The Habsburg jaw: how centuries of royal intermarriage showed up in portraits
Charles II of Spain, who died in 1700, is said to have had the most extreme Habsburg jaw on record, a jutting lower jaw passed down through a dynasty that married its own relatives almost without parallel. Geneticists now study the family's portraits to trace how the trait was inherited.
Prognathism simply means that one jaw sits forward of an imaginary reference line through the skull; the word joins Greek terms for forward and jaw. Which jaw matters. A protruding upper jaw or tooth-bearing ridge is often ordinary variation, differing noticeably between ethnic groups, and Neanderthals had far more forward-set upper faces than modern people. A protruding lower jaw is usually abnormal, arising from malformation, injury, disease or inheritance.
Clinicians only call it a disorder when it interferes with chewing, speech or social life. Mismatched jaws produce malocclusion: upper incisors well in front of the lower ones give an overjet, while a lower jaw reaching past the upper gives an underbite. Specialists judge the profile by eye, looking at the angle between nose and lip and the chin's position, but a cephalometric X-ray, which measures skeletal base, facial height and tooth angles, is the most accurate method. Habits such as thumb sucking can push teeth forward, and braces can realign them, though relapse is common without long-term retention.
Mandibular prognathism, sometimes called lantern jaw, is typically polygenic, and more common in East Asian populations. Inbreeding can exaggerate it in people and animals alike; flat-faced dogs such as boxers often have underbites. For the Habsburgs, the trait was allegedly brought in by a member of the Piast dynasty and appears on family tomb sculptures in Warsaw's St. John's Cathedral. Researchers disagree over inheritance: most cases look polygenic, but some argue for an autosomal recessive pattern.
There was no remedy before modern dentistry. Today orthodontics is usually paired with jaw surgery in adults. A 3D CT study of 100 patients with lower-jaw prognathism found that 69 percent also had some asymmetry of the upper jaw, mostly toward the back, and its authors argue that this should be built into surgical planning.
Source: Prognathism
