Neck function in rhythmic jaw activities

Neck function in rhythmic jaw activities. Birgitta Häggman Henrikson 2004. Department of Odontology, Clinical Oral Physiology, Umeå University, and Centre for Musculoskeletal Research, Gävle University, Sweden. Previous studies in animals and humans show anatomic and physiological connections between the trigeminal and the cervical regions. This investigation tested the hypothesis of a functional integration between the human jaw and neck motor systems in rhythmic jaw activities. By means of a wireless optoelectronic 3-D movement recording system, spatiotemporal characteristics of mandibular and head-neck movements were studied during rhythmic jaw opening-closing and chewing tasks, in healthy and in individuals with pain and dysfunction in the jaw and neck region following neck trauma, Whiplash-associated Disorders (WAD). As a basis, a methodological study evaluated the applicability of skin and teeth attached reflex markers fixed to the lower jaw and to the head in optoelectronic recording of chewing movements. The results showed concomitant and coordinated mandibular and head movements during rhythmic jaw tasks. The start of the head movement generally preceded the start of the mandibular movement. For chewing, larger size and harder texture of bolus were associated with larger head extension and larger amplitude of both mandibular and head movements. Immobilization of the head by mechanical fixation deranged jaw motor behaviour with regard to speed and amplitude of mandibular movements. Even with head fixation, muscle activity was present in neck muscles during jaw activities. Compared to healthy subjects, WAD individuals showed smaller amplitudes and disturbed coordination of mandibular and head movements. Furthermore, a dynamic load test showed a reduced endurance during chewing in the WAD group. In conclusion, the results suggest that optimal jaw function requires free unrestricted headneck movements and support the hypothesis of a close functional relationship between the jaw and the neck regions in rhythmic jaw activities. A new concept for human jaw function is proposed, in which “functional jaw movements” are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. The finding of an association between neck injury and disturbed jaw behaviour suggest that assessment and management of neck injured patients should include jaw function.