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46 IMAGING ESSENTIALS PEER REVIEWED endodontic disease (see Apical periodontitis and Relatively wide pulp cavities ) because the most common cause of endodontic disease is trauma. Apical periodontitis is inflammation of the periapical tissues that invariably occurs in the presence of untreated endodontic disease (eg, inflamed or necrotic pulp). This inflammatory process is detectable radiographically after enough lysis of the associated bone has occurred ( Figure 13B ). Typically, the lesion appears as an ill- or well-defined round, lucent area that encompasses the apical portion of the root(s). Lack of radiographically detectable periapical lucency does not rule out apical periodontitis. Relatively wide pulp cavities—when compared with contralateral, opposing, or adjacent teeth— may indicate a longstanding nonvital pulp ( Figures 13A and 13C ). Clinicians should be aware that a lack of discrepancy in pulp cavity width does not rule out endodontic disease, especially in cases of endodontic disease of relatively short duration (a few days or weeks). Pulp stones are considered incidental findings that appear as mineralized structures within the pulp cavity on dental radiographs, sometimes in otherwise clinically and radiographically healthy teeth ( Figure 13D ). In the event endodontic intervention is required for unrelated causes, pulp stones may interfere with root canal instrumentation. Chevron signs are widened periodontal ligament spaces in the apical areas of endodontically sound teeth, often in the shape of a chevron, resembling radiographic signs of apical periodontitis ( Figure 14 ). This occurs most frequently at the maxillary incisors, canines, and mandibular first molar teeth. It is believed these areas are normal anatomic variations and possibly correspond to vascular channels in the bone. 11 A chevron sign is suspected in the absence of clinical and radiographic signs of endodontic disease; in some cases, however, it is very difficult to differentiate between a chevron sign and pathologic changes. FIGURE 14. Chevron sign. This radiograph is the lateral view of the right maxillary canine tooth in an 8-year-old dog. Note the wide lucent space at the apex. The lesion is not bulbous, round, or encompassing of the entire apical area, and the lamina dura appears intact. Given the lack of other radiographic indicators of endodontic disease, and in the absence of clinical signs, this finding should not necessarily be considered pathologic. FIGURE 15. Tooth resorption. FIGURE 15A shows advanced inflammatory tooth resorption affecting the left mandibular fourth premolar and first molar teeth in an 8-year-old cat. FIGURE 15B shows advanced replacement resorption affecting the left and right mandibular canine teeth in a 14-year-old cat. FIGURE 15C shows replacement resorption affecting both roots of the left mandibular fourth premolar and mesial root of the mandibular first molar in a 7-year-old dog; note the loss of periodontal ligament space and sclerotic alveolar bone around the affected roots. FIGURE 15D shows inflammatory root resorption secondary to apical periodontitis at the left mandibular canine tooth in a 7-year-old dog; note the irregular and relatively short apical third of the tooth compared to the contralateral. B D A C