THE MERCK VETERINARY MANUAL
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Congenital and Inherited Anomalies of the Teeth

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In most species, a reduction in the number of teeth (termed anodontia) is rare, although in dogs, molars and premolars may fail to develop or erupt. Supernumerary teeth occasionally are found in the incisor or molar regions of horses; in dogs, they are usually unilateral and most often in the upper jaw. In dogs, although rare, improper germination of the permanent dental arcade may lead to splitting of the tooth bud to form 2 teeth. The result may be crowding and subsequent rotation of the teeth, which necessitates extraction to prevent or correct occlusal abnormalities. In horses, supernumerary teeth are either removed or periodically rasped, especially if they interfere with mastication or are irritated by a bit.

In premolar teeth of ruminants, the root of the temporary tooth may be absorbed, but the crown may persist as a covering or “cap” to the erupting permanent tooth. These caps are readily removed with forceps if they have not separated spontaneously. Delayed shedding of deciduous teeth in dogs is common and secondary to the failure of the periodontal ligament to detach from the deciduous tooth, with the permanent canine teeth erupting rostrally. This may cause permanent tooth displacement, which can occur within 2–3 wk, and 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.

In horses, this may affect the incisors and result in long-axis rotation or overlapping of adjacent teeth. In brachycephalic dogs, the upper third premolar and occasionally other premolar or molar teeth may rotate. Usually, this is of no clinical significance but may require extraction of some involved teeth if crowding or occlusal abnormalities occur. Abnormalities in shape, including dens in dente, are reported in various species and breeds. Clinical significance is variable and based on severity, with most being incidental findings.

Hypoplasia or disruption in enamel formation can occur in both large and small animals. Common causes are pyrexia, trauma, malnutrition, toxicosis (eg, fluorosis in cattle), and infections (eg, distemper virus in dogs). 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 in reducing 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.

Last full review/revision March 2012 by Walter Ingwersen, DVM, DVSc, DACVIM

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