title: MAS-NMR spectroscopy studies in the setting reaction of glass ionomer cements.
abstract: OBJECTIVE
  The main objective is the characterisation of the setting reaction in glass ionomer cements based on experimental ionomer glasses with different fluorine content and a commercial glass ionomer cement liquid by using 13C CP/MAS-NMR, 29Si, 27Al and 31P MAS-NMR spectroscopy in order to receive information specifically about the cross-linking process.
  
  
  METHODS
  Different fluorine containing glass compositions based on 4.5SiO2-3Al2O3-1.5P2O5-(5-z)CaO-zCaF(2) where z=0-3, were mixed with a commercially available polymer liquid to form glass ionomer cements. The cements were subjected to 27Al, 13C CP/MAS, 29Si, and 31P MAS-NMR analysis.
  
  
  RESULTS
  The 27Al spectra showed clearly the formation of six-fold coordinate Al(VI), that may crosslink the carboxyl groups in the poly-acid molecules. A shift towards to more positive values of the carboxyl peak in the 13C CP/MAS-NMR spectra showed clearly the proton dissociation of the carboxyl groups. A shift towards more negative values was observed in the 29Si MAS-NMR spectra, suggesting formation of hydrated silica gel and consequently formation of additional Si-O-Si bonds. 31P MAS-NMR spectra also reflected changes in the coordination state around a PO4(3-) tetrahedron. Increasing the fluorine content of the glasses resulted generally in increased reactivity during setting, due to promoting cross-linking and repolymerisation of the silicate phase, followed by clear changes in the MAS-NMR spectra.
  
  
  CONCLUSIONS
  The cross-linking process during the setting reaction of glass ionomer cements can be followed by MAS-NMR spectroscopy observing the conversion of Al(IV) to Al(VI). The acid base setting reaction is completed in 1 day and no further significant changes in the MAS-NMR spectra can be observed. Further study is required in order to understand the role of phosphorus.
authors.affiliation: School of Engineering, Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. a.stamboulis@bham.ac.uk
authors.forename: A
authors.initials: A
authors.lastname: Stamboulis
authors.forename: S
authors.initials: S
authors.lastname: Matsuya
authors.forename: R G
authors.initials: RG
authors.lastname: Hill
authors.forename: R V
authors.initials: RV
authors.lastname: Law
authors.forename: K
authors.initials: K
authors.lastname: Udoh
authors.forename: M
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuya
mesh_terms: D000535:Aluminum / Q000032:analysis; D017607:Aluminum Compounds / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis; D002626:Chemistry, Pharmaceutical; D003432:Cross-Linking Reagents; D005459:Fluorides / Q000737:chemistry; D005898:Glass / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000138:chemical synthesis / Q000737:chemistry*; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D015394:Molecular Structure; D010759:Phosphorus Isotopes / Q000032:analysis; D012825:Silicon / Q000032:analysis; D017655:Silicon Compounds / Q000737:chemistry
chemical_list: D017607:Aluminum Compounds; D002247:Carbon Isotopes; D003432:Cross-Linking Reagents; D005899:Glass Ionomer Cements; D007554:Isotopes; D010759:Phosphorus Isotopes; D017655:Silicon Compounds; D002245:Carbon Dioxide; C041069:carboxyl radical; D000535:Aluminum; C020328:fluoroaluminum silicate; D005459:Fluorides; D012825:Silicon