History and Physical Examination Findings

An 11-year-old 28-kg (61.6-lb) spayed female mixed-breed dog was referred to Husdjurshälsan Veterinary Clinic for evaluation of an oral mass on the rostral portion of the right maxilla and signs of oral pain. The owner reported that the oral mass did not seem to cause the dog discomfort, but intermittent signs of acute oral pain had been observed as well as reluctance to chew on the left side of the mouth. A review of the dental health history revealed that the dog had no damaging chewing habits, received no dental home care, and had not undergone dental treatments. No abnormalities outside the oral cavity were noted on physical examination. Hematologic and serum biochemical tests were performed, and results were within the respective reference ranges. On palpation, the mandibular lymph nodes were not found to be enlarged. The oral examination revealed severe calculus accumulation, especially in the caudal part of the mouth; generalized gingival enlargement; and generalized moderate gingivitis. The right maxillary third incisor tooth was missing, and a 10 × 10 × 12-mm, smooth, firm, lobulated pink gingival mass was present at the site of the missing tooth. Extensive loss of the left maxillary fourth premolar tooth crown was observed; only the distal part of the crown was present. The mesial part of the left maxillary first molar tooth had pink discoloration. The patient was anesthetized for full oral examination and dental radiography; selected images are shown (Figure 1).

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Photographs (A and B) and selected radiographic images (bisecting angle technique; C and D) of the maxilla of an 11-year-old mixed-breed dog that was evaluated because of a gingival mass in the region of the right maxillary third incisor tooth and signs of oral pain. A—A firm, lobulated gingival mass is present between the right maxillary second incisor and canine teeth. B—Extensive crown loss of the left maxillary fourth premolar tooth is evident. C—Lateral radiographic view centered on the right maxillary canine tooth. D—Lateral radiographic view centered on the left maxillary fourth premolar tooth.

Citation: Journal of the American Veterinary Medical Association 258, 2; 10.2460/javma.258.2.147

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Diagnostic Imaging Findings and Interpretation

An indirect digital imaging system^a,^b was used to obtain intraoral radiographs with size 2 and size 4 photostimulable phosphor plates, depending on the size of the target area. The lateral view of the right maxillary canine tooth revealed the contour of a soft tissue mass located between this tooth and the second incisor tooth (Figure 2). The right maxillary third incisor tooth was missing, and the alveolar margin in this area was irregular. The apical third of the right maxillary canine tooth root showed a loss of structure and periodontal ligament space, consistent with external replacement resorption, and an oval radiolucent defect was present in the center of the apical third of the tooth, consistent with either internal surface resorption or external cervical root surface resorption. External replacement resorption, internal inflammatory resorption, or external cervical root replacement resorption seemed to affect the roots of the right maxillary first and second incisor teeth, but accurate assessment would have required other views or a cone-beam CT scan.¹ A small remnant of the crown of the right maxillary first premolar tooth was visible. The distal root of the right maxillary second premolar tooth was completely resorbed. The crown was still visible but undergoing resorption, as was the mesial root of the tooth.

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Same radiographic images as in Figure 1. A—A soft tissue mass (circle) is present between the right maxillary canine and second incisor teeth. External replacement resorption is evident at the apical region of the canine tooth and the right maxillary second premolar tooth (arrows). Resorption of the second premolar tooth is extensive, and the distal root is completely resorbed. Although accurate assessment is not possible with this projection, the right maxillary first and second incisor teeth also appear to be undergoing external replacement resorption, internal inflammatory resorption, or external cervical root surface resorption (star). A small remnant of the right maxillary first premolar tooth is visible (arrowhead). B—Severe external replacement resorption of the left maxillary fourth premolar tooth is present, with only the distal part of the crown intact (short thin arrow). Internal inflammatory resorption or external cervical root surface resorption is also present at the distal root of this tooth (long thin arrow). The alveolar bone has a moth-eaten appearance in the region of this tooth, indicating a severe inflammatory process, infection, or neoplasia (star). A radiolucent region in the cervical furcation area of the left maxillary first molar tooth is consistent with internal inflammatory resorption or external cervical root surface resorption (thick arrow).

Citation: Journal of the American Veterinary Medical Association 258, 2; 10.2460/javma.258.2.147

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The lateral view of the left maxillary fourth premolar tooth revealed extensive loss of tooth substance with only a small part of the crown present distally (Figure 2). The root apices were visible but severely affected by resorption. A tunnel-shaped radiolucency was present in the distal root remnant and in the furcation area between the mesiobuccal and palatal root, consistent with either internal inflammatory resorption or external cervical root surface resorption (which can only be distinguished by use of CT or histologic examination). Alveolar bone in the region of this tooth had a moth-eaten appearance, consistent with severe inflammation, infection, or neoplasia. The left maxillary first molar tooth was also affected by either internal inflammatory or external cervical root surface resorption, as evidenced by a radiolucent area in the furcation region of the mesial-buccal and distal roots. Evaluation of the left maxillary second and third premolar teeth showed signs of a mixture of external replacement resorption, external inflammatory resorption, and internal inflammatory or external cervical root surface resorption.

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Lateral radiographic view of the caudal aspect of the right mandibular fourth premolar, first molar, and second molar teeth. External replacement resorption of the fourth premolar and first molar teeth is present (thin arrows). A mixture of external inflammatory resorption and external cervical root surface resorption or internal inflammatory resorption (star) is present with horizontal and vertical bone loss around the distal root of the first molar tooth (thick arrow). Notice the unusual shape of the distal root of the second molar tooth.

Citation: Journal of the American Veterinary Medical Association 258, 2; 10.2460/javma.258.2.147

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A lateral view of the right mandibular first molar tooth revealed a combination of external replacement resorption, internal inflammatory or external cervical root surface resorption, and external inflammatory resorption; horizontal and vertical bone loss were present at the distal root (Figure 3). Both roots of the right mandibular fourth premolar tooth were almost completely resorbed, with the resorptive process extending into the crown. Horizontal bone loss affected the mesial root of the second mandibular molar tooth together with minimal signs of resorption at the apex.

The clinical and radiographic findings supported the diagnosis of severe generalized tooth resorption, mostly present as a combination of external surface resorption, external replacement resorption, external inflammatory resorption, and internal inflammatory or external cervical root surface resorption. The fact that almost all teeth were extensively affected was considered a likely explanation for the clinical signs of oral pain.

Treatment and Outcome

The dog was treated under general anesthesia in 2 sessions. In the first session, scaling and polishing of the teeth, intraoral radiography, excision of the gingival mass, and extraction of the left maxillary fourth premolar tooth were performed. The oral mass was sent for histologic examination and was diagnosed as a peripheral odontogenic fibroma. The remaining affected teeth were treated in the second session.

The treatment plan was based on oral examination and radiographic findings. Generalized tooth resorption in dogs and cats is usually idiopathic.^2,3 However, neoplasia could be a possible cause of tooth resorption both at the tumor site and at sites distant from the tumor,⁴ and biopsy of the oral mass, affected teeth, and surrounding bone is indicated in these cases. Treatment options for affected teeth are limited, as has been described for cats.^2,5 When extensive loss of dental structure has occurred, extraction or crown amputation with intentional root retention is indicated; if the root or roots are intact and the periodontal ligament space is visible radiographically, extraction is indicated.^2,5 Conversely, crown amputation with intentional root retention can be performed for teeth with severe external replacement resorption in which successful extraction of the complete root is expected to be technically complex and excessively traumatic to the patient; however, crown amputation with intentional root retention is contraindicated if apical periodontitis is present.^2,5 It is acceptable not to treat teeth that have resorption limited to the roots (ie, the crown is not affected) when the patient has no indications of oral discomfort.^2,5

All teeth except for the 4 canine teeth were extracted or underwent crown amputation with intentional root retention. Crown amputation was performed on teeth that had severe external replacement resorption without signs of apical periodontitis. Teeth that had less compromised roots with intact lamina dura and periodontal ligament space were extracted. The oral cavity was rinsed with 0.12% chlorhexidine gluconate solution. Left and right infraorbital and inferior alveolar nerve blocks were performed with bupivacaine hydrochloride^c (0.3 mL/site). Long envelope flaps were raised, and the resorbing tooth roots were removed together with the crowns. All inflamed tissue was thoroughly curetted, and the area was rinsed with sterile isotonic saline (0.9% NaCl) solution and closed with absorbable monofilament suture material in a simple interrupted pattern. The dog was prescribed robenacoxib^d (1.5 mg/kg [0.68 mg/lb], PO, q 24 h) for 5 to 7 days, and the owner was advised to provide soft foods and not allow the dog to chew on bones or toys for 2 weeks.

On follow-up examination 1 week after each surgery, the dog appeared bright and in good condition. The extraction sites had healed well. The owner reported that the signs of oral pain had resolved. The 4 canine teeth were left without treatment, although there was an ongoing external replacement resorptive process at the tooth roots. No enamel defects were present on the canine tooth crowns. The importance of these teeth to the dog and the expected absence of pain were important considerations in making this decision. A 6-month follow-up visit for reevaluation was suggested.

Comments

Pathological tooth resorption is common in dogs and other species including cats, horses, and people. In dogs, reported prevalences range from 17% to 54%.^3,6,7 Tooth resorption is most frequent among older and large-breed dogs.⁷ Prevalence does not differ between males and females overall, but the percentage of affected neutered male dogs is significantly higher than that of sexually intact male dogs.⁷

Intraoral radiography is necessary to evaluate and classify tooth resorption. There are 2 main classification methods. The classification method by the American Veterinary Dental College puts an emphasis on the extent of the resorptive process rather than on the exact location and type of lesions and is normally used when classifying tooth resorption in cats, but it is not fully applicable when classifying tooth resorption in dogs.⁸ The most widely accepted human classification method, proposed by Andreasen and Andreasen,⁹ corresponds well with and is applicable to the types of tooth resorption found in dogs.⁷ This method separates tooth resorption into 7 categories (external surface, external replacement, external inflammatory, external cervical root, internal surface, internal replacement, and internal inflammatory resorption; Appendix).⁷ In dogs, external replacement resorption and external inflammatory resorption are the most common types, but external cervical root surface resorption, external surface resorption, internal inflammatory resorption, and internal surface resorption are also described.⁷

The resorptive process can occur on the wall of the root canal (internal resorption) or on the external surface of the root (external resorption). The mineralized tissues of permanent teeth are protected by predentin and odontoblasts in the root canal and by precementum and cementoblasts on the root surface.¹⁰ Factors such as trauma, high pressure (eg, strong bite forces), infection, inflammation, and hormone or vitamin imbalances are suggested to disturb, damage, or disrupt these structures, resulting in mineralization of predentin or precementum or denuding of the root surface. The mineralized or denuded areas of the root surface attract tissue-resorbing cells that colonize the damaged areas of the root and initiate the resorptive process.^2,10

Careful radiographic examination of the walls of the root canal and pulp chamber will indicate whether they are expanded (internal resorption) or not (external resorption). Differential diagnosis should include carious lesions when the defects are present on the buccal or lingual side of the root or above the alveolar margin,¹¹ even though caries most frequently develop on occlusal surfaces.

The dog of the present report had a diagnosis of severe generalized tooth resorption. Large-breed dogs are often active chewers, and this behavior together with strong bite forces could cause increased stress on the periodontal apparatus, triggering the resorption process. However, the exact etiopathogenesis of external replacement resorption is not fully understood. In human patients, replacement resorption is seen as a complication of luxation and avulsion injuries.^10,12 The long-term prognosis is poor even though the resorptive process is typically slow. In some instances, it takes many years to reach a stage where intervention is necessary, ideally in the form of implant treatment.¹² Replacement resorption results in increased tooth fragility, increasing the risk of crown fracture. The treatment of choice for severely affected teeth in dogs, as for cats, is crown amputation with intentional root retention.^2,5

External inflammatory resorption and internal inflammatory or external cervical root surface resorption were also present in the dog of the present report. Although the cause of external cervical root surface resorption is unknown, certain inflammatory dental diseases (eg, periodontal disease and apical periodontitis) are often accompanied by tooth resorption, suggesting that in these cases, the resorption is a secondary event.^3,10 This dog had severe calculus, gingival enlargement, gingivitis, and periodontitis, all possible contributing factors for external inflammatory resorption and certain types of internal resorption. In less severe cases, the aim of treatment is to eliminate infection and treat the underlying causes, but this will not prevent progression, even with an appropriate home oral care regimen.

As the case described in this report illustrates, tooth resorption can cause signs of pain and oral discomfort. Tooth resorption in dogs may be more common than expected, especially in older, large-breed dogs. Intraoral radiography and careful oral examination are crucial for establishing a correct diagnosis and treatment plan.