One of my young-star patient, N.S. was 1st referred to me by her pediatrician for evaluation of her underbite. Here she is at age 5.2 with a well-defined anterior cross-bite and prognathic appearing lower jaw. Because of this condition, she was an excellent candidate for early orthodontic treatment.
Anterior Cross-bite With True Skeletal Class III Discrepancy
Another indication for early orthodontic treatment (Two-Phase) is when a patient demonstrates an anterior cross-bite with a true skeletal jaw discrepancy. Most of these patients develop this type of dento-facial growth, at a young age. By age 5 it is well established and its time to have this malocclusion evaluated by an orthodontist. This kind of malocclusion is present in about 3-4% of the population in the U.S., but represents 1of 5 in the Asian population. Phase I orthodontic treatment is usually indicated for several reasons:
- an esthetic and functional improvement is achieved
- may alleviate or reduce the need for later surgery
- eliminates mandibular functional shift and possible asymmetric growth
- unlocks the maxilla and improves its position
The majority (63%) of these patients have a retruded upper jaw, not a prognathic lower jaw. Therefore, diagnosis is the key to a successful treatment. Usually Phase I will involve a palatal expander that is used, not only to expand, but also as a handle to the upper jaw. A reverse headgear that is worn 14 hrs/day is then connected to this appliance via rubber bands to place a forward force on the upper jaw and mobilize it anteriorly.
Research shows that when this kind of malocclusion is present, the normal forward growth of the jaw is restricted. During normal growth, the upper and lower jaw grows forward about 1mm/yr. But when this malocclusion is present, the upper jaw grows zero in its forward dimension, while the lower jaw continues its forward growth of 1mm/yr. Over many years of growth we then see a worsening of their underbite by about 1mm/yr. Early treatment moves and unlocks the upper jaw and allows it to move 1mm/month. We are then able to provide growth to the upper jaw that wouldn’t normally occur. Research also shows that the results are very stable, especially if the orthodontist over-corrects. What this means, is that an anterior overbite needs to be established beyond what normal would be. Without this, relapse may occur over the ensuing growing years.
Our lovely N.S. was a fantastic patient. She wore her appliance and headgear superbly well. Because of this, we were able to over-correct her incisor position, and unlock her upper jaw. As evident by her before (above) and after pictures (next page), what appeared to be a prognathic lower jaw was truly a retruded upper jaw that needed our help. Her profile now shows the normal convexity that children have from below the eyelid to around the commissures of the lip. Her lower jaw and chin-point does not appear prognathic anymore. We are now waiting for more teeth to erupt during the next few years. A 2nd phase is usually needed to complete the alignment of her teeth.
Below we see N.H. at age 9, two years after Phase I. Her correction is holding nicely, and her dento-facial growth has continued to be in balance. She still has a few more years in the mixed dentition and we anticipate a 2nd phase at around age 12.
Diplomate, American Board of Orthodontics
Children’s Braces & Dentistry