16 Facial pain and temporomandibular disorders
Whilst it is not the purpose of this book to reiterate the diagnosis of common dental disorders, it is worth restating some features of these conditions to aid in the distinction from pain not caused by disease of the teeth (see Table 16.1).
|Dental pain||Pain associated with temporomandibular disorders|
|Site||Teeth or alveolus. Almost always unilateral||Preauricular, temple, angle of mandible. May be bilateral|
|Duration||Hours to days||Weeks to months|
|Aggravated by||Thermal stimulation or pressure on a specific tooth||Jaw movement, chewing, yawning, cold windy weather|
|Relation to time of day||No||Often yes|
In general, pain of dental origin is of relatively rapid onset (hours to days) and very well localized to the causative quadrant of the mouth or even to the tooth itself. Pulpal pain is typically worsened by thermal stimulation. Periodontal pain (apical or lateral) is associated with tenderness of (usually) one tooth to biting or to finger pressure. There are other specific features that may be sought, such as caries, loss of vitality and radiographic signs of periodontal bone loss. Even in the case of more difficult diagnoses such as cracked teeth, local signs may be elicited.
Soft-tissue disorders such as aphthous ulceration, pericoronal infection and acute ulcerative gingivitis can occasionally be confusing, but nonetheless tend to have a short natural history, or at least rapidly make themselves obvious.
The term ‘temporomandibular disorders’ encompasses a group of conditions which can be the source of great controversy. As far as possible, this chapter will deal in fact, accepting that almost anything written may be challenged. It is the intention of the author to give enough information to allow the reader a basic understanding, sufficient to deal with those patients attending a general dental practice and to read further on the subject.
Unfortunately, each of these characteristics may take a variety of forms. This not only causes confusion for the learner but is partly responsible for the controversies concerning terminology and classification so common amongst the ‘experts’ in the field. Patients too may have considerable difficulty putting into words the experiences associated with their suffering.
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.
Sites of origin of pain are often tender to gentle palpation. Masseter and temporalis muscles are accessible to palpation over most of their surfaces. Medial pterygoid can only readily be felt on the midpoint of its anterior border (a finger can be run back along the occlusal surfaces of the teeth until it meets the muscle) or possibly where it joins the pterygomasseteric sling beneath the mandible. Access to the lateral pterygoid, however, is very restricted, it being found by passing a small finger between the maxillary tuberosity and the coronoid process of the mandible. Caution is needed in interpreting apparent tenderness of the masticatory muscles, as normal muscles may be quite sensitive to firm palpation; a major difference between the sides of the face is usually of diagnostic value.
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.
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.
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).
Classification of temporomandibular disorders is one area in which controversy is rife. It is worth taking a little time to consider the value of classification before suggesting a pragmatic approach to these disorders.
The setting of a variety of entities into more or less coherent groups enables rules to be drawn concerning the behaviour of these groups. As far as disease is concerned, this should allow a prognosis to be offered, specific treatments to be selected and research to be conducted, particularly to determine whether treatments are predictably successful. If a group of very different disorders is considered as if they are one condition, prognosis, treatment and research results are likely to be very confused. It is the case with temporomandibular disorders that disease is defined in terms of a wide range of over-lapping and ill-defined symptoms and physical signs, and both causes and predisposing factors are poorly understood. It should not be surprising that there remains uncertainty as to whether one, three or many conditions are being dealt with.
It is clear, however, that some distinctions can be made. Young adult patients do present with pain, muscle tenderness, variable stiffness, but no clicking or locking; similarly there are young patients with clicking and/or locking of the TMJ with no history of muscle-associated pain or stiffness; a third group is also seen with onset in middle life of joint-associated pain, joint tenderness, crepitus and radiological signs of bone loss within the joints. It is difficult to see these three ‘pure’ forms as parts of the same disorder, although ‘pure’ forms are relatively uncommon. There is also evidence that these disorders do interact with each other in some patients and some practitioners believe that there is a strong element of progression from one type to another.
At the other extreme there is a temptation to continue to subdivide and subdivide each category, which, without a clear understanding of the nature of the disorders, runs the risk of creating an unwieldy and confusing hierarchy of conditions when it cannot be certain they are all different.
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.