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 toothbearing 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.
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.
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 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.
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.
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 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.