Purpose: The aim of the present study was to investigate the influence of irradiation on the mandible of ovariectomized (OVX) rats.
Materials and Methods: Female rats were subject to OVX or a sham operation (SHAM) at the age of 14 weeks. Ten Gy doses of X-ray were applied to the mandibles twelve weeks after the operation. The experimental animals were divided into four groups: the OVX non-irradiation group, the OVX irradiation group, SHAM non-irradiation group and SHAM irradiation group. Four, eight and twelve weeks after irradiation, the animals were sacrificed and the mandibles removed. The mandibles were investigated using μCT and pQCT, and from the images obtained, the rate of mineralized tissue in the bone as well as the bone mineral content (BMC) were evaluated.
Results: The rate of mineralized tissue in the bone as determined from the images of μCT was significantly (P<0.05) lower in the OVX non-irradiation group than in the SHAM non-irradiation group at four weeks after irradiation. Similarly, the rate in the OVX irradiation group was lower than that in the SHAM irradiation group at twelve weeks after irradiation. In both the SHAM and OVX groups, there was no difference between the non-irradiation and irradiation groups. From the pQCT images, the change in the BMC in the cortical bone was negligible when the BMC was measured in the mandibles. In the OVX non-irradiation group, the trabecular BMC of the mandibles was significantly lower than that in the SHAM non-irradiation group at four and twelve weeks after irradiation. The trabecular BMC of the mandibles in the SHAM and OVX irradiation groups were significantly lower than that of the SHAM and OVX non-irradiation groups respectively throughout the experimental period.
Conclusions: In the rate of mineralized tissue in the mandibles, the influence of OVX was recognized, but the influence of irradiation was not. On the other hand, the BMC in the cortical bone was not significant through out the experiment. The influence of irradiation on the OVX group was recognized in the trabecular bone, in which the BMC was reduced.

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Objectives: To construct a patient-based oral radiology course for large classroom settings to enhance student interest in the oral radiology content and to evaluate the effectiveness of this method.
Methods: We developed an oral radiology course comprised of 32 90-minute lectures, one-third of which were devoted to patient-based learning. Four case-packages were developed by the oral radiology faculty of our institute. These included the following: patients with dental caries; patients with periodontitis; patients with intraosseous jaw lesions; and patients with neck masses. The cases were presented in a large classroom first, and the students learned the indications of the imaging findings, the principles of the imaging, the radiographic findings of the diseases in question, and the correct differential diagnosis for the diseases in question. Students addressed the patients' conditions by themselves and in small-group meetings after class. To complete a case-package, three plenary sessions, which were held once a week, were usually required. Lectures were given to facilitate student understanding between the sessions and these accounted for one-third of the total course time. The remaining one-third of course time was used for lectures not directly related to the case-packages but essential to oral radiological study. The students were asked to file logs for each session and, at the end of the case-package, were tested to determine how much of the learning objectives they were able to understand and retain. The logs and test results were used to assess student achievement. Students were also asked to fill out a questionnaire to evaluate the course.
Results: The case-packages simulated real clinical situations and this heightened students' interest in the study of oral radiology, which can sometimes be a dry subject. Although students did not have the opportunity to participate in group practice with a tutor, most students could join the plenary session in the classroom to identify and solve problems, and define their learning objectives. The students welcomed this patient-based study method as a break from lecture-based learning.
Conclusion: A patient-based, self-directed learning method can be applied to even large classrooms and this may reduce the workload of faculty members.

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