TMD: Temporomandibular Disorders

Introduction

You may have read articles in newspapers and magazines about "TMD" temporomandibular (jaw) disorders, also called "TMJ syndrome." Perhaps you have even felt pain sometimes in your jaw area, or maybe your dentist or physician has told you that you have TMD.

If you have questions about TMD, you are not alone. Researchers, too, are looking for answers to what causes TMD, what are the best treatments, and how can we prevent these disorders. The National Institute of Dental and Craniofacial Research has written this pamphlet to share with you what we have learned about TMD.

TMD is not just one disorder, but a group of conditions, often painful, that affect the jaw joint (temporomandibular joint, or TMJ) and the muscles that control chewing. Although we don't know how many people actually have TMD, the disorders appear to affect about twice as many women as men.

The good news is that for most people, pain in the area of the jaw joint or muscles is not a signal that a serious problem is developing. Generally, discomfort from TMD is occasional and temporary, often occurring in cycles. The pain eventually goes away with little or no treatment. Only a small percentage of people with TMD pain develop significant, long-term symptoms.

What Is the Temporomandibular Joint?

The temporomandibular joint connects the lower jaw, called the mandible, to the temporal bone at the side of the head. If you place your fingers just in front of your ears and open your mouth, you can feel the joint on each side of your head. Because these joints are flexible, the jaw can move smoothly up and down and side to side, enabling us to talk, chew, and yawn. Muscles attached to and surrounding the jaw joint control its position and movement.

When we open our mouths, the rounded ends of the lower jaw, called condyles, glide along the joint socket of the temporal bone. The condyles slide back to their original position when we close our mouths. To keep this motion smooth, a soft disc lies between the condyle and the temporal bone. This disc absorbs shocks to the TMJ from chewing and other movements.

What Are Temporomandibular Disorders?

Today, researchers generally agree that temporomandibular disorders fall into three main categories:

• myofascial pain, the most common form of TMD, which is discomfort or pain in the muscles that control jaw function and the neck and shoulder muscles;
• internal derangement of the joint, meaning a dislocated jaw or displaced disc, or injury to the condyle;
• degenerative joint disease, such as osteoarthritis or rheumatoid arthritis in the jaw joint.

A person may have one or more of these conditions at the same time.

What Causes TMD?

We know that severe injury to the jaw or temporomandibular joint can cause TMD. A heavy blow, for example, can fracture the bones of the joint or damage the disc, disrupting the smooth motion of the jaw and causing pain or locking. Arthritis in the jaw joint may also result from injury. Other causes of TMD are less clear. Some suggest, for example, that a bad bite (malocclusion) can trigger TMD, but recent research disputes that view. Orthodontic treatment, such as braces and the use of headgear, has also been blamed for some forms of TMD, but studies now show that this is unlikely.

And there is no scientific proof that gum chewing causes clicking sounds in the jaw joint, or that jaw clicking leads to serious TMJ problems. In fact, jaw clicking is fairly common in the general population. If there are no other symptoms, such as pain or locking, jaw clicking usually does not need treatment.

Researchers believe that most people with clicking or popping in the jaw joint likely have a displaced disc — the soft, shock-absorbing disc is not in a normal position. As long as the displaced disc causes no pain or problems with jaw movement, no treatment is needed.

Some experts suggest that stress, either mental or physical, may cause or aggravate TMD. People with TMD often clench or grind their teeth at night, which can tire the jaw muscles and lead to pain. It is not clear, however, whether stress is the cause of the clenching/grinding and subsequent jaw pain, or the result of dealing with chronic jaw pain or dysfunction. Scientists are exploring how behavioral, psychological and physical factors may combine to cause TMD.

TMD Signs and Symptoms

A variety of symptoms may be linked to TMD. Pain, particularly in the chewing muscles and/or jaw joint, is the most common symptom. Other likely symptoms include:

• limited movement or locking of the jaw,
• radiating pain in the face, neck, or shoulders,
• painful clicking, popping, or grating sounds in the jaw joint when opening or closing the mouth.
• a sudden, major change in the way the upper and lower teeth fit together.

Symptoms such as headaches, earaches, dizziness, and hearing problems may sometimes be related to TMD. It is important to keep in mind, however, that occasional discomfort in the jaw joint or chewing muscles is quite common and is generally not a cause for concern. Researchers are working to clarify TMD symptoms, with the goal of developing easier and better methods of diagnosis and improved treatment.

Diagnosis

Because the exact causes and symptoms of TMD are not clear, diagnosing these disorders can be confusing. At present, there is no widely accepted, standard test to correctly identify TMD. In about 90 percent of cases, however, the patient's description of symptoms, combined with a simple physical examination of the face and jaw, provides information useful for diagnosing these disorders.

The examination includes feeling the jaw joints and chewing muscles for pain or tenderness; listening for clicking, popping or grating sounds during jaw movement; and examining for limited motion or locking of the jaw while opening or closing the mouth. Checking the patient's dental and medical history is very important. In most cases, this evaluation provides enough information to locate the pain or jaw problem, to make a diagnosis, and to start treatment to relieve pain or jaw locking.

Regular dental X-rays and TMJ X-rays (transcranial radiographs)