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Today's VeTerinary PracTice | January/February 2016 | tvpjournal.com exTernal TooTh resorPTion in caTs Peer reviewed 22 CAUSES Many studies have improved the understanding of tooth resorption, but a specifc cause has not yet been identifed for resorption of multiple permanent teeth in domestic cats. Resorptions that affect the tooth crown may be caused by plaque accumulation, infammation, and release of cytokines and lipopolysaccharides that stimulate migration of clastic cells to the area. This type of tooth resorption extends to the root, infecting the periodontal ligament and preventing replacement of lost hard tissue with bone- or cementum-like material. Eventually, the tooth becomes mobile secondary to loss of attachment or fracture from weakening of tooth substance. Although it is tempting to incriminate plaque and periodontal disease as the cause of tooth resorption in cats, several studies have shown no cause-and-effect relationship between tooth resorption and periodontal disease. Plaque accumulation and periodontal disease may be promoted secondary to the tooth's external rough surface caused by resorption. Local pH changes may play a role in the pathogenesis of tooth resorption. Human bulimic patients have lesions with a similar appearance, which are caused by erosion at the cementoenamel junction due to low pH caustic stomach contents. It has been theorized, without confrmation, that tooth resorption in cats may be caused by hairball regurgitation. Additional research showed that osteoclast numbers and resorptive activity increased in an acidic environment. 3,7 Areas explored and found not to be directly associated with tooth resorption include increased acid content of dry food coating and specifc oral pathogenic bacteria (Actinomyces). CLASSIFICATION In general practice, tooth resorption in cats (and dogs) is commonly classifed in 2 ways: anatomic extent of the lesion (stages) for record-keeping purposes and radiographic appearance (types) to assist with treatment decisions. 4 Anatomic Classifcation (Infammatory or Noninfammatory) • Stage 1 (TR 1): Mild dental hard tissue loss (cementum or cementum and enamel). This stage is not observed clinically because the lesion is small and confined below the gingiva. • Stage 2 (TR 2): Moderate dental hard tissue loss (cementum or cementum and enamel, with loss of dentin that does not extend to the pulp cavity) (Figure 2 ). • Stage 3 (TR 3): Deep dental hard tissue loss (cementum or cementum and enamel, with loss of dentin that extends to the pulp cavity); most of the tooth retains its integrity (Figure 3 ). • Stage 4 (TR 4): Extensive dental hard tissue loss (cementum or cementum and enamel, with loss of dentin that extends to the pulp cavity); most of the tooth has lost its integrity (Figures 4–6). » Stage 4a: Crown and root are equally affected. » Stage 4b: Crown is more severely affected than root. » Stage 4c: Root is more severely affected than crown. • Stage 5 (TR 5): Remnants of dental hard tissue FIGURE 2. Intraoral radiograph of Stage 2 tooth resorption (arrow) of the right mandibular canine. FIGURE 3. Radiographic evidence of resorption extension into the root canal.