Effect of posture and head position on mandibular position and jaw function

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Introduction : Head posture effects on craniofacial morphology, and it is hypothesized that soft-tissue stretching by changes in head posture effects on neuromuscular system in jaw and head-neck regions. In this study, effect of head posture on mandibular rest position, jaw-neck muscles' activity and position of chin's skin was investigated.Subjects and methods : The subjects (ten adult males) sat on the chair, and head was held extended, protracted and rotated to right side for 3 seconds respectively after natural head position for 3 seconds keeping mandibular rest position. The head position, madibular rest position, electromyograms in right and left sides of sternocleidomastoid, anterior digastric and masseter muscles and position of chin's skin were recorded.Results : Postural activity was small during natural head position. When head was held extended keeping mandibular rest position, postural activity significantly increased in sternocleidomastoid, anterior digastric and right ma … More sseter muscles, and mandibular rest position and position of chin's skin inferiorly sifted compared with those during natural head position.When head was held protracted keeping mandibular rest position, postural activity significantly increased in left masseter muscle, and mandibular rest position scarcely sifted compared with those during natural head position.When head was held rotated to right side keeping mandibular rest position, postural activity significantly increased in sternocleidomastoid and left anterior digastric muscles, and mandibular rest position sifted to left side and upward compared with those during natural head position.Discussions : These findings indicate that head posture effects on mandibular position, jaw-neck muscles' activity and position of chin's skin. The results of postural muscle activity suggest that neuromuscular system in jaw and head-neck regions is modulated to keep mandibular rest position according to head position. The increased postural activity in anterior digastric muscle may cause the sift of mandibular rest position to opposite direction to that of head movement. Less