Yes, dogs can have underbites just like people can have them, but the snaggletoothed gaze of a dog with an underbite can certainly be endearing. Treating an underbite in a dog, though, can be vastly different than treating one in a person.
What is an Underbite?
An underbite is a type of malocclusion. The prefix, "mal," comes from Latin and literally means "bad," so a malocclusion is a bad occlusion. In underbites, the lower jaw juts out too far, leading to misalignment of the bottom and top teeth when the mouth is closed. Dogs with an underbite may have a snaggletoothed appearance, with one or both lower canines visibly sticking out of their mouth. Underbites are also sometimes termed Type 3 Malocclusion in dogs because, unfortunately, it's not the only type of malocclusion dogs can have. They can also have overbites (aka Type 2 Malocclusion) and cross-bites, just like people.
Causes of Underbites
Underbites are almost always congenital in nature. This means that it's present from birth. They are most commonly seen in brachycephalic breeds, such as Boxers, Boston terriers, Brussels Griffons, Bulldogs, Lhasa Apso, Shih Tzu, Pugs, etc. In fact, underbites are so commonly seen in these breeds that they are considered to be their normal dentition In rare instances, facial trauma can also cause an underbite.
Regardless of why your dog has an underbite, it's important to understand the repercussions a dog with an underbite may face. An underbite (or any dental malocclusion) can make a dog more prone to dental disease. If the upper teeth and lower teeth don't line up like they're supposed to, that can make some teeth more prone to tartar build up. It can also lead to more tooth-on-tooth wear and can also damage or irritate the gums, lips, or hard palate.
Treatment of Underbites
In people, an underbite is fixed by orthodontics and braces. Believe it or not, they make braces for dogs, too! However, they are used primarily under the supervision of a board certified veterinary dentist, not a general practitioner. Additionally, they aren't used for cosmetic purposes as in people. Braces are used in dogs only when there is a medical problem warranting their use. Application of the braces and subsequent adjustment of the brackets will require general anesthesia and dental radiography. A more common approach is to remove teeth that are badly affected by the malocclusion or are causing pain due to digging into the gums or lips.
For most dogs with underbites, management of problems created by the malocclusion is the treatment of choice. Dogs that have underbites may require more at-home, preventative dental care. Chews and oral rinses certainly don't hurt, but they are also not nearly as effective as brushing the teeth. If you have a dog with an underbite, training them to accept daily tooth brushing can be helpful. It's important that you use veterinary specific toothpaste as human toothpaste usually contains fluoride, which can be harmful if swallowed. Additionally, most dogs don't prefer the minty flavors of human toothpaste. Veterinary toothpaste comes in more dog-friendly flavors such as poultry and beef.
Eventually, though, even daily brushing may not be enough to stave off dental disease. If your dog has gingivitis, heavy tartar, and/or bad breath, your dog may need a dental cleaning. This is similar to when humans routine dental cleanings with ultrasonic scaling, followed by polishing the enamel smooth. The major difference being that dogs need to be put under anesthesia for safe, effective dental cleanings and in order to safely take dental radiographs.
If your dog has an infected or abscessed tooth, the most common treatment is to simply take out the tooth in question. Most dogs can do just fine without the infected tooth. However, those same veterinary dentists that can place braces when needed can also perform root canals to save infected and/or fractured teeth. The cost of this may be prohibitive in some cases, but it is a good option to look into to help maintain a healthy mouth.
Preventing Underbites in Dogs
Unfortunately, because the most common reason for an underbite to happen is congenital, it can be difficult to prevent one if you are looking for a breed of dog that is prone to them. As mentioned, this abnormality is considered to part of the breed standard for these snub nosed breeds because it's a result of their signature 'pushed-in' faces. A pug or bulldog isn't a pug or bulldog without a smushed-looking face, and breeding its snout to be so short predisposes it to problems.
Underbites in dogs can put them at risk for future dental disease and may cause chronic pain or difficulty chewing. If your dog has an underbite and you're worried about the health of its teeth, speak to your veterinarian.