A study on reliability of the tomographic image of the temporomandibular joint

Summary For this study, seven different types of phantom were made simulating the condyle. The phantoms attached to a human dry skull were tomographed using the Polytome-U, under identical conditions to those of tomography for patients. There was no significant difference of the images between tube side and film side of the mandible. The images of the medial part of the TMJ were clearer than that of the lateral part. A discrepancy of contours on the focal plane between the phantom and the tomographic image occurred when the inclination of the phantom surface was larger than the maximum exposure angle. Concerning the influence of focal movements to image quality, the images obtained from hypocycloidal movements were superior with minimum superimposition, although the contrast of the image varied when the phase of the hypocycloidal movements were altered. Any sectional images were not manifested with the phantoms when the inclination of the phantom surface was larger than 23 degrees. Furthermore, 106 condyles from human dry skull were examined on the area of which the inclination of the condylar surface was less than 23 degrees. The mean latero-medial distance of the area was 14.1mm, which corresponded to 75% of whole latero-medial distance of the condyle.