-Abstract-
This study was performed to investigate the factors affecting muscle activity and
cephalometric variables according to change 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 t body plumb line in sagittal plane were observed clinically and
electromyographic(EMG) activity of anterior temporalis, masseter, sternocleidomastoideus,
and trapezius on clenching were recorded with BioEMG in four head
postures, which were natural head posture(NHP), forward head posture(FHP), 20°
downward head posture(DHP).
Cephaloradiographs when 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, 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 program. 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 activity 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 showed correlation between these variables with change from
NHP to FHP, and from NHP to UHP.
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