Effects of experimental pain on jaw muscle activity during goal-directed jaw movements in humans

Abstract

To study the effects of masseter muscle pain on jaw muscle electromyographic (EMG) activity during goal-directed tasks. Mandibular movement was tracked and EMG activity was recorded from bilateral masseter, and right posterior temporalis, anterior digastric, and inferior head of lateral pterygoid muscles in 22 asymptomatic subjects at postural jaw position, and during three tasks: (a) protrusion, (b) contralateral (left), (c) open jaw movement. Tasks were performed during three conditions: control (no infusion), test 1 [continuous infusion into right masseter of 4.5% hypertonic saline to achieve 30-60 mm pain intensity on 100-mm visual analog scale (VAS)], and test 2 (isotonic saline infusion; in 16 subjects only); the sequence of hypertonic and isotonic saline was randomized. The average EMG root-mean-square values at 0.5 mm increments of mid-incisor-point displacement were analysed using linear mixed effects model statistics (significance: P < 0.05). Right masseter hypertonic saline infusion resulted in significantly (P < 0.0005) more pain (mean +/- SD VAS 47.3 +/- 14.3 mm) than isotonic infusion (12.2 +/- 17.3 mm). Although there was evidence of inter-subject variation, the principal EMG findings were that the significant effects of hypertonic saline-induced pain on EMG activity varied with the task in which the muscle participated irrespective of whether the muscle was an agonist or an antagonist in the tasks. The direction of the hypertonic saline-induced pain effect on EMG activity (i.e., whether the hypertonic saline-induced EMG activity was less than or greater than control EMG activity) could change with the magnitude of jaw displacement. Hypertonic saline infusion had no significant effect on postural EMG activity in any of the recorded jaw muscles. The data suggest that under constrained goal-directed tasks, the pattern of pain-induced changes in jaw muscle EMG activity is not clear cut, but can vary with the task performed, jaw displacement magnitude, and the subject being studied.

Reorganization of muscle activity in patients with chronic temporomandibular disorders

“…Results of the EMG during MVC and during chewing, taken together, confirm that pain in masticatory system may involve differential effects dependent of the task, among other factors (Sae-Lee et al, 2008;Hodges & Smeets, 2015;Peck et al, 2008;Shimada, et al, 2013;. Therefore, the nervous system seems, in fact, to have a range of options to achieve the goal of protection (Hodges & Tucker, 2011).…”

“…Therefore, researchers have investigated the relationship between orofacial motor function and pain by means of EMG analysis, in standardized settings, without the interference of confounding factors. Based on these studies (Sae-Lee et al, 2008;Shimada, Baad-Hansen & Svensson, 2015;Shimada, Hara & Svensson, 2013) and theories (Hodges & Tucker, 2011;Hodges & Smeets, 2015;Peck, Murray & Gerzina, 2008) it has been proposed that pain in jaw muscles, rather than a stereotyped change, may involve differential effects as increased, decreased, or redistributed activity with reorganization of activity occurring within and between muscles. Authors (Sae- Lee et al, 2008;Shimada et al 2013; have suggested that investigations with patients are required.…”

How does pain affect jaw muscle activity? The Integrated Pain Adaptation Model

“…10,18,20,21,23,30 Thus, many EMG studies have shown that clinical muscle pain has very little effect on jaw muscle EMG activity, whereas the Vicious Cycle Theory would predict increases in jaw muscle activity. Although some studies have reported increases in EMG activity in association with pain (see above), the increases are very small (only a few lV) and not to a level of clinical significance that would allow a muscle to be classified as ''hyperactive'' or expected to cause pain.…”

Dysfonctionnements musculaires douloureux de l’appareil manducateur et dysfonctionnements cervicaux et linguaux connexes (3e partie)

“…Mais récemment, on a montré que les parties latérale et médiale du chef supé-rieur n'avaient pas le même comportement ; sa partie médiale se contracte avec le chef inférieur, et seule sa partie latérale se contracte à la fermeture, en rétropulsion et en diduction homolatérale [21,22]. L'activité du chef inférieur du muscle ptérygoïdien latéral a été étudiée en présence de douleur musculaire expérimentale [23]. Mais actuellement, on ne sait pas comment ce muscle fonctionne dans les ADAM.…”