Dentofacial changes produced by extraoral forward force in the Macaca irus.

Eleven Macaca irus monkeys with a mixed or a permanent dentition were used in a study of the possible effects of extraoral forward force on the growth of the dentofacial skeleton. An intermittent forward force of 300 Gm. per side was applied, and the effects were analyzed by means of model casts, cephalometric radiographs, tetracycline bone marking, microradiographs, and histologic preparations. The results obtained were as follows: 1. An extraoral forward force caused significant changes in the circum-maxillary sutures and the maxillary tuberosity. 2. It was found that intermittent force of 300 Gm. per side resulted in desirable reactions in the sutures in young monkeys. 3. It was suggested that reactions in the suture might occur as a result of (1) an opening of the suture, (2) stretching of sutural connective tissue fibers, (3) new bone deposition along the stretched fibers, and (4) homeostasis which maintained the sutural width. 4. The maxillary complex showed a positional change with a little counterclockwise rotation. 5. A local reaction was observed histologically in the adult, but the degree was less than that seen in the young monkey. 6. It was considered that a forward movement of the maxillary complex would readily be accomplished by increasing sutural activity as early as possible. 7. Clinically, it was assumed that the hooks attached to the intraoral appliance should be placed as far frontally as possible. The present study seemed to indicate that forward movement of the maxillary complex would be performed with an extraoral anterior-pull appliance. Further investigation should be designed to evaluate a possible skeletal relapse after an orthopedic approach.