Learning from Malocclusions in Animals


Just one look at any animal’s teeth and it’s obvious they are a lot different in shape and size than ours. Also strangely different are the malocclusions displayed by certain breeds.

Let’s look at malocclusions commonly represented by certain breeds of animals and discuss why they might work for them, and not for us.

Photo Credit: Barbara Cagle

Overjet and Overbite

An overbite is an overlap of the upper front teeth in relation to the lower front teeth. Overjet refers to the distance in which the upper front teeth sit forward of the lower front teeth. This is sometimes referred to as “buck teeth.”

Animals commonly displaying overbites and overjets include:

  • Horses
  • Donkeys
  • Rodents
  • Rabbits
  • Parrot
  • Billfish

Like us, horses and donkeys display slight overbites. This discrepancy is beneficial to helping them maintain proper nutrition as herbivores, as it allows them to grip and tear forage such as grass.

Birds have an elongated mandible that is typically hooked. This allows them to debug themselves, grip when climbing, and shell seeds. Unlike humans, parrots actually have the ability to move their upper jaw independently thanks to a joint called the craniofacial hinge.

Ironically, too much of an overjet in horses, donkeys and some other herbivores, is referred to as parrot mouth, because of the shape their mouth takes on when they have an underdeveloped lower jaw- similar to that of a parrot. Extreme overjets make it difficult for herbivores to consume forage close to the ground because they cannot get a flush grip on it with their teeth.

Many rabbits and rodents who look like they have buckteeth have an overjet by design. This condition provides advantages in that it allows them to apply vertical shear forces without either excessive vertical movements of the head or vertical movements of mandible.

A fun fact you may not be aware of is that rabbits’ teeth grow continuously. The average amount of tooth wear required to keep a rabbit’s teeth at an ideal length is one eighth of an inch per week! Too much or too little of an overbite, or a diet rich in soft foods can make it difficult for the rabbit to chew and achieve the friction necessary to keep their teeth worn down.

Why abnormal overbites don’t work for us
An overjet or abnormal overbite can make it difficult to comfortably close your lips together. It also can make you more susceptible to injury and teasing.

Children who have an overjet greater than 3 millimeters are 50 percent more likely to suffer traumatic dental injuries to their front teeth, according to a study published in the European Journal of Orthodontics in 1999.

Overbite treatment
Appliances commonly used to correct overjet include the Herbst Appliance, headgear, elastics, twin block appliance and Invisalign. In cases where an adult patient’s lower jaw didn’t grow forward enough, jaw surgery may be necessary to achieve the desired result.

Photo credit: Florida Rep. Neil Combee


This is a condition where the lower teeth jut out farther than the upper teeth. Animals commonly displaying an underbite include:

  • Cows
  • Goats
  • Llamas
  • Camels
  • Bully-breed dogs
  • Dwarf rabbits

Cows, goats, llamas and camels may be said to have an underbite, because they are completely lacking in upper front teeth. What all of these animals have in common that shares insight into their unique bite is that they are all ruminants. Ruminants are animals with split hooves, sometimes they have horns, and their stomachs have four compartments. They also chew cud – regurgitated, partially digested material.

Underbites work for ruminants because they only need their lower front teeth to tear forage. Their regurgitated cud is chewed with a set of upper and lower molars in the back of their jaw.

Although they can occur naturally, some animals have acquired characteristic underbites through breeding, but they aren’t exactly beneficial, unless looking cute is a benefit. This is the case with English bulldogs and dwarf rabbits.

English bulldogs originally had very slight underbites, and were used for hunting and as watchdogs. Their wide, powerful jaws made them ideal for subduing ornery livestock and aggressive prey such as wild boars.

In an effort to give a bulldog a flatter face, which makes them appear to have more humanlike expressions, their upper jaw has gotten shorter over time. Many of today’s bulldogs – especially English bulldogs- cannot perform their original intended purpose of hunting and protecting because their short snouts make breathing difficult. We also have bred them to have such large heads that 80 percent of them must be delivered via cesarean section. The breed would have a difficult time surviving in the wild today.

Dwarf rabbits are a breed of small rabbits known to suffer from underbites. This puts them at danger because improper bite alignment can make it difficult, if not impossible to keep their ever-growing teeth worn down. Their teeth can become so overgrown that they are unable to chew and even consume food, and eventually die of starvation.

Why underbites don’t work for us
An underbite is a Class III malocclusion characterized by abnormal protrusion of the lower teeth, or of the lower jaw and teeth. It is the exact opposite of overbites. Although underbites are less common than overbites, their cases typically are more extreme and often warrant more invasive treatment if not diagnosed and corrected early.

Problems caused by underbites include:

  • Facial asymmetry- This distinct asymmetry might look cute on bulldogs, but it’s a major source of insecurity for human underbite sufferers.
  • TMJ disorders – An underbite increases pressure on the jaw joints, which can lead to temporomandibular joint dysfunction and pain.
  • Speech impediments- An underbite can make it difficult to pronounce certain words and sounds.
  • Enamel wear- Enamel can become worn where teeth overlap improperly.
  • Receding gums- Extreme underbites may cause the upper front teeth to rest on the gum line along the inside of the lower front teeth. This constant pressure can cause the gums to recede permanently.

Underbite treatment
Appliances commonly used to correct underbites include the maxillary expander, reverse-pull headgear, chin cap and comprehensive orthodontics. Extreme cases may require oral surgery. Early orthodontic treatment is the best way to avoid the need for oral surgery, but may not rule it out.

Photo credit: University of Florida


A crossbite is when a tooth or teeth are abnormally closer to the buccal (cheek) region or lingual (tongue) region of the mouth than the teeth above or below them. Essentially, a crossbite occurs when any of the upper teeth fit into the wrong side of the lower teeth.

Animals commonly displaying crossbites include:

  • Tyrannosaurus rex
  • Alligator

Two things Tyrannosaurus rex and alligators have in common is that they are carnivores and dinosaurs. Well, alligators are thought to be descendants of dinosaurs.

The crossbite of these animals is in the form of all of their lower teeth fitting inside their upper teeth. While we aren’t exactly sure of the mechanical advantages of this crossbite, there is no doubt it is ideal for gripping and tearing the flesh of their prey.

Unlike omnivores and herbivores, they have no use for flat molars for chewing. All of their teeth are conical.

Why crossbites don’t work for us
There are many complications stemming from crossbites that make them less than ideal for us including:

  • Facial asymmetry- A cockeyed jaw. If you look in the mirror and move your lower jaw to the left, right or forward until your lower teeth protrude past your upper teeth, this should give you an idea of what facial asymmetry caused by a crossbite looks like.
  • Temporomandibular joint disorders – Misaligned bite increase pressure on one or more of your temporomandibular joints, which can lead to disorders and pain.
  • Speech impediments- A crossbite can make it difficult to pronounce certain words and sounds.
  • Enamel wear- Enamel can become worn where teeth overlap improperly.
  • Receding gums- Extreme crossbites can cause teeth to press against the gum lines of the opposite jaw, which can cause gums to recede permanently.

Early diagnosis of your malocclusions increases the treatment success rate and may eliminate the need for invasive surgery- whether you are an animal or human. Call today to schedule your initial consultation.