Table of Contents
The causes of Temperomandibular Joint disorders
There are two basic causes of the TMD pain :
Traumatic injury and the parafunctional habits (habits that use the teeth and supporting structures beyond their normal functional design limits).
Injury to the face or jaws during automobile accidents, sporting accidents, fights or just about any activity in which the jaws or the TM Joints suffer a direct hit can cause physical injury to the joint, or to the muscles that make the jaws open, close and move side to side.
Injury to the joint itself can lead to swelling, tearing of the internal ligaments and cartilage, and can, in rare instances, lead to long term difficulties such as arthritis (chronic inflammation of a joint) or even in extreme cases, ankylosis (permanent welding of the otherwise separate structures of the joint). Thankfully, the majority of traumatic TMD cases are temporary, caused by muscle cramping, and will subside in several months. Some can hang on and be made much worse by the second (and major) cause of TMD, parafunctional habits.
The term “parafunctional” refers to any action that goes beyond normal function. Habits of this nature stretch the normal physiologic limits beyond the breaking point and thus cause pain, and often, permanent physical damage to the joint and supporting structures of the jaws and teeth.
Parafunctional habits Parafunctional habits come in numerous forms and depend on the nervous disposition and overall daily activities of the individual. They may range from grinding and clenching the teeth, to continuously tapping the teeth together, holding the jaw in eccentric positions throughout the day (see the discussion of posture), working the jaw muscles against each other without necessarily clenching or grinding the teeth, or even forcing the tongue against the roof of the mouth or the front teeth. Bruxing is defined as grinding the teeth with considerable force for a prolonged period of time, and clenching is defined as keeping the teeth together without grinding for a prolonged period. Together, these two habits account for the vast majority of the parafunction that leads to TMD. The one thing that all these habits have in common is that they overwork the muscles and overstress the teeth, the joints and the gums. Ultimately overuse of the muscles causes the patient headaches, neck aches, or earaches, while misuse of the teeth, gums and joints damages those structures. Because these habits are carried out unconsciously, the patient experiences pain without understanding that he/she is causing it themselves.
One of the most common reasons that people begin bruxing is having extensive dental work done. Every time a dentist changes a filling, or extracts a tooth, this changes the way a patient bites. A patient can feel, and react to changes in the height of a tooth that amount only to the thickness of a piece of cellophane. Even tiny changes in the bite can stimulate an unconscious habit of severe bruxing which can lead to serious pain.
Before you can understand what parafunction of the jaws actually means, it is important to understand what normal functioning involves. (For the purposes of this article, I am limiting the discussion to parafunction involving the forceful contact of the teeth — bruxing and clenching — and its effect on the temperomandibular joints.)
The relationship of the bite to the joints
In ideal circumstances, when a person closes his or her teeth together, each individual tooth should make even contact with one or more teeth in the opposite arch (upper and lower teeth are arranged in arches). When the teeth are in maximum contact, the ball portion of both temperomandibular joints should rest in a comfortable position at the highest point in their sockets.
In some people, however, there is a discrepancy in the positions of one or both of the joints when the teeth are fully closed. This is especially prevalent in patients who have lost back teeth. The ball of the joint (the “condyle“, colored blue in the diagram) on one side may be pressed hard against the top or the back of its socket (the socket, called the “fossa” is colored green in the diagram), crushing the cartilage disk (the Meniscus, colored red) . This can stretch the ligaments (yellow) that encapsulate the joint (they are shown cut away on this view, but can be seen just below the blue ball of the joint). In such an instance, one can see that when the teeth are pressed together with some force, this action can put considerable stress on the two joints.
The graphic above illustrates three different relationships between the ball and socket. The top illustration shows a normal anatomical arrangement, with the teeth together (in occlusion) and the condyle and the fossa in a normal relationship, separated by the meniscus. The two lower illustrations show situations in which the teeth are also together, but the condyle and fossa are pressed closer together, damaging the meniscus in the middle diagram, and crushing the meniscus in the lower diagram. Left untreated, continual bruxing causes both situations to deteriorate further causing more damage to the joint. Note that in all three diagrams, the teeth are together. What is different in each situation is the position of the condyle within the fossa. Since teeth move continuously throughout a person’s life, constant bruxing and clenching can create a dynamic in which the pressure placed on the teeth can cause the teeth to shift position. This, in turn causes a corresponding shift in the position of the condyle. This is how a single patient may progress from the normal anatomy seen in the top illustration, through the situation in the middle diagram to the situation in the lower diagram.
This is especially likely to happen if any of the back teeth are removed early in life. The loss of back teeth causes the remaining teeth to shift position over time. In order to understand this phenomenon better, click the icon to the left.
Dental students, as well as students of other dental and health related professions may wish to consult my page on occlusion which is the companion page to this piece.
The good news
No matter how bad the arrangement of the teeth, or how seriously the joints are misaligned when the teeth are forced together, if the teeth are not pressed together with force, and are kept slightly separated, the joints tend to fall back into their normal positions, and no stress is placed on them at all. This is the case with most people and is the reason that minor discrepancies in the joint/teeth arrangement do not cause the average person much pain and agony. The people who DO develop serious TMD problems are those with the nervous predisposition to brux (grind) and/or clench their teeth.
The most important thing to remember about Normal function is this:
This is true even when chewing food. You can prove this to yourself the next time you chew something. You will note that your own teeth barely touch each other when chewing gum or just about anything else. The only time the upper and lower teeth actually brace against each other with any force is when swallowing, and this is only for a fraction of a second, and they touch lightly at that! Nature designed the entire system; teeth, gums, joint and muscles to work under NORMAL circumstances. Thus, under NORMAL function, even discrepancies between the way the teeth come together and the way the joints sit in their sockets are not of practical importance. No stress on the teeth means no stress on the joints or the muscles! Unfortunately, Nature didn’t take the stress of civilization into account.
Now, it is perfectly normal for children 12 and under to grind their teeth while sleeping, so when you walk into their room at night and hear them grinding away, don’t worry. This is a natural, built-in mechanism to help us shed the baby teeth and to help the adult teeth erupt into the most stable positions within the dental arches. However, after the adult teeth are in place, the habit of grinding and clenching is supposed to disappear. Unfortunately, civilization is full of stress (as if you didn’t already know). And under stressful conditions, various infantile habits such as biting the nails, sulking, crying, screaming, throwing fits and grinding and clenching the teeth tend to return and manifest as stress relievers. Bruxing and clenching are socially acceptable while the other stress relievers are not, so people often resort to bruxing when they can’t scream at the top of their lungs!
Everyone bruxes or clenches!
Here lies the real root of 95% of all TMJ associated pain. All those headaches, ear aches, sensitive teeth and other symptoms mentioned above are the result of stress induced bruxing. What’s that?? You don’t grind or clench your teeth?? Yes you do!!! These habits are usually entirely unconscious. Everyone does it once in a while, but some people do it to such an extent that they make themselves sick, and they aren’t even aware that they are causing their own symptoms by unconscious bruxing habits.
Before proceeding further, it is important to understand that bruxing and clenching together constitute one of the four major factors that effect the health of the teeth. For the entire perspective on why some people never seem to have trouble with their teeth and jaws, while others never seem able to win the daily battle, read the entire article.