Jaw Malocclusions/Pet Orthodontics

It is important to understand the head shape when determining normal bite relationships in various breeds. There are three basic head shapes for dogs. Those with long and narrow muzzles (Rough Collies, Borzoi, Doberman, Greyhound, Saluki); those with a short and wide muzzles (Bulldog, Pug, Pekingese, Boxer, Boston Terrier, Shih Tzu); and dogs with medium length and width muzzles (Labrador Retriever, German Shepherd Dog, most Spaniels, Terriers, and Hounds).

The normal bite of dogs and cats with medium or long length and width muzzles is called a scissors bite. The upper incisors are located in front of the lower incisors when the mouth is closed, and there is a smooth curve from canine to canine without misplaced or rotated teeth. The lower canines should lie exactly between the upper lateral incisors and upper canines, yet touching neither. Premolar crown tips should point to a space between the crowns of the opposing premolars. In dogs that have a short, wide muzzle, a reverse scissors bite is considered normal where the lower incisors are in front of the upper incisors. The lower canines and premolars will also be shifted forward. While the reverse scissors bite is an acceptable breed standard, at times the upper incisors cause trauma and pain to lower jaw tissues.

Normal interdigitation of premolars

Occlusion is controlled by genetics, nutrition, environment, and by mechanical forces generated by the interlock of the upper and lower teeth. Some abnormal bites (malocclusions) have been proven to be genetically influenced, such as severe over or under bites, and wry bites. Other bite abnormalities are known to be acquired (non genetic). Acquired malocclusions can result from tug of war games played with towels or ropes which move teeth into abnormal position. Traumatic birthing can also responsible for some acquired abnormalities.

To help define whether the malocclusion is genetic in origin, interdigitation of the premolars is studied. In breeds that have medium and long muzzles, the premolars should meet in a saw-toothed fashion. For example, the tip of the lower third premolar should be positioned equally between the crowns of the upper third and fourth premolars. If the tip of one premolar points to the tip of another premolar, there may be a genetically induced malocclusion. This only holds true in those breeds that do not have shortened muzzles.

Some genetic bite problems do not show up in each litter because they are recessively passed on. The goal of selective breeding is to mate one animal to another that has superior occlusion.

genetic malocclusion because the premolars do not line up

Normally the deciduous tooth's root is resorbed, making room for an adult tooth. Should this fail, the adult tooth may deviate from it's normal position, producing malocclusion. The resulting double set of teeth overcrowds the dental arch, causing food to become trapped between the teeth, leading to early periodontal disease. A double set of roots may also prevent normal development of the socket, and erode periodontal support around the adult tooth, resulting in early tooth loss. A retained deciduous tooth should be extracted as soon as an adult tooth is noted in the same area as the baby tooth. If extraction is performed early, the abnormally positioned adult tooth usually moves to it's normal location.

A procedure performed by some breeders is to trim or cut deciduous teeth in hopes that they will be shed early preventing orthodontic problems. By cutting the tooth in half, pulp is exposed to oral bacteria causing infection, pain, and tooth loss. Unfortunately, the remaining infected root can interfere with the emerging adult tooth, which may not come in normally.

Retained upper canine
tooth

Missing lower fourth premolar

Dogs and cats may be born without the proper number of teeth. Extra (supernumerary) teeth can cause periodontal disease from over crowding. The American Kennel Club sets standards concerning minimum number of teeth accepted for each breed to be considered for show. Dental x-rays can be taken as early as ten weeks of age to evaluate if the correct number of teeth are present. X-rays are recommended as a part of the prepurchase examination in certain breeds. Missing teeth (hypodontia) usually occurs in the premolar area, but any tooth in the mouth may not erupt. Missing or extra teeth are considered genetic faults. Collies and Doberman Pinchers are most commonly affected. Sometimes the missing tooth is trapped below the gum line. A dental x-ray can be taken to determine if an unerupted tooth is present.

8 upper baby incisor teeth in boxer
puppy (normally should have only 6)

Rostrally deviated upper canine tooth
treated by crown reduction or elastic to
pull back tooth into normal occlusion

Misdirected canine syndrome is a bite abnormality, in which retention of the deciduous tooth tilts the erupting permanent canine tooth into abnormal location. The opposing canines may not have room to occlude properly, resulting in abnormal wear, periodontal disease, or early tooth loss.