Dental Update - Oral medicine: 15. radiolucencies and radio-opacities. b. odontogenic diseases and cysts

Article

Specialist referral may be indicated if the Practitioner feels:

The diagnosis is unclear;

A serious diagnosis is possible;

Systemic disease may be present;

Unclear as to investigations indicated;

Complex investigations unavailable in primary care are indicated;

Unclear as to treatment indicated;

Treatment is complex;

Treatment requires agents not readily available;

Unclear as to the prognosis;

The patient wishes this.

Odontogenic diseases may be related to the tooth or tooth germ.

Odontogenic infections

Caries, periodontitis or pericoronitis are the common oral pyogenic infections. Depending on the bacterial load and host immunity, dental pulpal infection may lead to apical periodontitis, abscess and fascial space infection, or granuloma or periapical (radicular) cyst.

Odontogenic cysts

Most jaw cysts arise from odontogenic epithelium. Odontogenic cysts (and tumours) arise from ectoderm, mesenchyme or a combination (ectomesenchyme) involved in tooth germ formation and they may be related to the site of a tooth germ, or may be associated with a tooth. There is an overall male predominance and the mandible is affected three times as commonly as the maxilla.

Clinical features

Jaw cysts are often asymptomatic presenting as an incidental finding, on radiographs, as a well-defined, corticated radiolucency owing to their benign, slow-growing nature. They may reach a large size before they give rise to:

Swelling: initially a smooth bony hard lump with overlying normal mucosa but, as bone thins, it may crackle on palpation like an egg shell. The cyst may resorb bone and show through as a blueish fluctuant swelling. Cystic expansion is more likely to give rise to buccal rather than lingual swelling.

Discharge.

Pain: if infected or if the jaw fractures pathologically.

Occasionally carcinomas may arise within some cysts.

Diagnosis

Most cysts are discovered on intra-oral radiography or on dental panoramic tomography. In the mandible they, by definition, arise above the inferior alveolar canal. Unless the lesion is very large, advanced imaging is rarely required. Cross-sectional imaging allows bucco-lingual expansion to be assessed more easily, especially in the maxilla. CBCT is now the imaging of choice if required (Figures 1 and 2: Nasopalatine duct cyst; CBCT panoramic and sagittal.)

Figure 1. Cone Beam CT panoramic of nasopalatine duct cyst; note the well-defined radiolucency with intact bony margins.

Figure 2. Cone beam CT sagittal view; note the buccal expansion and thinning of buccal cortical bone.

Other investigations may include pulp vitality testing, aspiration and analysis of cyst fluids, and histopathology.

Management

Enucleation (complete removal of the cyst) makes all tissue available for histological examination, the cavity usually heals uneventfully with minimal aftercare, but may render adjacent teeth non-vital. Marsupialization (partial removal) requires considerable aftercare and co-operation in keeping the cavity clean – the patient syringing the cyst cavity after meals. Healing may take up to 6 months and not all cyst lining is available for histopathology.

Odontogenic cysts are relatively common – most are inflammatory (55% of all) or dentigerous (22%) (Table 1). Odontogenic cysts that can be problematical, because of recurrence and/or aggressive growth, include especially the calcifying odontogenic and glandular odontogenic cysts.

Table 1. Jaw cysts. Modified from Regezi JA. Mod Pathol 2002; 15(3): 331–341.

Odontogenic		Non-odontogenic	Pseudocysts
Inflammatory	Developmental	Non-odontogenic	Pseudocysts
Apical radicularcyst/granulomaLateral radicular cyst Residual radicular cystParadentalBuccal bifurcation cyst	Dentigerous cystEruption cystLateral periodontal cyst	Nasopalatine cyst	Haematopoieticbone marrow defectStafne bone cyst Traumatic bone cyst

Periapical (radicular; or dental) cyst is inflammatory, and the most common odontogenic cyst (75% occur in the maxilla and 56% affect upper lateral incisors). It results from pulpal infections leading to periapical infection, a granuloma, and, finally, a cyst. The epithelial lining is derived from the rests of Malassez and is thick, irregular, squamous epithelium, with granulation tissue forming the wall in denuded areas. There may be areas of chronic or acute inflammation with abscess formation. Cholesterol crystal clefts and mucous cells may be found. The cyst fluid is usually watery but may be thick and viscid with cholesterol crystal clefts. The cysts have capsules of fibrous connective tissue.

Characterized by its position at the apex of a non-vital tooth (pulp necrotic because of caries, trauma or deep restoration), there is a round or pear-shaped, well-defined radiolucent lesion with sclerotic borders, larger (often >20 mm) than a periapical granuloma, with a rounder contour, and more well-defined border. It often involves a maxillary incisor or canine.

Any cyst that remains after surgery is termed a residual cyst – most arise from periapical cysts.

Follicular (dentigerous) cyst is the most common developmental odontogenic cyst. It forms from the follicle of an unerupted tooth and, therefore, the tooth crown projects into the well-demarcated cavity lined by flattened stratified epithelium (a pericoronal position may also be seen in the keratocystic odontogenic tumour (KCOT) and other benign tumours). Follicular cysts are unilocular, radiolucent, and may become extremely large (more so than the radicular cyst) but, in contrast to a malignant lesion, cortical bone is usually preserved. (Figure 3: Benign cystic lesion and Figure 4: Malignancy.)

Figure 3. Section of a DPT showing a well-defined, corticated radiolucency associated with the crown of a tooth. The differential diagnosis would be a slow-growing lesion, such as an odontogenic cyst or possibly an odontogenic tumour.

Figure 4. DPT radiograph showing a radiolucency with an ill-defined irregular margin which is not corticated. In the absence of signs of acute inflammation, a malignancy should be suspected.

A hyperplastic follicle, in contrast, is <2–3 mm, and neither displaces the tooth nor causes cortical expansion.

Eruption cysts are minor soft tissue forms of dentigerous cysts. They often burst spontaneously. In some cases, the teeth are prevented from eruption by fibrous tissue overlying them.

Lateral periodontal cyst is small, and lateral to a vital tooth root, often in mandibular canine and premolar regions (botryoid odontogenic cyst is similar except that it is polycystic).

Buccal bifurcation cyst is centred on the first or second mandibular molar, often presenting with delayed tooth eruption.

Glandular odontogenic cyst (GOC: sialo-odontogenic cyst) is rare but may superficially mimic a central muco-epidermoid carcinoma. Features include epithelial whorls, cuboidal eosinophilic cells, goblet cells, ciliated cells and mucous pools which, with expression of p53 and Ki67, may aid the diagnosis. GOC tend to be aggressive and may recur following curettage.

The main odontogenic cysts are listed in Table 2.

Table 2. Main odontogenic cysts.

Type	Decade at Presentation	Commonest Location	Usual Management
Dentigerous	3rd and 4th	Lower third molars, maxillary canines	Enucleation or marsupialization
Eruption	1st	Anterior to permanent molars	Nil unless impeding eruption
Radicular	3rd and 4th	Anterior maxilla	Enucleation
Residual	4th and 5th	Anterior maxilla	Enucleation or marsupialization

Reflective Practitioner

Vicarious Liability and the Moving Target of Dental Litigation: A Wake-up Call for Practice Owners?

Oral medicine: 15. radiolucencies and radio-opacities. b. odontogenic diseases and cysts

Authors

David H Felix

Jane Luker

Crispian Scully