Name that Bite . . .
by Dr. Jan Bellows, D.V.M.
Diplomate American Veterinary Dental College
Diplomate American Board Veterinary Practitioners
What is really meant by the words: Overbite, open bite, overjet, level
bite, overshot, underbite, anterior crossbite, wry bite, retained deciduous
teeth, base narrow canines? Breeders, show judges, veterinarians and others
who want to express specific dental conditions in dogs and cats need to use
the proper terms. This article will review commonly used and misused words
to describe tooth alignment.
Anatomy
Dogs normally have twenty-eight deciduous (primary or baby) teeth that
erupt during the first six months of life. Most breeds have forty-two adult
teeth. Cats have twenty-six deciduous and thirty adult teeth. There are four
types of teeth. Incisors of are the smaller teeth located between the
canines on the upper and lower jaws. They are used for grasping food and help
keep the tongue within the mouth. Canines (also called cuspids or fang
teeth) are located on the sides of the incisors and used to grasp food.
Premolars (bicuspids) are for shearing or cutting food and are located
behind the canines. The molars are the last teeth in the mouth. They are
used for grinding nourishment for entry into the esophagus.
Missing or Extra Teeth
Dogs and cats are frequently born without the proper number of teeth.
Extra (supernumerary) teeth can cause periodontal disease from over
crowding. The American Kennel Club sets the standards concerning minimum
number of teeth for each breed of dog that can be shown. Dental x-rays can be
safely taken as early as ten weeks of age to evaluate if the correct number
of adult teeth will emerge. This is recommended as a part of the prepurchase
examination in certain breeds. Usually missing teeth will not cause an
eating problem.
Occlusion
The way teeth align with each other is termed occlusion. Normal
occlusion in most breeds consists of the upper (maxillary) incisors just
overlapping the lower (mandibular) incisors (scissor bite). The lower canine
should be located equidistant between the last (lateral) incisor and the
upper canine tooth. Premolar tips of the lower jaw should point between the
spaces of the upper jaw teeth. Flat faced breeds (Boxers, Shih-Tzu, and
Lhasa Apso) normally do not have scissors bites.
Malocclusion
Malocclusion refers to abnormal tooth alignment. Overbite (overshot,
class two, overjet, mandibular brachygnathism) occurs when the lower jaw is
shorter that the upper. There is a gap between the upper and lower incisors
when the mouth is closed. The upper premolars are displaced at least
twenty-five percent toward the front when compared to the lower premolars.
An underbite (undershot, reverse scissor bite, prognathism, class 3) occurs
when the lower teeth protrude in front of the upper jaw teeth. If the
upper and lower incisor teeth meet each other edge to edge, the occlusion is
an even or level bite. When the upper and lower incisors do not overlap or
even meet each other when the mouth is closed, the pet has an open bite.
Anterior crossbite occurs when the canine and premolar teeth on both sides
of the mouth occlude normally but one or more of the lower incisors are
positioned in front of the upper incisors. Anterior crossbite is the most
common malocclusion, is not considered genetic or hereditary and is
correctable. If there is an anterior crossbite there must be a condition
termed posterior crossbite. Posterior crossbite occurs when one or more of
the premolar lower jaw teeth overlap the upper jaw teeth. This is a rare
condition that occurs in the larger nosed dog breeds. A wry mouth or wrybite
occurs when one side of the jaw grows longer than the other. It is
considered hereditary and difficult to correct. Base narrow canines occur
when the lower canine teeth protrude inward and can damage the upper palate.
Often this condition is due to retained baby teeth and can usually be
corrected through inclined planes used to push the teeth into normal
occlusion.
Dr. Jan Bellows is one of the thirty veterinary dental specialists in the
country recognized by the American Veterinary Medical Association. His
office, All Pets Dental Clinic located at 9111 Taft Street, Pembroke Pines,
Florida. (954) 432-1111.