This article explains the problems that can occur in the tiny temporomandibular joint (TMJ), which is found between the skull and the lower jaw, and how these can be treated.
- Where is the TMJ?
- Clicking jaw and TMJ disorder
- What causes jaw clicking?
- The stages of TMJ disorder
- Mild TMJ disorder: early diagnosis allows prevention of damage
- TMJ disorder progression
- Treating more severe TMJ disorder
- TMJ arthroscopy and joint injections
- Surgery for TMJ
- TMJ replacement
If you were to ask most people where their temporomandibular joint is they probably wouldn’t know. This tiny joint acts as the hinge between the base of the skull and the lower jaw and it allows us to eat, speak, smile and yawn. It is usually called the TMJ.
Like all joints, the TMJ can develop problems but awareness of the symptoms that arise and the assessments and treatments that are available is poor, even among general health professionals such as GPs and dentists. The reassuring news is that TMJ disorder of any severity can be managed effectively.
It is very common for the jaw to click when you yawn or move the lower jaw from side to side. Most people are not even bothered by this happening as it may cause no loss of function and no pain. Sometimes, however, the clicking is so frequent that sufferers begin to wonder whether it is a sign of something serious or if it could cause future problems.
Unless referred to a specialist in TMJ disorders this person may be left wondering for years, which can cause anxiety. A consultant with expertise in diagnosing and managing TMJ can provide reassurance and may recommend that no treatment is necessary. For patients who do have symptoms, such as locking and pain, an expert assessment can then be followed by treatment to help with the symptoms. In some cases clicking can in itself be damaging to the joint and early intervention may help prevent future arthritis.
The jaw joint is unique within the human body. It allows a full range of hinging and sliding movements so that the lower jaw can drop, move sideways and rotate to some degree. The jaw bone has a small projection, called the condyle, and a thin disc of cartilage to cushion the bone as the jaw moves. The disc resembles a baseball cap, fitting over the small domed condyle.
This is such a complicated mechanism that it is not really a surprise that things can go wrong. Often, the cartilage disc does not sit flush on the condyle and becomes squashed up as the condyle slides during jaw opening. The jaw then clicks when the cartilage pops back into place.
Jaw clicking due to a displaced cartilage disc on the condyle is more likely in people who:
- Grind their teeth– this often happens when you are asleep, but if it becomes excessive, it leads to a repetitive strain injury in the muscles around the jaw joint, which can cause pain due to inflammation in the joint and muscles.
- Sustain an injury to the jaw– in an accident or fall, for example, or after a whiplash injury to the cervical spine or a blow to the chin.
- Weightlift– repeated lifting of heavy weights and clenching and relaxing the jaw also causes repetitive strain injury.
- Have an underlying connective tissue disorder – people with hypermobility syndrome, for example, have very lax ligaments, which can make it more likely that the cartilage in the jaw will become displaced. For some people with these disorders the TMJ problem is the first manifestation of their condition and they will be referred by the TMJ specialist on to a rheumatologist.
TMJ problems range in severity, according to whether a patient has:
Reducible cartilage displacement: jaw clicking happens all the time as the cartilage becomes bunched up repeatedly and then returns to its original position. This is often painful and there may be intermittent episodes when a full range of movement is not possible but it settles over the course of a day or two.
Irreducible cartilage displacement: in some people, the cartilage can become completely and permanently displaced, usually in front of the condyle. This prevents the patient being able to open the jaw. Although their clicking has usually stopped, they then experience an increase in pain and, more worryingly, can no longer open their mouth more than a centimetre or two.
If TMJ disorder is recognised at an early stage, before the joint has been damaged, much can be done to prevent further injury and the development of more severe symptoms.
Occlusal splints (therapeutic gum shields) can be a simple solution that can stop unconscious teeth grinding at night (bruxism) and help the TMJ internal structure re-adjust to its correct state. When worn regularly, these reduce inflammation in the jaw joint as the repetitive strain injury subsides; however, the choice of shield is crucial. Soft gum shields routinely recommended by dentists for teeth grinders will protect the teeth, but they can in some cases increase the subconscious tooth grinding and therefore put more pressure on the joint. Hard shields, specially made and custom fitted, are recommended by TMJ specialists as these will protect the teeth and the jaw joint.
Jaw clenching and teeth grinding can also be a sign of stress and anxiety. Patients who see a TMJ consultant when they have fairly mild symptoms and may just be worried by jaw clicking, often respond to their diagnosis by taking a long, hard look at their lifestyle. It’s impossible to remove all stress from daily life, but being aware of the problem can be the trigger that some people need to re-evaluate the impact of work or family-related stress. People with this condition often suffer from tension related neck and shoulder pain as well and it is important that these are treated together as related conditions.
In the rare cases in which mild TMJ is due to hypermobility disorder, recognition of the underlying condition allows early intervention to prevent general joint degeneration and early arthritis. Patients can follow programmes of physiotherapy with muscle exercises to protect their joints for as long as possible.
As the muscles surrounding the joint become chronically strained and inflamed, and the cartilage of the joint displaces more erratically, this leads to increasing pain. Many instances of TMJ disorder are missed in general practice because the pain is not localised to the joint itself. It is more likely to radiate up into the ears or the side of the head.
Patients are often referred to an ENT consultant for detailed investigations of their ears, or to a neurologist who tries to determine the reason for their headaches. It may take some time for other possible causes to be ruled out before TMJ disorder is suspected and the patient is referred on to the correct specialist.
Sadly some patients will not be seen until they have progressed to the next stage, in which the cartilage within the jaw joint no longer goes back into place, leaving them with severely restricted jaw movement and constant pain. It’s hard to imagine, but only being able to open your mouth about 2cm has a major impact. Eating and chewing, even drinking becomes problematic. Speech and social interactions generally are affected. That, combined with increasing pain, means that someone with advanced TMJ disorder may become isolated and depressed.
Even someone who has lost jaw movement and is in constant pain can be treated effectively by a TMJ expert. The first step is to do a physical assessment and to take a medical history. Some detailed imaging of the TMJ will then be required.
An MRI scan is usually performed to reveal whether the cartilage disc over the condyle is badly displaced. This often includes a series of functional scans taken with the mouth closed and then open as wide as possible, which gives a clear picture of the status of the cartilage.
A therapeutic arthroscopy is usually the next step. Arthroscopy involves using an endoscope to examine inside the joint. This is often done for diagnosis but it also allows introduction of surgical instruments to treat the problems that are found as part of the same procedure.
Arthroscopy to investigate and treat TMJ disorder requires a specialised and very tiny arthroscope, only 1.2 mm in diameter. This is less than half of the size of the smallest general orthopaedic arthroscope. The treatment can therefore only take place at specialist centres that have the correct arthroscope and the TMJ consultant available to use it.
Even when a patient is in significant discomfort, using arthroscopy to see what is going on in the joint and then simply washing it out to remove debris can ease symptoms greatly. It is also possible to have anti-inflammatory injections directly into the joint, which work well for many people.
Around 60-70% of severe cases of TMJ can be helped by arthroscopy and surgery tends to be a last resort. However, if an arthroscopy shows that the cartilage disc is permanently displaced, the patient may then need an open operation to relocate the disc or if it is very badly damaged to remove the disc completely. This provides relief of symptoms but it is controversial; some experts suggest this may accelerate osteoarthritis of the TMJ, even though it removes the immediate cause of joint inflammation and inflammatory arthritis.
Although TMJ replacement by an artificial joint is rare, it is possible. The surgery removes the condyle and replaces it with a carefully designed titanium joint component. The bone within the skull that provides the entry point for the condyle is drilled away and re-surfaced using high-density polymer, which is fixed to the skull bone. This completely reconstructs the TMJ, allowing the same range of movement as a natural joint. In the most extreme cases, when severe arthritis is present in the patient’s own TMJ, joint replacement provides a huge improvement in function.