Primate models in surgical orthodontics

Between 1969 and 1980, 22 studies using nonhuman primates for experimental research in surgical orthodontics were published in the American Journal of Orthodontics, Angle Orthodontist, Journal of Oral Surgery, or International Journal of Oral Surgery. The most common species used was the rhesus monkey, Macaca mulatta. As laboratory animals, monkeys are relatively expensive and difficult to obtain. These problems have limited the design of experimental studies. Sample sizes are often too small for statistical analysis, control groups are small or omitted, and it has frequently been necessary to pool animals of different ages and sexes. These compromises might be appropriate if monkeys are the best available experimental model for humans, but there is little evidence that this is the case. Monkeys do not fill the usual role of good experimental models, which is to simplify a complex system. The monkeys used for craniofacial surgery have normal craniofacial function and morphology for their species, unlike human clinical patients. Cephalometric radiographs and skull measurements taken on monkeys of the five most common experimental species indicate that all experimental animals are much more prognathic than humans, and sex differences in prognathism are small. However, because many species have a large sex difference in canine size, females are a better experimental model than males for some questions. Considering recent federal legislative interest in animal research and the decreasing financial support for research, it is essential that the choice of experimental animals be justifiable and cost-effective. It would be worthwhile to consider alternatives to primates as the species of choice for experimental research in surgical orthodontics.