Reduction of redundant shadows using new rotational panoramic radiograph "PM 2002 CC"

Rotational panoramic radiography has diagnostic limitations caused by redundant shadows of the mandibular ramus or the cervical vertebrae. This study compared the appearances of redundant shadows in the PM 2002 CC, a new rotational panoramic radiograph, and the popular Orthopantomograph OP 5. Redundant shadows caused by the mandibular ramus and superimposed on the opposite molar and ramus regions, were carefully analyzed. A considerable difference was observed with respect to x-ray beam alignment. Since the rotational axis of the OP 5 was in the region medial to and behind the third molars, the mandibular ramus created a shadow between the x-ray tube and the rotational axis throughout the period of projection. On the other hand, the rotational axis of the PM 2002 CC was located outside and behind the mandibular ramus during the early stage of projection and with further shifting moved to the region medial to and in front of the mandibular ramus. Accordingly, in the PM 2002 CC, the mandibular ramus was superimposed on the opposite side as a real image and ghost image. The appearance of redundant shadows was influenced by differences in the position of the mandibular ramus in relation to the rotational axis of the x-ray beam. The PM 2002 CC reduced redundant shadows by significantly decreasing the scanning sphere through which x-ray beams from the opposite side project the mandibular ramus. Furthermore, altering the positions of the dry mandibular bone used in the experiments, such as the inclination of the occlusal plane or anterior and posterior shifts, caused greater reduction of redundant shadows in the PM 2002 CC than in the OP 5. Further appearances of redundant shadows caused by metallic wire, plates or bone screws used for the jaw reconstruction were also significantly reduced in the PM 2002 CC.