The influence of strontium substitution in fluorapatite glasses and glass-ceramics

Strontium is often substituted for calcium in order to confer radio-opacity in glasses used for dental cements, biocomposites and bioglass-ceramics. The present paper investigates the influence of substituting strontium for calcium in a glass of the following composition: 4.5SiO(2)3Al(2)O(3)1.5P(2)O(5)3CaO(2)CaF(2), having a Ca:P ratio of 1.67 corresponding to calcium fluorapatite (Ca-5(PO4)(3)F). The glasses were characterized by magic angle spinning nuclear magnetic resonance (MAS-NMR), by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). The Si-29, Al-27 and P-31 NMR spectra for the glasses with different strontium contents were identical. The F-19 spectra indicated the presence of F-Ca(n) and Al-F-Ca(n) species in the calcium glasses and in the strontium glasses F-Sr(n) and Al-F-Sr(n). It can be concluded that strontium substitutes for calcium with little change in the glass structure as a result of their similar charge to size ratio. The low strontium glasses bulk nucleated to a calcium apatite phase. Intermediate strontium content glasses surface nucleated to a mixed calcium-strontium apatite and the fully strontium substituted glass to strontium fluorapatite. (C) 2004 Elsevier B.V. All rights reserved.