Prognathism
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 it wears the teeth.3
Prognathism refers to a condition wherein the lower jaw (mandible) is longer than the upper jaw. Dog breeders refer to this condition as an overshot bite. Mandible supports the lower teeth and is the largest and strongest bone of the face (muzzle). All brachychephalic (short-nosed) breeds, including Pug, Boxer Bulldog, Boston Terrier, and Pekingese, have a prognathic occlusion pattern. The Bulldog is perhaps the most easily recognized of the brachycephalic breeds. The standards for brachycephalic heads all allow or require prognathism. Some breeds, such as German Shepherd Dog, will go through a normal stage as puppies in which the bite is overshot.3
One of the mild types of prognathism, level bite, refers to a condition when the incisors meet cusp-tip to cusp-tip rather than having the uppers overlap the lowers (scissor bite). Due to the abnormal incisor cusp-tip contact, all incisors will experience abnormal crown wear. Individual incisors will also experience a greater frequency of fracture than incisors with a scissor occlusion.
Brachygnathism
Brachygnathism refers to a condition in which an overbite, or overshot upper jaw exists. Both brachygnathism and prognathism are inheritable traits, passed from one generation to another. Although not life-threatening, these anatomic abnormalities can interfere with normal biting action and eating and can predispose to dental and jaw problems. Orthodontic correction of brachygnathism and prognathism can be utilized in select cases for medical purposes. Dogs suffering from a distinct overbite or underbite, unless normal for the breed, should be neutered to prevent propagation of these undesirable traits. The overshot bite may correct itself spontaneously in young puppies if the gap is no greater than the head of a wooden match.3
References
- Mordecai Siegal, Jeffrey E. Barlough. Uc Davis Book of Dogs.
- Chris C. Pinney. The Complete Home Veterinary Guide.
- Debra Eldredge, Liisa D. Carlson, DVM, Delbert G. Carlson, James M. Giffin. Dog Owner's Home Veterinary Handbook.
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