“In-standing K9” teeth, AKA “base narrow K9s” “medial displaced K9s”
The position of the K9 teeth in Bull Terriers and other affected breeds can be caused by several factors. Various theories have been proposed by Bull Terrier fanciers who are veterinarians, geneticists, general dentists, and oral surgeons. Among these theories are: narrowing of the mandible by breeding selection, changed eruption angle toward midline by rotation of the mandible, medial displacement of the tooth bud, and evolutionary changes induced by rapid generational breeding causing a decrease in length and width of the mandible without concurrent downsizing of the teeth resulting in crowding and displacement. Any or all of these may factor into the current changing position of K9 teeth in Bull Terriers and many other breeds.
With so many theories, it seems obvious there is no single answer. Still dentition and alignment of the bite should be of concern to all serious breeders to maintain correct structure and function required by their breed standards.
Recently, the focus of concern in this area has been directed to an impression that these displaced K9 teeth cause pain and suffering to the animals affected. This idea is based on the theory that the contact of the displaced crown of the K9 tooth with the palate causes a pain response. In my 48 years breeding and showing dogs and 37 years as practicing veterinarian, I have never personally observed a dog affected by in-standing K9 teeth to exhibit pain as a direct result of contact with the palate. In fact, when there is tooth contact with gum tissue or bone, the bone remodels away from the contact, which creates the indentation in the palate above the displaced K9. This is well documented in both veterinary and human dentistry. Once remodeled, there is no contact between crown and palate. If there is concurrent dental disease such as infections or periodontal disease, then there would be oral pain, however, these types of concurrent diseases are problem of husbandry unrelated to the displacement of the K9 teeth.
Carl L. Pew, DVM, MRCVS