Internal Temporomandibular Joint Derangement
The most common form of internal temporomandibular joint derangement is anterior misalignment or displacement of the articular disk above the condyle. Symptoms are localized joint pain and popping on jaw movement. Diagnosis is based on history and physical examination. Treatment is with analgesics, jaw rest, muscle relaxation, physical therapy, and bite splinting. If these methods fail, surgery may be necessary. Early treatment greatly improves results.
(See also Overview of Temporomandibular Disorders.)
The superior head of the lateral pterygoid muscle may pull the articular disk out of place anteriorly when abnormal jaw mechanics cause it to spasm. Abnormal jaw mechanics can be due to congenital or acquired asymmetries or to the sequelae of trauma or arthritis. If the disk remains anterior, the derangement is said to be without reduction. Restricted jaw opening (locked jaw) and pain in the ear and around the temporomandibular joint may result. If at some point in the joint’s excursion the disk returns to the head of the condyle, the derangement is said to be with reduction. Derangement with reduction occurs in about one third of the population at some point.
All types of derangement can cause capsulitis (or synovitis), which is inflammation of the tissues surrounding the joint (eg, tendons, ligaments, connective tissue, synovium). Capsulitis can also occur spontaneously or result from arthritis, trauma, or infection.
Disk derangement with reduction often causes a painless clicking or popping sound when the mouth is opened. Pain may be present, particularly when chewing hard foods. Patients are often embarrassed because they think others can hear noise when they chew. Indeed, although the sound seems louder to the patient, others can sometimes hear it.
Disk derangement without reduction usually causes no sound, but maximum opening between the tips of the upper and lower incisors is reduced from the normal 45 to 50 mm to ≤ 30 mm. Pain and a change in the patient's perception of their bite generally result. It usually manifests acutely in a patient with a chronically clicking joint; about 8 to 9% of the time, the patient wakes up unable to open the jaw fully.
Capsulitis results in localized joint pain, tenderness, and, sometimes, restricted opening.
Diagnosis of disk derangement with reduction requires observation of the jaw when the mouth is opened. When the jaw is opened > 10 mm (measured between upper and lower incisors), a click or pop is heard, or a catch is felt, as the disk pops back over the head of the condyle. The condyle remains on the disk during further opening. Usually, another, more subtle (reciprocal) click is heard during closing when the condyle slips over the posterior rim of the disk and the disk slips forward.
Diagnosis of disk derangement without reduction requires that the patient open as wide as possible. The opening is measured, and gentle pressure is then exerted to open the mouth a little wider. Normally, the jaw opens about 45 to 50 mm; if the disk is deranged, it will open about ≤ 30 mm. Closing or protruding the jaw against resistance worsens the pain.
MRI is usually done to confirm presence of a disk derangement or to determine why a patient is not responding to treatment.
Capsulitis is often diagnosed based on a history of injury or infection along with exquisite tenderness over the joint and by exclusion when pain remains after treatment for myofascial pain syndrome, disk derangement, arthritis, and structural asymmetries. However, capsulitis may be present with any of these conditions.
Disk derangement with reduction does not require treatment if the patient can open reasonably wide (about 40 mm or the width of the index, middle, and ring fingers) without discomfort. If pain occurs, mild analgesics, such as NSAIDs (ibuprofen 400 mg po q 6 h), can be used. Some patients benefit from doing passive jaw-motion exercises using commercially available mechanical devices.
If onset is < 6 mo, an anterior repositioning splint may be used to position the mandible forward and on the disk. This splint is a horseshoe-shaped appliance of hard, transparent acrylic (plastic) made to fit snugly over the teeth of one arch. Its chewing surface is designed to hold the mandible forward when the patient closes on the splint. In this position, the disk is always on the head of the condyle. The splint is gradually adjusted to allow the mandible to move posteriorly. If the disk stays with the condyle as the superior head of the external pterygoid stretches, the disk is said to be captured. The longer the disk is displaced, the more deformed it becomes and the less likely repositioning will succeed. Surgical plication of the disk may be done, with variable success.
Disk derangement without reduction may not require treatment other than analgesics. Splints may help if the articular disk has not been significantly deformed, but long-term use may result in irreversible changes in oral architecture. In some cases, the patient is instructed to slowly stretch the disk out of position, which allows the jaw to open normally. Various arthroscopic and open surgical procedures are available when conservative treatment fails.
Capsulitis is initially treated with NSAIDs, jaw rest, and muscle relaxation. Sometimes a splint worn at night or during the day may be used briefly until the inflammation decreases. If these treatments are unsuccessful, corticosteroids may be injected into the joint, or arthroscopic joint lavage and debridement are used.
The articular disk is pulled out of place anteriorly due to abnormal jaw mechanics; it may remain displaced (without reduction) or return (with reduction).
Disk displacement with reduction typically causes clicking and pain with chewing.
Disk displacement without reduction does not cause clicking but reduces maximum jaw opening to ≤ 30 mm.
Surrounding tissues may become painfully inflamed (capsulitis).
Analgesics, repositioning splints, and passive jaw-motion exercisers often help, but surgery is occasionally required.