CHAPTER 7 Tooth Resorption
Resorption of teeth can be a normal physiological process (exfoliation of primary teeth) or a pathological one. Causes of pathological resorption include pressure on the root (impacted tooth or expanding cyst or tumor), inflammation and infection (periodontal, apical, and internal resorption), orthodontic force, trauma (replantation), neoplasia, and after internal bleaching. There is a high incidence of tooth resorption (TR) in cats that are idiopathic, resembling the noncarious cervical tooth resorption seen in dogs, humans, and other species. These are unrelated to cervical lesions that are made by toothbrush abrasion. Although TRs in humans have been called many different terms they are often referred to as “invasive resorption,” “idiopathic cervical resorption,” and, more recently, “abfraction lesions.” The veterinary literature has also given them multiple labels over the years as is common with lesions and syndromes that are poorly understood. Resorption of dental tissue occurs through the action of odontoclasts regardless of the initiating cause, and similar tooth resorption occurs in many different species. Therefore, the term “feline” is inappropriately limiting and the term “odontoclastic” is redundant. For the purposes of this book we will refer to them simply as tooth resorption.
TRs that have no contact with the oral cavity (do not involve the enamel of the crown or are completely subgingival) are referred to as extraoral and may be present on clinically normal teeth. Extraoral TRs are not associated with discomfort in humans. Supragingival (intraoral) TRs, on the other hand, can cause dental discomfort in people and can be assumed to do the same in cats. Supragingival lesions are readily diagnosed clinically but require radiographs to determine the extent. Mild marginal gingivitis may be the only sign of an early lesion. Sites with localized inflammation should be investigated subgingivally with a sharp dental explorer. Lesions often appear as though the gingiva is growing up the crown of the tooth due to a tightly adherent gingival or granulomatous tissue (Figure 7-1). This upgrowth of tissue can be quite dramatic, particularly when it occurs on canine teeth (Figure 7-2). Lesions that extend above the gingiva have a sharp enamel margin that is readily identified with an explorer (Figure 7-3). Teeth with small clinical lesions frequently have extensive involvement that can only be identified radiographically (Figure 7-4). TRs can also appear as a missing tooth in an area with a raised alveolar marginal contour or as a pink spot on the crown at the site of internal resorption (Figure 7-5). Gingivitis in the furcation area of a multirooted premolar or molar tooth can mimic a site of resorption. Gingival hyperplasia can mimic the fibrogranulomatous tissue that often fills resorption defects (Figure 7-6). It is important to explore suspicious sites and radiograph the tooth.
FIGURE 7-1 TR on left mandibular fourth premolar tooth (arrow). A, Coronal migration of the mesial gingiva is the only evidence of an underlying problem (bleeding was caused by periodontal probing). There is no intraoral lesion visible and the gingiva is tightly adherent to the tooth. B, There is more extensive involvement of the fourth premolar (arrow) than clinically suggested with radiolucency of the crown and disruption of the furcation area. The roots of the third premolar tooth (open arrow) are also losing radiodensity.
FIGURE 7-2 A, The mesiolabial view of a right maxillary canine tooth in a cat shows extensive damage to the crown and gingival tissue filling a large resorption defect. B, On the mesiolingual view of the tooth, the adherent tissue extends far up the crown from the normal position of the gingival margin (arrows). C, The root and internal crown of the canine tooth is completely resorbed. There is a radiolucency at the site previously occupied by the root (arrow). This is consistent with root resorption without evidence of replacement by bone or other hard tissue.
FIGURE 7-3 A, TR on the distobuccal surface of a right mandibular molar tooth extends above the gingiva (arrow) and does not have adherent tissue in the defect. The margin of the enamel defect can be visualized and can be identified using a dental explorer. The bleeding on the mesial surface was caused by probing. B, On a radiograph of the tooth in A, a large area of the tooth is destroyed by a tooth resorption (arrow).
FIGURE 7-4 A, In this patient, TR on the right mandibular third premolar tooth (arrow) extends up onto the crown as a deep defect. B, On the radiograph, the internal resorption is far more extensive than expected based on the surface lesion.
FIGURE 7-5 Internal crown resorption. A, This patient is missing the left mandibular third premolar tooth (arrow) and has a pink discoloration of the crown of the molar tooth (open arrow). B, On the radiograph, there is an end-stage tooth resorption undergoing root replacement at the site of the missing tooth (arrow), and the molar tooth has areas of radiolucency in the crown (open arrow) and loss of detail of the roots with a regional increase in the alveolar bone opacity.
FIGURE 7-6 Gingival hyperplasia. A, The hyperplastic gingiva extending coronally onto the premolar tooth has a similar appearance to the tissue found in tooth resorption. However, in this case, the tissue is not adherent and there is no underlying resorption occurring either clinically or on a radiograph (B).
Radiographs of affected teeth often show root resorption that is far more advanced than expected. Every tooth with a clinical TR should be radiographically evaluated, not only to determine severity but also to determine the type of root changes that are occurring and to identify concurrent pathology. Multiple teeth are often involved in affected individuals. Therefore, full mouth radiographs of all teeth may be indicated when a patient is diagnosed with TR. Some practitioners recommend full mouth radiographs of all feline patients to identify pathology that is not clinically apparent.
Radiographs of teeth affected with TRs show distinct changes. The roots of some affected teeth seem to “disappear” as they lose radiodense root tissue at a similar rate to the simultaneously occurring osseous repair, effectively making the roots appear to blend with the surrounding bone. The periodontal ligament and structural details are lost. Other TRs retain areas of normal radiodensity interspersed with radiolucencies caused by resorption and do not lose the detail of the periodontal ligament space and root structures in those areas not directly undergoing resorption. Areas of root resorption are often patchy, remaining radiolucent because the lost root substance is not replaced by reparative tissue. This type of TR also commonly demonstrates concurrent periodontal or endodontic disease.