Characterisation of Mg, Sr, and Zn containing fluoro-aluminosilicate glasses and their glass polyalkenoate cements

Abstract

The glass polyalkenoate cements (GPCs) are formed by the acid-base reaction between fluoro-aluminosilicate glasses and polycarboxylic acid in the presence of water. Three series of glasses were produced by modifiying glass LG26 [32.1SiO2. 21.4Al2O3. 10.7P2O5. 21.4CaO. 14.3CaF2] (mole %). In the first series, calcium was substituted by magnesium, and in the second series, calcium in the first series was substituted by strontium. The last series were zinc substitution for calcium in LG26. These glasses were characterised by X-ray diffraction (XRD), magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy and differential scanning calorimetry (DSC). The gradual substitution of calcium by magnesium resulted in the formation of F-Mg(n) species and a disappearance of Al-F species on the 19F MAS-NMR. The 31P and 27Al MAS-NMR showed that all glasses contained Q1 pyrophosphate Al-O-PO3 3- species. In addition, the fully magnesium substituted glass showed the possible formation of magnesium pyrophosphate, Mg2P2O7. The fully zinc substituted glass, however, showed only Al-O-PO3 3- species charge balanced by Zn2+. An increase in Al(V) species was observed on the 27Al MAS-NMR with the fully magnesium and zinc substituted glasses. The presence of magnesium also increased the number of bridging oxygen on SiO4 tetrahedra, but the presence of zinc affected the Q structure of the aluminosilicate network less. GPCs with these glasses were formed with poly (acrylic acid) (PAA) and L-(+)-tartaric acid. The setting reaction of selected cements was studied by 19F, 31P and 27Al MAS-NMR spectroscopy. F-Ca(n) species were clearly shown to be consumed for cement formulation, and F-Mg(n) species were still present in the 19F MAS-NMR spectra of the magnesium containing cements. The Al-O-PO3 3- species were present in the cement. The conversion to Al(VI) from Al(IV) and Al(V) was observed by deconvoluting the 27Al MAS-NMR spectra. The experimental ratio of Al(VI):Al(IV)+Al(V) was higher than the theoretical ratio which may have resulted from the possibility of L-(+)-tartaric acid being involved in the Al conversion during the setting reaction. The working and setting times increased with magnesium substitution, but did not change with zinc substitution for calcium. The compressive strengths decreased with magnesium substitution, possibly resulting from the preferential crosslinking between Mg2+ and COO-. The highest release of fluoride was observed from the fully magnesium substituted cements. Another series of glasses [34.0SiO2. 22.6Al2O3. 5.7P2O5. (22.6-x)SrO. xZnO. 15.1SrF2] (mole %) was produced for formulating GPCs with poly (γ-glutamic acid), PgGA. All the glasses have Al-O-PO3 3- species with no change in the phosphorus environment with zinc substitution for strontium. Al(IV) was found to be the major aluminium species with a small presence of Al(V) and Al(VI). The Q structures of all the glasses were found to be a mixture of Q4(4Al) and Q3(3Al). Similarly, DSC showed a negligible change with zinc substitution for strontium. For cement formulations with PgGA, a co-polymer of PAA and poly (but-3-ene 1,2,4- tricarboxylic acid) was used due to the lower reactivity of PgGA than PAA, and cements with different proportions of PgGA and the co-polymer were formed. The working and setting times increased with PgGA content and zinc substitution. On the contrary, the compressive strengths decreased with PgGA content. The highest zinc containing cements in the series showed the highest compressive strength. A longterm fluoride release measurement showed the highest release from the highest PgGA containing cements, possibly resulting from the cements being less crosslinked. There was a slight increase in the adhesion to dentine.EThOS - Electronic Theses Online ServiceGBUnited Kingdo