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PubMed2001

Porous bioactive glass and glass-ceramics made by reaction sintering under pressure.

A glass and a rhenanite-wollastonite glass-ceramic were synthesized with the qualitative composition Na2O-CaO-SiO2-P2O5. Both materials were prepared by reaction sintering under isostatic pressure (RSIP) using powder mixtures. Solid state reactions were complete within a few hours at 950 degrees C under modest pressure. Formation of the glass and crystalline phases was driven by an intermediate, reactive, low viscosity Na2O-SiO2 phase. A reaction mechanism is suggested. Porous materials were obtained with two ranges of pore sizes: 100-200 microm and < or =5 microm in diameter. The glass and the glass-ceramic were corroded in simulated body fluid at 37 degrees C. The evolution of surface features was studied. Gel layers formed on both materials. Corrosion was fastest inside the pores. Microcrystals of apatite were identified by crystal structure analysis and by chemical analysis. During corrosion of the glass-ceramic, rhenanite most likely was converted into apatite. Comparison of these results with published information suggests that the glass and glass-ceramic are bioactive. We suggest that RSIP can be used (a) to control the surface porosity and pore size of bioactive implants, thereby increasing the stability of tissue/implant interfaces; (b) to make glasses and glass-ceramics with new properties; and (c) to make near net-shape materials.

Biocompatible Materials↗
PubMed2004

Clarifying the glass-transition behaviour of water by comparison with hyperquenched inorganic glasses.

The formation of glasses is normal for substances that remain liquid over a wide temperature range (the 'good glassformers') and can be induced for most liquids if cooling is fast enough to bypass crystallization. During reheating but still below the melting point, good glassformers exhibit glass transitions as they abruptly transform into supercooled liquids, whereas other substances transform directly from the glassy to the crystalline state. Whether water exhibits a glass transition before crystallization has been much debated over five decades. For the last 20 years, the existence of a glass transition at 136 K (ref. 3) has been widely accepted, but the transition exhibits qualities difficult to reconcile with our current knowledge of glass transitions. Here we report detailed calorimetric characterizations of hyperquenched inorganic glasses that, when heated, do not crystallize before reaching their glass transition temperatures. We compare our results to the behaviour of glassy water and find that small endothermic effects, such as the one attributed to the glass transition of water, are only a 'shadow' of the real glass transition occurring at higher temperatures, thus substantiating the conclusion that the glass transition of water cannot be probed directly.

Journal Article↗
PubMed1991

Glass ceramic approach to controlling the properties of a glass-ionomer bone cement.

Glass-ionomer dental cements have potential as bone cements in joint replacement surgery. However, commercially available glasses used in dental cements suffer from the loss of fluorine during the melting procedure and from phase separation of the glass upon quenching, giving rise to inter- and intra-batch variation. A model glass was examined in which minimal loss of fluorine is observed. This results in a glass whose composition is reproducible between batches. This glass will crystallize both above and below the glass transition temperature following heat treatments. Cements can be produced whose properties vary with the degree of crystallinity of the glass-ceramic. A commercial glass was also examined and was found to crystallize to an apatite phase.

Bone Cements↗
PubMed1998

Reactivity of fluoride-containing calcium aluminosilicate glasses used in dental glass-ionomer cements.

The glass component critically determines the properties of glass-ionomer cements (GIC). However, the exact relationship between the composition of the glass and these properties is not yet fully understood. To investigate this relationship, we studied the reactivity of glasses used in commercial GIC in acetic acid solutions, using a pH-stat method. Qualitative differences in the leaching behavior of these glasses can be explained by different pre-treatments. Acid-washing and silanization modify the surfaces of the glass particles, thus inducing a delay of the leaching process, whereas untreated glasses exhibit a fast initial leaching, but their acid reactivity slows very soon. Quantitative differences in acid reactivity can be correlated with the mean chemical composition of the glasses. In this respect, the leaching tends to increase with an increasing ratio of network-dwelling cations to Al3+ ions. These results provide a fundamental basis for the explanation, prediction, and control of cement properties as a function of glass characteristics.

Acetic Acid↗
PubMed2003

Bioactivity of gel-glass powders in the CaO-SiO2 system: a comparison with ternary (CaO-P2O5-SiO2) and quaternary glasses (SiO2-CaO-P2O5-Na2O).

Bioactive glasses react chemically with body fluids in a manner that is compatible with the repair processes of the tissues. This results in the formation of an interfacial bond between the glasses and living tissue. Bioactive glasses also stimulate bone-cell proliferation. This behavior is dependent on the chemical composition as well as the surface texture of the glasses. It has been recently reported that gel-derived monolith specimens in the binary SiO2 - CaO are bioactive over a similar molar range of SiO2 content as the previously studied ternary CaO-P2O5-SiO2 system. In this report, the preparation and bioactivity of the binary gel-glass powder with 70 mol % SiO2 is discussed and its bioactivity is compared with the melt-derived 45S5 (quaternary) Bioglass and sol-gel-derived 58S (ternary) bioactive gel-glass compositions. Dissolution kinetic parameters K(1) and K(2) were also computed based on the silicon release for all glass powders. It was shown that the simple two-component SiO2-CaO gel-glass powder is bioactive with comparable dissolution rates as the clinically used melt-derived 45S5 Bioglass powder and extensively studied sol-gel-derived 58S gel-glass powder.

Apatites↗
PubMed1993

Bioactive glasses and glass-ceramics.

Bioactive materials are designed to induce a specific biological activity; in most cases the desired biological activity is one that will give strong bonding to bone. A range of materials has been assessed as being capable of bonding to bone, but this paper is solely concerned with bioactive glasses and glass-ceramics. Firstly, the structure and processing of glasses and glass-ceramics are described, as a basic knowledge is essential for the understanding of the development and properties of the bioactive materials. The effect of composition and structure on the bioactivity is then discussed, and it will be shown that bioactivity is associated with the formation of an apatite layer on the surface of the implant. A survey of mechanical performance demonstrates that the structure and mechanical properties of glass-ceramics depend upon whether the processing involves casting or sintering and that the strength and toughness of glass-ceramics are superior to those of glasses. Attempts to further improve the mechanical performance by the use of non-monolithic components, i.e. bioactive coatings on metal substrates and glass and glass-ceramic matrix composites, are also reviewed and are shown to have varying degrees of success. Finally, some miscellaneous applications, namely bioactive bone cements and bone fillers, are briefly covered.

Biocompatible Materials↗
PubMed2001

Radiologic differentiation of intraocular glass: evaluation of imaging techniques, glass types, size, and effect of intraocular hemorrhage.

OBJECTIVE: The accurate detection of intraocular foreign bodies is critically important in treating ocular trauma. The purpose of this study was to evaluate the efficacy of CT, MR imaging, and sonography in detecting seven types of glass varying in size and placed in three locations in the globe, and to examine the effect of intraocular hemorrhage. MATERIALS AND METHODS: Glass pieces were cut into 1.5-, 1.0-, and 0.5-mm pieces and implanted on the corneal surface and the anterior and posterior chambers of 42 fresh porcine eyes. Twenty-one eyes were scanned comparing axial CT, helical CT, and MR imaging. The remaining 21 eyes were scanned using helical CT and sonography after implantation in a simulated human skull before and after placement of blood in the anterior chamber (hyphema). RESULTS: Detection rates were 57.1% for helical CT, 41.3% for axial CT, and 11.1% for T1-weighted MR imaging (n = 63 fragments). Results were significant (p < 0.0001). Sonography detected 43% of glass fragments in the posterior chamber and 24% in the anterior chamber. Detectability was greatest for green beer bottle glass (90.3%) and least for spectacle glass (43.1%) (p < 0.0001). Detection rates for size ranged from 96.2% at 1.5 mm to 48.3% at 0.5 mm, which was also significant (p < 0.0001). On helical CT, anterior chamber glass was easiest to detect (91.7%) and corneal surface glass the most difficult (64.9%). Hyphema made no statistical difference (p < 0.0001). CONCLUSION: Helical CT was the most sensitive imaging modality for the detection of intraocular glass. The sensitivity of detection was unaffected by hyphema but was determined by the type of glass, size, and location.

Animals↗
PubMed1994

Better histology and biochemistry for osteoblasts cultured on titanium-doped bioactive glass: bioglass 45S5 compared with iron-, titanium-, fluorine- and boron-containing bioactive glasses.

In the present study we used an established cell culture model to compare Bioglass 45S5 with four other bioactive glasses. Small substitutions or additions of certain ions like iron, titanium, fluorine or boron modified the basic 45S5 glass network. We used several histological and biochemical parameters to interpret the results found in terms of the used model. Regarding 45S5 as a reference, we found that osteoblasts cultured on iron-doped bioactive glass showed a more flattened morphology, and both lower proliferation rate and osteoblast expression. Osteoblasts cultured on titanium-doped glasses also showed a flattened morphology, but higher proliferation and remarkably higher osteoblast expression. On fluorine- and boron-containing glasses the osteoblasts showed a rather compact morphology, a normal proliferation but only moderate osteoblast expression. With microprobe analysis it was shown that the formation of calcium and phosphorus on titanium-doped glass was relatively lower and the release of sodium slower when compared with 45S5. Osteoblasts cultured on titanium-doped bioactive glasses demonstrated superior histological and biochemical parameters when compared with the other glass types. Further research into the physico-chemical properties and the in vivo behaviour of doped bioactive glasses is recommended.

Alkaline Phosphatase↗
PubMed2000

Comparison in in-vivo response between a bioactive glass and a non-bioactive glass.

The authors report on the in-vivo comparison, in the rabbit, between the response to a bioactive glass and the response to a non-bioactive glass. Implants have been performed in muscle and bone. Two different glasses were investigated, namely B01 and I02. B01 is a glass designed to be degradable and resorbable and has a percentual molar composition of: SiO2 49.6%; P2O5 2.7%; CaO + MgO + Na2O + K2O + Al2O3 47.7% with a 1 : 1 CaO/Na2O ratio. I02 is a sodium-calcium-silicate non-resorbable glass lacking P2O5 and has a percentual molar composition of: SiO2 70.7%; CaO + MgO + Na2O + K2O + Al2O3 29.3%. In-vivo tests were planned as: (a) intramuscular implants of glass cylinders in the rectus femoris and retrievals took place at 2, 16 and 43 weeks; (b) intraosseus implants of glass cylinders in the distal femural canal and retrievals took place at 8 and 43 weeks. Histology and light microscopy analysis followed. Bioactive degradable glass elicits a favorable response both in muscle and bone; a gradual degradation process leads to disruption and partial resorption of the material and a tight apposition is promoted with the newly formed bone. The non-bioactive sodium-calcium-silicate glass (named I02) may elicit, like the bioactive degradable B01, a favorable response which is characterized by the absence of inflammatory or other adverse reactions; anyway it does not change its structure at an optical microscopic level and it does not promote any tight apposition with bone.

Journal Article↗
PubMed2005

Randomised clinical trial of the effectiveness of base-in prism reading glasses versus placebo reading glasses for symptomatic convergence insufficiency in children.

PURPOSE: To compare base-in prism reading glasses with placebo reading glasses for the treatment of symptomatic convergence insufficiency (CI) in children aged 9 to <18 years. METHODS: In a randomised clinical trial, 72 children aged 9 to <18 years with symptomatic CI were assigned to either base-in prism glasses or placebo reading glasses. Symptom level, measured with a quantitative symptom questionnaire (CI Symptom Survey-V15), was the primary outcome measure. Near point of convergence and positive fusional vergence at near were secondary outcomes. RESULTS: The mean (SD) CI Symptom Survey score decreased (that is, less symptomatic) in both groups (base-in prism glasses from 31.6 (10.4) to 16.5 (9.2); placebo glasses from 28.4 (8.8) to 17.5 (12.3)). The change in the CI Symptom Survey scores (p = 0.33), near point of convergence (p = 0.91), and positive fusional vergence (p = 0.59) were not significantly different between the two groups after 6 weeks of wearing glasses. CONCLUSIONS: Base-in prism reading glasses were found to be no more effective in alleviating symptoms, improving the near point of convergence, or improving positive fusional vergence at near than placebo reading glasses for the treatment of children aged 9 to <18 years with symptomatic CI.

Adolescent↗
PubMed1996

Acidobasicity of oxide glasses used in glass ionomer cements.

OBJECTIVES: The purpose of this study was to provide a theoretical basis for assessing the cement-forming ability of oxide ionomer glasses based on concepts of glass acidobasicity. METHODS: Theoretical concepts of acidobasicity of ionomer glasses were developed based respectively on ionization potential, field strength and electronegativity. Calculations of acidobasicities were made for a range of glasses of the CaO-Al2O3-SiO2 type. These results were compared with experimental values obtained for the setting times of cements prepared from these glasses. RESULTS: Regression analysis showed a 99.96% correlation between acidobasicity values based on ionization potential with those based on field strength. There was only moderate correlation between these acidobasicity values and those based on electronegativity. Setting time was found to increase slowly as glass basicity decreased until a critical point was reached when setting time increased sharply. A Spearman rank correlation test was applied, and it was found that setting times correlated with acidobasicity values based on ionization potential and field strength with a coefficient of 98.7%. SIGNIFICANCE: Results show that calculated acidobasicity values of CaO-Al2O3-SiO2 glasses can be used to distinguish between glasses that form cements from those that do not. They are divided by a critical acidobasicity value. It was not found possible to relate setting time to acidobasicity by means of an equation because of this critical feature in the relationship. The critical acidobasicity value replaces the more complex criteria of Hill and Wilson (1988) using triangular diagrams.

Aluminum Oxide↗
PubMed1993

Development of a glass reinforced hydroxyapatite with enhanced mechanical properties. The effect of glass composition on mechanical properties and its relationship to phase changes.

Utilizing glasses of the types xNa2O-(1-x)P2O5 and xCaO-(1-x)P2O5 (where x = 0.2, 0.3, and 0.5), a systematic study of the effect of increasing network modifying oxides in glasses was made on the mechanical properties of a glass reinforced hydroxyapatite, at glass additions of 2.5 and 5 wt%. For the soda type glass, phase changes were promoted much more readily compared to the lime type glass. This was true for both 2.5 and 5 wt% additions of glass. For the lime type glass, considerable differences between the effects of 2.5 and 5 wt% additions were seen. At 5 wt%, the increased amount of liquid phase present promotes an increased level of phase inversion to alpha and beta tricalcium phosphate. At 2.5 wt%, a larger percentage of the HA remains stable at higher temperatures. Furthermore, the effect of the composition may be seen. As the mol% of network forming oxide increases, (i.e., the Ca/P ratio moves towards 1.67, (the ratio for HA) the HA remains more stable. This is seen in the maintenance of both the HA phase and also the enhanced mechanical properties.

Biocompatible Materials↗
PubMed2004

Corrosion behavior of glass and glass-ceramics made of municipal solid waste incinerator fly ash.

Glasses and glass-ceramics were prepared by melting municipal solid waste (MSW) incinerator fly ash and their corrosion properties were evaluated. Corrosion of both materials proceeded in two different steps. At the initial stage, the corrosion process is a diffusion-controlled process. After approximately 10 h at the initial stage, weight losses increased linearly with time due to the total dissolution of glasses or glass-ceramics. Leaching of heavy metals from glasses and glass-ceramics were well within international environmental regulations. Corrosion proceeded uniformly in fly ash glass while Na2CaSiO4 crystalline phase was preferentially dissolved in the glass-ceramics.

Carbon↗
PubMed1997

Enterovirus genomes in wastewater: concentration on glass wool and glass powder and detection by RT-PCR.

Standard methods for detecting enteroviruses in environmental samples require cell culture, which is time consuming and expensive. The reverse transcription-polymerase chain reaction (RT-PCR) is a rapid, sensitive method for detecting enteroviruses in water. However, environmental samples often contain substances that inhibit PCR amplification of target RNA. Hence the virus must be concentrated by procedures that do not interfere with amplification. This study shows that virus concentration by adsorption onto glass powder or glass wool supports is suitable for detecting viral genomes in treated wastewater by RT semi-nested PCR. No enterovirus genome was detected directly in 25 samples of treated wastewater by RT semi-nested PCR. However, samples concentrated by adsorption onto glass wool or glass powder showed that 48% (glass powder) and 56% (glass wool) contained virus. Secondary concentration by organic flocculation was unsuitable for detecting virus concentrated on glass wool (20% positive samples), but it helped to increase the detection of the genome after concentration on glass powder (72% positive samples).

Cell Line↗
PubMed1996

Tunnel restorations using glass ionomer or glass cermet: in vitro marginal ridge fracture and microleakage.

The purpose of this in vitro study was to compare the marginal ridge fracture resistance and microleakage following restorations of partial tunnel preparations using glass ionomer and glass cermet cements. Sixty eight sound premolars were selected for this study and were divided randomly into six groups. A standardized partial tunnel preparation was done on all the teeth except specimens belonging to Group I. The partial tunnel preparations of Groups III & V were restored with glass ionomer and that of Groups IV & VI were restored with glass cermet. The teeth belonging to Groups I, II, III & IV were subjected to marginal ridge fracture resistance testing. The teeth of Groups V & VI were tested for microleakage after immersing them in 5% methylene blue solution for 4 hours. The results indicated that the teeth restored with glass cermet were marginally better than that with glass ionomer in terms of marginal ridge fracture resistance. Both the materials failed to reinforce the marginal ridge to the level of an intact tooth. The microleakage which occurred around both the materials were statistically insignificant, but on comparison glass ionomer showed better results. Hence, glass ionomer is preferred as a restorative material for partial tunnel preparations because of additional inherent advantages like superior esthetics and fluoride leachability.

Bicuspid↗
PubMed1992

Behaviour of fetal rat osteoblasts cultured in vitro on bioactive glass and nonreactive glasses.

We examined the behaviour of fetal rat osteoblasts cultured upon bioactive glass and nonreactive glasses, and the supposed stimulatory effects of bioactive glass on osteoblasts. Nonreactive glass cultures showed flattened cells with almost no dorsal ruffles. Bioactive glass cultures showed compact cells with dorsal ruffles and filapodia resulting in the formation of a denser cell layer. For confluent nonreactive glass cultures the osteoblast expression was mainly concentrated in the clustered cells which were formed upon the monolayer, whereas for confluent bioactive glass cultures the osteoblast expression was more generally distributed. The production of type I collagen, osteocalcin and an osteoblast-specific antigen was shown by immunocytochemistry for all cultures, although differences in distribution were observed. The bioactive layer of bioactive glass is responsible for a better osteoblast-like morphology, a higher proliferation rate and generally a better osteoblast expression.

Alkaline Phosphatase↗
PubMed2003

Activated bond-breaking processes preempt the observation of a sharp glass-glass transition in dense short-ranged attractive colloids.

We study-using molecular dynamics simulations-the temperature dependence of the dynamics in a dense short-ranged attractive colloidal glass to find evidence of the kinetic glass-glass transition predicted by the ideal mode coupling theory. According to the theory, the two distinct glasses are stabilized, one by excluded volume and the other by short-ranged attractive interactions. By studying the density autocorrelation functions, we discover that the short-ranged attractive glass is unstable. Indeed, activated bond-breaking processes slowly convert the attractive glass into the hard-sphere one, preempting the observation of a sharp glass-glass transition.

Journal Article↗
PubMed2000

Influence of glass composition on the properties of glass polyalkenoate cements. Part III: influence of fluorite content.

The influence of fluorite content of the glass on the formation and properties of glass polyalkenoate cements was investigated. A series of glass powders based on 1.5SiO2 x 0.5P2O5 x Al2O3 x CaO x XCaF2 were synthesised. The glass transition temperature of the glass fell with increasing fluorite content. Setting and working times of the cement pastes decreased with increasing fluorite content of the glass. Compressive strength and un-notched fracture strength increased with increasing fluorite content of the glass. Fracture toughness and toughness of the cements were relatively insensitive to fluorite content.

Calcium Fluoride↗