Occlusal Splints for Painful Craniomandibular Dysfunction

Part   A

Practice of Occlusal Splint Therapy and Coordinative Training

1

INTRODUCTION

Jens C. Türp

Craniomandibular Dysfunction

Terminology

Technical terms must be clarified to avoid misconceptions and misunderstandings, especially when describing the factors relating to function. In particular, a distinction must be made between dysfunction of the masticatory system, craniomandibular dysfunction, and myoarthropathy of the masticatory system; these terms should not be considered synonymous. In 2016, the German Society for Functional Diagnostics and Therapy published proposed definitions for these and other important terms for the first time.¹

Dysfunction of the masticatory system

Dysfunction of the masticatory system refers to a short- or long-term disturbance of the homeostasis or economy of the masticatory system caused by any structurally or functionally substantiated deviation from normal function, such as functional deficits due to trauma, injury to the structural integrity, and functional/parafunctional stress, including deviations that justify prosthodontic, orthodontic, or surgical measures.¹

Craniomandibular dysfunction

Craniomandibular dysfunction (CMD) is classified as a specific functional disorder that affects the muscles of mastication, the temporomandibular joints (TMJs), and/or the occlusion.¹ Clinically, CMD encompasses the areas of pain and/or dysfunction.

Pain is manifest as:

Masticatory muscle pain

TMJ pain

Toothache of (para)functional origin

Dysfunction can appear in the form of:

Painful or nonpainful limitation of movement of the mandible (aspect aimed at mandibular movements)

Hypermobility or incoordination of the mandible (aspect aimed at mandibular movements)

Painful or nonpainful intra-articular dysfunction (aspect aimed at the TMJ)

Premature contacts interfering with function and gliding obstacles (aspect aimed at the occlusion)

CMD is a collective term that encompasses symptoms not in need of treatment and symptoms that do need treatment. In principle, there is always a need for treatment when pain is present; in the case of dysfunction, the need for treatment is dependent on the severity of the dysfunction.

Myoarthropathy of the masticatory system

Myoarthropathy of the masticatory system (MAP), a term introduced in 1970 by Tübingen dentist Willi Schulte,² denotes a subgroup of craniomandibular dysfunction. It refers to symptoms and findings affecting the muscles of mastication, the TMJs, or associated tissue structures; it does not take into consideration the occlusion. This term equates to the term temporomandibular disorder (TMD). If pain is involved, these symptoms can be summarized under the heading myoarthropathic pain.

Etiology

Numerous mechanisms have previously been held responsible for the etiology of myofascial pains of the muscles of mastication and pains in the TMJs. Nociceptive pain is currently the underlying basis of models for these musculoskeletal symptoms. This nociceptive pain can be triggered by overloading of the tissue and promoted by a number of disposing factors. Microtrauma and local ischemia³—together with their structural and functional counterparts, such as activated osteoarthritis,⁴ the myofascial trigger point,⁵ local muscle fatigue, and aching muscles⁶—essentially serve as overarching pathophysiologic explanatory models. Common to these hypotheses is the assumption that, at the end of the causal chain, afferent nerve fibers and tissue cells release protons⁷ and other endogenous algesic substances (eg, glutamate, substance P, bradykinin, histamine, prostaglandin E, serotonin, potassium ions, adenosine triphosphate) that mediate the excitation and sensitization of nociceptors (group III and IV muscle afferents).

Modern concepts⁴,⁸ distinguish between the following influencing factors:

Predisposing (eg, genetic, structural, systemic, psychologic)

Initiating (eg, microtrauma, macrotrauma, overloading)

Sustaining/perpetuating (eg, psychosocial)

The classification into the individual categories is not intended to be rigid. For instance, overload of the sustaining and psychosocial conditions may be the predisposing factor in one patient, whereas the opposite pattern will apply in another patient. It is important to interpret this conceptual framework correctly, in the sense that a single influencing factor is not usually capable of causing musculoskeletal pains.

Meanwhile, there is evidence that endogenous or exogenous substances, such as estrogen,⁹ nerve growth factor (NGF),¹⁰ and glutamate,¹¹ might play a key role in the etiology of painful CMD. The fact that glutamate is able to cause peripheral sensitization without discernible signs of inflammation is extremely important in this context.¹¹ These new findings have rarely been discussed in the dental literature, but they offer a plausible explanation for the observation, which has long been made and is proven through epidemiologic studies, that females, especially women of child-bearing age, more commonly suffer from myoarthropathic pain than men.¹²,¹³

Epidemiology

The typical patient with painful CMD is a woman of child-bearing age with pains in the muscles of mastication. Women seek professional assistance because of their symptoms at an overwhelmingly higher rate than men. The more specialized the facility, the higher the proportion of women patients. In university pain centers, the ratio of women to men can be as high as 9:1.

Individual Need for Treatment

The question of whether an individual needs treatment automatically follows from the preceding comments. Traditionally, the range of dysfunction has been widely interpreted in dentistry. In the past, anyone who did not function like an articulator performing symmetric, noise-free movements would have run the risk of being regarded by a dental practitioner as potentially dysfunctional. Fortunately, this view has changed considerably.

CMD treatment not required

Current thinking is that certain CMD symptoms do not usually require any special (additional) diagnostic investigation and do not need treatment when people are otherwise pain-free:

Clicking or popping noises in the TMJs. The most common cause of TMJ clicking or popping is an anterior position of the articular disc. Clicking or popping noises without other symptoms (pains) are also not an indication for further diagnostics or treatment in the field of orthopedics. Carrying out magnetic resonance imaging for TMJ clicking or popping can thus be viewed as an excessive use of diagnostic tools. If patients report joint pains as well as TMJ noises—if they have painful joint clicking—the pain symptoms, but not the noise, require a more thorough examination and (usually) need treatment. An exception is a very loud clicking or popping of the joints that is not tolerable for the patient and his/her social environment. In this case, the available treatment methods that are indicated need to be fully explored, bearing in mind their particular risk-benefit relationship.

Grating noises in the TMJs. Grating noises in the TMJs are generally a clinical sign of contact between two bone surfaces. However, grating without other symptoms (pain) is not an indication for treatment.

Deviation (corrected lateral deviation) of the mandible during mouth opening.

Differences in the extent of maximum laterotrusion to the left and right. These tend to be more the rule than the exception¹⁴ and reflect the fluctuating asymmetry typical of mammals.

Sensitivity on palpation of jaw muscles and/or TMJs detected during a routine functional diagnostic examination. These areas are not painful during the course of the patient’s daily mandibular function.

Signs of osteoarthritis on radiographs (dental panoramic radiography).

All these symptoms, which used to be classified as dysfunctions, are today viewed as a variation from normality. This means the range of normal function—or eufunction—has been greatly expanded. Albert Gerber (Zurich) warned as early as 1964 that not every TMJ that causes discomfort must eo ipso be diseased and not all discomfort must be treated.¹⁵

CMD treatment required

By contrast, further diagnostic investigation and treatment are advisable in certain clinical situations:

Painful symptoms in the area of the jaw muscles and/or TMJs. Pains reported by patients must always be taken seriously. As a general rule, pain-related information provided by patients must not be doubted in terms of its veracity. This is especially true of the maxillofacial area, since it is extremely unlikely that pains in this area will result in early retirement—unlike back pains, for example. Pains in the region of the jaw muscles or in one or both TMJs are the key symptom in more than 90% of dental patients with painful CMD—and not a reduced range of mandibular movement or TMJ noises. However, a large proportion of patients with myoarthropathic pains do not consult a clinician for treatment. Anxiety about their existing problems is an important factor in whether patients decide to have their symptoms investigated and, if necessary, get therapeutic assistance. Pains in the muscles of mastication and/or TMJs are accompanied by a distinct limitation of the range of mandibular movement in rare cases. Pain-induced repositioning of the mandible (relieving posture) can cause changes in the occlusion of the teeth (premature contacts), which patients may find very disturbing, especially in the case of acute malocclusion.

Reduced range of mandibular movement, which usually affects maximum mouth opening. Limitations of movement are noticeable to some extent on laterotrusion and protrusion of the mandible but far less frequently than during mouth opening. In patients with painful CMD, there are basically two reasons for limited movement of the condyles of the mandible:

Mechanical obstacle in one or both TMJs caused by anterior, medial, or lateral displacement of the articular disc or by adhesions in the joint.

Reflex adaptation of mandibular movement (splinting effect) resulting from pains in the area of the jaw muscles and/or TMJs; the wider the mouth is opened, the greater the intensity of the pain. Voluntary limitations of mandibular movement in terms of a relieving posture can be interpreted as an adaptive mechanism under reflex control that aims to relieve the existing pains and protect the affected anatomical structures.

There is a generally recognized threshold beyond which it is possible to talk of limited mouth opening (= sum of vertical overbite and maximum interincisal distance). The commonly quoted value of 40 mm (or 38 mm in women) is by no means generally accepted as the threshold between limited and not limited. Essentially, a certain tolerance should be applied to any threshold because the maximum mouth opening possible with identical rotation in the condyles is dependent on the length of the mandibular body. However, dental practitioners must carry out further diagnostic measures in the following cases:

Limitations of the range of mandibular movement reported by the patient

Continuous reduction of maximum mouth opening lasting a period of a few days, weeks, or months

Measured mouth opening of less than 35 mm (clinical rule of thumb)

In these cases, a careful diagnostic investigation (including imaging techniques) is needed to exclude causes other than CMD, especially tumors. A tumor should be suspected until it has been disproved with absolute certainty. It should also be borne in mind that non-neoplastic changes, such as scleroderma and undetected mandibular fractures, can cause limited mouth opening.

It is primarily the patient, not the dentist, who gauges whether diagnosis and treatment are required in a case of painful CMD—unlike with caries or periodontal diseases, for which the dental practitioner usually decides on the need for treatment. This is why screening tests, which aim to identify and treat subclinical, prepathologic dysfunctions, should be viewed as unjustified excessive diagnostics in people who are subjectively symptom-free. This does not mean to detract from the value of carrying out (simple) functional diagnostics prior to major therapeutic interventions for prosthodontics, oral surgery, or orthodontics.

During and/or after examination, the symptoms that have been observed or are troubling the patient must be explained in a one-to-one conversation, based on up-to-date, reliable information that the patient will understand. This applies as well to symptoms that do not require treatment. The patient should be told about the probable cause of the symptoms and whether or not further diagnostic tests and treatment will be required. A useful approach is to draw an analogy for the patient between muscles of mastication and back muscles, and between TMJs and the lumbar spine. In cases of normal variation, patients should also be told what diagnostic and therapeutic measures are not required (according to the most current information) but which might be proposed and carried out elsewhere. Armed with this knowledge, they will be able to argue against such proposals.

Diagnoses and Classifications

To address the lack of standardized diagnostic and classificatory criteria for differentiating myoarthropathies, internationally renowned experts presented a new system of diagnosis and classification in 1992¹⁶ that, despite some shortcomings, quickly gained a high degree of international recognition. The name of the system—Research Diagnostic Criteria for Temporomandibular Disorders, RDC/TMD for short—indicates that it was originally developed for clinical trials for research purposes. However, it was soon applied in daily practice, often in a less strict form. RDC/TMD enables diagnostic measures and diagnoses to be standardized in a field previously characterized by inaccurate information and systems that were not comparable to each other. In 2014, the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) were published as a further refinement.¹⁷ In both systems, diagnostics and classification are spread over two areas, which are designated as Axis I and Axis II.

Axis I

Axis I covers the somatic diagnoses (Table 1-1). These are based on information provided by the patient who is consulting a dentist with symptoms affecting the masticatory system and on the results of the clinical examination. The results of a clinical examination are not sufficient to make the somatic diagnoses. What is more decisive is what the patient tells the dentist when complaining of pain, limited mouth opening, or loud noises in the TMJs. The DC/TMD, like the RDC/TMD, distinguishes between pain-related and pain-unrelated diagnoses that arise during the assessment of a patient.

Table 1-1 Somatic diagnoses of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD), which are not compatible with each other

However, as the category-based diagnoses have no implications for therapy, it is usually sufficient in working practice to make the following diagnostic distinctions:

Myalgia (of the relevant muscle or muscles)

Arthralgia (of one or both TMJs)

(Anterior) position (displacement) of the articular disc (with or without reduction)

Limitation of the mandibular range of movement (maximum mouth opening)

It should be stressed that a patient who, for instance, exhibits tender masseter muscles on palpation of masticatory muscles during a routine functional assessment but finds that the muscles never hurt during daily functioning would not be given a diagnosis of myalgia of both masseters but merely sensitivity on palpation of both masseters.

Axis II

Axis II comprises (mostly pain-related) psychosocial parameters, such as depression, anxiety, distress, negative stress management strategies, tendency to somatization, catastrophizing, and impairment in activities of daily living. It is currently regarded as the diagnostic standard to take into account the patient’s pain-associated psychosocial well-being. To do this, it is helpful to use validated filtered questionnaires (see chapter 2). The psychosocial findings, like the somatic diagnoses, have direct and distinctive implications for treatment.

Diagnostics

History taking

Taking a CMD-related history forms the essential basis of the diagnostic process. It is a self-contained dental service and is regarded as more important than the subsequent clinical examination of the patient.¹⁸ History taking consists of a medical interview tailored to the particular case history of a patient. To standardize patient details, it is also advisable to use validated filtered questionnaires for assessing the psychosocial impairment of patients suffering from pain.

Immediately before first contact with the treating clinician, it is a good idea for (potential) CMD patients to complete a questionnaire about any functional impairments in their masticatory system; this also contains questions about nonpainful findings. For most patients, however, pain plays an important, if not the major, role. The official definition of pain from the International Association for the Study of Pain (IASP) is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.¹⁹

The subsequent discussion of a patient’s pain history picks up relevant answers in the questionnaire and should cover the following areas:

Main complaints

Localization of the pain

Onset of the pain

Duration of the pain

Frequency of the pain

Quality of the pain

Intensity of the pain

Factors influencing the pain

Accompanying symptoms

Previous treatments

Patient’s expectation of treatment

Patients should also be asked about psychosocial stress factors before and at the time their pain starts. An appropriate way of assessing the degree of emotional stress is to approach the matter via an imaginary third person, which often makes it easier for patients to cope with the conversation taking an unexpected turn. For instance, the dentist might say: A lot of patients who have the same kind of symptoms say that … Is that your experience as well?

The use of other diagnostic record forms, which patients complete in the dental practice or at home before or after their first dentist-patient contact, is suitable for diagnosing patients with persistent orofacial pain. Pains of this kind are not long-lasting acute pains, but they obey their own rules, which is why more intensive diagnostic investigation is required.

The following tools have proved valuable:

Pain questionnaire

Graded Chronic Pain Scale (GCPS)²⁰

Depression anxiety stress scales (eg, the German DASS²¹)

It is particularly important to ask patients about any pains that are localized outside the facial area. Patients who consult their dentist will not normally mention pain occurring outside the jaw region unless they are asked. However, recognition of localized pain or widespread pain makes a big difference to the treatment strategy as well as the prognosis. Patients can even be given this part of the form to complete before the first consultation. To help them record any such pain, the questionnaire includes the outlines of a human figure seen from the front, back, and both sides. Patients are asked to mark all the topographic regions in which they typically experience pain. The result from a clinical point of view is that the pain drawings often provide more information than that obtained from panoramic radiographs in CMD patients. If anything, there is a risk with imaging that normal variations are erroneously interpreted as being linked to clinical signs and symptoms.

A pain history enables a working diagnosis to be made, which is confirmed in many cases during the subsequent examination, but it may also be modified to some extent.

In view of the subjective nature of pain and variables accompanying pain, which can be described by sufferers verbally and/or in writing mainly with questionnaires, some therapists occasionally assume that patients’ descriptions are soft data. In terms of their quality and significance, these are seen as less valuable than hard data obtained from clinical, imaging, and instrumental investigations. However, this view is mistaken because the opposite is often the case: Ideally, the investigations performed after the pain history has been taken merely serve to confirm or modify the diagnosis.

Clinical examination

Elements of the clinical examination include the following:

Measurement of the range of mandibular movement (condylar movement with simultaneous assessment of the presence of joint noises; maximum mouth opening; maximum laterotrusion and protrusion of the mandible). It is advisable to use a ruler marked in millimeters to numerically record the range of mandibular movement; the ruler must start immediately at one end with the 0-mm mark.

Palpation of the palpable muscles of mastication (temporalis, masseter) and the TMJs. Use of a pressure algometer enables clinicians to standardize this examination.

Occlusal examination. This particularly involves checking for the presence of occlusal contacts in maximum intercuspation and any changes to the dental hard tissues that have occurred (areas of attrition and abfraction) as evidence of teeth grinding or jaw thrusting.

The findings of the clinical examination are documented on a standardized record form.

Imaging

In principle, a dental panoramic radiograph, also known as an orthopantomogram (OPG or OPT), should be taken during the diagnosis of patients with symptoms of painful CMD. In view of the concerns patients frequently express over radiographic procedures, it is worth mentioning the favorable risk-benefit ratio given the relatively low radiation exposure of panoramic radiographs. The main purpose of a panoramic radiograph lies in differential diagnosis. Furthermore, it reveals gross morphologic changes in the TMJs, although these changes often have no pathologic significance. The radiographic findings generally play much less of a role than the results of the clinical examination when making the diagnosis and deciding whether CMD patients require treatment.

The use of advanced imaging—primarily cone beam computed tomography (CBCT) and magnetic resonance imaging (MRI)—following pain-focused history taking, clinical examination, and the availability of a recent panoramic radiograph—is reserved for cases in which the anticipated findings of further imaging techniques are likely to have a clear relevance in terms of clarifying the diagnosis and the resulting treatment or prognosis. Such relevance exists if the individual’s signs and symptoms or the examination findings cause the clinician to consider in differential diagnostic terms (for the purpose of exclusion or differentiation) diagnoses that may have specific and, in some cases, irreversible therapeutic consequences. Relevance can also apply if the signs and symptoms or the examination findings cannot be satisfactorily influenced despite the initiation of conservative, reversible therapeutic measures. By contrast, clear relevance does not exist if the findings from the advanced imaging would have no implications for the diagnosis being made and the treatment being adopted but are only being gathered together with other data in the sense