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A. Rafferty - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of amorphous phase separation, leachability and surface area of an Ionomer Glass system and a sodium-boro-silicate Glass system
    Journal of Materials Science, 2003
    Co-Authors: A. Rafferty, R. Hill, B. Kelleher, T. O'dwyer
    Abstract:

    Glasses from a complex SiO_2-Al_2O_3-P_2O_5-CaO-CaF_2 Glass series, known as 'Ionomer Glasses' were investigated. For comparison, a sodium-boro-silicate (s-b-s) Glass system, which is known to undergo amorphous phase separation was also investigated. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and BET surface area and pore distribution analysis were the principal analytical techniques used in this study. SEM analysis of the Ionomer Glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the s-b-s Glass. EDX analysis of the s-b-s Glass confirmed that the sodium-borate phase was removed by leaching with 0.3 M HNO_3, leaving behind a silica-rich structure. EDX analysis of Ionomer Glasses leached with 10% NaOH showed that the calcium and phosphate phases were being removed, although not to completion. For the base s-b-s Glass a surface area of m 8^2 g^−1 was recorded. However, the base Glass after extraction with 0.3 M HNO_3 of the sodium borate rich phase gave a BET surface area of 330 m^2 g^−1 indicating that it had already undergone phase separation on quenching from the melt, giving rise to a fine scale interconnected structure. The leached s-b-s Glasses exhibited type 4 adsorption/desorption isotherms characteristic of mesoporous materials. Glasses which had been heat treated at 580°C for 4 h exhibited a surface area of 62 m^2 g^−1. This indicates that the as-quenched Glass is already phase separated and that the phase separated microstructure is coarsening on heat treatment. A surface area of 4 m^2 g^−1 was measured for the base Ionomer Glasses. After leaching with 10% NaOH this value rose 10-fold with a maximum surface area of 44.1 m^2 g^−1 being recorded. The Ionomer Glasses also exhibited adsorption/desorption isotherms characteristic of mesoporous materials.

  • An investigation into the amorphous phase separation characteristics of an Ionomer Glass series and a sodium-boro-silicate Glass system
    Journal of Materials Science, 2003
    Co-Authors: A. Rafferty, R. G. Hill, D. Wood
    Abstract:

    Amorphous phase separation of Ionomer Glasses, also known as fluoro-phospho-alumino-silicate Glasses, of generic composition SiO_2-Al_2O_3-P_2O_5-CaO-CaF_2 were investigated. A sodium-boro-silicate Glass system, which is known to undergo amorphous phase separation was also investigated. High Temperature Dynamic-Mechanical Thermal Analysis (DMTA), combined Differential Thermal Analysis/Thermo Gravimetric Analysis (DTA/TGA) and Scanning Electron Microscopy (SEM) were the principal analytical techniques used in this study. High temperature DMTA was used to measure the Glass transition temperatures ( T _g) of the original starting Glass compositions, as well as being able to follow amorphous phase separation (APS) within the Glass. High temperature DMTA traces of both the Ionomer Glasses and the sodium-boro-silicate Glasses exhibited two maxima in tan δ, corresponding to two Glass transition temperatures and demonstrating that amorphous phase separation of the parent Glass into two Glass phases had occurred. DTA/TGA of the Ionomer Glasses detected a Glass transition and two crystallisation peaks for apatite and mullite, accompanied by a gradual weight loss of 1–3% on passing through the crystallisation region. The sodium-boro-silicate base Glass showed no evidence of a Glass transition, but a prominent Glass transition was detected for a second sample which had undergone a heat-treatment of 240 min at 580°C. SEM analysis of the Ionomer Glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the sodium-boro-silicate Glass.

D. Wood - One of the best experts on this subject based on the ideXlab platform.

  • An investigation into the amorphous phase separation characteristics of an Ionomer Glass series and a sodium-boro-silicate Glass system
    Journal of Materials Science, 2003
    Co-Authors: A. Rafferty, R. G. Hill, D. Wood
    Abstract:

    Amorphous phase separation of Ionomer Glasses, also known as fluoro-phospho-alumino-silicate Glasses, of generic composition SiO_2-Al_2O_3-P_2O_5-CaO-CaF_2 were investigated. A sodium-boro-silicate Glass system, which is known to undergo amorphous phase separation was also investigated. High Temperature Dynamic-Mechanical Thermal Analysis (DMTA), combined Differential Thermal Analysis/Thermo Gravimetric Analysis (DTA/TGA) and Scanning Electron Microscopy (SEM) were the principal analytical techniques used in this study. High temperature DMTA was used to measure the Glass transition temperatures ( T _g) of the original starting Glass compositions, as well as being able to follow amorphous phase separation (APS) within the Glass. High temperature DMTA traces of both the Ionomer Glasses and the sodium-boro-silicate Glasses exhibited two maxima in tan δ, corresponding to two Glass transition temperatures and demonstrating that amorphous phase separation of the parent Glass into two Glass phases had occurred. DTA/TGA of the Ionomer Glasses detected a Glass transition and two crystallisation peaks for apatite and mullite, accompanied by a gradual weight loss of 1–3% on passing through the crystallisation region. The sodium-boro-silicate base Glass showed no evidence of a Glass transition, but a prominent Glass transition was detected for a second sample which had undergone a heat-treatment of 240 min at 580°C. SEM analysis of the Ionomer Glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the sodium-boro-silicate Glass.

Robert G. Hill - One of the best experts on this subject based on the ideXlab platform.

  • Glass Ionomer cements effect of strontium substitution on esthetics radiopacity and fluoride release
    Dental Materials, 2014
    Co-Authors: Saroash Shahid, R. W. Billington, Robert G. Hill, U Hassan, Paul H Anderson
    Abstract:

    Abstract Objective SrO and SrF 2 are widely used to replace CaO and CaF 2 in Ionomer Glasses to produce radiopaque Glass Ionomer cements (GIC). The purpose of this study was to evaluate the effects of this substitution on release of ions from GIC as well as its effect on esthetics (translucency) and radiopacity. Materials and methods Cements were produced from Ionomer Glasses with varying content of Sr, Ca and F. The cements were stored in dilute acetic acid (pH 4.0) for up to 7 days at 37 °C. Thereafter, the cements were removed and the solution was tested for F − , Sr 2+ , Ca 2+ , and Al 3+ release. Radiopacity and translucency were measured according to BS EN ISO 9917-1:2003. Results Ion release was linear to t 1/2 suggesting that this is a diffusion controlled mechanism rather than dissolution. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium. Radiopacity shows a strong linear correlation with Sr content. All cements were more opaque than the C 0.70 0.55 standard but less opaque than the C 0.70 0.90 standard which is the limit for the ISO requirement for acceptance. Significance This study shows that the replacement of calcium by strontium in a Glass Ionomer Glass produces the expected increase in radiopacity of the cement without adverse effects on visual properties of the cement. The fluoride release from the cements is enhanced where some or all calcium is replaced by strontium.

  • Heat-pressed Ionomer Glass–ceramics. Part II. Mechanical property evaluation
    Dental materials : official publication of the Academy of Dental Materials, 2004
    Co-Authors: Catherine M. Gorman, Robert G. Hill
    Abstract:

    Abstract Objectives . A series of Ionomer Glasses based on the formula: 4.5SiO 2 –1.5P 2 O 5 –( X )Al 2 O 3 –4.5CaO–0.5CaF 2 , were investigated where X was varied from 3.0 to 1.5 in order to develop heat pressable dental ceramics. Methods . The Glasses were heat-pressed and then subjected to different heat-treatment cycles. The mechanical properties of the Glass–ceramics were investigated, specimens were tested for hardness, fracture toughness (indentation method) and flexural strength (biaxial method). Results . Good mechanical properties were obtained for heat-treatments at lower temperatures (i.e. 1150 °C). At intermediate heat-treatment temperatures the Glass–ceramics were highly crystalline which did not favor the mechanical properties. There appears to be an inverse relationship between fracture toughness and flexural strength. High fracture toughness values of 2.7 (0.4) MPam 0.5 were produced for the X =2.8 Glass heat-treated for 8 h at 1150 °C, the flexural strength was lowest for this heat-treatment. High flexural strengths of 194.4 (75.0) MPa were obtained by heat-treating the same Glass for 1 h at 1150 °C. Increasing the hold time increases crystal size thereby increasing the extent of microcracking in the Glass–ceramic thus lowering the flexural strength. Microcracks appear to increase the fracture toughness of the Glass–ceramics probably by a crack termination mechanism. Significance . Good flexural strength and high fracture toughness are attainable in this system, but appear to be mutually exclusive in the materials studied. With further investigation this system could provide clinically useful materials.

  • Heat-pressed Ionomer Glass-ceramics. Part I: an investigation of flow and microstructure.
    Dental materials : official publication of the Academy of Dental Materials, 2003
    Co-Authors: Catherine M. Gorman, Robert G. Hill
    Abstract:

    Abstract Objectives . This study investigated a series of Ionomer Glasses based on the formula: 4.5SiO 2 –1.5P 2 O 5– ( X )Al 2 O 3 –4.5CaO–0.5CaF 2 , where X was varied from 3.0 to 1.5. The possibility of processing Ionomer Glasses using a heat-pressing method for dental restorations was investigated. Methods . A simple flow test was designed to measure the amount of flow the Glasses underwent as a result of heat-pressing at 1150 °C for different times. Heat-pressed samples of the X =3.0, 2.8, 2.4 and 2.0 Glass were further heat-treated for 1 and 4 h at 1150, 1200 and 1250 °C to promote crystal growth. Scanning electron microscopy was used to investigate the microstructure of the Glass-ceramics. X-ray diffraction was used to identify the crystalline phases in the Glass-ceramics. Results . The Ionomer Glasses exhibited excellent flow ability. Crystallization could not be suppressed during heat-pressing. Very fine scale fluorapatite crystals were present in all of the samples after heat-pressing. Mullite and/or anorthite formed as a second crystal phase. On further heat-treatment of the samples, changes in crystal phases took place. Significance . Apatite was the main crystalline phase produced in the Glass-ceramics; this factor is of clinical significance. In conclusion these Glass-ceramics could be suitable for all-ceramic dental restorations.

  • Thermal Analysis of a SiO2─Al2O3─CaO─CaF2 Glass
    Journal of the American Ceramic Society, 1992
    Co-Authors: Robert G. Hill, Christopher Goat, David Wood
    Abstract:

    A SiO 2 -Al 2 O 3 -CaO-CaF 2 Ionomer Glass was investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. The purpose of the investigation was to control the susceptibility of the Glass to acid attack. The differential thermal analysis trace exhibited a sharp Glass transition at about 645°C and two exotherms. The first exotherm corresponded to liquid-liquid phase separation followed by crystallization of fluorite. The second, much larger, exotherm was the result of crystallization of the remaining Glass phase to form anorthite. Prolonged heat treatment below the Glass-transition temperature demonstrated that crystallization of fluorite can occur without prior liquid-liquid phase separation

  • Structure-property relationships in Ionomer Glasses
    Clinical Materials, 1991
    Co-Authors: D. J. Wood, Robert G. Hill
    Abstract:

    Abstract A range of model Ionomer Glasses based on the generic composition 2SiO2.Al2O3.2(1 − X)CaO.2XCaF2 has been studied. The Glass transition temperature reduces as X is increased indicating that fluorine disrupts the Glass network, whilst the crystallisation behaviour of the Glasses supports the view that fluorine is bonded to the calcium ions present. The composition with X = 0·5 has been studied in detail. This composition undergoes amorphous phase separation followed by crystallisation to fluorite and anorthite. Heat treatment below the Glass transition temperature results in crystallisation of fluorite. A commercial Ionomer Glass composition was studied and found to have undergone amorphous phase separation. On heat treatment this Glass crystallised to an apatite phase and mullite.

T. O'dwyer - One of the best experts on this subject based on the ideXlab platform.

  • An investigation of amorphous phase separation, leachability and surface area of an Ionomer Glass system and a sodium-boro-silicate Glass system
    Journal of Materials Science, 2003
    Co-Authors: A. Rafferty, R. Hill, B. Kelleher, T. O'dwyer
    Abstract:

    Glasses from a complex SiO_2-Al_2O_3-P_2O_5-CaO-CaF_2 Glass series, known as 'Ionomer Glasses' were investigated. For comparison, a sodium-boro-silicate (s-b-s) Glass system, which is known to undergo amorphous phase separation was also investigated. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX) and BET surface area and pore distribution analysis were the principal analytical techniques used in this study. SEM analysis of the Ionomer Glass compositions revealed smooth spherical droplets of 2–15 nm while the background morphology appeared rough and speckled. A classic interconnected structure was observed for the s-b-s Glass. EDX analysis of the s-b-s Glass confirmed that the sodium-borate phase was removed by leaching with 0.3 M HNO_3, leaving behind a silica-rich structure. EDX analysis of Ionomer Glasses leached with 10% NaOH showed that the calcium and phosphate phases were being removed, although not to completion. For the base s-b-s Glass a surface area of m 8^2 g^−1 was recorded. However, the base Glass after extraction with 0.3 M HNO_3 of the sodium borate rich phase gave a BET surface area of 330 m^2 g^−1 indicating that it had already undergone phase separation on quenching from the melt, giving rise to a fine scale interconnected structure. The leached s-b-s Glasses exhibited type 4 adsorption/desorption isotherms characteristic of mesoporous materials. Glasses which had been heat treated at 580°C for 4 h exhibited a surface area of 62 m^2 g^−1. This indicates that the as-quenched Glass is already phase separated and that the phase separated microstructure is coarsening on heat treatment. A surface area of 4 m^2 g^−1 was measured for the base Ionomer Glasses. After leaching with 10% NaOH this value rose 10-fold with a maximum surface area of 44.1 m^2 g^−1 being recorded. The Ionomer Glasses also exhibited adsorption/desorption isotherms characteristic of mesoporous materials.

Paul V. Hatton - One of the best experts on this subject based on the ideXlab platform.

  • in vitro biocompatibility of a novel fe2o3 based Glass Ionomer cement
    Journal of Dentistry, 2006
    Co-Authors: K Hurrellgillingham, Ian M. Reaney, I M Brook, Paul V. Hatton
    Abstract:

    Abstract Introduction Since their invention in the late 1960s, Glass Ionomer cements (GICs) have been used extensively in dentistry but recently they have also been utilised in ear nose and throat (ENT) surgery. Unfortunately, Al 3+ , a component of conventional Ionomer Glasses, has been linked to poor bone mineralisation and neurotoxicity. Objective The aim of the research was to modify a commercial Ionomer Glass composition by substituting Al 2 O 3 with Fe 2 O 3 . Methods Glasses with the following molar compositions were fabricated: 4.5SiO 2 ·3M 2 O 3 ·XP 2 O 5 ·3CaO·2CaF 2 (M = Al or Fe, X = 0–1.5). The Glasses were characterised using X-ray fluorescence (XRF) and X-ray powder diffraction (XRD). Cements were prepared using a standard ratio of; 1 g of Glass powder: 0.2 g of dried polyacrylic acid: 0.3 g of 10% tartaric acid solution. Cement formation was assessed using a Gilmore needle and in vitro biocompatibility was investigated for novel cement formulations. Results XRF revealed that the Fe 2 O 3 -based Glasses had Al 2 O 3 contamination from the crucibles and also had undergone substantial F − losses. XRD gave peaks that corresponded to magnetite Fe 3 O 4 (JCPDS # 19-629) in all compositions. Apatite Ca 5 (PO 4 ) 3 (OH,F) (JCPDS # 15-876) was identified in P 2 O 5 containing Glasses. It was possible to fabricate cements from all of the Fe 2 O 3 -based Ionomer Glasses. Good in vitro biocompatibility was observed for the Fe 2 O 3 -based cements. Conclusion Ionomer Glasses may be prepared by entirely replacing Al 2 O 3 with Fe 2 O 3 . Cement setting times appeared to be related to P 2 O 5 content. Fe 2 O 3 -based cements showed good in vitro biocompatibility.

  • Devitrification of Ionomer Glass and its effect on the in vitro biocompatibility of Glass-Ionomer cements.
    Biomaterials, 2003
    Co-Authors: K. Hurrell-gillingham, Ian M. Reaney, Cheryl A. Miller, Aileen Crawford, Paul V. Hatton
    Abstract:

    Abstract The effects of devitrification of an Ionomer Glass with a molar composition 4.5SiO2·3Al2O3·1.5P2O5·3CaO·2CaF2 on cement formation and in vitro biocompatibility were investigated. Differential thermal analysis was used to study the phase evolution in the Glass, and to determine the heat treatments for production of Glass-ceramics. X-ray diffraction patterns from Glass frit heat-treated at 750°C for 2 h contained peaks corresponding to apatite (JCPDS 15-876), whereas for samples heat-treated at 950°C for 2 h apatite and mullite (JCPDS 15-776) were the major phases detected. Transmission electron microscopy (TEM) confirmed that apatite and apatite–mullite phases were present after heat treatments at 750°C and 950°C respectively. Glass and Glass-ceramics were ground to prepare