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
