This study was performed to investigate the factors affecting muscle activity and cephalometric variables according to changes of head postures. For this study, 150 patients with temporomandibular disorders and 80 dental students without any signs and symptoms of temporomandibular disorders were selected as the patients group and as the normal group, respectively. Head position to body-midline in frontal plane and upper quarter posture to body plumb line in sagittal plane were observed clinically and electromyographic(EMG) activity of anterior temporalis, masseter,,sterriocleidomastoideus, and trapezius on clenching were recorded with BioEMG® in four head postures, which were natural head posture(NHP), forward head posture(FHP), 20´ upward head posture(UHP), and 20´ downward head posture(DHP).
Cephaloradiographs were also taken in the same head postures as in EMG taking, but that was taken only in NHP for the patient group. Cephalometric variables measured were SN angle, CVT angle, atlas inclination angle, occlusal plane angle, Me-C2 angle, pharyngeal width, occiput-axis distance, area of pharyngeal space, and cervical curvature. The data were analyzed by SAS statistical t. _ ogram.
The results of this study were as follows
1. Between the patient and the normal group, there were significant difference in distance from plumb line to acromion, eye-tragus angle, electromyographic activity of the four muscles, and cephalometric variables of linear measurement.
2. There was no consistent pattern of correlation between upper quarter posture, EMG activity and cephalometric variables in any case without relation to cervical curvature and head position in frontal plane.
3. Sternocleidomastoid muscle only showed variation of electromyographic activty with changes of head
postures, but all the muscles did show correlation with head postures.
4. All the cephalometric variables measured in this study showed difference of mean value by head
posture, and CVT angle, pharyngeal width, occiput-atlas distance, and area of pharyngeal space
showed correlation between these variables with change from NHP to FHP, and from NHP to UHP.
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