[Clinical study on the relationship between chewing movements and temporomandibular joint abnormalities].

Chewing movements are accomplished by the harmonious function of the stomatognathic system. Therefore, TMJs play important roles in chewing movements. Recently, significant findings on TMJ abnormalities have been obtained from many studies. However, the relationship between chewing movements and TMJ abnormalities remains unclear. The purpose of this study was to examine how TMJ abnormalities were reflected in chewing movements. Incisor point movements during chewing (chewing pattern) were investigated in 150 abnormal and 25 normal subjects using Sirognathograph Analysing System. Abnormal subjects were composed of 45 patients with anterior disk displacement with reduction (reciprocal click), 20 patients with anterior disk displacement without reduction (closed lock), 50 patients with osteoarthrosis and 35 patients with MPD syndrome. Analysis of condylar movements during chewing were also performed in 9 normal and 20 abnormal subjects. The results were as follow; 1. Subjects with TMJ abnormalities tended to show abnormal chewing patterns when chewing at their non-abnormal sides. 2. TMJ abnormality of each different type tended to show its respective characteristic chewing pattern. 1) Subjects with osteoarthrosis and reciprocal click without condylar posterior dislocation tended to show deviation of the turning point to the non-chewing side, with a convex opening path in the frontal plane and a lack of anteroposterior width in the sagittal plane. This finding was associated with the limitation in movement of the abnormal-side condyle. 2) Subjects with reciprocal click with condylar posterior dislocation tended to show a concave opening path and reversed or cross-over patterns in the frontal and horizontal planes, respectively. This finding was associated with the movement of the abnormal-side condyle in the medio-anterior direction during the initial phase of opening. 3) Subjects with closed lock without condylar posterior dislocation tended to show deviation of the turning point to the non-chewing side, with a concave opening path in the frontal plane and a lack of anteroposterior width in the sagittal plane. This finding was associated with the severe limitation in movement of the abnormal-side condyle. 4) Subjects with closed lock with condylar posterior dislocation characteristically tended to show reversed or cross-over patterns in the horizontal plane. This finding was associated with the movement of the abnormal-side condyle in the medio-anterior direction during the initial phase of opening. However, this movement was smaller than that of the reciprocal click. 3. Subjects with MPD syndrome showed chewing patterns similar to those of normal subjects. From the results, close relationships were found between chewing movements and TMJ abnormalities.