History

An 8-month-old 20.5-kg sexually intact female German Shepherd Dog (Canis familiaris) was evaluated because of a slowly growing mass of 4 months’ duration on the buccal surface of the right mandible visibly protruding through the lips (Figure 1). The mass was on the labial surface of the mandible and did not interfere with the dog’s closure of the mouth and eating. The dog’s behavior was considered normal.

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Photograph of a mass (asterisk) on the right mandible of an 8-month-old German Shepherd Dog (Canis familiaris).

Citation: Journal of the American Veterinary Medical Association 259, 12; 10.2460/javma.19.05.0231

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Clinical and Gross Findings

Oral examination revealed a 5 × 5 × 3-cm, round, pink, multifocally hemorrhagic, firm, apparently nonpainful mass located mesially from the second premolar tooth distal to the fourth premolar tooth. The mass expanded the buccal surface of the mandible; no other abnormalities were observed in the oral cavity, and general physical examination findings were unremarkable. Intraoral radiography revealed that the mass contained small, radiopaque structures that disrupted the mandible and the adjacent premolar teeth. For surgical excision of the mass, the dog was anesthetized with propofol (6 mg/kg, IV) administered in 25% increments of calculated dose slowly until anesthesia was sufficient for tracheal intubation. Anesthesia was maintained by inhalation of isoflurane (2% to 3%) and oxygen (2 L/min). A right caudal mandibular nerve block with bupivacaine hydrochloride and lidocaine hydrochloride (50% mixture of each drug) was injected into the right alveolar foramen. A balanced electrolyte solution (lactated Ringer solution) was administered (10 mL/kg/h, IV). Throughout anesthesia and the surgical procedure, ECG and pulse oximetry were performed to monitor the dog’s condition. The mass was removed. Additional radiographic views were obtained to ensure complete removal of the mass.

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Histopathologic Findings

The excised mass was fixed in neutral-buffered 10% formalin and processed routinely; sections were stained with H&E stain and examined with light microscopy. Histologic examination revealed a nondemarcated and nonencapsulated mass. The mass contained odontogenic epithelium and ectomesenchyme resembling the dental (enamel) organ of a developing tooth. Multiple sections of the mass had developed tooth-like structures (denticles) composed of spindle-shaped to stellate mesenchymal cells (dental pulp), surrounded by pseudostratified columnar cells (odontoblasts), deep eosinophilic material (dentin), enamel that covered the dentin, and palisading epithelial cells consistent with ameloblasts (Figure 2). Mitotic figures and malignant features, including cellular atypia and pleomorphism, were not present.

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Photomicrographs of sections of the mass. A—The mass contains tooth-like structures (denticles [double arrows]). H&E stain; bar = 200 µm. B—The tooth-like structures are composed of spindle-shaped to stellate mesenchymal cells (dental pulp [P]), surrounded by pseudostratified columnar cells (odontoblasts) and deep eosinophilic material (dentin [D]). H&E stain; bar = 200 µm. C—Enamel (arrow) covers the dentin, and palisading epithelial cells consistent with ameloblasts (arrowhead) are present. H&E stain; bar = 100 µm.

Citation: Journal of the American Veterinary Medical Association 259, 12; 10.2460/javma.19.05.0231

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Morphologic Diagnosis and Case Summary

Morphologic diagnosis and case summary: mandibular compound odontoma in a young German Shepherd Dog.

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Odontomas are slow-growing tumors that develop during odontogenesis, which begins with the eruption of deciduous teeth weeks after birth and is completed with the development of permanent teeth at 6 to 7 months of age in dogs. Because the tumors are composed of normal dental tissues that develop in an abnormal manner and lack features of autonomous growth associated with true neoplasms, they are regarded as hamartomas.¹ Odontomas are the oldest recorded odontogenic neoplasms in animals with similar characteristics across affected species.^2,3

Canine odontomas are rare and mainly observed in young dogs. Although maxillary and mandibular swelling in dogs could be attributable to trauma, infection, developmental disorders (eg, craniomandibular osteopathy), or neoplasia, neoplastic oral maxillary or mandibular masses in juvenile dogs are usually of odontogenic origin.³ The tumors may disrupt dentition or prevent eruption of or displace normal teeth.⁴ Data regarding canine odontogenic neoplasms are sparse. Clinically, the tumors often appear as nonpainful, slowly growing, expansile masses in the maxilla or mandible,³ as highlighted by the case described in the present report. Clinical signs associated with odontomas are associated with the physical expansion of the masses and include facial or mandibular swelling, ocular and nasal discharges (in cases of maxillary odontomas), missing teeth, or eruption of tooth-like structures into the oral cavity. The tumors can become extremely large and cause facial deformity.³

In horses and cattle, odontomas can become very large and may necessitate euthanasia because of adverse effects on the affected animal’s quality of life.^3,5 Odontomas also develop in fish. Compared with other vertebrates, the location of odontogenic tissue in fish is more diffuse, and the tumor can be found in the lips, mouth, gill arches, oropharynx, and esophagus. Odontomas have been observed in the premaxilla, supramaxilla, and along the gill arches and lips in various fish species.¹

Unlike findings in other animals, odontomas are the most common odontogenic tumors in humans³ and are often diagnosed in the first 2 decades after birth⁶; usually, children < 15 years of age are affected.⁷ In humans, odontomas are usually very small and are the most common odontogenic tumors in the maxilla.⁶ The tumors can cause expansion of cortical bone and impaction of permanent teeth, contributing to the discovery of the lesion. Larger odontomas can also give rise to the development of cysts, which together may cause considerable jaw destruction. Additionally, the possibility of neoplastic transformation to ameloblastoma and cyst wall invasion justifies complete removal of the cyst, emphasizing the importance of radiographic and histologic examination findings for definitive identification and characterization of the lesions.⁶

The cause and pathogenesis of odontomas, either in humans or nonhuman species, are unknown.^3,4 However, hereditary factors, genetic alterations during dental development, infections, or trauma have been suggested to be involved in odontoma formation.⁴ In clownfish, which clean surfaces with their mouth before egg deposition, constant trauma to the mouth is suggested to predispose the fish to tumor formation on the lips. Odontomas in wild teleost fish in association with viral infections and pollution have also been reported.¹ Predisposing factors and causes that initiate odontoma formation in dogs are unknown, and history of trauma was not recorded for the dog of the present report.

Odontomas generally have an embryonic pattern of tooth development with production of enamel, dentin, cementum, odontogenic epithelium, and odontoblasts with variable degrees of organization that resemble developing teeth. Odontomas composed of many separate, small tooth-like structures known as denticles (odontoids)⁶ with variable degrees of maturation and anatomic similarities with normal teeth^2,3,4,7 are compound odontomas, whereas those with disorganized dental elements are complex odontomas. Radiographic features of odontomas vary and aid in the differentiation of tumor types.² Presence of denticles, which are visible radiographically, is pathognomonic for compound odontomas.³ For the dog of the present report, radiography revealed many denticles that disrupted the mandible and the associated second, third, and fourth premolar teeth. Differential diagnoses based on clinical and radiographic findings may include dentigerous cysts and epithelial odontogenic tumors, such as ameloblastoma or complex odontoma. Confirmation of the diagnosis can only be made with histologic examination of biopsy specimens.⁴

Compound odontomas are localized in the mandible or maxilla. However, in most reported cases in dogs, compound odontomas have been localized in the mandible,⁴ unlike in humans, in whom compound odontomas have a predilection for the premaxillary region. Complex odontomas have a predilection for the posterior portion of the mandible in humans.⁶ Compared with complex odontomas, diagnosis of compound odontomas in humans usually occurs at an earlier age. Among female humans, there is a predilection for both compound and complex odontomas.⁸ Given the rare nature of odontomas in dogs and the few published reports, a sex predilection for these tumors in dogs has not been determined.

Because an odontoma is not a true neoplasm, surgical removal is the treatment of choice and curative. The extent of surgery depends on the size of the mass and the involvement of the adjacent tissues. Complete surgical excision of the mass in combination with aggressive curettage results in a favorable outcome.^3,4 Surgical excision should include complete removal of the mass and associated teeth. Curettage may be effective for smaller lesions; however, more aggressive resection is preferred to minimize the incidence of tumor recurrence and reduce associated cost of additional surgery and treatment.² Tumor regrowth is rare and may be the result of incomplete removal of the mass. For example, 2 surgical procedures including cryotherapy were required to remove a complex odontoma in a horse.⁹ If bone loss is present, promotion of bone regeneration should be included in the treatment procedures. For the dog of the present report, the mass was excised along with all the small denticles detected radiographically and the involved premolar teeth; postoperative radiographic views were obtained to ensure all denticles and involved teeth had been removed. Three years after surgery, the owner was contacted by telephone and reported that the dog was doing well with no regrowth of the mass. For prognostic and treatment considerations, it is important to confirm diagnosis and differentiate odontomas from ameloblastic odontomas and ameloblastomas, which develop in old dogs. Confirmation of the diagnosis can only be made on the basis of histologic examination of biopsy specimens, the findings of which can be used to differentiate odontomas from clinically more aggressive, locally invasive odontogenic tumors (eg, ameloblastic odontomas) that may result in alveolar bone lysis.^4,7 Results of CT or radiography are helpful for surgical planning and facilitate complete excision of the mass with wider tumor-free margins, especially when tumors have a more biologically aggressive behavior.³ With regard to odontomas, histopathologic and radiographic findings are important for definitive diagnosis, assessment of a patient’s prognosis, and complete excision of the mass to avoid recurrence; such investigations should be considered to implement curative measures in the management and treatment of odontomas.