Odontogenic cysts are epithelial-lined pathologic cavities and surrounded by fibrous connective tissue that originate from odontogenic tissues that occur in tooth-bearing regions of maxilla and mandible. Cystic conditions of the jaw cause bony destruction and may cause resorption or displacement of adjacent teeth. Odontogenic cysts have developmental or inflammatory origins. More cases have been published in the adult age group than the pediatric population. Periapical cyst and dentigerous cysts are frequently reported conditions in dental practice. Histopathologic examination remains the gold standard investigation. Odontogenic cysts are managed with enucleation or marsupialization procedures. Early recognition and referral to oral surgery minimize the extent of jaw bone destruction.
Odontogenic cysts occur exclusively in tooth-bearing regions of maxilla and mandible.
Odontogenic cysts are usually asymptomatic, slow-growing, painless swellings of jaw bone.
Larger lesions may cause pain or discomfort. Pain is usually caused by secondary infection.
Palpation of affected area of the jaw swelling may show bony, hard consistency with normal-appearing overlying mucosa.
Early recognition and diagnosis of the jaw cyst may minimize the resorption and destruction of jaw bone.
Odontogenic cysts are unique disorder that affects oral and maxillofacial tissues. They arise as a result of inflammatory or developmental pathogenic causes associated with epithelium of tooth-forming apparatus. The 4 most frequently occurring odontogenic cysts are periapical cysts (PCs), dentigerous cysts, residual cysts, and odontogenic keratocysts (OKCs). However, other conditions, such as lateral periodontal cyst (LPC) and buccal bifurcation cyst, are included because they may be commonly seen in general practice. Glandular odontogenic cysts and calcifying odontogenic cysts are included in this article because they have a propensity to behave aggressively and recur frequently.
A United States study on oral biopsies from a dental school pathology service stated that the prevalence of cystic lesions was 10.7%. A demographic study from Canada stated that PCs were the most common odontogenic cysts (65.15%), followed by dentigerous cyst (24.08%) and OKC (4.88%). A study from the United Kingdom reported that a diagnosis of odontogenic cysts was made on 12.8% of the samples received by an oral pathology service. A Brazilian study reported a frequency of odontogenic cysts of 13.9%, with the most common being PCs.
Jaw cysts are more common among men than among women, with a ratio of 1.6:1. Most cases are reported in the fourth to sixth decade of life. Most odontogenic cysts are encountered in the maxillary anterior region, followed by the mandibular molar region. Periapical/radicular cysts, dentigerous cysts, residual cysts, and OKCs are the most frequently reported odontogenic cysts. Clinical misdiagnoses are possible because of the similar clinical and radiological presentations of theses cysts. However, a careful understanding and interpretation of clinical and radiological presentations helps in the recognition of jaw cysts and accurate diagnoses can be obtained through oral and maxillofacial pathology services.
For convenience, the types of odontogenic cysts are listed in Box 1 . No classifications are listed in this article, although there are many classifications that have been published. The intention is to provide specific information on the conditions that are discussed to aid the memory and understanding of commonly encountered jaw cysts.
Periapical cyst/residual cyst
OKC/orthokeratinized odontogenic cyst/nevoid basal cell carcinoma
Buccal bifurcation cyst/paradental cyst
Lateral periodontal cyst
Glandular odontogenic cyst
Calcifying odontogenic cyst
Periapical Cyst (Radicular Cyst)
PCs are the most common cyst of the jaw and are caused by inflammatory processes. All PCs are associated with nonvital teeth and identified at the apices of teeth (ie, the PC). Either carious process or trauma triggers the residual epithelial remnants at the periapical region and stimulates and proliferates the remnants, leading to cyst formation. These cysts are well identified through radiological investigations. Most cases are managed either by root canal treatment and periapical surgery or by extractions.
The carious or traumatic condition leads to the death of dental pulp tissue. However, carious or discolored teeth are often associated with PCs. The inflammatory stimulus from a pulpal region reaches a periapical region to cause stimulation of epithelial cell rests of Malassez, eventually forming a PC. The symptoms of the PC depend on the status of inflammation. Careful palpation over the mucosa at the periapical zone of the offending tooth may provide a clue to swelling, which may guide cortical plate expansion. PC are most often associated with unicortical plate expansion; that is, either buccal/labial or palatal/lingual cortical bones. Bilateral occurrence of PCs has also been documented ( Fig. 1 ). A tooth with acute inflammatory exacerbation is symptomatic and presents with pain or discomfort. Displacement of the tooth may be seen clinically when the cyst is large. Pulp testing and radiography are compulsory for diagnosing PC. Teeth associated with PCs must be nonvital and do not respond to thermal or electric pulp testing methods. Lymph nodes must be palpated during clinical examination. Regional lymph nodes may be enlarged in cases of PC. PCs are rare in deciduous tooth because deciduous teeth are usually resorbed. However, a radiolucent zone may be seen at the bifurcation or inter-radicular space of the deciduous tooth when infected.
Pulp testing, radiographs, and histopathologic evaluation are helpful in achieving an accurate diagnosis. PCs are radiologically recognized by well-defined, well-circumscribed, unilocular radiolucency that is closely associated with the apex of the affected tooth. Loss of lamina dura and a faint or thin radiopaque line (sclerotic border) that encircles the cystic region are also important radiographic markers for securing a diagnosis. Root resorption can be seen in cases with cytokine-related inflammatory action of the cyst. Cases with large radiolucent areas can be observed when the lesion is aggressive or left untreated for a long period. PCs with large radiolucency often flatten out as they reach the adjacent tooth; PCs rarely displace the adjacent tooth. Very few PC cases have reported radiopaque foci within the radiolucent area.
Misdiagnosis of PC may happen with periapical cemento-osseous dysplasia (PCOD). This condition has a similar radiological presentation: unilocular radiolucency at the periapical region of a tooth. Misdiagnosis can be easily prevented by the dentist subjecting the offending tooth to the pulp testing method. The tooth in PCOD usually responds to the thermal or electric pulp testing method. Misdiagnosis of PC may lead to unnecessary root canal treatment. Several cases have been reported of the misdiagnosis of PC in cases of PCOD.
Microscopically radicular cyst is observed with stratified squamous nonkeratinized epithelium often surrounded by an inflamed connective tissue stroma. Inflammatory hyperplasia of epithelium shows a characteristic loop-and-arcade pattern. The connective tissue stroma may show cholesterol clefts or Rhuston bodies.
The differential diagnosis may include periapical granuloma, because both periapical granulomas and PCs occur at the apex of nonvital teeth and radiologically appear as unilocular radiolucent areas. Although PCs usually appear larger than periapical granulomas, size should be considered as a definitive diagnostic criterion. In other words, periapical granulomas are usually tiny or small. Periapical granuloma lacks the radiopaque border; that is, the sclerotic area around the radiolucent zone. The periapical type of cemento-osseous dysplasia must be considered in the anterior mandibular region. Lateral radicular cysts appear as discrete radiolucent areas along the lateral side of the affected tooth because of lateral accessory canals. LPC should be considered when a lateral radicular cyst is observed. The exclusion can be made with pulp testing. PC does not respond to thermal testing, but LPCs do respond.
PCs are usually managed with conventional root canal treatment with periapical surgery; that is, apicoectomy (removal of tooth apex). Extraction with curettage is another mode of treatment. Inadequate curettage may lead to persistent radiolucent cavity (residual cyst).
Cyst that remains in the jaw bone on completion of exodontia is termed residual cyst. In addition, extraction with inadequate curettage may also lead to persistent cyst in jaw, leading to formation of residual cyst. The cyst may remain asymptomatic unless the cyst enlarges and causes pressure effects. Radiologically residual cyst shows well-defined, unilocular radiolucency at the site of previous extraction. A thin radiopaque border may surround radiolucent area. Cysts may degenerate with time and may lead to radiopaque masses (dystrophic calcification) within the cystic cavity (ie, radiolucent area). Symptomatic cases and larger residual cysts need to be managed through the surgical approach.
Paradental cyst is another type of cyst that originates from inflammation. This cyst is commonly associated with erupted teeth with periodontal pockets. The inflammation from the gingival sulcus of the pocket may trigger the cystic process. A radiologically radiolucent area is observed in the lateral aspect of the erupted tooth and in most cases the periodontal ligament space is not widened. Teeth associated with a paradental cyst are vital and react to thermal/pulp testing normally. Paradental cysts are commonly encountered in wisdom molars. Paradental cysts seldom recur. Paradental cysts associated with wisdom molars can be extracted; however, benign-appearing paradental cysts can be treated with cystic enucleation without removing the tooth ( Fig. 2 ).
Eruption cysts are commonly seen in the deciduous incisor or permanent mandibular first molar region. Eruption cysts occur because of fluid collection in the follicular space of an erupting tooth and appear blue to purplish brown. This cyst is normally considered as a soft tissue cystic variant of dentigerous cyst. No treatment is required because these cysts rupture and spontaneously degenerate. Watchful waiting is an option. Simple surgical excision of the cystic roof should be done when cysts do not rupture.
Dentigerous cyst is the second most common cyst of the jaw and has a developmental origin. Almost all of the dentigerous cyst encloses the crown of an unerupted tooth and the radiolucent area is attached to the tooth at the cementoenamel junction (CEJ). The cyst occurs because of fluid accumulation between the crown of the unerupted tooth and follicular epithelium (reduced enamel epithelium). These cysts are well-defined unilocular radiolucent areas associated with the crowns of unerupted teeth. Management of dentigerous cyst is done by enucleation of the cyst along with the removal of associated unerupted tooth. If the eruption path of an associated tooth is feasible, then the tooth may be left in the jaw.
The cyst occurs because of accumulation of fluid between the crown of an unerupted tooth and follicular epithelium. Dentigerous cysts are predominantly asymptomatic unless the condition is secondarily infected ( Fig. 3 ). Mandibular third molars and maxillary canines are the most frequently affected. Because of their asymptomatic nature, most cases are detected during routine radiographic examinations or accidental discovered during radiological investigation. Symptomatic cases are identified in larger cysts because of enlargement of the cyst. Symptoms such as pain and swelling may present. The enlargement of the cysts may show either unicortical or bicortical expansion. Larger cysts usually hollow out the affected jaw bone, which may lead to eggshell cracking on palpation. Pathologic fractures may be seen in larger cysts. Lymph nodes are palpable when the cyst is secondarily infected. Bilateral or multiple dentigerous cysts are observed in cleidocranial dysplasias and Maroteaux-Lamy syndrome. Cases have been reported of aggressive dentigerous cysts with transformation of squamous cell carcinomas or mucoepidermoid carcinomas. Few cases have been reported of dentigerous cyst being associated with adenomatoid odontogenic tumor. Supernumerary teeth are considered to be one of the common developmental disturbances, hence impacted supernumerary teeth have a risk for dentigerous cyst.
Radiological and histopathologic examinations are helpful in achieving accurate diagnosis. Dentigerous cysts are classically characterized by the unilocular radiolucent areas associated with the crowns of unerupted teeth at the level of CEJ. The radiolucent cavity is well defined and well circumscribed with a sclerotic border (radiopaque). The dentigerous cyst with secondary infection may show ragged margins or ill-defined borders. Roots of adjacent teeth may show resorption or displacement caused by the pressure from dentigerous cysts. Larger cysts may have a multiloculated appearance and should be considered in the differential diagnosis of ameloblastoma. Three types of radiographic appearance can be observed in dentigerous cysts: (1) central, (2) lateral, and (3) circumferential. Central radiographic appearance is the most commonly encountered. This appearance is characterized by the radiolucent cavity that surrounds the crown of an unerupted tooth. Lateral variant is characterized by radiolucent cavity observed laterally along the root surface and partially covers the crown of the unerupted tooth. Circumferential variant is challenging for diagnosing dentigerous cysts because the radiolucent cavity surrounds the entire tooth. Most clinicians are familiar with the radiolucent cavity being associated with the crown of an unerupted tooth and extending up to the level of the CEJ.
Microscopically, dentigerous cyst is observed with thin (2–3 layers) nonkeratinizing cystic epithelium. Scattered mucous cells may be observed. The fibrous capsule is loosely arranged and may show small inactive-appearing odontogenic epithelial islands. Inflamed dentigerous cysts may show multilayered cystic epithelium with hyperplastic rete peg formation. Complications associated with dentigerous cysts are ameloblastoma from potential transformation of odontogenic epithelial cell nests, mucoepidermoid carcinoma (a malignant salivary gland tumor that may arise as potential complication from mucous cells observed in the lining epithelium of cyst), and squamous cell carcinoma from the lining epithelium.
Differential diagnosis of radiolucency covering the crown of an unerupted tooth should include OKC and unicystic ameloblastoma. Ameloblastic fibroma should be considered in younger individuals. However, adenomatoid odontogenic tumor must be considered in the differential diagnosis of dentigerous cyst for pericoronal radiolucency observed on maxillary or mandibular canines.
Management involves careful enucleation of cyst along with extraction of associated unerupted tooth. Large cysts with extensive jaw destruction are managed with a marsupialization procedure.
OKC arises from the remnants of dental lamina either in mandible or maxilla. Posterior mandible is the most frequent site of involvement. Although OKCs are characterized by cavity filled with fluid, because of the higher recurrence rate, aggressive clinical behavior, and other biochemical protein content, OKCs are considered to be cystic neoplasm and termed as keratocystic odontogenic tumors. Association of multiple OKCs with multiple basal cell carcinomas is termed Nevoid Basal Cell Carcinoma (NBCC). OKCs have less tendency to expand buccolingually, but have a tendency to spread anteroposteriorly and have a tendency to cross the midline of the jaw bone. OKCs are usually recognized as multilocular radiolucencies; however, unilocular radiolucencies can be observed. OKCs are managed by surgical excision with peripheral osseous curettage or ostectomy.
OKCs can be observed in any adult age group but are most commonly observed in the second, third, or fourth decades of life. Children are rarely affected. OKCs more frequently affect mandible than maxilla. Posterior ramus is the most common region in the mandible, whereas in maxillae it is the third molar and cuspid region. Multiple OKCs are observed in association with NBCC syndrome. Most cases are asymptomatic. However, patients may present with pain or soft tissue swelling in infected OKCs. Bony expansion (buccal or lingual) and paresthesia of the lips are reported in fewer cases.
Radiological and histopathologic examinations are helpful in achieving accurate diagnosis. OKCs are characterized by well-defined unilocular or multilocular radiolucent areas with a clear peripheral radiopaque rim ( Fig. 4 ). The borders are usually scalloped. Displacement of roots may be seen, and root resorption of adjacent tooth is uncommon. Radiologically, OKCs can be differentiated as 4 types: replacement, envelopmental, extraneous, and collateral. OKC that forms in the location of a tooth are termed the replacement type. OKCs that embrace an adjacent unerupted tooth are the envelopmental type. The envelopmental type usually mimics the radiographic appearance of dentigerous cyst. OKCs occurring in ascending ramus (ie, away from the teeth) are extraneous type. OKCs occurring adjacent to the root surfaces are the collateral type. The collateral type radiographically mimics the LPC.