Reorientable electric dipoles and cooperative phenomena in human tooth enamel

A preliminary investigation of electric dipole reorientability in human tooth enamel (TE) in comparison to that in hydroxyapatite (OHAp) has been made with the fractional-polarization form of the thermally stimulated currents (TSC) method. The reorientable dipoles are the structural OH-ions. The OHAp exhibited compensation phenomena at 211.5 degrees C and at 356 degrees C which are associated here with the hexagonal form becoming quasi-statically stabilized and dynamically stabilized, respectively, against the monoclinic form. TE specimens were pretreated at various temperatures. All showed the onset of cooperative motions that could quasi-statically stabilize the hexagonal form at the same temperature, approximately 212 degrees C, as did OHAp, even though the TE was already statically stabilized in the hexagonal form. Parts of the TSC spectra that did not conform to the 212 degrees C compensation changed progressively with pretreatment temperature. Loss of incorporated H2O is identified as the most probable cause of most of these changes. This work shows considerable promise for TSC as a tool for further quantitative investigation of TE.