Palate expansion can provide important overall health benefits for people with narrow faces and limited nasal airway flow, because the roof of the mouth is the floor of the nose. If the palate is too narrow, the nasal airway may be too narrow to allow normal nasal breathing. The result is mouth breathing. Some people with very narrow palates are obligate mouthbreathers and can never beathe entirely through the nose. Their mouths are always slightly open. Other people with slightly narrow palates or partial obstructions such as enlarged turbinates or a deviated septum only mouthbreathe when their nasal passages swell slightly due to colds or allergies.
Mouthbreathing prevents the nose from moistening, filtering, and warming the air before it hits the throat. As a result, mouthbreathers are prone to upper respiratory problems. Normal nasal breathing also helps oxygenate the blood. A study in which normal nasal breathers wore nose clips to force them to mouthbreathe for a few hours found that they developed lowered blood oxygen. More recent studies indicate that nasal breathing may also release nitric oxide that helps regulate pulmonary blood flow.
Mouthbreathing also impairs normal facial growth, because it causes the jaw muscles to automatically attain a lowered jaw posture to allow an oral airway passage. Postural forces control the shapes acquired by bones. The lowered jaw posture produced by mouthbreathing causes the front of the face to lengthen and narrow.
Traditionally orthodontists only performed rapid palatal expansion, which could not be produced in adults without surgically breaking the palate's midline suture. They believed that the palate could only be expanded by completely separating the two sides of the midline palatal suture, therefore it had to be performed before most of the craniofacial sutures appear to close at the end of the second decade. However, we now know that the palate can also be expanded gradually at any age by wearing an by oral appliance that supplies light steady outward force on the sides of the palate. The process usually takes 3 to 6 months, depending on the type of appliance used. The oral appliance must be worn most of the time, but it need not be worn all the time.
Expansion screws embedded in removeable oral appliances are the most effective way to widen a palate. They employ a powerful turnbuckle located in the middle of the appliance, and the patient is given a key that turns it. With each turn of the screw, the two sides of the palate are driven slightly further apart. The patient uses the key to maintain light steady pressure on the upper teeth. Traditional expansion screw wideners were called Schwartz, Haas, or Hyrax appliances. One expansion screw widener called a DNA appliance is aggressively marketed as epigenetic, although there is no evidence that it actually affects genetics. Often an expansion screw can be added to an existing oral appliance which is then split down the middle and used as a palate widener.
Bent wire wideners (such as quad helix appliances, coffin spring appliances, bionators, and crozats) employ a framework of wires and springs that are soldered to thin metal bands that are usually glued to the teeth. They can be relatively unobtrusive, but their main disadvantage is that they tend to do more tipping of teeth and less expansion of the underlying basal bones, such as the pillars of the nasal cavity. ALF (advanced lightwire functional) appliances are bent wire appliances that apply very low forces for a long period of time. Because their forces are gentle, they are promoted as being compatible with cranial osteopathy, which is discussed extensively under the tab CRANIAL AND CRANIOSACRAL.