No abstract

The experimental and analytical difficulties associated with the measurement of mercury vapor in the oral cavity are considerable. In the present paper, the objective was to measure the amount of intra-oral mercury vapor in subjects with amalgams, by means of two sets of equipment based on different functional principles. In addition, it was found that the type of mercury source prevalent in the oral cavity had to be evaluated. The measuring technique used to obtain correct results is discussed, and an evaluation of the conditions for the application of the measuring equipment available was made. It was found that the amount of mercury released from the oral cavity was time-dependent. Furthermore, the amount of mercury released with the time kept constant was almost independent of the pumping flow rate up to 8 L/min. It was found that the tissue, saliva, and the amalgam restorations were not depleted of mercury during the measuring time. The results of the Mercollector-Mercometer measurements carried out on seven subjects with nine or more occlusal surfaces restored with dental amalgam and on three subjects without any amalgam restorations revealed that the rate of mercury release was in the range 0.03-0.34 ng/sec in the former group and less than 0.01 ng/sec in the latter. Based on the experimental results and on theoretical considerations, it was concluded that the amount of mercury released per time unit is the only quantity measurable.

The objective of the present investigation was to evaluate lithium formate electron paramagnetic resonance (EPR) dosimetry for measurement of dose distributions in phantoms prior to intensity-modulated radiation therapy (IMRT). Lithium formate monohydrate tablets were carefully prepared, and blind tests were performed in clinically relevant situations in order to determine the precision and accuracy of the method. Further experiments confirmed that within the accuracy of the current method, the dosimeter response was independent of beam energies and dose rates used for IMRT treatments. The method was applied to IMRT treatment plans, and the dose determinations were compared to ionization chamber measurements. The experiments showed that absorbed doses above 3 Gy could be measured with an uncertainty of less than 2.5% of the dose (coverage factor kappa = 1.96). Measurement time was about 15 min using a well-calibrated dosimeter batch. The conclusion drawn from the investigation was that lithium formate EPR dosimetry is a promising new tool for absorbed dose measurements in external beam radiation therapy, especially for doses above 3 Gy.

Measurements of intra-oral mercury vapor from amalgam fillings are discussed. It was shown that the only quantity which it is possible to measure is the mercury release rate, and that the concentrations of mercury vapor in the oral cavity published in most earlier studies are the mercury concentrations in the measuring cell of the measuring apparatus and not the concentrations in the oral cavity. The consequences for the daily dose equations of the facts that the mercury source is present inside the oral cavity and that the amount of mercury released during a certain time is limited are discussed. It was found that most daily dose equations used have a questionable mercury distribution on inspiration, expiration, and swallowing. Re-calculations of almost all the available daily dose data showed a mean daily dose value of about 1.3 micrograms Hg/day (range, 0.3-2.2 micrograms Hg/day). The mean swallowed amount of mercury from intra-oral mercury vapor was calculated as being in the order of 10 micrograms Hg/day (range, 2.4-17 micrograms Hg/day), resulting in an estimated absorption of about 1 microgram Hg/day from the gastro-intestinal tract.

No abstract