There is a critical reason why the term biopsychosocial begins with “bio,” especially relevant when it is applied to the diagnosis of temporomandibular disorders. Although there are some objective signs associated with TMD (internal derangement of the TMJ, joint effusion, sclerosis or necrosis, etc.), the most common TMD symptoms are orofacial pain, myalgia and arthralgia.1 Since pain is a completely subjective symptom and since physiologically induced pain without any observable evidence of overt trauma cannot be easily distinguished from a Somatic Symptom Disorder (SSD), it is critical to rule out any physical etiology before applying the diagnosis SSD.2 This concept applies equally to medicine and dentistry.
Painful TMD symptoms have been shown to correlate significantly with emotional disturbances ad nauseum, even to the level of severe depression.3–9 It is well established as a medical model that the psychological evaluation of a patient in severe physical pain inevitably results in a “diagnosis” of emotional distress, depression, somatization and/or illness behavior. However, correlation does not even suggest causation, let alone reveal it. A few misdirected authors have actually concluded that the emotional scores from the RDC/TMD Axis II might be more important than the physical findings in Axis I.10,11
The above wrong-headed conclusion is probably at least partly due to the poor performance of the RDC/DC/TMD Axis I and partly due to the widespread confusion in dentistry between correlation and causation. When the accuracy of a diagnosis is limited by low sensitivity and specificity, it can lead to a false conclusion of an emotional etiology. However, when a correlation exists between two factors, either one or a totally separate third factor may be the primary etiology. Correlation tells us nothing about primacy or dependence. Presuming that the emotional factors associated with TMD, such as depression, anxiety and treatment seeking are the primary etiologic factors and that the physical complaints are secondary is probably wrong most of the time. While it is not impossible for these emotions to create an apparent TMD condition, whenever it does happen, a psychiatrist is the proper provider, not a dentist. The only responsibility of the dentist is to discover any physical disorder that is present and provide an appropriate corrective treatment if competent to do so. When no physical disorder is found a referral is then appropriate.
Psychosocial etiology is at best currently a mostly untested hypothesis. In one study limited to non-traumatic muscle-pain TMD cases, (with minimal or zero internal derangements of the TMJs), also with substantial documented emotional disturbances, physical treatments significantly alleviated the painful symptoms and the emotional disturbances.12 This result does not prove that all TMD have physical etiologies, but it does prove that this group of TMD patients did not suffer from a psychosocial etiology. In this study an initial diagnosis of SSD, which could have been applied because of their depression scores, would have represented a false positive one. Although emotional disturbances are very commonly present with TMD, it is absolutely critical that the clinical provider exhaustively rule out any biological etiology before labeling a TMD patient with an SSD diagnosis.2 Just as physical treatments are usually inappropriate to treat mental illness, psychological counselling is unlikely to correct an internal derangement of the TMJ, malocclusion or other physical TMD etiology.
With respect to the RDC/TMD13 and its offspring, the DC/TMD,14 the Axis I represents a rather feeble approach to the diagnosis of the biological aspects of TMD. The addition of “imaging when indicated,” to the DC/TMD, but without any precise formal “indications” as to when imaging should be applied, has not substantially strengthened the diagnostic approach to the biology of TMD.15
Is TMD one entity?
A recurrent factor that inhibits the achievement of a precise biological diagnosis is the common dental expectation that a single test should be able to diagnose all forms of TMD. This has led to a plethora of publications (e.g. Systematic Reviews) all claiming that electromyography or CBCT imaging or MR Imaging or jaw tracking or any other technology cannot be used to diagnose all TMD. While technically true, when combined with a small measure of common sense, these technologies in aggregate can collectively supply accurate and timely help to the clinician seeking a more specific TMD physical diagnosis.16 With an accurate physical diagnosis in hand, the probability of developing a successful physical treatment plan for TMD, using methods such as splints or occlusal adjustments, is dramatically enhanced.17–22 Because there are literally dozens of physical etiologies underlying TMD, it is usually necessary to determine which ones are present before a successful treatment can be applied.
In spite of the overwhelming evidence in the dental scientific literature to the contrary, one systematic review actually concluded that Cognitive Behavioral Therapy is more effective at reducing emotional disturbances than physical treatments.23 At the extreme nihilistic end of the spectrum of etiologic concepts one author has opined publicly that the etiology of TMD is so idiopathically unique to each patient that it is indeterminate.24 If that were true, logically, no predictive treatment plan could ever be devised and all treatment outcomes would be left purely to chance. Of course, chance inevitably does play some role in all treatments, but it is extremely unscientific to rely exclusively on chance for a diagnosis.
Those who have promoted the concept that the emotional factors associated with TMD are primary have also usually suggested that one treatment, such as cognitive behavioral therapy or usual treatment, can be sufficient for all TMD cases.25 This has been followed by a habit of referring to Temporomandibular Disorder in the singular as if it included only one universal condition and requires only one usual treatment.26 Thus, the philosophical approaches to TMD range from “every case is unique” to “all are essentially the same.” With this range of TMD concepts being touted throughout the dental profession, it is no wonder that confusion and contention are so very prevalent.
The scientific method requires skepticism and an empirical effort to disprove any hypothesis, not embracing the so-called validation of it. The inability to disprove any hypothesis represents the only scientific support for it, but after rigorous empirical testing of it. The complete and egregious lack of empirical testing of the biopsychosocial hypothesis with respect to treatment of TMD is blatantly out of step with the scientific method.27,28 The test that could have been done twenty or more years ago to compare the psychosocial etiology theory to the physical etiology theory of TMD is very straightforward; 1) select a group of sixty TMD patients, 2) evaluate all patients, both physically29 and emotionally,30 3) divide the group randomly in half, 4) the first half receives only physical treatments appropriate to their diagnosed physical conditions, 5) the second group receives only psychological counselling (e.g. Cognitive Behavioral Therapy) appropriate to their determined emotional conditions, and 6) compare the levels of both physical and emotional symptom reductions as the outcome measures. If the psychosocial factors are more often primary in TMD, the counselled group will out-perform the physically treated group. However, if the physical factors are more often primary, both the physical and the emotional symptoms will be reduced more within the physically treated group. What is the most egregious disservice to the profession is the fact that the psychosocial approach has actually been tested repeatedly, but the negative results have not been reported within the dental literature.31 Consequently, all published Systematic Reviews and Meta-analyses evaluating the etiology of TMD for the past twenty or more years include a significant Risk of Reporting Bias due to unreported negative outcomes in previous studies of etiology.32–34 An additional Risk of Selection Bias is present in those Systematic Reviews that have limited their evaluated studies to ones dependent upon the RDC/TD or DC/TMD for physical diagnoses.32,34 Consequently, while many TMD studies may contain bias, the systematic reviews of them are also not exempt from the same contaminations.