History and Physical Examination Findings
A 15-year-old 8.0-kg (17.6-lb) sexually intact male North American river otter (Lontra canadensis) was evaluated because abraded teeth and a fractured tooth were noted during an annual physical examination by the zoo veterinarian. The otter was born in captivity and had been transferred to its current location approximately 7 years prior to this evaluation. No changes in appetite, signs of oral pain (eg, ptyalism, dropping of food, or preference for softer food), or changes in behavior had been detected by the veterinarian or zoo staff. The otter underwent oral and general physical examinations under general anesthesia annually, including collection of a blood sample for hematologic and biochemical analysis and thoracic or abdominal radiography when applicable. It did not have any prior dental history other than examinations. The otter's diet consisted of commercial dry cat food, fish (capelin, herring, mackerel, and smelt), carrots, and chicks; oxtails had also been provided in the past, but these had been omitted from the diet for approximately 1 year.
The zoo veterinarian reported that the river otter was in excellent overall health, and results of a physical examination were largely unremarkable. For oral examination and treatment by the dental specialty group, anesthesia was induced with ketaminea (10 mg/kg [4.5 mg/lb]) and midazolamb (0.3 mg/kg [0.14 mg/lb]) administered IM. An endotracheal tube was placed, and anesthesia was maintained with isofluranec (1% to 3%) in oxygen for the duration of the procedure. Meloxicamd (0.2 mg/kg [0.09 mg/lb], IM) was administered shortly after anesthetic induction. An oral examination revealed moderate generalized abrasion of the teeth, a calculus index of 3, and a gingival index of 2.1 The left mandibular canine tooth had pulp exposure, and there was a complicated crown fracture of the left mandibular fourth premolar tooth (Figure 1). Both of these teeth were nonvital. The right mandibular canine and fourth premolar teeth, although abraded, had no evidence of pulp exposure. Periodontal probing revealed no other abnormalities. Full-mouth, intraoral dental radiographs were obtained by use of bisecting angle (Figure 2) and parallel techniques.2
Photograph of the left mandibular and maxillary teeth of a 15-year-old male North American river otter (Lontra canadensis). There is moderate abrasion of the premolar and molar teeth and severe abrasion of the mandibular canine teeth. Pulp exposure of the left mandibular canine tooth and complicated crown fracture of the left mandibular fourth premolar tooth were detected. The image was obtained after a gingival flap was created.
Citation: Journal of the American Veterinary Medical Association 243, 5; 10.2460/javma.243.5.631
Right lateral (A), occlusal (B), and left lateral (C) radiographic views of the rostral mandibular teeth of the river otter in Figure 1, obtained with a bisecting angle technique.
Citation: Journal of the American Veterinary Medical Association 243, 5; 10.2460/javma.243.5.631
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Diagnostic Imaging Findings and Interpretation
On the lateral radiographic views, periapical lucency was evident around both mandibular canine teeth (Figure 3). On the occlusal radiographic view, root length of the mandibular canine teeth appeared similar; however, the pulp cavity width of the left mandibular canine tooth was slightly wider than that of the right. There was no evidence of resorption of the apex of either tooth. Additionally, periapical lucency was observed around the distal roots of both mandibular fourth premolar teeth. The lucency around the left mandibular fourth premolar tooth root was irregular and subjectively larger than that around the right. Because the lateral radiographs were obliqued caudorostrally, additional left and right lateral radiographs of the mandibular teeth were obtained to further elucidate the noted lucencies (Figure 4). Evaluation of these additional radiographs revealed that the periapical lucency of the left mandibular fourth premolar tooth was of endodontic origin and attributable to widened periodontal ligament space, loss of lamina dura, and external root resorption.2 The periapical lucencies of the mandibular canine teeth and right mandibular fourth premolar tooth were suspected to be radiographic features of the middle and caudal mental foramina because the periodontal ligament space, lamina dura, and periapical alveolar bone of these teeth appeared normal. Additionally, there were no obvious pathological changes of the apices of these teeth detectable in radiographs. Examination of a river otter skull confirmed the assessment that the mental foramina were superimposed over the roots of the mandibular canine teeth and the fourth premolar teeth (Figure 5).
Same radiographic views as in Figure 2 (A–C). Periapical lucencies of the right and left mandibular canine teeth (arrowheads) and the distal roots of the mandibular fourth premolar teeth (arrows) are present. All of the lucencies have distinct borders except for that of the distal root of the left mandibular fourth premolar tooth. The root canal of the left mandibular canine tooth is slightly wider than that of the right mandibular canine tooth.
Citation: Journal of the American Veterinary Medical Association 243, 5; 10.2460/javma.243.5.631
Additional right (A) and left (B) lateral radiographic views of the mandibular canine through first molar teeth of the otter in Figure 1. The radiographs were obtained with a bisecting angle technique and are not obliqued. The periodontal ligament space around the root of each mandibular canine tooth appears normal, and the lamina dura is intact. The distal root of the right mandibular fourth premolar tooth appears normal (arrowhead), and the periodontal ligament space and lamina dura are unremarkable. There is external resorption of the distal root of the left mandibular fourth premolar tooth and extensive loss of the lamina dura (arrow); the region of periapical lucency is subjectively large and has indistinct borders.
Citation: Journal of the American Veterinary Medical Association 243, 5; 10.2460/javma.243.5.631
The lateral (buccal) surface of the right mandible of a North American river otter. Notice the middle (arrowhead) and caudal (arrow) mental foramina. These 2 foramina created lucencies detected on lateral radiographs obtained for dental evaluation of the otter in this report. The radiographic lucencies stemming from mental foramina can be projected either rostrally or caudally depending on the angle or obliquity from which a radiograph is obtained, as has been reported in dogs.2
Citation: Journal of the American Veterinary Medical Association 243, 5; 10.2460/javma.243.5.631
The periapical lucency of the left mandibular fourth premolar tooth was determined to be of endodontic origin because of pathological changes to the root apex and periodontal structures. Although severe abrasion of the left mandibular canine tooth had resulted in pulp exposure, the only radiographic evidence that the tooth was nonvital was a slightly wider pulp canal, compared with that of the right mandibular canine tooth.
Treatment and Outcome
Orthograde endodontic treatment of the left mandibular canine tooth was performed, and the left mandibular fourth premolar tooth was surgically extracted. The otter recovered uneventfully from anesthesia and received meloxicam (0.2 mg/kg, PO, q 24 h for 3 days) and enrofloxacine (4.25 mg/kg [1.93 mg/lb], PO, q 12 h for 14 days) after surgery Because of the fractious nature of the patient, a 2-week postoperative oral examination could not be performed, but the zoo veterinarian remarked the otter had a rapid recovery and was eating well. Radiographic evaluation of the left mandibular canine tooth under general anesthesia was recommended in 6 to 12 months to monitor stability of the endodontic treatment as well as the vitality of abraded teeth, with additional follow-up at 2 and 5 years after surgery to monitor for periapical changes that could be suggestive of failure of the procedure.1,2
Comments
The case described in this report exemplifies the importance of understanding both the gross oral anatomy and the radiographic-topographic anatomy of a species. A thorough understanding of species-specific oral anatomy, in combination with basic anatomic and radiographic principles, allows a practitioner to make educated treatment decisions.
North American river otters are semiaquatic carnivores and, like domestic ferrets, are of the family Mustelidae.3 The diet of wild North American river otters consists mostly of fish but also includes amphibians (eg, frogs), crustaceans (eg, crayfish), and some other small animals. River otters, like all carnivores, have a specialized brachyodont dentition. The family Mustelidae is characterized by large carnassial teeth (the maxillary fourth premolar and mandibular first molar teeth) and maxillary first molar teeth.4 The permanent dental formula of North American river otters is I 3/3; C 1/1; P 4/3; M 1/2 = 36.4,5 The maxillary first premolar teeth are small and located palatally or are sometimes congenitally absent.4,5 Uncommonly, supernumerary premolar teeth can be present.4
The river otter of this report had extensive abrasion of its teeth; this is a common finding in the wild because these animals regularly consume many types of prey that have hard or abrasive anatomic structures.4 Interestingly, subjective macroscopic assessment of dental abrasion has been reported to be a noninvasive and relatively accurate means of estimating age in river otters.5,6 Radiographic assessment of the pulp cavity of canine teeth as well as microscopic cementum annuli analysis have also been described as accurate methods of age determination in river otters.3,5–7
Knowledge of the anatomy of North American river otters, combined with the use of intraoral dental radiography, led to the diagnosis and treatment of endodontic disease in the patient of this report. Radiographic changes suggestive of endodontic disease include increased apical periodontal ligament space; loss of apical lamina dura; periapical lucency due to bone lysis; irregular root-end anatomy resulting from apical root resorption; evidence of arrested tooth maturation such as a wide pulp cavity; changes suggestive of osteomyelitis such as proliferation, sclerosis, or lysis of surrounding alveolar bone; or some combination of these.1,2,8 A dental explorer can be used to confirm pulp exposure in a tooth with suspected complicated crown fracture or severe abrasion. However, if debris located in the pulp chamber is blocking access by the explorer, radiographs can aid in the confirmation of loss of tooth structure exposing the pulp cavity.8 In animals with pulpitis resulting in pulp necrosis, radiographs are needed to aid in the determination of tooth vitality. Importantly, gross discoloration of the crown secondary to pulpitis almost always indicates a nonvital tooth in dogs.9,10 Radiographic signs of endodontic disease in the case of this river otter included widened periodontal ligament space, a wide pulp cavity, loss of lamina dura, and apical root resorption.
The treatment for nonvital teeth secondary to fractured or abraded crowns resulting in pulp exposure, pulpitis, or trauma is either exodontia (extraction) or endodontic treatment (orthograde or surgical endodontic therapy).1,8 The decision to treat the left mandibular canine tooth with orthograde endodontic treatment and the left mandibular fourth premolar tooth with surgical extraction was made on the basis of the canine tooth being a more important or strategic tooth for a carnivore than the mandibular fourth premolar tooth.11
The extent of the pathological changes detected in this river otter's dentition could have only been determined with the use and understanding of intraoral dental radiography. Intraoral radiographs also were essential during treatment of the endodontic disease, specifically during the multiple steps of the endodontic procedure as well as for preoperative planning and postoperative evaluation of the surgical extraction. Additionally, radiographic reevaluation of the left mandibular canine tooth was recommended as a means of monitoring success of the treatment and continued vitality of abraded teeth.
Ketamine, Bioniche Pharma USA, Lake Forest, Ill.
Midazolam, Akorn Inc, Lake Forest, Ill.
IsoThesia, Butler Schein Animal Health, Dublin, Ohio.
Metacam, Boehringer Ingelheim Vetmedica, St Joseph, Mo.
Baytril, Bayer Animal Health, Monheim, Germany.
References
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11. Wiggs RB, Lobprise HB. Oral surgery. In: Wiggs RB, Lobprise HB. Veterinary dentistry principles and practice. Philadelphia: Lippincott, 1997; 232–258.
