Cardiovascular and muscle activity during chewing in whiplash-associated disorders (WAD).
From: Arch Oral Biol. 2010 Apr 20. [Epub ahead of print]
The present study aimed to elucidate possible physiological mechanisms behind impaired endurance during chewing as previously reported in whiplash associated disorders. We tested the hypothesis of a stronger autonomic reaction in whiplash associated disorders than in healthy subjects in response to dynamic loading of the jaw and neck motor system.
Cardiovascular reactivity, muscle fatigue indicies of EMG, and perceptions of fatigue, exhaustion and pain were assessed during standardised chewing. Twenty-one whiplash associated disorders subjects and a gender/age matched control group participated. Baseline recordings were followed by two sessions of alternating unilateral chewing of a bolus of gum with each session followed by a rest period.
More than half of the whiplash associated disorders subjects terminated the test prematurely due to exhaustion and pain. In line with our hypothesis the chewing evoked an increased autonomic response in whiplash associated disorders exhibited as a higher increase in heart rate as compared to controls. Furthermore, we saw consistently higher values of arterial blood pressure for whiplash associated disorders than for controls across all stages of the experiment. Masseter EMG did not indicate muscle fatigue nor were there group differences in amplitude and mean power frequency. Pain in the whiplash associated disorders group increased during the first session and remained increased, whereas no pain was reported for the controls.
More intense response to chewing in whiplash associated disorders might indicate pronounced vulnerability to dynamic loading of the jaw and neck motor system with increased autonomic reactivity to the test. Premature termination and autonomic involvement without EMG signs of muscle fatigue may indicate central mechanisms behind insufficient endurance during chewing.
In a previous study in J Dent Res. 2004 Dec;83(12):946-50, it was noted; Jaw movements are the result of coordinated activation of jaw and neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital, and cervical spine joints. Thus, jaw function involves integrative jaw and neck motor control. Given that natural jaw function requires a healthy state of both mandibular and neck motor systems, injury to any of the joints involved might derange jaw function. In fact, the authors had recently shown an association between neck injury and deranged jaw function, as reflected by reduced amplitude, speed, and disturbed coordination of head and mandibular movements.
They note that it has been reported that almost 25% of tmj pain patients have a history of trauma to the head-neck, mainly whiplash trauma. Compared with tmj pain patients without a history of trauma, patients with posttraumatic tmj pain seem to present with more severe jaw-facial pain and dysfunction, and it has been suggested that the prognosis for recovery from jaw-face pain and dysfunction is lower in this group.
Furthermore, it has been reported that post-traumatic tmj pain patients have more symptoms associated with
affective disorders, e.g., sleep disturbances, respond more poorly in reaction time tests, and overall tire more easily than do non-traumatic tmj pain patients. The fact that many of these symptoms are also associated with closed-head injuries indicates that the etiology of posttraumatic tmj pain differs from that of non-traumatic tmj pain.
The authors results corroborate the suggestion that patients with jaw-face pain and dysfunction and with a history of neck injury are unique and more complex with regard to the spread and severity of pain and dysfunction.
Their finding of a severely reduced endurance during chewing in whiplash associated disorders individuals suggests an association between neck injury and impaired functional capacity of the human jaw motor system. Based on these results, examination of jaw function seems recommendable as part of the routine evaluation of whiplash associated disorders patients, and for this, the endurance test described in this study could be a useful tool. Finally, from data suggesting that jaw function involves simultaneous neuro-muscular activation of movements in the temporomandibular, atlantooccipital, and cervical spine joints, and that neck injury can disturb natural jaw function, the authors propose that a suitable term for the condition involving both neck and jaw disorders could be “Cervico-Cranio Mandibular Disorders” (CCMD).
In Swed Dent J. 2004;28(1):29-36, their study indicated the individuals in the whiplash associated disorders group had also more signs of tmj dysfunction. The maximum mouth opening capacity was 48 mm in the whiplash associated disorders group and 54 mm in the C group. In the whiplash associated disorders group 17% had a mouth opening capacity < 40 mm compared with 2% in the C group. Pain on palpation of the jaw muscles and on lateral palpation of the temporomandibular joints was more common in the WAD group. Pain on mandibular mobility was reported by 30% in the whiplash associated disorderswhiplash associated disorders group and by 3% in the C group.
