Abnormal Tooth Shape or Structure

Trauma to a deciduous tooth or inflammation from a fractured deciduous tooth can damage the enamel epithelium of the underlying developing permanent tooth, resulting in a focal area of enamel hypoplasia or hypomineralization (Figure 9-1). This is usually radiographically unremarkable, but a radiograph should be made to evaluate pulp health prior to restoration (Figure 9-2).

FIGURE 9-1 Focal enamel defect (“Turner’s tooth”). A, An area on the labial surface of a left mandibular canine tooth is missing the enamel layer and has poorly attached enamel on the periphery of the lesion. This area was close to the apex of the deciduous tooth during development. B, On the radiograph of the tooth in A, the crown is irregular with radiolucent surface defects and the pulp cavity appears normal.

FIGURE 9-2 Enamel-dentin lesion with endodontic involvement. A, The coronal third of the canine tooth crown is deformed, is missing enamel, and has a defect extending into a groove in the dentin. B, On the radiograph of the tooth in A, there is a periapical lucency (arrow), indicating endodontic involvement. C, The contralateral tooth of the same patient has a narrower root canal space, indicating further maturation than the tooth in B.

Generalized enamel dysplasia can be caused by systemic diseases (for example, viral infection such as distemper) during development and also by hereditary or nutritional factors. Radiographs should be made to determine whether the tooth root development was also affected (Figures 9-3 and 9-4).

FIGURE 9-3 Enamel and dentin dysplasia. A, The root of the canine tooth (asterisk) is very short due to lack of development. B, On the contralateral tooth of the same patient a radiolucency (arrow) surrounds the shortened root, indicating loss of periodontal attachment. The wide root canal space is consistent with pulp necrosis.

FIGURE 9-4 Enamel and dentin dysplasia. A, These mandibular premolar and molar teeth had enamel defects. The roots are very short and attenuated with narrow apices. The shape of these roots is characteristic of radicular dentin dysplasia in humans (also called type 1 dentin dysplasia, rootless teeth, type 1 dentinogenesis imperfecta), an autosomal dominant hereditary disturbance of dentin formation. However, in the human syndrome, the pulp cavity is generally attenuated or absent and the enamel is not affected. B, This tooth was extracted after becoming necrotic due to trauma during development. Its shape demonstrates early crown development prior to any root formation. Interruption of dentin formation or damage to the root-forming cells at this stage would result in teeth shaped like those in A and C. C, Radiographs indicate the timing of the insult by which roots are involved. In this patient, development was hindered after most of the root of the first premolar tooth (asterisk) was formed but before those of the second and third premolars were formed. D, Resorptive lesions can mimic roots affected by dentin dysplasia. However, residual root tips (arrows) of the resorbing maxillary fourth premolar tooth can be seen. The third premolar tooth (asterisk) also has evidence of root resorption.

Supernumerary roots most commonly affect maxillary third premolar teeth in both dogs and cats (Figure 9-5). Most are not associated with pathology and may be considered a variation of normal. It can be clinically significant if it is associated with periodontitis, and during extraction or endodontic treatment of the tooth.

FIGURE 9-5 Supernumerary root. A, Palatal mirror image view of a maxillary third premolar tooth with a palatal root (arrow). B, Radiograph of the tooth in A. This tooth normally has two roots. C, Short supernumerary root on a third premolar tooth (asterisk). D, Long supernumerary root with vertical bone loss (arrow). E, Supernumerary root on a third premolar (arrow) of a cat.

Trauma to a deciduous tooth can also cause dislocation of the underlying permanent tooth bud. When one part of the developing tooth is repositioned relative to other parts, it can result in dilaceration of the tooth, a severe angular defect of the erupting tooth often occurring at the junction of the root to the crown. A deformed tooth may be unable to erupt (Figure 9-6).

FIGURE 9-6 Dilacerated unerupted tooth. A, On a ventrodorsal radiograph, the right mandibular canine tooth is incompletely erupted and has defects of the enamel (arrows). The left canine tooth crown is adjacent to the first, second, and third premolar teeth. There is an angular defect where the crown meets the root (open arrow). B, The developing root extended caudally in the mandible, displacing the third premolar tooth (arrow).

Fusion of two tooth germs results in a single large tooth and one fewer tooth in the arch (Figure 9-7).

FIGURE 9-7 Fusion of teeth in a cat. A, The right mandibular fourth premolar tooth (P) and molar tooth (M) are fused, forming one large central shared root. B, The clinical appearance of fourth premolar and molar tooth fusion.

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