Novel Zinc Containing Phosphate Glasses for Glass–Ionomer Cements for Bone Cement Applications
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Glass‐ionomer cements (GICs) are acid base reaction cements used in dentistry for restorative applications. In conventional GICs aluminosilicate glass is used to react with a polyalkenoic acid such as poly acrylic acid. Glass–ionomer cements have the potential to be used for bone cement applications, however there is a concern over the neurotoxicity of aluminium in the glass component of these cements. In this work zinc containing phosphate glass based glass–ionomer cement has been developed for the bone cement application. In this relation structure of zinc containing phosphate glasses in the system Na2O:CaO:ZnO:P2O5 ranging from metaphosphate compositions to invert phosphate compositions has been examined. Various advanced techniques in solid state nuclear magnetic resonance (NMR) such as dipolar recoupling and solid state NMR of low quadrupolar nuclei (67Zn and 43Ca) and neutron diffraction have been employed. Special emphasis has been focused on structural role of zinc in glasses of different composition and the effect of different cations on coordination of zinc along with the effect on phosphate tetrahedra. 67Zn and 43Ca solid state NMR spectra of selected glass samples have been successfully acquired at ultrahigh field 900 MHz using Solid Echo pulse sequence. In addition solid state NMR spectra of two polymorphs of crystalline Zn(PO3)2 have also been acquired at 850 MHz using DFS– WURST–QCPMG pulse sequence in order to distinguish between the magnitude and orientation of electric field gradient (EFG) of zinc in octahedral and tetrahedral coordination. Structure determined through various techniques has been related to the dissolution behaviour of glass compositions from metaphosphate to invert phosphate. A decrease in pH of surrounding medium has been observed due to the presence of zinc. Insertion of ZnO4 tetrahedra between PO4 tetrahedra has been observed in invert phosphate glasses with high zinc oxide content which renders them suitable for glass– ionomer cements. Glass–ionomer cement from glass composition 10Na2O:50ZnO:10CaO:30P2O5 and hydroxyapatite and, acrylic acid and vinyl phosphonic acid co‐polymer has been produced successfully.
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