(See also Overview of Temporomandibular Disorders.)
This condition is the most common disorder affecting the temporomandibular region. It is more common among women and has a bimodal age distribution in the early 20s and around menopause.
In the affected muscle, both pain and trigger points (which cause referred pain) may result from parafunctional behavior such as bruxism (clenching or grinding of the teeth), which is regarded as two distinct entities: sleep or awake bruxism, each having different etiologies.
Myofascial pain syndrome is not limited to the muscles of mastication. It can occur anywhere in the body, most commonly involving muscles in the neck, shoulders and back.
Symptoms and Signs
Symptoms include pain and tenderness of the masticatory muscles and often pain and limitation of jaw excursion. Both sleep bruxism and sleep-disordered breathing (such as obstructive sleep apnea and upper airway resistance syndrome) are associated with headache that is more severe on awakening and gradually subsides during the day. Such pain must be distinguished from giant cell arteritis. Awake symptoms, including jaw muscle fatigue, jaw pain, and headaches, usually worsen if parafunctional behavior continues throughout the day.
The jaw deviates when the mouth opens but usually not as suddenly or always at the same point of opening as it does with internal temporomandibular joint derangement. Exerting gentle pressure on the lower anterior teeth, the examiner can stretch the involved muscles and thereby assist the patient in opening the mouth another 1 to 3 mm beyond unaided maximum opening.
Diagnosis
A simple test may aid the diagnosis: 2 or 3 tongue blades are placed between the rearmost molars on each side, and the patient is asked to close the mouth gently (1, 2). The distraction produced in the joint space may ease the symptoms. X-rays usually do not help except to rule out arthritis. If giant cell arteritis is suspected, erythrocyte sedimentation rate (ESR) is measured.
Polysomnography should be done if sleep-disordered breathing is suspected.
Diagnosis references
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Schiffman E, Ohrbach R, Truelove E, et al: Diagnostic criteria for temporomandibular disorders (DC/TMD) for clinical and research applications: Recommendations of the International RDC/TMD Consortium Network and Orofacial Pain Special Interest Group. J Oral Facial Pain Headache 28(1):6-27, 2014. doi: 10.11607/jop.1151.
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Peck C, Goulet JP, Lobbezoo F, et al: Expanding the taxonomy of the diagnostic criteria for temporomandibular disorders (DC/TMD). J Oral Rehabil 41(1):2-23, 2014. doi: 10.1111/joor.12132.
Treatment
An oral appliance from a dentist can keep teeth from contacting each other and thereby reduce the damage caused by bruxism. Over-the-counter heat-moldable (boil and bite) mouth guards are available from many sporting goods stores or drugstores; however, these types of devices should be used briefly and only as short-term diagnostic tools. Because these mouth guards may cause unwanted tooth movement or create a paradoxical increase in muscle activity, oral appliances should ideally be fabricated, fitted, and adjusted by a dentist.
Low doses of a benzodiazepine at bedtime are often effective for acute exacerbations and temporary relief of symptoms; however, in patients with associated sleep disorders, such as sleep apnea, anxiolytics and muscle relaxants should be used with caution because they can aggravate these conditions. Mild analgesics, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen, individually or in combination are indicated. Cyclobenzaprine may help muscle relaxation in some people. Because the condition is chronic, opioids should not be used, except perhaps briefly for acute exacerbations. In some cases of chronic pain, antidepressant medication is useful under medical supervision.
The patient must learn to stop parafunctional behavior (eg, clenching the jaw, grinding the teeth) when awake. Hard-to-chew foods and chewing gum should be avoided. Physical therapy, biofeedback to encourage relaxation, and counseling help some patients. Physical modalities include transcutaneous electric nerve stimulation (TENS) and “spray and stretch,” in which the jaw is stretched open after the skin over the painful area has been chilled with ice or sprayed with a skin refrigerant, such as ethyl chloride. Botulinum toxin may be used successfully to relieve muscle spasm. Most patients, even if untreated, stop having significant symptoms within 2 to 3 years.
Key Points
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Myofascial pain syndrome is a more common cause of temporomandibular pain than temporomandibular joint derangement.
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Tension, fatigue, and (rarely) spasm of the masticatory muscles may result from parafunctional behavior (eg, bruxism).
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Patients have pain and tenderness of the masticatory muscles, painful limitation of jaw excursion, and sometimes headache.
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Bedtime use of oral appliances and a benzodiazepine may help, along with nonopioid analgesics.
