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ISSN : 1225-1577(Print)
ISSN : 2384-0900(Online)
The Korean Journal of Oral and Maxillofacial Pathology Vol.45 No.3 pp.99-104

Ameloblastoma Arising from Dentigerous Cyst in Mandible : A Case Report and Literature Review

Yoo Jin Hong, Ju-Yeon Seo, Kyoun-Tae Kim, Sung-Tak Lee, So-Young Choi*
Department of Oral & Maxillofacial Surgery, School of Dentistry, Kyungpook National University
* Correspondence: So-Young Choi, Department of Oral & Maxillofacial Surgery, School of Dentistry, Kyungpook National University, Korea Tel: +82-53-600-7576 Email:
May 25, 2021 May 28, 2021 June 4, 2021


Dentigerous cyst is considered one of the representative cystic lesions, which accounts for approximately 15%-30% of the odontogenic cysts. Although its recurrence rate is low, a small proportion of dentigerous cysts converted into ameloblastomas, squamous cell carcinomas, and mucoepidermoid carcinomas. Here we present an uncommon case characterized by histopathological transformation from a dentigerous cyst to an ameloblastoma, and further investigate the factors contributing to its conversion.

함치성낭으로부터 유래된 법랑모세포종: 증례보고 및 문헌 고찰

홍 유진, 서 주연, 김 균태, 이 성탁, 최 소영*
경북대학교 치과대학 구강악안면외과학 교실



    Dentigerous cyst constitutes approximately 15%-30% of the developmental odontogenic cysts, and represents the second most common cystic lesion1-3). It is formed by fluid accumulation between the enamel epithelium and the crown of an unerupted tooth4-6). Radiographically, a well-defined and unilocular radiolucency surrounding the crown of an impacted tooth is found5-8). An epithelial lining of flattened non-keratinizing cells is microscopically observed around a dentigerous cyst6-7). Occasionally, small islands of odontogenic epithelial rests are present in the fibrous wall of dentigerous cysts5,9). Enucleation and extraction of the unerupted tooth are usually performed for dentigerous cysts, and recurrence is uncommon6,8). However, a dentigerous cyst has been reported to have neoplastic potential to convert to other odontogenic tumors (i.e., ameloblastoma and adenomatoid odontogenic tumor) or malignant tumors (i.e., squamous cell carcinoma and mucoepidermoid carcinoma) 4,8-11). Particularly, this case report presents an uncommon case characterized by histopathological conversion from a dentigerous cyst to an ameloblastoma and further investigates the factors contributing to its conversion. Additionally, the differential diagnosis and postoperative follow-ups are emphasized for dentigerous cysts despite their low recurrence rates.


    A 16-year-old female patient presented to the Kyungpook National University Dental Hospital in Korea with chief complaints of consistent swelling and pain in her right cheek that persisted for a month. Radiographic examination revealed a large radiolucent lesion with a well corticated margin extending from the right mandibular body to the entire ramus area (Fig. 1A). The right mandibular third molar was unerupted and displaced by the cystic lesion. Furthermore, bone and dental root resorption were observed. Cone-beam computed tomography (CBCT) revealed buccolingual expansion and thinning of the cortical bone of the mandibular body (Fig. 1B, C). Under general anesthesia, the bony enlarged lesion was first marsupialized to reduce its size, and incisional biopsy was concurrently performed. To prevent mandibular fracture, arch bar fixation was performed before marsupialization. A slit was made on the cystic wall, and a penrose drain was inserted into the slit to keep it open and to ensure free drainage. The cystic lesion was diagnosed as a dentigerous cyst. Histopathological examination revealed thin, non-keratinized epithelial linings (Fig. 2A, B). Some part of the linings was thicker with hyperplastic rete ridges due to inflammation.

    Four months later, radiographic examination was repeated. The cyst size had slightly reduced, but no dramatic change was observed (Fig. 1D). Buccal expansion of the cortical bone of the right mandibular body had reduced compared with that at her first visit (Fig. 1E, F). However, marsupialization had a limitation in decreasing the cyst size. Thus, enucleation and extraction of the right mandibular third molar were followed by marsupialization. The final biopsy led to the diagnosis of an ameloblastoma. Microscopically, a combination of characteristics of dentigerous cysts and ameloblastomas was observed. The flattened, non-keratinized epithelial lining and several small islands of inactive-appearing odontogenic epithelial rests in the fibrous wall, which represent dentigerous cysts, persisted. Conversely, the histopathological features of ameloblastomas were more evidently noted. The thicker, loosely cohesive overlying epithelial cells were visible with a hyperchromatic and polarized basal layer. Islands of ameloblastic follicles in the fibrous connective tissue wall were another noticable characteristic of ameloblastomas. Although inflammation led to palisades and polarity in weaker basal layers, obvious stellate reticulum clearly indicated the lesion to be an ameloblastoma (Fig. 2C, D).

    Wide resection is an optimal treatment for ameloblastoma. Nonetheless, additional operation was not followed considering the patient’s young age. Instead, regular follow-up care was planned. At seven months after enucleation, bone healing in the mandible was favorable (Fig. 1G). Furthermore, thinning and expansion of mandibular cortical bone gradually resolved. To date, no dental symptoms and recurrence occurred. The close follow-up observation was continued to monitor its recurrence.


    Dentigerous cyst is considered one of the developmental odontogenic cysts enclosing the crown of an unerupted tooth4,6). It is the most common cause of pericoronal radiolucency, which is formed by fluid accumulation between the crown of an impacted tooth and the follicular epithelium4-6). The unilocular radiolucency with cortical expansion of buccolingual bone and thinning of the outer radiopaque border is one of the main radiographic features of dentigerous cysts6,8,12). Additionally, the resorption of bone and adjacent teeth and the displacement of teeth often occur simultaneously 6,12). It is commonly observed in individuals in the twenties and thirties and most commonly occurs in the impacted mandibular third molars9).

    Ameloblastomas are benign, slow-growing epithelial neoplasms that are locally aggressive and infiltrative7,9,12). They are the most common odontogenic tumors and represent approximately 10% of all such tumors6,9). They generally occur in the third to fifth decades of life6). The radiographic characteristics of ameloblastoma range from unilocular radiolucency to multilocular radiolucency with internal septa and a honeycomb or soap bubble appearance6,8). Particularly, ameloblastomas with unilocular and well-corticated radiolucent lesions enclosing the crown of unerupted teeth are radiographically indistinguishable from dentigerous cysts. Additionally, the epithelial linings of untreated dentigerous cysts are often reported to be converted into ameloblastomas 9). Thus, a differential diagnosis between dentigerous cysts and ameloblastomas greatly relies on histopathological evaluation.

    In this case, the cystic lesion represented indistinct radiographic aspects between dentigerous cysts and ameloblastomas. Hence, histopathological examination was required for differential diagnosis. At the first microscopic examination of marsupialization, most of the epithelial cell linings were thin and non-keratinized, which defined the cystic lesion as a dentigerous cyst4,6,7). The rete ridge proliferation due to inflammation might lead to its misinterpretation as other similar odontogenic cysts or tumors; however, the absence of polarity of nuclei and stellate reticulum- like basal layers indicated it to be a dentigerous cyst6,7). However, during the four months of cyst size reduction by marsupialization, the walls of the dentigerous cyst altered to ameloblastic linings. The flattened, non-keratinized linings and islands of inactive epithelial rests partially persisted, but the majority had developed hyperchromatic, reversely polarized basal layers with loosely arranged epithelial cells4,7). Although the peripheral palisading of columnar cells was weakly expressed owing to inflammation, some tumoral islands and stellate from epithelial cells clearly demonstrated ameloblastic characteristics. Consequently, the transformation from a dentigerous cyst to an ameloblastoma was noted based on histopathological examinations.

    Approximately 15%-20% of ameloblastomas develop from the walls of dentigerous cysts7,9,12). Kahn et al. proposed the etiopathogenesis of ameloblastomas arising from dentigerous cysts10). Furthermore, numerous factors, including non-specific irritating factors (extraction, caries, trauma, infection, inflammation, and unerupted tooth), nutritional deficit disorders, and viral infection have been suggested4,8-10). In our case, unerupted mandibular third molar and inflammation were the major doubtable etiologic factors. Microscopic images showed inflammatory infiltrates with the development of rete ridges and thicker epithelial linings13). Additionally, weak palisading basal layers and polarity of nuclei caused by inflammation were verified. Overall, this transition of lesion was assumed to be owing to irritating factors.

    Because ameloblastoma has an aggressive potential for local invasion and a high recurrence rate, the treatment method of ameloblastoma has been controversial13). According to several literatures, conservative treatments such as enucleation, marsupialization, and curettage resulted in a high recurrence rate of 55%-90%, whereas radical treatments resulted in a recurrence rate of less than 13%13). Thus, radical treatment such as wide resection was recommended for ameloblastomas11,13). Nevertheless, mandibular resection was not performed in this case to conserve the facial appearance, to allow the mandibular growth, and to reduce the functional sequelae, considering the patient’s young age. Accordingly, regular follow-up was ensured for seven months, and no recurrence has been noted to date.


    This case report represented the conversion from a dentigerous cyst to an ameloblastoma to emphasize the neo plastic potential of dentigerous cysts and the importance of histopathological evaluation for the differential diagnosis of cystic lesions. Although dentigerous cysts typically have a low recurrence rate, regular postoperative follow-ups are necessary because dentigerous cysts, particularly in the presence of irritating factors, nutritional deficiency, and viral infections, may undergo neoplastic changes to develop into odontogenic tumors or malignant lesions.



    (A) A well-defined and unilocular radiolucency surrounding the crown of the impacted right mandibular third molar extended from the right mandibular body to the entire ramus area. The unerupted tooth was displaced, and bone and dental root resorption were observed in the first panoramic radiograph. (B, C) The axial and coronal views of cone-beam computed tomography (CBCT) during the first visit represent a buccolingual expansion of cortical bone of the right mandibular body. (D) After four months of marsupialization, a panoramic radiograph was obtained. The cyst size had reduced, but no dramatic change was observed. (E, F) After four months of marsupialization, axial and coronal views of CBCT were obtained. The reduced cyst size was observed; however, the cortical bone expansion persisted. (G) At seven months after enucleation, the panoramic radiograph was obtained. Bone healing proceeded favorably. No recurrence occurred.


    Histopathological findings at marsupialization diagnosed the lesion as a dentigerous cyst (A, B), and those at enucleation defined it as an ameloblastoma (C, D). (A) A thin, non-keratinized epithelial lining was mostly observed. A thicker epithelial lining with hyperplastic rete ridges was partially visible owing to inflammation (×12.5). (B) The flattened, non-keratinized wall revealed nodular thickening at the end of the tissue. This area (red arrow) was suspected to be an ameloblastic change, but it was excluded because the polarity and stellate reticulum were absent (×40). (C) A combination of features of dentigerous cysts (blue arrows) and ameloblastoms (red arrows) was observed. The flattened, non-keratinized epithelial linings were observed (blue). Simultaneously, thicker ameloblastic epithelial lining was found, showing a hyperchromatic and polarized basal layer (red). Although palisaded and polarized basal layers were weakly expressed owing to inflammation, the stellate reticulum was visible (×40). (D) The cystic lining showed a hyperchromatic, polarized basal layer with loosely cohesive overlying epithelial cells, which resembles the stellate reticulum. Islands of follicular ameloblastoma were infiltrating the fibrous connective tissue wall (small box) (×100).



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