The temporomandibular joint is a synovial, condylar and hinge-type joint made up between the mandibular fossa, the articular tubercle and the head of the mandible.

It is a fibrocartilage joint with no hyaline and it is a unique joint because there is a disc called the articular disc that separates the joint into two synovial cavities.

There are four muscles of mastication, innervated by the mandibular branch of the trigeminal nerve.

They include the temporalis, which is the most powerful muscle of the temporomandibular joint muscles and is involved in elevation and retrusion of the mandible, the masseter, which is responsible for elevating the jaw, and the medial pterygoid muscle, involved in elevation and protrusion of the mandible.

The lateral pterygoid muscle functions to protrude the mandible and is the only muscle of mastication involved in depressing the mandible.

Pain is one of the main features of temporomandibular joint disorder, seen in 96% of patients.

Especially, this happens on palpation or with movement like chewing or yawning.

It is usually one-sided and just anterior to the ear, with a tendency to be worse in the morning.

The character is typically described as a poorly localized aching.

Ear discomfort and headaches are present in around 80% of cases.

Another main feature is jaw discomfort or dysfunction, seen in around 75% of cases.

This can include trismus, which is a limited range of movement in the mandible, which can make eating and talking difficult.

Alongside this, patients often complain of the jaw locking.

Clicking or popping noises are another feature of temporomandibular joint disorder, which can come from temporary dislocation of the articular disc and its subsequent return to normal position.

The locking of the jaw may occur when the disc does not go back to its usual position.

The noise is often louder to the patient than to others due to the proximity to the ear.

Other associated symptoms include pain in the neck or in the teeth, and in some cases hearing loss, tinnitus and dizziness.

Temporomandibular joint disorder is more common in younger adults, with the 20-40 age group being affected most commonly.

Some studies suggest that up to nearly 40% of the population have a sign or symptom associated with temporomandibular joint disorder, but only around 5% will have symptoms severe enough to seek medical advice.

It is between 2 and 9 times as common in females than it is in males.

Psychosocial factors also seem to play a role, particularly stress.

If you've seen the fibromyalgia and irritable bowel syndrome videos, you'll know that temporomandibular joint disorder was mentioned in those, which are also often associated with stress.

Between 50 and 70% of sufferers report having had stressful life events in the 6 months before the onset of symptoms.

Bruxism, which is a form of parafunctional activity, in this case grinding teeth and clenching the jaw, has been linked to temporomandibular joint disorder, but the relationship between the two isn't clear.

The exact cause is not known, but the temporomandibular joint disorders are divided grossly into articular disorders, meaning intra-articular, or masticatory muscle disorders, meaning extra-articular.

Articular disorders could be disc derangement, which is the most common intra-articular cause.

One theory suggests the lateral pterygoid muscle contracts instead of relaxing when the mouth closes, leading to disc displacement.

Degeneration of the joint, like osteoarthritis, congenital disorders, trauma or even infections are other articular disorders, while masticatory muscle disorders could be myofacial pain disorder, inflammation such as myositis, or muscle spasms.

The diagnosis is primarily made based on the history and physical exam, which can include painful palpation of the temporomandibular joint, abnormal movement of the jaw or poor range of motion, and associated clicking sounds, although these are not specific.

The cranial nerve exam should also be unremarkable.

In terms of imaging, x-rays, including panoramic x-ray, are the first line imaging for evaluation of potential temporomandibular joint disorder if the history and physical are not enough, although CT, MRI or even ultrasound can also be used to visualise the joint.

Differentials of facial pain include dental conditions, various forms of neuralgia such as trigeminal, glossopharyngeal or postherpetic neuralgia.

Disorders of the salivary glands, temporal arteritis and migraines are also included, as well as ENT infections such as sinusitis and ear infections.

For the treatment, symptomatic care is the first line, which includes a soft diet, hot and cold packs and analgesia. 40% of patients will have spontaneous resolution of symptoms.

Patient education is important, including counselling on stress reduction, sleep hygiene and avoidance of parafunctional habits like grinding teeth or chewing objects.

Cognitive behavioural therapy can also be effective and physical therapy has some evidence of benefit as well.

Medications that may be used include non-steroidal anti-inflammatory drugs, specifically naproxen as a first line, and tricyclic antidepressants like amitriptyline, muscle relaxants and anti-convulsants like diazepam or gabapentin are more advanced options.

In some patients occlusal therapy is useful, which focuses on the position of the mandible.

This can be altered temporarily with a splint that the patient places in the mouth, somewhat like a retainer, or more permanent modifications can be made to the teeth.

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