An 8-year-old 16.8-kg (36.9-lb) castrated male mixed-breed dog was examined for evaluation and treatment of periodontal disease. Four years prior to this evaluation, root canal treatment of the left mandibular canine tooth was performed at another practice because of a complicated crown fracture of that tooth. No follow-up evaluations had been performed in the interim. With the exception of a previous sliding hiatal hernia that had been surgically corrected, the patient' s medical history was unremarkable.No abnormalities were detected on general physical examination. Oral examination revealed mild localized gingival enlargement and moderate gingivitis associated with the left mandibular canine tooth. Several teeth were missing, and mild to moderate attrition or abrasion was evident at the occlusal surfaces of multiple teeth. The left mandibular canine tooth was discolored and had a complicated crown fracture. Evidence of previous root canal treatment was present; however, the restoration was missing and gutta-percha was visible. On further questioning, the clients had no knowledge of further damage to the tooth after the previous root canal treatment.Preanesthetic CBC and serum biochemistry results were unremarkable. The patient was anesthetized, fullmouth radiographs (Figure 1) were obtained, and charting was performed.Determine whether additional studies are required, or make your diagnosis, then turn the page → Figure 1-Left lateral (A) and occlusal (B) intraoral radiographic views of the rostral aspect of the left mandible of an 8-year-old mixed-breed dog examined for evaluation and treatment of periodontal disease.