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PubMed2004

Synthesis and degradation of sodium iron phosphate glasses and their in vitro cell response.

The degradation profiles of six sodium iron phosphate glass formulations have been investigated using simple dissolution trials in deionized water. The glasses were produced from the appropriate phosphate salts by melting at 1200 degrees C in 5% Au/95% Pt crucibles. Dissolution rates varied from 0.2 gcm(-2)h(-1) for the 1% Fe glass to essentially zero over the 6-week test period for the 15% Fe and 20% Fe glasses. The overall degradation rate was found to vary according to the approximate relation: rate = 1.3e(-0.79x) gcm(-2)h(-1), where x is the percentage iron content of the glass. Glasses with 10% or greater iron content were observed to maintain a constant density over the course of the tests and thus appeared to degrade from the surface and not the bulk. In vitro cell response tests were conducted on the glasses using macrophages and primary craniofacial osteoblasts. These tests were performed on the glasses with 10% or greater iron content because glasses with lower iron content degraded too quickly. Confocal microscopy revealed a rounded macrophage morphology and IL-1beta production was low, suggesting little macrophage activation. However, a significant level of peroxide production was observed. Osteoblasts were observed to attach to the glass surfaces and spread, exhibiting a similar cytosketetal organization to the cells on the Thermanox controls, with a high level of F-actin organization. On balance, the 15% Fe glass performed slightly better than the 20% Fe glass in these assays.

Animals↗
PubMed2006

Kinetics and mechanisms of the conversion of silicate (45S5), borate, and borosilicate glasses to hydroxyapatite in dilute phosphate solutions.

Bioactive glasses with controllable conversion rates to hydroxyapatite (HA) may provide a novel class of scaffold materials for bone tissue engineering. The objective of the present work was to comprehensively characterize the conversion of a silicate bioactive glass (45S5), a borate glass, and two intermediate borosilicate glass compositions to HA in a dilute phosphate solution at 37 degrees Celsius. The borate glass and the borosilicate glasses were derived from the 45S5 glass by fully or partially replacing the SiO(2) with B(2)O(3). Higher B(2)O(3) content produced a more rapid conversion of the glass to HA and a lower pH value of the phosphate solution. Whereas the borate glass was fully converted to HA in less than 4 days, the silicate (45S5) and borosilicate compositions were only partially converted even after 70 days, and contained residual SiO(2) in a Na-depleted core. The concentration of Na(+) in the phosphate solution increased with reaction time whereas the PO(4) (3-) concentration decreased, both reaching final limiting values at a rate that increased with the B(2)O(3) content of the glass. However, the Ca(2+) concentration in the solution remained low, below the detection limit of atomic absorption, throughout the reaction. Immersion of the glasses in a mixed solution of K(2)HPO(4) and K(2)CO(3) produced a carbonate-substituted HA but the presence of the K(2)CO(3) had little effect on the kinetics of conversion to HA. The kinetics and mechanisms of the conversion process of the four glasses to HA are compared and used to develop a model for the process.

Borates↗
PubMed2006

Bond strength between root dentin and three glass-fiber post systems.

STATEMENT OF PROBLEM: Glass-fiber posts were introduced for use after endodontic therapy instead of metal alloy and ceramic posts. There are several new types of glass-fiber post systems available, but little is known about how well these posts bond to the root surface. PURPOSE: The purpose of this in vitro study was to compare the bond strengths of 3 different types of glass-fiber post systems-opaque, translucent, and electrical glass-in 3 different locations of prepared post spaces. MATERIAL AND METHODS: Sixty human intact single-rooted extracted teeth were used. The root canals were prepared using a step-back technique and obturated with gutta-percha using lateral condensation. The roots were divided into 3 experimental groups and further divided into 2 subgroups according to testing time (n=10). Roots were restored with 1 of the following post systems according to the manufacturer's instructions: opaque glass-fiber posts (Snowpost), translucent glass-fiber posts (FiberMaster), and electrical glass-fiber posts (Everstick). A self-etching primer (Clearfil Liner Bond) was applied to the walls of the post spaces, allowed to etch for 30 seconds, and gently air dried. A dual-polymerized bonding agent (Clearfil Liner Bond, Bond A and B) was then applied to the same walls. A dual-polymerizing resin luting agent (Panavia F) was mixed for 20 seconds and then placed in the post spaces using a lentulo spiral instrument. The roots were placed in light-protected cylinders; then the light source was placed directly on the flat cervical tooth surfaces and the cement was polymerized. Specimens were stored in light-proof boxes for 24 hours or 1 week after the polymerization procedure. Each root was cut horizontally, and six 1-mm-thick root segments (2 apical, 2 middle, and 2 cervical) were prepared. Using a push-out test, the bond strength between post and dentin was measured after 24 hours or 1 week using a universal testing machine. Statistical analysis was performed with 3-way ANOVA followed by independent t tests (alpha=.05) to detect differences between groups defined by the specific interacting variables. The different combinations of posts and luting material from the cervical segments were analyzed with SEM. RESULTS: The 3-way ANOVA indicated that push-out test values varied significantly according to the post system used (opaque, electrical, and translucent) (P<.01); the root segments (cervical, middle, and apical) (P<.01), however, did not vary statistically according to the time of testing (24 hours and 1 week). Opaque and electrical glass-fiber posts showed higher bond strength values than translucent posts (P<.01). Push-out bond strength values of cervical segments were significantly higher than the middle and apical segments in translucent and electrical glass-fiber post groups (P<.01). In the opaque glass-fiber post group, there were no significant differences between cervical and middle segments. In SEM analysis, a distinct hybrid zone with long, numerous resin tags located between luting material and dentin was exhibited in all post systems. CONCLUSION: The opaque and electrical glass-fiber posts exhibited similar bond strengths, and translucent posts exhibited the lowest bond strength. The highest bond strength was observed in the cervical third of the post spaces for translucent and electrical glass-fiber post groups.

Dental Bonding↗
PubMed2006

The characterization of waste cathode-ray tube glass.

New re-use applications are needed to address the relatively large quantity of waste electronic products generated in the world. Cathode-ray tubes (CRTs) from computer monitors and TV sets are a large component of such waste. The three glass components of CRTs are the funnel, panel and neck, which are produced by various manufacturers and are now collected by asset-recovery centres. In this paper, we characterize waste funnel and panel glass from dismantled cathode-ray tubes with a view to assisting the development of new re-use applications. The heavy metal (lead, barium, and strontium) content of such glass represents an acute risk to the environment. Our results of the chemical composition for different kinds of waste CRT glass including black & white and color CRTs show that CRT glass from different producers have generally similar chemical compositions. In particular, the compositions of funnel and panel black & white CRT glass are similar, but are different to those of panel and funnel color CRT glass. We also measured the following specific properties of each type of CRT glass: density, glass transition temperature, and linear coefficient of thermal expansion. It was found that the coefficients of thermal expansion of CRT glass do not vary with their composition. In contrast, the measured densities and glass transition temperatures do vary with composition. On the basis of our experimental data and data found in the literature, we outline the main properties of several waste CRT glass currently in circulation. The aim of this study was to provide the data required to determine if this kind of waste could be entirely (or partially) re-used and to aid the search for promising methods of treatment.

Computer Terminals↗
PubMed1999

A comparison of the shear bond strengths of two glass ionomer cements.

The objective of this study was to determine the in vitro shear bond strength (in megapascals) and location of bond failure with two light-cured glass ionomer resin systems. One system was a hybrid glass ionomer cement with resin (GC Orthodontics, Aslip, Ill), and the other system a glass-filled resin system (Reliance Orthodontic Products, Inc, Itasca, Ill). These systems, Fuji Ortho LC (GC Orthodontics) and Ultra Band Lok (Reliance), respectively, were compared to a light-cured composite resin. Maxillary premolar brackets (n = 200) were bonded to the facial surface of human premolar teeth. The two glass ionomer resin systems were each evaluated by two protocols, one according to the manufacturers' direction plus a variation of their respective technique. The five distinct groups (n = 40) were stored in 37 degreesC distilled water for 30 days and subjected to thermocycling before shear bond strength testing. The findings indicated that large variations existed between the bond strengths of the materials tested. The laboratory shear bond strength of the glass-filled resin glass ionomer cement (Reliance), whether tested in a dry or moist field, was similar to the composite control with all of the previous materials being significantly (P <.01) higher than both the hybrid glass ionomer cement groups (Fuji Ortho LC). However, the hybrid glass ionomer cement with enamel conditioner demonstrated a clinically acceptable mean megapascal value. The Adhesive Remnant Index values ranged from 0.53 to 1.62. The hybrid glass ionomer cement without enamel conditioning recorded the lowest mean adhesive remnant index score and the lowest mean megapascal score. Although both products are glass ionomer resin systems, their individual chemistries vary; this affects their clinical performance. Clinically, it may be suggested that glass ionomers used in a dry field may be beneficial for orthodontic bonding, and that glass ionomer resin systems used in a moist environment need an enamel conditioner.

Acrylic Resins↗
PubMedDate not supplied

Critical evaluation of the standard hydrolytic resistance test for glasses used for containers for blood and parenteral formulations.

As prescribed by pharmacopoeias, containers should meet certain condition of stability to be used for pharmaceutical products. Glass containers are classified according to their resistance to chemical attack, a test executed by heating the glass in contact with water for 30 min at 121 degrees C. The USP powdered glass test for glass containers was applied to different kinds of glasses used as containers for parenteral formulations. In this experiment not only the released alkalinity was measured but also the release of glass constituents: silicate, borate, sodium, and aluminum, and also the release of some impurities as copper and lead. The USP powdered glass test was also carried out with glass ampoules, clear and amber, in the presence of solution of some inorganic salts, NaCl, KCl, CaCl2, MgCl2, NaHCO3, NaH2PO4, KH2PO4, and sodium gluconate, citric acid and glucose. The results showed that even when releasing very low alkalinity, glasses also released their constituents, in concentration ranges from 8.8 to 33 mg/l for silicate, 0.9 to 6.9 mg/l for borate, 3 to 37 for mg/l for sodium and 0.5 to 2.4 mg/l for aluminum. More expressive results were found, however, for the tests done with solutions instead of pure water. The tests showed that, for most of the solutions, while the measured alkalinity was very low, high levels of the other constituents were found. Basic solutions of bicarbonate and gluconate presented the higher levels of all investigated constituents, confirming the ability of basic solutions to attack and dissolve the glass network. Glucose and citric acid interacted with the glass surface, selectively extracting aluminum, copper, and lead. Whereas silicate, borate and sodium found in these solutions were at levels similar to those found with pure water, the aluminum level was almost 20 times higher. This specific action of citrate and glucose could be related to their metal-complexing ability. The results indicate that even so-called "chemical-resistant glasses," as measured by the hydrolytic resistance test, react with many substances when packaged in contact with them. The hydrolytic resistance test, when used as the sole measure of potential drug-container compatibility, is not reliable.

Blood Preservation↗
PubMed1986

Role of phagocytosis in Syrian hamster cell transformation and cytogenetic effects induced by asbestos and short and long glass fibers.

We have shown previously that asbestos and other mineral dusts, including glass fibers, induce cell transformation and chromosomal mutations in Syrian hamster embryo cells in culture. In the present study, we observed that both asbestos and glass fibers were phagocytized by these cells and accumulated in the perinuclear region of the cytoplasm. In order to understand the mechanism of fiber length-dependent cellular effects, we examined the phagocytosis and intracellular distribution of glass fibers of differing lengths in cells at various times after treatment. Glass fiber length was decreased by milling with a mortar and pestle. Cells treated with an equal dose of milled glass fibers (on a weight per surface area basis) were exposed to 7-fold more fibers since milling of glass fibers resulted in a 7-fold decrease in length with little change in diameter. However, cells exposed to milled glass fibers phagocytized a similar number of fibers as cells exposed to an equal mass of unmilled glass fibers, indicating that milled fibers were less readily phagocytized. In cells treated with either unmilled or milled glass fibers, the length of the intracellular fibers was more than 2-fold greater than the length of the fibers on the surface, suggesting that cells selectively internalized longer fibers. Fiber length, however, did not appear to affect the migration of intracellular fibers to the perinuclear region of the cytoplasm. Even though cells treated with milled glass fibers contained a similar number of fibers as those treated with unmilled glass fibers, the resulting cytotoxicity, transformation frequency, and frequency of micronuclei were greatly reduced in the cultures treated with milled glass fibers. Thus, fiber length appears to affect the phagocytosis of fibers as well as the ability of intracellular fibers to induce cytogenetic damage and the resultant transformation.

Animals↗
PubMed1991

Apatite formation on the surface of Ceravital-type glass-ceramic in the body.

Previous studies on surface structural changes in vitro as well as in vivo of bioactive A-W-type glass-ceramics and Bio-glass-type glasses showed that the essential condition for glasses and glass-ceramics to bond to living bone is formation of a bonelike apatite layer on their surfaces in the body. Gross et al., however, had explained the bone-bonding mechanism of Ceravital-type apatite-containing glass-ceramic without mentioning formation of the surface apatite layer. In the present study, apatite formation on the surface of one of Ceravital-type glass-ceramics was investigated in vitro as well as in vivo. An apatite-containing glass-ceramic of the composition Na2O 5, CaO 33, SiO2 46, Ca(PO3)2 16 wt%, which was named KGS by Gross et al., was soaked in an acellular simulated body fluid which had ion concentrations almost equal to those of the human blood plasma. The same kind of glass-ceramic was implanted into a rabbit tibia. Thin-film x-ray diffraction, Fourier transform infrared reflection spectroscopy, and scanning electron microscopic observation of the surfaces of the specimens soaked in the simulated body fluid showed that Ceravital-type glass-ceramic also forms a layer of carbonate-containing hydroxyapatite of small crystallites and/or a defective structure on its surface in the fluid. Electron probe x-ray microanalysis of the interface between the glass-ceramic and the surrounding bone showed that a thin layer rich in Ca and P is present at the interface. These findings indicated that Ceravital-type glass-ceramics also form the bonelike apatite layer on its surface in the body and bond to living bone through the apatite layer.

Animals↗
PubMed2004

Evaluation of glassy-state dynamics from the width of the glass transition: results from theoretical simulation of differential scanning calorimetry and comparisons with experiment.

The purpose of this study is to investigate the quantitative relationship between the width of the glass transition, DeltaTg, and glass fragility or activation energy for structural relaxation. The ultimate objective is the estimation of structural relaxation time as a function of temperature from the width of the glass transition region, allowing characterization of glass dynamics by a single simple measurement. The Moynihan correlation indicates that activation energy for structural relaxation should be inversely proportional to the width of the glass transition, but recent experimental studies suggest this relationship is a poor approximation for glasses of pharmaceutical interest. The present study is an effort to better understand the validity of the Moynihan correlation by selected experimental studies and a theoretical analysis of those factors that impact the glass transition width. Experimental data for glass transition widths for (poly)vinylpyrrolidone, sucrose, and trehalose are obtained using a variety of procedures, and relaxation time data are obtained using the thermal activity monitor. The theoretical analysis begins by simulating the temperature dependence of the heat capacity by breaking the cooling and heating scans into a large number of temperature steps followed by isothermal holds, during which relaxation of the material is calculated. Here, the modified VTF equation is used for relaxation time and the generalized Kohlraush-Williams-Watts stretched exponential function is used to describe the relaxation kinetics. Simulations are performed for materials of varying fragility and varying "stretched exponential" constants, beta, and the width of the glass transition region, DeltaTg, is evaluated from the simulated heat capacity versus temperature curves as one would do with experimental data. Agreement between the theoretical simulations and experimental DeltaTg data is excellent. The simulations demonstrate that although the Moynihan correlation is not valid for variable beta, a modification of the Moynihan correlation which includes variation in beta is a good approximation. Thus, an estimate of fragility may be obtained from glass transition width data provided an estimate of beta is available. Furthermore, it is shown that a first approximation for beta may be obtained from the magnitude (i.e., height) of the differential scanning calorimetry thermal overshoot. We also find that using the modified VTF equation to evaluate the temperature dependence of the structural relaxation time at the glass transition, and integrating this expression to lower temperatures, it is possible to obtain an evaluation of the relaxation time constant, tau(beta), in the glass at any temperature, using only the DeltaTg and beta values obtained from a single differential scanning calorimetry scan. These estimated time constants correlate very well with the values directly measured with the thermal activity monitor.

Algorithms↗
PubMed2001

Mobile silver ions and glass formation in solid electrolytes.

Solid electrolytes are a class of materials in which the cationic or anionic constituents are not confined to specific lattice sites, but are essentially free to move throughout the structure. The solid electrolytes AgI and Ag2Se (refs 1, 2, 3, 4, 5, 6, 7) are of interest for their use as additives in network glasses, such as chalcogenides and oxides, because the resulting composite glasses can show high electrical conductivities with potential applications for batteries, sensors and displays. Here we show that these composite glasses can exhibit two distinct types of molecular structures-an intrinsic phase-separation that results in a bimodal distribution of glass transition temperatures, and a microscopically homogeneous network displaying a single glass transition temperature. For the first case, the two transition temperatures correspond to the solid-electrolyte glass phase and the main glass phase (the 'base glass'), enabling us to show that the glass transition temperatures for the AgI and Ag2Se phases are respectively 75 and 230 degrees C. Furthermore, we show that the magnitude of the bimodal glass transition temperatures can be quantitatively understood in terms of network connectivity, provided that the Ag+ cations undergo fast-ion motion in the glasses. These results allow us to unambiguously distinguish base glasses in which these additives are homogeneously alloyed from those in which an intrinsic phase separation occurs, and to provide clues to understanding ion-transport behaviour in these superionic conductors.

Journal Article↗
PubMed2000

Safety assessment of continuous glass filaments used in eclipse.

Eclipse is a cigarette that produces smoke by primarily heating, rather than burning, tobacco. The Eclipse heat source assembly employs a continuous filament glass mat jacket to insulate the heat source. The glass mat insulator is composed of continuous glass filaments and a binder. The purpose of this article is to address the potential toxicological significance of the continuous glass filaments under the conditions of intended use. Transfer data and the unique physical characteristics of the filaments demonstrate that significant exposure of the smoker will not occur. The available environmental survey data clearly demonstrate that Eclipse smokers are extremely unlikely to be exposed to continuous glass filaments at a level that represents a biologically significant increase over background exposure to glass fibers. The chemical composition of the continuous glass filaments used in Eclipse is generally similar to C-glass fiber compositions such as MMVF 11 that have failed to produce either tumors or fibrosis in chronic inhalation studies conducted in rats. In vitro dissolution data demonstrate that the continuous glass filaments used in Eclipse are more soluble than biologically active fibers such as rock wool (MMVF 21) or asbestos. However, the continuous glass filaments used in Eclipse were not as soluble in simulated extracellular lung fluid as representative C-glass fibers (MMVF 10 and MMVF 11). In brief, exposure of Eclipse smokers to continuous glass filaments is extremely unlikely to occur at a level that may be construed to be of biological significance.

Animals↗
PubMed2001

Creation of microrough surface on sintered bioactive glass microspheres.

Bioactive glasses are surface-active, generally silica-based, synthetic materials that form a firm chemical bond to bone. The aim of this study was to further enhance the bioactivity of glasses by creating a microroughness on their surface. Microroughness increases potential surface area for cell attachment and biomaterial-cell interactions. Three bioactive glasses of different composition were studied. Each material was flame-sprayed into microspheres, and a selected fraction of the spheres (250-300 microm) was sintered to form porous bioactive glass specimens. To create microrough surfaces, different acid etching techniques were tested. Atomic force microscopy (AFM) and back-scattered electron imaging of scanning electron microscopy (BEI-SEM) were used to characterize surface roughness. The degree of roughness was measured by AFM. A novel chemical-etching method, developed through intensive screening of different options, was found consistently to create the desired microroughness, with an average roughness value (R(a)) of 0.35-0.52 microm and a root mean-square roughness value (R(rms)) of 0.42-0.64 microm. Microroughening of the glass surface was obtained even in the internal parts of the porous glass matrices. Measured by BEI-SEM, the etching of a bioactive glass surface did not interfere with the formation of the characteristic surface reactions of bioactive glasses. This was confirmed by immersing the etched and control glass bodies in a simulated body fluid and tris(hydroxymethyl) aminomethane/HCl. The etching process did not significantly affect the mechanical strength of the sintered bioactive glass structures. Based on these experiments, it seems possible to create a reproducible microroughness of appropriate size on the surface of porous bioactive glass. The biologic benefits of such a surface treatment need to be validated with in vivo experiments.

Analysis of Variance↗
PubMed2005

Effect of particulate bioactive glasses on human macrophages and monocytes in vitro.

Bioactive glasses, originally developed to promote tissue adhesion, are finding an increasing array of biomedical applications. The aim of the current study was to assess the ability of silicate- and zinc phosphate-based bioactive glasses to modulate the secretion of cytokines from activated human macrophages and monocytes. Human macrophages and monocytes were isolated and cultured on surfaces coated with a range of quantities of the bioactive glasses. Nontoxic concentrations of the glasses were selected and assessed further for their ability to modulate the secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-10 and -6, in the presence or absence of the stimulant lipopolysaccharide. 45S5 glass produced a significant reduction to the amount of TNF-alpha (p<0.05) and IL-6 (p<0.01) secreted by stimulated cells compared with cells stimulated in the absence of bioactive glass. A significant reduction in IL-6 secretion was also observed with the other silicate- and zinc phosphate-based glasses tested. IL-10 secretion was increased (but not significantly) in presence of all glasses tested. TNF-alpha and IL-6 secretion from stimulated cells was lower in presence of the silicate glasses compared with the zinc phosphate glasses, indicating that this system of bioactive glass might be of clinical use in conditions associated with inflammation.

Cells, Cultured↗
PubMed1999

Effect of serum proteins on osteoblast adhesion to surface-modified bioactive glass and hydroxyapatite.

Previous studies indicate that modification of the surface of porous bioactive glass promotes osteoblast function. We hypothesize that bone formation on treated bioactive glass is due to the selective adsorption of serum attachment proteins. To test this hypothesis, we examined the profile of proteins adsorbed to treated bioactive glass and compared these proteins with those adsorbed to untreated bioactive glass and porous hydroxyapatite. Porous bioactive glass was treated with Tris-buffered electrolyte solution to generate a calcium phosphate-rich surface layer and then immersed in tissue-culture medium containing 10% serum. Proteins adsorbed to the ceramic surfaces were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. Porous hydroxyapatite bound a higher amount of total protein than did the other substrates. However, surface-modified porous bioactive glass adsorbed more fibronectin than did hydroxyapatite. The effect of serum-protein adsorption on osteoblast adhesion to bioactive glass and hydroxyapatite was also evaluated. Cell adhesion to porous bioactive glass that was surface-modified and serum-treated was significantly greater than to porous bioactive glass that was either surface-modified or serum-treated. Furthermore, cell adhesion to porous bioactive glass treated to form the dual layer of calcium phosphate and serum protein was significantly higher than adhesion to porous hydroxyapatite with adsorbed serum protein. Results of the study strongly suggest that adsorption of serum fibronectin to the surface of modified porous bioactive glass coated with calcium phosphate may be responsible for enhanced osteoblast adhesion.

Absorption↗
PubMed2006

Study of yttrium containing bioactive glasses behaviour in simulated body fluid.

The influence of yttrium oxide on the bioactivity of glasses in the system SiO(2)-Na(2)O-P(2)O(5)-CaO-B(2)O(3)-K(2)O-MgO was studied in a simulated body fluid (SBF). Two series of glasses with different bioactivity were investigated. The reaction layers formed on the surface of the exposed glasses were evaluated by means of back scattered electron imaging of scanning electron microscopy equipped with energy dispersive X-ray analysis (BEI-SEM/EDXA). The concentration of Y, Ca and P released from the glasses into SBF, during 21 days was determined using inductively coupled plasma-emission spectroscopy ICP-AES and inductively coupled plasma-mass spectroscopy ICP-MS. Introducing yttrium in the selected bioactive glass tended to diminish the bioactivity of the glasses. The thickness of the calcium phosphate layer decreased with increasing yttrium oxide content. The same effect was also observed when yttrium oxide partially replaced only calcium, magnesium and phosphorous oxide in the precursor glass. The data show that we can produce bioactive glasses with yttrium oxide as a component. By suitable tailoring of the rest of the glasses the yttrium effect on the glass behavior in SBF should be possible to control and thus produce yttrium containing glasses with desired bioactivity.

Biocompatible Materials↗
PubMed2004

Characterisation of commercial ionomer glasses using magic angle nuclear magnetic resonance (MAS-NMR).

Five commercial ionomer glasses (Fuji IX, Ketac Molar, G338, G2, and G2SR) used to produce glass (ionomer) polyalkenoate dental cements were studied. 29Si, 27Al, 31P and 19F magic angle spinning nuclear magnetic resonance (MAS-NMR) Spectroscopy was used to characterise the glasses and the resulting spectra compared with previous studies of model glasses. The 29Si NMR spectra were consistent with Q4(3Al) and Q4(4Al) units being present and agreed with the low non-bridging oxygen contents calculated from the elemental composition. The 27Al NMR spectra typically exhibited three distinct sites at 45-60, 20 and 0 ppm which have been attributed to Al(IV), Al(V) and Al(VI) coordinate aluminium. The presence of Al(V) and Al(VI) are consistent with previous studies of model ionomer glasses. The 31P spectra all exhibited a chemical shift between -8 and -23 ppm with the exception of the Ketac Molar glass, which exhibited a peak at 2-3 ppm consistent with orthophosphate. The chemical shift of 31P in the range -8 to -23 ppm indicates a PO(4) tetrahedra surrounded by 1-4 Al moieties. The (19)F NMR spectra indicated the presence of Al-F-Ca(n) in the G2 and G338 glasses, Al-F-Sr(n) in the G2SR and Fuji IX glasses and crystalline CaF2, LaF3, Al-F-Ca(n) in the Ketac Molar glass. The G338 glass with a high non-bridging oxygen content showed the presence of a F-Ca(n) species. There was also present in all the glasses a peak corresponding to Al-F-Na(n). The intensity of this peak was approximately proportional to the sodium content.

Acrylic Resins↗
PubMed2005

The crystallization of an aluminosilicate glass in the K2O-Al2O3-SiO2 system.

OBJECTIVES: The aims of the study were to explore the nucleation and crystallization kinetics of an aluminosilicate glass in K2O-Al2O3-SiO2 system and to characterize it. OBJECTIVES: A starting glass composition of wt%; 64.2% SiO2, 16.1% Al2O3, 10.9% K2O, 4.3% Na2O, 1.7% CaO, 0.5% LiO and 0.4% TiO2 was heated in an electric furnace and later quenched to produce glasses. The glass powders were heat treated using differing heat treatment schedules and quenched. Dta, Xrd, Eds and Sem analyses were used to characterize and explore the crystallization kinetics of the glasses. RESULTS: Phase separation of the glasses was identified and characterized in the glasses. Tetragonal leucite, cubic leucite and sanadine glass-ceramics were produced. Fine leucite crystals (1 microm2) were crystallized with minimal matrix microcracking. SIGNIFICANCE: Amorphous phase separation appeared to be an important precursor to nucleation and crystal growth in the alkali aluminosilicate glasses explored. It was possible to control the crystallization of tetragonal leucite and sanidine phases by selected heat treatment of glass powders and monoliths, resulting in the production of fine grained tetragonal leucite glass-ceramics.

Aluminum Oxide↗
PubMed2006

Viscoelastic behavior and fracture toughness of six glass-ionomer cements.

STATEMENT OF PROBLEM: Viscoelastic behavior can influence the fracture properties of glass ionomers, which is of clinical relevance. Glass-ionomer cements can display viscoelastic behavior, defined as having displacement rate- or strain rate-dependent mechanical properties. Understanding and describing the viscoelastic behavior of glass ionomers is important to understanding their clinical behavior. PURPOSE: The purpose of this study was to evaluate the viscoelastic behavior of 6 glass-ionomer cements and determine whether there was a correlation to fracture toughness. MATERIAL AND METHODS: Three conventional glass-ionomer cements (alpha-Silver, alpha-Fil, and Ketac-Molar) and 3 resin-modified glass-ionomer cements (Vitremer, Fuji II LC, and Photac-Fil Quick) were evaluated using measurements of compressive strength (CS), flexural strength (FS), and diametral tensile strength (DTS) at displacement rates of 0.5, 1.0, 1.5, and 2.0 mm/min. The CS and DTS specimens were cured in glass tubes and cut to 4 x 6-mm and 4 x 2-mm disk-shaped specimens, respectively. The FS specimens were cured in bar molds (2 x 2 x 15 mm). The fracture toughness (FT) specimens were cured in a minicompact mold to obtain precracked specimens. The mechanical testing results were compared statistically using generalized linear model/analysis of covariance and the Ryan-Einot-Gabriel-Welsch multiple range test at the alpha=.05 level. RESULTS: For all 3 mechanical properties, there was a displacement-rate dependence on the mechanical property. However, there were no differences in the displacement-rate dependence based on the type of material-conventional glass ionomer or resin-modified glass ionomer-for any of the mechanical properties. Only for FS test was there a significant difference based on the brand of material. There was no statistical difference in FT among the glass-ionomer cements tested, although the resin-modified glass ionomers tended to display higher FT. CONCLUSION: A larger sample size and a much wider range of crosshead speeds are necessary to support a correlation between viscoelastic behavior and FT.

Analysis of Variance↗