Pantomograph に関する基礎的研究

Abstract

In dental panoramic radiography the Palomex (Orthopantmograph) and Panex (Ellipsopantomograph) are widely used in Japan. These two machines have different mechanical movements. The Palomex has a three-axis system and the Panex a mono-axis ellipsoid orbit system. In this study, thickness of the tomographic layer, magnification and obstacle shadows of the two machines were compared. The results obtained are as follows : 1. The thickness of the tomographic layer in a phantom was measured. The thickness in the anterior region was 5.4mm. in the N position and was 13.8mm. in S position with the Palomex. On the Panex, when the jaw-pad-width was maximum, the thickness in the anterior region was 6.4mm. ; the thickness was 6.8mm. when the jaw-pad-width was minimum. The thickness in the posterior region was 16.5mm. in the N position and 16.4mm. in S position with the Palomex. On the Panex, when the jaw-pad-width was maximum, the thickness of the posterior region was 18.0mm. and 23.0mm. when the jaw-pad-width was minimum. The thickness of the tomographic layer is directly proportional to the distance from the rotational axis to the object and is inversely proportional to the slit-width facing the film. 2. The vertical magnification factor of the anterior region was 1.31-1.37 in the N position and 1.17-1.26 in the S position with the Palomex. On the Panex the factor was 1.08-1.12. In the posterior region vertical magnification was 1.25-1.46 in the Palomex and 1.12-1.16 in the Panex. The horizontal magnification factor in anterior region was 1.08-1.60 in the N position and 1.01-1.38 in the S position with the Palomex. On the Panex it was 0.62-1.24. In posterior region horizontal magnification was 1.20-2.00 in the Palomex and 1.10-1.53 in the Panex. 3. In panoramic radiography, sometimes, a shadow of the opposite object is superimposed on the tomographic layer as an obstacle shadow. This phenomenon results from the presence of a very radiopaque substance in the irradiation area but outside of the tomographic layer.