Heating, crushing and exposure of dental enamel to sunlight and UV radiation can introduce paramagnetic signals similar to those following exposure to ionizing radiation. The objective of this work is to use infrared and electron spin resonance (ESR) spectra to study thermally treated enamel and dentin, and identify the chemical radical or mechanisms that produce these ambiguous ESR signals. Non-irradiated bovine teeth were used. ESR spectroscopy was performed in the X band and the infrared spectroscopy was performed on a FTIR spectrometer operating between 4000 cm -1 and 400 cm -1. The results show ESR signals in dentin heated at temperatures between 100°C and 1000°C and in enamel heated at temperatures ranging from 250°C to 1000°C. The ESR signal formed after heat treatment below 400°C could be assigned to degradation products of the organic material, while the ESR signals that predominate in tissues heated between 500°C and 900°C show a maximum amplitude at 750°C and could be assigned to the cyanate ion (NCO -).