Dentigerous Cyst

Etiology and Pathophysiology

• Considered a developmental odontogenic cyst, though inflammation from pericoronitis or an adjacent non-vital tooth may initiate some.
• Originates by accumulation of fluid between the reduced enamel epithelium (REE) and a completed tooth crown.
• Intrafollicular fluid accumulates between the reduced enamel epithelium (REE) and the enamel
• Pressure of the tooth on the impacted follicle leads to
  • obstruction of venous outflow
  • Serum transudation
  • Exudation
• Earliest event is separation of the REE from the crown to form the cyst space (REE is loosely attached after the normal eruption time).
• Because the REE stops at the cemento-enamel junction (CEJ), the lining is attached there and the fibrous wall is continuous with the periodontal ligament.
• Enlarges by internal pressure, expanding the dental follicle, displacing adjacent structures and eventually expanding the jaw.

Contributory factors :

• Teeth most likely to be impacted (upper canine, lower 3rd molar).
• Multiple dentigerous cysts are seen in cleidocranial dysplasia (many unerupted teeth).

Prevalence

• 10–15% of all jaw cysts (up to ~20% of all odontogenic cysts in some series).
• Most common developmental odontogenic cyst; second most common odontogenic cyst overall.
• Affects children and young adults; peak in the 2nd–4th decades (typically 10–30 years).
• Slight male predilection (M:F ≈ 1.6:1; reported as more than twice as common in males).

Histological Features

• Cyst contents: clear yellow fluid containing cholesterol; becomes purulent if infected.

• Epithelial lining:

  • Thin, flattened non-keratinised stratified squamous epithelium, only ~2–4 cells thick (cuboidal to flat); early lining may resemble REE / be bilaminar.
  • Continuous with the reduced enamel epithelium; flat epithelial–connective tissue interface (no rete ridges in uninflamed cysts).
  • May show mucous and ciliated columnar metaplasia, or focal keratinisation.

• Cyst wall: fibrous wall with variable inflammation; typically non-inflamed unless secondarily infected; outermost layer often woven bone.

  • Small islands/cords of inactive odontogenic epithelial rests may be scattered in the wall; cholesterol clefts may be present in the lumen.
  • Once significant inflammation supervenes, appearances resemble a radicular cyst and diagnosis can no longer be made on biopsy alone.

• Histological sections show a cystic structure with the tooth crown embedded in the lumen, the wall attached at the CEJ.

• Radiographic:

  • radiolucent lesion associated with unerupted teeth
    • Radiolucency surrounding the crown of an unerupted tooth
  • Unilocular radiolucency engulfing the crown of an impacted tooth
  • Potential displacement of adjacent roots
  • Clear demeracted

Clinical Features

• A cyst enclosing the crown of an unerupted tooth
• Attached to the cemento-enamel junction
• Also known as a follicular cyst
• Associated with permanent teeth.
• Usually asymptomatic; often a chance radiographic finding when investigating an unerupted/failed-to-erupt tooth.
• Painless enlargement / expansion of bone, missing tooth, tilting of adjacent teeth, root resorption.
• Secondary infection (e.g. extension from a peri-apical or periodontal lesion of an adjacent tooth) may cause pain and swelling.

Location

• Most common sites are teeth likely to be impacted:
  • Lower (mandibular) 3rd molar — ~two-thirds to 75% of cases.
  • Upper (maxillary) canine — next most common; lower premolars also affected.

Appearance

• Radiographic: well-defined, unilocular radiolucency with a corticated outline surrounding the crown of an unerupted tooth.
• Circumscribed and rounded; grows slowly.
• May attain a very large size (>10 cm); large cysts can appear multilocular (pseudoloculation) due to superimposed bony ridges.
• Affected tooth often displaced a considerable distance (e.g. lower 3rd molar to lower border of mandible or high in the ramus).
• In longstanding cysts, the enclosed tooth crown/root may show resorption.

Differential Diagnoses

• Enlarged/normal dental follicle — distinguished by size of radiolucent space (normal follicle width ~2–3 mm); use radiographic follow-up if uncertain.
• Odontogenic keratocyst — may grow around an unerupted crown simulating a dentigerous relationship; lining does not attach at the CEJ.
• Ameloblastoma and other radiolucent lesions simulating a dentigerous relationship.
• Radicular cyst — differentiated by vitality of the associated tooth (the tooth involved by a dentigerous cyst is unerupted; an adjacent vital tooth points away from a radicular cyst).
• Other lesions in a follicular relationship: adenomatoid odontogenic tumour, calcifying odontogenic cyst.

Relevant Clinical Investigations

• Radiographs (OPG/periapical; CT for extent) — primary diagnostic tool; identify clear attachment at the CEJ.
• Vitality testing of adjacent teeth — helps differentiate from radicular cyst.
• Histopathological examination of the enucleated specimen — diagnosis should always be confirmed histologically to exclude other unexpected lesions (OKC, ameloblastoma); submit whole specimen for biopsy.

Patient Management

• Enucleation with removal of the unerupted tooth (usual treatment for impacted lower 3rd molars, as there is no reason to conserve them).
• Marsupialisation / decompression for very large cysts (temporary decompression where jaw fracture is a risk) or to allow a favourably positioned tooth (e.g. maxillary canine) to erupt — orthodontic space/traction may be provided.
• Alternatively, the unerupted tooth may be transplanted (risk of long-term resorption).
• Prognosis: responds well to enucleation or marsupialisation and does not recur after treatment.
• Rarely, ameloblastoma or squamous cell carcinoma may arise in the cyst lining (especially in longstanding untreated cysts).