Experimental and postexperimental response to anteriorly directed extraoral force in young Macaca nemestrina.

An anteriorly directed extraoral force was applied to the maxillas of four healthy young M. nemestrina monkeys. Experimental, retention, and postretention alterations were evaluated through a combination of cephalometric, histologic, and gross techniques. In view of the results of the present study, the following conclusions can be made: 1. Skeletal remodeling occurs in all circummaxillary sutures following the application of an anteriorly directed extraoral force to the maxilla. The amount of remodeling appears to be proportional to a suture's distance from and orientation to the applied force system. 2. The maxillary complex exhibited a marked anterior positioning with a small amount of counterclockwise rotation during the experimental period. 3. The application of an extraoral force to the maxilia produces compensatory deposition and resorption of bone, not only at the sutural margins but also at the external surface of the bones themselves. 4. It is possible that the experimental appliance transmits its effect to the facial bones adjacent to the maxilla through an alteration in the skull's periosteal envelope. 5. A substantial reorientation of the maxillary complex occurs following the termination of active force, and the degree of relapse or reorientation is directly proportional to the length of stabilization. 6. The dentition, through the periodontal ligament, undergoes approximately four times as much relapse as do the facial bones through their sutural articulations, following a minimal period of stabilization. 7. Extraoral forces applied to the craniofacial complex are transmitted through the maxilla and related midfacial bones, resulting in changes in such deep cranial structures as the cartilaginous synchondroses of the sphenoid bone. 8. Anterior displacement of the maxilla by extraoral traction appears to have a minimal effect on the mandible and the temporomandibular joint. 9. The number of sinusoidal vessels in the sutural ligament tends to increase in those sutures subjected to a tensional force.