According to the psychophysiologic theory, masticatory muscle spasm is the primary factor in the myofascial pain-dysfunction syndrome. Emotional, rather than mechanical, factors are the prime etiologic agents in stimulating chronic oral habits that produce muscle fatigue.

https://jada.ada.org/article/S0002-8177(69)91026-5/pdf

Etiology of the pain-dysfunction syndrome

Epidemiologic surveys of temporomandibular disorders (TMD) have demonstrated that a considerable proportion of the population--up to 5% or 6%--will experience persistent pain severe enough to seek treatment. Unfortunately, the current diagnostic classification of craniofacial muscle pain is based on descriptions of signs and symptoms rather than on knowledge of pain mechanisms. Furthermore, the pathophysiology and etiology of craniofacial muscle pain are not known in sufficient detail to allow causal treatment. Many hypotheses have been proposed to explain cause-effect relationships; however, it is still uncertain what may be the cause of muscle pain and what is the effect of muscle pain. This article reviews the literature in which craniofacial muscle pain has been induced by experimental techniques in animals and human volunteers and in which the effects on somatosensory and motor function have been assessed under standardized conditions. This information is compared to the clinical correlates, which can be derived from the numerous cross-sectional studies in patients with craniofacial muscle pain. The experimental literature clearly indicates that muscle pain has significant effects on both somatosensory and craniofacial motor function. Typical somatosensory manifestations of experimental muscle pain are referred pain and increased sensitivity of homotopic areas. The craniofacial motor function is inhibited mainly during experimental muscle pain, but phase-dependent excitation is also found during mastication to reduce the amplitude and velocity of jaw movements. The underlying neurobiologic mechanisms probably involve varying combinations of sensitization of peripheral afferents, hyperexcitability of central neurons, and imbalance in descending pain modulatory systems. Reflex circuits in the brain stem seem important for the adjustment of sensorimotor function in the presence of craniofacial pain. Changes in somatosensory and motor function may therefore be viewed as consequences of pain and not factors leading to pain. Implications for the diagnosis and management of persistent muscle pain are discussed from this perspective.

Craniofacial muscle pain: review of mechanisms and clinical manifestations.

Background and aim. This review aims at presenting a current view on the most frequent factors involved in the mechanisms causing temporomandibular disorders (TMD). Method. We conducted a critical review of the literature for the period January 2000 to December 2014 to identify factors related to TMD development and persistence. Results. The etiology of TMD is multidimensional: biomechanical, neuromuscular, bio-psychosocial and biological factors may contribute to the disorder. Occlusal overloading and parafunctions (bruxism) are frequently involved as biomechanical factors; increased levels of estrogen hormones are considered biological factors affecting the temporo-mandibular-joint. Among bio-psychosocial factors, stress, anxiety or depression, were frequently encountered. Conclusions. The etiopathogenesis of this condition is poorly understood, therefore TMDs are difficult to diagnose and manage. Early and correct identification of the possible etiologic factors will enable the appropriate treatment scheme application in order to reduce or eliminate TMDs debilitating signs and symptoms.

/pdf/factors-involved-in-the-etiology-of-temporomandibular-406ww520ey.pdf

Factors involved in the etiology of temporomandibular disorders - a literature review.

Many variables determine how a person acquires a TMJ problem, how he reacts to it, and how he responds to therapy. Although clinical symptoms may be similar among TMJ patients, it is necessary to subdivide the total patient population in accordance with those variables. Only in this way can a meaningful diagnosis and a rational approach to therapy be provided for each individual patient.

The TMJ pain-dysfunction syndrome: heterogeneity of the patient population

Experimental occlusal discrepancies and nocturnal bruxism

Reasonable grounds exist for asserting that there is a significant relationship of psychological factors to nonorganic TMJ dysfunction, that these factors can be treated, and that this treatment results in relief of physical symptoms as well.

Daniel E. Lupton

Papers

Psychological aspects of temporomandibular joint dysfunction

Myofascial pain-dysfunction syndrome: attitudes and other personality characteristics related to tolerance for pain.