Pain-related temporomandibular disorder – current perspectives and evidence-based management

Epidemiology

TMD may affect up to a third of the population, however, the majority of patients do not seek help for their symptoms.1 The prevalence of pain-related TMD is seen to be higher in females,^3,4 however, women are also more likely to seek help for their symptoms.^5,6 The peak incidence of TMD occurs in the second and third decades, with a significantly lower incidence occurring in those aged between 45–64 years, and 65 years and over.7 Additionally, there is a significant financial cost attached to chronic TMD – in the United States, there is an estimated $4 billion per annum cost associated with TMD.8 This cost burden has implications for both patients and healthcare providers.9 Furthermore, it has been stated that 85% of the cost of treating TMD is attributable to the small percentage of patients who develop chronic pain-related TMD.10 Currently, there are no published United Kingdom figures for the financial burden of TMD. However, when looking at chronic pain in general, it has been reported that management of patients with chronic pain in primary care carries an estimated total cost of £69 million.11 It has also been reported that over 100,000 people are absent from school or work due to migraine (a condition closely associated with TMD and with similar prevalence) every working day, with the cost to the economy exceeding £1.5 billion per annum.^12,13 This reinforces the importance of early identification of patients at risk of developing chronic TMD and timely referral to secondary care, where appropriate. However, despite this, the prognosis for pain-related TMD remains good – the majority of patients who develop TMD will have transient symptoms and will not progress to a chronic pain state. One study looking at the determinants of treatment response found that 16% of the TMD patients included had persistent pain, which did not respond to treatment at one year follow-up.14

Aetiology

The cause of TMD is multifactorial and complex owing to the interaction of the numerous anatomical, physiological and psychosocial factors identified in the development of TMD.^15,16 These factors may be considered as predisposing, precipitating or perpetuating.17 It is important to note that TMD may also occur in the absence of these factors.18

Anatomical factors may be associated with TMD. Internal derangement of the joint may be classified as:

It should also be noted that patients with disc displacement with reduction may not have any clinical signs or symptoms of TMD.19

Table 1 summarizes the various pathophysiological factors associated with the development of pain-related TMD.

Genetic risk factors for the development of TMD have also been identified in relation to neurotransmission and mood regulation.^20,21,22 Similarly, psychological characteristics have been linked to the development of TMD. The results from a study published by Slade et al,23 looking at healthy females aged 18–34, found that depression, perceived stress and low mood were significant predictors for the development of TMD. This is supported by results from the OPPERA study (Orofacial Pain: Prospective Evaluation and Risk Assessment)1 – a recently published large, high quality series of four observational studies, designed to identify risk factors for the onset and persistence of TMD. The findings from the OPPERA study included higher levels of somatic awareness, affective distress, pain catastrophizing and psychosocial symptoms in patients with TMD.24

It has also been suggested that increased sensitivity in these patients may be due to central sensitization, which is also seen in other chronic pain conditions such as tension-type headache and fibromyalgia.25 Moreover, other chronic pain co-morbidities have also been found to be associated with chronic TMD, such as:

The prevalence of these conditions are also influenced by psychosocial risk factors.^1,7,26,27,28

Trauma may contribute to the development of TMD in some patients, for example, an acute phase of myofascial pain following a dental procedure, such as third molar extraction.^29,30 Chronic TMD pain may develop following head and neck trauma, if inflammatory and degenerative sequelae occur and other predisposing biopsychosocial and genetic factors are present.^{4,15,20,21,22,31,32}

Occlusion, orthodontics and parafunction (bruxism/clenching) have previously been reported as being aetiological factors for the development of TMD. Le Bell et al33 found that patients with a history of TMD and provided with artificial occlusal interferences, reported greater occlusal discomfort and chewing difficulties compared to healthy controls. It has been suggested that TMD patients may have a greater susceptibility to occlusal interference, though there is little evidence to support the role of occlusal interferences and malocclusion in the development of TMD.^30,33,34,35 Similarly, parafunction appears to have a limited role in TMD, as previous studies have not demonstrated that masticatory muscle hyperactivity is a primary aetiological factor in the development of TMD.29 Furthermore, orthodontic treatment has not been found to increase the risk of developing TMD.^36,37

Clinical features

The clinical features associated with TMD consist of pain affecting the pre-auricular region, which may also include the cheeks and/or temporal area and limitations in mandibular excursions, which may also be accompanied by joint sounds.18 Additionally, patients may also exhibit discomfort on palpation of the temporomandibular joint (TMJ) and muscles of mastication, headaches and otalgia.1

Temporomandibular disorders can be loosely categorized into three sub-groups:38

TMD may also be classified into acute and chronic TMD.18 Acute TMD pain is often of a short duration, self-limiting and frequently associated with an identifiable trigger, such as a stressful life event or mechanical trauma, such as prolonged dental treatment.18^,22 The condition normally resolves following rest, soft diet and analgesics. However, with chronic TMD, the pain normally exceeds three months' duration. This longer period of pain may result in depression, and the development of chronic pain behaviour and its associated disability.24

Diagnosis of TMD

The diagnosis of TMD is gleaned following an in-depth history and examination and exclusion of other potential causes for the pain. The history should include questions relating to pain character, development of the pain over time and any precipitating or exacerbating factors.18 The history should also include an up-to-date medical history and systems review, in order to take note of conditions which may demonstrate TMD pain as a symptom, such as rheumatoid arthritis, osteoarthritis or Ehler's Danlos syndrome.

Clinical examination should include both extra-oral and intra-oral examination. The recently published Diagnostic Criteria for Temporomandibular Disorders (DC/TMD)38 includes: assessment of history (presence of masticatory pain or headache) and examination (pain upon palpation of the associated muscles or upon jaw movement). Intra-oral examination should include a dental assessment to exclude any dental pathology, and assessment looking for any signs of parafunctional activity, such as tooth surface loss, tongue scalloping or frictional keratosis.18 Screening questionnaires may aid the clinician in identifying patients with TMD. Gonzalez et al39 have reported a sensitivity of 99% and a specificity of 97% for the correct identification of TMD, with the use of both short and long versions of a TMD screening questionnaire. The DC/TMD38 also recommends psychosocial assessment, which is sensible given the well documented link between psychosocial risk factors and the experience of pain.15 The chronic pain grade scale (CPGS)40 has also been validated for use as a grading tool for pain-related disability in TMD patients. Patients scoring 1 or 2 on the CPGS are considered ‘low pain-related disability’, and those scoring 3 or 4 are considered ‘high pain-related disability’. The hospital anxiety and depression scale (HAD)41 is a screening tool for anxiety and depression widely used in outpatient settings. However, primary care clinicians may find the HAD too cumbersome, and thus the National Institute for Health and Care Excellence (NICE)42 depression screening questions may provide a simpler way of screening for depression in these patients. The questions promulgated by NICE for this purpose are: ‘During the last month, have you often felt bothered by feeling down, depressed or hopeless?’ and ‘During the last month, have you been bothered by having little interest or pleasure in doing things?’42 These questions may be asked verbally or included in a written questionnaire. A positive response to either of these two questions should prompt a referral to a medical practitioner in order that a formal mental state assessment can be performed. TMD patients identified to have chronic pain risk factors such as depression, anxiety or pain-related disability should be considered high risk, and therefore should be referred early for specialist management.

Investigations

Special investigations, such as imaging, may also be considered in the management of TMD. Dental pantomogram radiographs are commonly performed in the investigation of TMD. However, condylar changes, erosion and degenerative changes have been noted, independent of TMD status.43

Epstein et al advise imaging patients based on clinical findings, rather than performing routine panoramic radiography for all patients with suspected TMD or facial pain.44 However, dental radiography may be considered at initial consultation, if a dental problem or other pathology is suspected.18 Magnetic resonance imaging (MRI) may also be used to assess disc position, arthrosis or synovial proliferation. The use of MRI in patients with rheumatoid arthritis and TMD has also been documented, although in some patients anterior disc displacement is the only finding. Therefore, MRI may not be required in all patients with rheumatoid arthritis and TMD symptoms.^45,46 Osseous changes can also be detected using computed tomography (CT) and cone beam CT, although more evidence is required in order to support their routine use in the management of TMD.47 Overall, current evidence has shown that imaging in most cases is unlikely to lead to changes in the diagnosis or management of TMD.^{44,45,46,47,48,49}

’Red flag’ differential diagnoses

The differential diagnoses of TMD include a range of serious conditions which clinicians should bear in mind when assessing a patient with suspected TMD.

Clinicians should be aware of certain ‘red flag’ signs and symptoms, which may mimic TMD and should prompt urgent referral.4^,18

Patients over the age of 50, presenting with new onset TMD-type symptoms, headache and visual disturbance, should be referred for screening for giant-cell arteritis (temporal arteritis)50 – a condition with potentially serious morbidity, including permanent blindness. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) can be conducted for such patients as, when both tests are within normal ranges, the patient can be considered not to have giant-cell arteritis (sensitivity 97%).51 Furthermore, systemic symptoms, such as progressive weight loss, neurological signs or symptoms and headache should prompt referral to a neurologist.52 It is also important that the clinician also screens for signs and symptoms suggestive of malignancy and actions prompt referral to a Department of Oral and Maxillofacial Surgery. Such referral would be indicated for patients presenting with TMD and a previous history of head and neck carcinoma, presence of suspicious oral mucosal lesions, such as persistent ulceration, erythroplakia, lymphadenopathy, profound trismus or cranial nerve abnormalities.^18,53,54 Additionally, persistent, usually painless swellings of the TMJ complex should be considered for neoplasia of the TMJ, such as chondrosarcoma (two cases reported) or osteochondroma (39 cases reported).55 Similarly, referral to Ear, Nose and Throat should be considered for patients demonstrating repeated nose bleeds, altered smell, difficulty swallowing and loss of hearing.56

Management of TMD

Most patients with TMD should be diagnosed and managed successfully in primary care. However, it may be appropriate to instigate early referral for patients with multiple unsuccessful treatments, chronic TMD, chronic pain co-morbidities, occlusal hypervigilance, significant psychosocial factors and disc displacement without reduction (unable to open or close mouth).18 Additionally, patients with conditions such as rheumatoid arthritis may benefit from referral to secondary care, as they are likely to require multidisciplinary management for their TMD. With regards to the management of patients with chronic TMD, one could consider following the British Pain Society's guidelines on the management of chronic pain in adults.57 This approach could be simplified into three ‘pillars’ of pain management:

Education and self-management

The management of TMD should be guided by reversible and non-invasive therapy.^18,58,59 The overall aim of TMD management should be to facilitate patients' engagement in the self-management of their condition. This can be achieved by helping patients to develop skills – problem solving, goal setting, accepting change, finding coping strategies, managing relationships through communication, and finding quality of life in difficult circumstances.60 The first line management in all cases of TMD should be to encourage self-management through patient education.18 Patients should be educated regarding the proposed causes and associations of TMD, and be given conservative strategies on how to manage acute exacerbations of their symptoms and limit functional disability. These educational discussions with patients should be supplemented with suitable patient information leaflets.61

Dworkin et al62 found that patients with minimal levels of psychosocial dysfunction demonstrated decreased pain, reduced pain-related interference on activity, improved muscular pain and reduced number of clinical visits, through the implementation of a tailored self-care programme for TMD. Similarly, Michelotti et al63 found that patients who received education about self-management demonstrated better outcomes compared to those who received treatment with occlusal splint therapy alone. It is important that patients understand that TMD is a fluctuating, often relapsing and remitting condition, and that they have a central role in the management of their condition.^18,58,59,62

Conclusions

Pain-related TMD is a common orofacial pain condition with complex pathophysiology and significant associations with a variety of other chronic pain conditions. Chronic TMD is associated with a considerable negative impact upon psychosocial function and wellbeing; in addition to a high economic burden placed on healthcare providers. Therefore, it is imperative that clinicians are able to recognize TMD, and instigate timely and appropriate management in keeping with current evidence-based practice. Identifying the presence of risk factors for the development of chronic TMD, such as anxiety, depression, pain-related disability and chronic pain conditions elsewhere in the body, will enable clinicians to identify which TMD patients require onward referral for multidisciplinary care. Clinicians should seek to adopt a holistic approach to the management of TMD. In addition to patient education and encouragement towards self-management, TMD care pathways should also consider the three ‘pillars’ of pain management: physical therapies, pharmacotherapy and clinical psychology.