Pet owners are often blown away when they hear orthodontics can be an option for their pets. Just like humans, pets can develop malocclusions that require treatment if the malocclusion is causing discomfort.
When a puppy or kitten enters your practice for the first time, the initial oral examination should be repeated at follow-up pediatric visits. Early evaluation of the teeth and jaws allows for early detection of malocclusions and developmental abnormalities.
Occlusion refers to the spatial relationship of teeth within the mouth. Malocclusion refers to the situation when teeth and/or jaws are not correctly aligned. Although cosmetic issues of misaligned teeth are not typically a concern in dogs and cats, malocclusions can result in discomfort from impingement of teeth on hard or soft tissue structures of the opposing dental arcade.
Dogs and cats with a normal occlusion have a scissors bite, in which the incisors come together to closely overlap, similar to the blades of scissors. When teeth are properly aligned in scissors occlusion, there is maximal function and no occlusal trauma. Variations of dental occlusion in dogs and cats occur, depending on the breed and the skull type.
Incisors: The mandibular incisors should be palatal to (behind) the maxillary incisors, and the coronal third of the mandibular incisors should rest on the cingulum of the maxillary incisors. The cingulum is a smooth convex bulge located on the palatal side of the gingival third of the incisor teeth.
Canines: When the mouth is closed, the mandibular canine tooth is distal to the maxillary third incisor and mesial to the maxillary canine, and it should be centered between these two teeth without touching either of them.
Premolars: The premolar cusps point to the interdental space of the opposing premolar teeth. The mandibular fourth premolar cusp points in the interdental space between the maxillary third and fourth premolars. When the mouth is closed, the mandibular first premolar is rostral to the maxillary first premolar. The premolars are not in occlusion with the opposing premolar teeth, but when the mouth is closed, the cusp tips should intersect a plane drawn midway between mandibular and maxillary occlusal planes.
Carnassial teeth
The term carnassial, interpreted literally, means “cutting of flesh.” This term describes the largest shearing tooth of the upper and lower jaw in dogs, cats, and other carnivores. These teeth work together during mastication and contribute most significantly to the masticatory effort. The carnassial teeth of dogs and cats are the maxillary fourth premolar and the mandibular first molar teeth. In most species, the upper jaw is wider than the lower jaw; this is referred to as anisognathism. Therefore, the maxillary fourth premolar tooth normally occludes lateral to the mandibular first molar tooth.1
Incisors, canines, and most of the premolar teeth have deciduous counterparts to the permanent teeth, but there are some exceptions. There are no deciduous precursors of the molars or the first premolar teeth in dogs. Eruption of deciduous teeth in an abnormal position can result in the first clinical signs of a malocclusion. However, patients rarely show outward clinical signs of a malocclusion, so it is important to look in the patient’s mouth during each puppy visit.
Malocclusion of deciduous teeth
With jaw length discrepancies, the deciduous teeth may penetrate the soft tissue of the opposing jaw, and an unfavorable dental interlock. In most cases, this interlock should be relieved by extraction of the deciduous teeth penetrating opposing soft tissue. These extractions can be very challenging due to the potential for damage to the developing enamel of the adjacent unerupted permanent tooth. Whether the permanent counterpart is erupted or unerupted, avoid leveraging on the permanent tooth in an attempt to loosen the deciduous tooth. Preemptively warn pet owners enamel hypoplasia of the developing adult tooth may occur if the deciduous teeth are extracted prior to eruption of the permanent counterpart. A skilled veterinary dental surgeon can minimize likelihood of complications.
Interceptive orthodontics
Interceptive orthodontics involves the extraction of deciduous or permanent teeth that are causing or will cause problems associated with malocclusion. Interceptive orthodontics can be extremely beneficial, and abnormally erupting permanent teeth sometimes will correct after extraction of retained deciduous teeth.
The most important factor determining success with this treatment is early detection of the problem. Many puppies and kittens have completed their vaccination series by the time they reach this mixed dentition stage and will not be seen again before a spay or neuter procedure, unless a dental examination can be scheduled to ensure early orthodontic problems do not go undetected.
Persistent deciduous teeth can occur in any breed of dog or cat, but they are common in small breed dogs, such as Yorkshire terriers, poodles, and dachshunds. Deciduous teeth should be shed before eruption of their permanent counterpart. When persistent (previously and mistakenly referred to as “retained”) deciduous teeth are identified, they should be extracted before they cause misalignment of their permanent counterparts. Most permanent teeth will erupt lingual or palatal to the retained deciduous teeth, with one exception. Permanent maxillary canine teeth erupt mesial to the persistent deciduous canine teeth. This will result in decreased space between the maxillary canine and the third incisor tooth, where the mandibular canine occludes. When this space is too narrow, the maxillary teeth will interfere with the mandibular canine tooth, and tooth wear (attrition) can occur.
Base-narrow or linguoverted mandibular canine teeth
Occasionally, the mandibular canine teeth may cause palatal trauma in the absence of a jaw length discrepancy, especially if the mandible is narrower than normal, or if the angle of eruption is abnormal. Identifying this early in the eruption process of the permanent teeth may allow for an inexpensive orthodontic treatment to be effective (rubber ball therapy).2 Playing fetch three times daily for 15-20 minutes, with a heavy rubber ball or other rubber toy that fits nicely between the mandibular canine teeth, may allow for splaying of the teeth into a more correct position.
When rubber ball therapy does not work, or if a jaw length discrepancy is too severe to attempt conservative therapy, a passive orthodontic device (inclined plane) may be placed on the maxilla to guide the mandibular canine teeth to a more acceptable position. A newer orthodontic option that has largely replaced the inclined plane is placement of composite extensions on the mandibular canine teeth.3
Lingually displaced (linguoverted) mandibular canine teeth may result from deciduous teeth that do not exfoliate properly. However, other factors may play a role, including the genetics responsible for the development of normal mandibular width. These malocclusions can be corrected by orthodontics in most cases, but clients must be willing to consider multiple sessions of anesthesia. Orthodontics can be an important treatment option when alternatives to extraction of large teeth, such as canine teeth, are considered.
Crown height reduction, along with partial pulpectomy, and direct pulp capping under sterile conditions may be an option for animals with malocclusions. This combination of procedures entails shortening the tooth to remove the interference it is causing with another tooth or surrounding soft tissue. This method is less invasive than extraction, removes the animal’s discomfort associated with the maloccluding tooth, and achieves results more rapidly than orthodontic movement. However, it does permanently alter the appearance and, to some degree, the function of the tooth. The pulp chamber is exposed when the crown is reduced, however, it seems these teeth rarely lose their vitality after this procedure.4
Unerupted teeth
The site of any missing permanent tooth should be radiographically assessed. Unerupted teeth are common, with the mandibular first premolar teeth leading the list, followed by mandibular third molars and maxillary incisor teeth.
When a permanent tooth does not erupt, the epithelial lining covering the crown persists beneath the gingiva. A dentigerous cyst may form, resulting in expansion of a large fluid-filled cyst. Left untreated, a dentigerous cyst can result in significant bone loss, resorption of adjacent teeth, and rarely, malignant transformation to a carcinoma.
Next month’s column will address the basics of orthodontic therapy.
John Lewis, VMD, DAVDC, Fellow, AVDC OMFS, practices at Veterinary Dentistry Specialists and teaches at Silo Academy Education Center, both in Chadds Ford, Pa.
References
- Lewis JR and Miller BM. Veterinary Dentistry. In: Bassert JM and Thomas JA, eds. McCurnin’s Clinical Textbook for Veterinary Technicians, 2014: 1297-1354.
- Verhaert L. A removable orthodontic device for the treatment of lingually displaced mandibular canine teeth in young dogs. J Vet Dent. 1999;16(2):69-75.
- Storli SH, Menzies RA, Reiter AM. Assessment of Temporary Crown Extensions to Correct Linguoverted Mandibular Canine Teeth in 72 Client-Owned Dogs (2012-2016). J Vet Dent. 2018;35(2):103-113.
- Niemiec BA. Assessment of vital pulp therapy for nine complicated crown fractures and fifty-four crown reductions in dogs and cats. J Vet Dent. 2001;18(3):122-5.