| 摘要 |
PURPOSE:To perform correct obliquity photographing of jaw by changing the position of the rotating center axis of an arm having an X-ray tube at one end and an X-ray film cassette at the other end in such a manner that the distance between the focus of the X-ray tube and the film is made constant over the entire area of the jaw. CONSTITUTION:The line Y-Y' including the anterior tooth P indicates the median sagittal plane of the jaw head part, and the direction of the orthogonal base line Ls is set at the horizontal incident angle (alpha=0 deg.)XCO of the radiation central axis XC of an X-ray tube 7X. The film 14M in the cassette is disposed opposite to the X-ray tube 7X. The rotating central axis position of an arm 6 for jaw photographing at up to horizontal incident angle alpha=49 deg. is at the point A and if alpha is above this, said position shifts to the point B, thus the distance between the X-ray tube 7X' and the film 14M' is constant and only the axial fulcrum 4 moves like an arrow. Further, the X-ray tube 7X', the film 14M' move to the positions 7X'', 14M'', respectively and when beta=49 deg. is reached, the axial fulcrum position 4 advances to the point C. If it advances further, it returns to the point A. Hence, all the X-ray radiation central axes XC intersect orthogonally, whereby the square projection is accomplished and the distortion-free image is obtained. |
