Structural and thermal behaviour of human tooth and three synthetic hydroxyapatites from 20 to 600 °C

The structural and thermal properties of human tooth enamel, dentine and three synthetic hydroxyapatite samples with Ca/P ratios of 1.57 (Ca deficiency), 1.67 and 1.77 (Ca excess), respectively, were analysed in the temperature range from 20 to 600 • C to have information on the parameters involved in the ionic/electrical conductivities reported for human tooth enamel between 200 and 350 • C approximately.Studies were carried out through x-ray diffraction, thermo-gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and temperature programmed desorption.Chemical analysis was performed by x-ray characteristic energy dispersive spectroscopy.Results indicate a strong correlation between the removal of the OH -groups from the hydroxyapatite unit cell and the expulsion of absorbed water and lattice water registered during heating.