how do I interpret periapical lucency and furcation involvement on veterinary dental radiographs?

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Periapical lucency indicates endodontic disease, and furcation involvement indicates periodontal disease — both require radiographic confirmation because clinical examination alone is insufficient to characterize either lesion fully. Periapical lucency is interpreted by evaluating the periodontal ligament space, lamina dura, and root apex. Pathological periapical lucency is identified by widening of the periodontal ligament space, loss of the lamina dura, and periapical alveolar bone destruction surrounding the root apex — findings consistent with pulp necrosis and apical periodontitis.46 A well-defined, round periapical radiolucency with its epicenter at the root apex is the classic radiographic appearance of chronic apical periodontitis.4 External inflammatory root resorption produces a flattened or blunted root apex alongside the periapical lucency, and loss of the lamina dura at the apex supports this diagnosis.4 A tooth with pulp necrosis may also show a pulp cavity that appears larger than that of adjacent teeth, reflecting failure of physiologic secondary dentin deposition — this is a supporting sign of nonvitality even when periapical lucency is subtle.4 The critical diagnostic pitfall for periapical lucency is superimposition of mental foramina. In dogs and river otters, the middle and caudal mental foramina can project over the roots of the mandibular canine and premolar teeth, creating lucencies that mimic endodontic disease.6 True endodontic periapical lucency is distinguished from a mental foramen by the presence of widened periodontal ligament space, loss of lamina dura, and root resorption at the apex — all of which are absent when the lucency is a normal anatomical structure.6 Obtaining additional radiographic views at different angulations resolves the superimposition: if the lucency shifts away from the apex or the periodontal ligament space and lamina dura appear intact on the additional view, the finding is a foramen rather than pathology.6 Furca