A dog’s bite is determined by how the upper and lower incisor teeth meet when the mouth is closed. The ideal occlusion is one in which the upper incisors just overlap and touch the lower incisors. This is called the scissors bite. In the even or level bite, the incisors meet edge to edge. This is a common occlusion, but is not considered ideal because the edge-to-edge contact wears the teeth. The correct bite for any given breed is described in the standard for that breed.
An incorrect bite causes breeders more concern than any other mouth problem. Bad bites interfere with the dog’s ability to grasp, hold, and chew food. Teeth that are out of alignment may injure the soft parts of the mouth.
Most malocclusions are hereditary, resulting from genetic factors that control the rate of growth of the upper and lower jaws. Some incorrect bites re caused by retained baby teeth, which push the erupting adult teeth out of line.
Overshot bite occurs when the upper jaw protrudes beyond the lower jaw, causing the upper teeth to overlap the lower teeth without touching. This condition is also called prognathism. Some breeds, such as German Shepherd Dogs, will go through a normal stage as puppies in which the bite is overshot. The overshot bite may correct itself spontaneously in young puppies if the gap is no greater than the head of a wooden match. Improvement may continue until the puppy is 10 months old, at which time the jaws stop growing.
Puppies with severe overshot bites may have problems, because as the adult teeth come in they can injure the soft parts of the mouth. This requires treatment.
Undershot bite is the reverse of the overshot bite; the lower jaw protrudes beyond the upper jaw. It is considered normal for brachycephalic breeds, such as Bulldogs and Pugs. Undershot bite is also called brachygnathism.
Wry mouth is the worst of the malocclusion problems. In a dog with wry mouth, one side of the jaw grows faster than the other, twisting the mouth. This can be a severe handicap in grasping and chewing food.
Treatment: Puppies should be examined by the veterinarian at 2 to 3 months of age to identify bite problems. In most cases treatment will not be necessary. If there is overcrowding or displacement of permanent teeth, however, the problem should be corrected by tooth extractions or orthodontic procedures such as crown-height reductions or the use of spacers. Interventional orthodontics will disqualify your dog for conformation competition.
The overshot bite is definitely hereditary and may be passed on to members of the next generation. The undershot bite is hereditary in some breeds. Dogs with hereditary dental malocclusions should be eliminated from breeding programs. This does not apply to brachycephalic dogs, in which malocclusion is a breed characteristic.
This condition, seen in Pekingese, Chihuahuas, and some other toy breeds, occurs when the cartilage that joins the two sides of the lower jaw at the chin fails to calcify. The lower incisors that are set in this soft cartilage become loose and unstable. Infection descends to the roots of these teeth and destroys the cartilage. This allows the two sides of the jaw to detach and move independently. This condition can be caused by an incorrect calcium to phosphorous ratio in the dog’s diet.
Treatment: The unstable jaw can be treated by removing the diseased teeth, administering antibiotics, and stabilizing the joint with wires or screws. If diet is a contributing factor, the diet must be corrected as well.