The Role of the Airway
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, the jaw muscles are programmed to protect the teeth by only allowing you to close your mandible (lower jawbone) in the one location where all the teeth fit together and by holding your mandible in a postural location just beneath that one biting location where the teeth fit in order to maintain fast easy access to bracing the mandible and thereby protecting the vital structures behind the mandible. In this manner, the bite controls mandibular posture, which affects body posture.
An even higher priority for the neuromuscular system is to protect the airway passage running through its center. Neuromuscular reflexes ensure that all the muscles of the head and neck will automatically acquire whatever resting postures are necessary to keep the airway passage open. As a result, the face grows around the airway.
When the bite forces the mandible back into the airway space, the neuromuscular system often responds by shifting the resting posture of the tongue to a location between the teeth in order to reposition the mandible. When it rests between the front teeth, it produces an anterior open bite that makes it impossible to incise (bite things off). When it rests between the back teeth, it causes visible scalloping in the sides of the tongue from the indents made by the teeth as it rests between them to form a cushion. In these cases, any orthodontics that moves teeth into the path of the airway passage will fail, because the tongue will eventually reposition the teeth in any way needed to keep the airway passage open.
When the mandibular posture shifts posteriorly, the head tips back (extends) in its resting posture to pull the mandible up and forward away from the cervical spine. This response restores airway passage space behind the mandible but 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.
In modern humans, there are two common locations for airway passage restrictions.
NASAL AIRWAYS usually become obstructed in modern people due to insufficient expansion of the midface. The palate, in the center of the midface, forms the roof of the mouth and the floor of the triangular nasal cavity. When the upper jawbone cannot fully unfold, the palate cannot grow wide enough to allow airway passage through the nose, and the base of the triangular nasal cavity remains narrow. Subsequently, if you cannot get enough airway passage through your nose, your mouth remains always slightly open to maintain an oral airway passage.
Mouth breathing then causes serious problems. Mouth breathing can be corrected at any age by wearing a palate expansion appliance for 3 to 6 months, as explained in the file entitled PALATE EXPANSION.
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 can be reshaped by forced nasal breathing, because localized areas of high speed turbulent airflow trigger regressive osseous remodeling that removes obstacles to airflow.
PERSONAL STORY - About 20 years ago, when I first began looking at how airway preservation reflexes affect facial growth, I realized that animals always nose breathe, even when running for their lives. They only mouth breathe to gasp, as 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.
PHARYNGEAL AIRWAYS - usually become obstructed due to a facial growth pattern in which the mandible has shifted backward or rotated down and back into the area needed for airway passage in the pharynx. The mandible is programmed to elongate slowly throughout life in order to gradually decrease resistance to airway flow just as muscle strength decreases slowly throughout life. However, when a steeply interdigitated bite or a deep overbite prevents the continued growth of the mandible from advancing its front end to enlarge its airway passage, the growth of the mandible gets redirected down and back into the oropharynx or hypopharynx.
The problem of the backwardly rotated or backwardly positioned mandible can be treated preventively by functional orthodontics that encourages mandibular advancement, it can be treated actively by forcing the mandible into an advanced position during sleep, or both. 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.