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ABSTRACT: An empirical mathematical model, comprising 17 compartments, has been produced to describe the biokinetics of ingested inorganic arsenic (As) in man - required to interpret bioassay data and to predict As tissue concentrations resulting from acute and chronic intakes of inorganic As. The rate constants used to describe the bi-directional transfer of As between compartments were chosen to result in model outcomes that match published data on the distribution of As in tissues and on the retention and excretion of radioisotopes of As administered to human subjects. The model was deployed in acute and chronic intake modes to produce predictions of tissue concentrations and excretion levels. Under conditions of chronic daily intake (1 μg d(-1)) for 50 years predicted final tissue concentrations vary by a factor of ∼ 2. Highest concentrations are predicted to occur in skin and bone (∼ 230 ng kg(-1)). Tissue concentrations in all tissues other than bone are predicted to reach equilibrium after ∼ 100 days, and at this time, the amount of As excreted in urine has also reached approximate equilibrium at 79% of the daily dietary intake. This level then remains relatively constant unless intake ceases when tissue levels of As fall rapidly. Data on organic and inorganic As concentrations in urine were used to predict inorganic As intake and average tissue content for the USA population. Predicted tissue concentrations ranged from 2.3 μg kg( -1) in skin to 1.1 μg kg(-1) in muscle for an average inorganic As intake of 9.3 μg d(-1).
Human & Experimental Toxicology 03/2010; 29(11):891-902. · 1.31 Impact Factor
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ABSTRACT: This study reports the development and evaluation of a novel method using quantitative light-induced fluorescence (QLF), which enables its use for quantifying and assessing whole tooth surface staining and tooth whitening. The method was compared with a spectrophotometer to assess reliability. Two experimental phases, intrinsic stain formation and tooth whitening, were conducted in vitro on 16 extracted bovine teeth. Intrinsic stains were developed via access through lingual surfaces and root canals of these teeth using tea solution (2 g/100 ml, Marks and Spencer Extra Strong Tea, Marks and Spencer, London, UK) for 6 days. Stains were removed using 33% hydrogen peroxide (VWR Prolab, Leicestershire, UK) in cycles over 150 min. Stain development/whitening was monitored with QLF (Inspektor Research systems, Amsterdam, Netherlands) and spectrophotometry (Easy shade, Vita Zahnfabrik, Bad Säckingen, Germany). Parameters Delta F for QLF and Delta E for the spectrophotometer were obtained. The progression of stain intensity and removal observed by the methods were tested for correlation using Pearson's correlation coefficient. Intra-examiner reliability for each method was tested. QLF showed a high correlation with spectrophotometry for detecting and monitoring intrinsic tooth stain progression (Pearson coefficient r was -0.987 with correlation significant p < 0.0001). For stain removal, the Pearson coefficient (r) between both methods was -0.906 with no significance p = 0.094. The use of an external reference material in combination with the inner patch QLF analysis technique had the ability to detect and measure whole tooth surface staining and its removal longitudinally. The reliability of the method shows a potential clinical application.
Clinical Oral Investigations 04/2009; 14(1):19-25. · 2.36 Impact Factor
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ABSTRACT: To report the use of Quantitative Light-induced Fluorescence (QLF) to determine if there was a tendency for bleached enamel to take up extrinsic stains more than unbleached enamel.
Bovine teeth devoid of stains were selected, the roots removed and enamel gently pumiced. Each tooth was sectioned into two and each half randomly assigned to two groups (bleached or unbleached). Windows were created on each half using clear acid resistant varnish. 38% Hydrogen peroxide gel was applied to the exposed windows of the bleached group for 1 hour. The teeth were rinsed and dried. Bleached and unbleached halves of the same teeth were then mounted on glass rods attached to pot lids using green stick. QLF images were taken. The teeth were subjected to a cycle of artificial saliva, chlorhexidine and tea (2 minutes in each solution). This was repeated 5 times. QLF images were taken at the end of each cycle.
The uptake and progression of stain was detected in all the sections by QLF. Using paired t- test (SPSS) there was no significant difference between the two groups for the change from baseline to the final stain cycle (p > 0.05), however there was variability in stain uptake within the groups as the cycles progressed.
Bleaching of enamel in vitro does not appear to increase the susceptibility of enamel to extrinsic staining.
International Dental Journal 09/2008; 58(4):208-12. · 0.96 Impact Factor
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ABSTRACT: Uncertainties exist both in the basic data from which a radiotherapy plan is produced and in the process whereby such a plan is translated into the patient set-up during treatment. Individual parts of the radiotherapy process are subject to checks, but the overall accuracy of treatment delivery is not routinely evaluated. In vivo dosimetry by means of a semiconductor detector system can be used to measure the cumulative error in the radiotherapy treatment dose delivered. A direct patient dosimetry system was commissioned and introduced in January 1993 for the routine evaluation of the doses patients receive. Since its introduction a total of 1000 patients have been monitored for a range of radiotherapy applications, comprising 300 breast treatments (6 MV X-rays), 150 head and neck treatments (6 MV X-rays) and 550 pelvis. abdomen and thorax treatments (10 MV X-rays). The results of this audit show that less than 5% of all patients monitored gave a systematic error more than +/- 5% for a single field, or more than +/- 2.5% for the "estimated overall error" in the isocentre dose. The causes of these errors were identified and appropriate action taken where necessary. It is suggested that this method could be used routinely in radiotherapy treatment to assess the overall performance of the treatment process.
British Journal of Radiology 05/1997; 70(832):399-408. · 1.31 Impact Factor
