The healing process of 18 cases of simple bone cyst following surgical intervention was studied radiographically. From the initial radiographic findings, 13 cases of them were classified into typical simple bone cyst and other 5 cases were into atypical one.
In the typical simple bone cyst, radiographic findings of the affected area changed with time from a ground-glass appearance to a fine-trabecular pattern, and further to a normal trabecular pattern, and finally replacement of a normal trabeculation was observed in all cases up to the latest examination.
In the atypicall simple bone cyst, however, no remarkable changes, recurrence of the lesion or radiopacities which were different from a normal trabecular pattern were found in the affected area following surgical procedures.
From these findings, it was suggested that the initial radiographic features of the simple bone cyst had a close relationship to its prognosis.

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An air-fluid border is used as a radiographic sign which evidences a liquid being accumlated in the maxillary sinus.
Though postero-anterior projection and Waters' projection have been usually used to examine a maxillary sinus in a field of rhinology, some reports indicate that the rotational panoramic radiograph are more useful for the detection of maxillary sinus pathosis. However there have been no investigations concerning the air-fluid border on the rotational panoramic radiograph.
The purpose of this study is to analyze the images of air-fluid borders on the rotational panoramic radiographs clinically and to make an experimental confirmation on the image formations of the air-fluid border. Rotational panoramic radiographs of 45 patients were selected for this investigation, whose maxillary sinuses clearly showed the liquid accumlation on the postero-anterior views and/or Waters' views. Radiographic appearances were analyzed and discussed on the various aspects of the air-fluid border such as clearness, shape, a level, superimposed structures on it, comparison with the radiopacity below it and discrimination from thickened mucosa.
Two models of the maxillaly sinus in the different shapes were prepared for the experimental study on the image formation of the air-fluid border. The models with lead wires on those walls were filled with liquid soap and were projected.
Following findings has resulted from the clinical and experimental study.
1. The air-fluid border was detected on all of 45 rotational panoramic radiographs. Twenty-seven of them revealed a continuous line from an anterior to a posterior border of the maxillary sinus. One of them showed a curved line ascending anteriorly, 7 a horizontal line and 19 a curved line ascending posterorly. A downward bulging of the air-fluid border was found just at the zygomatic process in 9 patients with well-developed pneumatized maxillary sinus. An experimental study proved that a lateral margin of the liquid surface was actually projected on a film as the image of the air-fluid border and that the air-fluid border bulged downward at the zygomatic process because the fluid extended into the zygomatic process in the experimental model with prominent pneumatization.
2. On 28 of 45 rotational panoramic radiographs (60.2%), the air-fluid border appeared as a white lines such as a corticated border. Experimental study suggested the posibility that the appearance of the air-fluid border was accounted for by the Mach-band effect.
It was indicated that the rotational panoramic radiograph was one of the most useful method for the detection of the air-fluid border as well as a postero-anterior view and a Waters' view.

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The present study is based on the roentgenological observation of 59 cases of cystic lesions that were occurred between the upper lateral incisor and the canine. 49 cases were radicular cysts, and 3 cases were primordial cysts which were confirmed by clinical, roentgenological and pathological examination. But the rest 7 cases suspected of the globulomaxillary cyst radiographically were needed to be differentiated. Further retrospective examinations of these 7 cases revealed that 3 cases were radicular cysts, 1 calcifying odontogenic cyst, 1 residual cyst in which the final diagnosis was not established, 1 odontogenic keratocyst, and in 1 case globulomaxillary cyst was not denied by radiologic and pathologic examinations. In 2 cases, the open end of deep invagination of dens in dente were present in close vicinity to the cysts. Therefore, it was thought that most of the cases suspected of the globulomaxillary cyst were radicular cyst and primordial cyst the next. Furthermore it was also suggested that there was a close relationship between the cyst resembled globulomaxillary cyst and these malformed teeth, especially the deep invagination of dens in dente.

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Radionuclide image offers qualitative information which is difficult to be obtained with the use of morphological imaging techniques like computed tomography (CT). However, in the spatial resolution and the ability to differentiate tumor from normal adjacent tissue, radionucleide image is inferior to CT. Particularly, physiologic uptake or false-positive uptake of ⁶⁷Ga-citrate was frequently seen in the oral and maxillo-facial region where inflammatory conditions, such as dental disease and salivary gland inflammation are quite common, resulting in difficulty for the correct evaluation.
To resolve these problems, superimposed images of ⁶⁷Ga-single photon emission CT (SPELT) and CT were constructed. Relative value of superimposed image versus CT, ⁶⁷Ga-planar image and ⁶⁷Ga-SPECT was studied in 8 patients of malignant tumors (In 1 patient, it was examined twice). Three points were marked on the patient's skin surface to adjust the both sections of CT and ⁶⁷Ga-SPECT in the same geometrical plane. Image superimposing procedure was archieved by a recently developed soft ware program after inputting the data of CT into the nuclear medical data processing machine through the medium of magnetic tape.
The tumor detection was well determined in 6 of 9 examined cases by ⁶⁷Ga-planar images. In 8 of 9 cases, tumors were well detected by CT. The tumors examined were detected in all cases by both ⁶⁷Ga-SPELT images and superimposed images.
The extent of lesions to the adjacent tissue was well determined in 3 of 9 examined cases by ⁶⁷Ga-planar images. In 5 of 9 cases, the lesion extent was determined by ⁶⁷Ga-SPELT images, and in 7 of 9 cases by CT. However, superimposed imaging method was more accurate than CT in determining the extent of lesions in all cases. Thus, the superimposing imaging method presented here has been proved to be very useful to obtain both morphological and qualitative information quite effectively.

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Absorbed doses in organs of the head and neck, the breasts, and the gonads were measured in both conventional lateral tomographic and computed tomographic examination of the temporomandibular joint. In addition, those in simultaneous multisection lateral tomography were also measured with 2 types of casette which were a five-film casette of 2 mm interspace with calcium tungstate screen and a seven-film casette of 2mm interspace with terbium activated gadolium oxysulfide screen. Following results were obtained.
1. In the lateral tomographic examinations, absorbed doses in the parotid and the sites in the vicinity of the condyle were larger than those in any other sites in either side, and it was found that absorbed doses were generally smaller when the examined temporomandibular joint was situated in the film side.
2. Absorbed doses were reduced with the use of simultaneous multisection lateral tomography, and absorbed doses per single exposure with the five-film casette of 2mm interspace with calcium tungstate screen were less than those with seven-film casette of 2mm interspace with gadolium oxysulfide screen.
3. In the computed tomographic examination of the temporomandibular joint, absorbed doses of any tissues involved in the x-ray beam were found to be extremely large. It was suggested that the indication and method for the computed tomographic examination should be carefully considered.

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We investigated the status of occupational dental radiation exposures in Japan for the period 1976 1988, by using data of 2 film badge (FB) service companies in Japan.
Results were as follows;
1) The number of FB-wearers in dentistry in Japan has been increasing, and yet it was only about 5, 000 and the rate of FB-wearers in dentists was about 1.96 % in 1988.
2) Mean annual dose equivalent per person in dentistry was 10-20 mrem for this last 13 years. It seems that they have had a tendency to increase slightly, and this tendency is in contrast to medicine which have been decreasing yearly.
The rate of FB-wearers less than the detective limit was about 90%, but the mean annual dose equivalent per person of dental workers except FB-wearers less than the detective limit was similar in level to that in medicine.
3) Mean annual dose equivalent per person in dentists and radiological technicians was larger than that in other dental workers, and the rate of FB-wearers exposed to less than the detective limit was smaller.
4) The majority of FB-wearers was 21-40 in age. In this age range, it seemed that the maj orty of FB-wearers was workers in university hospitals in which have the radiation control system, so the number of FB-wearers in general dental clinics were few.
5) Mean annual dose equivalent per person in FB-wearers of general dental clinics were larger than that of university hospitals and also percentage of FB-wearers exposed to less than the detective limit were smaller.
6) Work category and age range in data system of FB service companies was not necessarily suitable for dentistry, and moreover differs between these two. So, we propose a improvement and unity of data system of FB service companies.

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