resistance of Na+-selective microelectrodes increased and their selectivity for Na over K decreased. Na+-selective microelectrodes potential measured in NaCl solution remained constant with aging, while the potential measured in KCl solution decreased and became more positive. The changes in resistance and potential of Na+-selective microelectrodes may be due to the effects of the less mobile cation, i.e., H+ or K+ on the Na ion exchange in the Na-sensing region. The results indicate that Na+-selective microelectrodes must be used as soon after filling as possible. The selectivity of Na+-selective microelectrodes increased with increase of the sensitive exposed-tip length, whereas their response time became slow due to a large recessed volume, indicating requirement of an optimum exposed-tip length for intracellular applications. The changes in the properties of Na+-selective glass microelectrodes with aging contrasted with those of K+-selective glass microelectrodes in which resistance decreased and K+-selectivity increased. The K+-selective microelectrodes required aging before use for a high selectivity and low resistance. The K+-selective microelectrodes with low resistance after sufficient aging can be used without insulation to measure K+ and Na+ activities in aqueous solutions. The different properties between Na+- and K+-selective microelectrodes are understandable, because hydration of N+-selective glass is much less extensive than that of K+-selective glass.

Electric Conductivity↗
PubMed1995

Iohexol in patients undergoing urography: a comparison of polypropylene containers (Unique Soft Pack) and glass vials.

The purpose of the present phase IV multicentre trial was to evaluate general patient tolerance to Omnipaque 350 mgI/ml (iohexol) supplied in polypropylene containers compared to that of the same product supplied in routinely used glass vials, with emphasis on allergy-like adverse events. Polypropylene is a pure plastic material with practically no additives, and has been tested in vitro as a contrast medium packaging material for several years. Handling of these containers is easier and safer than handling of glass vials. Iohexol was administered to 1481 patients undergoing urography (741 patients in the glass vial group, 740 in the polypropylene container group), all of whom successfully participated in the trial. Six centres, representing four European countries, participated. Patients were randomized to receive iohexol from either polypropylene containers or traditional glass vials according to a double blind, parallel design. Pre-established inclusion and pre-admission exclusion criteria were followed, as well as routine procedures for preparation of the patients and conduct of the urography examinations at each hospital. Patient tolerance was assessed by recording all adverse events experienced over a period of up to 1 h after the procedure. Allergy-like events were defined as coughing, sneezing, nausea, vomiting, urticaria or itching. No adverse events were experienced by 56.5% of the patients in the glass vial group, nor by 58.0% of those in the polypropylene group. Discomfort (mainly a sensation of warmth) was reported by 39.4% and 38.6% of the patients, and adverse events other than discomfort by 7.4% and 5.9% of the patients, respectively. There seemed to be a correlation between the speed of injection and the frequency of discomfort (an increase with increasing speed), both of which varied a lot between centres. There was no significant difference in the incidence of allergy-like events between the two groups. Such reactions were seen in 2.0% of patients in the glass vial group and 1.9% of those in the polypropylene container group. There was no significant difference between the patients' tolerance to iohexol supplied in traditional glass vials or in polypropylene containers. Therefore, the new polypropylene container can be recommended as a container for Iohexol.

Adolescent↗
PubMed1998

Effect of glass fiber reinforcement on some mechanical properties of autopolymerizing polymethyl methacrylate.

PURPOSE: This study investigated the different effects of quantitative percentages of glass fiber intensity on the transverse strength, maximum deformation, and the modulus of elasticity of acrylic resin. MATERIALS AND METHODS: Fifty-four specimens were formed in a specially designed mold to produce identical specimens in accordance with the manufacturer's recommendations. Six percentages of glass fiber reinforcement in loose random form were studied. Each glass fiber treatment percentage (0%, 1%, 2%, 5%, 10%, 15%) was related to the total powder/liquid mass. RESULTS: The results indicated that 1% glass fiber treatment enhanced the transverse strength of the tested specimen. Maximum deformation at failure in the tested treatment groups was found to be different. The interaction of glass fiber concentration on fracture strength and deformation was significant (p < 0.0001). CONCLUSION: The 1% glass fiber concentration was found to give the best fracture strength and deformation results. Significantly higher glass fiber percentages was found to weaken the resin.

Analysis of Variance↗
PubMed1997

In vitro toothbrush-dentifrice abrasion of resin-modified glass ionomers.

OBJECTIVES: This study was conducted to compare the rate of abrasive wear and change in surface roughness of resin-modified and conventional acid-base glass ionomers when subjected to toothbrush-dentifrice abrasion. METHODS: Two resin-modified and two conventional glass ionomers were used. Samples of a high-copper amalgam and a hybrid resin composite were used as reference materials. Specimens of each material were prepared and subjected to toothbrush-dentifrice abrasion using 20,000 strokes of brushing. The amount of vertical loss of material was determined by profilometry (Surfcom-4A, Tokyo-Seimitsu, Tokyo, Japan). The surface characteristics after abrasion were evaluated on secondary electron images by SEM, and the surface hardness (KHN) was also measured for all materials. Data were analyzed by one-way ANOVA (p < 0.05), followed by a multiple comparisons test using LSD (Least-significant difference) at a level of p < 0.05. RESULTS: The abrasion resistance of resin-modified glass-ionomers was statistically lower for the amalgam and the resin composite reference materials. Statistically lower abrasion resistance and surface hardness were observed for the resin-modified glass ionomers than for their conventional acid-base counterparts when two forms of products from the same manufacturer were compared. SEM observations made after abrasion testing showed a significantly rougher surface for all glass ionomer materials than for the amalgam and the resin composite. SIGNIFICANCE: When comparisons were made between products from the same manufacturers, it was found that in vitro resistance to toothbrush-dentifrice abrasion of the resin-modified glass ionomers is inferior to that of the conventional acid-base glass ionomers. The lower abrasion resistance found in the resin-modified products appears to be related to their lower surface hardness.

Aluminum Hydroxide↗
PubMed2002

Effects of Si speciation on the in vitro bioactivity of glasses.

The surface reactivity of glasses belonging to the (mol%) 31SiO2-11P2O5-(58-x)CaO-xMgO series, with x ranging from 0 to 32, was studied in Kokubo's simulated body fluid (SBF). Scanning electron microscopy, inductively coupled plasma spectroscopy and Fourier transform infrared spectroscopy were used to characterise the glass surface and the SBF compositional changes. All glasses develop surface layers rich in silica and calcium phosphate. An increasing surface activity with increasing MgO/CaO ratio was observed. In a previous investigation using magic-angle spinning nuclear magnetic resonance it was found that there is an increasing abundance of Q0 species in the glass structure with increasing MgO content. The present work shows that, when immersed in SBF, Q0-rich glasses are easily leached to form a silica gel layer. It is concluded that MgO in the glass indirectly improves the early stages of mineralisation by favouring Q0 speciation. This mechanism plays an important role in glass bioactivity.

Glass↗
PubMed2002

In vivo bone tissue response to a canasite glass-ceramic.

The aim of this study was to determine the biocompatibility and osteoconductive potential of a high-strength canasite glass ceramic. Glass-ceramic rods were produced using the lost-wax casting technique and implanted in the mid-shafts rabbit femurs. Implants were harvested at 4, 13 and 22 weeks and prepared for light and electron microscopy. Hydroxyapatite was used as a control material. Hydroxyapatite implants were surrounded by new mineralised bone tissue after 4 weeks of implantation. The amount of bone surrounding the implant increased slightly at 13 weeks. In contrast, canasite glass and glass ceramic implants were almost entirely surrounded by soft tissue during all the time periods. Close contact between bone and canasite glass-ceramic implant without the intervening fibrous tissue was observed in only a few regions. The canasite formulation evaluated was not osteoconductive and appeared to degrade in the biological environment. It was therefore concluded that the canasite formulation used was unsuitable for use as implant. Further work is required to improve the biocompatibility of these materials with bone tissue. It is possible that this could be achieved by reducing the solubility of the glass and glass ceramic.

Animals↗
PubMed2003

Bioactive sol-gel glasses with and without a hydroxycarbonate apatite layer as substrates for osteoblast cell adhesion and proliferation.

The biocompatibility of three sol-gel bioactive glasses with SiO(2) as the main constituent (75, 72.5 and 70 mol%), identical CaO content (25mol%), and without or with P(2)O(5) as third constituent (0, 2.5 and 5 mol%), have been analyzed (S75, S72.5P2.5, and S70P5 glasses). These studies were performed on both untreated glasses and on glasses coated with a hydroxycarbonate apatite (HCA) layer formed in vitro by soaking 7d in an acellular simulated body fluid. Cell attachment, spreading and proliferation were studied using neonatal rat calvaria osteoblasts. Cells attach to the three untreated glasses but show a higher efficiency on that with the higher phosphate content (S70P5). The formation of the HCA layer significantly enhances this process (1.7-fold). In all cases, attachment is followed by cell spreading on the surface of the materials, adopting the cells a flattened morphology and showing diverse anchoring cell projections. Mitotic activity has been detected on osteoblasts growing on the sol-gel glasses, being this process 2-4-fold higher when the apatite-like layer is already formed. Taking into account the results herein presented, these bioactive glasses can be considered biocompatible. In addition, their biocompatibility is greatly enhanced after induction of the formation of an HCA layer.

Animals↗
PubMed2000

Effect of monovalent ions in glass ionomer cements on their interaction with sodium fluoride solution.

The effects on surface morphology of glass ionomer cements following exposure to 0.2% NaF solution were studied. The effect of cement on the solution was also evaluated. The four cements were chosen to contain Na and F, Na alone, F alone and neither Na nor F to show any interactions produced by having the same ion in both the cement and solution. Four glass ionomer cements were formulated so that they differed only in respect of the glass component. AH2 (a glass used in dental restorative cement) contained both Na and F, MP4 (a glass used in orthopaedic cement) contained Na only, LG26 (a glass used in surgical cement) contained F only and LG30 (an experimental control glass) contained neither F nor Na. Discs of cement were set in moulds at 37 degrees C for 1 h, then matured in water for 3 d. Each test disc was then immersed in 10 ml 0.2% NaF for 24 h at 37 degrees C whereas control discs remained in water. The test and control disc surfaces were assessed qualitatively using electron microscopy and quantitatively by linear profilometry generating roughness values (Ra). Test solution pH was measured before and after cement immersion. Inspection of the electron micrographs showed considerable disruption of AH2 and LG26 test surfaces compared to their controls whereas MP4 and LG30 showed similar surfaces for test and control. Statistical analysis of the Ra values showed that AH2 and LG26 test surfaces were significantly rougher than their controls as well as LG30 and MP4 test surfaces, which were not significantly different from their controls. All NaF solutions show pH increases; those for AH2 and MP4 were significantly higher than those for LG26 and LG30. The F-containing cements were subject to surface disruption whereas F-free cements were not. The Ra values of test surfaces correlated strongly (r = 0.998) with the F uptake of the cements (data from a previous study) but it was not possible to ascribe the causality to this association. The pH changes appear to be influenced by whether or not Na is present in the cement. The resultant pH values are too near to neutral for pH alone to explain the surface disruption observed. In addition, it is concluded that the changes in OH ion concentration are too low to permit F-/OH- interchange as a possible explanation for F uptake by these cements.

Anions↗
PubMed1997

A simple method for the construction of a recording-injection microelectrode with glass-insulated microwire.

A rapid method for the production of a glass-insulated microwire electrode is described. A microwire was threaded into a glass capillary which was then pulled on a vertical pipette puller. A conical tip of the microwire was formed when the strongly heated glass capillary broke together with the wire in it. A tight seal of the glass-insulated microwire electrode between the glass and the metal was accomplished with silicone glue. The manufactured electrode performed consistently at different immersion depths, and yielded stable recordings of single units in the cerebral cortex and the medulla of rats. The strength and low impedance characteristics of the glass-insulated microwire electrode may make it useful for the recording of single units in deep brain structures. Furthermore, the electrode can be easily combined with another glass micropipette to form a dual recording-injection microelectrode unit.

Animals↗
PubMed1993

Association of the actin cytoskeleton with glass-adherent proteins in mouse peritoneal macrophages.

When mouse peritoneal macrophages adherent to glass surface were removed by treatment with triethanolamine and Nonidet P-40, fine thread structures of unique loops were left behind on glass at the sites of cell adhesion. To examine the ultrastructural relationship between such looped threads and cytoskeletal components in glass-adherent macrophages, we successfully used the 'zinc method' to remove most of the cytoplasm including nuclei and to expose the cytoskeleton associated with the ventral plasma membrane. The cytoskeleton was seen to be mainly composed of actin filaments forming dense networks. The network contained scattered star-like foci from which actin filaments radiated. When the ventral plasma membrane-cytoskeleton complex was further treated with Nonidet P-40, the membrane was dissolved to expose the glass surface with actin foci persisting on glass. When the complex was removed by further treatment with Nonidet P-40 and DNase I, the looped threads became visible. Confocal laser microscopy of glass-adherent macrophages stained with fluorescent phalloidin showed the preferential distribution of F-actin in the ventral cytoplasm along the plasma membrane, where intense fluorescent spots were also scattered. Confocal interference reflection microscopy revealed densely populated dark dots and striae of focal contact, which corresponded in overall distribution to actin foci and looped threads. These observations suggest that actin cytoskeleton is closely associated with looped threads to reinforce cell adhesion to glass.

Actins↗