Canine Underbite (Mandibular Prognathism): Causes, Symptoms, and Treatment

What Is an Underbite?

A canine underbite is a type of malocclusion formally classified as Class III malocclusion or mandibular prognathism. In this condition, the lower jaw protrudes beyond the upper jaw, often due to an excessively long mandible or a relatively shortened maxilla. As a result, the lower teeth extend in front of the upper teeth when the dog’s mouth is closed.

Brachycephalic (short-headed) breeds—such as Bulldogs, French Bulldogs, Pugs, Pekingese, and similar dogs—commonly exhibit this feature. In these breeds, a mild underbite is often considered part of the breed standard, giving the face a characteristic “protruding jaw” appearance. However, when pronounced, an underbite can lead to abnormal tooth wear and oral trauma. The lower canines or incisors may repeatedly rub against the upper gums or palate, causing gingivitis, oral ulcers, and chronic discomfort. Studies indicate that malocclusion in dogs is frequently associated with chronic pain, meaning that even so-called cosmetic dental corrections can have significant implications for a dog’s quality of life.

Breeds Predisposed to Underbite

Underbite is relatively common in dogs, particularly among brachycephalic breeds. In addition to Bulldogs, Pugs, French Bulldogs, and Pekingese, breeds such as Boxers, Bull Terriers, Shih Tzus, and West Highland White Terriers are also predisposed. Selective breeding for shortened facial structures has resulted in inherited skeletal traits—specifically, a shortened upper jaw combined with a relatively elongated lower jaw—leading to a naturally protruding mandible.

While a mild underbite may be acceptable or even expected in certain breeds, excessive mandibular protrusion can compromise oral health and overall well-being.

Causes of Canine Underbite

The development of an underbite typically involves multiple contributing factors:

Genetic factors:

Genetics play a dominant role, particularly in brachycephalic breeds. Long-term selective breeding has favored traits such as shortened maxillae and elongated mandibles. Research consistently identifies heredity as the primary cause of malocclusion in dogs.

Abnormal tooth development:

During puppyhood, retained deciduous (baby) teeth can occupy space in the dental arch and interfere with the proper eruption of permanent teeth. This crowding can force permanent teeth into abnormal positions, exacerbating mandibular protrusion. If retained baby teeth are not removed promptly, permanent teeth may erupt incorrectly, worsening the underbite.

Jaw trauma or disease:

Fractures of the jaw during growth that heal improperly, or congenital abnormalities affecting jaw development, can result in disproportionate jaw lengths. Additionally, chronic mechanical stress from improper chewing habits or frequent gnawing on hard objects may gradually shift tooth positions and intensify malocclusion.

In summary, genetic predisposition is the primary driver of underbite, while environmental and developmental factors can trigger or worsen its severity.

Common Signs and Clinical Features

Early recognition of an underbite allows for timely intervention. The most obvious sign is mandibular protrusion: when the dog closes its mouth, the lower canines or incisors extend in front of the upper teeth. The dog may appear unable to fully close its mouth, and the lower canines may not align correctly with the upper dental arcade.

Continuous contact between the lower canines and the upper soft tissues can lead to oral pain and injury, including inflamed gums and ulceration. Owners may notice:

• Inability to fully close the mouth, with the lower lip or corners of the mouth remaining open
• Difficulty eating, dropping food, or chewing preferentially on one side
• Recurrent oral injuries or signs of infection, such as excessive drooling or worsening bad breath

During the teething phase, the presence of retained baby teeth and misaligned permanent teeth should raise concern for developing mandibular prognathism.

Potential Health Consequences

An underbite is more than a cosmetic issue; if left untreated, it can lead to several long-term complications:

Increased risk of periodontal disease:

Crowded or misaligned teeth create areas that are difficult to clean, allowing plaque and tartar to accumulate more easily. This accelerates the progression of gingivitis and periodontal disease.

Oral trauma and abnormal tooth wear:

Lower canines may repeatedly traumatize the upper gums or hard palate, leading to chronic ulceration and pain. Abnormal tooth-to-tooth contact can also cause excessive or uneven wear.

Chewing and digestive difficulties:

Severe underbite can reduce chewing efficiency, resulting in difficulty eating and swallowing. Over time, this may impair nutrient intake and digestion.

Temporomandibular joint (TMJ) stress:

Uneven bite forces place additional strain on the jaw joints, increasing the risk of TMJ inflammation, arthritis, and chronic pain.

Associated conditions:

Many dogs with severe underbite—particularly brachycephalic breeds—also suffer from airway disorders. Jaw abnormalities may exacerbate breathing difficulties, making affected dogs more prone to respiratory distress during exercise.

Overall, untreated underbite can significantly compromise oral health and quality of life, making veterinary evaluation and intervention essential when problems arise.

Correction and Treatment Options

Is treatment always necessary?

Mild underbite without signs of pain or functional impairment may not require immediate intervention. Regular dental examinations are recommended to monitor changes. However, if oral trauma, pain, or feeding difficulties are present, treatment should be considered. Common therapeutic options include:

Orthodontic correction:

Dental appliances such as acrylic bite plates or orthodontic wires can apply controlled forces to gradually reposition misaligned teeth and establish a more comfortable bite. This approach is most effective in young dogs and typically requires multiple follow-up visits for adjustment.

Crown reduction:

For lower canines that consistently injure the upper tissues, crown height can be reduced, often combined with root canal therapy, to eliminate painful contact while preserving tooth function.

Tooth extraction:

Severely displaced, crowded, or non-correctable teeth—including retained deciduous teeth or malpositioned permanent teeth—may be extracted to create space and reduce traumatic occlusion. Extractions are often combined with orthodontic techniques to optimize bite function.

The primary goal of all treatments is to eliminate tooth-to-tissue conflict, relieve pain, and establish the most functional and comfortable occlusion possible. Most dental procedures require anesthesia and careful postoperative care. Each case should be individually evaluated by a qualified veterinarian or veterinary dental specialist.

Daily Care and Management

Oral hygiene:

Regular tooth brushing is the cornerstone of preventing periodontal disease. Daily brushing with pet-specific toothpaste, combined with professional dental cleanings and early dental evaluations, significantly reduces plaque accumulation and oral disease.

Appropriate chewing items:

Dental chews and safe chew toys can help clean tooth surfaces and stimulate healthy gums while reducing destructive chewing behavior. Dogs undergoing orthodontic treatment or recovering from oral surgery should not be allowed to chew hard objects such as bones, which may damage teeth or appliances.

Soft-food diet:

During orthodontic treatment or after dental surgery, a soft diet is often recommended to minimize chewing stress and promote healing. Dry kibble and hard treats should be avoided until recovery is complete.

Regular re-examinations:

Underbite requires long-term monitoring. Even after correction, periodic veterinary dental checkups are necessary to assess appliance function, healing sites, and overall oral health.

Breeding and Prevention Considerations

Because underbite has a strong hereditary component, dogs with severe malocclusion are generally not recommended for breeding. Responsible breeders should prioritize dogs with normal occlusion to reduce the incidence of inherited dental abnormalities. Affected dogs are often advised to undergo neutering or spaying and receive appropriate dental care.

Preventive monitoring should begin in puppyhood. Between three and six months of age, owners should closely observe the teething process. Early detection of abnormal bite development allows for timely intervention and can prevent more severe problems later in life.

Conclusion

Canine underbite is particularly common in brachycephalic breeds and is closely linked to genetic and developmental factors. Mild cases may require only observation and good oral hygiene, while more severe cases necessitate orthodontic or surgical intervention. Early detection, timely treatment, and diligent dental care are essential to maintaining comfort and long-term oral health. Responsible ownership and breeding practices, in collaboration with veterinary professionals, play a critical role in ensuring a functional bite and a good quality of life for affected dogs.