Radiation effects of relatively low dose irradiation on tooth germ cells in rats were studied electron microscopically. These radiation effects were estimated with the changes of cell organelles of the preodontoblasts, that is, mainly chromatin clumpings and developments of lysosomes.
From these studies, following results were obtained:
1) Radiation effects such as chromatin clumpings and developments of lysosomes were detected even in the rats irradiated with 25 rad (0.25 Gy) of radiation. These changes increased according to the increment of radiation dose.
2) The most remarkable changes were shown at 6 and/or 12 hours after irradiation in each groups. Reparative signs of these changes were shown at 24 hours after irradiation.
3) The more remarkable changes were found in the zone of undifferentiated preodontoblasts than those of precursor of preodontoblasts or well differentiated preodontoblasts. Consequently, the undifferentiated preodontoblasts were shown to be most radiosensitive.
4) Slight or moderate enhancement of radiation effects were found in the groups irradiated under high pressure oxygen, especially in the groups irradiated with 250 and 500 rad (2.5 and 5 Gy) of radiation.

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This study represents an attempt to clarify the vagueness brought about in X-ray dia-gnosis, by means of questionnaires. This study is also designed to explore appropriate countermeasures for coping with the phenomenon of Fuzzy reasoning used in the complicated X-ray diagnostic outcome.
The case material comprised patients examined at Nihon University Dental Hospital during the year of 1979. Thirty dentists on the teaching staff of Nihon University School of Dentistry and 100 dental students in clinical training participated for collaboration in the study. Each subject was shown a radiogram or a set of radiograms and asked to read a specified region so that his X-ray findings and diagnosis were entered by himself in a questionnaire sheet. Each film or set of films were accompanied by pertinent clinical data from the assigned case which included the past history, present history and present illness.
Calculation of the membership function set up for proper evaluation of the answered diagnostic X-ray findings was achieved by regressive principal component analysis, on the grounds of previously summarized clinical and X-ray finding data from 101 cases at this hospital. Namely, principal components representing overall characteristic values for establishing the diagnosis were derived from the groups of clinical findings, whereupon a multiple regression model was estimated for each group of X-ray findings, assigned as objective variable, employing the extracted principal components as explanatory variables.
The reasoning was carried out as modus ponens linking the answered diagnostic findings to the membership function, with a connective:
a) An X-ray finding (yj) is true and that the corresponding clinical finding (xi) is also true.
b) If the clinical finding is true, then the X-ray diagnosis of the case is (dk).
c) Therefore, the X-ray diagnosis of the case is (dk) as far as the X-ray finding (yj) is true.
Although plurality of diagnosis was obtained for each according to the data collected in questionnaires, the diagnosis inferred on the basis of Fuzzy's theory coincided with the established diagnosis. The variations seen in the results of judgement to a stimulus may indicate that there were inter-subject differences in criteria for judgement.
While it is true that insufficiency in the amount of information and ambiguity in the wording of the serial questions on the questionnaire has to be taken into account, the results of the present study seem to indicate that a possible involvement of institution and subjectivity peculiar to humans mainly gave rise to uncertainty in the judgement. Introduction of the Fuzzy's theory would be most advisable in dealing with such human subjective values that cannot be treated with the theory of probability.

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The images on the orthopantomographic screen, which change with lapse of time, provide informations concerning all the tomographic layers of the deep area of objects. With the current orthopantomography which uses analog method in processing data, only certain layers are reflected on the film, with the images of other sites discarded as dims. If the informations at the different depth in the objects were necessary, another X-ray exposure to the patients is required.
Therefore, we have developed a method by which the image produced on the screen during orthopantomography is photographed through a television system and recorded on a videotape recorder (VTR). Through this VTR, informations of the desired tomographic layer can be reproduced; each frame of the reproducd image is digitized on a matrix of 16×128 dots and superposed by shifting the row. The resultant tomographic picture is equivalent to that obtained by an ordinary film treating method. In the present basic experiment, the numerical figures (from 1 to 7) written on a circle of 8 cm in radius and alphabetic letters (A, B and C) written on a circle of 3 cm in radius could be separated as the tomographic picture. Moreover, the tomographic images on a circle of 8 cm in radius were changed continuously into that on a circle of 3 cm by changing the other leapt numerical figures during production of image. Thus, it is possible to reproduce the desired tomographic image by computerized treatment of the picture through a single orthopantomographic recording.

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