Crooked teeth are a modern phenomenon and a telltale sign of an underlying epidemic.
by SANDRA KAHN and PAUL R. EHRLICH
If the jaws fail to develop properly, the receding lower jaw (the mandible) can put stress on the airway. The problems associated with modern jaw-face-airway development are only now beginning to be uncovered, largely through the work of a series of dedicated scientists and practitioners who have observed dramatic changes in facial structure that correlate with higher incidence of chronic diseases. Reducing the size of the airway can, for instance, eventually lead to breathing problems, such as sleep apnea, which itself has become a significant factor in public health. Some 20 percent of American adults are afflicted, and about 3 percent have a sufficiently serious case to cause daytime sleepiness. But sleepiness is the least of it: As many as half of all cardiac patients suffer from the disease. Sleep apnea also appears to generate mental problems, including lowered IQ, shortened attention span, and difficulties with memory.
Twin studies help researchers differentiate between genetic and environmental factors. As an orthodontist, John Mew has treated many sets of twins. His results show clearly the difference that treatment can make.
The tongue position influences the whole body. If the tongue is positioned against the palate, the parasympathetic system will reduce its systemic activity (for example, heartbeats and respiratory rhythm increase), but if it is positioned against the soft palate, the sympathetic system will reduce its activity 
1Effects of tongue position on mandibular muscle activity and heart rate function. Schmidt JE, Carlson CR, Usery AR, Quevedo AS. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009;108:881–888.[PubMed] [Google Scholar]