Masticatory muscle pain (MMP) is the major cause of chronic nondental orofacial pain and is experienced by about 12–14% of the adult population, of which approximately 16% seeks treatment. In the vast majority of patients pain is short-lasting or episodic, and only becomes chronic in about 20%. There is often an overlap between MMP and head and neck pain as well as fibromyalgia. The MMP etiology is still unclear, and several risk factors have been described, such as gender, age, stress and other psychological factors, phenotype, parafunctional oral habits, physical and psychological trauma. It is assumed that the pain is initially caused by muscle overuse. Its persistence may lead through nociceptive bombardment to central sensitization, enhancing pain sensitivity. Cognitive, emotional, and affective factors are involved in this pain enhancement process.