Thermal behavior of orientated and non-orientated CO2− radicals in tooth enamel

Isothermal heating experiments on enamel fragments show that there are two pronounced increases in the intensity of the orientated CO₂⁻ radicals, after heating for 15 min at 225 °C and 1440 min at 175 °C. While the powder spectra virtually remained unchanged at these heating steps, it was found that the angular intensity variability in the fragments greatly increased. In general, it is not possible to explain these increases by transfers from non-orientated CO₂⁻ radicals to orientated, because there are simply not enough non-orientated CO₂⁻ radicals in the unheated sample. Instead we attribute the increased angular intensity variability by a higher crystallinity in certain domains in the enamel. It was found that after heating for 15 min at 225 °C, newly occurring orientated CO₂⁻ radicals had a somewhat different orientation to the unheated.