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This study aims to demonstrate that excellent bioactivity of glass can be achieved without the presence of an alkali metal component in glass composition. In vitro bioactivity of two sodium-free glasses based on the quaternary system SiO2-P2O5-CaO-CaF2 with 0 and 4.5 mol% CaF2 content was investigated and compared with the sodium-containing glasses with equivalent amount of CaF2. The formation of apatite after immersion in Tris buffer was followed by Fourier-transform infrared spectroscopy, X-ray diffraction, 31P and 19F solid-state MAS- NMR. The dissolution study was completed by ion release measurements in Tris buffer. The results show that sodium-free bioactive glasses formed apatite at 3 h of immersion in Tris buffer, which is as fast as the corresponding sodium-containing composition. This signifies that sodium is not an essential component in bioactive glasses and it is possible to make equally degradable bioactive glasses with or without sodium. The results presented here also emphasize the central role of the glass compositions design which is based on understanding of structural role of components and/or predicting the network connectivity of glasses. [ABSTRACT FROM AUTHOR]

The bioactivity of a series of fluoride-containing sodium-free calcium and strontium phosphosilicate glasses has been tested in vitro. Glasses with high fluoride content were partially crystallised to apatite and other fluoride-containing phases. The bioactivity study was carried out in Tris and SBF buffers, and apatite formation was monitored by XRD, FTIR and solid state NMR. Ion release in solutions has been measured using ICP-OES and fluoride-ion selective electrode. The results show that glasses with low amounts of fluoride that were initially amorphous degraded rapidly in Tris buffer and formed apatite as early as 3 h after immersion. The apatite was identified as fluorapatite by 19 F MAS-NMR after 6 h of immersion. Glass degradation and apatite formation was significantly slower in SBF solution compared to Tris. On immersion of the partially crystallised glasses, the fraction of apatite increased at 3 h compared to the amount of apatite prior to the treatment. Thus, partial crystallisation of the glasses has not affected bioactivity significantly. Fast dissolution of the amorphous phase was also indicated. There was no difference in kinetics between Tris and SBF studies when the glass was partially crystallised to apatite before immersion. Two different mechanisms of apatite formation for amorphous or partially crystallised glasses are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Due to the ability of bioactive glasses to form chemical and biological bonds with bone, these glasses have been used as a coating of orthopaedic and dental implants. However, the bioactivity of the glasses might be compromised by incorporating certain compounds such as MgO to reduce the high thermal expansion coefficient of these glasses. Therefore, fluorapatite has been added to maintain and improve bioactivity of the glass coatings. In this study we investigate the effect of FA crystals at two loadings on bioactivity of glass coatings containing 9.9, 16.1 and 22.1mol% MgO. The glass/FA composite coatings have been fabricated by enamelling technique. The bioactivity of the composite coatings was investigated after 1month immersion in Tris-buffer solution and SBF. The immersed coating samples were investigated by X-ray diffraction, Fourier transform infra-red spectroscopy and scanning electron microscopy for any structural changes. The filtrate was analysed using inductively coupled plasma spectroscopy and the released fluoride was measured by fluoride selective electrode. The results indicate that FA crystals have a positive effect on the apatite forming ability of the coatings. This is confirmed by XRD, FTIR and SEM–EDS analyses of composite coatings which showed structural changes that indicate the growing or formation of new FA phases. [Copyright &y& Elsevier]

Abstract: In orthopedics and dentistry bioactive glasses are a suitable material to improve the bone-bonding ability of titanium implants. Yet, these glasses have high thermal expansion coefficients. Attempts have been made to reduce the thermal expansion coefficient of these glasses by incorporating oxides such as MgO into glass composition. However, it has been shown that this retards the glass bioactivity. Therefore, mixing fluorapatite (FA) with bioactive glasses has been carried out to speed up the process of surface apatite formation, without modifying the glass composition. In this study we investigate the effect of fluorapatite crystals at two loadings on the bioactivity of glasses containing 9.9, 16.1 and 22.1mol% MgO. These glasses have been synthesized by a melt-derived route. These glass compositions contain SiO2, CaO, MgO, MgF2, Na2O, K2O and P2O5. FA crystals were produced by solid state reaction. The glass powder was mixed with FA at two ratios by weight (4:1 and 14:1). The composite powder was characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The bioactivity of the composite (glass/FA) powder of the two series was assessed in Tris-buffer solution at two time points. The immersed composite powder was investigated by XRD and FTIR, and the filtrates were analyzed using inductively coupled plasma spectroscopy and fluoride-selective electrode. The results indicate that FA additions can enhance and improve the apatite forming ability of the original glass powder. [Copyright &y& Elsevier]

Abstract: The main priority in designing reproducibly successful dental implants is to generate a surface that accelerates bone formation at the bone/implant interface. This is especially true in areas where bone quality and quantity are insufficient to fully stabilise implant prosthesis. Fluorapatite (FA) has comparable biocompatibility to hydroxyapatite (HA) and has been used as a coating of titanium implants. In this study the effect of composite coatings containing FA at two different ratio glasses: FA (4:1 and 14:1) on osteoblast cell adhesion, bone nodule formation and alkaline phosphatase (ALP) activity was investigated in vitro. The biological behaviour of fibroblast cells on both of these composite coatings was studied as well. The results showed that the composite coatings 4:1 and 14:1 were biocompatible to osteoblast-like cells. The composite coatings induced bone-like nodule formation and the attached osteoblasts exhibited gradual increase of ALP activity with time. The composite coatings containing low FA content were more biocompatible to fibroblast cells compared with high FA content. [Copyright &y& Elsevier]

Abstract: Objectives: The purpose of this study was to characterize commercial glass polyalkenoate cement (GPC) or glass ionomer cement (GIC), Glass Carbomer®, which is designed to promote remineralization to fluorapatite (FAp) in the mouth. The setting reaction of the cement was followed using magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Methods: Glass Carbomer® initial glass powder and cements were subjected to 27Al, 31P, 19F and 29Si MAS-NMR analysis. X-ray powder diffraction (XRD) was employed to determine the presence of crystalline phases. Results: 27Al MAS-NMR showed the Al to be predominantly four coordinate, Al(IV), and the presence of Al–O–P species in the glass. The proportion of Al(IV) was reduced with setting reaction of the cement and significant amount of six coordinate Al, Al(VI), was found in the cement. The 31P MAS-NMR spectra showed clearly a decrease of the orthophosphate peak of apatite on initial setting. 19F MAS-NMR showed only a small fraction of FAp. 29Si MAS-NMR demonstrated the presence of largely Q4(2Al) in the glass which changed only little in the aged cement. Significance: This study also demonstrated how the setting reaction in Glass Carbomer® cement and other GICs can be followed by 27Al MAS-NMR examining the conversion of Al(IV) to Al(VI). Our data revealed that the apatite in this cement was not FAp but largely hydroxyapatite, which was partially consumed during the cement formation. [Copyright &y& Elsevier]

Abstract: Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoride-releasing bioactive glasses are of interest for both orthopaedic and, in particular, dental applications for caries inhibition. Melt-derived glasses in the system SiO2–P2O5–CaO–Na2O with increasing amounts of CaF2 were prepared by keeping network connectivity and the ratio of all other components constant. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37°C over up to 2weeks were investigated. Crystal phases formed in SBF were characterized using infrared spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy (19F and 31P MAS–NMR). Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF2) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and possibly favour formation of apatite. [Copyright &y& Elsevier]

Abstract: Objective: Dentin hypersensitivity (DH) is a commonly occurring dental condition, and bioactive glasses (BG) are used in dentifrice formulations for treating DH by forming a surface layer of hydroxycarbonate apatite (HCA) on the tooth, thereby occluding exposed dentinal tubules. Fluoride-containing BG, however, form fluorapatite, which is more stable toward acid attack, and provide a more sustainable option for treating DH. Methods: Melt-derived multi-component BG (SiO2–P2O5–CaO–CaF2–SrO–SrF2–ZnO–Na2O–K2O) with increasing CaF2+SrF2 content (0–32.7mol%) were prepared. Apatite formation, occlusion of dentinal tubules in dentin discs and ion release in Tris buffer were characterized in vitro over up to 7 days using X-ray diffraction, infrared spectroscopy, scanning electron microscopy and inductively coupled plasma emission spectroscopy. Results: The fluoride-containing bioactive glasses formed apatite from as early as 6h, while the fluoride-free control did not form apatite within 7 days. The glasses successfully occluded dentinal tubules by formation of apatite crystals and released ions such as fluoride, strontium and potassium. Significance: Fluoride significantly improved apatite formation of the BG, allowing for treatment of DH by occlusion of dentinal tubules. The BG also released therapeutically active ions, such as strontium and fluoride for caries prevention, zinc for bactericidal properties and potassium, which is used as a desensitizing agent in dentifrices. [Copyright &y& Elsevier]

Alkali free bioactive glasses with the presence of Ca/SrF2 were synthesized and then characterised by Differential Scanning Calorimetry, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Magic Angle Spinning-Nuclear Magnetic Resonance Spectroscopy. The crystallisation of the glasses was explored by heat treatment. An increased crystallisation tendency of the as quenched glasses was evident with an increase in the Ca/SrF2 content, where Ca10(PO4)6F2 (fluorapatite), Ca4Si2O7F2 (cuspidine) and CaF2 crystallise in sequence for the Ca-containing system, and Sr10(PO4)6F2, SrSiO3 and SrF2 for the Sr-containing system. Upon heat treatment, Ca10(PO4)6F2 or Sr10(PO4)6F2, which is mainly nucleated from bulk is the primary crystalline phase. Although partially crystallised these sodium free fluorapatite glass ceramics are proposed to have enhanced bioactivity comparable to bioactive glasses. [ABSTRACT FROM AUTHOR]