1. Peripheral cell division: It is proposed that the cyst enlarges at the peripheries because of active division of the cells of the epithelium lining the cyst (Figure 1). It is believed that the division of these cells is a response to any irritating stimulus. The theory further suggests that once the stimulus is withdrawn the cyst regresses in size. This theory has not found many supporters as cyst regression will result in irregular inner surface of the cyst as the bone surrounding the cyst offers resistance. One should remember that the contents of the cyst will support the cystic lining and it can cause rapid resorption of surrounding bone to accommodate the enlarging cyst.

2. Accumulation of cellular contents: This theory was proposed by Kramer (1974) to explain the enlargement of OKCs. He proposed that as mural squames are shed off the lining epithelium they accumulate, thereby increasing the cyst volume. The sites of expansion and growth are represented by finger-like projections which are zones of active cell division or proliferation (Figure 2).

Clinical features

Eruption cysts are usually seen in childhood. These cysts are commonly seen in the age groups of 5 and 9 years. However, Woldenberg (2004) published a case report of an eruption cyst in the maxilla of a 40-year-old female. Studies by Anderson (1990), Woldenberg (2004) and Aguiló (1998) show that these cysts are more prevalent in the maxillary arch. In a study of 24 cases of eruption cysts by Bodner et al (2004), it was found that eruption cysts were associated with natal teeth in two cases, with primary teeth in 10 cases and with permanent teeth in 12 cases. It was seen that males more commonly presented with eruption cysts than females (2:1). The primary mandibular central incisors and the permanent first molars were the most common site involved. Though most of the eruption cysts are reported as solitary entities, literature review reveals report of a patient presenting with multiple eruption cysts. Ramón Boj and García-Godoy (2000) described a case of a 15-month-old child who had six eruption cysts simultaneously.

On clinical examination, the cyst is visible as a soft fluctuant mass on the alveolar ridges and may vary in size from about 1 to 1.5 cm in diameter. It may have the same coloration of healthy oral mucosa or appear bluish or bluish black. Eruption cyst histologically mimics dentiger-ous cyst.

Management

Usually the cysts open up spontaneously. In some children the overlying soft tissue can be incised to facilitate the tooth to erupt. Literature reveals that marsupialization is sufficient to manage eruption cysts.

Clinical features

It occurs frequently in association with impacted mandibular (Figure 3), maxillary third molars (Figure 4), and maxillary canines (Figure 5). Dentigerous cyst is commonly seen in the 2nd and 3rd decades of life. Males are relatively more predisposed. It grows aggressively and produces facial asymmetry, bony expansion, displacement and resorption of teeth. Entire ramus might be hollowed if associated with mandibular third molar (Figure 6A, B). In case of maxillary canine, anterior maxilla is expanded. There will be no pain unless secondarily infected. On aspiration, yellow-colored fluid is obtained.

Radiographic features

Radiographically, dentigerous cysts exhibit three different presentations, namely, the central, lateral and circumferential types. In central variety, the cyst symmetrically envelops crown. The cyst occurs on lateral aspect of the crown in lateral variety and envelops crown entirely in circumferential variety (Figure 7). Dentigerous cyst may appear as welldefined unilocular or multilocular radiolucency (Figure 8A, B). Occasionally these cysts may cause displacement and resorption of the adjacent teeth (Figure 9). Large cysts often cause expansion of the cortical plates.

Histologic features

It has no characteristic microscopic features. It has cyst lining and connective tissue wall. The connective tissue wall consists of very loose fibrous connective tissue and sparse collagenized myxomatous tissues. It has presence of odontogenic epithelium (Figure 10). The inflammation leads to presence of Rushton bodies of hematogeneous origin in the lining epithelium. Cholesterol clefts might be present.

Potential complications

The odontogenic cyst has following complications: the development of mural ameloblastoma (Figure 11), squamous cell carcinoma and mucoepidermoid carcinoma.

Syndrome association

Multiple cysts can be formed in association with Gorlin-Goltz syndrome, cleidocranial dysplasia and Maroteaux-Lamy syndrome.

Management

Surgical removal of cyst and tooth is recommended (Figure 12). Marsupialization is done in case of very large cysts. The cyst recurs if incompletely removed.

Clinical features

Orthokeratinized odontogenic cyst usually presents as a solitary cyst in the posterior part of the mandible. It is usually seen in males commonly in the 2nd to 5th decade of life. In comparison to OKC it is less aggressive and has a very low recurrence rate (2.2%). Literature review reveals that almost two-thirds of the cases of OOC appear like dentigerous cyst on clinical and radiographic examination.

Histopathologic features

Orthokeratinized odontogenic cyst has a thin epithelial lining with a luminal surface of orthokeratin. The basal cell layer contains flattened squamous or cuboidal cells and a well-developed granular cell layer (Figure 13).

Radiographic features

Orthokeratinized odontogenic cyst presents either as a well-defined unilocular or multilocular radiolucency. Radiographically, OOC may resemble a dentigerous cyst when it is unilocular and resembles ameloblastoma when it is multilocular. Occasionally, it may cause cortical plate expansion and thinning of the lower border of the mandible. Roots of teeth may be displaced (Figure 14). However, resorption of roots is seldom seen.

The cyst should be surgically excised (Figure 15).

Radiographic findings

The cyst reveals no radiographic findings. However, in large cysts superficial erosion of bone represented by a faint shadow of radiolucency may be appreciated.

Hegde (2004) reported a rare finding (supposedly the first case in literature) calcifications within cystic lumen of the gingival cyst.

Histologic findings

Histologically, these cysts have a variety of presentations. The epithelium generally has three forms of presentation: (i) extremely thin epithelium, (ii) thicker stratified squamous epithelium and (iii) localized epithelial thickenings or plaque formation (similar to those evident in lateral periodontal cyst).

The thinner form of epithelium mimics the reduced enamel epithelium. It is generally composed of one to three layers of flat or cuboidal cells. The thicker variety may not show any rete pegs. The nuclei are pyknotic and show perinuclear cytoplasmic vacuolation. The localized thickening of epithelium or plaque may occasionally project into the cystic cavity. The cells in the localized thickenings have a whorled morphology. Rarely, these cells are swollen and clear and are referred to as water-clear cells.

Management

The cyst is removed surgically. Recurrences have not been reported.

Histologic features

The cyst is lined by a thin non-proliferating cuboidal to stratified squamous non-keratinizing epithelium, ranging from 1 to 5 cell layers, and thus resembling the reduced enamel epithelium.

The cyst wall and the lining usually show no signs of inflammation. The lateral periodontal cyst presents two important histologic features, namely, the presence of epithelial thickenings or ‘plaques’ and the presence of glycogenrich clear cells either in ‘plaques’ or in the superficial layers of the lining epithelium.

Radiographic findings

The cyst may appear as a round, oval or teardrop-like well-circumscribed interradicular radiolucent area, usually with a sclerotic margin, lying usually between the apex and the cervical margin of the teeth. Resorption of adjacent teeth though uncommon, has been reported. Occasionally, loss of lamina dura and widening of the periodontal ligament space may be present.

Management

Lateral periodontal cysts can be effectively managed with enucleation. A sound tooth can be retained. Recurrences though uncommon, have been reported in literature.

Cystic entity

It was classified as:

Neoplastic entity

It was described as an odontogenic tumor with ghost cells. The epithelial elements consist of numerous ameloblastomatous proliferations of tissue in the connective tissue of the stroma. Varying amounts of ghost cells are present within the epithelial islets. The hard tissue is composed of different amounts of dentinoid in direct contact with the epithelium.

Clinical features

It produces slow growing painless non-tender swelling of jaws (Figures 16 and 17). It occurs more in 2nd decade of life. It is commonly seen in the anterior part of the jaws. In the maxilla, the canine region is the most commonly affected site. In the mandible, the cyst is rarely found posterior to the first molar. Occasionally the cyst may be seen crossing the midline. On aspiration, it yields viscous granular yellow fluid. According to Wood et al, 68% of cases occur in mandibular molar area. At least 52% cases are associated with unerupted tooth, occasionally associated with pain.

Radiographic features

The radiographic features are quite variable. The central lesion may be radiolucent with a variable margin that is smooth and well-defined or, irregular and poorly defined. It might contain small foci of calcified material. It is usually present as a unilocular radiolucency. However, in about 5–13% of the cases, it may present as multilocular radiolucency. Intraosseous lesions may produce expansion of the lingual cortical plate. Resorption of the roots of adjacent teeth is frequently seen (Figure 18).

Differential diagnosis

Calcifying odontogenic tumor and ameloblastoma.

Management and prognosis

The management of calcifying odontogenic cyst is/>