An overview of dentigerous cysts in dogs and cats.

Many dental diseases can be easily treated or even prevented if the diagnosis is made early. A simple example is the dentigerous cyst, although many veterinarians are not familiar with this condition. This article presents an overview of dentigerous cysts in dogs and cats, in the hope that more of these cysts will be prevented or diagnosed early. Dentigerous cysts (follicular cysts) are, in my experience, the most common odontogenic cysts in dogs and cats, and are similar to those described in humans (1–3). Dentigerous cysts are associated with the crown of an unerupted tooth, usually a permanent tooth. They arise from the epithelial remnants of the enamel organ or the reduced enamel epithelium that surrounds the crown during odontogenesis (1,3) (Figure 1). Dentigerous cysts enclose the crown of the unerupted tooth and are attached to the tooth at the cementoenamel junction. Unerupted teeth are usually a developmental problem due to a physical barrier (impacted tooth) or a lack of eruptive forces (embedded tooth) (4,5). An iatrogenic dentigerous cyst was also reported in a dog following the extraction of a deciduous tooth. The permanent tooth bud was damaged which resulted in a malformed impacted tooth (6). Figure 1 Intraoral dental radiograph of a 2-month-old doberman pinscher showing the developing permanent tooth buds (asterisks). In the middle, the contour of the permanent right mandibular first molar crown is clearly visible. The radiolucent area around the ... Dentigerous cysts are more common in dogs than in cats (7). Brachycephalic dogs are more frequently affected and the condition is sometimes bilateral (5,8–12). Although these cysts could be associated with any tooth, the mandibular first premolar of the dog is the most frequent (8,10,11,13). The maxillary and mandibular canine are also often implicated (5). They can be diagnosed at any age but late diagnosis is usually associated with larger lesions. Affected animals often have no clinical signs apart from the absence of 1 or more teeth (hypodontia). These cysts are capable of achieving significant size, and their slow growth causes a thinning and expansion of the adjacent cortical bone. Facial asymmetry and an oral mass may then be observed. This mass may be fluctuant or hard on palpation depending on the presence or absence of a thin layer of bone over the cyst cavity. The soft tissues overlying the cyst generally have a normal appearance but can sometimes have a bluish tint, mainly with larger lesions (Figure 2). It is usually not associated with pain unless it becomes infected. Dentigerous cysts can greatly weaken the surrounding bone or invade the nasal cavities. They may even cause pathological fractures (10,11,13). Figure 2 Photograph of a 2-year-old shih tzu with a large dentigerous cyst (arrow) associated with an unerupted left maxillary canine. The condition was bilateral. The left maxillary third incisor and the left maxillary second premolar were absent on the radiographs. ... During the initial oral examination, large dentigerous cysts may be mistaken for other common causes of oral swelling such as an abscess, a granuloma, a tumor or any other cystic lesion. If there is no bleeding, fine-needle aspiration of a dentigerous cyst will normally give a clear, yellowish to brownish, more or less viscous liquid. Cytology usually provides little additional information but may help to rule out other conditions, for example, bacterial infection. The diagnosis of a dentigerous cyst is essentially based on radiography and histopathology. On radiographs, a dentigerous cyst typically appears as a circular radiolucent lesion with a well-defined cortex (fairly uniform, thin, radiopaque line) (2,14). This border could be less defined or missing if the cyst is infected (2). The lesion is usually unilocular and encloses the crown of an unerupted tooth (Figure 3). The shape and position of the tooth are often abnormal. The relationship of the cyst with the cementoenamel junction is not always visible when the cyst becomes larger (Figure 4). The unerupted tooth and the adjacent teeth in contact with the cyst can have tooth resorption or be displaced (Figure 5). Although the radiographic findings are nearly pathognomonic (15), they are not diagnostic because other lesions may appear similar on radiographs (14). Histopathology is always recommended. In humans, the epithelial lining may, in rare cases, change into an ameloblastoma or a carcinoma (1). Carcinomas have also been found in the epithelium of odontogenic cysts in dogs (16). An ameloblastic fibro-odontoma has also been described in a dog in relation to a dentigerous cyst (17). In humans, it is also important to differentiate the dentigerous cyst from the odontogenic keratocyst, the latter having a higher rate of recurrence after excision (3). Figure 3 Intraoral dental radiograph of the unerupted left mandibular first premolar of a Japanese spaniel. A small dentigerous cyst (arrowheads) is seen enclosing the crown of this tooth. The left mandibular third premolar is absent. Figure 4 Intraoral dental radiograph of a 6-year-old shih tzu. A large dentigerous cyst (arrowheads) has formed around the deciduous left maxillary third incisor. Note that its root is fractured (arrow). The permanent third incisor is absent. There is no more ... Figure 5 Intraoral dental radiograph of a 2-year-old Boston terrier. A large dentigerous cyst (arrowheads) is enclosing the crown of the unerupted right mandibular canine. Note the expansion of the mandible and also the resorption and displacement of adjacent ... The management of dentigerous cysts is simple and easily performed if the cyst is small. Extraction of the unerupted tooth and enucleation of the entire cyst wall is definitive therapy in most instances. Incomplete excision may lead to recurrence of the cyst which is then called a residual cyst. The excised tissue should be submitted to a pathologist for the reasons previously mentioned. In large lesions, marsupialization of the cyst wall may be performed in a first stage to allow continuous drainage and eventual reduction in cavity size, facilitating enucleation in a second stage (1,3,18). In my opinion, large lesions should be referred to a specialist (Figure 6). Caution is required with the treatment of these cysts because important adjacent structures could be injured (for example, mental nerve). The use of bone graft material is usually not necessary to fill the cavity left by the cyst (9,12). Teeth adjacent to the cyst may require different treatments depending on whether or not there is tooth resorption, significant loss of the alveolar bone, or loss of the vascular supply. Not all unerupted teeth will develop a dentigerous cyst. Nevertheless, if for any reason an unerupted tooth is not extracted, a radiographic follow-up should be recommended since the formation of a dentigerous cyst is always possible in the future (10). This conservative approach is sometimes chosen for the geriatric patient in whom a tooth has not yet caused any problems. The prognosis of most dentigerous cysts is excellent. Radiographic monitoring is recommended to evaluate bone healing after excision. Figure 6 Intraoperative photograph of the dog in Figure 5. The crown of the unerupted right mandibular canine is seen through the osteotomy previously performed. The cyst was also protruding into the middle mental foramen (arrow). In conclusion, the prevalence of dentigerous cysts appears to be low in general (8,11). Nevertheless, given the severity of lesions that can be caused by dentigerous cysts, the absence of a tooth beyond the normal period of eruption should be confirmed by dental radiographs. Early surgical treatment is simple and can prevent many complications. Other conditions may also be encountered when a tooth is apparently absent. For example, the tooth may have been resorbed or had the crown fractured and the root retained.

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