The Role of the Airway
The face and neck grow around the airway, and the particular way they grow to accommodate resting airway flow determines resting mandibular and head posture, therefore considering airway dynamics in treatment planning is critical to success in TMJ, orthodontic, and postural treatment.
THE PROBLEM - During evolution, the teeth were the fragile components of our jaw systems, so protecting them became a high priority for our neuromuscular systems. As a result, your jaw muscles are programmed to protect your teeth by only allowing you to close your mandible (lower jawbone) forcefully in the one central bite location where all your back teeth fit together and making that position feel normal, wherever it is. Also, your jaw muscles are programmed to hold your mandible in a postural location just beneath that central bite location in order to maintain fast easy access to mandibular bracing, because mandibular bracing was critical for protecting the vital structures behind the mandible during our evolution. As a result, both the strained mandibular bite location and the strained mandibular posture location feel perfectly normal. By this mechanism, the bite controls mandibular posture.
However, an even higher priority for the neuromuscular system is to protect the airway passage. The neuromuscular system will maintain whatever muscle tonus is needed to keep the airway patent at rest. If the bite forces mandibular posture into the area needed for airway passage, the body will use the tongue, jaw, and neck muscles to create a new mandibular resting posture that re-establishes an adequate resting airway passage. There are two areas where our airways become restricted and trigger such adaptative muscle responses - the nose and the pharynx.
NASAL AIRWAYS usually become obstructed due to insufficient expansion of the midface and upper jawbone. The palate, in the center of the midface, forms the roof of the mouth and the floor of the nose. When the upper jawbone cannot fully expand and the palate remains narrow, the base of the triangular nasal cavity can be too narrow to allow sufficient airway passage at rest. The body's response is then to create and maintain an oral airway passage by mouth breathing and keeping the lips always slightly parted. These people are usually obligate mouth breathers.
Mouth breathing then causes serious problems. It prevents the nose from warming, filtering, and moistening the air that strikes the back of the throat. It prevents nitric oxide from getting to the lungs. It leads to poor upper respiratory health. Mouth breathing can usually be corrected in adults by wearing a palate expansion appliance for 3 to 6 months, as explained in the file entitled PALATE EXPANSION.
Some people have nasal passages that are not narrow enough to make them obligate mouth breathers, but their nasal airway flow is not laminar, because it is restricted in one or more areas, sometimes even just at the nostrils. The airway flow restriction in the nasal area can produce turbulent airway flow downstream, leading to snoring or obstructive apnea.
If the nasal airway passage is obstructed by structures within the nasal cavity, such as overgrown turbinates or a deviated septum, the internal nasal cavity will need to be reshaped. In extremely obstructed nasal cavities, this will require surgery. When the obstruction is less severe, a routine of forced nasal breathing may be able to restore an adequate nasal airway passage by internally remodeling the nasal cavity, because localized areas of high speed turbulent airflow trigger regressive osseous remodeling that removes obstacles to airflow, which is one of the mechanisms by which the face grows around the airway passage.
PERSONAL STORY - About 20 years ago, when I first began looking at the relationship between facial growth and airway flow, I realized that animals always nose breathe, even when running for their lives. They only mouth breathe to gasp, when fighting. I also realized that, when I went jogging, I could keep my lips sealed and breathe through my nose if I went slow enough. That summer I went jogging twice a week, always nose breathing and limiting my pace to what my nasal airway could accomodate. By the end of that summer, it could accommodate natural jogging. I could run a good natural pace with my lips sealed, and I still do.
SMALL NOSTRILS - In some people, the limit to nasal airway flow is at its entry through the nostrils, and normal nasal airway flow during sleep can sometimes be restored by using simple technologies like nasal cones or nasal strips to enlarge the restricted area.
PHARYNGEAL AIRWAYS - usually become obstructed due to a facial growth pattern in which the mandible keeps shifting backward or rotating down and back into the area needed for airway passage through the pharynx. The mandible is programmed to elongate slowly throughout life so its corpus (the portion containing the teeth) can continuously advance in order to gradually decrease resistance to airway flow as muscle strength also decreases slowly throughout life. However, that advancement is powered by the jaw muscles, and weak jaw muscles can prevent the corpus from being pushed forward. The advancement can also be blocked by a steeply interdigitated bite or a deep or steep overbite, because that locks the corpus to an upper jawbone that grows by expanding rather than advancing.
When the forward growth of the mandible is blocked, its growth usually gets redirected vertically, and it rotates down and back, where it can impinge on the space needed for oropharyngeal airway passage. In some cases, strong jaw closing muscles prevent excessive vertical growth while deepening the overbite, because their biting forces are mostly applied to the back teeth. In other cases, the tongue intervenes to maintain a resting airway passage by positioning itself between the teeth, as evidenced by visible scalloping in the sides of the tongue. When the tongue acquires an adaptive position by resting between the front teeth, it separates those front teeth and produces an anterior open bite that makes it impossible to incise (bite things off). In these cases, any orthodontics that straightens teeth by moving them into the path of the resting tongue posture will fail, because the tongue will eventually reposition the teeth in any way needed to keep the airway passage open.
The body's adaptative response to the pharyngeal airway restriction is to extend (tip back) the head back, which pulls the mandible up and forward away from the cervical spine to increase the amount of airway space behind the mandible. However, head extension also produces a forward shift of head posture, as described in THE ROLE OF BODY POSTURE under the TMJ DISORDERS tab and in more detail in BITES AND POSTURE under the FOR DOCTORS tab.
The problem of the backwardly rotated or backwardly positioned mandible can be treated preventively by advancing the mandible. This can be accomplished using functional orthodontics to move the jawbones, dentally by adjusting the bite, or just nightly for treatment of obstructive sleep apnea. In children, mandibular advancement appliances, like the Herbst appliance, can produce significant advancement. Treatment by functional orthodontics is described in the file entitled THE ROLE OF ORTHODONTICS under the tab TMJ DISORDERS. Active treatments for snoring and sleep apnea are summarized under the tab SLEEP APNEA and described in detail in the file entitled, MULTILEVEL TREATMENT OF SLEEP APNEA under the tab FOR DOCTORS.