Temporomandibular joint dysfunction

Temporomandibular joint dysfunction
Classification and external resources
ICD-10	K07.6
ICD-9	524.60
DiseasesDB	12934
MedlinePlus	001227
eMedicine	neuro/366 radio/679 emerg/569
MeSH	C05.500.607.221.897.897

Temporomandibular joint dysfunction (sometimes abbreviated to TMD and also termed temporomandibular joint dysfunction syndrome or many other names), is an umbrella term covering pain and dysfunction of the muscles of mastication and the temporomandibular joint, which connects the mandible to the skull. The most important feature is pain and impairment of function, which can cause difficulty eating or speaking. Although TMD is not life threatening, it can detriment quality of life. TMD is thought to be very common, with one estimate stating that about 20-30% of the adult population are affected to some degree. It most common in people between 20 and 40 years of age.

There is disagreement over the causes of TMD, and there are many treatments available, although there is a general lack of evidence for any treatment in TMD.

Classification

Example classification of temporomandibular disorders.

Muscular: Hyperactivity, spasm, and trismus Inflammation (myositis) Trauma Myofascial pain and fibromyalgia Atrophy or hypertrophy Arthrogenic: Disc displacement (internal derangement) Hypomobility of the disc (adhesions or scars) Dislocation and subluxation Arthritis Infections Metabolic disease (gout, chondrocalcinosis) Capsulitis, synovitis Ankylosis (fibrous or bony) Fracture Condylar hyperplasia, hypoplasia or aplasia Neoplasia

Definition and variation in terminology

Temporomandibular joint dysfunction is sometimes described as the most common form of temporomandibular disorder, whereas many other sources use the term temporomandibular disorder synonymously, or instead of the term temporomandibular joint dysfunction. In turn, the term temporomandibular disorder is described as "a clinical term [referring to] musculoskeletal disorders affecting the temporomandibular joints and their associated musculature. It is a collective term which represents a diverse group of pathologies involving the temporomandibular joint, the muscles of mastication, or both". Another definition of temporomandibular disorders is "a group of conditions with similar signs and symptoms that affect the termporomandibular joints, the muscles of mastication, or both." Temporomandibular disorder is a term that creates confusion since it refers to a group of similarly symptomatic conditions, whilst many sources use the term temporomandibular disorders as a vague description rather than a specific syndrome, and refer to any condition which may affect the temporomandibular joints (see table). The temporomandibular joint is susceptible to a huge range of diseases, some rarer than others, and there is no implication that all of these will cause any symptoms at all.

The preferred terms in medical publications is to an extent influenced by geographic location, e.g. in the United Kingdom, the term "pain dysfunction syndrome" is in common use, and in other countries different terms are used. In the United States, the term "temporomandibular disorder" is generally favored. It is common for sources to arbitrarily use a preferred term and then list a handful of other synonyms. A more complete list of synonyms for this topic is extensive, with some being more commonly used than others. In addition to those already mentioned, examples include "temporomandibular joint pain dysfunction syndrome", "temporomandibular pain dysfunction syndrome", "temporomandibular joint syndrome", "temporomandibular joint disorder", "temporomandibular dysfunction syndrome", "temporomandibular dysfunction", "temporomandibular disorder", "temporomandibular syndrome", "facial arthromyalgia", "myofacial pain dysfunction syndrome", "craniomandibular dysfunction", "myofacial pain dysfunction", "masticatory myalgia", "mandibular dysfunction", and "Costen's syndrome".

The lack of standardization in terms is not restricted to medical papers. Notable internationally recognized sources vary in both their preferred term, and their offered definition, e.g.

"Temporomandibular Pain and Dysfunction Syndrome - Aching in the muscles of mastication, sometimes with an occasional brief severe pain on chewing, often associated with restricted jaw movement and clicking or popping sounds." (Classification of Chronic Pain, International Association for the Study of Pain).

"Headache or facial pain attributed to temporomandibular joint disorder." (International Classification of Headache Disorders 2nd edition (ICHD-2), International Headache Society).

"Temporomandibular joint-pain-dysfunction syndrome" listed in turn under "Temporomandibular joint disorders" (International Classification of Diseases 10th revision, World Health Organization).

In this article, the term temporomandibular disorder is taken to mean any disorder than affects the temporomandibular joint, and temporomandibular joint dysfunction (here also abbreviated to TMD) is taken to mean symptomatic (e.g. pain, limitation of movement, clicking) dysfunction of the temporomandibular joint, however there is important to remember that there is no single, globally accepted term or definition concerning this topic.

Classification by duration

Sometimes distinction is made between acute TMD, where symptoms last for less than 3 months, and chronic TMD, where symptoms last for more than 3 months. Not much is known about acute TMD since these individuals do not typically attend in secondary care (hospital).

TMD is considered by some to be one of the 4 major symptom complexes in chronic orofacial pain, along with burning mouth syndrome, atypical facial pain and atypical odontalgia.

The disorder transcends the boundaries between several health-care disciplines — in particular, dentistry and neurology.

Signs and symptoms

Signs and symptoms of temporomandibular joint disorder vary in their presentation and can be very complex, but are often simple. The symptoms will usually involve more than one of the various components of the masticatory system, muscles, nerves, tendons, ligaments, bones, connective tissue, and/or the teeth.

The three cardinal signs and symptoms of TMD are:

• Pain and tenderness on palpation in the muscles of mastication, or of the joint itself (preauricular pain - pain felt just infront of the ear). Pain is the defining feature of TMD and is usually aggravated by manipulation or function, such as when chewing, clenching, or yawning, and is often worse upon waking. The character of the pain is usually dull or aching and intermittent, although it can sometimes be constant. The pain is more usually unilateral (located on one side) rather than bilateral. It is rarely severe.
• Limited range of mandibular movement, which may cause difficulty eating or even talking. There may be locking of the jaw, or stiffness in the jaw muscles and the joints, especially present upon waking. There may also be incoordination, asymmetry or deviation of mandibular movement.
• Noises from the joint during mandibular movement, which may be intermittent, e.g. clicking, popping, or crepitus (grating).

Other signs and symptoms have also been described, although these are less common and less significant than the cardinal signs and symptoms listed above. Examples include:

• Headache (possibly), (e.g. pain in the occipital region (the back of the head), or the forehead), or other types of facial pain including migraine, tension headache. or myofascial pain.
• Pain elsewhere, such as the teeth, neck, or shoulder.^{[medical citation needed]}
• Diminished auditory acuity (hearing loss).
• Tinnitus (occasionally).
• Dizziness.
• Blinking^{[medical citation needed]}
• Sensation of malocclusion (feeling that the teeth do not meet together properly).

Pathophysiology

Left temporomandibular joint, lateral view.

Left TMJ, medial view, showing sphenomandibular and stylomandibular ligaments.

Sagittal TMJ cross-section showing articular eminence, articular disc, and upper and lower joint spaces.

Anatomy and physiology of the mastication system

Temporomandibular joints

Main article: Temporomandibular joint

The temporomandibular joints are the dual articulation of the mandible with the skull. Each TMJ is classed as a "ginglymoarthrodial" joint since it is both a ginglymus (hinging joint) and an arthrodial (sliding) joint, and involves the condylar process of the mandible below, and the articular fossa (or glenoid fossa) of the temporal bone above. Between these articular surfaces is the articular disc (or meniscus), which is a biconcave, transversely oval disc composed of dense fibrous connective tissue. Each TMJ is covered by a fibrous capsule. There are tight fibers connecting the mandible to the disc, and loose fibers which connect the disc to the temporal bone, meaning there are in effect 2 joint capsules, creating an upper joint space and a lower joint space, with the articular disc in between. The synovial membrane of the TMJ lines the inside of the fibrous capsule apart from the articular surfaces and the disc. This membrane secretes synovial fluid, which is both a lubricant to fill the joint spaces, and a means to convey nutrients to the tissues inside the joint. Behind the disc is loose vascular tissue termed the "bilaminar region" which serves as a posterior attachment for the disc and also fills with blood to fill the space created when the head of the condyle translates down the articular eminence. Due to its concave shape, sometimes the articular disc is described as having an anterior band, intermediate zone and a posterior band. When the mouth is opened, the initial movement of the mandibular condyle is rotational, and this involves mainly the lower joint space, and when the mouth is opened further, the movement of the condyle is translational, involving mainly the upper joint space. This translation movement is achieved by the condylar head sliding down the articular eminence, which constitutes the front portion of the articular fossa. The ligament directly associated with the TMJ is the temporomandibular ligament, whilst the stylomandibular ligament and the sphenomandibular ligament are not directly associated with the joint capsule. Together, these ligaments act to restrict the extreme movements of the joint.

Left temporalis muscle.

Left medial pterygoid muscle, and left lateral pterygoid muscle above it, shown on the medial surface of the mandibular ramus, which has been partially removed along with a section of the zygomatic arch.

Left masseter muscle (red highlight), shown partially covered by superficial muscles.

Muscles of mastication

Main article: Muscles of mastication

The muscles of mastication are paired on each side and work together to produce the movements of the mandible. The main muscles involved are the masseter, temporalis and medial and lateral pterygoid muscles. They can be thought of in terms of the directions they move the mandible, with most being involved in more than one type of movement due to the variation in the orientation of muscle fibers within some of these muscles.

• Protrusion - Lateral and medial pterygoid.
• Retraction - Posterior fibers of temporalis (and the digastric and geneihyoid muscles to a lesser extent).
• Elevation - Anterior and middle fibers of temporalis, the superficial and deep fibers of masster and the medial pterygoid.
• Lateral movements - Medial and lateral pterygoid.

Each lateral pterygoid muscle is composed of 2 heads, the upper or superior head and the lower or inferior head. The lower head originates from the lateral surface of the lateral pterygoid plate and inserts at a depression on the neck of mandibular condyle, just below the articular surface, termed the pterygoid fovea. The upper head originates from the infratemporal surface and the infratemporal crest of the greater wing of the sphenoid bone. The upper head also inserts at the fovea, but a part may be attached directly to the joint capsule and to the anterior and medial borders of the articular disc. The 2 parts of lateral pterygoid have different actions. The lower head contracts during mouth opening, and the upper head contracts during mouth closing. The function of the lower head is to steady the articular disc as it moves back with the condyle into the articular fossa. It is relaxed during mouth closure.

Mechanisms of main signs and symptoms

Joint noises

The sounds commonly produced by TMD are usually described as a "click" or a "pop" when a single sound is heard and as "crepitation" or "crepitus" when there are multiple, grating, rough sounds. Clicking often accompanies either jaw opening or closing, and usually occurs towards the end of the movement. The noise indicates that the articular disc has suddenly moved to and from a temporarily displaced position (disk displacement with reduction) to allow completion of a phase of movement of the mandible. If the disc displaces and does not reduce (move back into position) this may be associated with locking. Clicking alone is not diagnostic of TMD since it is present in high proportion of people who have no pain. Creptius often arthritic changes in the joint, and may occur at any time during mandibular movement, especially lateral movements. Due to the proximity of the TMJ to the ear canal, joint noises are perceived to be much louder to the individual than to others. Often people with TMD are surprised that what sounds to them like very loud noises cannot be heard at all by others next to them. However, it is occasionaly possible for loud joint noises to be easily heard by others in some cases and this can be a source of embarrassment e.g. when eating in company.

In people with TMD, it has been shown that the lower head of lateral pterygoid contracts during mouth closing (when it should relax), and is often tender to palpation. To theorize upon this observation, some have suggested that due to a tear in the back of the joint capsule, the articular disc may be displaced forwards (anterior disc displacement), stopping the upper head of lateral pterygoid from acting to stabilize the disc as it would do normally. As a biologic compensatory mechanism, the lower head tries to fill this role, hence the abnormal muscle activity during mouth closure. There is some evidence that anterior disc displacement is present in proportion of TMD cases. Anterior disc displacement with reduction refers to abnormal forward movement of the disc during opening which reduces upon closing. Anterior disc displacement without reduction refers to an abnormal forward, bunched-up position of the articular disc which does not reduce. In this latter scenario, the disc is not intermidiary between the condyle and the articular fossa as it should be, and hence the articular surfaces of the bones themselves are exposed to a greater degree of wear (which may predispose to osteoarthritis in later life).

Pain

The surfaces in contact with one another (cartilage) do not have any receptors to transmit the feeling of pain. The pain therefore originates from one of the surrounding soft tissues, or from the trigeminal nerve itself, which runs through the joint area. When receptors from one of these areas are triggered, the pain can cause a reflex to limit the mandible's movement. Furthermore, inflammation of the joints or damage to the trigeminal nerve can cause constant pain, even without movement of the jaw.^{[medical citation needed]}

Patients with TMD often experience pain such as migraines or headaches, and consider this pain TMJ-related.^{[medical citation needed]}

Due to the proximity of the ear to the temporomandibular joint, TMJ pain can often be confused with ear pain. The pain may be referred in around half of all patients and experienced as otalgia (earache). Conversely, TMD is an important possible cause of secondary otalgia. Treatment of TMD may then significantly reduce symptoms of otalgia and tinnitus, as well as atypical facial pain. Despite some of these findings, some researchers question whether TMJD therapy can reduce symptoms in the ear, and there is currently an ongoing debate to settle the controversy.

Limitation of mandibular movement

The jaw deviates to the affected side during opening, and restricted mouth opening usually signifies that both TMJs are involved, but severe trismus rarely occurs. If the greatest reduction in movement occurs upon waking then this may indicate that there is concomitant sleep bruxism. In other cases the limitation in movement gets worse throughout the day.

The jaw may lock entirely.

Degenerative joint disease, such as osteoarthritis or organic degeneration of the articular surfaces, recurrent fibrous and/or bony ankylosis, developmental abnormality, or pathologic lesions within the TMJ. Myofascial pain syndrome.^{[medical citation needed]}

Theories of underlying causes

TMD is a symptom complex (i.e. a group of symptoms occurring together and characterizing a particular disease), which is thought to be caused by multiple factors, but the exact etiology is unknown. There are factors which appear to predispose to TMD (genetic, hormonal, anatomical), factors which may precipitate it (trauma, occlusal changes, parafunction), and also factors which may prolong it (stress and again parafunction). Overall, 2 hypotheses have dominated research into the causes of TMD, namely a psychosocial model and a theory of occlusal dysharmony. Interest in occlusal factors as a causative factor in TMD was especially widespread in the past, and the theory has since fallen out of favor and become controversial due to lack of evidence.

Psychosocial factors

Emotional stress (anxiety, depression, anger) may increase pain by causing autonomic, visceral and skeletal activity and by reduced inhibition via the descending pathways of the limbic system. The interactions of these biological systems have been described as a vicious "anxiety-pain-tension" cycle which is thought to be frequently involved in TMD. Put simply, stress and anxiety cause grinding of teeth and sustained muscular contraction in the face. This produces pain which causes further anxiety which in turn causes prolonged muscular spasm at trigger points, vasoconstriction, ischemia and release of pain mediators. The pain discourages use of the masticatory system (a similar phenomenon in other chronic pain conditions is termed "fear avoidance" behavior), which leads to reduced muscle flexibility, tone, strength and endurance. This manifests as limited mouth opening and a sensation that the teeth are not fitting properly.

In the 6 months before the onset, 50-70% of people with TMD report experiencing stressful life events (e.g. involving work, money, health or relationship loss). It has been postulated that such events induce anxiety and causes increased jaw muscle activity. Muscular hyperactivity has also been shown in people with TMD whilst taking examinations or watching horror films. Depression and sleep deprivation are important risk factors for TMD.

Others argue that a link between muscular hyperactivity and TMD has not been convincingly demonstrated, and that emotional distress may be more of a consequence of pain rather than a cause.

Bruxism and other para-functional activities

Main article: Bruxism

Bruxism is an oral parafunctional activity where there is excessive clenching and grinding of the teeth. It can occur during sleep or whilst awake. The cause of bruxism itself is not completely understood, but psychosocial factors appear to be implicated in awake bruxism and dominergic dysfunction and other central nervous system mechanisms may be involved in sleep bruxism. If TMD pain and limitation of mandibular movement are greatest upon waking, and then slowly resolve throughout the day, this may indicate sleep bruxism. Conversely, awake bruxism tends to cause symptoms that slowly get worse throughout the day, and there may be no pain at all upon waking.

The relationship of bruxism with TMD is debated. Many suggest that sleep bruxism can be a causative or contributory factor to pain symptoms in TMD. Indeed, the symptoms of TMD overlap with those of bruxism. Others suggest that there is no strong association between TMD and bruxism. A systematic review investigating the possible relationship concluded that when self reported bruxism is used to diagnose bruxism, there is a positive association with TMD pain, and when more strict diagnostic criteria for bruxism are used, the association with TMD symptoms is much lower. Self reported bruxism is probably a poor method of identifying bruxism. There are also very many people who grind their teeth and who do not develop TMD.

Other parafunctional habits such as pen chewing, lip and cheek biting (which may manifest as morsicatio buccarum and/or linea alba), are also suggested to contribute to the development of TMD.

Jaw thrusting, excessive gum chewing, nail biting, eating very hard foods. A majority of TMJD patients believe bruxism to be a contributory factor.^{[medical citation needed]}

Trauma

Minor injuries are occasionally identified as a possible cause of TMD, however the evidence is not strong. Prolonged mouth opening (hyper-extension) is also suggested as a possible cause. It is thought that this leads to microtrauma and subsequent muscular hyperactivity. This may occur during dental treatment, with oral intubation whilst under a general anesthetic, during singing or wind instrument practice (really these can be thought of as parafunctional activities). Damage may be incurred during violent yawning, laughing, road traffic accidents, (e.g. sudden neck hyper-extension, or "whiplash"), sports injuries, interpersonal violence, or during dental treatment, (such as tooth extraction).

when eating large sized foods, sneezing.^{[medical citation needed]}

Occusal factors

Abnormalities of occlusion (problems with the bite) are often blamed for TMD but there is no evidence that these factors are involved. Occlusal factors as an etiologic factor in TMD is a controversial topic, and when formally investigated, there are no statistically significant differences in the number of occlusal abnormalities in people with TMD and in people without TMD. There is also no evidence for a link between orthodontic treatment and TMD. The modern, mainstream view is that the vast majority of people with TMD, occlusal factors are not related. Theories of occlusal factors in TMD are largely of historical interest (see History).

Possible associations

• Scuba diving

Diagnosis

Dynamics of temporomandibular joint during voluntary mouth opening and closing visualized by real-time MRI.

Pain is the most common reason for people with TMD to seek medical advice. Joint noises may require auscultation with a stethescope to detect. The differential diagnosis is with degenerative joint disease (e.g. osteoarthritis), rheumatoid arthritis, temporal arteritis, otitis media, parotitis, mandibular osteomyelitis, Eagle syndrome, trigeminal neuralgia,^{[medical citation needed]} oromandibular dystonia,^{[medical citation needed]} deafferentation pains, and psychogenic pain.

Diagnostic criteria

Various diagnostic systems have been described. Some consider the Research Diagnostic Criteria (RDC/TMD) method the gold standard. This method involves 2 diagnostic axes, namely axis I, the physical diagnosis, and axis II, the psychologic diagnosis. Axis I contains 3 different groups which can occur in combinations of 2 or all 3 groups.:

• Group I: muscle (myofascial) pain with tenderness of muscles when palpated.
• Group II: disk displacements with and without reduction, where there is clicking from the TMJs and locking of the jaw respectively.
• Group III: TMJ pain and degeneration. Group III can include arthralgia (joint pain), where there is local TMJ tenderness, arthrosis, where there is crepitus (grating from the TMJ), and arthritis, with crepitus and local TMJ tenderness.

McNeill 1997 described TMD diagnostic criteria as follows:

• Pain in muscles of mastication, the TMJ, and /or the periauricular area (around the ear), which is usually made worse by manipulation or function.
• Asymmetric mandibular movement with or without clicking.
• Limitation of mandibular movements.
• Pain present for a minimum of 3 months.

The International Headache Society's diagnostic criteria for "headache or facial pain attributed to temporomandibular joint disorder" is similar to the above:

• A. Recurrent pain in one or more regions of the head and/or face fulfilling criteria C and D
• B. X-ray, MRI and/or bone scintigraphy demonstrate TMJ disorder
• C. Evidence that pain can be attributed to the TMJ disorder, based on at least one of the following:
  • pain is precipitated by jaw movements and/or chewing of hard or tough food
  • reduced range of or irregular jaw opening
  • noise from one or both TMJs during jaw movements
  • tenderness of the joint capsule(s) of one or both TMJs
• D. Headache resolves within 3 months, and does not recur, after successful treatment of the TMJ disorder

Management

It is suggested that before the attending dentist commences any plan or approach using medications or surgery, a thorough search for inciting para-functional jaw habits must be performed. Correction of any discrepancies from normal can then be the primary goal.

Patients may employ a nighttime biofeedback instrument such as a biofeedback headband or biofeedback device to help them modify para-functional jaw habits which take place in sleep. In addition, there are various treatment modalities which a well-trained experienced dentist may employ to relieve symptoms and improve joint function.^{[citation needed]} They include:

• Manual adjustment of the bite by grinding the teeth (occlusal adjustment). This, too, is not a widely accepted practice and should be avoided as it is irreversible.
• Nighttime biofeedback for para-functional habit modification
• Mandibular repositioning splints which move the jaw, ligaments and muscles into a new position and myofunctional therapy
• Reconstructive dentistry
• Orthodontics
• Arthrocentesis (joint irrigation)
• Surgical repositioning of jaws to correct congenital jaw malformations such as prognathism and retrognathia
• Replacement of the jaw joint(s) or disc(s) with TMJ implants (this should be considered only as a treatment of last resort)

In line with the recommendations of the National Institute of Dental and Craniofacial Research (NIDCR) of the National Institutes of Health (NIH), treatments for TMJD should not permanently alter the jaw or teeth, but need to be reversible. To avoid permanent change, over-the-counter or prescription pain medications may be prescribed.

Other interventions include:

• Stabilization splint (biteplate, nightguard) is a common but unproven treatment for TMJD. A splint should be properly fitted to avoid exacerbating the problem and used for brief periods of time. The use of the splint should be discontinued if it is painful or increases existing pain.
• Cognitive Behavioral Therapy (CBT). Psychosocial risk factors have also been linked to TMJ syndrome. Studies have shown that changes in psychosocial issues can help reduce pain and increase jaw movement.

Occlusal splints

A lower, full coverage occlusal splint.

An upper, full coverage occlusal splint.

Occlusal splints (also called night guards or mouth guards) reduce nighttime clenching in some patients, while increasing clenching activity in other patients.^{[citation needed]} Thus, while occlusal splints do prevent loss of tooth enamel from grinding, use of a "one size fits all" splint can worsen TMJ disorder symptoms for some people.

All appliances are not equal in effectiveness. When patients have a problem 24 hours/ day 7 days a week the use of a nighttime appliance may not be the best approach. An orthotic is worn all day and night and allows for permanent healing of the joints and muscles. A neuromuscular orthotic that is made to a physiologic rest position is one of the most effective treatments but usually requires a long term correction. Neuromuscular dentistry addresses the healthy muscle physiology and body posture as well as the TM joints.^{[citation needed]}

Frequently patients with TMJ disorders also have sleep apnea or UARS, upper respiratory airway resistance syndrome and receive the most benefit from a night-time airway appliance and a daytime orthotic. Patients with long-term chronic pain respond extremely well to this type of therapy.

Medication

Medication is the main method of managing pain in TMD, mostly because there is little if any evidence of the effectiveness of surgical or dental interventions. Many different drugs have been used to treat TMD pain, such as analgesics (pain killers), benzodiazepines (e.g. clonazepam, prazepam, diazepam), anticonvulsants (e.g. gabapentin), muscle relaxants (e.g. cyclobenzaprine), and others. Analgesics that have been studied in TMD include non-steroidal anti-inflammatory drugs (e.g. piroxicam, diclofenac, naproxen) and cyclo-oxygenase-2 inhibitors (e.g. celecoxib). Topical methyl salicylate and topical capsaicin has also been used. Other drugs that have been described for use in TMD include glucosamine hydrochloride/chondroitin sulphate and propranolol. Dispite many randomized control trials being conducted on these commonly used mediciations for TMD a systematic review carried out in 2010 concluded that was insufficient evidence to support or not to support the use of these drugs in TMD. Low-doses of anti-muscarinic tricyclic antidepressants such as amitriptyline, or nortriptyline have also been described. Injections of local anesthetic into the muscles are sometimes used.

Elimination of para-functional habits

An approach to eliminating para-functional habits involves the taking of a detailed history and careful physical examination. The medical history should be designed to reveal duration of illness and symptoms, previous treatment and effects, contributing medical findings, history of facial trauma, and a search for habits that may have produced or enhanced symptoms. Particular attention should be directed in identifying perverse jaw habits, such as clenching or teeth grinding, lip or cheek biting, or positioning of the lower jaw in an edge-to-edge bite. All of the above strain the muscles of mastication (chewing) and result in jaw pain. Palpation of these muscles will cause a painful response.

Treatment is oriented to eliminating oral habits, physical therapy to the masticatory muscles, and alleviating bad posture of the head and neck. A biofeedback headband or biofeedback device may be worn at night to help patients train themselves out of the para-functional habit of nighttime clenching and grinding (bruxism). A flat-plane full-coverage oral appliance, e.g. a non-repositioning stabilization splint, reduces bruxism in some patients, and can take stress off the temporomandibular joint, although some individuals may bite harder on it, resulting in a worsening of their conditions. The anterior splint, with contact at the front teeth only, may prove helpful to some patients, but for those patients who bite harder on this type of splint, even more damage may occur. Thus, different types of splint therapy may work for different patients.

Biofeedback

Nighttime EMG biofeedback (for instance by using a biofeedback headband or biofeedback device) can be used to reduce bruxism and thus reduce or eliminate the ongoing nightly cycle of damage that contributes to the majority of TMJ disorder symptoms. This treatment is non-invasive. A mirror can be used as a biofeedback device. The patient, watching in the mirror, relaxes the jaw vertically while exhaling. With daily practice the jaw opens midline and the symptoms usually abate. Low level laser therapy may be effective in reducing pain from TMJD, however, further research is still required to determine the optimal treatment protocols. There is some evidence that some people who use a biofeedback headband to reduce nighttime clenching experience a reduction in TMD.

Occlusal adjustment/reorganization

If the occlusal surfaces of the teeth or the supporting structures have been altered due to inappropriate dental treatment, periodontal disease, or trauma, the proper occlusion may need to be restored.^{[citation needed]} Patients with bridges, crowns, or onlays should be checked for bite discrepancies. These discrepancies, if present, may cause a person to make contact with posterior teeth during sideways chewing motions. These inappropriate contacts are called interferences, and if present, they can cause a patient to subconsciously avoid those motions, as they will provoke a painful response. The result can be excessive strain or even spasms of the chewing muscles. Treatment could include adjusting the restorations or replacing them. (Christensen 1997, A Consumer's Guide to Dentistry).

Surgery

Attempts in the last decade to develop surgical treatments based on MRI and CAT scans now receive less attention. These techniques are reserved for the most difficult cases where other therapeutic modalities have failed. The American Society of Maxillofacial Surgeons recommends a conservative/non-surgical approach first. Only 20% of patients need to proceed to surgery.

Examples of surgical procedures that are used in TMD, some more commonly than others, include arthrocentesis, arthroscopy, menisectomy, disc repositioning, condylotomy or joint replacement. Invasive surgical procedures in TMD may cause symptoms to worsen.

Arthrocentesis

TMJ arthrocentesis refers to lavage (flushing out) of the upper joint space with saline via the introduction of cannulae. It is theorized that the hydraulic pressure generated within the joint combined with external manipulation is capable of releasing adhesions or the anchored disc phenomenon and leads to an improvement in the movement. It is also suggested that undesirable contents within the synovial fluid of the joint can be washed out, such as microscopic debris (from breakdown of the articular surfaces) and pain mediators (enzymes and prostaglandins), and there is also stimulation of the synovial membrane to restore its normal lubricating function. It was initially used to treat acute closed lock, however it has since come to be used chronic closed lock, chronic anterior displaced disc with reduction, and degenerative joint disease (e.g. arthritis). This is the least invasive, and easiest to carry out of the surgical options. It can be carried out under local anesthetic (and for this reason is cheaper than arthroscopy) and has minimal complications. Although it has been suggested that arthrocentesis decreases pain, increases maximal incisal opening and has prolonged affects, when the procedure was investigated by a systematic review, the impact on pain was comparable to arthroscopy and the results are unstable. The review concluded by suggesting that arthrocentesis only be used for TMD within well designed randomized controlled trial (i.e. for the purposes of further research and not for routine management).

Arthroscopy

Arthroscopy involves the introduction of an arthroscope (a very thin, flexible camera) into the joint via single cannula (as opposed to arthrocentesis which involves 2 cannulae and no arthroscope), allowing the joint space to be visualized on a monitor and explored by the surgeon. The arthroscope has a built in capacity to pump in or suck out saline. Arthroscopy may be intended as a purely diagnostic procedure, or it may be employed in combination with surgical interventions within the joint, such as release of adhesions (e.g. by blunt dissection or with a laser) or release of the disc. Arthroscopy is usually carried out under general anesthesia. Arthroscopy has advantages over arthrocentesis in that it allows for detection of problems inside the joint such as perforation or synovitis.

Prognosis

TMD is benign and self-limiting, but the pain involved may detriment quality of life. Importantly, TMD does not cause permanent damage and does not progress to arthritis in later life.

Epidemiology

TMD mostly affects people in the 20 - 40 age group, and the average age is 33.9 years. People with TMD tend to be younger adults who are otherwise healthy.

About 75% of the general population may have at least one abnormal sign associated with the TMJ (e.g. clicking), and about 33% have at least one symptom of TMD. However, only in 3.6-7% will this be of sufficient severity to trigger the individual to seek medical advice.

For unknown reasons, females are more likely to be affected than males, in a ratio of about 2:1, although others report this ratio to be as high as 9:1. Females are more likely to request treatment for TMD, and their symptoms are less likely to resolve. Females with TMD are more likely to be nulliparous than females without TMD.

History

Temporomandibular disorders were described as early as the ancient Egyptians. An older name for the condition is "Costen's syndrome", after James B. Costen, who partially characterized it in 1934.