Why Some Dog Breeds Have Pronounced Underbites: Causes & Care

An underbite in dogs is when the lower jaw and teeth extend beyond the upper teeth, creating a distinctive facial feature that many pet owners find endearing, though medically it is considered a structural flaw. Unlike the typical scissor bite where upper and lower teeth align evenly, an underbite causes the bottom teeth to jut in front of the top ones.

This trait occurs most frequently in brachycephalic breeds—dogs that have short noses and compressed facial structures. In the United States, breeds commonly exhibiting underbites include the English Bulldog puppies, Boston Terrier puppies, Pug puppies, Shih Tzu puppies, and Lhasa Apso puppies. This condition, medically recognized as mandibular prognathism or Class 3 malocclusion, commonly arises from genetics and selective breeding for shorter skulls, leading to disproportion in jaw lengths. However, underbites might also develop from jaw trauma during growth phases or dental abnormalities like retained puppy teeth impacting adult tooth alignment.

Causes of Underbites in Dogs

Several factors contribute to the formation of an underbite:

• Genetic Influence: The primary cause is hereditary, notably in brachycephalic breeds where breeding practices have shortened the upper jaw relative to the lower jaw.
• Developmental Issues: Delayed loss of baby teeth or abnormal eruption of adult teeth can push permanent teeth out of alignment, causing an underbite to form.
• Injury: Trauma or fractures to the jaw during puppyhood can alter bone growth, resulting in misaligned jaws.
• Chewing Behaviors: Excessive or uneven chewing on hard objects may sometimes shift tooth positions later in life, affecting bite alignment.

Which Breeds Commonly Have Underbites in the US?

Breeds most often affected by underbites include:

• English Bulldogs
• Boston Terriers
• Pugs
• Shih Tzus
• Lhasa Apsos
• Cavalier King Charles Spaniels
• Boxers
• Pekingese
• Various terrier breeds

Mixed-breed dogs with ancestry from these breeds may also present underbites. In recent years, responsible breeders in the U.S. have placed greater emphasis on health-oriented breeding, selecting for balanced jaw structures to reduce severe underbite occurrences.

Possible Complications of Underbites

While many dogs with underbites experience no discomfort, serious cases can lead to:

• Dental Problems: Uneven tooth wear, crowded or crooked teeth increasing the likelihood of gum disease, and difficulties maintaining oral hygiene.
• Jaw Pain: Misaligned pressure on jaw joints (temporomandibular joints) may cause pain or problems with chewing mechanics.
• Feeding Challenges: Difficulty closing the mouth fully or inefficient chewing can impact nutrient intake and digestion.
• Additional Health Concerns: Many brachycephalic breeds with underbites in the U.S. also contend with brachycephalic obstructive airway syndrome (BOAS), contributing to breathing difficulties and exercise intolerance.

Treatment and Care for Underbites

Minor underbites generally do not require medical intervention if the dog eats well and shows no discomfort. Regular dental check-ups with a licensed U.S. veterinarian and proper mouth care are important to prevent complications.

Veterinarians may recommend treatment for severe cases, which can include:

• Extraction of retained or misaligned teeth to improve comfort and alignment.
• Orthodontic or corrective procedures to realign teeth or jaws in necessary cases.
• Supportive care for jaw pain and treatment of secondary oral infections.

Unlike the UK, the United States does not have centralized kennel clubs imposing mandatory health entry requirements specific to underbites. However, organizations such as the American Kennel Club and veterinary dental associations encourage ethical breeding standards and health monitoring to improve breed welfare.

Early Identification of Underbites in Puppies

Quick Insight: An underbite often becomes noticeable when puppies begin transitioning from baby to adult teeth, typically between 4 to 6 months of age. The lower jaw or teeth visibly protrude past the upper teeth.

Owners should keep a close eye on their puppy's dental and jaw development, watching for signs like retained puppy teeth or misalignment. Consulting a U.S. licensed veterinarian early helps address potential problems proactively, improving the dog’s comfort and preventing long-term oral health issues.

Health Concerns Associated with Underbites?

Brief Answer: Minor underbites usually do not cause health problems, but severe malocclusions can lead to dental disease, jaw pain, and feeding issues requiring veterinary care.

Underbites can increase the risk of periodontal disease because of tooth crowding and irregular contact between teeth. Additionally, uneven jaw stress might cause temporomandibular joint discomfort or arthritis. If a dog shows difficulty eating, signs of oral pain, or excessive wear, consulting with a veterinary dental specialist is crucial for proper management and quality of life.

Promoting Responsible Ownership and Breeding

Ethical breeding in the U.S. prioritizes health over extreme physical characteristics like severe underbites. Prospective owners interested in breeds prone to underbites should select reputable English Bulldog breeders or breeders of other affected breeds committed to breeding for functional, healthy jaw alignment.

Proper puppy care includes regular veterinary treatments focusing on dental health, using safe chew toys designed to encourage healthy jaw development, and close monitoring of bite progression during teething phases.

Summary

Pronounced underbites in certain dog breeds primarily result from genetics tied to brachycephalic facial types. Although often a harmless cosmetic trait, significant underbites can pose dental, jaw, and eating difficulties. Responsible pet ownership in the U.S. involves attentive puppy development monitoring, appropriate veterinary dental care, and supporting ethical breeding to enhance the overall wellbeing of these dogs.