Influence of crushing and additive irradiation procedures on EPR dosimetry of tooth enamel

Abstract

-The effect of the crushing and additive dose procedures used in EPR dosimeuy of enamel was studied on the signals with g-factors of 2.0045 and gl = 2.0018, g, = 1.9975. Eight~tions,~g~g fi size from <75 micrometers to 2 mm, were prepared from one tooth. Two cases wem investigated: crushing of a non-irradiated sample and of a sample previously irradiated (6 Gy tinm Wo gamma ray source). In the non-imadiated study, the intensity of the native signal at 2.0045 inaeased by circa 1.75 times as the grain size &cmased from maximum to minimum. A small decrease in radiation sensitivity (< 8%) was also observed with decreasing grain size. In the irradiated samples, crushing resulted in slight variations of reconstructed doses from expecmd values, but the worst possible case (grain sizes c 75 pm) showed that additional errors were less than 10%.The radiation sensitivity of enamel measumd immediately atter exposure is underestimated. It increases by about 15% in the fmt month. Based on the decomposition of the observed specq a new interpretation of transient signals is proposed which explains the above phenomena. Recommendations about how to use this interpretation in retrospective EPR dosimetry are given.

EPR dosimetry with tooth enamel: A review

“…Grinding was found to intensify the native signal in some cases (Fattibene et al, 1998;Sholom et al, 1998a;Aldrich et al, 1992;Desrosiers et al, 1989), but there is no conclusive evidence that this is a real growth of the native signal and not a generation of a different, although closely resembling, signal. Polyakov et al (1995) went as far at to propose that the native signal was due to grinding, in view of the increase in intensity and line width with prolonged grinding that resulted in smaller grain size (their g-value of 2.0038, most likely, should be corrected).…”

“…As a consequence, it is now accepted not to use grain sizes smaller than 150 µm. However, the situation may be more complex than presented by Sholom et al (1998a). Iwasaki et al (1993) reported a 10% higher radiation response for grains smaller than 75 µm in samples irradiated before grinding, which was attributed to an underlying distortion of the baseline between 0 and 500 mT.…”

“…Other authors do the opposite: first, they use a mechanical procedure to separate the dentin from enamel and then treat enamel with an alkaline solution to complete dentin separation . Enamel and dentin can also be separated by gravitation methods using a high-density liquid (e. g., sodium-polytungstate with the density of 3.1 g/cm 3 ) (Brik et al, 1996;Sholom et al, 1998a).…”

“…Indeed, Sholom et al (1998a) irradiated enamel powder samples of grain sizes ranging from less than 75 µm (the exact dimensions were not reported) to 800 µm. The radiation sensitivity was independent of grain size from 800 µm down to 150 µm, below which a small decrease of the radiation sensitivity was detected.…”

“…It should be mentioned that radiation also induces unstable signals (see Chapter 11 and the chapters below), which seem to decay in two weeks (Sholom et al, 1998a). They can also be eliminated by the annealing procedures described above or storage for two to eight weeks .…”