History and Physical Examination Findings
A 6-month-old 3.7-kg male Chihuahua presented for neuter, removal of persistent deciduous maxillary canines, and dental imaging of unerupted teeth. The owner reported no discomfort or atypical teething/chewing. Aside from bilaterally absent mandibular first premolars and third molars, his preoperative exam was unremarkable. Intraoral dental radiographs were taken of the right and left first premolar and third molar regions (Figure 1). The owner was advised to schedule for reevaluation in 2 months (allowing time for natural dentition eruption) with imaging and removal of any unerupted teeth.
Selected intraoral radiographic images of the mandibular dentition of a 6-month-old (A through D) and 2.5-year-old (E through H) Chihuahua. A and B—Bisecting-angle intraoral radiographs of the mesial portion of the right and left mandible, respectively, at 6 months of age. C and D—Parallel-technique intraoral radiographs of the distal portion of the right and left mandible, respectively, at 6 months of age. E and F—Bisecting-angle intraoral radiographs of the mesial portion of the right and left mandible, respectively, at 2.5 years of age. G and H—Parallel-technique intraoral radiographs of the distal portion of the right and left mandible, respectively, at 2.5 years of age.
Citation: Journal of the American Veterinary Medical Association 260, 14; 10.2460/javma.22.04.0160
Two years later, the dog presented for a dental treatment of mild periodontitis. Aside from grade 1 periodontitis and unerupted left mandibular first premolar and third molar, he was diagnosed with seasonal environmental allergies that were controlled. Oral and extraoral examinations were performed. Rotation and crowding of the maxillary second and third premolar teeth and abrasion of the maxillary fourth premolar teeth were noted bilaterally. On both mandibles, the second and third premolar teeth were rotated, and there was crowding of the fourth premolar and first molar teeth. The left mandibular first premolar and third molar teeth were not visible, while the right mandibular first premolar and third molar teeth were visible but appeared incompletely erupted. Intraoral radiographs were obtained (Figure 1).
Formulate differential diagnoses, then continue reading.
Diagnostic Imaging Findings and Interpretation
The initial (6-month-old) intraoral radiography revealed generalized wide pulp cavities consistent with the patient’s reported age. The right mandibular first premolar and third molar were appropriately developed. The right first premolar had a mesioangular inclination (31° to 60° in the mesial direction).1 The left mandibular first premolar had a horizontal inclination (0° to 30° in the mesial direction).1 Both mandibular third molars had a vertical inclination (61° to 90° in the mesial direction)1 with a portion of the crowns still unerupted through the alveolar bone at the curvature into the ramus. The left mandibular third molar is slightly ventral to the eruption level of the second molar. None of the four teeth were completely encased in bone (Figure 2). There is an increased lucency noted on the distal aspect of the left mandibular third molar extending along the crown to the midpoint of the root and on the distal aspect of the right mandibular third molar extending along the crown to the level of the cemento-enamel junction.
Same intraoral radiographic images as in Figure 1. There is generalized pulp chamber enlargement (A through D), with alveolar bone visible above the coronal aspects of both mandibular third molars (C and D; arrowhead). A slight lucency is noted distal to the crown of the left mandibular third molar extending approximately half the length of the root (D; open star). The left mandibular first premolar has a horizontal inclination (B and F), and the right mandibular first premolar has a mesioangular inclination (A and E). There is a focal, smoothly marginated radiolucency noted at the left mandibular first premolar and third molar (F and H; arrows) with the left mandibular third molar being displaced ventrally compared with initial imaging (D). There is slight vertical bone loss on the distal aspect of the right mandibular third molar to the level of the cemento-enamel junction (G; white X). The right mandibular first premolar has completely erupted (E).
Citation: Journal of the American Veterinary Medical Association 260, 14; 10.2460/javma.22.04.0160
The adult (2.5 years old) intraoral imaging reveals that the right mandibular first premolar and third molar have erupted through the alveolar bone. The occlusal surface of the third molar is below the level of the occlusal surface of the second molar, and there is vertical bone loss noted on the distal aspect of the right third molar extending to the cemento-enamel junction of the tooth (Figure 2). The left mandibular first premolar crown is surrounded by a focal, smoothly marginated radiolucency extending mesially to the middle of the canine and distally to the mesial root of the second premolar and from the occlusal surface of the first premolar ventrally to approximately 50% of the height of the mandible. At the caudal aspect of the left mandible, there is a focal, smoothly marginated radiolucency surrounding the third molar, extending mesially over the distal root of the second molar and distally along the mandible and from the occlusal surface of the mandible to just dorsal to the mandibular canal. The entire left mandibular third molar crown is ventral to the occlusal surface of the mandible (Figure 3).
Additional parallel-technique intraoral radiograph of the left mandibular third molar. The periodontal ligament is slightly widened at the apex of the left mandibular third molar. A focal, smoothly marginated radiolucency is extending around the left mandibular third molar to overlap with the distal root of the left mandibular second molar (arrows).
Citation: Journal of the American Veterinary Medical Association 260, 14; 10.2460/javma.22.04.0160
Based on the patient history, radiographic imaging, and presence of unerupted teeth in both locations, a diagnosis of dentigerous cyst was made for both the left mandibular first premolar and third molar.
Treatment and Outcome
The patient was placed under general anesthesia, and a complete periodontal exam, full mouth radiographs, and cleaning were performed. A left inferior alveolar nerve block was performed using 2% mepivacaine (0.5 mg/kg, once). A full-thickness envelope flap was created extending from the distal aspect of the canine to the mesial aspect of the second premolar. Clear fluid erupted from the incision at the region of the first premolar. A periosteal elevator was used to reflect the gingiva, and the crown of the first premolar was visible. Using a dental winged elevator, the first premolar was extracted. Curettage was then performed on the cyst lining using a periosteal elevator, and the bone was gently debrided using a football-shaped, diamond burr to ensure complete removal of any cyst lining. The site was flushed using oral chlorhexidine solution 0.10% and closed using 4-0 polyglactin 910 suture in a simple interrupted pattern. A similar envelope flap was created extending from the caudal aspect of the second molar distally along the occlusal surface. The flap was elevated from the mandible using a periosteal elevator. Due to visualization of multiple surfaces of the distal root of the second molar, both the second and third molars were extracted. The same techniques were used for curettage, debridement, and closure as for the first premolar (Figure 4). Throughout the anesthetic procedure, the patient was maintained on lactated Ringer solution (3 mL/kg/h, IV). Preanesthetic protocol included methadone (0.3 mg/kg, IM, once), and the dog was given carprofen (4.4 mg/kg, IM, once) prior to recovery. The patient was discharged that evening with carprofen (2 mg/kg, PO, q 12 h for 4 days, to be started the following afternoon). The owner was instructed to monitor for bleeding or swelling and feed soft food only, with no access to hard treats or chew toys, for 2 weeks. The owner was informed that a small amount of blood-tinged saliva is typical in the first few days but that gross evidence of drops of blood should not occur. A recheck visit was scheduled for 2 weeks later to assess both sites for healing. The owner was advised to schedule a 6- to 12-month imaging recheck.
Postoperative bisecting-angle intraoral radiograph of left mandibular first premolar (A) and parallel-technique intraoral radiograph of left second and third molars (B). A thin margin of alveolar bone is visible on the mesial aspect of the left mandibular second premolar (A). The radiolucency noted from the dentigerous cyst of the third molar includes the majority of the distal root of the left mandibular second molar (B).
Citation: Journal of the American Veterinary Medical Association 260, 14; 10.2460/javma.22.04.0160
Histologic submission of the lining and retained teeth was declined by the owner due to finances. On the basis of the dog’s clinical and radiographic findings, a diagnosis of dentigerous cysts secondary to retained first premolar and third molar was made.
At the 2-week recheck, the patient was exhibiting no evidence of pain or swelling. Both sites appeared to have healed appropriately.
Comments
There are many reasons that a tooth may appear to be absent. The tooth may be congenitally absent, previously fractured or extracted, or unerupted (ie, it failed to erupt at the time of the surrounding or contralateral teeth).2 Ideally, absent teeth should be radiographed as early as possible after the surrounding or contralateral primary teeth have erupted.2 In this case, the absent teeth were initially imaged at approximately 6 months of age. At that age, an operculectomy (removal of the obstructive tissue above the crown) may allow unerupted teeth to passively erupt, either completely or incompletely.2 Upon completion of closure of the root apex (between 9 and 13 months of age), passive eruption is not possible, and extraction is typically the preferred treatment option for unerupted teeth, especially in young patients.2 In a recent retrospective study, 44.4% of unerupted teeth in dogs showed some degree of radiolucency consistent with a dentigerous cyst forming around the crown of unerupted teeth.1
Dentigerous cysts are the most common of the 4 classifications of odontogenic cysts,3,4 the remaining classifications being odontogenic keratocyst (typically not associated with a tooth), radicular (periapical) cysts (associated with the apex of a nonvital tooth), and lateral periodontal cysts (typically located between the roots of vital teeth).3 While definitive diagnosis requires histopathologic analysis of the cyst lining, a dentigerous cyst can often be identified radiographically due to having a sharply defined, unilocular radiolucency encompassing the crown of an unerupted tooth and expanding from the cemento-enamel junction.3,4 While local swelling can occur in relation to a dentigerous cyst, as many as 14 out of 29 dentigerous cysts in 1 study3 were incidental findings with no gross pathology noted beyond the absence of the adult dentition.
Odontogenic cysts are uncommon overall, being identified in only 1.4% of dogs being presented for dental treatment and imaging.3 Dentigerous cysts consist of approximately 71% of those cysts.3 Since approximately 30% to 50% of bone must be destroyed before osteolysis is radiographically visible5 and the propensity for unerupted teeth to develop along the mandible1 (though they can present at any unerupted tooth in either arcade), early diagnosis and surgical treatment with extraction and complete curettage of the dentigerous cyst lining is necessary to prevent progression or recurrence of these expansile, fluid-filled, osteolytic lesions. Untreated cysts, or cysts that recur secondary to incomplete removal of the cyst lining, can contribute to jaw fractures, root resorption of adjacent teeth, and additional extractions secondary to bone loss and can potentiate infection within the cyst secondary to periodontitis. Histopathology and follow-up imaging should always be recommended to rule out neoplasia and confirm complete removal of the cyst lining.
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
References
- 1. ↑
Bellei E, Ferro S, Zini E, Gracis M. A clinical, radiographic and histological study of unerupted teeth in dogs and cats: 73 cases (2001–2018). Front Vet Sci. 2019;6:357. doi:10.3389/fvets.2019.00357
- 3. ↑
Verstraete FJM, Zin BP, Kass PH, Cox DP, Jordan RC. Clinical signs and histologic findings in dogs with odontogenic cysts: 41 cases (1995–2010). J Am Vet Med Assoc. 2011;239(11):1470–1476.
- 5. ↑
Konde LJ. Aggressive versus nonaggressive bone lesions. In: Thrall DE, ed. Textbook of Veterinary Diagnostic Radiology. 3rd ed. Saunders; 1998:37–43.
