A malocclusion is any occlusion which is not standard for the breed. These conditions may have a purely cosmetic consequence. However, they often create some form of occlusal trauma which creates significant pain and discomfort for the patient. If left untreated these malocclusions can result in significant ramifications such as oronasal fistulation, tooth wear and subsequent fracture and/or tooth death. They can also result in periodontal disease due to crowding. In general, jaw length (or skeletal) malocclusions are considered genetic. Conversely, tooth (non-skeletal) discrepancies (class I) are considered nongenetic, with the notable exception of mesiocclusion of the maxillary canines (lance effect) seen in Shetland Sheepdogs and Persian cats, which is considered genetic.

Class I Malocclusions: Neutroclusion

This is defined as an occlusion with normal jaw lengths (scissor bite), where one or more teeth are out of alignment. Class I malocclusions can result from lip/cheek/tongue pressure (or lack thereof), significant systemic or endocrine issues, and less commonly neoplastic or cystic formation may also result in tooth deviation. Displacement in some situations was previously believed to result from persistence of the deciduous teeth. However, research shows that deciduous tooth persistence is caused by improper eruption of the permanent teeth. This class of malocclusion includes: linguoversion of the mandibular canine teeth, mesioversion of the maxillary canines (lance teeth), anterior cross bite or malalignment of the incisor teeth. These conditions often create traumatic situations requiring therapy.

Class II Malocclusion: Mandibular Distocclusion

This is also termed overshot or mandibular brachygnathism. This is a jaw length discrepancy where the mandible is shorter than the maxilla. This typically results in the mandibular canines causing significant occlusal trauma to the palate, gingiva, and or teeth. Therefore, intervention is almost always required (see below).

Class III Malocclusion: Mandibular Mesiocclusion

This is also called undershot and is a jaw length discrepancy where the mandible is longer than the maxilla in a non-brachiocephalic breed. This condition in animals is often caused by line breeding for a specific size and shape of the head. The great variety in the size and structure of canine maxilla and mandible as well as tooth size between breeds, in combination with cross breeding have also resulted in malocclusions.

This condition, while common and “normal” in certain breeds often creates painful gingival and tooth trauma. However, as in all malocclusions, it is rare to have the patient show clinical signs. Regardless, therapy of the traumatic malocclusion is recommended (see below).

Class IV Malocclusion: Maxillomandibular Asymmetry

This is a jaw length discrepancy in which one of the mandibles is shorter than the other resulting in a shift of the mandibular midline. A true class IV malocclusion occurs when one mandible is longer than the maxilla and the other is shorter. In general, this malocclusion also creates palatine or gingival (+/- tooth) trauma and if this is occurring, therapy is recommended.

Therapy for Malocclusions

Therapy for malocclusions can be classified into several categories.

1.  For purely cosmetic cases no therapy is recommended. It is quite common for breeder/show clients to wish cosmetic therapy; however, this is strongly discouraged by the AVDC, AKC, and other organizations for ethical reasons.

2.  Surgical - which generally consists of extraction of teeth causing occlusal trauma.

3.  Orthodontic - This is where the maloccluded teeth are moved into the correct or a non-traumatic position via the use of various appliances.

4.  Coronal amputation and endodontic/restorative - where the offending teeth are shortened and undergo endodontic therapy (vital pulp therapy or root canal) or their shape is changed by odontoplasty and a restoration/sealant placed.

Key Points

• Malocclusions in veterinary patients often cause trauma which can result in significant morbidity and, therefore, require treatment, regardless of lack of clinical signs.
• The majority of malocclusions have a genetic component.
• Correction of cosmetic (non-traumatic) malocclusions for show purposes is considered unethical.
• There are several treatment options for traumatic malocclusions.