Pain

Pain of muscular origin is often described as aching, but may also be throbbing or sharp, or described as ‘burning’, ‘stiffness’, ‘tightness’, ‘pressure’, ‘fullness’ or even ‘numbness’. It may be unilateral, but is the only common pain of the head and neck experienced bilaterally (Table 16.1). That may aid distinction from pain derived from third molar infection, which is rarely bilateral (at any one time). Muscular pain may be clearly localized to a ‘trigger point’ centred in one muscle (e.g. masseter), or may be less well defined in distribution in, for example, the preauricular or temporal areas.

The time scale of the pain is also important as it rarely develops to a point which causes a patient to seek help over less than a few weeks, in contrast to pain of pulpal or periodontal origin, which tends to develop over hours to days. Activities involving stretching or use of the masticatory muscles, such as chewing, yawning, laughing or singing, usually worsen the pain. Variation over time is common, with pain often being worse in the mornings, but this is by no means always so.

Pain may also derive from the TMJ itself, in which case it tends to be more localized to the joint (but is not always), may be sharp, aching or throbbing, tends to vary less during the day and is usually worsened by joint movement.

Noises

The most common noise associated with the TMJ is clicking (or snapping, cracking, bumping or popping). The noise may be experienced by the sufferer only or may be audible to others, but is always associated with joint movement. The clinician may detect inaudible sounds by palpation or auscultation over the joints during joint movement. Often clicking is worse during eating and occasionally it is audible to others over the sound of conversation at a considerable distance.

A number of surveys have demonstrated that clicking of the TMJ is common, possibly affecting one-third of the adult population. Most people with a clicking TMJ do not ‘suffer’ from their joint noise to the point that they seek help, and that brings us to one of our difficulties. If a majority of people who have a clicking TMJ do not seek help about them, can clicking per se be regarded as an abnormality? The resolution of that question is probably beyond the scope of this book, but it is right to caution against the automatic treatment of all people with a clicking TMJ.

Other noises encountered come under the general term ‘crepitus’ and may be described by the patient as ‘grating’, ‘grinding’, ‘crackling’, ‘rubbing’ and other terms. Such noises are rarely audible to others, but again may be detected by palpation or auscultation. These noises should be clearly distinguished from clicking-type noises as they almost certainly represent different aspects of disease.

Limitation of jaw movement

This may take the form of ‘stiffness’ or pain on attempted mouth opening, thus restricting mobility. Where this is associated with muscular problems, it is often slow in onset (and recovery) and variable in severity.

Muscular stiffness should be distinguished from ‘locking’, which is very sudden in onset (and, if relieved, recovery is also instantaneous).

To determine the degree of restriction some measure of the normal, which is itself very variable, is required. A reasonable measure of the lower limit of interincisal opening for an adult with a class 1 occlusion is 40 mm, measured between the upper and lower incisal edges. The upper limit of the range is about 65 mm. However, these values should be used with caution as some normal people have measures outside this range. Lateral excursive and protrusive movements give some degree of measure of translatory movement within the joints and may be less affected than interincisal opening by muscular influences. Lower limits for these measures are approximately 7 mm. Some allowance should be made for variation in incisor relationship and for bodily size (the larger the body, the greater the opening).

Diagnosis

In its pure form this is a condition affecting only the muscles, though it may affect neck and scalp musculature as well as masticatory ones and is probably analogous to ‘fibromyalgia’ affecting more distant muscle groups. It is predominantly a young patient’s condition and (at least as far as hospital practice is concerned) affects women far more commonly than men. Muscles are painful, particularly during use, often particularly so in the mornings. Specific tender spots (trigger points) may be found in individual muscles, or many muscles may be tender. The condition often develops over weeks to months but with some degree of variation in severity over that time.

Mouth opening is often, but not always restricted, but interincisal opening is rarely less than 15 mm. There is usually some capacity to extend opening with passive stretching by finger pressure; this is also often accompanied by a hesitant or jerky jaw movement. Occasionally the condition appears in a severe form of rapid onset. In this case mouth opening may be restricted to a few millimetres.

The condition appears to be almost always self-limiting over a period of a few weeks to a few years, although for some patients the condition can be remarkably persistent. The cause(s) is unknown. However, several factors have been linked to it:

Almost certainly each of these factors is of some importance in individual cases, but no one factor has been shown to be consistently present in all cases, nor are all those who exhibit these features affected by myofascial pain dysfunction. This inconsistency must shed some doubt on either the causative role of these factors or the coherence of the diagnostic category, and probably implies some form of ‘susceptibility’ which as yet is not understood.