Biomechanics of maxillary expansion and protraction in Class III patients.

During a 1981 presentation at an American Association of Orthodontists meeting, David Turpin recommended that early treatment should be considered for young patients who present with positive factors such as convergent facial type, anteroposterior functional shift, symmetrical condyle growth, mild skeletal disharmony, some remaining growth, good cooperation, no familial prognathism, and good facial esthetics. For patients who present with negative factors, he suggested delaying treatment until growth was completed. In the 20 years that have passed, what have we learned to help us better treat our patients? We now know, for example, that Class III patients with maxillary deficiency can be treated quite successfully with facemask therapy in conjunction with maxillary expansion. In a prospective clinical trial, 20 patients with skeletal Class III malocclusion were treated consecutively with maxillary expansion and a protraction facemask. A positive overjet was obtained in all of them after 6 to 9 months of treatment. These changes were caused by forward movement of the maxilla, backward and downward rotation of the mandible, proclination of the maxillary incisors, and retroclination of the mandibular incisors. The molar relationship was overcorrected to a Class I or II dental arch relationship, and the overbite was reduced with a significant increase in lower facial height. We have also learned that overcorrection is a key to long-term stability. At the end of the 4-year observation period, and after half of the patients completed their pubertal growth spurt, 15 of the 20 (75%) maintained a positive overjet or an end-to-end incisal relationship. Patients who reverted to a negative overjet were found to have excess horizontal mandibular growth. Clinically, the success rate of treating Class III patients with maxillary expansion and a protraction facemask is at best 50% to 60% at the completion of the pubertal growth spurt.