Rotations of the Maxilla and Mandible by Class III Orthopedics Followed by Upper Molar Distalization

Protraction of the midface in growing individuals always results in an anterior rotation of the maxilla, and downward movement of the upper molars. The vertical displacement of the upper molars is restrained by the occlusal forces from the opposing lower molars, and by bonded acrylic bite plates. The increased occlusal forces in the lower molar region, combined with the forces applied by a face mask to the chin, will result in a posterior rotation of the mandible and increase of the vertical dimension of the face. However, when bone anchored class III orthopedics are used, a slight closure of the mandibular plane angle may be expected. More anterior rotation of the maxilla results in more forward projection of point A, but also in higher occlusal forces in the molar region, which finally limits the amount of midface protraction. If rotations of the maxilla could be better controlled, this could be in favor of more forward translation of the zygomatico-maxillary complex. Successful midface protraction commonly results in a class II molar occlusion. The upper miniplates can be (re)used for upper molar distalization. In contrast to cervical headgear, upper molars are not extruded, and some bite deepening instead of bite opening is observed in the incisor region. Appropriate timing of the bite opening mechanics is needed for efficient bone anchored upper arch distalization.

Learning Objectives:

• Assess rotations of the maxilla and mandible during class III orthopedics.
• Asses the biomechanics for bone anchored upper arch distalization.
• Identify the best timing for bite opening mechanics.