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When human tooth enamel is heated either in vacuum or air it presents drastic changes in electrical susceptibility, conductivity and structural properties. In this paper we report an insulator-conductive transition which is observed in air around 350°C where enamel conductivity changes drastically and its electrical resistance decreases from 1015 to 105 Ω that is, it goes from an insulator to a super-ionic ceramic behavior. This transition, first evidenced in vacuum by electron microscopy observations, is now completely determined by a.c. impedance spectroscopy technique and its characterization was carried out as a function of the frequency and temperature. X-ray in situ heating diffraction experiments show that there is no structural phase transition during a wide range of temperature including the one where the conductivity transition occurs.