The temporomandibular joint (TMJ) is one of the most complicated joints in your body. You have one on each side of your face, just in front of your ears, where the temporal bone of the skull connects to the lower jaw (mandible). Your TMJs open and close like a hinge and slide forward, backward, and from side to side. When you bite and chew, they sustain an enormous amount of pressure.
As with other joints, the surfaces of your TMJs are covered with cartilage. Like the knee joint, the two parts of the joint are separated by a small disc, or meniscus, that prevents the bones from rubbing against each other. Muscles that enable you to open and close your mouth also serve to stabilize these joints, which are located about ½ inch (1.25 cm) in front of each ear canal.
A range of problems can affect the TMJs and the muscles surrounding them. These problems usually occur between the ages of 20 and 50. Most often, the cause of TMJ is a combination of muscle tension, anatomical problems, and injury. Sometimes, there may be a psychological component as well.
Like all of your joints, your TMJ may develop osteoarthritis, rheumatoid arthritis, and other inflammatory conditions. In rare instances, tumours may develop in this area. But for most people, pain in the area of the TMJ isn't serious. Discomfort and pain may be temporary or chronic and sometimes goes away with little or no treatment.
In order for you to open your mouth and operate your jaw in the way that it should, your left and right TMJs must work in unison. If the movement of both of these joints isn't coordinated, the disc that separates your lower jaw from your skull can slip out of position, and problems will result. Dislocation of your TMJ may take place if your mouth is forced to open rapidly or too widely.
In addition, muscle pain and tightness around the jaw can often come from muscle overuse as a result of clenching or grinding the teeth (bruxism) brought on by psychological stress or overuse. Extreme jaw clenching can also lead to pain over the temples. This occurs because the muscles that control jaw movement are also attached to a nearby bone of your skull. Excessive gum chewing or forceful biting, such as cracking nuts in your teeth, may also strain the TMJs and cause pain.
Some additional and less common ways of developing TMJ problems include:
- sports-related injury
- auto accident injury
- ankylosis, which is loss of joint movement resulting from a fusion of bones within the joint or calcification of the ligaments around it
- certain inherited facial characteristics that produce misalignments
- congenital abnormalities where the top of the jawbone doesn't form or is smaller than normal
- dental conditions such as a high filling, a tipped tooth, or teeth displaced due to earlier loss of other teeth
- developmental abnormalities such as in some children where the top of the jawbone may grow faster or for a longer time than normal (congenital and developmental abnormalities are rare, but can cause facial deformities and misalignment of the upper and lower sets of teeth)
- hypermobility (looseness of the jaw), when the ligaments that hold the joint together become stretched
- internal derangement, where the disc inside the joint lies in front of its normal position
- structural abnormalities of the temporal joint
Symptoms and Complications
There is an easy test you can do yourself to check whether you're able to open your jaw as much as you should. Most people can place the tips of their index, middle, and ring fingers held vertically in the space between the upper and lower front teeth without forcing. If your space is smaller, or if you experience pain or a clicking or grinding noise when you try to open your mouth this far, you probably have TMJ problems.
Common symptoms of TMJ problems include:
- a clicking sound or grating sensation on opening the mouth or chewing
- dull aching pain in front of the ear
- headaches that don't respond to the usual medical treatment
- locking of the joint, making it difficult to open
- tenderness of the jaw muscles
- pain made worse by pushing on the TMJ when the mouth is open
The pain will often occur only on one side of the face, and sometimes the pain may seem to occur near the joint rather than in it. Pain and muscle tightness may be present after waking up in the morning or during and after stressful periods. These symptoms result from muscle spasms brought on by repeated muscle or tooth clenching and tooth grinding. Many people grind their teeth during their sleep and aren't even aware of it, and clenching and grinding is more forceful when a person is asleep than when they are awake.
Making the Diagnosis
If you experience any of the above symptoms, you should speak to your doctor or, better yet, to your dentist. Dentists commonly diagnose and prescribe treatment for TMJ problems. In order to make the diagnosis, he or she will take your medical history and perform a physical examination of your jaw and face. The dentist may push on the side of your face or place a finger by your ear and gently press forward while you open and close your jaw. Also, in order to detect pain or tenderness, your dentist may gently feel the muscles you use to chew. He or she will also check to see whether your jaw slides when you bite, and can tell if you're grinding your teeth by looking for excessive wear on the biting surfaces of your teeth.
Special X-ray techniques may be used to help make the diagnosis. If your dentist suspects that the disc lies in front of its normal position (a condition called internal derangement), he or she may order an X-ray in which a dye is injected into your joint (an arthrogram). Computed tomography (CT) or magnetic resonance imaging (MRI) may be used in rare cases to find out why a person isn't responding to treatment.
Laboratory tests for TMJ problems aren't often done, as they're rarely useful. Dentists occasionally use electromyography, which analyzes muscle activity, to monitor treatment and occasionally to make a diagnosis.
Treatment and Prevention
Many people with temporomandibular joint problems (TMJ ) recover without any treatment. TMJ disorders that may require treatment are those that include:
- damage to the inside of the joint
- developmental or congenital abnormalities
- muscle pain and tightness
- reduced or excessive mobility of the joint
If the TMJ disorder is caused by inflammation within the joint, physical therapy and medications such as acetylsalicylic acid* (ASA), other nonsteroidal anti-inflammatory drugs (NSAIDs), or muscle relaxants work quite well. If a person is experiencing severe pain and inflammation, the doctor or dentist may recommend that a corticosteroid or a local anesthetic medication be injected into the joint to reduce discomfort. Acupuncture, acupressure, massage, and hypnosis are other techniques used by some dentists to decrease pain and to relax muscles.
A soft diet may be recommended to reduce the strain on the TMJ caused by biting and chewing.
If you're aware that you clench or grind your teeth, you can take steps to break the habit. Splint therapy is the most popular and least invasive treatment. A thin plastic night guard is specially made to fit over either your upper or lower set of teeth and is then adjusted to provide you with an even bite. Most night guards are worn at night to reduce grinding, although they can also be used during the day. They can also prevent damage to your teeth. In addition, biofeedback or relaxation therapy, physical therapy, other behaviour modification techniques, and therapeutic jaw exercises can help.
If you have abnormalities in the alignment of your teeth that are causing TMJ problems, your dentist may correct this by balancing biting surfaces, replacing missing teeth, or replacing uneven or defective fillings or crowns.
Misalignment of the TMJ is usually treated with a plastic bite plate or splint that helps promote better alignment of your jawbones. This corrective device is also worn over your teeth and will help to re-establish proper alignment. As with the night guard used to prevent grinding, you should bring this device with you when you visit your dentist, as it may need to be adjusted occasionally.
Your dentist may also recommend changes in your chewing habits such as limiting gum chewing or avoiding firm foods such as caramels, non-tender meats, raw carrots, and celery. You may also be asked to try to limit opening your mouth wide when you yawn.
If your symptoms continue despite treatment, you may be referred to a specialist in oral and maxillofacial surgery to repair or to remove the disc that separates the adjacent bony surfaces of the TMJ or to realign the bones.
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