CYSTS OF THE JAWS Cysts may occur centrally

CYSTS OF THE JAWS Cysts may occur centrally (within bone) in any location in the maxilla or mandible but are rare in the condyle and coronoid process. Odontogenic cysts are found most often in the tooth-bearing region. In the mandible, they originate above the inferior alveolar nerve canal. Odontogenic cysts may grow into the maxillary antrum. Odontogenic cysts Radicular cyst Periapical cyst, apical periodontal cyst, or dental cyst. A radicular cyst is a cyst that most likely results when rest of epithelial cells in the periodontal ligament are stimulated to proliferate and undergo cystic degeneration by inflammatory products from a nonvital tooth.

RADIOGRAPHIC FEATURES In most cases the epicenter of a radicular cyst is located approximately at the apex of a nonvital tooth. Occasionally it appears on the mesial or distal surface of a tooth root, at the opening of an accessory canal, or infrequently in a deep periodontal pocket. Most radicular cysts (60%) are found in the maxilla, especially around incisors and canines. Because of the distal inclination of the root, cysts that arise from the maxillary lateral incisor invaginate the antrum. Radicular cysts may also form in relation to a nonvital deciduous molar and be positioned buccal to the developing bicuspid. The periphery usually has a well-defined cortical border. In most cases the internal structure of radicular cysts is radiolucent. Occasionally, dystrophic calcification may develop in long-standing cysts, appearing as distributed, small particulate radiopacities.

RESIDUAL CYST A residual cyst is a cyst that remains after incomplete removal of the original cyst. The term residual is used most often for a radicular cyst that may be left behind most commonly after extraction of a tooth. Radiographic features Residual cysts occur in both jaws, although they are found slightly more often in the mandible. The epicenter is positioned in a periapical location. In the mandible the epicenter is always above the inferior alveolar nerve canal. A residual cyst has a cortical margin unless it becomes secondarily infected. Its shape is oval or circular. The internal aspect of a residual cyst typically is radiolucent. Dystrophic calcifications may be present in long-standing cysts.

DENTIGEROUS CYST Dentigerous cysts are the second most common type of cyst in the jaws. They develop around the crown of an unerupted or supernumerary tooth. The clinical examination reveals a missing tooth or teeth and possibly a hard swelling. Radiographic features The epicenter of a dentigerous cyst is found just above the crown of the involved tooth, which usually is the mandibular or maxillary third molar or the maxillary canine, the teeth most commonly affected. An important diagnostic point is that this cyst attaches at the cementoenamel junction. Dentigerous cysts typically have a well-defined cortex with a curved or circular outline. The internal aspect is completely radiolucent except for the crown of the involved tooth.

ODONTOGENIC KERATOCYST An odontogenic keratocyst is a noninflammatory odontogenic cyst that arise from the dental lamina. Unlike other cysts which are thought to grow by osmotic pressure, the epithelium in this cyst appears to have innate growth potential, much as in a benign tumor. Radiographic features The most common location of an odontogenic keratocyst is the posterior body of the mandible (90% occur posterior to the canines) and ramus (more than 50%). The epicenter is located superior to the inferior alveolar nerve canal. This type of cyst occasionally has the same pericoronal position as, and is indistinguishable from, a dentigerous cyst.

RADIOGRAPHIC FEATURES As with other cysts, odontogenic keratocysts usually show evidence of a cortical border unless they have become secondarily infected. The cyst may have a smooth round or oval shape identical to that of other cysts, or it may have a scalloped outline. The internal structure most commonly is radiolucent.

LATERAL PERIODONTAL CYST Lateral periodontal cysts are thought to arise from epithelial rest in periodontium lateral to the tooth root. Radiographic features Fifty percent to 75% of lateral periodontal cysts develop in the mandible, mostly in a region extending from the lateral incisor to the second premolar. Occasionally these cysts appear in the maxilla, especially between the lateral incisor and the cuspid. A lateral periodontal cyst appears as a well-defined radiolucency with a prominent cortical boundary and a round or oval shape. The internal aspect usually is radiolucent.