December 1, 2006
by David J. Wilson, BSc & Bruce R. Pynn, MSc, DDS, FRCDC
Dentigerous cysts (DC) are a developmental cyst arising when fluid accumulates between the reduced enamel epithelium and the crown of an unerupted tooth.1 The result is a unilocular expansion around the crown of the tooth. DC make up for approximately 20% of odontogenic cysts and are most often found in the second to fourth decade of life.2 While the lesion is typically asymptomatic, larger lesions will cause a painless expansion of bone, while infected cysts can cause pain and draining sinus tracts. Occasionally, paraesthesia has been reported as a consequence of a DC creating pressure on a vital structure.3
DC are typically associated with unerupted third molars, maxillary canines, and mandibular second premolars and are often discovered during routine dental radiographic examination.1
In the case of third molars, one may be tempted to assume that the teeth are congenitally missing, however, as the reported case shows one must be aware of the possibility of lesions with or without the capacity to move teeth.
During a recall appointment to her dentist, a 51-year-old lady reported a vague pain in her upper teeth. A clinical exam revealed healthy teeth and gums, however, there was a firm expansion in the molar region. A panoramic radiograph showed an impacted tooth #18 , appearing to be in the sinus under the infraorbital rim (Fig. 1).
The patient was referred to an oral and maxillofacial surgery office where a CT scan was ordered to assess the three-dimensional position of the lesion. The large unilocular cyst (3.5 x 3.5 x 4.5cm) obliterated the maxillary sinus with the impacted tooth abutting the nasal cavity (Fig. 2). Despite some concern about the size of the lesion and limited access in the posterior maxilla, the cyst was removed with minimal bone removal (Figs. 3 & 4). The patient’s recovery was uneventful and she follows up regularly with her dentist. The pathology was confirmed to be a DC.
When expansile lesions in the maxillofacial region are present, the differential diagnosis should include cysts, (DC, odontogenic keratocyst calcifying odontogenic cyst), benign tumors (ameloblastoma, ameloblastic fibroma, adenomatoid odontogenic tumours), and malignancies. DC are the most common developmental odontogenic cyst, representing approximately 20% of cysts of the jaws.1 Approximately 1% of impacted maxillary third molars will develop a DC.4
A patient presenting with clinically missing teeth should be evaluated for impaction of these teeth. A panorex radiograph will provide information regarding the presence and position of impacted teeth as well as any associated pathology.
Clinical and radiographic features of the DC may mimic a number of other lesions, most notably odontogenic keratocysts, or unicystic ameloblastoma. DC are unilocular lesions but may appear multilocular radiographically due to undisplaced bony trabeculae within the lesion.1 DC have been reported to be more likely to cause tooth movement than odontogenic keratocysts, although this is possible with both lesions.5 While DC, by definition extend from the CEJ of the tooth, three possible presentations are possible: central, having the appearance of the crown projecting into the cavity of the cyst; lateral, where the cyst extends along one root surface; and circumferential where the cyst extends along the root, giving the appearance of the cyst encompassing the crown and roots of the tooth. It should be noted that larger cysts may obscure this relationship.4
Definitive diagnosis is made by histological examination of the cyst lining. Differentiation from unicystic ameloblastoma and odontogenic keratocyst is important due to the higher recurrence rate, and more destructive nature of these lesions compared to the DC.2
Management of the DC depends on factors such as size, location, patient age, and proximity to vital structures.6 DC may be treated by enucleation with extraction of the involved tooth in cases where there is insufficient space for normal eruption or in cases where the tooth will not add function. The involved tooth may be saved in some cases after enucleation of the cyst which may allow the tooth to erupt normally due to removal of pressure preventing eruption. Orthodontic assistance may be necessary to allow the tooth to erupt completely. More extensive lesions, especially those in close proximity to vital structures, or in medically compromised patients may be treated by marsupialization, minimizing the need for radical surgery.2
In the case of complete removal, DCs have a very low incidence of recurrence. The possibility exists for malignant transformation of the cyst lining in a small minority of cases. Possible transformations are ameloblastoma, squamous cell carcinoma, and intraosseous mucoepidermoid carcinoma.1
The reported case highlights the importance of properly investigating impacted third molars for the presence of pathology. The incidence of cystic changes in impacted third molars has been reported to be approximately 2%, with the incidence increasing with the duration of impaction.7 It has also been reported that even in impacted, radiographically normal teeth, cystic changes are very common.9 For this reason, as well as the potential for more destructive lesions associated with impacted third molars, regular follow-up for patients with impacted third molars is indicated, even in the case of asymptomatic teeth in an older patient.
Mr. Wilson is a 4th year dental student at the Faculty of Dentistry, University of Toronto.
Dr. Pynn is an oral and maxillofacial on staff at Thunder Bay Regional Health Sciences Center and maintains a private practice in Thunder Bay, Ontario.
Oral Health welcomes this original article.
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