Nonneoplastic Conditions

Radicular cyst (also known as apical periodontal cyst, dental cyst), apical granuloma and chronic dental abscess: these inflammatory lesions form a spectrum of changes related to the apical region of a non-vital tooth (usually a consequence of dental caries), with considerable overlap in clinical, radiological and pathological findings. Granulomas tend to be smaller (< 10 mm), have a sparser inflammatory cell infiltrate and show less-active inflammation than radicular cysts. Very large radiolucencies tend to be cysts rather than abscesses, although they may be infected. Very common, 70% of jaw cysts; 60% occur in maxilla; all ages but rare in children and with deciduous teeth. Arise when the contents of the necrotic pulp canal leak out of the apical foramina and set up an inflammatory reaction at the apex. The persistent inflammatory stimulus induces granulation tissue formation to help wall off the necrotic debris. Epithelial rests around the root ("cell rests of Malassez") proliferate, initially as complex strands and arcades then as a well-defined lining; when present the epithelium allows the term radicular cyst to be used. Cysts enlarge by a hydrostatic mechanism - the high protein content of the inflammatory exudate in the lumen draws water into the cyst while the lack of lymphatics in the wall prevents it draining away -producing a rounded radiolucency usually with a sclerotic border. May resorb the apical portion of the tooth. Most are located apically but 10% are seen in lateral relationship (accessory apical foramina). Treatment usually involves endodontic therapy (root canal treatment), apicectomy (removing the apical 2 mm of the tooth root via a surgical approach and sealing off the pulp canal) or removal of the tooth. Recurrence is uncommon but relates to a failure to control the contents of the pulp canal.

Dentigerous cyst (follicular cyst): a developmental cyst that surrounds the crown of an un-erupted tooth and is attached at the cervical region. Common, 15% of jaw cysts; often in younger patients but not exclusively; usually seen in the upper canine, lower second premolar and third molar regions. Well-defined radiolucency, unilocular in form with a sclerotic border surrounding the crown of an unerupted tooth (so-called "dentigerous relationship"). May resorb roots of adjacent teeth. Develops from the dental follicle surrounding the crown of the unerupted tooth but through an unknown mechanism. Enlargement is by hydrostatic mechanisms but what generates the forces is not clear. Has a thin fibrous wall, minimal inflammatory cell infiltrate (if any) and a thin lining of stratified squamous epithelium. Treatment requires removal of the unerupted tooth, the cyst being delivered at the same time. Recurrence is rare.

Odontogenic keratocyst: a developmental cyst characterised by a distinctive lining of keratin-ising stratified squamous epithelium and a marked tendency for recurrence. Common, about 10% of jaw cysts; all ages, any site (but especially near angle of mandible) - "any cyst in the jaw can be a keratocyst". Well-defined radiolucency, often multilocular in form with a sclerotic border, which may be in dentigerous relationship. May resorb roots of adjacent teeth. Histology shows a thin lining of highly organised keratinising stratified squamous epithelium, which has a prominent palisaded basal layer. Daughter cysts within the wall are common. Derived from primordial dental structures, the epithelium has an active growth potential of its own, unlike that of radicular cysts and dentigerous cysts. Probably enlarges by epithelial growth; epithelium proliferates between trabeculae of bone where it accumulates fluid and keratin in the centre. This infiltrative growth pattern produces a multilocular radiolucency, in contrast to the ovoid or circular unilocular lesion of expansile cysts like the radicular cyst. Recurrences (20%) are due to small pieces of lining and/or daughter cysts that remain following curettage. Large cysts are treated by marsupialisation and packing; over time the cyst shrinks in size and may disappear completely. A small proportion of patients with keratocysts, particularly those aged under 18 years, have Gorlin's syndrome (many stigmata, including multiple synchronous and metachronous keratocysts, skeletal abnormalities especially of skull form, ribs and vertebrae, multiple basal cell carcinomas).

Other cysts: a large variety of cysts can occur in the jaws. Some will be developmental cysts unrelated to teeth (nasopalatine duct cyst, nasolabial cyst, dermoid cyst), others will be associated intimately with the odontogenic apparatus and will be developmental (lateral periodontal cyst, gingival cyst of adults, glandular odontogenic cyst) or inflammatory in nature (paradental cyst). In addition, samples from a periodontal pocket or inflamed dental follicle can mimic cystic lesions. Of these only the glandular odontogenic cyst is likely to recur because of the presence of daughter cysts in its wall.

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