Acidobasicity of oxide glasses used in glass ionomer cements

The purpose of this study was to provide a theoretical basis for assessing the cement-forming ability of oxide ionomer glasses based on concepts of glass acidobasicity.

Theoretical concepts of acidobasicity of ionomer glasses were developed based respectively on ionization potential, field strength and electronegativity. Calculations of acidobasicities were made for a range of glasses of the CaO-Al2O3-SiO2 type. These results were compared with experimental values obtained for the setting times of cements prepared from these glasses.

Regression analysis showed a 99.96% correlation between acidobasicity values based on ionization potential with those based on field strength. There was only moderate correlation between these acidobasicity values and those based on electronegativity. Setting time was found to increase slowly as glass basicity decreased until a critical point was reached when setting time increased sharply. A Spearman rank correlation test was applied, and it was found that setting times correlated with acidobasicity values based on ionization potential and field strength with a coefficient of 98.7%.

Results show that calculated acidobasicity values of CaO-Al2O3-SiO2 glasses can be used to distinguish between glasses that form cements from those that do not. They are divided by a critical acidobasicity value. It was not found possible to relate setting time to acidobasicity by means of an equation because of this critical feature in the relationship. The critical acidobasicity value replaces the more complex criteria of Hill and Wilson (1988) using triangular diagrams.