To investigate the effects of substituting strontium for calcium in fluoroaluminosilicate glass on the handling variables, setting reaction, mechanical and ion-releasing properties of high-viscosity GICs.
Method:
A series of five glasses in which strontium substitutes for calcium and based on the general formula: 4.5SiO2 - 3Al2O3 – 1.25P2O5 – xSrO - ySrF2 – zCaO - yCaF2, where x = 0, 0.5, 1.5 or 3; y = 0, 1 or 2; and, z = 0, 1.5, 2.5 or 3 were synthesized; powders were characterized by X-ray diffraction (XRD), particle size analysis and thermal analysis then mixed with poly(acrylic acid) and aqueous tartaric acid to form glass ionomer cements, whose properties were then investigated after 24hrs, 7days and 28days: working time (WT) and setting time (ST) were determined by rheometry; setting reaction was studied by Fourier Transform-Infrared spectroscopy; compressive strength (CS) and bi-axial flexure strength (BFS) were tested; and, ion release profile was studied by fluoride ion selective electrode and Inductively-coupled plasma/Optical emission spectroscopy.
Result:
XRD confirmed the amorphous nature of the glasses, while thermal analysis showed mixed alkaline/entropic effect on glass transition temperature. WT and ST did not vary significantly with strontium content but the shortest times were recorded for the cement with the smallest glass particle size. CS and BFS strength values again did not vary with strontium content. Strontium ion release was directly proportional to the quantities of strontium.
Conclusion: Results suggest that substitution of strontium for calcium has insignificant effects on manipulation, setting and mechanical properties of the cement; however substitution enables controlled release of strontium which may have an important cariogenic role particularly in combination with fluoride.