The objective of the proposed research is to determine the craniofacial adaptations which occur subsequently to total maxillary osteotomy in actively growing Macaca fascicularis monkeys. Specifically, the study will investigate the effect of surgical repositioning of the maxilla on the growth and development of the facial bones, nature of healing, eruption and migration of teeth and neuromuscular complex. In addition, the role of occlusion and change in the position of the mandible associated with the surgically obtained increase as well as the decrease in the vertical height of the face will also be studied. Interpositional bone grafts will be used during the LeFort I osteotomy to increase the vertical height of the face. Both normally growing and monkeys with skeletal-dental malocclusion will be used. The biologic changes, either due to growth and/or surgery, will be studied with the help of conventional and stereometric caphalometry, muscle implants, and carefully executed histologic and histochemical techniques. The long-term goals of the project are to improve our understanding of the effect of maxillary osteotomy, with controlled parameters of occlusion and vertical height, on the nature of osseous and muscular adaptation. Furthermore, the results of surgery on growing monkeys will help delineate procedures and biologic parameters to be considered in the surgical correction of moderate to severe malocclusions in adolescent patients.