オルソパントモグラムにおける歯槽部拡大率に関する実験的研究

抄録

Orthopantomography is being increasingly used not only for radiographic examination of the edentulous jaws, but also for the examination of the alveolar region in dental implants or denture construction. It is essential that dentists know the magnification factor of the alveolar region when orthopantomography is utilized for comprehension of alveolar bone content. In this study, therefore, the vertical magnification factor of the alveolar region at different jaw positions in orthopantomography was obtained experimentally. The results were as follows : 1. The test piece used in this experiment had a bucco-lingual width of 14 mm at the [numerical formula] region, 12 mm at the [numerical formula] region, and 10 mm at the [numerical formula] region. The difference in the vertical magnification factor of the buccal and lingual regions usually varies in proportion to the width between them. But, when the jaws are kept in the standard position and their occlusal plane is horizontal, the vertical magnification factor of the [numerical formula] region is larger than that of the [numerical formula] region. Therefore, the bucco-lingual width and the difference of the vertical magnification factor do not always correspond to each other. 2. When the jaws are kept in the standard position and their occlusal plane is horizontal, the difference in the calculated vertical magnification factor at the middle of the alveolar region is not so different in the upper and lower jaws, nor in the individual regions. The maximum vertical magnification factor in the upper jaw is 1.23 of the <7|>___- region and the minimum factor is 1.22 of the <3|>___- region. Also the maximum vertical magnification factor in the lower jaw is 1.23 of the <7|>^^^- region and the minimum factor is 1.20 of the <4|>^^^- region. 3. The vertical magnification factor in the bucco-lingual portion of the alveolar region does not correspond to the estimated factor while the jaws are kept in the standard position while their occlusal plane is moved upward. Theoretically, the vertical magnification factor of the lingual portion should be larger than that of the buccal portion, but estimated factors were not always obtained. In this experiment the vertical magnification factor of the middle of the alveolar region did not change mathematically when the occlusal plane was moved upward. 4. The vertical magnification factor of the middle of the upper alveolar region is smaller than that of the lower alveolar region while the jaws are kept in the standard position and their occlusal plane is moved downward. The vertical magnification factor changes gradually to a smaller one moving to the <4|>___- region from the <7|>___- region. The vertical magnification factor of the lower jaw also changes gradually to a smaller one moving to the <4|>^^^- region from <7|>^^^- region as in the upper jaw. 5. The vertical magnification factor of the middle of the alveolar region, while the jaws are kept anteriorlly 10 mm from the standard position and their occlusal plane is horizontal, is smaller than that of the jaws kept in the standard position and kept posteriorlly 10 mm from the standard position. 6. Because the x-ray beam in orthopantomography is projected upward to the jaws, it makes a different vertical magnification factor in the upper and lower alveolar region. The antero-posterior position of the jaws and the vertical angulation of the occlusal plane are very influential in changing the vertical magnification factor. Then, it is essential to keep the jaws in the standard position and their occlusl plane horizontal when the orthopantomography is applied for the survey of the vertical alveolar bone content. However, it is more important to keep the horizontal occlusal plane than to keep the jaws in the standard position.