Odontogenic Cysts

Odontogenic cysts are epithelium-lined, fluid-filled cavities of the jaws that arise from remnants of the tooth-forming apparatus. They are among the most common pathological lesions of the jaw bones and are conventionally divided into developmental cysts, which form from residual odontogenic epithelium, and inflammatory cysts, which form in response to infection or inflammation around a tooth.

Definition

An odontogenic cyst is a pathological epithelium-lined cavity within the jaw bones derived from the residual epithelium of odontogenesis, classified as developmental or inflammatory according to its presumed origin.

Scope

This topic covers the origin, classification, and characteristic features of the main odontogenic cysts — including the radicular (periapical) and residual cysts among inflammatory types and the dentigerous and lateral periodontal cysts among developmental types — and the diagnostic distinction between cysts and cystic tumours. The classification of the odontogenic keratocyst, which has shifted between cyst and tumour categories in successive WHO editions, is noted as a particular point of nomenclature. It is a reference description, not a management protocol.

Core questions

• From which remnants of the tooth-forming apparatus does each odontogenic cyst arise?
• How are developmental and inflammatory odontogenic cysts distinguished clinically, radiographically, and histologically?
• How is a cyst differentiated from a cystic odontogenic tumour?
• Why has the classification of the odontogenic keratocyst moved between cyst and neoplasm categories?

Key concepts

• Developmental versus inflammatory cysts
• Radicular (periapical) cyst
• Residual cyst
• Dentigerous (follicular) cyst
• Lateral periodontal cyst
• Rests of Malassez and epithelial cell rests
• Cyst versus cystic neoplasm
• Odontogenic keratocyst nomenclature

Mechanisms

Developmental odontogenic cysts arise when residual islands of odontogenic epithelium — such as the rests of Malassez, the reduced enamel epithelium of an unerupted tooth, or rests of the dental lamina — proliferate and undergo central degeneration, forming an epithelium-lined cavity. Inflammatory cysts, chiefly the radicular cyst, develop when the rests of Malassez are stimulated to proliferate by inflammation arising from a non-vital (necrotic) tooth pulp, with the resulting cavity enlarging through osmotic and inflammatory processes. The radiographic hallmark of many is a well-defined radiolucency related to a tooth root or crown.

Clinical relevance

Odontogenic cysts are a frequent reason for the radiographic and histological assessment of jaw radiolucencies, and distinguishing a simple cyst from a cystic tumour or a keratocyst materially affects expected behaviour and follow-up. This entry explains how these lesions are categorised and recognised; it describes diagnostic concepts and is not a basis for individual treatment planning.

Epidemiology

Inflammatory radicular cysts associated with non-vital teeth are the most common odontogenic cysts, followed by developmental dentigerous cysts associated with unerupted teeth. Frequencies vary across reported case series and populations and depend on classification conventions, particularly for the odontogenic keratocyst.

Evidence & guidelines

The accepted nomenclature follows the WHO Classification of Head and Neck Tumours; the 4th edition (Wright & Vered, 2017) reclassified the keratocystic odontogenic tumour back to the odontogenic keratocyst, and the 5th edition (Vered & Wright, 2022) maintained this. Dedicated reference texts (Shear & Speight, 2007; Neville et al., 2016) describe the individual entities, and systematic review evidence (Dias et al., 2016) addresses treatment-associated recurrence of the keratocyst.

History

The classification of jaw cysts has been repeatedly revised. The odontogenic keratocyst was reclassified by WHO in 2005 as the keratocystic odontogenic tumour on the basis of its growth behaviour and genetic findings, then returned to a cyst designation in the 2017 WHO classification, illustrating how nomenclature in this area tracks evolving histological and molecular evidence.

Debates

Is the odontogenic keratocyst a cyst or a neoplasm?

Its locally aggressive behaviour, high reported recurrence, and association with PTCH1 alterations led WHO to designate it a tumour in 2005, but the 2017 and 2022 classifications returned it to a developmental cyst, and its biological categorisation remains debated.

Seminal works

• wright-vered-2017
• vered-wright-2022
• dias-2016

Frequently asked questions

What is the most common type of odontogenic cyst?

The inflammatory radicular (periapical) cyst, which forms at the root apex of a tooth with a non-vital pulp, is generally reported as the most common odontogenic cyst, followed by the developmental dentigerous cyst.

Is the odontogenic keratocyst classified as a cyst or a tumour?

It has moved between categories: WHO classified it as a keratocystic odontogenic tumour in 2005, but the 2017 and 2022 WHO classifications list it again as the odontogenic keratocyst, a developmental cyst.