The lower jawbone is an integral component of the postural system, and the posture of the lower jawbone is determined by the bite.  Therefore improving your posture may require an adjustment of your bite, just as improving your bite may require an adjustment of your posture.


In the body's habitual weight bearing posture, the lower jawbone has natural resting place (neutral zone) at an equilibrium between opposing passive tensions within the curtain of muscles and fascia that hold all the skeletal components together in one big continuous myofascial sheath.  However, because of neuromuscular reflexes that were designed to protect the teeth, the lower jawbone's resting posture is also determined by the bite - in particular by the exact position that the lower jawbone acquires each time the back teeth of both sides are closed firmly together in a full natural bite.  Lower jawbone posture is automatically programmed to rest just below that full natural bite in order to maintain fast easy access to bracing the lower jawbone.  If that full natural bite position is displaced, lower jawbone resting posture also becomes displaced in the same direction, creating a discrepancy between the two jaw postures.


To see if there is a discrepancy between the lower jawbone posture that would be determined by the resting forces of the weight bearing body stance and the lower jawbone posture that is determined by the full natural bite requires wearing a front flat plate appliance during sleep.  The flat plate removes the signals from the teeth that constantly program the jaw muscles to always bring the lower jawbone closed wherever the teeth fit.  After this deprogramming of the jaw muscles, we can see the jaw posture that is preferred by the muscles, without any influence from the teeth.


If there is a discrepancy between these two lower jawbone postures, mechanical strain is shared between the jaw and postural systems.  Frequently in these cases, muscular or myofascial symptoms seem to fluctuate back and forth between the two systems.  If overall posture is otherwise good, the symptoms can be relieved by making jaw posture better fit body posture by altering the bite of the teeth in the direction of the desired change in jaw posture.

If there is no discrepancy between the lower jawbone posture that would be determined by the resting forces of the weight bearing body stance and the lower jawbone posture that is determined by the bite, your posture may be stable, but it may still be strained.  Improving it requires a change in all the postural components, including the lower jawbone, and changing jaw posture requires changing your natural bite. 


However changing the bite is not always simple.  Major bite changes involve dental work, which can be very costly.  In addition, there is much confusion among dentists regarding bites, as explained in the OCCLUSION: CURRENT CONCEPTS under FOR DOCTORS.  Therefore any change in the bite requires first understanding how the jaw system and the postural system are connected.  This relationship is explained in detail in OCCLUSION AND POSTURE under FOR DOCTORS.


Most TMJ disorder patients have both backward jaw posture and forward head posture.  Backward jaw posture can cause forward head posture, because the face grows around its airway.  The lower jawbone surrounds the airway in front and on both sides, and the cervical spine borders it from behind.  Backward lower jawbone posture constricts the airway against the cervical spine (middle illustration below). The muscles automatically respond by tipping the head backward (extending it) in order to rotate the lower jawbone forward out of the airway space.  However, the head cannot just tip, because it has to stay level for the visual and balance systems.  Therefore the head simultaneously tips back and shifts forward, as seen in the illustration on the right below.



Forward head posture diminishes the normal cervical curve (lordosis) of the neck by bringing its top end forward over its base, as seen in the progression below.  First the cervical lordosis flattens, as seen in the middle illustration.  Eventually the cervical lordosis may reverse, as seen on the right side illustration.  The tilting of the vertical line shows the cervical spine bending forward to support the forward head posture, the descent of the upper horizontal line shows the loss of vertical height that occurs when the position of the head rotates from a 12:00 position to a 1:00 position, and the tilting of the lower horizontal line shows the rotation of the inner and upper aspects of the shoulder blades as these areas follow the forward shifting of the base of the neck.  Since the outer and lower portions of the shoulder blades do not follow the forward movement of the base of the neck as closely as the upper and inner portions, the shoulder blades rotate around a largely vertical axis, often leaving their outer and lower portions sticking out like wings (winged scapulae). 
                                                          NORMAL HEAD POSTURE         FORWARD HEAD POSTURE                EXTREME FORWARD HEAD POSTURE
Forward head posture produces strains in the spine.  The head is a heavy weight perched on the top of the spinal column like a bowling ball on a broomstick. When it shifts off center, torque is produced along the length of the broomstick.  However, forward head posture also triggers an adaptive change that maintains physical balance by shifting the lower portions of the spine forward beneath the forward positioned head. Typically, flexion of the hip joints thrusts the abdomen forward under the head, and the thoracic curve (kyphosis) increases as the chest sinks backward, as can be seen from left to right in the illustrations below.
 NORMAL POSTURE                                   FORWARD HEAD POSTURE                    EXTREME FORWARD HEAD POSTURE
When treating forward head posture by treating backkward jaw posture, adjusting the bite usually requires shaving down portions of teeth that are high when the lower jawbone comes forward, building up portions of teeth that are too low when the lower jawbone comes forward, or a combination of the two.  The choice usually depends on face height and dental needs.  
When a deep overbite is present, it is often the contact between the top front edges of the lower front teeth and the backs of the upper front teeth that most directly locks the lower jawbone backward.  This contact can be felt easily by placing a finger on the front edges of the upper front teeth while trying to tap only the back teeth together.  Short term relief can be obtained by reducing the top front edges of the lower front teeth.  Long term relief can be obtained by wearing a front flat bite plate that redirects nocturnal clenching forces onto the front teeth to gradually reduce overbite.
In some TMJ disorder patients, the lower jawbone is shifted sideways, as can be estimated by comparing the positions of the midlines between upper and lower front teeth in a mirror.  Typically, in these cases, placing a grid over a picture of the face shows that the chin is shifted toward one side and the eye of the opposite side appears higher, because the head tilts toward the side of the lower jawbone (and chin) shift due to increased postural tensions in the temporalis muscle of the same side. 
The asymmetric lower jawbone position forces the face to keep growing asymmetrically, because it cannot even access the midline due to the way the teeth fit together.  Therefore the adult facial growth that continues slowly in adulthood cannmot correct the problem unless the bite is adjusted to at least allow the lower jawbone access to the midline.
The sidebending of the head disrupts the normal parallel relationship between the laterally extended postural members - head, jawbone, shoulders, hips, and two feet spread slightly apart.  Typically, as the lower jawbone shifts and the head tilts to one side, the head tilt pulls upward on the shoulder girdle of the opposite side.   The hips often follow, depending on the adaptation of the spine to the shifting of the weight on top.  
In these cases
, adjusting the bite almost always involves repositioning the lower jawbone toward the midline by either building up teeth on the side of the displaced lower jawbone, shaving down teeth on the side opposite the displaced lower jawbone, or some combination of the two.  The choice depends on factors like your face height and the condition of your teeth.
Changing body posture can create mechanical strains in the intervertebral joints as the compressive forces from weight bearing become unevenly distributed among spinal segments. Localized areas of high pressure can squeeze a portion of an intervertebral disk backward out of the intervertebral joint space and into the spinal nerves, causing pain, numbness, and loss of muscle strength.  
Degenerative changes in the intervertebral joints can limit their ranges of motion, depriving the specialized articular surfaces of the rubbing movements they need for local circulation.  Because the weight bearing surfaces of joints function under compression, they cannot be directly supplied by blood vessels.   Instead, they receive their nourishment from a hydrostatic process that circulates fluids like repeatedly squeezing out a sponge in one spot at a time.  Waste products are driven out of the part of the sponge under compression, and then new fluids flow back in to that area as soon as the point of compression moves to a different area. When movement of the bones at the joint is smooth and variable enough to spread this compression and release process widely around the surface of the joint, it keeps the entire surface of the cartilage healthy. For that reason, passively moving a damaged joint has been shown to dramatically reduce its healing time, and immobilizing a healthy joint causes it to undergo arthritic changes.  Restoring normal ranges of motion to injured joints is one of the mechanisms by which chiropractic adjustments relieve pain.

Muscles far from the source may be affected, because the postural muscles, including the jaw muscles, function as members of long myofascial chains running up and down the length of the body.  A change in the resting length of one muscle affects all the muscles in the chain.  Backward jaw posture and forward head posture can upset the balance between the chains of postural muscles on the front and back of the body and thereby lead to the loss of a single central upright resting posture.  Subsequently the muscles and bones no longer fit together well enough in a single weight-bearing stance to allow them to rest simultaneously.  They may avoid discomfort by frequently shifting stances such as rocking back and forth to alter the muscle groups receiving the strain.   

When muscles have been held tight for long periods of time, they shorten anatomically and acquire a decreased resting length in a process known as contracture.  When your jaw muscles are in contracture, your mouth no longer hangs so far open at rest, as when you fall asleep in a chair.  It may be only open slightly or the teeth may be held touching, and they may go into a tight clench whenever overall resting muscle tensions are increased even slightly by stress (as explained below).  Muscles in contracture have diminished resting circulation.  For short term relief, they can be massaged to flush waste products from their capillary beds.  For long term relief, they need stretching (along with their fascia) to restore their resting lengths.  
An easy way to stretch the jaw muscles is by icing them while the jaw is mechanically propped open.   The stretching can be accomplished by propping the jaw open using a block such as a wine cork or a piece of wood placed between the front teeth.  The jaw does not need to be open as wide as possible.  At the same time, the jaw muscles are iced by holding ice packs or bags of frozen vegetables against the sides of the face. The ice with stretch is maintained for 5 to 10 minutes. Then the block is removed and the ice is replaced by a hot wet towel. 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.   
Muscles in contracture often develop trigger points - commonly described as pea shaped nodes that are exquisitely sensitive to manual pressure.  They can cause pain at locations surprisingly far away in typical "pain referral" patterns, and they can persist long after their original cause has been eliminated.   For short term relief, trigger points can be treated by forceful compression of the site using a finger, knuckle, or elbow. The greater the force used, the more sustained the relief.  There are many dentists and doctors who inject trigger points with novocaine or saline.  The process hurts like crazy for a few minutes, but the relief can last for weeks. 
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.  When a muscle has already been operating at borderline resting circulatory levels due to tightness from automatic bracing to protect an injured joint, even a slight increase in overall stress can bring its resting circulation below a threshold level that results in pain. For that reason, a period of increased central nervous system stress often precedes the onset of TMJ disorder and other postural symptoms, and relief can often be obtained from stress lowering measures like relaxation, meditation, humor, spiritual inspiration, or feeling loved.
While stress increases all resting muscle tensions, attitude selectively alters resting muscle tensions.  The motor nerves are anatomically and physiologically extensions of the brain; and, by controlling their resting tensions, the state of the brain determines which muscles are held tightly and which are held loosely.  Feeling sad makes the lower jawbone drop back, the chest sink, the head hang, and the shoulders slump. The extremely retrusive lower jawbone posture in grief causes a lump in the throat by triggering an airway protective response to compensate for airway space lost due to extreme lower jawbone retrusion. Conversely, feeling proud or determined causes forward thrusting of the chest, standing tall, and jutting the lower jawbone, which can also be seen in facial expressions of anger or determination.
The passive physical support provided by your furniture influences your posture.  In order to accommodate the "average" person, most seats on planes, trains, and buses have head rests that force the head forward.  Back sleeping on a soft mattress such as a waterbed, an air mattress, or memory foam also produces forward head posture, because it allows your body to sink down at its center of mass (usually at the hips or abdomen) and thereby stay in flexion. A mattress made of inexpensive foam rubber (without memory) or a futon reinforces good body posture by constantly pushing your spine towards a straight axial alignment that supports your legs and head in the same plane as your abodmen, hips, and shoulders.

Pillows are extremely important in head posture.  When sleeping on your back, the back of your head should be in contact with your mattress. A pillow that holds the back of your head above your mattress reinforces forward head posture. Your pillow should provide support under your neck rather than under your head. The neck support can be provided by U shaped pillows (such as travel pillows), a rolled up towel, or a pillow with a hole in the middle. A roll under your neck can be combined with pillows on each side of your head so that, when you roll over to either side, your head rolls up onto a pillow that is roughly as thick as the distance between your ear and your shoulder.

The same improved skeletal alignment that you maintain with passive physical support must also be acquired habitually by your skeletal muscles in a normal weight bearing stance.  A simple way to improve your standing posture is by holding yourself as tall as possible.  Both the flattening of the cervical spine and the increased thoracic and lumbar curvatures that accompany it cause loss of vertical height, and restoring some of that height restores some of the lost spinal support.  
You can't just hold your skeleton in an ideal alignment, or your muscles will rapidly become exhausted. Before you can hold an improved posture, you will need to strengthen the muscles that can pull you out of your old posture and into a better one.  One way to selectively strengthen those muscles is by making an exercise of repeatedly allowing yourself to slouch and then pulling yourself back up out of the slouch and into ideal posture. 
NECK exercises are particularly important for improving head posture.  You can work your head back against resistance provided by a head rest in a car or your hands held behind your head without taking time out of your life. 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 muscles.  Dynamic exercises (involving movement) are generally healthier for joints than isometric exercises, because movement provides weeping lubrication and circulation at the joint surfaces.
Exercises used to rehabilitate muscles for health are different from exercises used to strengthen muscles for maximal muscle power output. Rehabilitation exercises should be performed in rhythmically alternating contractions of about a second each, much like the muscle firings during functional activities like chewing, walking, climbing, hitting, etc. While one muscle group (agonists) is contracting, its antagonists relax and receive a quick shot of fresh blood.  In this manne, healthy exercise rhythmically flushes tissues and pumps circulation.
Just as some muscles need to be strengthened or tightened, other muscles need to be stretched and loosened. The balance depends on the individual. Generally muscular people need more stretching, and frail people need more strengthening.  To have longlasting effects, stretching also has to include the tough sheets of fascial webbing that bind all the muscles together into long functional units (myofascial release). 
COMBINING stretching and strengthening can be accomplished by exercises such as Yoga, Tai Chi, swimming, or pulling yourself upward using overhead bars. Even if you don't pull yourself off the ground, applying some traction to your spine by pulling upward with your arms serves to distract the compressed vertebral segments, and pulling upward rhythmically creates an exercies which strengthens the arms and shoulders while restloring circulation to the vertebral segments by repeatedly distracting and compressing them.
Lower jawbone posture and head posture are intimately interconnected, and they are best treated together.  Dentists performing treatments that affect the bite, such as multiple crowns, dentures, or orthodontics, should recognize that stabilizing the existing natural bite also stabilizes the existing body posture, and the patient may be best served by incorporating a period of time for improving posture before finalizing the bite.  Postural adjustments should be undertaken with the awareness that, unless the bite is addressed, they will tend to relapse shortly after the patient resumes biting on his or her natural teeth, which causes a return of the previous lower jawbone posture and subsequently also the same head and body posture.