Abstract
This paper described a rare case of jaw trismus caused by the hyperplastic coronoid process and reported the result of a study on the positional interrelation between the process and the zygomatic arch.
A 19-year old boy visited our clinic with complaint of long-standing jaw trismus. The trismus was severe and no lateral movement of the jaw was noticed. Clinical examinations could not reveal any pathologic finding except tenderness on the coronoid process region. On orthopantomograhic and horizontal tomographic films, the overgrown process was found and the coronoid process was situated near the inner surface of the zygomatic arch. By these results, it was found that the overgrown coronoid process interfered with the movement of the mandible.
The coronoidectomy was carried on the both sides. The positional interrelation between the inner surface of the arch and the process detected by the preoperative X-ray films was found to be correct. Good jaw movement was gained postoperatively.
The extirpated process was very thick and extremely elongated and was examined histopathologically. Narrow bone marrow and its surrounding thick cortical layer in which some lines dyed densely by H-E, which were thought to be the result of the bone deposition, were observed. But no neoplastic figure could be found.
The positional interrelation between the process and the arch was examined by using both sagittal and horizontal tomography. The results concerned with volunteers were as follows: At the time of teeth occluded, the tip of the process was situated vertically 1.1mm±5.0 (right side) and 0mm±3.9 (left side) above the lower border of the arch.
The horizontal distance between the inner aspect of the arch and the process was calculated as 9.5mm±5.1 (right) and 9.7 mm±5.2 (left). From these data, it was clarified that the diversity of the coronoid position was unexpectedly great. Regarding the reported case, the tip of the process was situated extremely above the lower edge of the arch (right was 16 mm above and left 18 mm) and the process situated near the inner surface of the arch (the distance was 3mm on the right and 0mm on the left). These findings were greatly out of the range of the standard classfication of the controls. By the facts mentioned, tomography was thought to be valuable in examining the anatomic position of the coronoid process.
