Use of electrochemical impedance spectroscopy to evaluate resin-dentin bonds.

Electrochemical impedance spectroscopy (EIS) offers a potentially nondestructive quantitative method for measuring the stability of resin films and or resin-bonded dentin over time. The purpose of this study was to measure the electrical impedance of five experimental dental adhesives of increasing hydrophicities as 30-microm films and as resin-bonded coatings on acid-etched dentin. Resin films or resin-coated dentin disks were placed in U-shaped chambers containing pairs of Ag-AgCl electrodes in 0.1M KCl. Electrical impedance spectra were run at day 0, 1, 7, 14, and 21 days. All resin films and resin-bonded dentin showed increases in capacitance during the first day of storage in electrolyte. This was usually associated with an increase in the pore resistance of the resins. Generally, resin-bonded dentin gave lower impedance values than their respective resins (resins 1-4) but solvated resin 5 bonded to water-saturated dentin gave higher capacitance and impedance values than resin 5 films. However, solvated resin 5 films gave higher impedance values than resin 5-bonded dentin. This behavior was confirmed by TEM examinations of silver uptake into films of neat resin 5 vs. ethanol-solvated resin 5, where water tree-like structures seen in the former were not seen in the latter. EIS is useful in examining changes in the capacitance and electrical impedance of very hydrophilic, ionic methacrylate resins. Its utility in detecting degradation in resin-bonded dentin interfaces remains to be determined in longer term studies.