Odontogenic neoplasms and hamartomas provide a bewildering array of complex histological patterns although they are relatively uncommon clinical problems. Classification is based on resemblance to normal tooth formation. Most are benign or self-limiting and can be managed in a similar semiconservative fashion. Of the many different types, only ameloblastoma and odon-tome are common.
Ameloblastoma: the commonest odontogenic neoplasm, accounting for 1% of all jaw tumours. Usually found in the mandible, especially near the angle (60%), although up to 20% arise in the maxilla. Peak in fourth and fifth decades, but all ages affected. X-rays usually show multilocular radiolucency, often in dentigerous relationship; erosion of the lingual cortex or lower border is a characteristic sign; roots can be resorbed. The tumour may be solid, cystic or microcystic; in solid areas the histology is characteristic but can be very subtle in more cystic areas. Peripheral tall columnar ameloblast-like cells with polarised hyperchromatic oval nuclei and clear cytoplasm ("piano keyboard") surrounding more centrally placed cells resembling stellate reticulum. The tumour grows by epithelial proliferation and infiltrates along the soft tissues between bone trabec-ulae, usually extending far beyond the radiographic margins. Recurrence is inevitable if not resected completely. Multiple recurrences run the risk of soft tissue involvement (especially into the parapharyngeal spaces) and dissemination of tumour into lungs and lymph nodes.
There are many different histological subtypes: follicular, plexiform, acanthomatous, desmo-plastic, granular cell, etc., which probably have no real clinical significance. Two variants have a better prognosis - the unicystic ameloblastoma and the extraosseous ameloblastoma.
Unicystic ameloblastoma: younger patients (teens/early twenties), predominantly in the lower third molar region: associated with unerupted tooth in dentigerous relationship. A single large cystic cavity is lined by epithelium that is not always typical of ameloblastoma; sometimes there is epithelial proliferation into the wall or as a luminal polyp. On account of the subtle character of the epithelium, diagnosis is easily missed. Fortunately, this type of ameloblastoma usually responds to thorough curettage and does not always require resection.
Extraosseous ameloblastoma: less than 5% of ameloblastomas arise in gingival soft tissue alone without bone involvement where they may resemble a fibrous epulis. Histologically fairly typical of ameloblastoma, less radical surgery is required than their intraosseous cousins; nevertheless cortical bone may have to be removed from the deep aspect of the tumour to ensure clearance.
Odontome: hamartomatous malformation forming distinct tooth-like structures (compound), disorganised masses of dentine, enamel, cementum (complex) or any combination of the two forms. Commonly identified in teenagers or young adults. Most are small, are related to the permanent dentition and are discovered accidentally when an unerupted tooth is being investigated; larger ones may produce bony expansion. X-rays show dense radio-opaque masses surrounded by a well-defined radiolucent zone; lesions in younger patients may have large radio-lucent portions. Complex odontomes are seen most often in the posterior segments; compound odontomes in the anterior segments (especially maxilla). Multiple odontomes suggest Gardner's syndrome. Histologically they are composed predominantly of dentine with varying amounts of enamel, cementum and other soft tissue components typical of the odontogenic apparatus. Less well-developed forms have abundant pulpal and ameloblastic areas and can resemble other types of odontogenic tumour (e.g., ameloblastic fibroma, ameloblastic fibro-odontoma) while odon-tomes may be associated with other odontogenic tumours such as the calcifying odontogenic cyst.
Other rarer benign tumours or hamartomatous lesions include calcifying epithelial odontogenic tumour of Pindborg, adenomatoid odontogenic tumour, calcifying odontogenic cyst, ameloblastic fibroma, odontogenic fibromyxoma, cementoblastoma. Many will display speckled calcification on X-ray, differentiating them from cysts.
Malignant tumours: involvement of the jawbones by malignant tumour is usually a consequence of direct spread into the bone from mucosal or salivary lesions, although a number of primary bone and soft tissue sarcomas can arise in the jaws. Malignant tumours of the odontogenic apparatus are rare and are usually only diagnosed histologically although pain, paraesthesia, rapid growth, mucosal fixation or ulceration may be present. Radiographs may show irregular bone destruction.
They include: malignant ameloblastoma/ameloblastic carcinoma, clear cell odontogenic tumour, carcinoma arising in an odontogenic cyst (any type of odontogenic cyst and usually squamous cell carcinoma), primary intra-osseous carcinoma and odontogenic sarcomas, the latter being very rare. Overall, they tend to be low-grade malignancies, although recurrences and metastasis complicate some cases.
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