The purpose of this study is to evaluate internal derangements of the temporomandibular joint radiographically by Computed Radiography (CR).
CR system, which uses a process known as scanning laser stimulated luminescence, made it possible to show the soft tissue images as well as the bony structures, owing to wide latitude of Imaging Plate (IP) and image processing.
The following results were obtained:
1) The images of TMJ were obtained clearly by a tomographic angle of 16° (spiral movement) and collimating to a 5cm diameter at the IP's surface. The spatial frequency enhanced imge (0.75c/mm) which emphasized edge effect were clearer than the gradient enhanced image.
2) A comparison of the disk images between arthrogram and CR in 10 cases was performed. In six out of seven cases, CR images gave signs of the anterior disk displacement that was subsequently confirmed with arthrograms, while three others hardly showed the disk images in CR which were demonstrated arthrographically as normal joints.
3) In the CR analysis of 176 cases (244 joints), the disk images were divided into 3 patterns: Type A similar to anterior disk displacement with reduction, Type B to without reduction and No abnormality detected to no anterior displacement. The disk abnormalities such as Type A and Type B were seen in about one half of all joints.
4) In the correlation between clinical symptoms and the disk images, Type A was definitely associated with clicking and Type B with limitation of opening. Bony changes were predominant in cases which showed Type B group than other groups.
5) With regard to follow-up examination of 36 cases (50 joints), improved and advanced cases were seen in 15 (30%) and 9 joints (18%) respectively. 26 joints (52%) remained unchanged. The position of mandibular head to fossa changed from posterior to central, anterior and inferior in improved cases.
From these results, it was suggested that CR was valuable to diagnose internal derangements as a non-invasive method, and further, has provided useful informations for treatment planning and follow-up examinations.
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