Causes of Symptoms

ROOT CAUSE - Although 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 OF TMJ DISORDERS under the FOR DOCTORS tab; and long term treatment should improve the growth pattern to progressively reduce those strains; short-term elimination of the symptoms, within hours or days, requires only addressing their direct causes, primarily TMJ inflammation and jaw muscle tightness.

TMJ INFLAMMATION - is the acute stage, usually shortly after disk dislocation, when the TMJ is swollen, which also triggers reflex protective jaw muscle bracing. During function, the muscles fire slowly and carefully, often overlapping the firing patterns of the jaw opening and closing muscles (co-contraction) to more tightly control jaw movements. At rest, the muscles stay on guard. 

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. Muscles can undergo pain from over-working, such as following athletic performances; but the jaw muscles in chronic TMJ disorders are not overworked or tired, they are tense and tight. They hold excessive tonus, because they cannot fully relax.  The problem is a high ratio of tonus to maximal strength. Effective treatment can either lower the tonus (relaxation) or increase the maximal strength (exercise).

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. Increasing that tonus can prevent adequate drainage, leading to accumulation of waste products and pain. 

Causes of jaw muscle tightness (hypertonus) include:

            UNSTABLE BITES can 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, like an arm stuck in a box where it cannot fully extend. Reactions to the restriction vary. More aggressive people usually push against the walls of the box to try to achieve more freedom of movement (strong bruxism which reduces facial height). Their muscles become hyperactive and undergo hypertrophy. More passive people usually accept the restriction. Their muscles become hypoactive and undergo atrophy, simply living in the box rather than fighting it, which enables the eruption forces built into the growth pattern to increase facial height. 

        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; so increasing overall resting muscle tonus does not move the bones, - it just holds them more tightly. However, in the jaw system, the closing muscles dwarf the opening muscles, so increased overall resting muscle tonus holds the mandible further closed. It may even hold the mandible closed far enough to create tooth contacts that trigger forceful jaw closing in a chewing reflex, sometimes in a full clench. 

NOCTURNAL BRUXISM - clenching and grinding during sleep, has long been considered a cause of TMJ disorders; but there is no evidence for that. It is not more forceful or frequent in people with TMJ disorders. 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, while the frequency of TMJ disorders increases. Nocturnal bruxism certainly increases with stress, and it can forcefully work the muscles, but it only harms them when it works them against an exercise template that is unstable or displaced. The jaw system was designed for extreme exercise on an unstrained exercise template. Oral appliances can provide an ideal exercise template for absorbing the forces of nocturnal bruxism without damaging the components of the jaw system. 

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 form the top 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, which can dislocate the articular disk. 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.