Deviation from the dental formula has been seen in several species. Complete lack of development of teeth, or anodontia, is rare. Hypodontia or oligodontia has been described as inherited by a recessive manner in Kerry Blue Terriers and associated with X-linked hypohidrotic ectodermal dysplasia in other breeds. Most cases appear to affect the premolars. Hyperdontia, also called polyodontia or supernumerary teeth, is seen most often in the permanent teeth and can affect the incisors, premolars, or molars. Presumably, these teeth arise from overproliferation of the dental lamina during development. Supernumerary teeth tend to cause crowding and malocclusions, which can cause dysphagia, dental disease, and discomfort. In horses, supernumerary incisors are typically not extracted and are managed with regular reduction. For supernumerary cheek teeth, diastema and sinusitis due to oromaxillary sinus fistula formation are possible sequelae. Teeth are either extracted or reduced often to prevent complications.
Retention of the deciduous teeth in horses is common. The incisors tend to retain rostrally to the permanent incisors; however, radiographs will help to discern their identity. Incisors retained in other orientations can result in malocclusion and/or displacement of permanent incisors. Retained cheek teeth are called “caps,” which are typically shed as the permanent tooth erupts underneath them. Loose caps can cause discomfort to the horse, manifest as headshaking, inappetence, quidding, and training issues. Caps can be extracted if they are loose, if the contralateral cap has already been shed, or if there is space between the cap and the permanent tooth below.
Retained deciduous teeth are common in dogs and secondary to the failure of the periodontal ligament to detach from the deciduous tooth, with the permanent canine teeth erupting rostrally. One study showed highest incidence in dogs <2 yr old, with small breeds overrepresented, particularly Toy Poodles. Retention may cause permanent tooth displacement, which can result in malocclusion or food entrapment and subsequent periodontal disease. Therefore, retained deciduous teeth should be removed as soon as possible, taking care not to damage the underlying permanent tooth bud.
Displacement or rotation of teeth has been described in many species. In horses, the cheek teeth are affected more commonly than the incisors, with the permanent teeth most often affected rather than the deciduous teeth. Most displacements are due to crowding during eruption. Sequelae include malocclusion, uneven wear and development of sharp points, and diastema with associated feed packing. Treatment includes regular floating of unopposed surfaces, or extraction if severe. Diastema can be addressed by mechanical widening. In dogs, rotation has been described commonly in brachycephalic and large breeds, with the first mandibular premolar or upper third premolar often affected. Abnormally located or directed teeth can result in malocclusions or affect the positioning of adjacent teeth. Extraction can be performed in severely affected animals; many cases are considered incidental findings.
Enamel hypoplasia, hypomineralization, or dysplasia is seen in both large and small animals. Common causes are pyrexia, trauma, malnutrition, toxicosis (eg, fluorosis in cattle), congenital disorders (eg, epitheliogenesis imperfecta in Saddlebred foals), and infections (eg, distemper virus in dogs or bovine viral diarrhea virus in calves) that affect ameloblast and odontoblast activity. Lesions vary, depending on the severity and duration of the insult, from pitted enamel to the absence of enamel with incomplete tooth development. Affected teeth are prone to plaque and tartar accumulation and subsequent bacterial penetration and formation of caries. In small animals, resin restoration has been used to cover defects, although diligent dental hygiene and home care is critical to reduce the incidence of complications. Enamel may also develop discoloration. In small animals, administration of tetracyclines to pregnant females or to puppies <6 mo old may result in a permanent brownish yellow discoloration of the teeth. In ruminants, the enamel of some teeth may demonstrate flecks of varying color. The condition is thought to have a genetic etiology but generally is of no clinical significance; however, some believe affected teeth may be prone to more rapid wearing.