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PubMed2005

Sol-gel synthesis of luminescent InP nanocrystals embedded in silica glasses.

III-V semiconductor nanocrystals rarely exist as spherical inclusions inside glasses, due to difficulties during their preparation, such as high toxic reagents or fast oxidation under usual glass technology temperatures. In this letter a sol-gel method for synthesis of InP nanocrystals embedded in silica glasses was described. Gels were synthesized by hydrolysis of a complex solution of Si(OC2H5)4, InCl3.4H2O, and PO(OC2H5)3. Then, the gels were heated at 600 degrees C in the presence of H2 gas to form fine cubic InP crystallites. Raman spectrum showed an InP longitudinal-optic mode (342 cm(-1)) and a transverse-optic mode (303 cm(-1)). The size of InP nanocrystals was found to be from 2 to 8 nm in diameter by transmission electron microscopy. A strong photoluminescence with a peak at 856 nm was observed from InP nanocrystals embedded in silica glasses. The results suggest that it might be possible to synthesize other III-V semiconductor nanocrystals embedded in silica glasses through the sol-gel process.

Adsorption↗
PubMed1984

Long-term F release from glass ionomer cements.

Fluoride release from three commercial glass ionomer filling cements and three glass ionomer luting cements was measured in the laboratory over a 12-month period. Fluoride release from these glass ionomer cements was compared with that released from a silicate, silicophosphate, and a fluoride-containing polycarboxylate cement. The fluoride released from the glass ionomer cements throughout the one-year period was similar, both in quantity and pattern, to that released by the silicate cement. The silicophosphate cement tended to release fluoride in somewhat lesser amounts, while the amount of fluoride released by the polycarboxylate was negligible after the first few days. Analysis of these data indicates that these glass ionomer cements probably possess anticariogenic properties similar to those of silicate cement.

Chemical Phenomena↗
PubMed1987

Thermal diffusivity of glass-ionomer cements.

Thermal diffusivity, a property related to the thermal insulative efficiency of a material, was measured in nine glass-ionomer cements and compared with results from a silicate and a polycarboxylate cement. Each cement was mixed at various powder-liquid ratios (P/L) and moulded into a rectangular prism of approximate dimensions 2 cm cube with a thermocouple embedded in it. The prism was immersed in a constant-temperature bath at 1 degree C, and the fall in temperature was observed over a period of three min. Except for the initial and later stages, the plot of the logarithmic difference between external and internal temperatures of each block of cement against time showed a straight line in accord with theoretical prediction. From the slope, the thermal diffusivity of the material was calculated. The values for the silicate, polycarboxylate, and glass-ionomer-metal (cermet) showed a marked rise with increasing P/L, whereas at higher P/L, glass ionomer cements showed gradual change, with values being only slightly higher than the thermal diffusivity of dentin. Glass-ionomer cements are good thermal insulators over a wide range of P/L, and close agreement between experimental and theoretical data shows that glass-ionomer cements are homogenous isotropic materials.

Dental Cements↗
PubMed1990

Shear bond strength of light-cured glass ionomer to enamel and dentin.

The shear bond strengths of a light-cured glass-ionomer cement to enamel and dentin were determined with use of extracted human maxillary permanent canines and molars. Bonding sites on the ground, etched enamel and ground dentin surfaces were demarcated by the punching of a hole, 3 mm in diameter, in an adhesive tape. The mixed glass-ionomer cement was transferred to the demarcated site, cured by exposure to visible light for 30 s, and the cement surface treated with Scotchprep Dentin Primer followed by Scotchbond 2 Light Cure Dental Adhesive. The embedded teeth were positioned in an assembly apparatus, and Silux composite was bonded to the glass-ionomer-cement surfaces. The specimens were disassembled after 15 min and subjected to a shear load (in an Instron machine) immediately after disassembly; after storage in water at 37 degrees C for 24 h, without and with temperature cycling; and after storage in water for four weeks, without and with temperature cycling. The shear bond strength of the glass-ionomer cement to etched enamel was in the order of 12 MN.m-2, and to dentin it was 9 MN.m-2. Temperature cycling and duration of storage had no adverse effect on the shear bond strength. The enamel and dentin aspects of fractured test specimens were examined, and the percentage of the bonding area that failed in the cement was estimated. Most of the test specimens failed partly at the enamel and dentin interfaces and within the glass-ionomer cement.

Analysis of Variance↗
PubMed1990

Mutans streptococci in plaque from margins of amalgam, composite, and glass-ionomer restorations.

Levels of mutans streptococci in plaque samples from margins of Class II amalgam (Dispersalloy), composite (P-10), and glass-ionomer (Ketac Silver) restorations were compared. Fifty-one children, each having one of the restorations in a permanent first molar, were part of an inter-individual comparison, giving 17 restorations of each material. The age of the children, the age of the restorations, and the salivary levels of mutans streptococci were comparable in the three groups. Another seven children--each having both a composite and a glass-ionomer restoration of the same age placed on contralateral premolar or molar teeth--were part of an intra-individual comparison. The percentage mutans streptococci of total CFU count in plaque was higher on composite (mean 13.7) and amalgam (mean 4.3) than on glass-ionomer (mean 1.1) restorations in the inter-individual comparison, and higher on composite (mean 4.2) than on glass-ionomer (mean 0.4) restorations in the intra-individual comparison. In both comparisons, the differences in values between samples from glass-ionomer restorations and samples from composite or amalgam restorations were statistically significant (p less than 0.05).

Adolescent↗
PubMed1993

Flexural strength and fracture toughness of Dicor glass-ceramic after embedment modification.

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Aluminum↗
PubMed1993

Release of fluoride and other elements from light-cured glass ionomers in neutral and acidic conditions.

The purpose of this study was to measure the release of fluoride, sodium, silicon, calcium, strontium, and aluminum from light-cured glass ionomers. The materials tested were: (1) Baseline VLC thick mix; (2) Baseline VLC thin mix; (3) Fuji Lining LC; (4) Vitrebond; and (5) XR-Ionomer. A conventional glass ionomer, Ketac-FilAplicap, and a silver-reinforced glass ionomer, Ketac-Silver, were used as controls. Each test specimen was first stored for 16 days in de-ionized water, followed by a further 16 days in 0.01 mol/L lactic acid (pH 4.0); both solutions were replaced at predetermined intervals. After that, the specimens were immersed for up to 122 days in de-ionized water. During the immersion, light-cured glass ionomers showed considerable variation in the release of fluoride and other elements. In lactic acid, all cements eluted the matrix-forming cations, aluminum and calcium or strontium. This suggests that light-cured materials are as equally susceptible to erosion as are chemically cured glass ionomers. During the immersion, some of the light-cured materials showed a considerable weight gain.

Absorption↗
PubMed1993

The effect of fluoride application on fluoride release and the antibacterial action of glass ionomers.

The aim of this study was to investigate whether the release of fluoride and the antimicrobial effect of freshly mixed glass ionomers could be prolonged by application of fluoride on aged material. Test slabs of freshly mixed and aged (14 d in water) conventional and silver glass ionomer (Ketac-Fil and Ketac-Silver, Espe, Seefeld, Germany) and composite (Silux Plus, 3M, St. Paul, MN) were fitted into the bottom of a test tube. A layer of S. mutans Ingbritt cells was centrifuged onto the test slabs, and the samples were incubated for 20 h in 1.7% sucrose solution. After the incubation, pH, F, and Ca contents of the fluid phase, and F, Mg, P, and K contents of the cells were determined. The aged glass-ionomer samples were then covered with toothpaste (0.1% F) or with fluoride gel (1.25% F), and the composite samples with fluoride gel. After being thoroughly rinsed, S. mutans cells were incubated on the samples as above. The pH fall was significantly inhibited by freshly mixed glass ionomers, and there were changes in cellular cation and phosphorus contents. Large amounts of fluoride were found in the fluid and cells. For old glass ionomers, no inhibitory effect on pH fall could be seen. Fluoride release had decreased to a low level.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1998

Chemical durability of Dicor and fluorocanasite-based glass-ceramics.

Fluorocanasite (Al2O3-CaO-F-K2O-Na2O-SiO2) glass-ceramics exhibit fracture toughness values of up to 5.0 MPa x m1/2. However, their chemical durability is not adequate for dental applications. The objective of this study was to test the hypothesis that an increased concentration of Al2O3 can increase the chemical durability of fluorocanasite-based glass-ceramics. Glass frits containing 2 wt% (CAN2), 5 wt% (CAN5), and 10 wt% Al2O3 (CAN10) were melted individually, poured into a graphite mold, and cut into 16-mm-diam. x 2-mm-thick disks. Each disk was crystallized at 850 degrees C for 6 hrs. The disks were immersed in a solution of de-ionized-distilled water, 4% acetic acid, or a pH 1 buffer solution, and sealed in 90-mL Teflon containers. Corrosion testing was performed by means of vibrational motion at 60 cycles per min in a shaker-bath at 80 degrees C for 15 days. Solution analyses were performed by means of a pH meter, an atomic absorption spectrophotometer, and an inductively coupled plasma spectrometer. Samples exposed to 4% acetic acid solution exhibited a mean weight loss rate (WLR) for the control group (Dicor) of 0.04+/-0.01 mg/cm2 day, which was significantly lower (p < or = 0.0001) than the mean WLR of the CAN2 (1.08+/-0.02 mg/cm2 x day), CAN5 (1.31+/-0.02 mg/cm2 x day), and CAN10(1.51+/-0.05 mg/cm2 x day) groups. The reduced durability of fluorocanasite-based glass-ceramics with increasing Al2O3 concentration is most likely associated with a more uniform distribution of smaller crystals during heat treatment of the glass.

Acetic Acid↗
PubMed1999

Glass-ionomer restoratives: a systematic review of a secondary caries treatment effect.

It is generally accepted that glass ionomers inhibit secondary caries in vivo, and data from in vitro studies support this effect. The aim of this review was a systematic assessment, from the literature, of clinical evidence for the ability of glass-ionomer restoratives to inhibit secondary caries at the restoration margin. Inclusion and exclusion criteria for selection of the review papers were established prior to commencement of the literature search. Papers which conformed to these criteria, and reported on secondary caries as an outcome, were selected (N = 52). Primary and secondary lists of systematic criteria for use in the assessment of the papers were drawn up. The primary list of 14 criteria was applied to each paper. No paper fulfilled all these criteria, necessitating the use of the secondary measures: (i) a prospective study and (ii) use of an appropriate control. This yielded 28 papers. Tabulation of these papers by occurrence of secondary caries in the glass-ionomer or control groups demonstrated an even distribution between positive and negative outcomes. Valid evidence is considered to be best obtained from randomized, controlled studies of sufficient sample size. No conclusive evidence for or against a treatment effect of inhibition of secondary caries by the glass-ionomer restoratives was obtained from the systematic review. There is a need for appraisal of the methods currently adopted for the clinical evaluation of glass-ionomer restorative materials, and for further development of the methodology to support future systematic reviews.

Dental Caries↗
PubMed1988

An in vitro study of the bond strength of a glass ionomer cement in the direct bonding of orthodontic brackets.

The shear/peel bond strength of a 'no-mix' composite orthodontic bonding resin was compared in vitro with that of a glass ionomer cement. The effect of pre-treatment of the enamel, with either phosphoric acid or polyacrylic acid, prior to using the glass ionomer cement was also assessed. The composite resin had a significantly higher bond strength than the glass ionomer cement. Simple prophylaxis and drying of the enamel achieved the best results when using the glass ionomer cement, whilst etching the tooth surface with phosphoric acid produced a significantly poorer bond to the enamel. Investigation of the site of failure showed the composite resin bonded very well to the tooth and less well to the bracket, whilst the glass ionomer adhered significantly better to the bracket base than to the tooth surface.

Acid Etching, Dental↗
PubMed1998

Glass-ionomers in medicine and dentistry.

This paper describes the current uses and future prospects for glass-ionomer cements in dentistry and medicine. Glass-ionomers divide into two chemical types, one is known as self-hardening and sets entirely by a neutralization reaction to give relatively brittle materials, the other is known as resin-modified and sets partly by polymerization and partly by neutralization to give slightly tougher materials. Compared with the self-hardening cements, these latter materials have improved aesthetics and easier clinical handling. Both types bond well to enamel and dentine, and release clinically useful amounts of fluoride. They have been used in a variety of applications in dentistry, including as liners/bases, luting cements for stainless steel crowns, and in various restorative procedures for both permanent and primary teeth. The resin-modified glass-ionomers are particularly promising for these latter uses, though it is too soon to be sure how durable they will prove to be over the longer term. Self-hardened glass-ionomers have been shown to have much better biocompatibility than resin-modified glass-ionomers in a variety of situations and consequently they have been used for various non-dental applications, such as ear, nose and throat surgery and craniofacial reconstruction.

Biocompatible Materials↗
PubMed1994

Glass fiber dissolution in simulated lung fluid and measures needed to improve consistency and correspondence to in vivo dissolution.

The dissolution of a range of glass fibers including commercial glass and mineral wools has been studied using a modification of Gamble's solution in a flow system at pH 7.4 and 37 degrees C. Dissolution has been followed by weight loss, effluent analysis, and morphology change of fibers and bulk glass. Flow per glass surface area can strongly affect both dissolution rate and morphology due to the effect of the dissolution process on the fluid. Effluent pH is shown to be a guide for choice of optimum flow/area conditions. These conditions provide measurable concentrations of dissolved glass in the effluent while maintaining their concentrations below the point at which they significantly affect the dissolution process. SiO2 and Al2O3 vary widely in the extent to which they are involved in the leaching process, which removes alkalis, alkaline earths, and B2O3. This makes analysis of a single component in the effluent unsuitable as a means of comparing the dissolution rates of a wide range of compositions.

Body Fluids↗
PubMed1994

Phagosomal pH and glass fiber dissolution in cultured nasal epithelial cells and alveolar macrophages: a preliminary study.

The dissolution rate of glass fibers has been shown to be pH sensitive using in vitro lung fluid simulant models. The current study investigated whether there is a difference in phagosomal pH (ppH) between rat alveolar macrophages (AM) and rat nasal epithelial cells (RNEC) and whether such a difference would influence the dissolution of glass fibers. The ppH was measured in cultured AM and RNEC using flow cytometric, fluorescence-emission rationing techniques with fluorescein-labeled, amorphous silica particles. Glass fiber dissolution was determined in AM and RNEC cultured for 3 weeks with fast dissolving glass fibers (GF-A) or slow dissolving ones (GF-B). The mean diameters of GF-A were 2.7 microns and of GF-B, 2.6 microns, the average length of both fibers was approximately 22 to 25 microns. Dissolution was monitored by measuring the length and diameter of intracellular fibers and estimating the volume, assuming a cylindrical morphology. The ppH of AM was 5.2 to 5.8, and the ppH of RNEC was 7.0 to 7.5. The GF-A dissolved more slowly in RNEC than in AM, and no dissolution was evident in either cell type with GF-B. The volume loss with GF-A after a 3-week culture with AM was 66% compared to 45% for cultured RNEC. These results are different from those obtained using in vitro lung fluid-simulant models where dissolution is faster at higher pH. This difference suggests that dissolution rates of glass fibers in AM should not be applied to the dissolution of fibers in epithelial cells.

Animals↗
PubMed2005

Surface-enhanced Raman spectroscopy using silver-coated porous glass-ceramic substrates.

Surface-enhanced Raman scattering (SERS) has been studied using a silver-coated porous glass-ceramic material as a new type of substrate. The porous glass-ceramic is in the CaO-TiO2-P2O5 system prepared by controlled crystallization and subsequent chemical leaching of the dense glass-ceramic, leaving a solid skeleton with pores ranging in size from 50 nm to submicrometer. Silver was coated on the surface of the porous glass-ceramic by radio frequency (RF) sputtering or e-beam evaporation in vacuum. SERS spectra of excellent quality were obtained from several dyes and carboxylic acid molecules, including rhodamine 6G, crystal violet, isonicotinic acid, and benzoic acid, using this new substrate. This new substrate showed a good compatibility with these molecules. The porous glass ceramic with a nanometer-structured surface accommodated both test molecules and silver film. The absorbed molecules were therefore better interfaced with silver for surface-enhanced Raman scattering.

Benzoic Acid↗
PubMed1990

Microleakage at gingival dentin margins of Class V composite restorations lined with light-cured glass ionomer cement.

This study compared the microleakage of light-cured and auto-set glass ionomer liners used in Class V composite laminated glass ionomer restorations by determining the amount of microleakage at the gingival cementum/dentin margins. Standardized nonundercut V-shaped Class V cavities with gingival margins below the cementoenamel junction were prepared on the mesial and distal surfaces of 40 molars, establishing a total of 80 cavities, which were randomly divided into four groups. Each was lined with glass ionomers: group 1, Ketac-Bond (ESPE-Premier), which served as the control; group 2, XR-Ionomer (Kerr); group 3, XR-Ionomer with polyacrylic acid (PAA) pretreatment (Kerr); and group 4, Vitrabond (3M). Specimens were thermocycled for 300 cycles in 0.5% aqueous solution of basic fuchsin between 4 and 55 C with a 1-minute dwell time, and individually embedded in an epoxy resin. Statistical analysis indicated no differences among groups using the light-cured glass ionomer (groups 2 to 4), and they showed significantly less leakage than the control (group 1) at P less than 0.00001). Removal of the smear layer using 10% polyacrylic acid solution did not influence microleakage in restorations with light-cured glass ionomer liners.

Acid Etching, Dental↗
PubMed1981

Non-specific adsorption of corticotrophin-releasing factor (CRF) to powdered glass.

CRF activity from various sources (rat hypothalamic median eminence and posterior pituitary, bovine hypophyseal stalk, and human peripheral blood) was adsorbed to finely ground glass (Quso, Corning, CRF activity was eluted from the glass with 30% acetone. Up to 85% of the total CRF activity originally present in the crude CRF preparation was adsorbed to Quso or Corning glass; up to 25% of the original total CRF activity was recovered from the glass with 30% acetone. We conclude that CRF is among the hormones adsorbed by glass.

Adrenocorticotropic Hormone↗
PubMed1983

[Biological effects of mineral fibers on lymphocytes in vitro. Comparative studies of asbestos and glass fibers].

The biological effects of asbestos and glass fibers on lymphocytes in vitro were investigated. Blastoid transformation and beta 2 microglobulin production of human peripheral blood lymphocytes (PBL) induced by phytohemagglutinin were inhibited by Canadian chrysotile B (Standard sample of the Union Internationale Contre le Cancer; UICC standard sample) but it was not the case for crocidolite (UICC standard sample) and small and large glass fibers (John Manville, Canada). Cytotoxic activities of natural killer and killer cells of PBL were investigated using K562 cells and Chang liver cells as target cells respectively. Chrysotile inhibited the both activities but crocidolite and two kind of glass fibers not. In regard to release of lactic dehydrogenase and beta-glucuronidase from mouse peritoneal macrophages exposed to mineral fibers, chrysotile showed more effective reaction compared to crocidolite and amosite (UICC standard sample), on the other hand large glass fiber showed the similar reaction to chrysotile but small glass fiber and milled amosite did not induce any more enzymatic release than the control. In addition to chemical compositions of mineral fibers, the morphological characteristics were also discussed in relation to their biological effects.

Animals↗