Abstract
Chronic pain in the orofacial region is common worldwide. Pain seems to affect the jaw motor control. Hence, temporomandibular disorders (TMD) are often accompanied by pain upon chewing, restricted mouth opening and impaired maximal bite forces. However, little is known on the effects of pain, in particular the effects of chronic jaw muscle pain on precision biting. The aim of the study was to investigate the effect of chronic and acute jaw muscle pain on oral motor control during precision biting in humans. Eighteen patients with chronic masseter muscle pain and 18 healthy participants completed the experiment. All participants were examined according to the Diagnostic Criteria for TMD. Experimental acute pain was induced by bilateral, simultaneous sterile hypertonic saline infusions into the healthy masseter muscles. A standardized hold and split biting task was used to assess the precision biting. The data was analyzed with non-parametric statistical tests. The results showed no significant differences in the hold forces, split forces, durations of split or peak split rates within or between the pain and pain-free conditions. The mean split rate increased significantly compared to baseline values both in the chronic patients and the pain-free condition. However, this increase was not evident in the experimental acute pain condition. Further, there were no significant differences in the mean split rates between the conditions. The data suggest that jaw muscle pain does not seem to alter precision biting in humans, however, the possibility that a nociceptive modulation of spindle afferent activity might have occurred but compensated for cannot be ruled out.
Highlights
Chronic pain is a large and worldwide health problem with approximately 20% of the population reporting chronic pain of moderate to severe intensity (Breivik et al, 2006)
There were no significant differences between the chronic pain patients and the healthy participants regarding any of the psychosocial symptoms (Mann-Whitney Rank Sum test; P > 0.05) (Table 1)
Majority of the chronic pain patients (61%) were diagnosed with local myalgia in the masseter muscles and 39% were diagnosed with myofascial pain with referred pain in the masseter muscles according to DC/temporomandibular disorders (TMD). 61% of the chronic patients had low pain intensity and low grade of disability (GCPS-7), 33% had high pain intensity and low grade of disability, about 6% had moderately limiting high disability and none of them had severely limiting high disability
Summary
Chronic pain is a large and worldwide health problem with approximately 20% of the population reporting chronic pain of moderate to severe intensity (Breivik et al, 2006). Several studies have either failed to or have presented contrary data to the fundaments of these theories (Stohler et al, 1988; Lund et al, 1991; Svensson et al, 1997, 1998; Svensson and Graven-Nielsen, 2001; Sae-Lee et al, 2008a,b). This contrasting evidence in the association between pain-related TMD and masticatory muscle function led to the integrated pain adaptation model which was presented in 2007 (Murray and Peck, 2007). The theory proposes that just as an individual’s experience of pain varies, so will an individual’s motor response
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