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

Abstract

Pain and limitation of movement are two cardinal symptoms of temporomandibular disorders but it is unclear how one influences the other. The relationship between pain and movement is clinically significant but controversial with two major theories having been proposed: the Vicious Cycle Theory and the Pain Adaptation Model. The Vicious Cycle Theory proposes a vicious cycle between pain and muscle activity. This theory has little scientific basis but underpins many management strategies. The Pain Adaptation Model is more evidence-based and proposes that pain causes changes in muscle activity to limit movement and protect the sensory-motor system from further injury. The Pain Adaptation Model has many positive features but does not appear to explain the relation between pain and muscle activity in all situations. We propose that the relationship is influenced by the functional complexity of the sensory-motor system and the multidimensional nature of pain. This new Integrated Pain Adaptation Model states that pain results in a new recruitment strategy of motor units that is influenced by the multidimensional (i.e., biological and psychosocial) components of the pain experience. This new recruitment strategy aims to minimize pain and maintain homeostasis. This model emphasizes the individual reaction to pain and suggests a tailored approach towards management.

Reorganization of muscle activity in patients with chronic temporomandibular disorders

“…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.…”

Propriedades clinimétricas da variável eletromiográfica duty factor para desordem temporomandibular

“…The results support the introduction of EMG and muscle duty factor as a possible part of clinical history and physical examination for Type 1a TMD (myofascial) patients, so as to reliably measure activation time relative to a threshold of masticatory muscle effort. Muscle activation time, whether voluntary or involuntary, during muscle rest or contraction, can help identify situations of hyperactivation or hypoactivation that are a result, for example, of the pain inhibition reflex or a protective spasm (13) . This variable could be considered when formulating therapeutic conduct with the goal of altering the duration of a certain level of muscle activation.…”

“…Researchers found a reduction in electrical activity of the muscles during the opening movement of the jaw after a TENS intervention, an indication that its pain inhibitory properties reduced the hyperactive reflex generated by pain in those muscles. When this reflex is inhibited, the vicious cycle of pain is broken (3,13) . Considering the inclusion of duty factor as a variable for analyzing the activity of masticatory muscles and as a complement to the functional diagnosis of temporomandibular muscle disorder, it is important that tests on the clinimetric properties of reliability and responsiveness be conducted.…”

Regulación voluntaria de la actividad contráctil del músculo masetero en individuos sanos y con trastornos temporomandibulares. Un potencial test diagnóstico

“…Similarly, the pain present in some temporomandibular disorders has been linked to alterations in the motor function of the mandible (13,16) , for it affects the isotonic and isometric contractile activity of the masticatory muscles due to the alteration of the sensorimotor system (17,18) .…”