Estimates of patient doses are generally required to justify and to optimize the process of diagnostic radiology. To ensure that the dose to the patient in medical exposure is as low as can be reasonably achieved, diagnostic reference levels are the first step in the optimization of radiation protection subsequent to justification. The diagnostic reference levels provide a practical method for measuring, comparing, and managing patient doses to develop quality assurance and clinical audit programs in medical imaging.

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Effective cumulative doses and the risks of dental radiographic examinations were estimated from data obtained by a nationwide survey performed during 1999 in Japan. The trend until 1999 of the number of radiographic examinations and cumulative doses were also estimated from the accumulative data of nationwide surveys. The number of dental radiographic examinations including intraoral radiography and panoramic radiography per year was approximately 100,000,000. As the speed of intraoral film became higher, the exposure time was reduced to about 20%. The use an of automatic processor instead of “instant” processing has become more popular in general dental clinics, and also the use of X-ray rooms have increased in last 20 years. The mean effective dose has been estimated to be 9.1-9.5μSv for intraoral radiography per film in 14 full-mouth examination films and 9.7-10.9 μSv per panoramic radiographic film. The effective cumulative dose was 905.5 man · Sv for intraoral radiography and 128.9 man · Sv for panoramic radiography. The corresponding mean effective cumulative dose was 7.2μSv per person for intraoral radiography and 1.0μSv per person for panoramic radiography.

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The current epidemiological data on radiation carcinogenesis in humans and the biological mechanisms are discussed in this review. It was concluded that a threshold dose for radiation carcinogenesis above order of 1 mSv is an unlikely possibility. The prudent approach in procedures required for justification and optimization should be considered in practice of radiography.

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The aim of quality assurance (QA) in dental radiography is to provide higher quality and more informative images with the least exposure to patients at a minimum cost. The application of a QA program has been clearly shown to have benefits. The level of a QA program implemented depends on the type and extent of radiography at each dental facility. While a QA program for analog systems has been established, such a program has not yet been created for digital systems in dentistry. A QA program for dental digital radiography should be prepared as soon as possible.

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Objective : To investigate the micro structural and histomorphometrical changes in mandibular condyles in ovariectomized cynomolgus monkeys.
Material and Methods : The experimental animals were female cynomolgus monkeys (n = 24) with a mean age of 10 years, range 9-15 years. The animals were divided into 2 groups : an experimental group to be ovariectomized (OVX group) and a control sham operated group (Sham group). The animals in each group were housed under the environmental condition outlined in the appropriate guidelines from the National Institutes of Health U.S.A.
Two years post-operatively, the animals were killed and the maxillo-facial bones were dissected and fixed with 10% buffered formalin. The bone mineral density (BMD) of the mandibular condyle was determined by densitometric analysis of the lateral oblique transcranial projection radiograph. Bone X-ray microanalysis on the mandibular condyle was performed using micro computed tomography (μCT). The following parameters were examined in cancellous bone : bone volume (BV/TV), trabecular thickness and number, trabecular separation, structure model index (SMI), number of node struts, and total strut length of tissue volume. Further, cortical bone volume was additionally examined.
The condyles were immersed in Plank-Rychlo's solution for demineralization, embedded in paraffin, and used for standard light microscopic observation. Thickness of the cartilage was measured and the unit number of hypertrophic cartilage cells was counted on each coronal section.
Results : Densitometric analysis of lateral oblique transcranial projection radiograph showed that BMD of the mandibular condyle did not significantly decrease in the OVX group in comparison with the Sham group. However, CT analysis did show that BV/TV of the cancellous bone, trabecular thickness and number, SMI, number of node struts, and total strut length of tissue volume in the OVX group were significantly lower than those found in the Sham group. Further, trabecular separation in the OVX group was significantly higher than that in the Sham group. However, cortical bone volumes were similar in those two groups.
Histomorphometrical analysis on condylar cartilage showed that both thickness of the hypertrophy stratum and unit number of hypertrophic cartilage cells were lower in the OVX group than in the Sham group.
Conclusion : Bone loss and trabecular fragmentation in the monkey condyle could be induced with ovariectomy. The changes occurred only in cancellous bone, but not in cortical bone.

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