Can headache originate from the masticatory system and associated structures including the dentition? According to the dental literature, this is often the case (9,11,27,29,39,43). Although temporomandibular disorder (TMD) and headache occur together frequently, it could be simply by chance, because both disorders are extremely prevalent (3,17,30,32). Guidelines for the evaluation, diagnosis, and management of TMD have been presented (4,26) but as yet cannot be regarded as internationally accepted. Of the variables included, only masticatory muscles painful to palpation have been found consistently to have a distinct relationship to headache (9,12,23). It is not clear if this represents a specific peripheral response to central sensitization or of there is local pathology. Because tenderness may be a part of a generalized myofascial syndrome, the real question of whether occlusal and mandibular abnormalities may be the cause or the effect of tenderness and pain remains largely unanswered.

The Headache Classification Subcommittee of the International Headache Society (IHS) tried to obviate such problems by creating a new term, oromandibular dysfunction (OMD) (12), as a fourth-digit code number, one of several most likely causative factors to tension-type headache (TTH), in the hierarchical classification system. These operational diagnostic criteria of OMD included some signs and symptoms of morphologic abnormalities and dysfunctions as well as parafunction of the jaw, tongue, and mouth. It does not include pericranial or jaw-muscle tenderness (Table 73-1). This term is no longer present in the revised IHS classification (13). Since the introduction of the IHS classification in 1988 (12), only a few studies have dealt with this term, and the terminology and diagnostic criteria in this field are still intensely debated. In the IHS classification (12,13), diagnostic criteria for temporomandibular joint (TMJ) disease are also listed as a secondary specific headache form; however, scientific evidence for the exact relation of TMJ disease to headache and orofacial pain is rather limited, and hopefully further research and exchange between the dental and medical specialties can be encouraged.

In the following discussion, TMD refers to the fulfillment of the IHS criteria.

IHS Code and Diagnosis: 11.7 Headache or facial pain attributed to temporomandibular joint (TMJ) disorder

World Health Organization (WHO) ICD-10A code: G44.846

In this discussion some population-based investigations are presented. Normative data from healthy subjects are compared with findings in subjects with TTH and related to the clinical literature.

A brief orofacial interview and examination is easy to perform during examination of a headache patient and will reveal most of the dental dysfunction that may be associated with headache. The items of oromandibular dysfunction 2.1.X.2 in the IHS classification 1988 are included in the suggested questionnaire (Table 73-1). These also help in defining the new IHS criteria for TMD listed in Table 73-2. The appropriate screening questionnaire and examination for this disorder are described in Tables 73-3 and 73-4. The use of such diagnostic tools is, however, controversial; Gerstner and colleagues reported that a brief questionnaire was valuable to distinguish between patients with TMD and healthy controls but was unable to separate these TMD patients from patients with TTH (10). Because many patients relate their pain to previous trauma, infections, extractions, and joint problems, a short history of these factors also may be included, although the
relationship between trauma and TMD is quite uncertain. In addition to the present IHS criteria of oromandibular dysfunction, a brief evaluation of the bite function may be recommended as well. A significant loss of molars, impaired chewing ability, significant history of bruxism with tooth wear, or malfunctioning dentures should be noted during the examination, because any of these factors may be a perpetuating factor to the pain (5,37,43). For research purposes, blinded designs must be used because of the subjectivity of the examination and because 13% of a general population had three or more symptoms or signs of TMD, thus fulfilling the IHS criteria (17).

Disorders affecting the oromandibular system may be occlusal (e.g., lack of molars, occlusal disorders), parafunctional (e.g., bruxism, clenching, tongue pressure), or articular factors (arthritis, arthrosis, clicking at function). Some of these disorders are purely organic, whereas some may have a behavioral background. Various terms, such as temporomandibular joint pain dysfunction syndrome, myofascial pain dysfunction syndrome, craniomandibular disorders, and temporomandibular dysfunction, including jaw-muscle tenderness, have been used. Therefore, the prevalence of a specific disorder is difficult to determine because of this lack of a universally accepted classification system. The complexity of the field is also reflected by the fact that objective signs often show a distribution of age and sex that is different from the distribution of symptoms (17,29,39,43), and that the correlation between signs and symptoms is generally poor (4). In various series, the proportion of subjects with TMD in need of orofacial treatment is 3.5 to 9.7%, depending on the definition used (2,30).

The prevalence of TMD, headache, and muscle tenderness was studied in a random sample of 735 adults representative of the total Danish population (9,11, 12, 13). The investigation was performed in a standardized way, with the observer of TMD and tenderness blinded to the previous history of TMD and headache and any other
information about the subjects (14,16, 17, 18). The most common symptoms of TMD were clenching (22%) and grinding of teeth (15%), and the most common sign was irregular jaw movements on opening and closing (29%). In total, 13% of the subjects had three or more symptoms or signs of TMD as required by the IHS definition of TMD (13). Female subjects were affected more often than male subjects, but no significant relation to age was noted (17). Similar data were obtained in a Canadian epidemiologic study in which 12.9% reported functional pain or pain at rest, with women and younger age groups more likely than men and older age groups to report one or more symptoms (22). Significant associations between symptoms and potential risk factors as parafunctional behaviors were also reported (22).