Description

• Syndrome characterized by
  • Pain and tenderness involving the muscles of mastication and surrounding tissues
  • Sound, pain, stiffness, or grating in the temporomandibular joint (TMJ) with movement
  • Limitation of mandibular movement with possible locking or dislocation
  • Recent research suggests that TMD is a complex disorder with multiple causes consistent with a biopsychosocial model of illness (1)[B].
• System(s) affected: musculoskeletal
• Synonym(s): TMJ syndrome; TMJ dysfunction; myofascial pain–dysfunction syndrome; bruxism; orofacial pain

Epidemiology

• Annual first-onset incidence is 3.9%.
• Peak incidence in ages 30 to 50 years

• 6–12% in both adults and older children
• Twice as common in female patients
• Up to 1/2 the population may have at least one sign or symptom of TMD, but most are not limited by symptoms, and <1:4 seek medical or dental treatment.

Etiology and Pathophysiology

• Pathophysiology is multifactorial, involving anatomic, behavioral, emotional, and cognitive factors.
• The American Academy of Orofacial Pain categorizes TMD according to three anatomic origins of pain. The change in name from TMJ to TMD emphasizes that many do not suffer from true articular pain.
• Muscle disorders involving the muscles of mastication
  • Occlusomuscular dysfunction (bruxism)
  • Masticatory muscle spasm
  • Myositis
  • Myofibrosis
  • Poorly fitting oral devices (dentures, splints, etc.)
  • Contracture
  • Neoplasia
• Articular disorders of the joint
  • Congenital disorders
  • Inflammatory disorders: synovitis, arthritides, capsulitis, ankyloses
  • Avascular necrosis (rare)
  • TMJ disk derangement, osteoarthritis
  • Hyper- or hypomobile TMJ
  • TMJ trauma: condylar fractures, dislocation
• Cranial bone disorder including the mandible
  • Congenital and developmental disorders
  • Acquired disorders (fracture, neoplasm)
• Current consensus is that TMD is not only a local condition, so much as a family of complex disorders that can lead to chronic pain, and often overlap with other chronic pain conditions that reflect CNS sensitization.
• OPPERA study (Orofacial Pain: Prospective Evaluation and Risk Assessment) is assessing the heterogeneity in these disorders.

Genetics
Research is ongoing in gene polymorphisms associated with TMD and other pain disorders. These include the catechol O-methyltransferase (COMT) gene, which is thought to be associated with changes in pain responsiveness.

Risk Factors

• Macrotrauma to the face, jaw, and neck, including cervical whiplash injuries and hyperextension of jaw
• Rheumatologic and degenerative conditions involving the TMJ
• Psychosocial stress and poor adaptive capabilities
• Repetitive microtrauma from dental malocclusion, including inappropriate dental treatment
• Link with bruxism and jaw/teeth clenching is inconsistent.

General Prevention

• Elimination of tension-causing oral habits
• Reduction in overall muscle tension

Commonly Associated Conditions

Craniomandibular disorders, somatization disorder, somatoform pain disorder, other chronic pain syndromes, fibromyalgia, juvenile idiopathic arthritis, tension headache, sleep disturbance, tobacco use