Diagnostic Application of Functional Coupling between Jaw Function and Balanced Head Movement

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We have previously demonstrated the existence of a functional-coupling between the head and the mandible. The objective of the present study was to reveal mechanisms of this functional coupling and effects of occlusion on this coupling.We measured tridimensionally both the movement of the head and mandible and the electromyographic activities in the masticatory and head-neck muscles in healthy subjects and patients of temporomandibular disorders.In healthy subjects, heads moved cyclically in the same cycle time as that of both masticatory and tooth-tapping jaw movements. The head underwent a rotation-like sagittal movement whose rotation center located above the cranial base point. The masticatory muscles and the neck muscle (the stemocleidmastoid muscle) showed rhythmical activities synchronized with jaw movements. The neck muscle activity showed a linear correlation with masticatory force. Additionally, it was seem that the neck muscle began the activity before the occlusal phase of jaw movements. It is demonstrated that the neck muscle contribute to the synchronized head movement in the anticipatory manner. However we could not confirm that this coordinated head movement would influenced on whole body flicking.In patients of temporomandibular disorders, the degree of synchronization between head and jaw movement was approximately three-quarters of that with healthy subjects during mastication and tooth-tapping. This variable was influenced by existence of TMD symptoms, especially limited jaw opening, which suggests mechanical feature of the coupling between head and jaw movement. Contribution of occlusal features to head movement has not been confirmed in our study.