This study was performed to investigate the factors that might affect mandibular body rotation. For the study, 115 patients with temporomandibular disorder_- and 35 dental students without any signs and symptoms of temporomandibular disorders were randomly selected as the patient group and the control group. respectively. Preferred chewing side, Angle´s classification, lateral guidance pattern, and affected side were clinically recorded, and the amount of mandibular body rotational torque movement was measured in wide opening and closure, in right and left excursion with BioEGNR of Biopak system(Bioresearch Inc., USA). The measured items in each movement were vertical and lateral distance in frontal plane,, right and left rotaional angle in horizontal and in frontal plane: Masticatory Muscle activity and occlusal contact pattern on maximum :hard bitink were also observed synchronously with BjoEMG´K and T-Scan(T ekscan Inc., USA), respectively. The observed items were muscle activity of anterior tern poralis and superficial masster, and tooth contact status related to contact number, force, duration, and occlusal unbalance between right and left arch. The data collected were analyzed by SAS statistical program.
The results of this study were as follows:
1. Mean value of vertical distance in frontal plane in wide opening and closure was more in control subjects than in patients, but there was no difference for rotational angle. In right excursion, rotational angles were greater in patient group than in control group.
2. Comparison among the subjects by preferred chewing side did not reveal any significant difference, but comparison among patients by affected side showed more rotational amount in bilaterally affected patients than in unilaterally affected patients.
3. Comparison among the subjects by Angle´s classification or lateral guidance pattern revealed no difference. There was also no difference between preferred chewing side and contralateral side, and between affected side and contralateral side.
4. Positive correlation in mandibular rotational torque movements were observed among vertical distance, total horizontal rotation angle, electromyographic activity of anterior temporalis, tooth contact number, and tooth contact force but total frontal rotation angle almost did not show any correlation with other variables except vertical distance.
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