Diagnostic Imaging in Veterinary Dental Practice

Suanúa Serrano-García The Dentistry and Oral Surgery Service, William R. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.

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Amy J. Fulton Cordova Veterinary Hospital, 2939 Mather Field Rd, Rancho Cordova, CA 95820 (Fulton).

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History and Physical Examination Findings

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, full-mouth radiographs (Figure 1) were obtained, and charting was performed.

Figure 1—
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.

Citation: Journal of the American Veterinary Medical Association 244, 1; 10.2460/javma.244.1.41

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Diagnostic Imaging Findings and Interpretation

Bilateral diastemata were evident between the third and fourth mandibular premolar teeth and between the mandibular fourth premolar and first molar teeth. Root fragments of the left mandibular first, second, and third incisor teeth and of the right mandibular first incisor tooth were present (Figure 2). An uncomplicated crown fracture of the right mandibular canine tooth was evident as well as abrasion or attrition of the occlusal surfaces of the left mandibular first through third premolar teeth. The previously fractured left mandibular canine tooth had evidence of prior endodontic treatment; however, the restoration was missing, along with the coronal third of the tooth. The apical third of the pulp cavity was poorly obturated, with several air-filled voids present. Severe external inflammatory resorption of the root was evident, and comparison with the right mandibular canine tooth revealed that approximately one-third of the affected root tip was absent. A large area of well-defined geographic bone loss extending from the level of the apex of the left mandibular canine tooth to the level of the left mandibular third premolar tooth was evident, encompassing the roots of the canine and 3 premolar teeth, with loss of the lamina dura and periodontal ligament space at the apices of these 4 teeth.

Figure 2—
Figure 2—

Same radiographic views as in Figure 1. There is a complicated crown fracture of the left mandibular canine tooth, and the restoration performed as part of a previous root canal treatment is missing. There is suboptimal obturation of the apical third of the pulp cavity, with several voids present (arrows). An area of geographic bone loss associated with the root of the left mandibular canine tooth is evident in both views (arrowheads). The lucency extends to the third premolar tooth. There is evidence of external inflammatory root resorption of the left mandibular canine tooth root. Root fragments of the left first, second, and third mandibular incisor teeth and the right first mandibular incisor tooth are present (asterisks), and mild to moderate horizontal and vertical bone loss of the right mandibular second and third incisor teeth is evident.

Citation: Journal of the American Veterinary Medical Association 244, 1; 10.2460/javma.244.1.41

The radiographic findings were considered suggestive of an odontogenic cyst; in this patient, the presence of a nonvital tooth associated with the lesion was consistent with a radicular cyst.1–5 Other differential diagnoses that were considered included periapical abscess, periapical granuloma, canine odontogenic parakeratinized cyst, and neoplasia.

Treatment and Outcome

Routine periodontal treatment was performed on all teeth. Prior to extractions, left and right inferior alveolar nerve blocks were performed with 2.5 mg of bupivacaine/site. A full-thickness mucogingival flap was created to surgically extract the left mandibular canine tooth and the first and second left mandibular premolar teeth as well as the root fragments of the left mandibular first, second, and third incisor teeth and of the right mandibular first incisor tooth. After extractions were performed, the lining of the cyst cavity was enucleated by means of curettage and osteoplasty. Extreme care was taken to avoid the neurovascular structures within the mandibular canal, which was exposed during tooth extraction.

The teeth and part of the epithelial lining of the cyst were submitted for histologic analysis, which revealed stratified squamous epithelium with multifocal lymphocytes and plasma cell infiltrates. This, in association with histologic evidence of a nonvital canine tooth, confirmed the presence of a radicular cyst. The premolar teeth were histologically normal, consistent with vital pulp.

Postoperative care included administration of antimicrobials (amoxicillin-clavulanate potassium, 20 mg/kg [9.1 mg/lb], PO, q 12 h for 7 days), analgesics (tramadol, 2.0 mg/kg [0.91 mg/lb], PO, q 8 h for 7 days; carprofen, 2.2 mg/kg [1.0 mg/lb], PO, q 12 h for 3 days), and oral rinse with diluted chlorhexidine gluconate solution (q 12 h for 2 weeks). The clients were instructed to restrict oral play and feed soft food for 6 weeks.

At a 3-month postoperative visit, follow-up intraoral radiographs were obtained (Figure 3). Results revealed appropriate bone healing with no evidence of cyst recurrence. A second follow-up visit 1 year after surgery, to include routine periodontal treatment and dental radiographs, was recommended.

Figure 3—
Figure 3—

Left lateral (A) and occlusal (B) intraoral radiographic views of the rostral aspect of the mandible of the dog in the previous figures. The images were obtained at a follow-up visit 3 months after surgical treatment. Bone remodeling (arrows) is present (A), with increased bone density in the area of previous geographic bone loss (arrowheads; A and B). There is no evidence of cyst recurrence. The alveoli from which the left mandibular canine tooth, left mandibular first and second premolar teeth, and root fragments of the incisor teeth had been extracted appear to have healed normally.

Citation: Journal of the American Veterinary Medical Association 244, 1; 10.2460/javma.244.1.41

Comments

Odontogenic cysts arise from remnants of odontogenic epithelium. Different types of odontogenic cysts have been reported in dogs, such as dentigerous cysts, canine odontogenic parakeratinized cysts, lateral periodontal cysts, and radicular cysts.5 A recent retrospective study5 showed that dentigerous cysts were the most common type of odontogenic cysts in dogs; these were identified in 29 of 41 (71%) dogs with odontogenic cysts during a 15-year study period. These cysts are associated with unerupted teeth, most commonly the mandibular first premolar teeth.5

Radicular cysts, also known as periapical cysts, are the most common odontogenic cysts in humans2–5 and represented 3,215 of 9,723 (> 33%) periapical lucencies in 1 large study6; however, they are rare in dogs.5,7–9 Radicular cysts result from inflammation and develop in the presence of a nonvital tooth.1–5 Necrotic pulp tissue or the presence of bacterial infection of the pulp stimulates the formation of a periapical granuloma,2,4 and chronic inflammatory stimulation from this lesion induces proliferation of the epithelial rests of Malassez.2 These cell rests, which are remnants of odontogenic epithelium within the periodontal ligament, form the epithelial lining of radicular cysts.1–3 Cellular byproducts of the epithelial lining accumulate within the cystic lumen, increasing protein concentration within the cyst and therefore increasing the osmotic pressure. As a result, fluid is drawn into the cyst, resulting in its expansion.1,2

Radicular cysts are often asymptomatic in humans and are frequently an incidental finding on dental radiographs.2 However, these cysts can enlarge to the extent that clinical signs such as swelling and pain develop.1,3 If left untreated, growth of the cyst can result in bone resorption, weakening of the jaw, and mobility of the adjacent teeth.1,2

Treatment is aimed at removal of the cyst lining and elimination of the inflammatory stimulus. Options include surgical root canal treatment or extraction of the affected tooth, with subsequent enucleation and curettage of the cyst and its epithelial lining.1–3 Standard root canal treatment without surgical débridement of the periapical region will result in a persistent lesion.2 If the epithelial lining of the cyst is not completely removed, a residual cyst may form in the following months or years.2,3 For this reason, and to evaluate bone healing, regular radiographic follow-up is highly recommended.

This report demonstrates the importance of obtaining follow-up dental radiographs after performing endodontic treatment to assess the outcome. Moreover, routine dental radiographs are of great importance to identify potentially destructive lesions, such as odontogenic cysts, that may not be associated with clinical signs. In addition, histologic analysis is necessary to determine the nature of these lesions and to rule out the need for further treatment.

References

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