AKC regulations for canine orthodontics

A dog is considered changed in appearance by artificial means if it has been subjected to any type of procedure, substance or drugs that have the effect of obscuring, disguising or eliminating any congenital or hereditary abnormality or any undesirable characteristic, or that does anything to improve a dog's natural appearance, temperament, bite or gait. 

Even procedures, substances and drugs that are absolutely necessary to the health and comfort of a dog shall disqualify that dog from competition if the former had the incidental effect of changing or even improving the dog's appearance, bite or gait …

Procedures that would in and of themselves be considered a change in appearance by artificial means and make a dog ineligible for shows include, but are not limited to … restorative dental procedures, the use of bands or braces on teeth, or any alteration of the dental arcade.

From: Dog show entries, conditions of dogs affecting eligibility. In: Rules applying to dog shows. New York: American Kennel Club, 2015;46-47. Available at: http://images.akc.org/pdf/rulebooks/RREGS3.pdf.