Cervical retraction of the maxillae in the Macaca mulatta monkey using heavy orthopedic force.

Heavy, interupted orthopedic forces were employed for the cervical retraction of the maxillae in two Macaca mulatta monkeys. The nature, location and magnitude of resultant movements and remodelling were studied with the help of plaster casts, amalgam implants, lateral cephalometric tracings, and of gross and microscopic study of the skulls themselves. The principal effect of the retractive force was a marked downward and backward rotational movement of the maxillae which carried the maxillary teeth into posterior crossbite and a severe Class III molar relationship. Posterior movement of the tuberosity entirely closed the pterygomaxillary fissure so that the tuberosity impinged upon the pterygoid plates. Like the maxillae, the mandible, premaxilla, and nasal boned also moved downward and backward. These changes increased the vertical dimension of the face and diminished it horizontally leaving a flattened facial profile from the nasal opening to the maxillary incisors. Movement of facial elements posteriorly against an unhielding anterior cranial base imposed a number of other compensatory changes. These included generalized resorption at the craniofacial sutures and sliding of the sutures upon each other. They also involved mutual resorption of the maxillary tuberosity and of the pterygoid plates together with remodelling and lateral extension of the malar bones. Tolerance of the animals and of the localized tissues for these intensive forces suggests a significant role for this form of therapy. Clinical application, however, should be tempered by judicious concern for the vital structures of the pterygomaxillary fissure which could be impinged or strangulated by excessive retrusive force.