Widening of the periodontal space has been regarded to be one of the important early radiographic signs of jaw bone injury following irradiation. To disclose the initiation process of this change, an experiment with 540 male, 9-week-old, Wister rats was carried out, in which the left mandibular first molar region was irradiated with a single dose of Co-60 γ-ray, 20, 40, 60, 80 and 100Gy in absorbed doses. Irradiated mandibles were excised at 6 hours, 1, 3, 6, 14, 26, 54, 110 and 166 days after irradiation. Animals not irradiated, spending at the same experimental period, were used as a control. Changes in the periodontal ligament, alveolar bone and their cellular elements were evaluated in the first molar region radiographically, histologically, fluorescence-microscopically and mocroradiographically, and following results were obtained.
1. Widening of the periodontal space was observed in the groups irradiated with 40Gy or more at 110 and 166 days after irradiation.
2. Although dilatated and engorged blood vessels were observed in the periodontal ligament up to 14 or 26 days after irradiation, narrowing and numerical decrease of blood vessels became predominant thereafter.
3. Osteoblasts, cementoblasts and fibroblasts in the irradiated periodontium exhibited the pyknotic changes of nuclei and decrease in cell number after 1 to 3 or 26 days following irradiation. Although osteoclasts also decreased at 3 to 6 days after irradiation, their number became irregular thereafter regardless of the absorbed doses.
4. Newly formed bone area, as indicated by labeling with fluorescence agents, within the interradicular alveolar process was always smaller in the irradiated groups than in the control group, with the degree corresponding to the absorbed doses.
Based on these results, it was suggested that the widening of the periodontal space following irradiation might be induced by both quantitative and qualitative changes in the cellular elements comprising the periodontal ligament and alveolar bone and the subsequent disturbance of bone remodeling due to these cellular changes.

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Percussion sound or occulusal sound has been the subject of many studies by investigators. The objective of such studies was to detect the dentis which contacts earlier than the others at time of occulusion.
For the purpose of diagnosing diseases which arise within the mandible and the maxilla, the authors have conducted studies to analyse percussion sound to obtain parameters of diagnostic use. In the present study, we attempted to elucidate the mechanism of generation of percussion sound, at first, in the mandible for the sake diagnosing diseases which occur in the mandible.
As the sensor to collect oscillation wave, we used an acceleration gage. Waves were recorded through a 12 channel storage scope. For analysis of the shapes of these waves, a microcomputer was used. Fourier and inverse Fourier transformations were performed.
Experiments were carried out in terms of the following items:
1. Analysis of oscillation using a model of a mandibule
1) Analysis of oscillstion of a fiat board
2) analysis of oscillation using a model of a simplified mandible
3) Analysis of oscillation of a desicated human mandibule
2. In vivo analysis of osillation of a mandible
3. In vivo analysis of percussion sound of a mandible
4. Analysis of oscillation in the presence of a disease within the mandible
1) Analysis of oscillation of a mandible showing disease associated with cyst formation
2) Analysis of oscillation of a fractured mandible
The results obtained were as follows:
1. The percussion sound generated by tapping of the mandibular dentes could be regarded as transverse oscillation, assuming the mandible as a bar.
2. This oscillation mode was found to be represented as the basic oscillation mode of a tunig fork and the 1st upper oscillasion mode of transverse oscillation of a bar.
3. It was found that both of these two modes of oscillation are inducted by both vertical and horizontal percussion of the mandibular dentes.
4. In vivo in normal mandible, the frequency of percussion sound was proven to distribute in the range between 500Hz and 1500Hz.
5. In the presence of disease associated with cyst formation, the resonans frequency shifted toward the low frequency side with an increase in the size of the cyst.
6. In the presence of fracture, althogh various findings are obtained according to the size of fractured fraction, the resonance frequency tended to shift toward the high frequency side.

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The extensions of the lesion in osteomyelitis of mandible were evaluated in terms of the rediographic methods employed. 26 patients suffered from the chronic osteomyelitis limited in the molar area were examined using the panoramic and occlusal radiographs in evaluating the vertical and buccolingual extensions respectively. Osteosclerotic change extended below the mandibular canal may be accompanited by the extension to the cortex of bucco-lingual side. This indicates that the extensive lesions should be complemented by the occlusal radiograph to define their bucco-lingual extension. On the other hand, osteolytic change tends to be limited above the mandibular canal and not to be extended to the cortex of bucco-lingual side. This means that the occlusal radiograph may be somewhat useless for this defined osteomyelitis.

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The purpose of this investigation was to evaluate the integral absorbed dose of radiation in routine intraoral radiography. The graphical method using isodose charts was used in this study.
A phantom (15×20×25cm) made of XAC (C₅H₈O₂) was used to simulate a human head. A dental X-ray unit^* with three open-ended metal cylindrical cones was used. The focus-skin distance was 20.75cm, 30.75cm and 40.75cm. The beam diameter was 6cm at the cone end. The tube voltage was varied in 10kVp steps from 50 to 90kVp. For exposures, 0.5 or 1.5mmAl was added to the inherent filtration of the X-ray unit. The X-ray beam was directed at right angles to the surface of the phantom and depth doses were measured with an ionizing chamber, radiographic films and TLD chips. Exit doses were also measured with another ionizing dosimeter. The integral absorbed doses were calculated from the twenty isodose charts.
Results were as follows: 1) The integral absorbed dose per 1cGy at the skin was estimated to range from a maximum of 2.35mJ to a minimum of 1.25mJ. 2) The integral absorbed dose per 1 exposure on the mandibular molar region was estimated to within the range from a maximum of 0.59mJ to a minimum of approximately 0.4mJ. 3) The typical integral dose for one examination was 0.5mJ using 60kVp and F. S. D. 20.75cm. 4) The integral absorbed doses had less differences between 70 and 90kVp. These values were equal to or below 0.45mJ using F. S. D. 20.75cm and 0.4mJ using F. S. D. 30.75cm or 40.75cm. 5) Use of long-cone techniques at 70kVp, as compared with a short-cone technique at 50kVp, should reduce the integral absorbed dose by about 30 per cent.
^*Coronis, Asahi Roentgen Ind. Co. Ltd., Japan

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The genetically significant dose (GSD), per Caput mean bone marrow dose (CMD), the leukemia significant dose (LSD) and the malignant siginificant dose (MSD) from dental intra-oral and orthopantomographic examinations were estimated on the basis of a nationwide survey. The survey was carried out on the frequency of dental radiographic examinations and exposures by sex, age-group and type of examination and on technical factors for the patients from a known fraction of dental hospitals and clinics throughout Japan. The resultan annual number of exposures was estimated to be 3.73×10⁷ for male and 4.73×10⁷ for female, with a total of 8.46×10⁷ for intra-oral radiography. The annual number of orthopantomographic examinations was 5.40×10⁶ for male and 5.83×10⁶ for female, with a total of 1.123×10⁷.
Organ or tissue doses related to the stochastic effects were determined with a phantom measurement using a typical dental X-ray apparatus. The average organ or tissue doses for intra-oral radiographic and orthopantomographic examinations were determined using thermoluminescent dosimeters and thimble chambers (0.6cm³ and 6cm³ in effective volume) placed in the RANDO-Woman-Phantom. The phantom was irradiated with dental X-rays under the condition of 60kV and 10mA and orthopantomographic X-rays of 85kV and 10mA. These technical conditions were evaluated from the results of nationwide survey. The effective dose related to the MSD and the effective dose equivalent recommended by the International Commission on Radiological Protection (ICRP) were calculated using the corresponded weighting factors and the organ tissue doses from the phantom measurement.
The resultant annual population doses per person were 70.8nGy from intra-oral radiography (IOR) and 6.4nGy from orthopantomography (OPR) for GSD, 8.61μGy from IOR and 2.4μGy from OPR for CMD, 7.5μGy from IOR and 2.1μGy from OPR for LSD, and 7.1μGy from IOR and 1.4μGy for MSD, respectively. The population risks of Japaneses were estimated to be 0.124 for the genetic effects, 2.30 for fatal leukemia and 16.8 for fatal malignant diseases.
The annual collective dose equivalents were about 2430 man Sv from dental intra-oral radiography and 480 man Sv from orthopantomography, with a total of 2910 man Sv.

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Two cases of ameloblastoma with bone formation in a 22-year-old male (case 1) and a 64-year-old female (case 2) were reported.
Radiograms (case 1) showed a extensive bone destruction in the right mandible, in which a spot-and/or trabecula-like bone formation was dominantly observed. Radiograms (case 2) showed a cystlike bone destruction in the left maxilla, in which coarse irregular bone formation was scattered.
Radiographically, there was a slight difference in the bone formation between case 1 and case 2, which was histologically confirmed.

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In the past, it was difficult to find out the supernumerary tooth of the latent state. But recently, Panoramic radiography has become so popular that we have a good opportunity to detect it. This case report is based on 6547 patients who have taken Panoramic radiography in Okayama University affiliated hospital of the Depertment of Oral Radiology from April 1982 to March 1985. In these cases, we have found 171 patients who have supernumerary teeth. Making a clinical and radiological examination, the following conclusions can be drawn from the study.
1) It was 171 (2.6%) patients who have supernumerary teeth, and 225 supernumerary teeth was detected in all 171 patients.
2) With respect to the age of the patients, most were under the age of 9. As to distinction between sexes, the ratio was 5 males: 2 females.
3) As for the common locations, the maxillary anterior region was most common, followed in turn by the maxillary molar region, the mandibular premolar region, and the maxillary premolar region.
4) Most of patients had one supernumerary teeth. Bilateral supernumerary teeth were found in 91.1per cent of those who had more than two.
5) The malformation was most frequently found in the anterior region and in the posterior region. In the premolar region, it was equal to normal formation.
6) Frequency of the embedded supernumerary teeth was 5.6 times that of erupting supernumerary teeth. Embedded supernumerary teeth were seen with horizontal or inverted dislocation or with cystic formation.
7) Malocclusion was most frequently seen in the anterior region as the sequelae of supernumerary teeth.

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Parosteal osteosarcoma showed typical radiographic features including an existance of a thin lucent zone between the tumor and the underlying cortical bone, and a peculiar tendency to encircle the involved bone. Since the jaw bones are rarely involved and only 13 cases have been reported, radiographic features of the jaws have not been well interpreted. We reported a case and reviwed radiographic features of the jaws and the long bones previously reported.
A 70-year-old Japanese woman was affected by an increasing swelling of the left angle of mandible. Although ground glass and expansive findings in a initial stage was similar to fibrous dysplasia, but during her clinical course, the affected radiopaque lesion have been more and more accelerated and the typical lucent zone around the left mandible could be observed in a later stage. This patient was suspected as parosteal osteosarcoma by these radiographic and gross findings.

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