Temporomandibular joint dysfunction (myofascial pain dysfunction) consists of pain in and around the temporomandibular joint, joint sounds, and limitation of opening the mouth. A more recent term, facial arthromyalgia, describes the condition more precisely. The symptoms can range from a minor click to a debilitating pain. In its varying forms it is a very common condition affecting up to 25 per cent of the population, with a female/male predominance of up to 9:1. Most patients present at the age of 15 to 25 years, although a few will complain of trouble up to the age of about 45. Beyond this age the condition is uncommon although in recent years there is a tendency for children to present under the age of 15.

The temporomandibular joint is a diarthrodial joint with articulation between the mandibular condyle and the skull base. Interposed between the bony structures is a meniscus or disc which envelops the head of the condyle, and has a similar shape to that of a jockey's cap (Fig. 1) 2382. It separates the bones, creating two synovial spaces which allow rotation and gliding movement. Its shape spreads load from the convex condyle on to the varying shape of the glenoid fossa and eminence.

The movement of the condyle as the mouth opens is complex (Fig. 2) 2383. With the teeth in occlusion the condyle lies approximately in the centre of the fossa. When the mouth is opened, the condyle rotates and translates downwards and forwards across the backward facing slope of the articular eminence. On wide opening, the condyle may pass forward, until it leaves the eminence completely. Closing follows a reverse path. As the condyle translates, the meniscus does so too at approximately half the rate, much as the slide does on a filing cabinet drawer. The shape and elasticity of the meniscus allows it to accommodate the ever-changing shape of the articular surfaces. It has a posterior band approximately 3 mm thick lying immediately over the condyle in the closed position, and an anterior band, with an intermediate zone between the two. The two bands converge and fuse at the medial and lateral poles of the condyle and in effect make an elongated ring into which the anterior part of the condyle fits (Fig. 3) 2384. This ring maintains its positions abreast the condyle, held by insertions at the medial and lateral pole, by the close apposition of the joint, and by the joint capsule. Behind the posterior band elastic fibres insert into the squamotympanic fissure. Under the load of mastication, the joint is stabilized against the eminence by contraction of the upper head of lateral pterygoid, which is inserted partly into the anterior band, and partly into the condylar neck. It contracts as the mouth closes.

For the joint to move smoothly and without dysfunction, there must be well co-ordinated muscle action, an uninflamed synovium and a correctly positioned meniscus. Where these fail, temporomandibular joint dysfunction (facial arthromyalgia) may result.

The cause of temporomandibular joint dysfunction has been a contentious issue over many years. Many hypotheses have been put forward, from occlusal disharmony to psychosomatic illness. In recent years the aetiology has become clearer. The painless click is created by sudden movement of the posterior band of the meniscus, backwards over the condyle on opening and forwards on closing. Meniscus subluxation is generally anteromedial and may be acute or progressive. Whiplash injuries damage the posterior ligamentous structures and allow the meniscus to sublux forwards acutely. Progressive subluxation may result from joint overload. Joint overload causes degeneration of the fibrocartilagenous articular surfaces and results in increasing friction and tension in the posterior ligamentous insertions of the meniscus. These may weaken, stretch, and fail, causing progressive subluxation of the meniscus. Chronic compressive stress may cause the joint surfaces to change shape, particularly where the meniscus is subluxed; this leads to radiographic changes. These changes can be arrested or reversed if normal loading is restored. There is disagreement as to how the original overload occurs.

A popular hypothesis, held for many years, is that occlusal discrepancy can lead to temporomandibular joint stress. Occlusal interferences encourage the patient to bite in an awkward way and stimulate bruxism. This has never been proven to be a primary cause of temporomandibular joint dysfunction. Lack of posterior teeth may be associated with facial arthromyalgia and it is thought here that this creates overload on the eminence simply because patients have to protrude their jaw to chew. Protrusive habits, particularly nail biting and lip chewing, are predisposing factors which seem to confirm this suggestion.

There is no doubt at all however, that stress plays a very important part in this condition. Some people respond to stress by clenching their teeth during the day, and by bruxing at night. Patients suffering from temporomandibular joint dysfunction and exposed to stress, will tend to show hyperactivity of the masticatory muscles over a number of subsequent nights. This hyperactivity, if it persists, overloads the joint. Overload produces synovitis and changes in the fibrocartilage and the degenerative sequence begins. If parafunctional habits can be reduced and stress-related clenching and bruxing can be reduced, the joint surfaces may heal, and the bone permanently remodelled. There is much evidence to suggest that temporomandiubular joint dysfunction is a self-limiting condition.

Anomalies in the occlusion, such as a painful premature contract, or painful lesions in the mouth may occasionally be found. These encourage the patient to find a more comfortable position in which to occlude their teeth, but may produce more pain in the joint. Such intraoral anomalies should be sought and their elimination included in the treatment plan.

Many patients presenting with facial arthromyalgia have experienced trauma in the past, such as a blow to the jaw or a wide yawn. This may have lead to an acute pain with limitation of jaw movement. A painless click or joint noise may follow initial recovery. Some months or years later a further episode may occur with pain over the joint, and over the side of the face and head, and further limitation of opening. The pain may become severe at the limit of opening and the click may cease. Recovery follows, only to return after an inadvertent wide yawn, or a prolonged visit to a dental practitioner.

Exacerbations often occur at times of stress: there is often some joint pain, but mainly an ache felt in the muscles of mastication. These patients fall mainly into two groups: a large group that has pain and trismus on waking, and a smaller group in whom the pain comes on later in the day. Simple analgesics help but do not abolish the pain and, in a few patients, the discomfort is so severe and prolonged that enjoyment of life is impossible. Many will be found to have parafunctional habits such as bruxing, clenching the teeth in response to stress, lip biting, and nail biting. One joint tends to be affected predominantly. Rarely younger patients may present with very severe acute symptoms with are incapacitating.

The examination starts and the treatment begins as the patient enters the room. It is important continually to assess the patient's emotional state as the history is taken and the patient is examined. Specific questions should be directed to family problems, school examinations, etc.

The general demeanour of the patient is noted with abnormalities of facial contour, swellings, etc. The temporomandibular joints should be palpated bilaterally over the lateral poles of the condyles, both when stationary and in motion. Tenderness suggests local inflammation. Any clicks identified should be timed in relation to opening and closing. From this the position of the meniscus may be assessed: an early opening click suggests a minor displacement, a late one a major displacement. Joint crepitus may also be detected. The muscles of mastication should be palpated with the teeth clenched. Tenderness suggests hyperactivity. The distance between the upper and lower incisor teeth on maximal opening should be measured (normal = 40–55 mm) and any deviation from the midline noted. This is the most sensitive test for temporomandibular joint dysfunction. Tenderness of the sternomastoid and suboccipital group of muscles suggest a more generalized hyperactivity, and indicates a disorder beyond the masticatory apparatus.

All patients should undergo general intraoral examination. The mucous membranes of the tongue and floor of mouth should be inspected, the teeth should be examined for caries, periodontitis, and pericoronitis. The patient should be asked to tap the back teeth together; a normal occlusion produces a solid single click, while discrepancies will be recognised as an irregular sound. Lack of posterior teeth may be noted. Patients should be asked to go into each lateral excursion and any painful areas in the occlusion noted. An edentulous patient with old dentures may be ‘overclosed’ due to loss of alveolar bone. This is a common cause of temporomandibular joint pain in the elderly.

The most potent investigation of patients with temporomandibular joint dysfunction is the examination. Plain radiographs either in the form of orthopantomograms or even close-cut corrected tomograms of the joint, have been shown to be of no value except in patients with extreme and chronic disease. CT scans may be of value especially where serious pathology is suspected as, by imaging soft tissues, the position of the meniscus may be ascertained. Magnetic resonance imaging is now replacing CT as it gives better images of the meniscus without irradiation.

Arthrography is a most valuable investigation. Radio-opaque medium is injected, usually only into the lower joint space. Video recordings of the moving joint identify and visualize the meniscus, and assess its mobility. Perforations and adhesions maybe seen.

Arthroscopy is a recent development for the assessment of the temporomandibular joint, and is likely to become a most valuable investigation in patients with intractable discomfort.

Where other causes of joint pain are suspected (rheumatoid arthritis, gonococcal arthritis, for example) appropriate blood tests and investigations should be instituted.

Patients may present with varying degrees of arthralgia and myalgia. Arthralgia alone is uncommon: limitation of opening (locking) with the pain restricted to the joint suggests a subluxed meniscus with inflammation and fibrosis. Crepitus may indicate inflammatory exudate or arthrotic degeneration. Treatment will be directed towards the joints alone. However, most patients will have a large element of myalgia with painful tender muscles. Where this is evident, treatment is directed primarily to the causes of muscle hyperactivity.

At least 90 per cent of patients suffering temporomandibular joint dysfunction respond to conservative treatment. Treated with consideration, 40 per cent of patients will get better within 6 to 8 weeks with little more than reassurance. Explanation as to the cause of the pain helps the patient to identify parafunctional habits, such as clenching or the biting or nails, and to eradicate them. A simple exercise regimen (Table 1) 615 has been found most beneficial. Any intraoral cause for acute inflammation which may interfere with a normal closing pattern should be identified and removed.

Those who fail to improve on the above regimen should undergo further treatment, aimed at reducing muscle hyperactivity. There are two main approaches to this stage of treatment: appliance therapy and drug therapy.

Many dental appliances have been constructed for the management of facial arthromyalgia. They may be upper or lower, worn continuously, or worn only at night. Research has indicated that it is the parting of the teeth which seems to bring the benefit, and an opening of 3 to 4 mm is generally found to be the most satisfactory. Proponents of this method report considerable success. Some appliances are constructed to ‘catch the disc,’ forcing the patient into protrusion so that the condyle at rest coincides with the subluxed meniscus. It is doubtful if this approach succeeds in more than a minority of patients.

Tricyclic drugs are most successful, usually in doses well below those for the treatment of depression. Sedative forms such as dothiepin are said to impart more benefit than less sedative forms such as nortriptyline. They act to reduce anxiety, improve sleep patterns so reducing bruxism, and may function as a centrally acting analgesia. Doses start at between 25 and 50 mg at night and are increased every 3 to 4 weeks until a good response is obtained. It is important to explain to the patient why the drugs are given, to discuss the side-effects, and to explain that there will be a slow response. With a very agitated or anxious patient, some mild sedative such as fluphenazine or stellazine may be added. Diazepam does not seem to be effective and can lead to dependence. With this regime a further 40 or 50 per cent of patients will get better in 2 to 3 months.

Some dental practitioners feel that there is benefit in equilibrating the occlusion by spot grinding (coronoplasty) once muscle pain and tenderness is relieved.

Where the above regimens fail, or where the patient has had intractable pain over a number of years with failed conservative treatment, then there is benefit in investigating the joint further by arthrography, arthroscopy, or MRI (see above).

The aim of surgery is to reconstruct the joint.

The meniscus is identified through a preauricular incision and arthrotomy. It is mobilized by incising adhesions, and then sutured into a more posterior and lateral position.

This is reserved for occasions when the meniscus cannot be mobilized satisfactorily or where it is perforated. A temporal muscle flap may be mobilized and sutured across the joint surfaces to make a satisfactory substitute for the meniscus.

Many artificial materials have been used to replace the meniscus, the most popular in recent years being a bilaminate of Teflon and Proplast. There have been so many complications of this procedure that most surgeons have abandoned it.

Very recently techniques have been developed using arthroscopy with a second puncture to introduce minute surgical instruments. Not only can the joint be inspected with up to 15 times magnification, lavage can be performed to remove inflammatory substances where synovitis is identified, adhesions can be incised, and the subluxed meniscus can be mobilized and repositioned.

Materials have been developed for total temporomandibular joint replacement. Generally these are reserved for gross joint destruction such as post-traumatic ankylosis or where the joint is severely damaged by rheumatoid disease.

The conservative forms of surgery have a report success rate for facial arthromyalgia of up to 90 per cent.

Norman JEdeB, Bramley P, eds. A Textbook and Colour Atlas of the Temporomandibular Joint. London: Wolfe Medical Publications Ltd, 1990.