Читать книгу Feline Dentistry - Jan Bellows - Страница 41

Abnormalities in the number of teeth in cats can be inherited or result from disturbances during the initial stages of tooth formation. Anodontia, complete absence of all teeth, and oligodontia, decreased number of teeth, are uncommon conditions in cats. Supernumerary teeth are more common and may result in crowding and misalignment of teeth, which may predispose to the development of periodontal disease. The mandibular fourth premolars are the most common supernumerary teeth observed in the cat. Supernumerary teeth that result in crowding should be extracted early (Figure 1.30a–d).

Persistence of primary (deciduous) teeth occurs in cats much less frequently than in dogs. The terms “retained” and “persistent” are often used synonymously however there is a difference. Persistent primary teeth are teeth that have failed to exfoliate whereas retained teeth are those that have failed to erupt.

Persistent primary teeth should be extracted as soon as they are diagnosed to make sufficient room for the permanent teeth to erupt into their normal positions. When persistent deciduous teeth are not removed, permanent teeth can deflect lingually (mandibular canine teeth) or rostrally (maxillary canine teeth) (Figure 1.31).

Gemination has been observed in deciduous as well as in permanent dentition. It is an attempt to form two teeth from one enamel organ. This results in a structure with two completely or incompletely separated crowns each with a single pulp chamber and a shared root canal. Occasionally, complete cleavage or twinning occurs resulting in two teeth from one enamel organ. The etiology is unknown, but trauma has been suggested as a possible cause, though a familial tendency has been observed (Figure 1.32a,b).

Figure 1.30 (a) Supernumerary maxillary left canine tooth. (b) Radiograph confirming supernumerary tooth versus deciduous. (c) Supernumerary maxillary third premolars causing crowding. (d) Supernumerary mandibular fourth premolar resulting in advanced periodontal disease.

Figure 1.31 Persistent maxillary primary canine teeth, note that the secondary canines are malpositioned rostrally.

Figure 1.32 (a) Abnormally shaped right mandibular fourth premolar consistent with gemination. (b) Radiograph confirmation of one tooth with two incompletely separated crowns, and 3 roots.

Fusion is the joining of two tooth germs, resulting in a single large tooth. Fusion may involve the entire length of the tooth or only the roots, depending on the stage of development of the teeth at the time of the union. The root canal can be shared or separate. The etiology is unknown, but trauma and a familial tendency have both been suggested as possible causes. Fusion is also observed in deciduous as well as in permanent dentition. Occasionally, it is difficult to differentiate fusion of supernumerary teeth from gemination (Figure 1.33a,b).

Concrescence is a condition of teeth where the cementum overlying the roots of at least two teeth join together. It involves only two teeth.