Imaging Features
As the epithelial lining is derived from the reduced enamel epithelium, on radiographic examination, a dentigerous cyst appears as a unilocular radiolucent area that is associated with just the crown of an unerupted tooth and is attached to the tooth at the cementoenamel junction. Dentigerous cysts may also involve odontomas, which by their nature also have “tooth crowns”. The radiolucency is generally well-defined and well-corticated. The radiolucency often have a sclerotic border indicating bony reaction, but a secondarily infected cyst may display ill-defined borders. However, a large dentigerous cyst may give the impression of a multilocular process due to the persistence of bone trabeculae within the radiolucency. The cyst-to-crown relationship presents several radiographic variations which are explained as follows:
Central variantThis is the most common variant which the cyst surrounds the crown of the tooth and the crown projects into the cyst. Lateral variantThis variant is usually associated with a mesioangular impacted mandibular third molar that is partially erupted. The cyst develops laterally along the root surface and partially surrounds the crown. Circumferential variantThe cyst surrounds the crown and extends for some distance along the root surface so that a significant portion of the root appears to lie within the cyst, as if the tooth was erupting through the centre of the cyst. The radiographic distinction between an enlarged dental follicle and a small dentigerous cyst can be difficult and fairly arbitrary. Generally, any pericoronal radiolucency that is greater than 3 to 4mm in diameter is considered suggestive of cyst formation.
Odontogenic keratocysts do not result in the same degree of bony expansion as dentigerous cysts and teeth resorption are less likely to be seen in association with odontogenic keratocysts. In addition, dentigerous cysts are more likely to have smooth periphery and odontogenic keratocysts are more likely to display a scalloped periphery. Unicystic ameloblastomaIt is the most common radiolucent, benign odontogenic tumor that may be unilocular or multilocular. It may result in expansion and destruction of the maxilla and mandible. It is not possible to differentiate unicystic ameloblastomas from dentigerous cysts with clinical and radiographic examinations. Histopathologic examination revealed that the basilar cells in unicystic ameloblastoma become columnar and demonstrate prominent nuclear hyperchromatism. The polarization of nuclei may be away from the basement membrane (reverse polarization). Besides, the superficial epithelial layers may become loosely arranged and resemble the stellate reticulum of the enamel organ. Pindborg tumorIt is a rare odontogenic tumor that is radiolucent with well-defined border and associated calcified radiopaque foci. Adenomatoid odontogenic tumorAdenomatoid odontogenic tumor also shows similar features as dentigerous cyst; however, the  differentiation is by the presence of intra-cystic radio-opaque structures. In younger patients, the periapical radiolucencies associated with deciduous teeth may mimic pericoronal radiolucencies of succedaneous permanent teeth and may result in a false impression of dentigerous cyst. A definitive diagnosis will not be made based on radiographs alone. The diagnosis can only be confirmed by histopathological examination. OdontomaIt is a lytic lesion that is frequently accompanied by amorphous calcification.