Temporomandibular disorders

An exact cause is unknown. A combination of multi-factorial and biopsychosocial causes has been suggested.[1] TMDs have been associated with trauma, orthodontic treatment, rheumatoid arthritis, and para-functional habits such as bruxism (grinding or clenching the teeth at night).[21][22][23] Excessive use of the joint and muscles of mastication seems to be common. Psychological distress and pain amplification are thought to contribute to the onset and persistence of TMD.[3] Patients with persistent TMD are more sensitive to mechanical and thermal pain stimuli, compared with controls.[24] Patients with TMD are more likely to have other painful conditions (e.g., headaches, low back pain), compared with controls.[21] TMDs are associated with depression and stressful life events.[25] One study reported that patients who underwent dental treatment and progressed to active TMD perceived the treatment as the cause of TMD.[26] TMDs have been linked with malocclusion; however, the association was proven to be insignificant.[16][27][28]

Studies have evaluated the role of genetics in TMDs.[29][30] An association between TMDs and genes COMT and HTR2A was confirmed by the findings of the OPPERA study.[3][29][30] One systematic review found that the association between TMD pain and heritance was supported by modest evidence.[30]

Despite extensive studies, the pathophysiology of TMDs is not completely understood. TMDs affect different areas of the temporomandibular joint, resulting in slightly different symptoms. Some patients have an acute onset with mild and self-limiting symptoms, whereas some (about 30%) may progress to chronic TMD, with persistent pain (≥3 months) similar to those reported by patients with other chronic symptoms.[4][31][32] In myofascial pain, the muscles of mastication are affected. Myofascial pain is often associated with bruxism or clenching. Excessive use of the muscles leads to muscle tenderness, which can prevent maximal opening of the mouth and limit mandibular movement. It may also affect the feeling of the teeth biting in a consistent position. Muscle pain can cause headaches in the temporal regions of the head and may also be associated with cervical and shoulder girdle myofascial pains.[12] Patients with myofascial pain have cyclic pain, particularly with pain and locking occurring in the mornings, as bruxism most often occurs at night. These patients may have tooth pain and wear facets on the teeth from bruxing and clenching.[11]

Internal derangement results when the articular disc is displaced usually forwards from its position overlying the condylar head. As the mandibular condyle moves during normal function, the disc clicks back to lie over the condylar head. This catching is the reduction of the disc over the condyle.[18] As the discs reduce they may cause clicking and pain. The pain is due to catching the tissues behind the disc as the disc itself has no nerve or blood supply. The location of the disc may prevent the condyles from translating normally over the articular eminence in front of the glenoid fossa.[12] When this occurs, the patient feels the jaw has locked or is restricted.

Osteoarthritis involves degeneration of the bony structures of the glenoid articular fossa, condyle, and articular disc and is usually seen in older people.[12]

Clinical classification

Disorders related to pain (myalgia, headache related to TMD, and arthralgia) and those associated with the temporomandibular joint (disc displacements, degenerative diseases) are the most common types of TMDs.[1]

According to the Axis I domain of diagnostic criteria for TMD (DC/TMD), which is an evidence-based diagnostic system, the 12 most common TMDs are broadly divided into four main categories: myalgia (local myalgia, myofascial pain, myofascial pain with referral), arthralgia, intra-articular disorders (four disc displacement or internal derangement disorders, degenerative joint disease, and subluxation), and headache attributed to TMD.[1][2][5]

Myalgia

Most common form of TMD. Occurs in 80% of patients.

Includes local myalgia, myofascial pain, and myofascial pain with referral (defined as myofascial pain plus pain outside the muscle, such as in the ears, teeth, or eyes).

Arthralgia

Usually occurs alongside myalgia.

Occurrence of only arthralgia is rare (2% cases).

Headache attributed to TMD

Headache involving the temporomandibular region, which is affected by jaw motion, function, or parafunction.[6]

Intra-articular disorders

Consist of four disc displacement (internal derangement) disorders (disc displacement with reduction, disc displacement with reduction with intermittent locking, disc displacement without reduction with limited opening, and disc displacement without reduction without limited opening), degenerative joint disease, and subluxation.

Anchored disc phenomenon, a type of internal derangement, involves development of acute severe restriction of opening in a young adult due to lack of lubrication in the joint.[7][8] A considerable reduction in mouth opening may be seen, compared with disc displacement without reduction with limited opening, indicating that these may be different stages of the same clinical entity.[9] Anchored disc phenomenon warrants urgent referral, as leaving the situation without intervention can lead to permanent restriction of mouth opening.

Pathophysiology

Classification

Clinical classification