Electron spin resonance-native signal in thermally treated dental tissue

Although the dosimetric Electron Spin Resonance (ESR) signal of hard tissues, particularly enamel, has been extensively studied, little attention has been paid to the native signal. This signal is known to be affected by the health of the tissue, as well as by socio-economic factors. In dental applications several clinical procedures, including the use of laser irradiation, can heat the tissue locally with side effects that must be studied. The purpose of the present work is to study the ESR signals in enamel and dentin tissues after thermal treatment with temperatures in the range of 100degreesC-300degreesC. Non-irradiated permanent bovine teeth were studied. ESR measurements were performed with a Varian E-4 ESR spectrometer operating in the X band range. Progressively larger ESR signals were produced in dentin tissues previously heat treated at and above 100degreesC. No detectable signals were observed in similarly treated enamel. The signal shows partial decay at four and six months after thermal treatment. The experimental data for dentin show a correlation with the Arrhenius function with an activation energy of (41+/-2)10(3) J/ mol. After six months, the ESR signal shows a higher activation energy (67+/-3)10(3) J/mol and the decay shows a activation energy of (38+/-2)10(3) J/mol. A possible assignment of the signal origin in dentin is difficult. The water lost during thermal treatment and reincorporated during the following six months correlates with the signal gain and subsequent decay. The water lost can produce point defects in the hydroxyapatite, or structural changes in the collagen structure. The results observed here are useful for understanding the thermal effects produced in dentin by infrared laser irradiation, and provides a cautionary warning that annealing conditions in ESR studies of biological tissues should be standardized.