Around five percent of the population has an underbite, where the lower teeth are too forward compared to the uppers. It is easy to spot, because of the distinctive face appearance. It does not usually provoke teasing from the schoolmates, but rather is usually spotted and referred by dentists.
It is routine for orthodontists to treat underbites early, sometimes as early as age four, but more often at age eight after the permanent incisors have grown in. The reasons treatment is done early are that the teeth and face bones are more easily moved at a younger age, and it is easier to get a child to wear the necessary devices (braces etc.) at an earlier age. It is assumed that they will still need orthodontic treatment again in a second stage at age 12 or so, but the early treatment is felt to give them a result that would not have been attainable if they had waited.
Treatment of underbites will often involve upper jaw expansion in order to loosen the bone sutures, and simultaneous facemask headgear to pull the upper jaw forward. In eight-year-old children who wear the facemask 12 hours per night, underbites can be corrected in less than a year. They are sometimes overcorrected in anticipation of relapse and partial return of the underbite.
Years ago it used to be taught that underbites should not be treated until growth was complete (age 18), and then jaw surgery would correct the underbite. It is now preferred to treat children early while the sutures are immature, but with the understanding that two stages will be needed.
