The anodic process during electro-thermal poling of one bioactive and three bioabsorbable glasses was investigated. by means of impedance spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The bioactive glass with the nominal composition 46.4% SiO2, 25.2%,Na2O, 25.2% CaO, 32% P2O5 (46S4) and the three bioabsorbable glasses of the CaX series ((55 - X)% Na2O, X% CaO, 45% P2O5, with X = 20, 30,40) were poled at temperatures between 473 K and 513 K using voltages between 50 V and 490 V. Both impedance spectroscopy studies during poling and subsequent ToF-SIMS profiling show that the thickness of the Na+ ion depletion layer under the anode increases in a linear fashion with increasing poling voltage. However, the same absolute values for the thickness were only obtained under the assumption that the dielectric permittivity of the depletion layer is about 2-3 times lower than the dielectric permittivity of the bulk glass. (C) 2013 Elsevier B.V. All rights reserved.