Causes of Symptoms
MUSCLE PAIN
Muscles can undergo pain as a result of over-working, which often occurs right after athletic performances. The overworked muscles are filled with by-products (such as lactic acid) that have accumulated in their capillary beds, they have low tonus, and they need rest to allow time for circulation to flush out the waste products from their capillary beds. This is a different situation from the muscle pain that we see in TMJ disorders, where the muscles have high tonus, and it causes an accumulation of waste products in the capillary beds, because the background compression due to the high tonus impairs resting circulation from flushing out the capillary beds. Thus, in TMJ disorders, the muscles are not suffering from overworking, and the capillary beds don't get flooded with waste products. Instead, the muscles gradually accumulate waste products because they cannot adequately drain them.
In both of these cases, pain results from the accumulation of waste products in the capillary beds. These capillary beds function like big sponges. The heart can easily pump new blood into them, but it cannot so 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 pumping during firing, with relaxation between firings to allow inflow of new blood. In this manner, functional circulation assists resting circulation in flushing out waste products. 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 good resting circulation.
Resting circulation depends on muscle tonus, because it determines the passive compression in the capillary beds. Normally muscles maintain 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 of the capillary beds and produce symptoms.
The common causes of jaw muscle tightness include:
TMJ INFLAMMATION causes jaw muscle tightening by triggering 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 - they hold themselves on guard to protect the joint. 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 cannot fully relax. The causes of inflamed TMJs are discussed below.
UNSTABLE BITES cause jaw muscle tightening by triggering reflex protective bracing in the jaw muscles. 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. Without a stable platform to rest on, the jaw muscles cannot fully relax.
STRAINED BITES restrict the range of motion of the mandible. Patients often report feeling like they cannot find a comfortable place for their mandible. Often they cannot access a comfortable place for resting their mandible, because its range of motion is restricted by the bite. The mandible cannot rest where it wants to. Reactions to the restriction vary. In more aggressive people, the muscles become hyperactive and react by pushing on the box to try to achieve more freedom of movement. In more passive people, the muscles react by becoming hypoactive and undergoing atrophy rather than fighting back against it.
CENTRAL NERVOUS SYSTEM STRESS causes jaw muscle tightening by increasing tightness in all the body's muscles; and it has an especially powerful effect on TMJ disorders because of the size discrepancy between the jaw opening and jaw closing muscles. In other parts of the body, bones rest between equally sized muscles pulling in opposite directions; therefore increasing resting tension in the muscles does not move the bones, - it just holds them more tightly. However, in the jaw system, the closing muscles dwarf the opening muscles. As a result, when stress increases the body's overall resting muscle tonus, it holds the jaw further closed, even sometimes in a full clench. For that reason, a period of increased central nervous system stress is such a common trigger for TMJ disorder symptoms that it was thought for decades to be the cause of TMJ disorders.
POSTURAL MUSCLE TIGHTNESS can spread to and from the jaw muscles, because the jaw muscles, especially the temporal muscles, are postural muscles. They are integral members of the chain of postural muscles running up and down the front of the body.
CONTRACTURE - After muscle tightness has persisted for long enough, the muscle fibers actually shorten anatomically in a process called myostatic contracture. They lose some of their resting length due to a reduction in the number of sarcomere units. If your jaw muscles are in contracture, and you fall asleep in a chair, your jaw will not hang open very far. Instead, your teeth may be almost touching, fully touching, or even clenched together.
JOINT (TMJ) PAIN
Joints, including the TMJs, cannot have sensory nerves in the area of compression; therefore they become don't painful until inflammation within the joint, usually triggered by cellular damage at the specialized articular surfaces, causes swelling of the joint that stretches the joint capsule or its ligamentous reinforcements. In TMJs, the inflammation and cellular damage at the specialized articular surfaces usually follows a dislocation of the disk.
DISLOCATION OF THE DISK from one or both of the TMJs is the event that begins the vast majority of TMJ disorders. Joints are designed to hold a cushion (in this case a flexible fibrous disk) between two opposing bones so those bones do not rub directly together. The joint capsule bathes the disk and the articular surfaces in lubricant. When a mandibular condyle get driven back into the back end of a TMJ, the lubricated disk get squeezed out its front end, like squeezing a watermelon seed out from between two fingers. The dislocated TMJ then functions like a door off its hinges. Damage can occur to the door (the lower jawbone), the door frame (the upper jawbone), or its hinges (the TMJs).
The role of disk dislocation has been controversial, and opinions have swung like a pendulum, as they often do after new information is uncovered. The new information was Farrar's surprising discovery in the 1980's that most of the clicking and popping sounds heard in the TMJs of patients who suffer from TMJ disorder symptoms are due to dislocated articular disks, unlike the clicking sounds commonly heard in other joints. For the next decade, many dentists tried to relocate (recapture) previously dislocated disks without understanding how to establish the necessary therapeutic bite, and consequently most of their attempts failed. In addition, many of those dentists trying to recapture dislocated disks did not understand the self-limiting nature of TMJ disorders and were unintentionally overtreating patients who actually had little pain and an excellent prognosis without treatment. About a decade later, the pendulum swung back the other way. Dental authorities warned that, because TMJ disk dislocation occurs in about 30% of the general population, it should be considered a variation of normal.
Now we know that dislocation of a TMJ disk can produce severe symptoms in some people and no symptoms in others. It can be anatomically relocated to its proper position in some cases, especially when the dislocation is recent and the joint noises are clear, but such extensive treatment is rarely necessary to eliminate the pain and other symptoms, because eventually dislocated TMJs adapt by fibrosing of the retrodiskal (behind the disk) tissues to create a pseudo-disk that can restore functional capacity (described further in MANAGING THE ARTHRITIC TMJ under the tab TREATMENTS), and the soft tissues of the articular eminence at the front of the TMJs thicken to restore some cushioning. TMJs have remarkable healing abilities.
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 head rests prevent overextension and 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 whiplash injury is more likely to result in damage to the teeth than to the TMJs.
CAUSAL FACTORS IN TMJ DISORDERS
While the ultimate cause of TMJ disorders is a strained facial growth pattern involving the jawbones, as summarized in CAUSES OF TMJ DISORDERS under the FOR DOCTORS tab and described in detail in ETIOLOGY, the symptoms can be treated effectively by addressing the causal factors involved in the symptom generating cycles, which are explained below.
PAIN-MUSCLE-PAIN CYCLES involve both the jaw muscles and the TMJs in a pain generating cycle that prevents the damaged TMJs from healing naturally. The inflammation from cellular damage at the articular surfaces triggers reflex tightening of the vertically aligned jaw closing muscles, which increases the pressure on the TMJ, which causes more damage at the cellular level of the articular surfaces, which triggers more inflammation. In these situations, anything that breaks the cycle, even a new injury or a treatment for a different problem, can provide short term relief. In fact, the relief that people sometimes feel from Botox is due to the sudden temporary weakening of the injected muscles, which breaks the cycle by removing one of its key elements.
NOCTURNAL BRUXISM (clenching or grinding the teeth during sleep), certainly puts large pressures on the whole jaw system, including the TMJs; and it varies with the amount of stress that a person is under. If a TMJ has lost its cushion by dislocation of its articular disk, that pressure could damage cells and trigger an inflammatory response, making it appear to be the whole cause of the disorder. If a person is under extreme stress, nocturnal bruxism could overwork the jaw muscles and cause accumulation of waste products in their capillary beds, making them tired sore. However, nocturnal bruxism is a by-product of normal sleep, and it is not found more frequently in TMJ disorder patients than in other people. Nothing will prevent it. Oral appliances can only reduce or redirect its forces.
LOSS OF ADAPTIVE CAPACITY can also function as a trigger that seems like a cause. Frequently a strained facial growth pattern due to a bite that slowly and progressively displaces the mandible exists without causing symptoms for many years before increased stress or an unrelated injury leaves the body unable to adapt to the strain and permits tissue damage, resulting in clinical symptoms. In these cases, the symptoms can be eliminated by anything that restores adaptive capacity; including nutritional support, relaxation, meditation, aerobic exercise, or feeling loved.
CENTRAL SENSITIZATION is a recently understood phenomenon that explains why some pains persist, even after their original cause has been removed. Central sensitization occurs in a pain pathway after a long period of chronic stimulation has caused sprouting of nerve endings at both ends of the pathway (the brain and the area of injury), which has made the pathway so excitable and hyperactive that its responses to all inputs become exaggerated and prolonged. In evolution, this nerve sprouting probably helped us be extra careful with an injured part until it healed. Today, when an injury does not heal and the pain pathway between it and the brain is stimulated chronically, that pain pathway can become so sensitized that even normal physiologic stimuli can trigger it and thereby produce pain without any apparent cause. We now understand that this is the cause of phantom limb pain. In treating central sensitization, therapy that is solely directed at the periphery may only provide limited relief; unless combined with centrally acting modalities such as anti-depressants, cognitive behavioral therapy, cannabis, meditation, or even just time. Therefore, in TMJ disorders that have undergone central sensitization, treatment of the jaw muscles and TMJs may be insufficient. Central sensitization is often associated with endocrine abnormalities, persistent elevation of sympathetic tone, fibromyalgia, chronic headache, and idiopathic dental pain.