The head had to be completely reshaped with a severe bend in its middle so its front half (containing the balance and visual systems) could maintain their necessary orientation level with the ground, while its back half (containing the brain) rotated ninety degrees along with the top of the spinal column. It was this folding of the skull around its front half which made room for expansion of the brain on its back half.  To keep the head erect, muscles from all around the upper part of the body exerted traction down all around the periphery of the head, surrounding the head with a curtain of downward pulls that kept it upright much like stays pulling down on the mast of a sailboat or wire cables pulling down on a radio tower. The pull down on each side prevented the head from tipping to the opposite side. Selective relaxation of muscles provided the flexibility needed for function. In this manner, decreasing the pull along any side allowed bending toward the opposite side.

 

On the sides, this structure was symmetrical and stable. The shoulders and hips extended out widely to form strategic points for muscle attachments.  Underneath, two feet placed side by side created a stable foundation to resist sideways tipping. 

 

From front to back, stability was far more difficult for a body so tall and flat. In this plane, symmetry was lost right from the top. The center of mass of the head was located in front of its pivot point on the top of the spine so that gravity alone would bring the head rolling down onto the chest. To counterbalance this gravitational pull down in front, a massive chain of thick postcervical muscles attached from all over the spine onto thick bony prominences located on the back of the head. 

 

A means for pulling downward was still required at the front of the head, but there was no room for bony prominences in the face. The face contained sense organs that could not function properly if surrounded by the thick bone needed for big muscle attachments.  Furthermore dense muscles could interfere with the freedom of movement necessary for yawning, swallowing, coughing, vomiting, spitting, talking, and turning the head. Thus the traction down at the front of the head was provided by a large number of smaller muscles with varied directions of pull that maximized their leverage. The muscles attached to the chest and clavicles exerted their downward pull on the hyoid bone, which in turn transmitted the downward pull onto the independently moveable lower jawbone. Then the long rigid horseshoe shaped lower jawbone transferred the pull down in front around to the sides of the skull where the cheekbones and the temples provided plenty of room for thick bony prominences to which muscles could be attached.

The way this sophisticated arrangement of multiple small muscles and bones at the front of the head counterbalances the straight straps of thick muscles at the back of the head to achieve a stable head posture is illustrated below:

 

  

 

This mechanical arrangement in humans made the jaw muscles an integral part of the head posture mechanism. The neck muscles fire with the jaw muscles during chewing and swallowing, and the jaw muscles fire with the neck muscles during moving or bracing of the head. 

 

Backward Jaw Posture and Forward Head Posture
The particular way the lower jawbone was integrated into the head posture mechanism makes lower jawbone posture and head posture inversely proportional in a forward-backward direction. Shifting the lower jawbone backward causes the head to shift forward, and shifting the head forward causes the lower jawbone to shift backward. In large population studies, backward lower jawbone posture is strongly correlated with forward head posture. TMJ disorder patients typically have both forward head posture and backward lower jawbone posture.

 

Shifting the lower jawbone backward causes a forward shifting of the head, because head posture is under the control of neuromuscular reflexes which determine the background forces maintained by each jaw and neck muscle.  These reflexes are arranged in a heirarchy of importances.  In this heirarchy, the relaxation of the muscles in resting posture is far less important than the maintenance of the airway or the maintenance of a line of visual sight.. 

 

Airway protection is top priority. The craniofacial area literally grows around its airway. The lower jawbone surrounds the airway channel in front and on both sides, while the cervical spine forms a wall behind it. When the lower jawbone shifts backward toward the cervical spine, it impinges on the airway space available in the throat, triggering a reflex which tips the head backward in order to rotate the lower jawbone forward and thereby away from the cervical spine and out of the airway space.

 

At the same time, the visual orientation reflex keeps the part of the face containing the visual system level with the horizon. There have been cases in which drooping of the eyelids due to paralysis of the eyelid muscles caused the head to permanently tip backward in order to maintain the visual field and thereby create a permanent scoliosis.  In experiments with growing rats forced to spend their lives standing upright on their hind legs, the visual orientation reflex was powerful enough to bend the entire skull so the eyes could still look straight ahead at rest.

 

Because of these two reflexes, a facial growth pattern that shifts the lower jawbone backward causes the head to shift forward to maintain its level orientation as well as an adequate distance between the lower jawbone and the cervical spine. The mechanism involved is illustrated below.

 

 

Forward shifting of head posture to protect airway space has been well documented in the medical literature.  In patients with tonsillitis, the swollen tonsils narrow the airway space available in the throat, causing forward head posture to preserve airway space. After the tonsils are removed, head posture normalizes quickly.  When an injury such as TMJ ankylosis or a growth disorder such as micrognathia stops the normal forward growth of the lower jawbone and therefore causes the lower jawbone to shift backward relative to the upper jaw, patients simultaneously develop extreme forward head posture.

 

Conversely, retrusive lower jawbone posture can also be a result of protrusive head posture. When the head shifts forward, the lower jawbone and the lower teeth cannot shift as far forward as the head, because they are still tethered to the clavicles by the muscles of the front of the neck. Thus the upper teeth (fixed to the skull) shift forward farther than the lower teeth (fixed to the lower jawbone). As a result, the bite changes in a way which produces a relative retrusion of the lower jawbone (increased overjet and overbite and class 2 malocclusion).

 

Forward head posture produces a loss of the normal S-shaped cervical curve in the neck, in a progression which is shown below. Normal head posture on the left shows the weight of the head balanced over the shoulder girdle.  In the middle figure, shifting the top of the S-curve forward flattens the whole top half of the S-curve so it becomes more of a J curve with a slanted vertical portion. In the right side figure, further forward head posture can even reverse the middle of the cervical curve so the slanted vertical portion of the J is no longer flat but concave down and forward, producing a hump at the back of the neck. 

 

NORMAL HEAD POSTURE       FORWARD HEAD POSTURE      EXTREME FORWARD HEAD POSTURE                   

 

 

As the head and top portion of the neck shift forward, the inner portions of the shoulders follow the neck, causing the shoulders to rotate around a vertical axis so their outer portions are often left sticking out like chicken wings.

 

Whether backward lower jawbone posture causes forward head posture, forward head posture causes backward lower jawbone posture, or something else causes them both, the forward shifting of the head exerts torque all along the length of the spine. The head is a heavy weight perched on the top of the spinal column like a bowling ball on a broomstick. When the bowling ball stays centered on the top of the broomstick, it can be easily balanced. When the bowling ball shifts forward so it is cantilevered forward off the top of the broomstick, bending forces are produced along the length of the broomstick. For that reason, EMG studies have shown that every centimeter of forward head posture produces a tripling of the background tension (measured as resting electrical activity) in the muscles of the lower back.

 

Beneath the upper quarter of the body, a realignment of structural elements must occur to support the forward shifting of the head, neck, and shoulder girdle. Most frequently, the pelvis rotates clockwise to thrust the abdomen forward under the forward shifting weight on top. Between the forward shifting abdomen and head, the chest sinks backward, increasing the curve of the thoracic spine.  This progression from left to right is shown below.

 

                                   SPINE IN NORMAL POSTURE                           SPINE UNDER FORWARD HEAD POSTURE

These changing alignments of body posture create mechanical strains within the intervertebral joints as the compressive forces from weight bearing become unevenly distributed among spinal segments. Localized areas of high pressure can crush a portion of an intervertebral disk, squeeze it out from between the bones where it can impinge on blood vessels or nerves, or lead to arthritic changes in the structures of the bones at the joints.

 

Any of these degenerative changes in the intervertebral joints can limit the range of motion of the surrounding spinal segments, which then causes further degenerative changes in the intervertebral joints. Range of motion limitations damage joints by depriving their specialized articular surfaces of the rubbing movements they need for ''weeping'' circulation. The weight bearing surfaces of joints (the articular cartilage) cannot be directly supplied by blood vessels like other tissues, because these areas function under direct compression. Therefore, the weight bearing surfaces of joints rely on a process known as weeping circulation. Weeping circulation sequentially replenishes each area of the articular cartilage by driving out fluids when the area is under direct compression and then allowing new fluids to flow back in as soon as the compression in the area is released. When movement of the bones at the joint is smooth and variable enough to spread the compression widely around the surface of the joint, this weeping circulation keeps the cartilage healthy by alternately working the waste products out of the tissues and into venous circulation and then allowing freshly oxygenated blood to seep back in.  The importance of weeping circulation is well known clinically. Immobilizing a healthy joint causes arthritic changes in the joint within two months, and passively moving a damaged joint back and forth through a normal range of motion dramatically reduces its healing time. Restoring normal ranges of motion to injured joints is one of the mechanisms by which chiropractic adjustments relieve pain.

 

The changing alignment of body posture also creates a pattern of strains in the postural muscles as they first resist and then adapt to the new alignment. Any change of resting posture requires a change in the resting lengths of the muscles so they can maintain a state of relative relaxation while holding that posture. The muscles respond by altering the resting lengths of their fibers so that all the muscles can be at rest together in a posture that they can easily maintain. Joint damage and other sources of pain can increase surrounding muscle tensions enough to prevent adaptation by alteration of muscle resting lengths from succeeding in re-establishing a stable resting posture.

 

Even when the pain is felt in only one muscle, the problem is not isolated to that muscle. The postural muscles can be studied individually, but they don't act by themselves. They function as members of long myofascial chains which run up and down the length of the body. A tightening which occurs in anyone portion of a chain is immediately shared among all the members of the chain. A tightening which occurs in a chain is also immediately responded to by the opposing chain as the involved muscles either resist or stabilize any resulting movement.

 

When the body is at rest, there is a stable balance between opposing tensions distributed evenly among the members of these chains. The slight tension maintained relatively evenly by all the muscles is sufficient to hold the body in a stable and comfortable posture. Forward head posture upsets the balance between the chains on the front and back sides of the body in resting posture.  When the even symmetrical balance between joined and opposing muscle resting lengths is altered so the muscles and bones no longer fit perfectly together in a comfortable resting posture, the body loses an important source of relaxation and resting circulation. It's as if the resting postures of all the individual muscles no longer add up to a single weight bearing resting posture which can be used by the whole body. Most patients with this condition are unable to stand very long in one position. To avoid discomfort, they frequently shift stances or rock back and forth so they can alter the muscle groups receiving the strain.

Muscles which don't relax fully experience impaired resting circulation, and muscles which don't get adequate resting circulation often develop tender spots known as trigger points.  There is good evidence that trigger points occur where little pockets of waste products have accumulated due to poor resting microcirculation. Trigger points usually occur in a small number of common locations, and they can cause pain to be felt surprisingly far away from the source of the problem in typical "pain referral" patterns. The presence of a certain minimal number of these trigger points and their pain referral patterns constitutes a condition commonly known as fibromyalgia.

Trigger points are often able to maintain themselves even long after the cause of the trigger points has been eliminated.  This tendency to retain a dysfunctional state is sometimes referred to as muscle memory.  In TMJ disorders, the jaw muscles may need direct treatment to remove their trigger points even long after the cause of the muscle tightness and resulting trigger points is long gone.

 

Trigger points can be treated by mashing them directly, by massaging the whole muscle, or by icing the muscle while stretching it.   Forcefully mashing trigger points can be achieved using a finger, knuckle, or elbow.  The greater the force used, the longer the subsequent relief will last.  Massage can be combined with trigger point work or used by itself to flush the waste products out of the muscle and restore resting circulation to the capillary beds.  Icing the jaw muscles while stretching them can be achieved by using a block such as a wine cork placed between the front teeth to hold the mouth open fairly wide and then using an ice pack, (such as a bag of frozen corn or peas) on the sides of the face.  The ice with the stretch is maintained for as long as you can tolerate it, and then the block is removed and a hot wet towel is placed on the sides of the face.  The heat will feel good after the ice, and the ice will feel good after the heat.  The two modalities (ice with stretch, and heat with relaxing) can be alternated several times while watching a movie at home.

Increased central nervous system stress can worsen a muscle related condition in any part of the body by increasing resting muscle tensions all over the body. In the muscles,  Studies have shown that even a 5% increse in resting tension decreases resting circulation in a muscle. When jaw muscles are already operating at borderline circulatory levels because of reflex tightness due to operating across an injured TMJ, even a slight increase in stress can bring resting circulation below a threshold level that results in jaw muscle pain, while any decrease in stress can increase resting circulation enough to eliminate jaw muscle pain.  Because of that inverse relationship between jaw muscle tension and resting circullation, a period of stress often precedes the onset of TMJ disorder symptoms, and relaxation is often an effective short term treatment for symptoms. This makes stress a triggering factor, but not a cause, of symptoms.

 

The primary goal of treatment is to re-establish a stable balanced resting posture for the head, the body, and the lower jawbone.   This process has both mechanical and psychological components.  The mechanical component involves the physical support you provide for your body, primarily when you stand, sit, and sleep.  The psychological component involves the way your mental state affects the resting postures of your muscles and thereby also the stance you use for weight bearing.  Both components need to support the same ideal resting alignment of your spine if that alignment is to become habitual.

You can't improve your body's resting posture simply by trying to hold an improved posture, or your muscles will get exhausted rapidly. Thus the first step in improving your posture is to learn what an improved posture feels like. Once you’ve identified a good posture, you can practice shifting into and out of it.  This strengthens the muscles which can pull you into the good posture and stretches out the myofascial components which maintained the old strained resting posture. When sitting, you can repeatedly let yourself go into a slouch, then pull out of the slouch, creating an exercise which strengthens the muscles which pull you out of the slouch.

Similarly, you can't improve the resting posture of your lower jawbone simply by trying to hold your jawbone in an improved posture, because the posture of your lower jawbone is determined by the way your teeth fit together in the bite.  The reason for this is explained in the paper entitled THE ROLE OF THE BITE.

 

A simple way to learn ideal standing posture is by holding yourself as tall as possible. Over time, gravity takes its toll on the postural system, especially if you are carrying more weight than you were when your bones and joints attained their adult proportions. The illustration below shows how loss of overall height occurs together with forward head posture and the adaptive spinal changes which accompany it.  Because of this relationship, successful postural work frequently causes an increase in standing posture at any age.

 

NORMAL POSTURE          FORWARD HEAD POSTURE                NORMAL POSTURE      FORWARD HEAD POSTURE

 

Maintaining good posture depends on adequate musculature, because the muscles need to develop sufficient strength to acquire and maintain the good posture.  In most cases certain muscles in particular need to be strengthened.  There are an enormous number of exercises which can be used to strengthen muscles, and many different practitioners have their own favorites. 

 

Neck exercises are particularly important for people with TMJ disorders, because the neck muscles are the primary determinants of head posture. Many people with relatively thin necks and large heads need to increase the muscle mass in the neck (and collar size) just to adequately support the head.  Isometric neck exercises can be done without any equipment or taking time out of your life simply by working your head against your hands while waiting in line, reading a book, talking on the phone, etc. The most valuable isometric neck exercise is working your head backward against your hands held behind your head or even against a head rest in a car.  These exercises strengthen the muscles responsible for holding your head back over the long axis of your spine.

 

The neck muscles can't be strengthened without also strengthening the muscles of the shoulders and back, because the shoulder girdle is the base of operation for the neck musc;les.  Simple isometric exercises used for the arms and shoulders can be combined with the isometric exercises used for the neck muscles to strengthen the whole upper quarter.

 

Dynamic exercises (which involve some movement) are generally healthier for joints than isometric exercises, because movement provides weeping circulation as described earlier. Dynamic exercises should incorporate the neck with the rest of the body, especially in long strokes which recruit many muscles working together. Strengthening exercises which are used to rehabilitate muscles for health are different from strengthening exercises which are used simply to increase the capacity for maximal muscle power output, as in weight lifting and other power sports. Rehabilitation exercises should be performed in brief rhythmic contractions of about 1/2 second to a second, each contraction separated by a rest interval of similar duration. Such rhythmic firings are characteristic of muscle behavior during most functional movement patterns like chewing, walking, climbing, pounding, and rowing. While one muscle group (agonists) is contracting, its antagonists relax so they can be replenished with fresh oxygen and nutrients. Then when the antagonists contract, the agonists can relax and become replenished. Studies have shown a surge of blood flow to exercising muscles immediately following contraction, and permitting such frequent regular surges can produce a significant pumping mechanism.

 

To keep muscles and joints healthy, strengthening needs to be balanced with stretching. Stretching flushes out areas of the muscles and the ligaments which don't get fully flushed during normal functional movements. Icing a muscle while it is held in a stretched position, such as using an ice pack on your cheeks while you bite on a cork, is an easy way to restore length to muscles which have shortened from being held too tight for too long.  The periodic gentle tugs that stretching applies to the ligaments probably help produce circulation in the relatively avascular areas where the ligaments attach to bones.  Yoga, Tai Chi, and swimming are popular exercises which provide both stretching and strengthening.

Another way to combine strengthening with stretching is to pull yourself upward using overhead bars.  You don't need to pull yourself off the ground.  The exercise strengthens your arms and shoulders while using the force they generate to rhythmically distract the compressed vertebral segments.