208 Theories and techniques of oral implantology

intact, mucosal tissues. An x-ray of the area shows a circumscribed radiolucent lesion (Fig. 6-8). Al-though a median palatine cyst is painless, it may interfere with mastication and speech.

A globulomaxillary cyst is another example of a fissural cyst. This cyst extends from between the maxillary cuspid and lateral incisor toward the hard palate as a pear-shaped lesion (Fig. 6-9). It may cause a local enlargement of the bone and usually forces the teeth bordering it apart.

Other fissural cysts are the median alveolar and nasoalveolar cysts. The median alveolar cyst occurs in bone near the alveolar process, just posterior to the central incisors (Fig. 6-10). The nasoalveolar cyst occurs in the soft tissues at the base of the nostril, producing a noticeable swelling under the upper lip and in the nasal floor. Although not in bone, pressure from the cyst on bone may cause some re-sorption. A nasoalveolar cyst is relatively rare, usually occurring only in Negroes.

The most common nonodontogenic cyst is the nasopalatine cyst. This cyst derives from epithelial tissue that lined the fetus' nasopalatine duct. Post-embryonic remains of this duct exist in the nasopalatine canal and in the area of the incisive papilla. Thus the cyst has been subdivided into the incisive canal cyst, which occurs within the nasopalatine canal, and the papilla palatine cyst.

The incisive canal cyst appears in the anterior part of the maxilla. Because the shadow of the nasal spine is visible, the lesion appears to be heart-shaped (Fig. 6-11). A papilla palatine cyst, while not usually itself radiolucent, may produce a corresponding area of radiolucency in the palate if it erodes bone from the palatal surface.

Pseudocysts. Pseudocysts, although traditionally called cysts, are not true cysts because they are not lined by epithelium. Included in the category of pseudocysts are the traumatic cyst, the idiopathic bone cavity, and the aneurysmal bone cyst. Two of these cysts, the traumatic cyst and the aneurysmal bone cyst, usually occur before the age of 20 in the mandible and in patients with a history of trauma. They also occur elsewhere in the body.

The traumatic cyst, also called a solitary or unicameral bone cyst, hemorrhagic cyst, or extravasation cyst, usually occurs in the mandible between the cuspid and the ramus. It is distinguished by its scalloped outline (Fig. 6-12). A traumatic cyst is rarely painful but may cause enlargement of the jaw.

A traumatic cyst is either empty or contains a small amount of clear or blood-stained fluid. Its walls

Fig. G-10. A median alveolar cyst occurs in the bone just posterior to the central incisors. (From Bhaskar, S. N.: Synopsis of oral pathology, ed. 3, St. Louis, 1969, The C. V. Mosby Co.)

Fig. 6-11. The incisive canal cyst is typified by a heart-shaped appearance in a radiograph. (From Kolas, S., and others: Radiographic patterns of resorption seen in some gnathodental hard-tissue disturbances, Dent. Clin. N. Amer., November, 1968.)