The genetically significant dose (GSD), per Caput mean bone-marrow dose (CMD) and leukemia significant dose (LSD) from orthopantomographic examinations have beenestimated on the basis of a nation wide survey. The annual number of orthopantomographicexaminations in 1974 was estimated to be 1.65×10⁶. The organ or tissue doses weremeasured with an ionization chamber and a thermoluminescent dosimeter placed on variouspositions of the RANDO phantom. The resultant GSD, CMD and LSD was 0.088 pradper person per year, 66 μrad per year and 61 μrad per person per year, respectively.
The risk of stochastic effects associated with dental X-ray diagnostic examinations includingintra-oral radiography was estimated using data on the number of dental diagnosticexaminations and a weighting factor recently recommended by the International Committeeon Radiological Protection. The annual total effective dose of dental X-ray diagnostic examinationsfor adult patients was 86.2 krad (0.862 kGy) for intra-oral radiography and 20 krad (0.2 kGy) for orthopantomography, with a total 106.2 krad (1.062 kGy). The InternationalCommittee on Radiological Protection has concluded that the mortality risk factorfor radiation induced stochastic effects is about 10^-4 rad^-1 (10^-2 Gy^-1). The total stochasticrisk from dental X-ray diagnostic examinations was estimated to be 0.13 person per yearfor the whole adult population in Japan.

抄録全体を表示

Dental porcelain has been added small concentrations of uranium salts for hue andfluorescence by simulating the color and appearance of natural teeth. The dosimetry ofthese radiation from the uranium and their daughters are important in an aspect of radiologicalhealth. In this paper, the measurements of alpha-ray by surface barrier siliconsemi-conductor detector and of gamma-ray by lithium drifted germanium semi-conductordetector were reported. These techniques are very easy and conventional. In the alpha-raydosimetry, the factors of geometry and the loss of the alpha-ray energy in the procelainwere calculated by the computer simulation and the distribution of the kinetic energy ofalpha-rays was estimated. Also in the gamma-ray spectroscopic measurements, we observedthe gamma-ray peaks at 63.0 keV and 92.3 keV (from ²³⁴Th) and 185.4 keV (from ²³⁵U). Thecontent of uranium were estimated about 200 ppm in the samples of U.S.A. by both measurements.The uranium contents of the sample of Japan other than U.S.A. were almostone third of the sample of U.S.A.

抄録全体を表示

In most of the dental x-ray machines, cathode filament heating current and tube hightension to the x-ray tube, are supplied by one iron core transformer. In those machines, x-rays at an intended constant intensity can not be generated from a moment when x-raytimer is switched on. It is generally found that about 0.2 seconds time delay exists untilx-rays reach at an intended intensity after the timer is in action.
When an intra oral film needs to be exposed to x-rays 0.2 seconds, patient should notmove at least 0.4 seconds. Such fact has to be recognised by every dentist, especially concernedto exposing children.
In this investigation two kinds of pulses were recorded simultaneously, one was pickedup from electric source supplied to x-ray generator, and the other was obtained from aphotomultiplier tube by which emitted fluorescences from a small piece of fluoroscopic screentransmitted through lead glass during x-ray exposure were converted into puls current.Comparing both kind of pulses obtained from each dental x-ray machine the time delays were obtained.
Following conclusions were obtained;
1. Time duration of timer in action was defined as radiographic time not as exposure time. The exposure time was defined as the time obtained from number of pulses of which height reach at a constant of an intended x-ray intensity. Time difference between the radiographic time and the exposure time was defined as non effective time (so-called preheating time).
2. Non effective time was differed among machines from 0.16 seconds to 0.2 seconds.
3. Adequate radiographic time using Group D speed dental x-ray film for maxillary molar region was from 0.5 seconds to 1.1 seconds in different machine. The lowest exposure air dose was 0.38 R and the highest was 1.28 R.
4. In use of automatic exposure control timer, DOSIMATIC, with lower input voltage than the nominal, decrease of penetrating power of generated x-rays was smaller than that of expected. Half Value Layer of generated x-rays by 95 volts was 1.5mm Al, being 1.6mm Al by nominal 100 volts. Therefore, it may be considered that droped tube voltage might be somewhat depressed by compensating phenomena with small tube current.
5. The pulsmeasurement method applied in this study may be used to find some disorders existing in x-ray generator. When an irregularity of pulsheight in exposure time is noticed, some disorders may exist in generator even though the machine is yet usable. These phenomenon were observed in two old dental x-ray machines.
6. Single transformer x-ray machines which are widely used in dentistry are not prefered for intra-oral radiography in children of under five years old.

抄録全体を表示

Positional abnormalities of teeth is mainly composed of impaction, transposition, androtation, all of which are rarely observed in deciduous dentition but more frequently in permanentdentition. Generally, rotation of teeth can be classified as follows: (A) long axisrotation, (B) medio-distal inclination, (C) labio-lingual inclination. The present researchchiefly analyzed the process of (A) long axis rotation. The present authors selected thechronological radiograms stored in the Department they belong to, which submitted a greatdeal of information about individual patterns of the successional replacement. They specificallyanalyzed the behavior of first and second premolars in the mandible where long axisrotation was observed and obtained the following results. The appearance of rotated premolarsin the mandible, when examined chronologically to obtain radiographic findings oftheir developemental process, could be traced back to when such teeth had already beguneven in the stage of crypts, and the rotation was rarely observed to commence during thestage of eruptive acceleration.
1.) Out of 386 first premolars in mandible, 57 (14.7%) and also out of 431 second premolars in mandible, 89 (20.6%) were observed to have the axial rotation begun either in the period of tooth germs, eruptive acceleration, and alveolar emargence.
2) The authors observed that 28 first premolars, out of 57, and 58 second premolars, out of 89, had the history of their rotation already begun in the state of tooth germs and continued until the terminal stage of successional replacement.
3) In a comparatively fewer cases, the rotation of axis was corrected by the approximate teeth already erupted, on the contrary, the rotation began away from the normal direction.

抄録全体を表示

To evaluate the usefulness of conventional periapical examination, the fourteen intraoralroentgenograms of 447 students (the average age of 23.4) in Aichi-Gakuin University, School of Dentistry were examined.
The results obtained were as follows:
1) In 12516 total teeth observed, 12171 were present, 337 missed and 8 embedded respectively. Of the present teeth, 2399 treated and 879 untreated teeth were observed.
2) 1062 teeth of the treated or untreated, that is 8.5% of the total, were suspected the invasion upon pulp cavity. About 70% of the 849 treated teeth showed inadequate root canal fillings. About a half of 213 untreated teeth had no evidence of endodontic therapy, and about 40% of the teeth showed inadequate root canal fillings.
3) The size of periapical lesions was varied according to the conditions of root canals. In the teeth of inadequate root canal fillings, various sizes of the lesions were observed, but over 50% of the teeth of adequate root canal fillings showed no periapical lesion.
4) Regarding to the size of periapical lesions between 2-4 mm and over 4 mm in diameter, the boundary and the shape were compared. As to the shape, the ratio of circle to non-circle was about 3: 2 in both size, but on the boundary the ratio of the indefinite to the definite was not the same. In the former 7 3 and in the latter 5.5: 4.5 were obtained.

抄録全体を表示

Now, so called Orthopantomography plays an important role in diagnostic radiology.Therefore, a many researches were carried out about the image producing principle and itsapplication of orthopantomography. Notwithstanding its significant standpoint, however, the image producing factor and the principle in orthopantomography have been confusedwith that of tomography in textbook and another articles because orthopantomography isgenerally said to be a modified tomographic method for a long period of time.
The authors suggested that the principle of orthopantomographic method seems to be more like that of curved surface slitgraphic method than of true tomography, and certified the principle of orthopantomography for the adjustment of aforementioned misconception in the past. The obtained results are as follows;
1. In empirically and theoretically, the authors demonstrated that the image producing principle of orthopantomography seems not to be the applied form of tomographic conception.
2. Orthopantomography is the roentgenographic method as termed “curved surface slitgraphy” and in principle, is no other dissimilarity between orthopantomography and NUMATA's roentgenographic method that is considered to be another roentgenographic method.

抄録全体を表示

X-ray film emulsion consists of silver halide grains of various sizes, which have a large dispersion. If therefore, silver halide grains are considered to be bleached by reversal development from larger grains of higher sensitivity to smaller ones of lower sensitivity, it is to be expected that the image will be formed by the blackening of minute silver halide grains at the second exposure
Based on the assumption, the image quality of reversal X-ray film was experimentally investigated.
As the result of experiment, it became clear that reversal X-ray films had better granularity than that of negative X-ray films in the high exposure domain above a certain exposure time. They are also excellent for clinical purposes and detailed diagnostic views can be formed from them.

抄録全体を表示

A case of pyknodysostosis in 10-year-old girl has been reported, especially on the radiographic findings. Our case revealed that a sclerosing tendency of the mandible is slight as compared with the adult cases of this syndrome previously reported. We also pointed out the following as a specific feature, that is; mandibular notch was deeply depressed and therefore, both mandibular condyle and coronoid process appeared to be quite lo ng at a glance.

抄録全体を表示

An unusual case of multirooted premolars has been reported. The patient was 31-year-old man and all his premolars in the maxilla showed three-rooted and all premolars in the mandible showed double-rooted appearance radiographically. Survey was also carried out on the cases of premolars with supernumerary roots in the maxilla and the mandible reported in Japan during the past 42 years (1935-1977). Multirooted lower premolars showed rather variable root bifurcation compared with upper premolars and it was also emphasized that these findings should be taken into consideration as clinical care.

抄録全体を表示