Circuit 4, station 2

Odontogenic Cysts
Definition:
Odontogenic cysts are epithelial-lined cavities that arise from the odontogenic epithelium, which includes the reduced enamel epithelium (REE), the epithelial cell rest of Serres, and the epithelial cell rest of Malassez (ERM). The REE surrounds the developing crown of the tooth, while the rests of Serres are remnants of the degeneration of the dental lamina responsible for initiating tooth formation during embryonic development. The ERM is residual cells that remain after the breakdown of Hertwig’s epithelial root sheath, which initiates root development. These rests become entrapped within the maxillary and mandibular gingiva and the alveolar bone, leading to the development of odontogenic cysts.

Classification
Odontogenic cysts can be classified into two main categories: inflammatory and developmental. Inflammatory odontogenic cysts include periapical cysts, residual cysts, and paradental cysts, while developmental odontogenic cysts include dentigerous cysts, eruption cysts, lateral periodontal cysts, gingival cysts, odontogenic keratocyst (OKC), orthokeratinizing odontogenic cysts, and glandular odontogenic cysts.

Causes of the different types
Periapical cysts are inflammatory in nature and are the most common type of odontogenic cyst. They typically develop at the root apex of a non-vital tooth due to inflammation caused by dental caries or trauma. This inflammation activates and multiplies the ERM, which is positioned towards the apex of the affected tooth. As a result, there is an increase in osmotic pressure, which causes the expansion of the cyst. Periapical granulomas, which are histologically similar to periapical cysts but lack an epithelial lining, are considered a precursor to periapical cysts.
Residual cysts are very similar to periapical cysts and also have an inflammatory aetiology. They result from inadequate removal of a periapical cyst at the time of extraction and are microscopically identical to periapical cysts.
Paradental cysts are odontogenic cysts caused by inflammation. They occur at the crown or root of a partially or fully erupted tooth and result from inflammation of the junctional epithelium within the gingival sulcus of an erupting or erupted tooth. Depending on the location and tooth involved, they may be referred to as a buccal bifurcation cyst or mandibular infected buccal cyst.
Dentigerous cysts are developmental in origin and typically occur in association with an impacted tooth that has failed to erupt. They develop as fluid accumulates between the tooth crown and enamel epithelium, dilating the tooth follicle and ultimately preventing the tooth from erupting.
Eruption cysts are considered the soft tissue variant of the dentigerous cyst and are caused by a lack of separation of the dental follicle from an erupting tooth. Lateral periodontal cysts are developmental cysts that arise from the rest of Serres.
OKCs, orthokeratinizing odontogenic cysts, and glandular odontogenic cysts also have developmental etiologies and arise from the rest of Serres or ERM. Gingival cysts are rare developmental odontogenic cysts that are usually found on the alveolar ridge or the buccal mucosa.

Clinical Features
Different types of odontogenic cysts have varying clinical features. Periapical cysts and residual cysts are usually asymptomatic and cannot be seen clinically, but can be diagnosed through radiographs. Paradental cysts are associated with young patients and present with gingival edema, purulent discharge, and deep pockets on probing.
Dentigerous cysts are associated with impacted teeth and are asymptomatic unless they become inflamed. Eruption cysts occur in young children or infants during tooth eruption and present with alveolar edema with a bluish hue.
Lateral periodontal cysts are usually incidental radiographic findings and occur later in life, often in the 40s and 50s, with a male predilection. Odontogenic keratocyst is typically asymptomatic but may present with intra-oral edema, pain, trismus, neurosensory deficits, and infection.
Orthokeratinizing odontogenic cysts are similar to odontogenic keratocyst clinically but have a better prognosis. Glandular odontogenic cysts are aggressive and may present with an increase in tooth mobility and cortical perforation. A detailed clinical and radiographic evaluation is important for the accurate diagnosis of these cysts.

Treatment / Management
Treatment options vary based on the type of cyst and can include surgical enucleation or marsupialisation, depending on the size and location of the cyst, and the patient’s age and overall health.
Periapical cysts, for example, are commonly treated with root canal therapy, and surgical endodontic therapy or extraction may be required if symptoms persist. On the other hand, residual cysts require enucleation, while paradental cysts are typically enucleated or extracted depending on the location of the cyst.
Dentigerous cysts require tooth extraction followed by curettage and enucleation, while eruption cysts are self-limiting and require no treatment unless they are symptomatic. Lateral periodontal cysts and botryoid odontogenic cysts require curative enucleation and curettage, respectively. For odontogenic keratocyst, treatment options range from enucleation to resection, depending on the size and location of the lesion.
Orthokeratinizing odontogenic cysts require surgical excision, while glandular odontogenic cysts are treated with enucleation and curettage, with more extensive cases requiring resection. Regardless of the treatment option, close follow-up is necessary to ensure a successful outcome.