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Orthognathic classification - Prognatism - pseudo prognatism

The word 'prognathism' is derived from the ancient Greek words pro (forwards) and gnathos (jaw).
Lower jaw too long
Synonym: Lower jaw prognathism, mandibular hyperplasia, protruding lower jaw
The dental signature for both ‘Protruding lower jaw’ and ‘Receding upper jaw’ is an Angle dental Class III. The lower teeth are in front of the upper teeth, a condition also called underbite. Both conditions will be discussed under the same heading for reasons that will become clear in my further discussion.
Lower jaw prognathism is a genetic-developmental disorder where the lower jaw outgrows the upper jaw, resulting in an extended chin. Mandibular prognathism is a protrusion of the mandible, affecting the lower third of the face. Pure prognathism is corrected by a lower jaw set-back.
Upper jaw too small
Synonym: pseudo-prognathism, maxillary hypoplasia
Facial Sculpture Clinic - Dr Joël Defrancq - Jaw surgery and implant reconstructive surgery Pseudo-Prognathism or upper jaw hypoplasia is an underdevelopment of the upper jaw and affects the middle third of the face. This condition gives the midface a sunken appearance. It makes the lower jaw stick out, even if it is anatomically normal (= pseudo prognathism - false prognathism).

This antero-posterior condition of the upper jaw is often combined with a vertical deficiency and/or transversal deficiency (the upper jaw is then deficient in all three dimensions).

Maxillary hypoplasia is a developmental growth anomaly, but it may also be the result of poorly planned dental extractions (i.e. iatrogenic!) or missing teeth or is a congenital condition as in cleft patients.
A major concern of both conditions are the aesthetics. 
Undeniably, both conditions are clinically linked and show more or less the same features. The sunken appearance of the upper jaw or the extended chin of the lower jaw can make a person feel uncomfortable or look sad and depressed, but this may not necessarily be the case. The bite is also a suboptimal class III or rand-bite. It affects the smile and most often a person's feeling of well-being.

Corrective surgery is most often carried out on both jaws, not just one jaw. This is merely for aesthetic reasons, but also the consideration of sleepapnea later in life. Surgery aims to reposition the upper jaw by means of a Le Fort I advancement osteotomy or Le Fort I advancement and vertical extrusion (with bone interposition). The lower jaw is treated with a lower jaw setback and often a genioplasty (advancement most often). The transversal dimension in the upper jaw needs to be adjusted often with a transversal bone born expander (Smile distractor®), or in the lower jaw with a tooth born device.
It seems essential to establish clinically the difference between the two conditions, prognathism and pseudo-prognathism. However, although this seems essential, both conditions are usually present in the same person. Indeed, both conditions are developmental in spread and nature. Since one jaw is not supportive to the other in outgrow, each grows in their own way, driven by all kinds of forces, except their guiding inter-relational muscles forces. More importantly and practically, both conditions generally need treatment in both jaws: BSSO setback (-) and Le Fort I advancement (+++). Genioplasty and/or vertical adjustments are often necessary as well. We try to avoid all too much setback of the lower jaw for risks of future sleep apnea.
Important note: An exclusive set back of the lower jaw could result in the development of sleep disorders, snoring, and sleep apnea. The set back makes the pharyngeal airway smaller. It can also create a heavy or obtuse neck region.
Facial Sculpture Clinic - Dr Joël Defrancq - Jaw surgery and implant reconstructive surgery Historical note: This condition is commonly known as Habsburg jaw or Austrian jaw due to its prevalence in that bloodline. To me, it is obvious that the Imperial House had a pronounced mid-face deficiency combined with lower jaw prognatism. This was caused by inbreed over many generations to preserve their power and wealth within their families. 

Correcting their facial malformation would have included: Le Fort I advancement and extrusion with bone graft, BSSO setback, a smile distractor for transversal widening, cheek bone augmentation, genioplasty and, most probably, some facial lipofilling. Just imagine how magnificent the opportunities of our times are. Those were the wealthiest people on earth at that time. Charles II died at very young age leaving no successors. This was directly related to facial and inbreed condition.