Temporomandibular Joint Dysfunction

Introduction

The cause of temporomandibular pain can include masticatory dysfunction, myofacial pain syndromes, atypical facial pain, and temporomandibular joint (TMJ) abnormalities.

An estimated 30-40 % of the Western population may experience symptoms suggestive of TMJ dysfunction. A preponderance of young women are affected by these disorders.

Anatomy

The gross anatomy of the TMJ is unique but typical of most diathrodial synovial joints except for the following features:

1. Both TMJs function as a single unit (the so-called craniomandibular articulation)

2. The articular surfaces are lined by fibrocartilage,

3. Finally, the articular disk separates the joint into two spaces, each with a different function.

The articular disk is a biconcave structure composed of dense fibrous connective tissue.

It is anchored anteriorly to the superior head of the lateral pterygoid muscle and the eminentia articularis, inferiorly to the medial and lateral aspect of the mandibular condyle, and posteriorly in two zones.

Joint mechanics

The prime function of the mandible is chewing and speech. During a maximal jaw opening, the TMJ undergoes two separate motions, which are permitted by the two distinct joint spaces. The lower ginglymoid compartment is capable of simple hinge motion only, and it is here that the first 20 mm to 25 mm of interincisor jaw opening is achieved. The upper gliding compartment is capable of translatory motion anteriorly along the eminence and allows the last 15 mm to 20 mm of interincisor jaw opening to occur. It is only after translation past the height of the eminence that the additional 20 mm of rotation is possible.

The TMJ is capable of protrusion and retrusion as well as lateral excursion, with unilateral or bilateral movement in the upper joint spaces only. Humans display an envelope of jaw motion reflective of a combination of hinge and translation movement in the mandible. At rest the mandibular condyle lies inferior to the TMJ disk. On jaw opening, the condyle rotates to engage the intermediate zone of the disk, causing it to move anteriorly and come in contact with the eminence. At this point, further opening is achieved by translating with the condyle along the slope of the eminence. In the final stage of opening, the condyle rotates beneath the disk.

Assessing the patient with facial pain

The evaluation of the patient with features suggestive of a TMJ disorder should include a complete history and physical examination. It is important to consider and exclude the possibility of diseases (teeth, sinuses, and ears, as well as neoplastic processes of the oral cavity and central nervous system ) that mimic TMJ dysfunction and may be of a more serious and sinister origin.

History

Traditionally, patients with TMJ dysfunction have the classic triad of pain in the preauricular area, noises emanating from the region of the TMJ, and limited mandibular movement. Although we know this is true, it is of value to assess these features more thoroughly.

Pain may originate from the joint, be more diffuse and originate from the muscles, or be radiated from the teeth, ear, or neck.

The onset of pain may suggest its origin,

1. early-morning pain may result from nocturnal bruxism causing muscular pain,

2. later in the day after jaw function may suggest intracapsular pathology.

3. joint pain is commonly aggravated by activity and tends to be constant,

4. muscle pain may worsen with stress and may be intermittent.

Physical examination

1. observing for any signs of facial asymmetry

2. occlusion and dentition

3. a complete check for oral cancer

4. inspection of the ear canals and tympanic

5. examination of cranial nerves II through XII

6. palpation of the masticatory muscles ( local tenderness )

7. joint motion should be assessed in all directions, beginning with the measurement of the maximal opening of the jaws. This so-called interincisor opening distance should be about 40 mm to 50 mm.

Joint imaging

1. Conventional radiography (normal in up to 85% of patients with TMJ)

2. Computed tomographic (CT) scanning

3. Arthrography

4. MRI scan

Temporomandibular joint disorders

1. Myofascial problems

2. Inflamation of capsule and ligaments

3. Internal derangement of the joint

4. Condyle and bone problems

5. Congenital and developmental abnormalities

6. Condylar fractures

7. Osteoarthritis

8. Rheumatoid arthritis

Myofascial Pain Dysfunction (MPD) Syndrome

MPD syndrome represents a constellation of symptoms, including;

1. preauricular pain,

2. occasional joint clicking,

3. restriction of jaw opening,

4. tenderness localized to the masticatory muscles, and

5. normal radiograph.

6. no discernible anatomic abnormalities are present within the TMJs.

The cause of MPD syndrome is multifactorial, and includes occlusal prematurity, overclosure, bruxism, and anxiety. These lead to spasm of the jaw muscles and cause pain around the TMJ.

Producing an ache in the jaw masseter muscle is the most common. Next most common is pain in the temporalis muscle. Lateral pterygoid muscle can generate an earache behind the eyes. Medial pterygoid involvement causes pain on swallowing or stuffiness in the ear.

Inflamation of capsule and ligaments

Posterior capsulitis can be due to acute trauma and infection. Medical occlusal treatment is necessary.

Internal Derangement

Internal derangement refers to an abnormal relationship between the disk and the other joint structures, but because of the usual progressive nature of such a derangement, it also includes the sequelae.

The most common cause of internal derangement is acute trauma. This is usually of the macro type and commonly includes automobile accidents or any type of blow to the head or whiplash injury. Some investigators report chronic trauma, malocclusion associated with prognathism, and open-bite deformity.

The pathogenesis usually begins with the anterior displacement of the disk relative to the superior aspect of the condyle. This in turn causes the well-innervated retrodiskal tissue to become trapped between the condyle and fossae. The abnormal arrangement of these tissues is thought to be the source of pain. With time the altered load-bearing properties of the joint cause premature wear of articular surfaces manifested by the initial stretching, then perforation, of the posterior attachment of the disk and the characteristic progressive changes of degenerative arthritis.

The usual clinical manifestation of internal derangement depends on the stage when first seen and includes some elements of pain, otalgia, headache, and neck ache in all but stage I and becomes more constant and severe as the stage progresses. Joint noises occur in most stages of internal derangement and range from painless clicking to painful clicking with crepitus associated with degenerative arthritic changes. Motion of the joint becomes progressively more restricted as the stage advances.

The investigation of the patient with suspected internal derangement should aim to confirm an intra-articular abnormality and exclude other unrelated causes of symptoms. Simple laboratory studies, such as erythrocyte sedimentation rate, presence of autoimmune antibodies, and uric acid levels, may uncover inflammatory causes of the arthropathy.

Ankylosis

The incidence of ankylosis appears to be decreasing and the techniques for its correction have improved as a result of the principles learned from orthognathic surgery. It can be classified as true (intra-articular) or false (extra-articular) and also as bony or fibrous, depending on the type of fusion between the articulating elements.

There are many causes of true ankylosis of the TMJ, but the more common include trauma, infection, and juvenile rheumatoid arthritis. These conditions lead to destruction of the disk and bony elements such that a fibrous union narrows the joint space and then produces a bony fusion. The most common cause of a false ankylosis is a fracture of the zygomatic arch with impingement on the cornoid process. This leads to a fibrous union outside the joint and immobilizes it.

Patients with ankylosis can display problems in nutrition and often will have serious oral hygiene problems, leading to dental decay and abscess. If the ankylosis occurred early in life, mandibular growth and facial development will be retarded and produce deformities that will subsequently require considerable orthognathic surgery to correct.

Temporomandibular joint dislocations

Acute dislocations of the TMJ occur as the condyle extends anteriorly beyond the eminence as a result of hypermobility secondary to trauma or exaggerated mouth opening as in yawning. Spontaneous reduction usually follows, but in some cases the dislocation persists and requires manual reduction. This is accomplished by placing the surgeon’s thumbs along the lower buccal sulci and the fingers along the inferior border of the mandible and exerting firm downward force to overcome the muscle spasm, accompanied by posterior motion to replace the condyle into the fossa. Occasionally the spasm is so great as to prevent reduction and some form of muscle relaxant or anesthesia is required.

Infectious arthritis

The TMJ may become infected by local spread or rarely, from hematogenous seeding from a distant septic focus. The occurrence infectious arthritis is relatively infrequent.

Avascular necrosis

Although rare, avascular necrosis of the condyle is possible after trauma or devascularization at the time of TMJ surgery. The patient will present with the typical symptoms of TMJ syndrome including pain and limited jaw motion. Diagnostic imaging is particularly important including MRI to detect devascularization of a portion of the condyle. The management of avascular necrosis involves the debridement of the necrotic condyle and possible condylar replacement in severe cases.