The mouth and jaw are used for many important functions including eating, speaking, and facial expression. When these functions are disrupted by a temporomandibular disorder (TMD) and accompanied by pain, the result is often great distress. TMD may affect the temporomandibular joint (TMJ), the jaw muscles, or both. These disorders are characterized by:
- facial pain most often in front of the ear
- alterations in the way the jaw moves including jaw locking or sticking
- clicking or popping noises during jaw movement
- pain with chewing and headache
The temporomandibular joint and other jaw muscles may also refer pain to other sites causing headache. For example, the temporalis muscle occupies a large area on the side of the head and is sometimes responsible for headaches. Headaches require investigation and diagnosis since there are many reasons for headaches and the jaw is only one possibility.
Causes of TMD
The cause of most TMD remains unknown. There are many factors that are thought to contribute to the development of these disorders but the mechanism and the importance of each is still unknown. Factors that may contribute to developing TMD include:
- hyperactivity of the jaw muscles - tooth clenching or bruxing (tooth grinding during sleep)
- stress leading to increased jaw muscle activity and reduced coping ability when the jaw becomes painful
- the form of the joint and jaw and the looseness of the joint ligaments
- abnormal positioning and habitually tensing the jaw muscles
- the way in which the jaw is used for functions such as chewing
- habits that may add stress on the jaw such as leaning on it or pressure from sleeping postures
- habits that overwork the jaw such as gum chewing, nail biting, chewing on pencils or pens
- injuries to the jaw such as overextending it or biting into hard foods
- injuries occurring during accidents
Classification of TMD
The most common TMD involve the jaw muscles, the disc, and the bony surfaces of the jaw joint bones. It is possible and not uncommon for someone with a TMD to have problems in more than one area at the same time. These conditions are often described using the following terms:
- Myofascial pain (muscle problems): Jaw muscle problems are characterized by pain during palpation examination of the muscles. Normally pressing or stimulating the muscle during examination should be perceived as pressure and not pain. The muscle or muscles may not be able to achieve normal length or may be guarding to avoid pain resulting in restricted jaw movement.
- Articular disc displacement (disc problems): Changes in normal disc position are characterized according to what happens to the disc during mouth opening and closing. If the disc returns to a normal position during mouth opening it is said to reduce. This movement of the disc usually causes a click that can be felt or heard during mouth opening and closing. If the disc remains out of place during mouth opening and closing it is said to be nonreducing. Nonreducing discs are a common cause of limited jaw movements and are sometimes described as "jaw locking."
- Osteoarthritis and arthralgia (joint bone problems): Osteoarthritis (inflammation) and arthralgia (joint pain) are other terms used to describe these joint bone problems. A smooth surface covers the joint bones that is bathed in a fluid produced by the joint lining that allows movements with very little friction or wear. When bony surfaces are placed under stress, remodeling occurs. This response may cause a loss of the normal smooth covering that is replaced by an irregular surface. These changes may lead to stresses on the bones during functions such as chewing.
There are other conditions that may affect this joint or the muscles, but the above are the most common.