What Causes Underbite in Dogs?

While in the human world, perfectly aligned pearly whites are sought after for a flawless smile, in the doggy world, pooches could care less about having a 'malocclusion'--that is, misaligned teeth. Depending on the dog's breed, underbites in particular may be considered standard, or they may be hereditary abnormalities which, for some dogs, may even lead to eating difficulties or other problems. Knowing the causes for a dog's underbite can help minimize problems and prevent the reoccurrence of improper bites in bloodlines.

Genetic Factors

Normally, the upper teeth and lower teeth of dogs meet in what is called a "scissor bite." In this case, upon closing the jaw, the dog's lower canines should nicely intersect in front of the upper canines. However, in some cases, the lower teeth may protrude in front of the upper teeth, often because of genetic factors. The correct term for this type of malocclussion is underbite or reverse scissor bite. It's considered an abnormality when observed in medium or long muzzled dogs, according to All Pets Dental Clinic.

Skeletal Factors

For some breeds of dogs, an underbite is a much cherished quality that is part of the breed standard. For instance, boxers, bulldogs, Pekingese and pugs are known for having brachycephalic features. In this case, the underlying cause for the underbite is the skeletal predisposition for having a shorter than normal upper jaw. With those irresistible pushed-in faces and shorter jaws many people are fond of, the space into which the teeth erupt is limited in these pooches resulting in a “malocclusion.”

Dental Factors

In this case, unlike dogs with brachycephalic features, the underbite is not caused by a skeletal abnormality but a dental one. As puppies grow, they start losing their milk teeth, which gradually are replaced by the permanent ones. In some cases though, the puppy's baby teeth may fail to fall, and the puppy may then be stuck with the baby teeth interfering with the permanent teeth, which potentially will grow crooked due to lack of space. In some cases, in slightly undershot bites, the incisors may be the only teeth contributing to the misalignment.

Growth Factors

At times, a puppy's lower jaw may grow faster than usual becoming longer compared to the upper jaw. This uneven growth condition can be seen in puppies as young as 8 weeks of age. What happens is that certain teeth in the upper jaw may get caught behind the teeth of the lower jaw, causing the upper jaw to fail to grow at the proper rate.

Acquired Factors

In some cases, the cause for the malocclusion may not be genetic, but acquired. For instance, inappropriate chewing and tugging during the delicate phase of teething may cause bite problems in puppies where their growing teeth shift from their original position. In this case, you may want to avoid playing rough games such as tug-of-war. Tug-of-war played using towels or ropes may cause teeth to move into an abnormal position causing them to be pulled out of alignment.

Important Factors

Dogs with severe cases of undershot bites may have difficulty eating, develop improper wear and suffer damage to the soft tissues. In some cases, the undershot bite is severe enough to necessitate orthodontic treatment or tooth extraction. If you notice an underbite developing in your pup, tell your vet. Early intervention is key in order prevent more serious problems.

By Adrienne Farricelli

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References

AKC Canine Health Foundation: It's More than Just Bite!
Marvista Vet: Dogs with Special Faces
Dental Vet: Pet Orthodontics
Small Animal Dentistry; Cecilia Gorrel
Web MD: Malocclusions in Dogs
Merck Veterinary Manual: Dental Disorders of Dogs
German Shepherd Help: Misalignment of Teeth

About the Author
Adrienne Farricelli has been writing for magazines, books and online publications since 2005. She specializes in canine topics, previously working for the American Animal Hospital Association and receiving certification from the Certification Council for Professional Dog Trainers. Her articles have appeared in "USA Today," "The APDT Chronicle of the Dog" and "Every Dog Magazine." She also contributed a chapter in the book " Puppy Socialization - An Insider's Guide to Dog Behavioral Fitness" by Caryl Wolff.