The word orthognathic comes from the root words "ortho" meaning correct or straight and "gnathos" meaning jaw and those two words actually describe quite well the function of orthognathic surgery. This type of surgery is intended to correct skeletal mismatches. That is, when one jaw is too large, too small, too far forward or too far back in relation to the cranial base (the bones which house and protect the brain). It is not intended to replace orthodontics (braces) which can straighten the teeth out over the existing bone but cannot change the bony relationships however, orthodontics are often needed both before and after orthognathic surgery in order to give the patient the best possible result.

Perhaps you have seen or know someone who can close their back teeth together and yet a space remains open between their front teeth. These people lose the ability to incise their food. They are unable to bite effectively into a sandwich and pizza becomes a food that must be consumed with a fork and knife. This condition is called apertognathia or open bite and can often be corrected by changing the angle at which the whole upper jaw is attached to the facial skeleton. The name of this surgical procedure is Le Fort I osteotomy.

Or perhaps you know someone with a prognathic mandible, popularly called "an underbite". The problem may be a mandible (lower jaw) that has grown too large or too far forward. Alternatively, the same problem can be caused by a maxilla (upper jaw) that has failed to develop enough. Depending on the cause, this condition may be corrected by surgery in the lower jaw ("sagittal split" or "intraoral vertical ramus osteotomy") or surgery in the upper jaw ("Le Fort I") or both.

Or perhaps you have met someone whose smile is just "too gummy". Now often, particularly in women, showing a bit of gingiva (gums) can be quite attractive but there are times when it is not attractive and it is an indication of a maxilla that has grown too far down. The name of the condition is Vertical Maxillary Excess and the surgical correction is via Le Fort I osteotomy and maxillary intrusion; all fancy ways to say, you move the upper jaw upwards.

Probably the most common problem for which orthognathic surgery is performed in the United States is retrognathia, more commonly (though not always correctly) referred to as "overbite".

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