Causes of Symptoms

The root cause of TMJ disorders is a dysharmonious facial growth pattern that continuously produces strains between the jawbones and the postural system, as described in CAUSES under the FOR DOCTORS tab. For lasting treatment success, these strains must be taken into account in the orthopedic measures applied. Thus all our long term use appliances are designed to gradually diminish strains by controlling the slow facial and jawbone growth of adulthood. However, for short term treatment success; both the strains and the symptoms can be eliminated by addressing their more immediate and direct causes, primarily jaw muscle tightness and TMJ inflammation.

JAW MUSCLE TIGHTNESS - in the form of increased resting tonus, the background tension that is maintained by muscles, is responsible for most of the symptoms in TMJ disorders. Muscles can undergo pain from over-working, such as following athletic performances, and theoretically they could be over-worked in some people by nocturnal bruxism during times of extreme stress; but the jaw muscles in chronic TMJ disorders are not overworked or tired, they are tense and tight. They have excessive tonus, because they cannot fully relax.  

Chronically increased muscle tonus produces pain, because sustained compression prevents resting circulation from removing the waste products from all areas of the capillary beds. These capillary beds function like big sponges. The heart can easily pump new blood into them, but it cannot easily suck the old blood out of them. In most areas of the body, the removal of waste products from the capillary beds is assisted by functional forces, which alternately compress and release the veins, which have one-way valves that turn the compression and release process into a pumping action. Agonists and antagonists alternate firing so each group can relax between firings to allow inflow of new blood (post-exercise hyperemia). However, we no longer chew hard enough to provide sufficient functional circulation to keep our jaw muscles healthy; therefore modern jaw muscle health relies on low resting tonus to maintain circulation in the capillary beds. Normally muscles maintain a resting tonus in the form of a light contraction that is about one percent of a muscle’s maximal voluntary contractile force. A tonus of two or three percent of maximal voluntary force can prevent adequate drainage, leading to accumulation of waste products and pain. 

Increased jaw muscle tonus also affects subsequent facial growth, because postural tonus provides the light steady forces that shape bones. In this manner, the increased jaw muscle tension can inhibit healthy jawbone growth and thereby become self-sustaining. Typically jaw muscle hypertonus makes faces grow shorter, wider, and more retrusively (backwardly positioned mandible).

Causes of jaw muscle tightness (hypertonus) include:

            TMJ INFLAMMATION - triggers reflex protective bracing. If your TMJ is inflamed, you have a bone on the edge of a swollen area, which automatically sends your jaw muscles into a state of hypervigilance. During function, they fire carefully and often overlap the firing patterns of the jaw opening and closing muscles (co-contraction) to more tightly control jaw movements. At rest, they hold themselves on guard to protect the joint. 

            UNSTABLE BITES also cause jaw muscle tightening by triggering reflex protective bracing. Instability in any joint triggers reflex bracing in the muscles which cross that joint, the bite functions like a joint between the jawbones, and the muscles which cross that joint are the jaw muscles. 

          STRAINED BITES cause jaw muscle tightening by restricting the mandibular range of motion. Patients sometimes feel like their arm is in a box, and the walls of the box are the teeth. Reactions to the restriction vary. Aggressive people fight against it. Their muscles become hyperactive and push on the box to try to achieve more freedom of movement (strong bruxism which limits facial height increases). Passive people accept the restriction. Their muscles become hypoactive and undergo atrophy, simply living in the box rather than fighting it, which usually results in facial height elongation. 

        CENTRAL NERVOUS SYSTEM STRESS increases tightness in all the body's muscles; but it has an especially powerful effect on TMJ disorders because of the size discrepancy between the jaw opening and jaw closing muscles. In most of the body, bones rest between equal sized muscles pulling in opposite directions; therefore increasing overall resting muscle tensions does not move the bones, - it just holds them more tightly. However, in the jaw system, the closing muscles dwarf the opening muscles, so increasing the body's overall resting muscle tonus holds the mandible further closed. The tooth contacts can trigger reflex jaw muscle firing, sometimes resulting in a full clench. For that reason, a period of increased central nervous system stress often precedes jaw muscle symptoms.

NOCTURNAL BRUXISM - clenching and grinding during sleep, has long been considered a cause of TMJ disorders; but there is no evidence for that, and there is good evidence against it. Nocturnal bruxism is a by-product of normal sleep, when the sleeping brain sends firing signals to the motor root of the jaw muscles, usually during transitions between sleep stages following increases in sympathetic activity, heart rate, and suprahyoid muscle tonus. It is not more frequent in TMJ disorder patients, and its frequency decreases during childhood and adolescence, when the frequency of TMJ disorders increases. Nocturnal bruxism increases with stress, and it can certainly work the muscles, but it only harms them when it works them against an exercise template that is unstable or displaced. Oral appliances can enable the jaw system to better withstand bruxism, and deep relaxation can reduce it, but nothing can stop or prevent it. 

POSTURAL MUSCLE TIGHTNESS can cause jaw muscle tightness, just as jaw muscle tightness can cause postural muscle tightness; because the temporal muscles are postural muscles, and the jaw closing muscles are members of the myofascial chain running up and down the front of the body.  

WHIPLASH is certainly one cause of disk dislocation and other TMJ injuries. Before head rests became universal on car seats, the damage to TMJs in whiplash was thought to be due to overextension of the head. Now that rear end collisions still cause TMJ damage, it is apparent that the cause of the TMJ damage in whiplash is the sudden forward movement of the head causing a free floating mandible to strike the back of the TMJ like the clanger in a bell. If the victim sees the impact coming, the teeth will be clenched tightly together at the time of impact; and the injury is more likely to result in damage to the teeth than to the TMJs.