Analysis of reactions in glass-polyalkenoate/resin systems by dielectric impedance spectroscopy.

The principles of impedance spectroscopy are surveyed, with consideration of both low and high impedance dielectric biomaterials where the response mechanisms are dominated, respectively, by dipolar relaxation and ionic charge migration. The situation of dental biomaterials is considered with special reference to glass-ionomer polyelectrolyte systems and to the impedance changes that may arise in consequence of setting mechanisms. Measurements have been conducted using both static and frequency-dependent potentials; where appropriate, with a high impedance interface and frequency-response analyser. Data are presented for the control situation of poly(methyl methacrylate) (PMMA) and for a series of glass-ionomer and resin-modified glass-ionomer biomaterials. It is observed that in the glass-polyalkenoate (G-PA) materials, ionic conduction and polarization are the dominant factors contributing to the impedance. This contrasts with the dipolar relaxation characteristic of PMMA. It is concluded that a more extended programme of data-acquisition is required, where possible from a 'homologous' series of formulations, to lay a firm foundation of mechanistic interpretation.