The relationship between the teeth of the maxilla (upper jaw) and mandible (lower jaw) can be characterized as either normal occlusion or malocclusion.

In cats and dogs with normal occlusion, well-aligned mandibular teeth engage in an interlocking pattern with well-aligned maxillary teeth. The interaction between the teeth of the mandible and maxilla allows for catching prey, picking up and carrying food, chewing, and biting. These actions should not result in any trauma.

The mandible is hinged to the maxilla at the temporomandibular joint (TMJ). The mandible is moved by masticatory muscles against the maxilla.

22. Skull: Base

Normal occlusion: The teeth are aligned such that they interlock without causing trauma to soft tissues when the jaw is closed.

21. Skull: Jaw Open

The mandible is hinged to the maxilla at the temporomandibular joint (TMJ).

Misaligned teeth, jaws, or temporomandibular joint can cause malocclusion, which may result in oral disease, pain, and loss of function ranging from mild to debilitating.

Malocclusion can be something a pet was born with (congenital), something that occurred as the pet was growing (developmental), or acquired, usually due to trauma. Skeletal malocclusion is due to abnormalities of the jaws (either in length or symmetry) or temporomandibular joint, while dental malocclusion is caused by the abnormal position of one or more teeth in otherwise-normal jaws.

Consequences of malocclusion

Animal Dental Clinic-crowding

Crowding (a form of malocclusion) of permanent teeth caused by retained deciduous (baby) teeth, with associated periodontal disease.

While the direct result may be mild tooth attrition with associated various degrees of discomfort, the malocclusion can also create ideal conditions for development of oral disease. For example, a jaw that is too short can result in crowding of teeth, which predisposes to periodontal disease.

Major malocclusions can result in significant oral trauma. For example, when mandibular canine teeth do not align properly with the maxilla, they can cause trauma to the palate (roof of the mouth). In severe cases, this trauma can even penetrate the palate, causing an oro-nasal fistula, a communication between the mouth and the nasal

Animal Dental Clinic: exploring-the-oronasal-fistula-caused-by-malocclusion
Periodontal probe inserted into the oronasal fistula caused by the sharp mandibular canine tooth contacting the hard palate (roof of the mouth) when the mouth is closed. This communication between the mouth and nose is not normal and causes inflammation of the nasal cavity and sneezing when food and water enter the nose.
Animal Dental Clinic: radiographing-the-oronasal-fistula
Dental radiograph showing loss of the bone of the hard palate that separates the oral and nasal cavities (left side). The right side of the image is normal, for comparison.

Diagnosis of malocclusion

Malocclusions can be classified based on oral examination, but oral diagnostics, including dental radiographs and probing are required for treatment planning. When the malocclusion originates in the temporomandibular joint area, advanced imaging such as computed tomography (CT or CAT scan) may be needed to plan treatment.

Animal Dental Clinic-class-ii-malocclusion
In class II malocclusion, the mandible is short, relative to the maxilla.
Animal Dental Clinic-class-iii-malocclusion
In class III malocclusion, the mandible is long, relative to the maxilla.

Orthodontic treatment

Any painful condition caused by malocclusion, or any malocclusion that causes oral trauma should be treated.

There are several ways to address malocclusion. Depending on the type of problem, a variety of orthodontic treatments to move or align teeth, or surgical treatment to reshape or extract teeth may be needed.

Animal Dental Clinic-ball-therapy-for-mild-mandibular-canine-linguoversion
In young patients where the mandibular canine teeth are mildly linguoverted (pointed too far inward toward the tongue), supervised intermittent placement of pressure can cause the teeth to rotate into a more normal position. For some patients, this can be accomplished by encouraging them to hold a ball of a selected size and texture in their mouth. This “ball therapy” requires repeat evaluations to ensure that the teeth are moving appropriately.
Animal Dental Clinic-inclined-plane
An inclined plane is a customized device that changes the position of certain teeth gradually, by changing the forces placed on them when the mouth is closed.
Animal Dental Clinic-mandibular-canines-crown-extensions
Similar to an inclined plane, placement of temporary crown extensions (made of composite resin) gradually changes the position of teeth by changing the forces placed on them when the mouth is closed. In this case, the “longer” crowns help to direct the crowns of the linguoverted mandibular canines outward, into a more normal position.
Animal Dental Clinic-crown-reduction-with-root-canal-treatment
For some patients, changing the position of the tooth isn’t an option. When a mandibular canine tooth is causing trauma to the palate or maxillary soft tissues, altering the shape of the tooth can keep it from causing further damage. In this image, the right side is normal, and the left mandibular canine tooth has undergone crown reduction (removal of a part of the crown) with root canal treatment. Crown reduction without root canal treatment (older animals) or vital pulp therapy (younger animals) would leave the tooth a source of pain and infection.
Animal Dental Clinic-orthodontic-active-movement-for-mesioverted-canines
In this patient, the canine teeth are mesioverted (pointed too far forward). Orthodontic active movement is being used to cause the crowns to rotate downward, into a more normal position.
Animal Dental Clinic-crown-reduction-with-vital-pulp-treatment
Photograph of a mandibular canine tooth in a young adult dog that has undergone crown reduction and vital pulp therapy. This tooth was causing trauma to the maxillary soft tissues. In order to prevent further problems, a portion of the crown was removed and the tooth underwent vital pulp therapy. The tooth root will continue to mature and provide support to the mandible, but the crown will not “grow back.”