History and Physical Examination Findings

An 8-month-old spayed female Beagle mix was evaluated because of a missing right mandibular canine tooth. The referring veterinarian had extracted persistent left and right maxillary deciduous canine teeth when the dog underwent ovariohysterectomy at 6 months of age and referred the patient for further dental evaluation and treatment.

General physical examination findings were unremarkable. The dog was active, alert, and responsive. Heart rate and rhythm were considered normal, and results of a CBC and serum biochemical analysis were within respective reference ranges. Initial examination of the oral cavity revealed mild generalized gingivitis associated with mild generalized plaque accumulation. All teeth were fully erupted except for partially erupted right mandibular first and second premolar teeth and a missing right mandibular canine tooth (Figure 1). The right mandibular third premolar tooth was rotated, and the mandibular incisor teeth were crowded. The right mandibular third incisor tooth was present, but the crown appeared to be malformed or fractured, consistent with odontodysplasia. A firm swelling was observed buccal and ventral to the right mandibular first and second premolar teeth.

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Photograph of the rostral aspect of the right mandible in an 8-month-old spayed female Beagle mix evaluated because of a missing right mandibular canine tooth. The crown of the right mandibular third incisor tooth is malformed (white arrow). The right mandibular first and second premolar teeth are visible but have not completely erupted through the gingiva (outlined arrows). The right mandibular third premolar tooth is rotated (black arrow), and the mandibular incisor teeth are crowded.

Citation: Journal of the American Veterinary Medical Association 245, 3; 10.2460/javma.245.3.281

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The dog was anesthetized for dental and oral examination. Findings were consistent with those in the awake patient. The right mandibular third incisor tooth crown was malformed, consistent with odontodysplasia; except for the partially erupted right mandibular first and second premolar teeth and missing right mandibular canine tooth, all other dentition was present and appeared normally developed and fully erupted.^1–3 Results of periodontal probing of the gingival sulci were normal at ≤ 2-mm depth, except for that of the right mandibular third incisor tooth, which had a probing depth of 5 mm, indicating presence of periodontal disease. Full-mouth dental radiographs, including occlusal and lateral radiographs of the mandibular incisors, canines, and premolar teeth, were obtained with a size 2 digital sensor (Figure 2).

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Intraoral lateral radiographic views of the right (A) and left (B) mandibular canine and premolar teeth and occlusal view (C) of the rostral aspect of the mandibles and incisor teeth of the dog in Figure 1. Note that the lateral view of the left mandibular canine tooth is slightly foreshortened and oblique, and it is not entirely symmetric to the image of the impacted right canine tooth.

Citation: Journal of the American Veterinary Medical Association 245, 3; 10.2460/javma.245.3.281

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Diagnostic Imaging Findings and Interpretation

All teeth were present and fully erupted except for the right mandibular canine tooth and first and second premolar teeth (Figure 3). Severe odontodysplasia of the right mandibular canine tooth was evident; the crown was distoverted apical to the right mandibular first through third premolar teeth and surrounded by alveolar bone, indicating impaction of the tooth. A larger pulp cavity was suspected, compared with that of the left mandibular canine tooth, but no periapical lesion was identified.^2,3

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Same lateral view of the right mandibular canine tooth and premolar teeth (A) and occlusal view of the rostral aspect of the mandibles and incisor teeth (B) as in Figure 2. On the lateral view, severe odontodysplasia of the impacted right mandibular canine tooth is evident (black arrows). The right mandibular third premolar tooth is rotated (arrowhead). Consistent with the results of periodontal probing, there is probable vertical bone loss associated with the right third incisor tooth (white arrows). On the occlusal view, the right mandibular third incisor tooth is partially erupted and malformed, compared with the left mandibular third incisor tooth. The pulp cavity (black line) appears to be wider than that of the contralateral tooth.

Citation: Journal of the American Veterinary Medical Association 245, 3; 10.2460/javma.245.3.281

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Treatment and Outcome

Unerupted teeth that are not extracted may be associated with dentigerous cyst formation, so the treatment plan included extraction of the impacted right mandibular canine tooth.^4,5 The right mandibular first, second, and third premolar teeth appeared to directly contact the impacted right mandibular canine tooth or interfere with surgical access to it, and extraction of the affected canine tooth without further damage or compromise to these teeth was unlikely.⁵ With the patient under general anesthesia, the periodontally affected right mandibular third incisor tooth was extracted first.^6,7 Next, extraction of the right mandibular first, second, and third premolar teeth and impacted canine tooth was performed through standard surgical extraction techniques.^5–7 The procedure included a sulcular incision to release the gingival epithelial attachment; development of a full-thickness mucogingival flap; removal of the alveolar buccal bone of the right mandibular first, second, and third premolar teeth; and sectioning of the multirooted right mandibular second and third premolar teeth to facilitate elevation.^6,7 The premolar teeth were elevated from their alveoli, and additional alveolar bone was removed until the impacted right mandibular canine tooth could be elevated. Alveoloplasty was performed to smooth all rough or irregular alveolar bone prior to flap closure.^6,7 A bone allograft consisting of osteoinductive demineralized bone matrix and osteoconductive cancellous bone chips^a was rehydrated with sterile saline (0.9% NaCl) solution and placed into the void created by extraction of the right mandibular canine tooth.⁷ The gingival flap was closed with monofilament suture^b in a simple interrupted pattern.^6,7 Carprofen^c (2.2 mg/kg [1.0 mg/lb], PO, q 12 h) was prescribed as treatment for postoperative pain. Clinical healing was evident at the initial 1-month follow-up visit and no complications were reported. The dog was scheduled for a follow-up visit 12 months after oral surgery to include dental radiography and oral examination under anesthesia.

Comments

Differential diagnoses for the missing canine tooth in the dog of this report included failure of an impacted or embedded tooth to erupt, developmental or congenital anodontia, unerupted tooth associated with a dentigerous cyst, or previously extracted tooth.^1,4 In this dog, impaction of the right mandibular canine tooth was considered the most likely cause for failure of eruption.

Deciduous teeth erupt in puppies between 3 and 12 weeks of age and are replaced by permanent teeth between 3 and 7 months of age.² Eruption is a continuous process that begins with tooth bud formation. Tooth development is initiated in the embryo by the formation of dental lamina, which eventually forms the dental arches.⁵ The enamel organ develops from invagination of the lamina, which corresponds to the deciduous dentition. Extensions of the dental lamina bud form the permanent dentition. If a deciduous tooth bud does not form, the permanent tooth bud fails to develop.^2,5 The pre-eruptive stage of tooth development involves movement of the dental germ, an aggregation of cells that eventually forms a tooth, to keep its position within the developing jaws.¹ The prefunctional phase is the period after the crown has formed and root formation has started, and the functional phase begins when a tooth comes into occlusion and ends when the tooth is lost or ankylosed or the host dies.¹

A tooth that has fully formed but has failed to erupt may be embedded or impacted. An embedded tooth has not erupted, usually because of the lack of eruptive forces, and is typically completely covered with bone, whereas an impacted tooth is located or wedged against another tooth, bone, or soft tissue that acts as a physical barrier so that complete eruption is unlikely.⁴ If the tooth is blocked by a tough layer of gingival soft tissue, called an operculum, the tissue should be incised and removed to facilitate eruption of the tooth.^2,4

Horizontal impaction of a canine tooth is one of the most common types of tooth impaction in dogs.⁴ It usually results from failure of the tooth's normal pre-eruptive movement or from genetic displacement of the tooth bud. Failure of a tooth bud to develop normally and completely can result in failure of eruption, and injury to the jaw during the growth period may affect the position of the tooth bud and impair eruption.¹

Treatment options for an impacted or embedded canine tooth include operculectomy, observation for clinical problems, orthodontic treatment to extrude the impacted tooth, or surgical extraction.^1,5 Simple monitoring of an unerupted tooth in young dogs is not advised. Unerupted teeth are commonly associated with dentigerous cyst formation, which can lead to potentially painful swelling and loss of adjacent teeth as reported in humans.⁸ Malignant transformation of dentigerous cysts can also occur.^2,8 Surgical removal of the impacted mandibular canine tooth and adjacent teeth was elected to prevent potential complications.^2,5 The cause of tooth impaction in the dog of this report was not determined, but the obvious tooth malformations suggested a traumatic injury to the rostral aspect of the mandible during the puppy's rapid growth phase or development of scar tissue blocking the eruption pathway.¹ Iatrogenic trauma was not considered because only maxillary persistent deciduous canine teeth had been extracted by the referring veterinarian. No evidence of trauma to the maxillary canine teeth was found.

Any edentulous region of the mouth (and the contralateral region for comparison) should be examined carefully, and high-quality dental radiographs should be obtained.² Intraoral dental radiographs helped to identify the presence and location of the impacted mandibular canine tooth in this young dog and aided in surgical planning for extraction.