Causes of Symptoms
MUSCLE PAIN
Muscles can undergo pain as a result of over-working, which often occurs right after athletic performances, but that pathology is very different from what is seen in the jaw muscles in TMJ disorders. Muscles that are painful from overworking are filled with by-products (such as lactic acid) that have accumulated in their capillary beds, and they have low tonus (tension at rest). In contrast, muscles that are painful from a TMJ disorders have chronically elevated tonus, which produces compression that prevents resting circulation from removing the waste products from the capillary beds, where they accumulate and produce pain.
The capillary beds where the waste products accumulate 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 pumping during firing, with relaxation between firings to allow inflow of new blood. In this manner, functional circulation helps flush 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 in the capillary beds.
Resting circulation depends on low muscle tonus. 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 thereby produce pain.
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 tighten the jaw muscles by restricting their range of motion, forcing them to do all their chewing and clenching on an exercise template that is strained, much like lifting weights off to the side or riding a bicycle with the seat too low. Patients often report feeling like they cannot find a comfortable place for their mandible. It feels like an arm that is in a box that prevents it from being able to stretch out all the way. 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, simply living in the box rather than fighting back against it.
CENTRAL NERVOUS SYSTEM STRESS increases 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 generally equal 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 a common trigger for TMJ disorder symptoms.
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 contracture. They lose some of their resting length. 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, resting in contact, or even clenched together.
JOINT (TMJ) PAIN
TMJ joint pain frequently causes jaw muscle pain, but TMJ joint pain is different from jaw muscle pain, because joint pain involves inflammation and swelling. Joints cannot have sensory nerves in the area of compression; therefore they only become painful when inflammation of the joint causes swelling that stretches the joint capsule or its ligamentous reinforcements. The TMJs typically undergo inflammation after dislocation of the disk has pulled the delicate retrodiskal tissues into the joint space where the disk used to be, subjecting those tissues to bruising as a result of normal chewing or nocturnal bruxism (grinding or clenching).
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. When a mandibular condyle get driven posteriorly into the back end of a TMJ, the lubricated disk gets squeezed out from 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 in the TMJs 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) these 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 TMJs have remarkable healing abilities. Eventually the TMJs adapt to disk dislocation 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 cushioning.
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 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 - can prevent 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, including a Botox injection, a new nightguard, or even a new injury, can provide at least short term relief.
NOCTURNAL BRUXISM (clenching or grinding the teeth during sleep), certainly puts large pressures on the whole jaw system, including the TMJs; and it increases with stress. 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. 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.
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 some other cause of reduced adaptive capacity leaves the body unable to withstand the strain and permits tissue damage that results 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 - 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 helped protect an injured part while it healed. Today, when an injury does not heal, 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.